Full moth rehabilitation/certified fixed orthodontic courses by Indian dental academy

CONTENTS
1. INTRODUCTION
2. INDICATIONS FOR OCCLUSAL REHABILITATION
3. GOALS OF FULL MOUTH REHABILITATION
4. ANATOMY AND PHYSIOLOGY OF MASTICATORY MECHANISM
5. THE HINGE AXIS
6. CENTRIC RELATION
7. VERTICAL DIMENSION
8. FUNCTIONAL ASPECTS OF COMPLETE MOUTH REHABILITATION
9. DIAGNOSIS AND TREATMENT PLANNING
10. PREPARATION OF THE MOUTH FOR REHABILITATION ll.PMS
PHILOSOPHY
12. SELECTING INSTRUMENTS FOR OCCLUSAL REHABILITTION
13. MOUNTING MODELS
14. FUNCTION AND IMPORTANCE OF ANTERIOR GUIDANCE
15. PRINCIPLES OF OBTAINING OCCLUSSION IN OCCLUSAL
REHABILITATION
16. RATIONALE AND TECHNIQUE OF BIO MECHANICAL OCCLUSAL
REHABILITATION
1.7. RESTORING LOWER ANTERIOR TEETH

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18. RESTORING UPPER ANTERIOR TEETH
19. THH PLANE OF OCCLUSION
20. POSTERIOR OCCLUSAL MORPHOLOGY 2!. RESTORING LOWER
POSTERIOR TEETH
22.WAXING TECHNIQUE FOR LOWER POSTERIOR TEETH
23. RESTORING UPPER POSTERIOR TEETH
24. FUNCTIONALLY GENERATED PATH
25. PROCEDURAL STEPS IN RESTORING OCCLUSION
26. REVIEW OF LITERATURE
27. SUMMARY

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INTRODUCTION
Planning and executing the restorative rehabilitation of a decimated occlusion
is probably one of the most intellectually and technically demanding tasks
facing a restorative dentist.
The term "occlusal rehabilitation has been defined as the restoration of the
functional integrity of the dental arches by the use of inlays, crowns, bridges
and partial dentures". Occlusal rehabilitation therefore involves restoring the
dentate or a partially dentate mouth. The aim is to provide an orderly pattern of
occlusal contact and articulation that will optimize oral function, occlusal
stability and esthetics.
Occlusal adjustment by grinding may be required, as part of the rehabilitation
but does not constitute rehabilitation per se.
Occlusal rehabilitation is discussed in the context of cases where restorations
are supported by natural teeth and doesn't include the restoration of the fully
edentulous arch or maxillofacial defects, nor does it include the use of
osseointegrated implants.
Definition: Full mouth rehabilitation entails the performance of all the
procedures necessary to produce healthy, esthetic, well functioning, and selfmaintaining masticatory mechanism.

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INDICATIONS FOR OCCLUSAL REHABILITATION
The reasons for undertaking occlusal rehabilitation may include the restoration
of multiple teeth, which are missing, worn, broken-down or decayed.
Increasingly occlusal rehabilitation is also required to replace improperly
designed and executed crown and bridge work. In certain circumstances
treatment of temporomandibular disorders may also be considered an
indication for rehabilitation, but great caution is advisable in such cases.
Regardless of the clinical reason, the decision to carryout any treatment should
be based upon achieving oral health, function, esthetics and comfort, and
treatment should be planned around these rather than the technical possibilities.
If these goals are to be achieved certain biological considerations are necessary
when planning and carringout occlusal rehabilitation. They are
1. The indications for reorganizing the occlusion
2. The choice of an appropriate occlusal scheme
3.

The occlusal vertical dimension

4.

The need (or otherwise) to replace missing teeth

5. The effects of the material used on occlusal stability control of parafunction
and TMD
The indications for reorganizing occlusion:
When undertaking relatively small amounts of restorative treatment, for
example up to two or three units of crown and bridge work, it is often
acceptable, and it is often advisable to adopt a confirmative approach that is to
construct the restoration to conform with the patient's existing intercuspal
position.

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The alternative strategy is to reorganize the occlusion by establishing a new
occlusal scheme around a stable condylar position. The condylar position
usually chosen is termed "centric relation' (CR).
The decision to re organize a patient's occlusion may be made on the grounds
either that the existing IP is unacceptable and needs to be changed, or where a
very large amount of treatment is to be undertaken and the operator has the
opportunity to optimize patient's occlusion. The decision should (and can) only
be made after a detailed and careful examination of the occlusion, preferably
with the use of accurate study casts mounted-in a semi adjustable articulator in
the retruded arc of closure. Mounted casts should allow the discrepancy (slide)
between CR and IP to be analysed as vertical, horizontal and lateral
components both at tooth and condylar level. Moreover, adjustments can be
tried and potential restorations waxed allowing the feasibility and difficulty of
reorganization to be judged properly.
It must be borne in mind that jaw movement will be simulated only partially by
any type of articulator. Nevertheless, the semi adjustable articulators are an
invaluable supplement to diagnosis and can save time with occlusa!
adjustments when restorations are fitted.
Reorganization maybe considered when the existing IP is considered
unsatisfactory for any of the following reasons:
Repeated fracture or failure of teeth or restorations:
Clinical experience suggests that persistently failing restorations (for example
crown and bridge debonding) are very commonly attributed to unfavorable
occlusal loading which may be improved by reorganization. Bruxism:
An optimally constructed occlusion will better be able to deal with the forces
generated in parafunction.

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Lack of interoeclusal space for restoration:
Reorganising the occlusion to eliminate a large horizontal component of slide
between CR and IP can create a valuable interoeclusal space for the restoration
of worn.anterior teeth. Alternatively, the occlusion may be reorganised at an
increased vertical dimension necessitating occlusal coverage for at least one
arch.
Trauma from occlusion:
This may be soft tissue trauma (due to teeth impinging on the cheek or alveolar
ridge) or periodonlal trauma (due to excessive or aberrantly directed occlusal
forces) the latter may have an accelerating effect on periodontal disease
although the evidence is conflicting. Reorganisation of the occlusion to direct
forces axially and eliminate interferences and premature contacts can reduce
tooth mobility. However, the overall gain in periodontal attachment is marginal
and should be considered as no more than adjunct to periodontal management.
Unacceptable function:
Poor tooth to tooth contact with tilting and overeruption of teeth may create
problems with masticatory function, particularly when large number of teeth
have been lost. Unacceptable esthetics:
Alteration in the clinical crown height may be necessary to improve esthetics,
and this may be made possible by constructing the restorations to a reorganised
occlusion, possibly at an increased vertical dimension.
The presence of TMD: The link between the occlusion and TMD is
controversial.

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Reasons for Full Mouth Rehabilitation:
The most common reason for doing full mouth rehabilitation is to obtain and
maintain the health of periodontal tissues.
Clinical periodontal findings are correlated with radiographs to determine the
extent and character of any disease findings must then be correlated to function
of the mouth in examining the function of the mouth, many factors must be
considered. The most important factor is discrepancy known as the "premature
contact" a contact between an upper and lower tooth that prevents or interferes
with the normal path of closure of mandible. The area that receives the force of
closure after the patient "skids" off the prematurity may relate to a greater
degree of disease. This area receives the force in the form of a rebound as the
normal path of closure is interfered with by the premature contact.
The various excursions of the mandible must be examined to determine how
much harmony exists between the jaw movement and the tooth contacts, and
the teeth that receive most of the load in the different positions should be noted.
A definite correlation between the malfunction and the clinical periodontal
findings is usually possible. This correlation generally precludes all other
potential causes of the pcriodontal condition. Even so, in order to attack the
problem from every conceivable angle, we must consider and investigate each
of the other factors.
In conjunction with malfunction, we must consider oral habits that could have a
bearing on the condition present. These may include such things as bruxism.
lip-chewing, thread-biting, tongue habits, and soon.
Temporomandibular joint disturbance is another reason for full mouth
rehabilitation. This may be difficult to diagnose, and great care must be taken
to determine the etiological factors involved. Frequently, there is a poor

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relationship between the articulation and the movements of the joint -a
disharmony of function. Sometimes there is a muscular dysfunction that is
caused by some irritant or a nervous affliction. This muscular dysfunction may
be caused by the poor articulation, which produces muscle spasms, and these in
turn may be interpreted as a joint disturbance. In joint cases, the periodontal
condition is usually very good, which is probably why the joint has been
injured instead of the periodontium. When a disharmony exists, we must
ascertain whether the patient is injuring his joint as a result of malfunction, a
bad habit, or an emotional disturbance. Emotional disturbances are very
difficult to deal with and often require the assistance of a competent
psychiatrist.
Still another reason for full mouth rehabilitation is the need for extensive
dentistry. In such cases, some teeth are missing, others are worn down, and
there are old fillings that need replacing. Usually, the patients have little
periodontal involvement and no joint symptoms. These are the easiest cases to
treat, and the beginner should limit his or her full mouth rehabilitation to them.
As long as extensive dentistry is necessary, why not work on the case as a
whole so that ail the parts will be related to each other and to the function of
the individual?
By far, the most difficult patients to treat are the few who have succeeded in
developing a severe periodontal condition as well as a malfunctioning joint.
Even though the joint may be asymptomatic, it may exhibit a behavior pattern
that is troublesome to deal with. It may be mobile, and the dentistry may
require frequent adjustment as the joint begins to function properly with
possible heaiing. In addition, tooth settling and migration will increase the
discrepancies. These are the cases that try men's souls, they require one to
proceed with extreme care and to anticipate the possible contingencies.

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Sometimes it is impossible to predict the extent of treatment necessary in order
to resolve the condition.
The treatment of the emotionally disturbed patient with a joint probiem is
probably the most exasperating. Although it is possible to treat the condition
physiologically, the emotional disturbance is another problem. Patients
with beautifully functioning masticatory mechanisms may still be able to
produce joint symptoms almost at will. It is unpleasant to have to suggest
psychiatric treatment, but if the dentist is convinced that this is the problem,
then he owes it to the patient and to himself to recommend such a course.
Which Patients Should Not Be Treated by Full Mouth Rehabilitation?
Frequently, friends and relatives of one's rehabilitation patients will request
similar treatment. There are many malfunctioning months that do not need
extensive dentistry and have no joint symptoms. These cases are best left alone.
Some mouths that have the potential to break themselves down, never actually
produce the destruction, for some reason. We are not justified in prescribing a
full mouth rehabilitation unless there is definite evidence of tissue breakdown.
One may argue, as many have, that it should be undertaken as a preventive
measure. But there are many malfunctioning mouths that do not break down,
proving that we cannot predict such things. If there is need for extensive
dentistry, then by all means it should be carefully correlated to the rest of the
mouth by complete rehabilitation. Some times one or two "good" teeth may
have to be operated on in order to satisfactorily accomplish our objective.
Ideally, dental procedures should be directed toward the prevention of such
conditions: in short, no pathology -no treatment.

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THE GOAL OF FULL MOUTH REHABILITATION
History
The modern practice of renewing and reorganizing (he teeth by prostheses
began with the idea of'raising the bite" to rectify closure resulting from
excessive wear of the occlusal surfaces. Later, such closure was associated with
hearing loss, noted by Costen. This view, though later questioned, served to
stimulate interest increasing the length of the patients own teeth and thus in
increasing the vertical dimension.
In correcting articular disturbances, the best procedure came to be the retention
of the remaining natural teeth in so far as this was possible. To accomplish this,
these teeth were rebuilt to harmonize with the movements of the joints in order
to protect them from further injury.
With our present understanding of traumatic occlusion and its deleterious effect
upon the supporting structures, the procedure known as "bite raising" has
shifted in emphasis and broadened in scope and is now designated by a term
that describes it accurately. Full mouth reconstruction, jt now includes therapy
which will, by improving the relationship of the teeth, improve the condition
and health of the supporting structures.
When the teeth have been realigned through full mouth reconstruction, the
general tone of the supporting tissues invariably improves. What factors
account for this improvement? Obviously, the removal of excessive lateral
forces and the elimination of plunger cusps and similar forces attendant upon
the realignment of full mouth reconstruction lessen continuous injury to the
supporting structure. But these factors, though helpful in improving the
condition of these structures, are less important than the increased stimulation
of and circulation in the tissues that are brought about by the improved
function.

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The masticating apparatus that is normal, healthy, and functioning is able not
only to carry out the work for which it is designed, but also to maintain itself in
health. The various structures involved, through their form and arrangement,
provide for both the synchronization of, and mutual protection against, all
forces. When function is good, a generous blood circulation furnishes the tissue
with the elements needed to keep them in a healthy condition. When function is
disturbed by malocclusion, the relation between the mutually protective parts
of the masticating apparatus is disrupted; moreover, because of lessened use,
blood circulation is diminished.
As indicated by O'Rourke, the force of a persons masticatory muscles remains
fairly constant. It is the use of the force that changes under conditions of
traumatic occlusion. The patient's ability or willingness to use his muscular
force is dependent upon the comfort, or absence of pain, he experiences each
time he brings his jaws together.
Mutilated mouths with chronically inflamed supporting structures, due to
traumatic occlusion, will support very little force without producing some
discomfort. The result is continuous subnormal use of, or at best failure to
make vigorous use of, the teeth and jaws. The vascular tissues of the
periodontium can be stimulated only by the teeth in function. Such stimulation
is lacking when this function is impaired by the inability of the patient to use
the musculature in chewing because of the tenderness of these tissues.
The results, in the words of Merritt, "are" atrophy of the alveolar process,
malocclusion of the teeth, dental caries, impacted and missing teeth,
periodontal lesions, and so on. Unfortunately, subnormal function lower vitality
at the same time that it increases susceptibility to disease.
Patients who have had full mouth rehabilitation commonly say that their
mouths feel "stronger". The masticatory muscles have obviously not been

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strengthened by therapy. What has happened is that out patients can exert
greater force with comfort and without anticipation of pain than they could
before and that therefore they do exert greater force.
The therapeutic benefit of improved tooth arrangements and improved
functioning have been indicated. The individual patient's reaction bears witness
to these benefits and should inspire us, in terms of human satisfaction as well
as of scientific progress, to strive continuously for improvement in the
techniques of full mouth rehabilitation.
It should be kept in mind that although the operations of all mouth
rehabilitation procedures are performed on tooth units, they have one basic
objective: the equalization of the forces directed against the supporting
structures. Any disharmony at the occlusal or incisal aspects of a tooth will
direct forces against these malaligned surfaces and thus subject the supporting
structure to traumatic injuries. Similarly, any impairment of buccal or lingual
harmony will be reflected in injury to the gingival tissue and subsequently to
the deeper tissues involved in supporting the tooth. The proximal contact
anatomy is also vital in maintaining the health of the underlying soft tissue.
Poor contact relationships encourage food impaction with resultant periodonlal
tissue loss.

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ANATOMY AND PHYSIOLOGY OF THE MASTICATORY
MECHANISM
An understanding of the anatomy and physiology of the masticatory
mechanism is essential to intelligent diagnosis and adequate treatment. If we
know, how the normal masticating mechanism functions, we will be able to
recognize its malfunction and be, in a position to correct it. A correlation of the
anatomy of the parts and the function of the parts will help one understand the
intricacies of the mechanism.
The Osseous Structures:
The masticating mechanism is primarily made up of three osseous structures:
the temporal bones, the maxillae, and the mandible. The maxillae and the body
of the mandible house the teeth -the instruments of mastication. The temporal
bone and the condyle portion of the mandible form the contact or articulation
between the osseous structures of the mechanism. In addition, the muscles that
activate, the chewing mechanisms obtain their anchorage from and are attached
to these osseous structures. Continuous contact is made between the mandibles
and the temporal bones by means of the temporomandibular joints. The glenoid
fossa of the tempoial bone is concave antero-posteriorly as well as
mediolaterally. It is the shape of the anterior slope of the-fossa that determines
the condyle paths (lateral, protrusive, and lateral-protrusive). The head of the
condyfe is oval in shape, with its long axis at an oblique angle to the median
axis of the skull. The synovial membranes and the meniscus are inter-posed
between the fossa and the condyle(fig-l).
In function, the head of the condyle rotates on the undersurface of the
meniscus. It is in this compartment of the joint that the hinge-like action of the
joint takes place. The hinge-like action is the center of action of the parts: the
disc, the condyle head, and the synovial membranes. The upper surface of the

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disc makes contact with the articular eminence of the glenoid fossa. It is the
simultaneous sliding of the disc and condyle that produces the translatory
movement of the temporomandibular joint. In other words, the head of the
condyle rotates on the undersurface of the disc the condyle and the disc
together translate in the fossa (anteroposteriorly, mediolaterally, or inbetween).
The meniscus, or disc, consists of fibrocartilage, which is oval in shape and
thinner at the center than at the circumference. "The inferior surface is concave
and Fits on to the condyle of the lower jaw; while its superior surface is
concavoconvex from before backward, and is in contact with the articular
surface of the temporal bone" (Morris. 1933).
The stress-bearing character of the disc is evident in the fact that ihe blood and
nerve supply is in the periphery, the center being devoid of these tissues.
Contact between the head of the condyle and the articular eminence is made by
the cenier of the disc. The stress of mastication in the joint is absorbed in this
relation. The meniscus has its bearing against the articular surface of the
temporal bone(fig-2), which forms the anterior wall (articular eminence) of the
glenoid fossa. It is in this relationship that the forces of mastication are
absorbed by the temporomandibular joint.
Lubrication of the joint is accomplished by the synovial membranes. Each
compartment of the joint has its own synovial sac.
The disc and the synovial membranes are neither compressible nor variable in
the normal course of events, but serve as ball bearings between the skull and
condyle.
Function of Ligaments and Muscles:

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Ligaments and muscles hold the temporomandibular joint and the chewing
mechanism together. The ligaments limit the amount of movement of the
mechanism and prevent the mechanism and joint from falling apart when the
muscles are relaxed.
They help to determine the position to the mandible when the muscles relax:
thus, to some extent, physiological rest is govcrneu by these ligaments.
The most important ligaments of the temporomandibular joint are the capsular
and the temporomandibular. The temporomandibular ligament forms the lateral
part of the capsule and reinforces it. The upper part of the ligament is broad and
is attached to the zygoma and to the tubercle (articular eminence of the
zygoma). It is inclined downward and backward and is inserted into the
condyle and neck of the mandible laterally(fig-3). The fibers coming from the
tubercle are short and nearly vertical. Together, the capsular and
temporomandibular ligaments enclose the structures of the joint and tend to
limit its1 movements. Sphenomandibular and stylomandibular ligaments are the
two accessory ligaments that protect the joint during wide excursions (fig-4).
These ligaments are loosely attached in the upper compartment of the joint to
permit translator;' movements. They are more firmly ' attached in the lower
compartment where the hinge-like action takes place. The temporomandibular
joints are movable fulcrums activated by the muscles of mastication. These
joints have some of the elements of a ball and socket. They glide forward and
backward as well as sidewise. Actually, they can glide and rotate at the same
time in the manner of a movable ball and socket.
Muscles of mastication:
In a discussion of the muscles of mastication, there is a tendency to speak of
individual muscles and describe I heir separate actions, but muscles function in
groups as kinematic chains. The Temporalis Muscle:

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The temporal is muscle is a large, strong muscle of mastication. It has its origin
in the temporal fossa on the side of the skull. Its origin covers a considerable
area and. by means of an aponeurosis, it connects with its mate on the other
side of the skull very much in the manner of a saddlebag. Its insertion is in the
coronoid process of the mandible and reaches down to the ramus of the
mandible

should

be

noted

that

the

insertion

is

anterior

to

the

temporomandibular joint. Although the fibers of the temporal is muscle are
described as vertical, oblique, and horizontal, contraction of any or all of these
fibers has a definite tendency to elevate and relrude (he mandible. This is
understandable if we recall that the temporomandibular joint is made up of the
glenoid fossa, the anterior surface of which slopes upward and backward, and
that the meniscus is interposed between the head of the condyle and this slope.
Any contraction of a muscle attached in front of this upward slanting guide
must have a tendency to brace the condyle head in a posterior and superior
position(fig-5).
The Masseter Muscle:
The masseter muscle has its origin in the zygomatic arch. It arises in two heads:
a superficial one from the outer border of the arch, and a deeper one from the
inner and more posterior portion of the arch. Its insertion is in the outer angular
region of the mandible. Fibers of the masseter muscle are almost at right angles
to the occlusal surfaces(fig-5).
The masseter is a very powerful muscle of mastication. Its contraction elevates
the jaw and forcibly brings the teeth together. Like the temporalis muscle, its
contractions tend to seat the condyle in a posterior-superior position in the
glenotd fossa. Neither the temporalis nor the masseter has anything to do with
lateral movements of the jaw. Their contractions primarily elevate the jaw and
bring the teeth together. It is because of this action that the occlusal surfaces of
the teeth must harmonize with the hinge-like action of the mandible. The

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masseter can snap the teeth together in any position from centric to protrusive.
Having the occlusal surfaces of the teeth in harmony with this action permits a
better dissipation of the forces of this muscle to the periodontal tissues of the
teeth as they come together through a bolus of food.
The External and Internal Pterygoid Muscles:
The external and internal pterygoid muscles are responsible for the lateral
movements of the mandible. The external pterygoid has its origin, by means of
two heads, in the great wing of the sphenoid bone and the outer surface of the
pterygoid plate. The uppermost fibers of this muscle are inserted in the articular
disc through the articular capsule. The majority of the remaining fibers are
inserted in the anterior surface of the neck of the mandible.
The fibers of the external pterygoid muscle are in a horizontal and medial
direction, and their contraction pulls the head of the condyle and the meniscus
forward and medially. This action sets the mandible into position for chewing.
If the external pterygoid on one side relaxes while the one on the other side
contracts, the mandible will be moved into a lateral position. It guides the
mandible into lateral position and steadies it while the subject bites (contraction
of the temporal and masseter) in the lateral position, Contraction of the fibers
of the external pterygoid also tends to act as a brake against the posterior pull
of the temporalis muscle. It effects a muscular balance against any violent
jamming of the head of the condyle posteriorly(fig-6).
The internal pterygoid muscle originates from the palatine bone and the maxilla
and from the internal surface of the pterygoid plate. Its fibers are inserted in the
lower part of the inner surface of the ramus of the mandible at the angle. They
run laterally, downward, and backward(fig-7).

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Neuro-Muscular Coordination:
The various structures and individual movements just described are
coordinated by a complex integration of the nervous function. During
mastication, sudden contact of a tooth with a hard object produces discomfort
and reflexively opens mouth. This is called a nociceptive reaction and is
partially responsible for protecting the chewing mechanism when there are
premature contacts in the articulation.
Reciprocal Inncrvation:
The nociceptive reaction is able to protect the mechanism because of the
phenomenon known as reciprocal innervation. This is the simultaneous
activation of a flexor reflex and the inhibition extensor (stretching) reflex, and
vice versa.
Rhythmic chewing is made possible by the efficient reciprocal innervation of
the masticatory muscles as they alternately depress and elevate the lower jaw.
During mastication, proprioceptors in the muscles, tendons, and joints send
messages through afferent fibers in the trigeminal nerve to the chief sensory
nucleus of this nerve. Secondary fibers cross the brain stem, ascend to the
thalamus, and finally arrive in the sensory cortex via tertiary tracts. In this
manner, awareness of motion in the jaws and of the position of the mandible in
relation to the maxillae during chewing movements is permitted. Some
proprioceptive impulses pass from the chief sensory nucleus to the cerebellum,
thence through a chain of neurons to the motor cortex. The motor cortex is thus
informed of the position of the teeth and jaws. and its action makes possible the
synchronous mastication movements. Motor activity, whelfter reflex or
voluntary, demands little conscious effort: so it becomes necessary to have all
the parts of the masticating mechanism working in harmony with each other to
prevent its self-destruction.

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Movements of Mastication:
The masticatory movements of the mandible are automatic and occur under
considerable force. Mastication begins with the incision of a morsel of food: To
accomplish this, the mandible is dropped open by the contraction of the
external pterygoids and the infrahyoid and digastric group of muscles. If the
external pterygoids contract equally (which is improbable), the patient will
execute a straight protrusive movement. More likely they will contract
unequally,

and

a

lateral protrusive position will be assumed. Now the

incisor teeth have to be propelled through the food to cut it, and this is
accomplished by the contraction of the elevators of the jaw: the lemporalis,
masseter, and internal pterygoids.
After some food has been grasped, mastication proceeds. The bolus is
propelled into the mouth by the lips, tongue, and checks and probably is rolled
onto the bicuspids, which cut it up further with the crushing and shearing action
of their blades. The temporalis and masseter muscles partially relax allowing
the food to be replaced on the chewing surfaces. The external and internal
pterygoids are in a state of alternate relaxation and partial contraction, and the
temporal is and masseter again contract to crush the food some more. By this
time, and after several strokes, the bolus has reached the molar teeth, where
now it will get a final milling before is swallowed. The masseter and temporalis
muscles relax; the external and internal pterygoids on the same side contract
while those on the opposite side relax, thus cocking the mandible in a lateral
protrusive position. The food is now repositioned on the occlusal surfaces of
the molars, and the real power of mastication is applied by the masseter,
temporalis, and internal pterygoid muscles. As the masseter and temporalis
muscles contract and crush the food, the alternate contractions of the internal
pterygoids cause a wiping of the lower occlusal surfaces of the molars across

19

the upper occlusal surfaces in a finely triturating action that comminutes the
food preparatory lo swallowing.
More specifically, if the bolus of food is on the lower right first molar and
ready for its final comminution, the temporalis and masseter muscles on both
sides relax. The external and internal pterygoids on the right side relax; the
external and internal pterygoids .on the iefi side contract and cock the mandible
to execute a working occlusion on the right side. Now the temporalis and
masseter muscles on both sides contract forcibly to crush through the food. The
external pterygoid on the left side relaxes, permitting she mandible on the left
side to return home. As the condyles both approach centric position, the
internal pterygoid of the right side contracts, executing the Bennett movement.
The masseter and temporalis on the right side soon relax, permitting the followthrough of the masticating stroke as the external pterygoid on the right side
contracts.
It must be remembered that during all of the jaw movements the condyles and
menisci are moving together. Again we must emphasize the harmonious
relation of the teeth to these movements that should exist if the investing
structures are to be protected from destruction.
Harmony of Form and Function:
Because of the complexity, automation, and force fullness with which the
chewing cycle is executed, it should be apparent that a high degree of harmony
must exist between the form and function of the 'parts. Although nature has a
buiit-in safety device in the proprioceptive reflex mechanism, repeated insults
in the form of a premature contact may impose the learning of a new reflex
pattern. It may not be as effective as it should be, and soon the additive trauma
will begin to take its toll. Then too, with advancing age the sharpness of the
protective reflex is lost, and more and more damage is done to the mechanism.

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Protection by Proprioception:
It is interesting to note that the protective proprioceptive reflexes operate best
during normal function. The self-protective mechanisms are weak or missing
during non functioning movements. It has also been shown that reflex activity
is reduced during sleep, with the nonsecretion of the parotid gland. The
protective proprioceptive reflex apparently fails to function during bruxism.
This is one reason for correcting the malocclusion of patients who practice
bruxism, for while it may not cure the habit, it will minimize the damage that is
done.
Up to now we have attempted to briefly outline the chewing movements and tc
describe the anatomy of the masticatory mechanism. Very little has been said
about the teeth, the chewing implements: but we have implied that a harmony
of form and function is necessary.
The objective of maintaining the health of the structures of the mechanism is of
prime importance. To accomplish this, we strive to prevent any part of the
mechanism from overworking or being abused. A certain amount of work has
to be done in the form of chewing. For the moment, let us disregard any bad
habits and consider only the normal use of the apparatus to masticate food.
A certain amount of muscular force is necessary and available. How that
muscular force is dissipated by the various components (the joints, teeth, and
investing structures) is of extreme importance. For instance, if, in the chewing
cycle previously described, a single tooth came into contact before the others,
what would be the result? As the patient penetrated the food bolus, the
premature tooth would receive all the muscular force exerted after penetration
of the food. This force in turn would be transmitted to the periodontal tissues
and in time would cause their destruction.

21

By harmony of form and function, then, we mean an equal distribution of the
forces of mastication that will permit the periodontal tissues of all the teeth and
the stress-bearing portion of the joints to equal) absorb this muscular force.
Equal distribution of the functional forces over as much tissue and as great an
area as possible will guarantee the health of the entire mechanism: this is the
objective of our treatment.

22

THE HINGE AXIS
The successful application of the hinge axis in dentistry was the greatest single
contribution of the Gnathological Society. It was the cornerstone of all future
accomplishments and still is the basis for articulation.
The hinge-like action of the temporomandibular joint has been described by
anatomists for over a hundred years. Its application to dentistry, however, had
to wait for the Gnathological Society in the 1920s. Prior to that, Snow, Gysi,
and others had been aware of the presence and importance of an opening and
closing axis. Yet their methods were so crude that they concluded that the axis
was somewhere below the condyles. This inaccuracy led them to believe that
changing vertical dimensions was still a chair operation.
The desirability of being able to reproduce the opening and closing component
of jaw movements on an articulator must have been evident. That they were not
able to accomplish this was the fault of the methods used and the fact that there
was no articulator that could duplicate this movement. The Gnathological
Society developed a means of attaching a face-bow rigidly to the mandibular
teeth. This permitted accurate location of the opening and closing axis. Many
refinements in equipment were, of course, -necessary to make this a practical
procedure. For example, easy adjustment of the caiiper points was a "must."
After it had been clinically demonstrated that there was a usable hinge axis, it
became necessary to design an instrument that would duplicate this component.
The articulator had to have an intercondylar axis that could be aligned with 'he
axis located on the patient.

23

Definition of the Hinge Axis:
What is the Hinge Axis?
The head of the condyle rotates on the undersurface of the meniscus. While it
rotates on the-meniscus, the meniscus and condyle can move on the surface of
the articular eminence. The movement can be forward, to the side, or anything
in between. While the meniscus and condyle are thus translating, the condyle
can execute a pure hinge movement anywhere along this translation.
Consequently, mandibular movements appear to be very complicated and
confusing. It is practical to locate the center of vertical motion; it is also
practical to locate the center of lateral motion. The center of vertical motion
and the center of lateral motion are one and the same -the center of rotation and there is one in each condyle.
The hinge axis is an imaginary line connecting the center of rotation of one
condyle to the center of rotation of the other condyle(fig-8). The vertical
opening and closing movements, as well as the pure lateral movements
originate from the centers of rotation. Any combination of vertical and lateral
movement has its center in the same point. The center of rotation of each
condyle is constant to the condyle, and therefore to the mandible. The hinge
axis (the imaginary line joining these centers) then is constant to the mandible
(and teeth). As the mandible moves in its various excursions, the hinge axis
moves right along with it. The mandible is capable of executing a hinge-like
closure in any position(fig-9). This is one reason why the hinge axis is so
important. It permits us to duplicate all the arcs of closure of the mandible on
an instrument and thus tailor our cusps to harmonize with these arcs.
One point of confusion about the hinge axis stems from the method of locating
it. It is located in the rearmost position of the mandible - the terminal hinge
position. It is located in this position because only here can it be repeatedly

24

separated from the other components of jaw motion. The patient, of course,
does not function in this terminal hinge position. We purposely make him
execute a terminal hinge closure so that we can locate the center. Once it is
located, we endeavor to trace the path of this center to enable us to duplicate
every possible combination of the two movements (rotation and translation)
that the patient will use in function.
By determining the hinge axis and transferring it to an articulator, it is possible
to make casts of the mouth (teeth) in the exact dynamic relationship to each
other that exists in the patients head. Only by use of the hinge axis is it possible
to have teeth approach each other on an articulator exactly as they do in the
mouth. The hinge axis permits us to have the vertical dimension under our
control on the articulator and to duplicate all the eccentric relations and all the
possible contacts of the teeth in these relations. We can study and diagnose
tooth relations thoroughly; confident that they are exactly as they exist in the
patient's mouth, and we can return our work (whether dentures or natural tooth
reconstruction) to the instrument for correction with knowledge any changes in
vertical relations will be harmonious when placed in the patients mouth. It is
only by means of the hinge axis (and centric relation) that the teeth can be
related accurately to the terminal hinge position.
The Hinge Axis and Centric Relation:
To secure a centric interocclusal record, we attempt to "freeze" the terminal
hinge closure at a convenient opening. Without the hinge axis, we would be
unable to secure an accurate centric interocclusat record because to obtain such
a record, the recording medium must not be penetrated by the teeth or the
occlusion rims. (The implication is that the mandible would deviate because of
the guidance of the penetrating teeth or rims). In order to avoid penetration (at
least in dentulous cases), we must obtain centric interocclusal record in an open
relationship, and if we were not on the same arcs of closure, our efforts would

25

be useless. It is impossible to check a centric inlerocclusal record without an
axis mounting.
Technique for Locating the Hinge Axis (fig-10):
The location and transference of the hinge axis are not very difficult
procedures, but they must be carried out with great care because they form the
foundation for many other procedures. A convenient type of facebow is used. It
must be rigidly attached to the mandible so that it actually forms an extension
of the mandible.
A reference plate or clutch is cemented to the lower teeth with Truplastic.
Graph-lined flags are placed on the side of the face over the condyle areas to
eliminate any skin movement distraction. These flags may be attached to the
maxillae by means of a crossbar and a maxillary clutch, or they may be held in
place by a head frame or other contrivance. A crossbar is attached to the lower
reference plate or dutch.
Adjustable side arms are placed on the lower crossbar with the styli in the
vicinity of the condyles. The patient must now be instructed in the hinge-type
of movement. As previously indicated, this is not a normal movement for the
patient it is for our convenience only. The patient must be coached to let his
mouth drop open. This necessitates the relaxation of the external pterygoid
muscles, and some patients may have difficulty in comprehending this
movement. It helps sometimes to have the patient place his hand on our chin as
we demonstrate the type of relaxed opening and closing desired.
Possible Need for Bite Plane Therapy:
If a patient has difficulty in executing a pure hinge movement, it may be
necessary to train him in This abnormal opening and closing movement.
Training can be accomplished by using the jig.

26

In some cases where joint pathology may be present it may be necessary to
have the patient wear a bite appliance of some kind to disclude the teeth and
allow the joint to return to a more normal condition. Three or four days will
usually suffice, but sometimes several months of bite plane therapy may be
required. The patient must be carefully monitored during any extended period
of wearing a bite appliance for tooth movement.
The patient naturally opens downward and forwards a combination of rotation
and translation. We must separate the rotation from the translation so that we
can locate the center of vertical opening. In addition, this opening and closing
must be accomplished in the terminal hinge position, for here we can get
repeated concentric arcs that will permit us to locate their center. Any other
arcs will serve only to confuse the issue, at this point. What we actually have is
a compass with bent rigid arms. The pivoting part of the compass is on the
center of rotation in the patient's condyle. The stylus point is the tracing part of
the compass. If we succeed in getting the tracing point exactly over the
pivoting point, there will be no arcing of the tracing point. Geometrically, if we
had two concentric arcs, and if we erected bisecting perpendiculars to the
chords of these arcs, they would intersect at the center of the arcs(fig-11).
However, there is no practical method for making such a plot. The trial and
error method first used by Dr. McCollum is still the only practical way to
locate the axis.
When we succeed in getting the patient to execute a rhythmic opening and
closing in the terminal position and the stylus point is arcing, we visualize
where a center would have to be for scribing such an arc. Thus, we will have an
idea of which way to move the stylus in order to reach the center. After making
an adjustment in this direction, we try it again. As we approach the center, the
arcs will become smaller and a little more opening will be required to magnify
the arc. After several adjustments, we will be close to the center. A magnifying

27

glass should now be used to help us see whether there is still any arcing of the
stylus tip. The graph lines will aid the eye in determining this. By viewing
down one line and then down the crossing line, we can see whether there is any
slight arcing. If there is, we continue adjusting until it disappears completely.
We must learn to distinguish between the pure hinge movement and the
movement with some translation. The patient will inadvertently make a
translatory movement every third or fourth try. Some patients will
be most cooperative; others will be exasperating. Nevertheless, we must arrive
at an axis if the rest of the procedures are to be correct.
The axis center must be located on each side. What we arc locating is the hinge
action on the side of the face. It is a point on the hinge axis and not the actual
center of rotation. The actual center is approximately 10 or 11mm medial to
this location. Consequently, the location of this point must be made as close to
the skin as possible. This means that the flag must be very close to the skin
(fig-12).
Marking the Axis Location on the Patient:
When we are satisfied that we have located these points on the axis, we remove
the flags from the patient. A marking medium, such as an indelible pencil, is
rubbed on the end of the stylus. We make sure the patient is in the terminal
hinge position and then have him move his head out of the headrest, making
sure that he does not also move out of the terminal hinge position. The stylus is
gently pushed against his face to transfer the paint to the skin. These marks are
made permanent by using a special needle and a little pink marking dye sulfide of mercury (fig-13).
In all of our subsequent transfers we must try to simulate these conditions -the
skin in the same relaxed position and the stylus pins locked the same distance
from the face as they were before the flags were removed. This is usually 1/16

28

of an inch from the skin. By doing so, we reduce to an absolute minimum any
possible error in transference. In addition, the stylus pins must be locked and
not moved until the mounting is completed. The articulator has to have an
intercondylar axis that can be extended to these points so that the transfer is
accurately lined up with the axis of the machine.
Selection of a Face-Bow:
From a purely theoretical point of view, an ordinary face-bow such as a Snow
or Hanau can be used to locate the hinge axis. To attempt to use either one of
them in actual practice, however, is impossibility. It is a bit more practical to
use one of these bows as a transfer instrument, provided the styli are perfectly
lined up one to the other. As a matter of fact, if the styli are perfectly lined up
and we are able lock the bow by means of the universal joint in front so that the
points of the styli are on the axis locations then it will not be necessary to have
an articulator with an expandable intercondylar axis. Under these
circumstances, it is possible to bring in the styli pins an equal degree towards
the intercondylar axis of the articulator and still stay on the axis. However, it is
far easier and more accurate to use a fully adjustable face-bow (i.e.. one with
arms that can be independently adjusted by means of micrometer screws) for
both the axis locations and transfers.
By means of a face-bow transfer and the mounting frame, the upper cast can be
properly mounted to the axis of the patient.
The Hinge Axis and the Plane of Reference:
The hinge axis is constant to the mandible, as has been indicated. The terminal
hinge position, which is actually the centric relation, is constant to both the
mandible and the maxillae. All our mountings are made in this relation.
Therefore, the only practical way to maintain constant relationships throughout
treatment is to use the axis points and a fixed third point at the base of the right

29

orbit as our plane of reference. Thus, the axis orbital plane gives us a constant
position for the upper jaw, and a correct centric interocclusal record will
establish the position of the lower jaw to the constant upper jaw. In this way,
repeated mountings will have a constant, relation to our records and to the
patient's centers of rotation.
Discussion and Conclusion:
Many have attempted to find fault with the hinge axis and to disprove it. Their
criticisms cover such things as skin mobility, change of the axis, the
introduction of errors by moving the stylus tip a slight degree, and the presence
of a separate axis for each condyle.
Actually, skin mobility is reduced to a minimum by the precaution of having
the patient move his head out of the headrest when all references are made to
the marks. Any changes that might occur over the years from loss of weight
and the like would be minor. As far as change of the axis is concerned, the only
changes observed have been in the joints with some pathology.
If a patient has a painful joint, or if a patient does not execute a hinge-like
closure after a few guided opening and closing movements, it would be
desirable to do one of two things: either train the patient with the jig as you do
when getting a centric relation record, or put the patient on a bite plane for
several days. This will usually relieve the pain and give a smoother hinge-like
movement.
If there are symptoms in a temporomandibular joint, there may be some slight
change in the axis location. Always plan to relocate the axis on such patients a
year or two after the pathology has cleared up.

30

Why use the hinge axis in these cases?
The answer is simple: it is still the only means of establishing a starting point to
which we can repeatedly return and to which we can definitely relate our work
as it progresses. In every normal joint case that we have rechecked over the
years for demonstration purposes and to satisfy our own curiosity, we have
always been able to relocate the axis within very acceptable limits, that is, by
the thickness of the tattoo mark.
The most ridiculous criticism is the charge that error is introduced because the
stylus pin has to be moved through the thickness of the card covering the face.
A Single Transverse Axis:
The allegation that there is a separate axis for each condyle is mumbo-jumbo.
The anatomy and physiology of the joints would not permit a two-axis
arrangement.
About 1950, Dr. William Branstad, Dr. Raymond Garvey, and Dr. Robert Okey
conducted an experiment to determine whether there was one transverse axis
through both condyles or an axis for each condyle. They found that there was
one transverse axis. Dr. Arne Lauritzen, working with a study group, repeated
the same experiment about 1957 and arrived at the same conclusion. Dr. Frank
Celenza and V.O.Lucia repeated the experiment during the summer of 1959,
with the same result. In the fall of 1959, the Hinge Axis Committee of the
Greater New York Academy of Prosthodontics repeated this experiment and
concluded that there was only one transverse axis through both condyles.
This, in brief, was the experiment:
Clutches were cemented to the patient's teeth. A crossbar, 36 inches long, was
attached to the upper clutch, and another of the same length was attached to the

31

lower clutch. Four graph-lined flags were attached to the, upper bar for the
purpose of accurately locating the center of rotation(fig-14).
One flag was placed on each side of the face, close to the skin. The other two
were attached near the ends of the upper bar, about 12 inches from the Hags
against the face. Attached to the lower bar were four adjustable side arms, to be
used in locating the center of rotation. Each side arm was placed against a flag.
The center of rotation was located in each of the four areas, that is, each side
arm was adjusted against its corresponding flag until there no longer was any
arcing, but only rotation of the stylus point. When all four centers of rotation
had been accurately located and the patient was held in centric relation
(terminal hinge position), the cards on the flags were carefully marked with the
tips of the styli. The upper bar with flags attached was then removed from the
clutch. With a fine, heated instrument, a tiny hole, was burned through each
card where it had been marked. When the four flags were held up to the light, it
was possible to see the light through all four flag holes, proving that the four
points had to be on a straight line(fig-15). Thus, it was concluded that there was
only one transverse axis.
To demonstrate this more emphatically, we set up the bar and flags and with a
small penlight passed rays of light through the four holes. The camera at the
other end of the four flags recorded the light rays coming through the four
pinholes. In addition. a piece of dental floss was threaded through the holes.
When pulled taut, it was perfectly straight. This was conclusive proof of the
existence of only one transverse hinge axis.
The existence of a usable hinge axis component to the temporomandibular joint
movement is one of the greatest luxuries that we could have when treating the
oral mechanism.

32

Proof Positive of a Usable Hinge Axis:
On a patient whose axis was located, we proceeded to take centric relation
records at increasing vertical dimensions and compared them with a split cast
mounting. An accurate set of casts was made of the patient's teeth. The upper
cast was prepared for a split cast to accurately examine the likeness of the
various records. The
CENTRIC RELATION
Centric relation means many things to many people: to some, it means the
contact of teeth after a jaw closure; to others, it means a closure in a particular
position, the particular position having many interpretations, varying from an
habitual closure to a forced retrusion, or somewhere in between. Still others
identify it as the most retruded position from which right and left lateral
excursions can be made. Some dentists refer to centric relation when they are
talking about the mandible, disregarding the teeth depending upon their belief
and understanding, they decide that the mandible is in centric position, and that
if the teeth occlude in this mandibular relation, then the teeth are in centric
relation. Other dentists describe "mandibular centricity" as a mandible-tomaxillae relationship at a certain vertical dimension. It is unfortunate that
centric relation means so many things to so many people, because no other
phase of dentistry is as important as a clear understanding of centric relation.
Obviously, it should have one and only one connotation to the dentist.
To understand centric relation and to appreciate its great importance, we must
understand how the jaw functions. We must set about to make restorations that
will function normally in that jaw: they must neither interfere with nor force a
particular action on the chewing mechanism. In other words, the restorations
must fit into the pattern of jaw movements: they should follow, without any
detrimental effects, the movements of the masticating mechanism. Our present

33

concern is with the type of motion, how it takes place, and its bearing on the
all-important subject of centric relation. This, of course, directs our attention to
the temporomandibutar joint. For the moment, we may forget about the ether
important structures -the muscles, tendons, ligaments, nerves, blood supply,
and teeth and confine our consideration to the action of the temporomandibular
joint.
Location of the Centers of Rotation:
It is possible to demonstrate beyond any doubt that there exists a recordable
center of vertical rotation in the condyles. An imaginary line joining these
centers has been termed the hinge axis.
In practice, when we locate the point on the side of the face for the hinge axis,
we are actually locating the hinge action in the facial plane (on the side of the
face).
This is not the true center of vertical motion, however, for that is located in the
condyle. What we are locating is a point on a line-that has been extended from
the centers of vertical motion. In other words, the point we locale on one side
of the face is on the same line passing through the actual centers of vertical
rotation in each condyle and through the point on the other side of the face. For
this reason, when making a transfer, we must not move the points of the stylus
in or out once we have located the point of hinge action. In practice, we must
have a means of transferring these hinge- action points to a suitable articulator,
the intercondylar axis of which can be lined up with these points. This is
accomplished with the mounting frame.
We can locate the centers of hinge action only when the condyle is in a position
where it can repeatedly perform the hinge action. Because patients normally do
not execute a hinge action in the most retruded position of the mandible, they
must be educated to this movement. When we consider this, as well as the

34

many habits patients can acquire over the years and the conditioned reflex
action forced by habits and tooth relations, it is easy to understand why some
patients reluctantly produce the hinge action during treatment.
This hinge action (and the imaginary line called the "hinge axis") is constant to
the mandible. In other words, the vertical motion of the mandible (and
condyles) is produced by the action of the heads of the condyles on the
undersurface of the meniscus. Thus, as the condyle and the meniscus translatemove down the incline of the glenoid fossa or across the trough of the fossa in
the Bennett movement the mandible can produce this hinge-like action in any
position of the condyle. As a matter of fact, it will start to produce a hinge-iike
action as it glides down or across the condyle path. We must remember that the
hinge action is constant to the meniscus in any position in which it may find
itself, but it is constant to the maxillae or fossae only when the condyle is
executing the hinge action in the terminal position..
In addition to the centers of vertical (opening and closing) motion of the
mandible, there exist centers of lateral rotation: The patient can make pure
lateral movements that have centers of rotation located in the condyles. At one
time, there was considerable confusion about these centers because they are
seldom stationary. In other words, the centers themselves move as the mandible
(condyle) is making the movement. The-path of these centers of lateral rotation
on the rotating or working side is the Bennett path. The confusion arose
because it was claimed that the center of lateral rotation was some where in
back of each condyle or in the vicinity of the foramen magnum. The moving
centers of lateral motion were called "loci." Actually, what was termed the
center of lateral movement behind the condyies or "somewhere else" was the
center of the locus. The center of the path that the center of lateral movement
was making on the working side was, in fact, the center of the Bennett path. It
is practical to locate the exact centers of lateral rotation by means of two gothic

35

arch tracings taken in the same plane in front of each condyle and on either side
of the midline of the face and reproduce their path across the fossae (fig-16).
When this has been done in conjunction with the location of the centers of
vertical rotation (hinge action), then we have truly found centric relation. The
terminal hinge action is the vertical component of centric relation; the centers
of lateral rotation are the lateral components of centric relation. Why this is
centric relation, we shall now attempt to explain. We shall also show why. it is
so important.
It might be stated categorically that unless we locate the centers of rotation, we
are disregarding centric relation. This statement will immediately draw protests
because, regardless of one's understanding of centric relation, all will agree that
centric relation is essential to the practice of dentistry and cannot be ignored.
Let us analyze what really happens:
In the course of constructing occlusal surfaces for dentures, bridges, or natural
teeth, we take a centric interocclusal record, using the material of our choice.
The casts on which the restorations are going to be fabricated are mounted on
some sort of instrument, and the case is constructed.
In order for a centric interocclusal record to be usefui, it must register the
maxillomandibular relationship without any tooth contact or tooth penetration
of the recording medium. If tooth surfaces contact through the recording
medium, we can be sure that the proprioceptive reflexes have crossed us up and
caused us to record an improper relationship.
It is apparent that one of two things must be done even to begin to get an
accurate interocclusal record either it must be secured at the exact level of
vertical dimension without tooth contact (a nice trick if it can be
accomplished), or else the casts must be mounted on the articulator to the same
opening axis that the mandible has to the maxillae of the patient. If the latter is

36

done, then the centric interocclusal record can be secured in an open position to
clear the tooth contacts; and when the registering medium is removed, the teeth
on the casts can be approximated as they are in the mouth.
It is also most desirable that we check our centric mounting because many
hours of laboratory work will depend on this relationship. It is utterly
impossible to check a centric interocclusa! record accurately unless hinge axis
procedures and transfers have been used.
In order to check a centric intcrocclusal record, it is necessary to take a second
record, using all the care taken with the first one. It would be pure chance if the
second record were of the exact thickness as the first. The wax might be softer,
or the patient might close further. Whatever the reason, chances are against our
getting records of exact thickness. Yet, unless we were on the same arc of
closure on the articulator as in the mouth, the thick ness of the two records
would have to be absolutely identical.
The seating of a wax interocclusal record on casts can be quite deceptive. The
second record might appear to fit between the casts without causing any
malposition of the articulator parts. However, if we really want to determine
whether our two centric interocclusal records are identical, we must resort to
the following procedure frequently demonstrated in the clinics of Dr. Arne
Lauritzen
The Split Cast Technique:
Before mounting the upper cast on an articulator, second section (the split cast)
is carefully prepared. First, it is very important that the upper cast be poured
with extreme accuracy, care being taken to avoid any bubble formation. The
mounting side the upper cast is trued up on a model trimnifr. "V'notches are cut
on the edges of the mounting side of the upper cast -two in front, two on the
sides, and one in the posterior region. These notches are carefully made so that

37

they are truly wedge shaped. A piece of electrician's tape is wrapped around the
periphery of the cast, producing a form into which the second section of the
split cast is poured. Prior to this pour, the cast has been carefully lubricated
with Kerr Separating Medium. Three knobs of stone are placed on top of the
pour to serve as handles in the separation of the disc from the original cast. In
pouring the disc, it is extremely important to prevent any bubbles from
forming. When the disc pour has hardened, the cast is separated from the disc
by removing the electrician's tape and using the stone knobs on the disc as a
handle. Immediately after separation, the two parts are reassembled to prevent
any dust or loose fragments of stone from adhering lo the contacting surfaces.
The knobs are now cut down with a model trimmer, leaving just enough of
them to engage the new mix of stone that will be used to fasten the disc and
cast to the upper bow of the articulator.
An impression (whether it is for a study cast, a master working cast, or a
remount cast) is poured in stone. The excess stone is vibrated into the plastic
mold groove former and quickly inverted and placed on top of the poured
impression. Press it into place as you center and level the former. Do not invert
the impression. When the stone has set, remove the former and replace it with
the ring mold and secure it with periphery wax. Lubricate the grooved stone
with a separating solution and vibrate a mix of stone of a different color into
the ring mold. Level the surface with a spatula and place several knobs of
excess stone for retention when mounting to the articulator. Remove the ring
'after the stone sets and separate the impression. Trim the sides on ? model
trimmer and you are ready to mount it on the articulator by means of the facebow transfer.
By means of a face-bow transfer, the upper cast and disc are accurately
attached to the upper bow of the articulator. By means of our centric
interoccltisal record, the lower cast is next attached to the lower bow of the

38

articulator. This completes the mounting of the split cast and the lower cast in
what we believe to be a centric relation.
If we now open the articulator, separate the disc from the upper cast, press the
upper cast into the centric interocclusal record to be sure it is accurately seated
in place, and then attempt to close the upper bow and disc into the "V" notches
on the upper cast, we will soon find out whether: our mounting was accurate. If
it is satisfactory, we proceed to check this mounting and interocclusal record
with the second record taken. The first wax record is replaced by the second
one; the upper cast is seated into the indentations; and again an attempt is made
to close the disc into the "V" notches of the upper cast. It is amazing how often
an apparently acceptable interocclusal record is inaccurate. This technique
should be ample proof that a centric interocclusal record cannot be accurately
checked unless the hinge axis and hinge transfer procedures are used.
If these procedures are as far as we go, the restorations constructed on such
casts will come together accurately in centric closure. If we add one more step
and reproduce a protrusive path with a protrusive record, it is possible to have
proper contacts in both the centric and protrusive relationships. Unfortunately,
though, patients do not chew only in these positions. .
How does a dentist manage without using the axis and a protrusive record?
Like the dentist who simply takes a static closure, by proceeding to do a great
deal of work in the mouth, grinding here and there until some surfaces come
together. Considerable work is involved for an inferior result.
The dentist who takes a hinge-closure record, relating it properly to an
instrument by means of a face-bow, and then takes a protrusive record is only
slightly better off because there are all the laterals to contend with. Even if one
believes that the patient does not use his lateral excursions, the fact is that he
will use them if he is permitted to. The apparent shortcuts -not locating an axis,

39

not reproducing all of the patient's movements are responsible for the creation
of flat, useless occlusions. To avoid these headaches, we must locate the
centers of rotation. In addition to locating the hinge axis and obtaining a proper
centric interocclusal record, we must locate the centers of lateral rotation. This
is accomplished by means of the twin gothic arch tracings. Moreover, we must
trace the paths of these centers of lateral rotation. This is done with an extraoral tracing device, the pantograph: the pantograph is the only practical means
of accomplishing this today. With the pantograph, we can trace the protrusive
paths of the centers of rotation, as well as the right and left lateral paths. From
the pantograph tracings made by the path of travel of the centers of rotation, we
can reverse the procedure and duplicate the centers and their paths on an
articulator capable of full adjustment. Now when the restorations are
constructed and placed in the mouth, they will be in harmony with the patient's
movements. It will not be necessary to grind them, with the resultant
destruction of proper function.
To recapitulate: A thorough understanding of centric relation is essential 10 the
proper practice of dentistry. However, unless we locate the centers of rotation,
we are disregarding centric relation, which entails the following:
1. Location of the hinge axis
2. Location of the centers of lateral rotation
3. Transference of the casts to the axis
a) Face-bow transfer of the upper cast to the axis
b) Relation of the lower cast to the upper by a correct centric interocclusal
record.

40

Obtaining Centric Relation - Various Materials for Various Situations
Methods of manipulation for centric relation:
1. One handed technique by Anderson and Tanner (fig-16a).
2. Anterior stop technique a) Lucia jig technique
b) Leaf gauge technique advocated by Long (fig-l6b)
3.

Central bearing point method (fig- 16c)

4.

Bilateral manipulative technique (Dawson technique fig-l6d) Methods for

taking centric bite records
l. wax bite procedures
2. Anterior stop techniques
3. Use of preadapted bases
4. Central bearing point technique.
The technique for obtaining a centric relation is secondary to an understanding
of the phenomena. Various materials will produce acceptable results, but the
important thing is to know what we have to get and to be aware that we have
what we want.
From our preceding discussion we know that we must locate the centers of
rotation. By means of the two gothic arch tracings we are able to locate the
centers of lateral rotation, and by means of the hinge axis location we are able
to locate the centers of vertical rotation. Our practical problem now is to couple
these two centers of rotation into the center of rotation. To do this, we must
relate the lower jaw to the fixed member, the upper jaw. Having related the
upper jaw (cast) to the center of vertical rotation by means of the face-bow and

41

having set the articulator for the centers of lateral rotation, it now remains for
us to orient the lower jaw (cast) to these centers.
We accomplish this by "freezing" the lower jaw (cast) in the terminal hinge
closure at a convenient vertical dimension. This is the problem of obtaining
centric relation. There are many factors that complicate this procedure; and
patience and experience are required to complete the task satisfactorily. Among
the complicating factors are the patient's reluctance to make a pure hinge
closure; the patient's neuro-muscular pattern, which may have developed
around a deflective occlusal contact; the natural tendency of many patients to
go into a physiological rest position at the completion of any jaw movement;
and the natural tendency of a patient to exercise his prehensile reflex whenever
anything is placed between the teeth.
Certain procedures and materials are required lo overcome these factors. The
very first procedure is to practice with the patient until he is able to execute a
pure hinge closure. Second, we must block out some of the neuro-muscular
reflexes by preventing the teeth from coming together. We can accomplish this
by using our thumbnail as a controllable anterior stop. Third, we must keep the
patient under function, swinging up and down so that he cannot go into
physiological rest. As long as the jaw is functioning, its bracing position is
maintained. The natural prehensile reflex can be minimized if we have the
patient close his eyes during these procedures. If he sees the wax wafer (the
recording medium) approach his mouth, he will automatically begin to reach
out to grasp it with his teeth; and this is not a centric closure. We must take
care not to violate these precautionary procedures as we make our recording.
This presents quite a problem because what is really needed is a magic material
-a material that by its lack of resistance will not cause any unequal
displacement of the joint or teeth; a material that will remain sufficiently soft

42

long enough to ensure a dynamic registration, but will "freeze" just as soon as
all the procedures are completed.
Two-Stage Registration:
One method that has proved acceptable is a two- stage registration. A wafer is
made of one sheet of DeLar wax and one sheet of Tenax wax. These are luted
together. The reason for using two kinds of wax is to permit an easy
indentation on one side and to provide a stiffer side that will act as a carrier.
The wafer is placed vertically- in a water bath at 138°F. The anterior part is
kept out of the water so that it will remain stiffer and offer some resistance
anteriorly, thus ensuring the bracing position of the condyles.
While the wax is softening, the patient is rehearsed in the terminal hinge
closure. The patient is instructed to open and close his jaw without clenching
his teeth together. By avoiding the tooth contacts, the patient does not receive
the pcriodontal proprioception that could cause an abnormal reflex closure.
This is what we are trying to avoid: we desire a pure hinge closure free of any
"acquired" malpositions. This procedure will help the patient to execute a pure
hinge closure. It permits the temporomandibular ligament to be extended to its
normal position. It trains the patient to separate the rotation from the natural
combination of rotation and translation that makes up all functional
movements.
The patient is rehearsed in the terminal hinge closure while the cheek retractors
are in place. These conditions will simulate the actual taking of an interocclusal
record. The patient is instructed to close his eyes, and when the wax wafer is
sufficiently soft on the Tenax side, it is inserted into the mouth, with the Tenax
side against the upper teeth. The patient is told to swing his jaw several times
without closing on the wax, and then when we can "feel" the terminal hinge
closure, lie is instructed to close lightly against the wafer. At this stage we are

43

chiefly interested in getting an accurate imprint of the upper teeth in the Tenax
wax(fig-!7).
The wafer is removed from the mouth and placed in water of room
temperature. After partial chilling, it is trimmed to the outside edges of the
tooth indentations to remove the bulk. We also remove the anterior portion,
cutting it off across the center of the cuspids. There is a twofold reason for
removing this part of the wafer: first, with the anterior teeth exposed, we can
use our thumbnail as the anterior resistance; and second, without the anterior
portion, there is that much less area to seat against the casts when we make the
mounting. Consequently, should there be a slight discrepancy in the anterior
part of the casts, it will not cause their malrelationship. In short, our only
concern will be with the posterior areas.
The wax wafer is now replaced on the upper teeth and held in place with the
thumb and forefinger of the left hand. It must be evenly seated against the
upper teeth. The patient is instructed to close into it again to correct any
warpage. The wafer is then removed, and with a Bard Parker knife4 we trim
away with the excess wax around the indentations on the Tenax side, leaving
only the cusp tip indentations so that the cast may be accurately seated when
we make our mounting. Again, we seat it on the upper teeth and have the
patient close once more to eliminate any warpage that may have resulted from
the trimming process. When we are satisfied that we have an accurate seating
of the wafer against the upper teeth, we proceed to complete the interocclusal
record.
We remove the wafer and dry it with a blast of compressed air. Taking a sheet
of AI u wax, we form a "pencil," melt it, and apply the softened wax to the
underside (DeLar side) of the wafer, dripping it on as if using a candle. Aluwax
melts at a lower temperature than DeLar or Tenax, and thus provides us with a
soft surface that can be easily carried to the mouth without warping the

44

wafer(fig-18). We place the wafer on the upper teeth, holding it in place with
our left thumb and forefinger. With our right thumb on the patient's chin, we
guide the patient into the terminal hinge closure.
During this procedure, the patient's eyes arc closed. We have him execute the
terminal hinge closure, but do not allow him to contact the softened Aluwax
until we are sure of the "swing." Gradually, we let him close more and more
after each swing until the Aluwax is contacted. It may be necessary to add wax
several times before we can obtain an acceptable interocclusal record(fig-!9).
The Tests of an Accurate Interocclusal Record:
There are several ways of determining whether an interocclusal record is
accurate.
1. We should hold the wax wafer up to the light to see whether there is any
penetration. If there is. it will not be correct. Likewise, if there are one or two
thin spots, the chances are that it is incorrect. Areas of penetration or thin areas
are likely to cause a slight deviation of the mandible -so slight that we may be
unaware of it. Variations of thick and thin spots will offer variations in
resistance and may cause as much inaccuracy as a penetration.
2. If the thickness is satisfactory, we place the wafer on the upper teeth and
carefully examine it to determine whether the seat is accurate. There must not
be any "give" in any area.
3. We have the patient close into the wafer, first guiding him as we did during
the taking of the interocclusal record and then allowing him to close by his own
muscular force. If there is a hesitation in finding the indentations, the
interocclusal record is probably inaccurate,
4. If the foregoing requirements are satisfied, there is one final test lo make:
we have the patient close into the wafer and hold it firmly; then we examine the

45

posterior portion for any play between the teeth. Both sides should be
examined carefully.
If the interocclusal record meets all these tests, we are justified in accepting it
as correct. This may seem to be a long and tedious procedure but bear in mind
that everything we have done previously and everything we do subsequently
will depend absolutely upon this one procedure. An error in some other part of
the operation may be tolerated but an error here is disastrous.
Up until 1961, the preceding technique was reasonably successful. We still use
this technique for a preliminary record, before locating the hinge axis.
In 1961 and 1962 the "jig" was developed. There was nothing new in the
principle of the jig. The late Ernest Granger used his thumbnail as an anterior
resistance. His analogy of taking a centric record to the driving of a golf ball
said a great deal. He described it. as an art -driving a golf ball well is not
accomplished by many. The late Steve Brown used a wax wafer with chilled
wax anteriorly to seat the condyles. Dr. Grubb and his technician, "Jonsey".
used a gold casting on the lower teeth to maintain vertical and centric relation
while they carved the restorations in the mouth. I am certain that Dr. Pete
Dawson captures the correct centric relation with his jaw manipulation
technique. Dr. Stuart uses a tongue blade for his anterior resistance.
The Jig Technique:
Constructing the Jig:
It is preferable to make the jig on an upper study cast. Some clinicians make it
in the mouth, but this can be dangerous because of the heat generated when the
self-curing plastic cures.

46

Block out any undercuts in the anterior teeth of the cast with wax. Adapt tin
foil over the anterior teeth of the prepared cast. Lubricate the tin foil with
petroleum jelly.
Make a mix of Dura Lay in a dappen dish. When the mix has a doughy
consistency, place it on the tin foil and adapt it labially and lingually over the
centrals. Labially it should extend just over the margin of the gums. Lingually
it can extend onto the palate about 1/2 inch. The sides are tapered to the lingual
'and extend to the distal of the two centrals. Occlusally, ihe surface is a flat
plateau, thick enough to have sufficient material to adjust and separate the
teeth. As the Dura Lay polymerizes, keep removing and readapting it so that
you have a well-fitting jig that can be removed from the model without
breaking the model.
The occlusal surface is not inclined -we don't want a wedge effect Some
dentists have used the jig as an inclined plane. This is absolutely wrong! The
wedge is one of the most powerful mechanical devices in existence. A wedge
can split a mighty oak. The jig used as a wedge can displace the
temporomandibular joint distally with great ease. The platform on the
mandibular surface of the jig is just that a platform against which the lower
anterior teeth will close. It acts as the third leg of a tripod -the other two legs
are the condyles. The platform (mandibular surface of the jig) must not
influence the direction of closure. It must not force the lower jaw to the right or
to the left- It must not force the mandible forward or backward. It just stops the
closure. A very, very slight posterior inclination will assist the patient in
holding this position while the recording material sets. Even in very deep
overbite cases, the contact area is a flat platform, not an incline.
When the jig has cured, we trim it as shown in(fig-20). The labial frenum is
cleared and the labial margin of the jig just goes beyond the tree margin of the
gums. It should fit onto the anterior teeth without being displaced.

47

Three wax wafers are prepared on the upper study cast. Use one sheet of DeLar
wax. Soften the wax in water and place it on the cast so that you can cut it to
proper dimensions. Have the wax extend about % inch outside the buccal
surfaces of the teeth. In the anterior region, cut out a "U" large enough to
accommodate the Dura lay jig
We are now ready to go to the patient. A DeLar wax wafer is softened in water
at 1380 F. The wax wafer is placed in the mouth and the patient is guided into a
closure (hopefully somewhere near centric relation). Before the wax solidifies,
bend the corners of the wax over the labial of the cuspids{fig-21). These “ears"
will serve to reposition the wafer after we cover the indentations with the zinc
oxide and eugenol paste that we will use later. The indentations will be covered
with the paste and will not help us to reseat the wafer in the same position in
which it was imprinted. The "ears" will help us to reseat it in the same place as
when it was formed. The three wafers are so prepared.
Now we are ready to train the patient with the jig. This is one of the important
functions of the jig-to break the patient's habitual closure. It prevents the teeth
from reinforcing together, and thus it prevents the teeth from reinforcing the
reflex act of closure. It short-circuits the proprioception that directs the engram
of closure. Therefore, it is essential that the teeth are not allowed to come
together during the training process. If they did contact, the reflex act would be
reinforced and we would defeat our efforts. A piece of carbon paper is placed
between the mandibular surface of the jig and the lower anterior teeth. The
patient is instructed to move to the right, move to the left, move forward, and
move backward. This has the tendency to free the jaw movement. The jig is
removed and the patient is prevented from bringing his teeth together by
placing a saliva ejector in his mouth. The jig is reduced in thickness with an
abrasive rubber wheel. There usually is a gothic arch traced on the jig. Remove
the tails of the gothic arch and slowly reduce the apex -the area of lower

48

tooth contact. This is area is ground flat -not inclined. The procedure is
repeated again and again until the vertical is reduced, but there is still ample
intcrocclusal space. This should be continued for about 20 minutes. When you
are finished, place one of the wax wafers between the teeth, and with the
patient closing firmly against the jig, the wax wafer must still be free to be
moved up and down between the teeth. There must not be any contact between
the teeth and the wax. When we take the zinc oxide and eugenol wash, the
wafer should literally be floating between the teeth. In this way, there is no
conduction of stimuli from the upper teeth to the lower teeth.
We are now ready to take our final registration. The teeth are lubricated with
petroleum jelly. The jig is secured on the anterior teeth with denture adhesive.
A mix of Temp Bond or a bite registration paste is made and applied sparingly
on the indentations of the wax wafer on both sides. The wax is sandwiched
between the paste. Do not use too much paste. Place the paste-covered wax
wafer in the mouth using the "cars" to seat the wafer on the upper teeth. The
patient is guided into a hinge closure and instructed to hold this position firmly.
The patient is closing firmly against the jig. Hold your thumb on the patient's
chin with the index and middle fingers cradling the undersurface of the
chin(fig-22). This will enable you to know if the patient relaxes before the
paste sets. Keep reminding the patient to close firmly. This will place the
condyles upward and on the posterior slope of the articular eminence -a
position that most believe to be the correct position for the heads of the
condyles.
The record is carefully removed after the paste has set. In order to avoid
warpage, a simple procedure is followed. The thumbs of both hand* are placed
on the patient's 'chin, and the index fingers are placed on the outer edge of the
wax record. The patient is instructed to gently separate his teeth. The wax

49

wafer is braced against the lower teeth -the lower jaw acts as a form. Then the
patient is guided into closure again. Now the thumb and index fingers of the
left hand are placed to support the wafer against the upper teeth, and the patient
is again instructed to gently separate his teeth. The upper jaw now acts as the
form to prevent the wafer from being distorted. The wax wafer is removed
from the mouth and chilled. With a pair of surgical scissors (those with a
serrated jaw to grab the set paste), the excess paste is removed. All we want are
the cusp tip indentations so that we can accurately seat the casts into the wafers
and see if they are perfectly seated. The trimmed wafer is returned to the mouth
(with the jig in place) and the patient is guided into centric relation closure.
This will correct any possible slight warpage that could have taken place in the
removal and trimming. The two other wafers are treated the same way. After
the third record has been taken and trimmed and reseated, we remove the jig
and again guide the patient into centric closure (this time with out the jig).
Remove the third wafer "and don't allow the patient to close. Insert each of the
other two records, one at a time, and have the patient close into them (guided)
without the jig in place. The records are now completed and we arc ready to go
to the laboratory and make our mounting and check our centric relation
records.
There are some considerations for special situations. When taking a centric
relation record for working (master) casts, it is necessary to use several
thicknesses of wax for the record. The reason for this is that because of the
increased interocclusal space after tooth preparations, the paste will not register
the tips of the preparations unless the space is reduced by means of the thicker
wafer. In other words, the paste will not stand up long enough to capture an
imprint.
In a remount record, a single wax wafer is sufficient, because now the
restorations are in place and the interocclusal space is reduced. When anterior

50

teeth are missing, you might have to make a Duralay bridge. Your own
ingenuity is your only limitation. When posterior teeth are missing, you may
have to make a Forma Tray wafer with cones to contact the soft tissue in very
small areas. A little thought will allow you to handle almost any situation.
In the laboratory, the upper cast with the split cast wafer is attached to the
upper bow of the articulator, related by a face-bow transfer. A centric relation
record is used to relate the lower cast to the lower bow of the articulator. When
the mounting in completed, we are read;' to verify our results.
Open the articulator separating the two halves of the split cast arrangement.
Make sure the centric relation record is satisfactorily seated between the upper
and lower casts, and close the articulator. The split cast should come together
perfectly. This assures a correct mounting. Next we must verify the centric
relation records. Remove the record used for mounting the lower cast and
replace it with one of the other records. Again, make sure of correct seating of
the casts in the record and close the articulator. The split cast should go
together as it did with the first record. Repeat with the third record. If ail three
records check out the same, there can be no doubt about the accuracy of the
centric relation you obtained.
The Jones Bite Frame:
Another method of taking an interocclusal record is with the Jones Bite Frame.
After the patient has been "trained" with the bite jig. the recording is made with
a zinc oxide and eugenol paste, taken in a gauze "sandwich." This is a rather
tricky, but accurate, procedure. A Jones Adjustable Bite Frame is used to carry
gauze strips. These are glued to a thin wire insulation known as "spaghetti" in
the radio trade. The insulation tubes with the gauze strips attached are cut into
1 1/2 -inch lengths. These are slipped on the wire frame, which is adjusted

51

according to the size of the patient's jaw. This is best done on a cast of the
upper jaw.
A zinc oxide and eugeno! paste, such as Opotow's Mandibular Paste? or Kerr's
Registration Paste is used. The mixed paste is placed on the surface of the
gauze, and the gauze, which is about 3 inches long, is wrapped around the
outside wire of the frame and then around the inside wire until there is no loose
end. In other words, the gauze, with paste on its surface, is wrapped around the
buccal and lingual wires of the frame. This neatly wraps the paste between the
gauze and between the buccal and lingual wires. A slight amount of paste may
be applied on the upper and lower surface of this roll, on both sides of the
frame. It will take a little practice to learn to manipulate the paste without
becoming entangled in it.
The patient is retracted, after being trained with the jig, and the loaded bite
frame is inserted between the teeth. The patient closes firmly against the jig
until the paste sets (fig-23). The lower jaw is supported by your thumb and first
two fingers to ensure against patient relaxation. The set gauze "sandwich" is
removed and carefully trimmed (fig-24), This record is used tc accurately relate
the lower cast to the upper cast. It is best used to remount procedures where the
actual restorations are involved.
VERTICAL DIMENSION
A simple rule to help us determine the vertical dimension of occlusion on
patients with natural teeth is: do not change the vertical dimension of occlusion
that the patient has when the teeth are intcrcuspated in maximum contact.
Another rule that can be used with natural teeth to keep out of trouble is: do not
open the bite.
Bite raising refers to increasing the vertical dimension of occlusion. It is usual!;
done for one of the following reasons:

52

1. To relieve a temporomandibular joint syndrome
2. To restore "lost" vertical dimension in a severely worn occlusion
3.

To get rid of facial wrinkles

None of these reasons is valid:
Opening the vertical in each of these situations is an invitation to problems. U
is almost always contraindicated. Some facts should be understood about each
of these problems before any treatment is considered.
Bite raising for temporomandibular joint syndrome:
The vertical dimension has nothing to do with temporomandibular joint
syndromes. The pain-dysfunction syndrome can be solved at any vertical
dimension up to the point of condylar translation and down to the point of
coronoid impingement. As long as the condyles are free to go to their terminal
hinge position, the syndrome can be relieved.
Correcting the occlusion at an increased vertical may eliminate Lhe joint pain
but it almost always results in depression of the teeth, instability of the
occlusion, and excessive stresses on the periodontium. Besides, the
temporomandibular joint syndrome often recurs as the teeth shift under the
added stress.
Restoring "lost" vertical dimension:
More study is needed, put much clinical evidence indicates that even severely
worn occlusions do not lose vertical dimension. Restoring "lost" vertical
dimension in a worn occlusion really amounts to opening the bite because wear
does not normally produce a loss of vertical dimension. Patients can wear their
teeth down to the gum line and still not lose vertical dimension, because the
eruptive process matches the wear to maintain the original vertical dimension.

53

This process of eruption and alveolar development may continue throughout
life as teeth are worn because of the continual addition of layers of cementum
on the root and concurrent passive vertical development of the alveolar process.
So even with wear the jaw-to-jaw relationship remains the same when the teeth
are together.
Opening the bite to eliminate facial wrinkles:
On patients with natural opposing teeth, this procedure may have very
detrimental effects. When the masticatory and facial muscles are at rest, the
teeth should not be in contact. Increasing the vertical dimension to the extent of
stretching the wrinkles out puts such an unnatural demand on the stretched
muscles that It may actually accelerate further wrinkling. The increased length
of the teeth positions them in continuous interference to both normal
contracting and resting lengths of the muscles. Such continuous stretch
stimulation may cause reflex contraction of the muscles with damaging results
to the teeth and supporting structures. The stresses exerted on the teeth are
amplified by unfavorable crown root ratios that result from increasing the
length of the clinical crowns. Furthermore, the effect on the continuously
stretched muscle is to "age" it faster and produce worse wrinkles.
Patients who have previously had bite raising procedures to eliminate wrinkles
are often very insistent about further increases. As the teeth depress or the
wrinkles return, they express the need for more and more increase in vertical
dimension. Some patients tell us they were more comfortable when the bite
was first raised and they would like to regain that comfort. It is difficult not to
give in to such z request because it sounds so reasonable. If we understand that
their early comfort was the result of an improved occlusal relationship rather
than the increased vertical dimension, we can almost always regain the comfort
by equilibration without further increase of vertical dimension.

54

The patient must be made to understand that the muscles should be allowed to
position the jaw without interference from the teeth. "Support" from the teeth at
an opened vertical dimension constitutes an interference to the contracted
muscle in a normal power stroke.
Why not increase vertical dimension?
Occlusions get into trouble primarily from stress. The safest approach when
restoring an occlusion is to keep the teeth from interfering with normal muscle
activity.
When a muscle is neither hypotonic nor hypertonic, it is said to be "at rest".
Even resting muscle is in a mild state of contraction. This mild contraction of
antagonistic muscles is necessary to maintain the posture and position of the
bony parts. We cannot contract one muscle beyond its resting length without
affecting its antagonistic muscle to some degree. The antagonist must release
and give the contracting muscle its way or it may respond by isometrically
contracting more forcefully itself to counterbalance the effect of its antagonist.
Either way, the harmony of resting muscle is disturbed. Any restoration,
appliance or denture that interferes with the optimum lengths of the resting
muscles serves as a stimulus that produces hypertonicity. Such hypertonicity
may result clinically in destructive clenching or bruxism patterns.
Many years 'ago, Niswonger defined the rest or postural position as "that
position of the mandible in which it is involuntarily suspended by the
reciprocal coordination of the muscles of mastication and the depressor
muscles with the upper and lower (teeth) separated". He referred to this as a
neutral position of the mandible.
The rest position has often been a popular starting point for determining the
occlusal vertical dimension, but it is an unreliable approach because the
dimension between the rest position and occlusal contact is not a consistent

55

measurement for different patients. The rest position itself is not consistent.
Atwood found variations as great as 4mm, at the same sitting and even greater
variations at different sittings. Finding the vertical dimension of the rest
position and then arbitrarily closing a specific amount is a very unsatisfactory
approach.
If the occlusal vertical dimension can be established in harmony with the
optimum length of contracting muscles, the muscles will be free to rest at
whatever length is comfortable. The practical approach therefore is to
concentrate on accurately recording the occlusal vertical dimension and
allowing the freeway space to be the natural result of the difference between
the optimum length of contracted muscles and the length of the muscles at rest.
Stoneking has proposed that the definition for occlusal vertical dimension be:
"The vertical relationship of the dental arches when there is maximum
inlercuspation of the natural teeth, and the mandibular muscles arc contracting
through their maximum power cycle".
Some muscles may contract as much as 50% to 75% of their natural length.
Mahan has pointed out that the maximum force with which muscle resists
elongation is applied when it is completely committed to contraction.
It is also apparent that an increase in the vertical dimension would interfere
with the optimum length of contracting muscle in its power stroke.
Several studies have shown that there is a significant relationship between the
power point" of muscular contraction and repcatable phonetic and comfort
measurements. Tueller, using electronic means on dentures, found an average
variation of less than 0.5mm from the vertical established at the muscular
power point when compared with either preextraction records or phonetic
methods.

56

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