Dental Implant Design Considerations for Optimizing Surface Area and Load Distribution

IMPLANT DESIGN
AND
ITS CONSIDERATIONS
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com

Contents
 Introduction
 Character of forces applied to dental implants
 Surface area
 Bone volume
 Bone quality
 Implant macrogeometry
 Implant width
 Thread geometry
 Implant length
 Crest module consideration
 Apical design consideration
 Different implant designs
 Parts of implants
 Surface coatings and its consideration
 Review of literature
 Conclusion
 References www.indiandentalacademy.com

INTRODUCTION

A SCIENTIFIC RATIONALE FOR ROOT
FORM DENTAL IMPLANT DESIGN
 Dental implants function to transfer load to surrounding biologic
tissues. Thus the primary functional design objective is to manage
(dissipate and distribute) biomechanical load to optimize the implant
supported prosthesis function.
 Biomechanical load management is dependent on two factors:
 the character of the applied force and
 the functional surface area over which the
load is dissipated.

CHARACTER OF FORCES
APPLIED TO DENTAL IMPLANTS
 Stress and strain have been shown to be important parameters for
crestal bone maintenance and implant survival. These factors may be
measured and compared for different implant body designs.
 Forces applied to dental implants may be characterized in terms of
five distinct, although related, factors : magnitude, duration, type,
direction, and magnification. Each factor must be carefully
considered, with appropriate weight, in the critical analysis of implant
design.

1. Force Magnitude
 Forces in molar, premolar and canine.
 Titanium alloy
 Commercially pure titanium
 Density of bone.

2. Force Duration
 Swallowing and eating
 Bruxism
 High stress

3. Force Type
 Physiologic Constraints on Design
 Three types of forces may be imposed on dental implants within
the oral environment: compression, tension, and shear. Bone is
strongest when loaded in compression, 30% weaker when
subjected to tensile forces, and 65% weaker when loaded in
shear .
 Endosteal root-form implants load the bone-to-implant interface
in pure shear (e.g., a smooth sided cylinder) unless surface
features are incorporated in the design to transform the shear
loads to more resistant force types.

 Influence on Implant Body
Design
 A smooth cylinder implant body results
in essentially a shear type of force at the
implant-to-bone interface. Thus this
body geometry must use a microscopic
retention System by coating the implant
with titanium or hydroxyapatite.
 Threaded implants have the ability to transform
type of force imposed at the bone interface
through careful control of thread geometry.
Thread shape is particularly important in
changing force type at the bone interface.

Thread shapes in dental implant designs includes :
 square
 V-shape
 buttress

4. Force Direction
 Physiologic Constraints on Design
 The anatomy of the mandible and maxilla places significant
constraints on the ability to surgically place root form implants
suitable for loading along their long axis. Resorptive patterns
following prolonged edentulism exacerbates the normally
occurring angulation challenges .
 Bone is strongest when loaded in its long axis in both
compression or tensile forces. A 30-degree offset load reduces the
compressive strength of bone by 11%, and reduces the tensile
strength by 25%.

 Influence on Implant Body Design
 As the angle of load increases, the stresses around the implant
increase, particularly in the vulnerable crestal bone region. As a
result, virtually all implants are designed for placement
perpendicular to the occlusal plane. This placement allows a
more axial load to the implant body and reduces the amount of
crestal stress. Additionally, axial alignment places less stress on
the abutment components and decreases the risk of short- and
long-term fracture.

The face angle of the thread can change the direction of load from
the prosthesis to abutment connection, to a different force direction
at the bone.
 As a result, the axial load on the implant
platform may be a compressive load, but
the 30-degree angle of the V -shape
thread can reduce the amount of load the
bone interface is able to resist.
 The power thread design can take the
axial load of the prosthesis to abutment
connection and transfer a more axial load
along the implant body to compress the
bone, rather than convert it to 10 times
more shear.

5. Force Magnification
 A surgical placement resulting in extreme angulation of the implant
and/or a patient exhibiting parafunctional habits will likely exceed the
capability of any dental implant design to withstand physiologic loads.
 Cantilevers and crown heights act as levers and therefore are, force
magnifiers.
 Careful treatment planning with special attention to the use of multiple
implants to increase functional surface area is indicated when a clinical
case presents the challenge of force magnifiers.

Surface area
 For a given bone (and implant) volume, implant surface area must
be optimized for functional loads.
 Thus an important distinction is made between total surface area
and functional surface area.

Functional surface area is defined as the area that actively serves
to dissipate compressive and tensile non-shear loads through the
implant-to-bone interface and provide initial stability of the implant
following surgical placement.
 Total surface area may include a "passive" area that does not
participate in load transfer
 For example, plasma spray coatings are often reported to provide'
up to 600% more total surface area however, the amount of area
that is actually exposed to bone for compressive or tensile loading
may be less than 30% of the total surface area.

Design Variables in Surface Area
Optimization
 Implant Macro geometry
 Smooth-sided, cylindric implants provide ease in surgical
placement however; the bone-to-implant interface is subjected to
significantly larger shear conditions.
 In contrast, a smooth-sided, tapered implant allows for a
component of compressive load to be delivered to the bone-to-
implant interface, dependent upon the degree of taper.

 Implant Width
 Over the past five decades of endosteal implant history, implants
have gradually increased in width.
 Today, dental implants generally have reflected the scientific principle
that an increase in implant width adequately increases the area over
which occlusal forces may be dissipated. For root form implants of
circular cross-section, the load bearing area of the abutment platform
increases as a function of the radius squared.
 A 4-mm root form implant has 33% greater surface area than a 3-
mm root form implant.

 Thread Geometry
 Functional surface area per unit length of the implant may be
modified by varying three thread geometry parameters:
 Thread pitch,
 Thread shape
 Thread depth.

 Thread Pitch is defined as the distance measured parallel with its
axis between adjacent thread forms
 Or the number of threads per unit length in the same axial plane and
on the same side of the axis

The thread shape is another very important characteristic of overall
thread geometry. As described previously, thread shapes in dental
implant designs include:
 Square
 provides an optimized surface area for
intrusive, compressive load
transmission
 V-shape
 the V -thread design is called "fixture"
and is primarily used for fixturing
metal parts together-not load transfer.
 Buttress
 is optimized for pullout loads

Differences in shear loading on the standard V-
thread and the square thread
 V-thread has 10 times greater
shear loads on bone compared
with a square thread
 The reduction in shear loading at
the thread-to-bone interface
provides for more compressive
load transfer, which is particularly
important in compromised D3 and
D4 bone.

 The thread depth refers to the distance between the major and
minor diameter of the thread.
 Conventional implants
provide a uniform thread
depth throughout the
length of the implant.
 This unconventional design
feature results in dramatic
increases in functional
surface area at the crest
of the bone, where the
stresses are highest.

 As the length of an implant increases, so does the overall total surface
area. As a result, a common idea has been to place an implant as long
as possible preferably, into the opposing cortical plate.
 Attempting to engage the opposing cortical plate and preparing a
longer osteotomy may result in overheating the bone.
 Longer implants have been suggested to provide greater stability
under lateral loading conditions.
 Studies have shown that the highest stresses were observed in the
crestal bone regions, regardless of the implant length.
 This biomechanical analysis supports the opinion- that longer implants
are not necessarily better.
 Instead, there is a minimum implant length for each bone density,
depending on the width and design.
 The softer the bone, the greater the length suggested.
Implant Length

Crest Module Considerations
 The crest module of an implant body is the transosteal region from
the implant body and characterized as a region of highly
concentrated mechanical stress.
 Instead, it is a transition zone to the load-bearing structure of the
implant body
 In. fact, bone loss has been observed so often, many implant crest
modules are designed to reduce plaque accumulation once bone loss
has occurred

 A smooth, parallel-sided crest module
will result in shear stresses in this
region, making maintenance of bone
very difficult.
 An angled crest module of more than
20 degrees, with a surface texture
that increases bone contact, will
impose a slight beneficial compressive
component to the contiguous bone
and decrease the risk of bone loss.

Apical Design Considerations
 Most root form implants are
circular in cross-section. This
permits a round drill to
prepare a round hole,
precisely fitting the implant
body.
 Round cross-sections,
however, don’t resist
torsional/shear forces when
abutment screws are
tightened or when free-
standing, single tooth implant
receive a rotational (torsional)
force.
 The apical end of each
implant should be flat rather
than pointed. www.indiandentalacademy.com

 As a result, an anti-rotational feature is
incorporated, usually in the apical region of
the implant body, with a hole or vent being
the most common design.
 The apical hole region may also increase the
surface area available to transmit compressive
loads on the bone.

Surface Coatings
Titanium Plasma Spray
Hydroxyapatite Coatings
 The clinical advantages of TPS or HA coatings may be summarized
as the following:
 Increased surface area ( can be up to 600%)
 Increased roughness for initial stability
 Stronger bone-to-implant interface
 Additional advantages of HA over TPS include the
following:
 Faster healing bone interface
 Increased gap healing between bone and HA
 Stronger interface than TPS
 Less corrosion of metal

Disadvantages of coatings include
1. Flaking, cracking, or scaling upon insertion
2. Increased plaque retention when above bone
3. Increased bacteria and nidus for infection
4. Complication of treatment of failing implants
5. Increased cost

Machined surface Blasted surface (Tio-blast)
Plasma sprayed surfacewww.indiandentalacademy.com

 The present designs fall into four morphological
categories:
 Screw or Threaded
 Bullet or Conical
 Basket or Vented
 Fin or Plateau
 Others are:
 Titanium plasma sprayed screw implant system
 Cylindrical Hydroxyapatite coated implant
 Grooved Hydroxyapatite coated cylinder
 Vitreous carbon implants

Screw root forms are threaded into bone
site and have macroscopic retentive elements for initial
bone fixation. Screw type of implants have been used for
more than two decades.
 Earlier placement technique resulted in traumatic site
preparation of bone and immediate or early loading of the
implant that interfered with bone healing.
 Branemark showed 2 keys to predictable screw implant
technique and success: avoid traumatizing and
overheating the bone during site preparation and allow
adequate time for bone healing. Almost all commercially
available screw-type implant systems recommend not to
loading the implant for several months to allow
osseointegration to occur.
 The only system that still recommends immediate loading
of the implants is the titanium plasma sprayed screw
system (TPS screws).
 Different surface finishes range from machine tooled, sand
blasted, acid etched, to hydroxylapatite coated; an implant
design can range from self tapping to those needing
threads cut into the bone.www.indiandentalacademy.com

Screw Root Form contd….,
 Branemark Standard Fixture
 Branemark Self tapping Fixture
 Fixture (Impla-med)
 Self tapping fixture (Impla med)
 Osseo-Dent (Collagen)
 Screw Vent (Core-Vent)
 Swede Vent (Core-Vent)
 Steri OSS standard
 Steri OSS mini
 Steri OSS HAITI solid screw
(Straumann Inc )
 Osteo implant (OIC)
 Star-vent
 Star-vent TPS

Cylindrical Basket
 The hollow basket design provides nearly twice the bone contact of a
solid cylinder of the same length and diameter.
 The receptor site is prepared with trephines, producing minimal bone
destruction and leaving a vital bone core over which the implant is
seated.
 Perforations in the cylinder walls enable bone growth through the
implant to increase stability and improve load distribution.
 Titanium or titanium alloy is used, permitting osseointegration. The
fenestrated hollow-cylinder design minimizes stresses within the implant
on vertical loading and providing a greater area for load transmission to
the surrounding bone.
 Two system currently incorporate the hollow-basket concept:
 The ITI implants
 The Core-Vent implant

Cylindrical Basket
 The ITI implants are made from
CP titanium, have a titanium
plasma-sprayed surface and
promote increased bone contact
by increasing the surface area by
6 fold.
 Were previously provided in
several designs – designated as
C,E,F,H and K.- to fit alveolar
ridges of varying ht. and width.
 ITI hollow Cylinder
 ITI 150 offset Hollow Cylinder
 ITI hollow Screw

Cylindrical Basket
 Core-Vent basket design
combines a superior threaded
screw section with an inferior
hollow vented basket.
 The self tapping threaded neck
provides initial stability to help
prevent micro movement during
healing.
 Within the superior threaded
region there is a hexagonal-
threaded chamber that extends
downward towards the basket
area but does not communicate
with it.

Cylindrical Basket
 The Core-Vent implant is
manufactured in two
diameters: 3.5 and 4.5 mm
 The threaded portion adds 0.8
to overall dimension, creating
outsides diameter of 4.3 and
5.3 respectively
 Four length available are 16,
13, 10.5, and 8 mm

Cylindrical Fin Finned or serrated root form
implants can offer advantages in
certain clinical situations.
 These implants sometimes called
plateau implants have a series of
circumferential fins spaced along
the bone interfacing portion of the
implant.
 They usually provides more
functional load bearing surface
area for efficient transmittal of
occlusal loads than other
implants.
 Proper socket preparation should
result in light friction fit for
implant after insertion.
 Omni (Omni Intl)
 Miter 2000 (Miter Inc)
 Stryker Precision
 Stryker Precision/HA
 Micro-Vent (Core-Vent)

Titanium Plasma Sprayed Screw Implant
 It consist of fine grain titanium particles applied to the
cylinder in an argon environment under extremely high
temp., pressure and velocity.
 It offers an increase in surface area over the smooth
surface and, thus also more retention in the bone.
 Some research has also shown that initial integration
into the host bone is somewhat accelerated through
that.
 Available in diameter of 3.3 & 4 mm
and length of 8, 11, 13 & 15 mm.

Titanium Screw Implant with a
Hydroxyapatite (HA) coating
 Beyond an increase in surface area as
compared to smooth surface implants,
this surface has also shown to have an
accelerated initial integration, which
makes it ideal for quick initial post-
surgical stabilization in weak bone.

Subperiosteal Implants :
Are implants, which
typically lie on top of the
jawbone, but underneath
your gum tissues. The
important distinction is
that they usually do not
penetrate into the
jawbone.

 Indications…
 Some conditions that are contraindicated for root and blade form
may be indicated such as:
 An unusual position of mental foramen
 A dehiscence of mandibular canal
 Generally atrophic mandible
 A mutilated oral condition from extensive surgery
 Severe gagging problems
Subperiosteal Implants :

Transosseous Implants:
 Are implants, which are
similar in definition to
Endosseous implants in that
they are surgically inserted
into the jawbone.
 However, these implants
actually penetrate the entire
jaw so that they actually
emerge opposite the entry
site, usually at the bottom of
the chin.
 Adv are immediate denture
placement and function

BLADE IMPLANTS
 Linkow blade implants invented in 1967.
 Long thin blade that will be surgically inserted into the groove in the bone .
 Abutment projecting out from the blade to this crown or attachment for
denture can be placed.
 It required the shared support of natural teeth also.
 Restored within month so became most widely used in united states.
 Linkow modified the design configuration for broad applicability in
maxilla & mandible, narrow ridges.

 RAMUS FRAME IMPLANT developed Roberts & Roberts in 1970 .
 The endosseous implant received stabilization from its anchorage
in ramus area bilaterally & in the symphyseal region.
 It is now made of grade 2 CP titanium and used as posterior
support for a mandibular fixed partial denture when insufficient
height and width exist in body of the mandible.
 The implant remain unloaded until proper osseous healing occurs.
These were used when insufficient bone(less than 6mm bone
height,and 3mm bone width)is present in body of mandible to
support an endosteal implant.
 These are one piece blade implants which take support from bone
in ramus region

ITI BONE FIT IMPLANT SYSTEM
 Developed by ‘International Team for Implantology’.
 Three different types
 Single stage & two stage.
 Transgingivally placed in healing phase so second surgical procedure
for uncovering the implant is avoided.

ZYGOMATICUS FIXTURES
 Branemark.
 The long fixture can be anchored in zygoma by approaching through the
sinus .
 Severely resorbed maxilla.

OSTEOPLATE 2000
 Atrophic RAR
 The conical plate with
shoulder width 1.3 mm &
base 0.9 mm.

 1.crest module:- the
crest module of an implant is that
portion designed to retain the
prosthetic component.
 It represents the transition zone
from implant body design to
transosteal region of the implant
at the crest of the ridge.
IN THE IMPALNT BODY:-

Antirotational features
External hex
o Most widely available
o Found on top of abutments
o Hexagonal geometry
Internal hex
o Provides more precise implant
abutment interface
o Disadvantage – screw loosening
o Seats the abutment into hexagonal
depression

 Most common external connections
 Hexagonal (Hex) type
 Octagonal (Octa) type
 Spline
 Most common internal connection
 Morse taper
 Internal Hex
 Internal Octagon

EXTERNAL CONNECTION

THE STANDARD EXTERNAL HEX TAPERED EXTERNAL HEX
EXTERNAL SPLINE CONICAL, NO HEXwww.indiandentalacademy.com

INTERNAL HEX
 IT HAS CONICAL OPENING TO
AN INTERNALLY THREADED
SHAFT
 LATERAL STABILITY IS
PROVIDED BY TIGHTENING
WITH A MATHCHING CONICAL
SURFACE

BICON NO HEX
 1 DEGREE -2DEGREE TAPERED
ABUTMENTS FRICTIONALLY
FITS INTO NON THREADED
SHAFT OF THE IMPLANT WHICH
HAS A MATCHING TAPER

INTERNAL CONNECTION

Internal
Connection
Octagonal
Hexagonal
Cone screw

 Connection can be further classified
as
 SLIP FIT JOINT
Slight space exists between the mating
parts
Passive connection

 FRICTION FIT JOINT
 No space between the mating parts
 Parts are literally forced together
ONE PIECE MORSE TAPER 5 degree TWO PIECE TAPERED HEXAGONAL
8 DEGREES 11 DEGREES

SPLINE ATTACHMENT
Splines are fin to groove anti rotational design
Consist of six external components called tines which
protrude 1mm from implant and are matched to a
female embedded in a abutment base

Implant collar:-
 Designs that incorporate a microscopic component into the
implant bodies by coatings with hydroxyapatite, at the superior
aspect of the crest module.
 The collar allows functional remodeling to occur to a more
consistent region on implant.
 It suggests that crestal modeling is limited to the smooth region
of the implant.
 Its designs varies from straight to flared neck, beveled, reverse
beveled, tapered, smooth surfaced or micro threaded.

COVER SCREW:-
 At the time of insertion of the
implant body or stage 1
surgery, a first stage cover is
placed into the top of implant
to prevent bone, soft tissue,
or debris from invading the
abutment connection area
during healing.


HEALING
SCREW:-
 After a prescribed healing
period sufficient to allow a
supporting interface to
develop, the second stage
may be performed to expose
the implant andor attach a
transepithelial portion.
 This transepithelial portion is
termed a permucosal
extension because it extends
the implant above the soft
tissue and results in
development of permucosal
seal around the implant

 Abutment :- is the portion of the implant that supports andor
retains a prosthesis or implant super structure.
 Three categories of implant abutments are available.
1.screw retained
2.cement retained
3.abutment for attachment uses an attachment device to
retain a removable prosthesis.
 HYGIENE COVER SCREW:-place over the abutment to prevent
debris and calculus from invading the internal portion of abutment
during prosthesis fabrication.

 TRANSFER COPING:-transfer
coping is used to position an
analog in an impression and
defined by the portion of
implant it transfers to the
master cast, either the implant
body transfer coping or the
abutment transfer coping.
 Direct transfer coping
 Indirect transfer coping

 IMPLANT ANALOG:-used in
the fabrication of the
master cast to replicate
the retentive portion of the
implant body or abutment.
 After the master
impression is obtained, the
corresponding analog is
attached to the transfer
coping and assembly
poured in the die stone

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Dental Implant Design Considerations for Optimizing Surface Area and Load Distribution

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Dental Implant Design Considerations for Optimizing Surface Area and Load Distribution