simplified from fixed prostho

1. INTERIM FIXED RESTORATIONS
(PROVISIONAL RESTORATION)
INDICATIONS
1.
2.
3.
4.
prevent overeruption of opposing teeth
prevent tilting of adjacent teeth
for phonation
for esthetic appearance of anterior segment
REQUIREMENTS
1) Biological Req
Pulpal protection
1. IFR must seal & insulate the prepared tooth struc from oral environment
2. prevent sensitivity to pulp & irritation to pulp
- certain pulp trauma is unavoidable
- due to sectioning of dentinal tubules
- each tubules contains odontoblasts, whose nucles in pulp cavity
3. prevent leakage
- can cause irreversible pulpitis
Periodontal health
1. when placing the crown margin apical to free gingival margin, the IFR must have :
- good marginal fit
- proper contour
- smooth surface
- for easy plaque removal
2. IFR must avoid inflammed/hemorrhagic gingival tissue → tissue blanching → ischemia → necrosis
Occlusal compatibility & tooth position
1. IFR should maintain proper contacts with adjacent & opposing teeth
2. prevent supraeruption & horizontal (tilting) movement of adjacent & opposing teeth
- result in excessive/deficient prox contact
- prox crown contours are distorted
- root proximity
- impairs oral hygiene measures
Prevention of enamel fracture
1. IFR should protect teeth weakened by crown preparation
- in partial coverage designs, margin of preparation is close to occlusal surface of tooth
- could damage during chewing
2. even small chip of enamel makes
- unsatisfaction restoration
- need time consuming-remake
2) Mechanical Req
Function
1. IFR should overcome the greatest stressses during chewing
2. not a prob with full coverage crown
- as tooth has been adequately reduced
3. breakage often occur with partial coverage & partial FDPs
- weaker
- not completely encircle the tooth
4. increase the size of the connectors for partial FDP
- as partial FDPs must function as a beam in which occlusal forces transmitted to abutments
- will create high stresses in connectors (often site of failure)
5. reduce the depth & sharpness of embrasures
- this will reduce the cross-sec area of connector
- reduce the stress conc at sharp internal line angles
6. dont overcontoured near gingiva
- to avoid dangering periodontal health
- must have good access for plaque control

2. 7.
use cast metal/heat-processed restoration
(indications)
- for long span post partial fixed dental prosthesis
- for treatment that have prolonged treatment time
- for patient that have inability to avoid excessive forces on prosthesis
- for above-average masticatory muscle strength
- when there is history of frequent breakage
Displacement
1. displaced IFR must be recemented immediately
- to avoid irritation to pulp & tooth movement
Removal for reuse
1. IFR often need to be reused
2. IFR should not be damaged when removed from teeth
3. IFR will not break upon removal if it has been well fabricated
- even cement is sufficiently weak
3) Esthetic Req
1. important for incisors, canines & sometimes premolars
2. may not possible tp duplicate exactly the appearance of natural tooth
3. material of IFR must match the color of adjacent teeth
4. IFR often used as a guide to achieve optimum esthetics in definitive restoration
5. greatly influenced the appearance when fixed prostho is performed in anterior seg
6. patient should be given opportunity to voice an opinion
7. obtain the opinions of others whose judgement is valued is important
8. accurate IFR is a practical way to obtain specific feedback for the design of a definitive restoration
9. IFR is shaped & modified until its appearance is mutually acceptable to dentist & patient
MATERIALS & PROCEDURES (prefabricated)
External Surface Form (ESF)
1. to create the mold cavity
2. 4 types :
Polycarbonate
1. has most natural appearance of all preformed materials
2. available in one shade only
3. but can be modified to a limited extent by the shade of lining resin
4. supplied in incisor, canine, premolar
5. procedures :
a. armamentarium
- assorted polycarbonate crowns
- boley gauge/dividers
- green stone/straight handpiece
b. steps
1.
measure MD width of crown space with dividers
2.
select a shell that is same/slightly larger width
3.
mark the crown height with pencil
4.
use this measurement as a guide to trim the shell to match with approxmiate curvature of
prepared cavosurface margin
- use green stone/small diameter carbide
5.
try the shell on prepared tooth
- make sure incisal & labial surface of shell align with adjacent teeth

3. - internal surface of shell often needs reduction
- occlusal will be adjusted after lining
6.
when shell can be properly positioned w/o forceful gingival contact, it is ready to be lined
with resin
7.
apply uniform thin coat of petrolatrum to the prepared teeth & adjacent gingivae
- to prevent direct contact of monomer with these tissues
- prevent injury
8.
mix autopolymerizing resin & fill the shell
- recommended to use poly(R'methacrylate)
9.
when surface just loses its gloss or resin forms a peak w/o slumping, place shell over the
tooth
10. align incisal & labial surfaces with adjacent teeth
11. eliminate any resin excess at the margin immediately
- if too polymerized, resin will pull away from margin
- need repair later
12. after about 2mins, when rubbery stage of polymerization is reached, rock the crown
faciolingually
- to loosen & remove it
13. keep the Backhaus forceps within easy reach
- to prevent difficulty separating crown from tooth
14. place the crown in warm water (37'c)
15. after about 5min, resin has fully set
16. mark margins with sharp pencil
17. axial surface can be shaped
- eliminate the excess with straight handpiece
- use carbide burs/abrasive disks
18. try the newly lined crown on prepared tooth
19. adjust lingual surfaces to desired occlusion & contour
20. polish & cement the restoration
Aluminium & Tin-Silver
1. suitable for posterior teeth
2. have anatomically shaped occlusal & axial surfaces
3. most basic & least expensive forms ; cylindrical shells resembling a tin
4. nonanatomical cylindrical shells are inexpensive but require modification
5. more efficient to use preformed crowns as individual max and mand post teeth
6. avoid fracturing the delicate cavosurface margin of tooth preparation when metal crown is fitted
- edge of shell engage the margin & fracture it under biting pressure
- greater risk occurs when crown has constricted cervical contour
7. tin-silver crown are carefully designed
- highly ductile alloy
- allows crown cervix to be stretched to fit tooth closely
- use feather edge margins (most practical way for direct strecthing on tooth)
- for other margin designs, cervical enlargement should be performed indirecly on swaging
block
supplied with crown kit
8. procedures :
a) armamentarium
- assorted aluminium crowns
- dividers
- crown-and-collar scissors

4. - contouring pliers
- cylindrical green stone
- straight handpiece
- coarse garnet paper disk
b) steps
1.
measure MD width of crown space using dividers
2.
select appropriate shell type with a width close as possible to the measurement
- slight larger/smaller shell can be deformed with contouring pliers to attain proper fit
3.
measure OC height
4.
trim shell with crown-and collar scissors
- so that it extends 1mm apical to cavosurface margin
- smooth/round the sharp burrs with green stone
5.
place trimmed shell over prepared tooth
6.
apply seating pressure gradually while observing gingiva
7.
trim the margins at any location where the gingiva blaches
- shell margin should not engage prepared tooth margin
8.
repeat evaluation and trim again
9.
instruct the patient to close with moderate force
10. the soft aluminium should deform until normal intercuspation is reached
11. apply petrolatum to prepared tooth & adjacent gingiva
12. mix resin & fill the shell
13. when resin surface becomes matte, place shell over tooth
- guide it to slightly supraclusal position
14. let patient close again
15. immediately remove the excess resin at the margin
- to avoid pulling the resin away from cavosurface margin
16. after about 2mins, rubbery stage of polymerization is reached, engage the crown with Backhaus
forceps to just penetrate the aluminium shell
17. loosen & remove the crown by rocking it buccolingually
- or use thumb & index finger of other hand to apply occlusally directed force under the tines
- small bucal/lingual holes created in the surface of aluminium not a prob, can be ignored until the
patient returns
18. place shell in a cup of warm water (37'c)
19. after about 5mins, mark margins and trim away any excess
- ground away the shell in certain areas to establish periodontally healthy axial contours
20. replace crown & adjust the occlusion
21. if proximal surface lack contact, add resin to correct the deficiency
- ground away metal in the contact area to provide resin-to-resin bond
22. polish, clean & cement the restoration
Nickel-chromium
1. used primarily for children with extensively damaged 1ry teeth
2. may be applied to 2ndry teeth but more suitable for 1ry teeth (longevity is less critical)
3. not lined with resin but are trimmed, adapted with contouring pliers & luted with high strength cement
4. very hard so can be used for longer-term IFR

5. Cellulose acetate
1. thin (0.2-0.3mm) transparent material
2. available in all tooth types & range of sizes
3. shades are entirely dependent on autopolymerizing resin
4. resin not chemically/mechanically bond to the inside of surface of shell
5. after polymerization, shell is peeled off & discarded
- to prevent staining the interface
6. after shell is removed, add resin to reestablish proximal contacts
Post & Core Interim Restorations
1.
2.
to gain support & intraradicular retention from a cast metal post & core
procedures :
a) armamentarium
- wire
- wire cutting pliers
- cylindrical green stone
- straight handpiece
- wire bending pliers
- paper points
b) steps
1.
place a piece of wire (a straightened paper clip) in the post space
- extend passively to the end of post space to avoid root fracture
- taper the wire with mounted stone if binding occurs
2.
mark the wire with pencil at the mouth of the post space
3.
then use pliers to make 180' bend in the wire at the point slightly occlusal to the pencil mark
4.
lubricate the tooth & surrounding soft tissues with petrolatum
- use paper points for lubricating the post space
5.
fill ESF with interim resin
6.
when resin loses its surface gloss, place wire in post pace and set the ESF over it
- precautions must be taken to protect patient from swallowing wire
7.
after about 2-2 ½ min, remove ESF while resin still rubbery
8.
stage of polymerization should be monitored
9.
mark the margins with pencil, trim & contour the restoration
- use disks/ straight handpiece carbide burs
10. evaluate restoration in mouth, adjust if necessary
11. polish, clean & cement restoration
pae.