Lect.
crown and Bridge
Dr. Ameer Hamdi AL-Ameedee
Provisional Restorations
Functions of Provisional Restorations:
1. Comfort/tooth vitality
2. Occlusion and positional stability
3. Function
4. Gingival health and contour
5. Aesthetics
6. Diagnosis
7. Other practical uses
Assessment of Aesthetic Changes:
1. Assess appearance of intended restorations.
2. Make directly or use a matrix made from the wax-up.
3. Ensure patient’s acceptance.
4. Record the temporary crowns and instruct technician to copy their form and shape into the final
restoration.
Occlusal Changes:
1. Prevent unwanted tooth movement by maintaining occlusal and interproximal contacts
2. Evaluate patient’s tolerance to change in anterior guidance or increased occlusal vertical
dimension:
3. Cement temporary crowns made from diagnostic wax up and review for aesthetics, guidance,
drifting, mobility, decementation, and comfort
4. Copy the provisional crowns guidance by a custom guidance table, to transfer to definitive
restorations.
5. It is recommended to assess tolerance to change in vertical dimension by a reversible method
such as splint.
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Periodontal Changes:
1. Allow for resolution of inflammation
2. Improve gingival healing and stabilization of gingival margin position
3. Used after surgical crown lengthening during the healing period before definitive preparation and
impression.
Change in Tooth Shape:
Accurately copy a satisfactory and successful provisional restoration to:
1. Avoid minor or major changes in tooth shape.
2. Avoid disrupting fine mouth movements and lip/tooth contact
3. Avoid incorporating wide cervical embrasure to prevent air leakage.
Provisional Restorations Materials:
A- Preformed crowns:
1. Plastic shells: polycarbonate or acrylic. Used for anterior and premolar teeth.
2. Metal Shells: aluminum, stainless steel or nickel chromium.
B- Self or light cured resins:
1. Polymethyl methacrylate
2. Polyethyl methacrylate (Snap, Trim)
3. Biacryl composite (Protemp)
4. Urethane dimethacrylate (light cured).
5. Restorative composite
Cast Metal:
1. Nickel chromium, silver and scrap gold.
2. Durable.
3. Can be made with external retention beads to retain acrylic or composite.
4. Rarely used.
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Provisional Cements:
1- Creamy mix of zinc oxide eugenol
2- Most practitioners use proprietary cements such as Temp Bond
 Available with modifier to soften the cement
 Non-eugenol Tem Bond is available and used to:
3- Cement temporary restorations for preparations for definitive adhesive restorations (eg All ceramic,
veneers) to avoid interference with bonding of resin cements.
 If eugenol containing cement used, eugenol residues should be removed with pumice and water.
Direct Provisional Restorations Techniques:
 Proprietary Shells:
 Plastic Shells: Polycarbonate relined with resin, trimmed, polished and cemented.
 Metal shells:
1. Aluminum shells: relined with resin (short term). Soft and galvanize with opposing amalgam
2. Stainless steel and nickel chromium: used with bruxist patients.
 Custom shells: beaded acrylic and Mill crowns.
Matrices for Provisional Restorations:
 Impressions:
 Alginate: absorbs resin exotherm
 Elastomers: reusable
Advantages: simple, quick, inexpensive.
 Vacuum formed thermoplastic:
 clear vinyl sheet on stone duplicate of the wax up.
 used only in presence of number of adjacent locating teeth
 could be used with light cured resins.
 Proprietary celluloid crown form.
Techniques:
1-Direct Syringing: polyethyl methacrylate.
2- Indirect Provisionals:
 Used for long term provisionals.
 Strong heat cured materials can be used
 Aesthetics and occlusion made on articulated wax up.
 Indicated or multiple restorations and for an increased vertical dimension.
 Alginate impression of the preparations, cast in fast set stone, and fabricate provisionals.
Provisionals of Adhesive Restorations:
1- No temporary coverage
2- Simple coat of zinc phosphate cement
3- Composite resin bonded to a spot etched on the preparation
4- Composite bonded to opposing tooth.
Problem Solving:
1- Insufficient bulk of material: Inadequate
2- reduction, or make it bulkier by relieving the matrix (impression).
3- Gross occlusal errors, air blows and voids: trim away suspected areas (interpoximal), an educe
hydrostatic pressure by cutting escape vent.
4- Locking in of provisional restorations: material engaging the adjacent tooth proximal undercut.
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5- Marginal discrepancy: polymerization shrinkage, distortion on removal, reline with resin around the
margins.
6- Multiple crowns: joined restorations prevent drifting, gingival embrasures should be opened to
access brushing.
7- Premature decementation: Ensure harmony with occlusion, use stronger cement
8- Partial denture abutment: fabricate with the denture fully seated.
9- Eugenol containing cements: do not use if the underlying core is composite.
10- Removing temporary cement: use modifier.
11- Removal of excess cement: apply petroleum jelly to outside of the restorations.
Die:
It is the positive reproduction of the individual (single) prepared tooth on which wax pattern is done. It is
obtained from Working cast (master cast) of the final impression. It is the positive reproduction of the
form of the prepared tooth in any suitable substance. A reproduction of a prepared tooth made from a
gypsum product, epoxy resin, a metal or a refractory material.
A die is a model of a single tooth, again prepared from an impression. The die is a positive reproduction of
the prepared tooth and consists of a suitable hard substance of sufficient accuracy usually an improved
stone, resin or metal. The die is a model of the individual prepared tooth on which the margins of the wax
patterns are finished.
A cast and die system captures the necessary information so that it can be transferred to the laboratory.
There are two basic working casts and die systems: A working cast with a separate die and a working cast
with a removable die.
Accurate duplication of prepared teeth and maintaining their relationship to one another are important in
constructing fixed partial prosthesis. For this it is necessary to obtain an accurate reproduction of prepared
tooth, adjacent opposing tooth and surrounding soft tissues. Since direct fabrication in the mouth is
inconvenient, difficult, times consuming and virtually impossible all wax patterns for extracoronal
restorations are made by indirect technique in the laboratory.
An accurate working cast with removable dies is essential to make a well fitting restoration. Detailed
reproduction of die materials for fixed prostheses affects the accuracy of working casts and is related to
the compatibility between the die and impression materials. A working cast is the replica of the prepared
teeth, ridge areas and other parts of the dental arch.
Requirements of the die and die materials:
1.
It must reproduce the prepared tooth details and all fine details in the impression exactly.
2.
It must be free from air bubbles, cracks and voids.
3.
It must return to its exact position on the cast when it is removed.
4.
It must be stable in their position even when the cast is inverted.
5.
The dimensional stability (or accuracy) and abrasion resistance during the construction of the
wax pattern.
6.
They should be dimensionally stable.
7.
They should be; Setting expansion, contraction and dimensional variation in response to
setting or change in temperature should be minimal.
8.
The die should have a smooth surface that is sufficiently strong to withstand the subsequent.
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9.
Manipulative procedures without abrasion of the surface that is it should have the ability to
resist abrasion.
10.
They should be compatible with impression materials and there should be no interaction
between the surface of the impression and cast or die.
11.
Toughness to resist breakage during fabrication or burnishing of fine edges.
12.
Color of the die should be in contrast to the color of wax. This helps to facilitate the
manipulative procedures that will be carried out.
13.
It should be reasonably easy to use without excessive manipulative procedures. It should be
relatively inexpensive.
14.
Die must be given a form that allows easy handling during waxing and other procedures.
The die must have root like extension that serves as a handle.
15.
The remaining unprepared tooth structure immediately cervical to finish line should be easily
distinguished on the die, ideally with 0.5 to 1mm visible. Adequate access to the margin is
necessary.
Types of die spacers (coat layer):
Spacers are applied in several coats to within 0.5mm of the preparation finish line to provide relief for the
cement luting agent and to ensure complete seating of an otherwise precisely fitting casting or coping.
aResins (Commonly used).
bColored nail polish.
cPaint or liquids Model paint.
dThermoplastic resins dissolved in volatile solvents.
Types of dies according to materials investment use:
Investment materials:
1. Silver-plated dies.
2. Copper-plated dies.
3. Amalgam dies.
7. Silicophosphate cement.
4. Stone dies.
8. Metal sprayed dies.
5. Epoxy resins.
6. Polyurethane Alternative die materials.
9. Ceramic die materials.
10. Flexible die materials.
11. Die stone - Investment combination.
12. Gypsum products- Type IV Dental Stone Type V Dental stone.
13. Electroformed die (Besides resins, electroplating can be used to overcome the poor resistance of
gypsum. The metal dies that are produced when an impression material is electroplated have moderately
high strength, adequate hardness and excellent abrasion resistance. Detail reproduction of a line 4µ-m or
less is readily attainable on an electroplated die when a no aqueous elastomeric impression material is
used).
Types of die according to construction:
1. Working cast with separated dies.
2. Working cast with removable dies:
a. Straight dowel pin.
b. Curved dowel pin.
c. Pindex system.
d. Di-Lok tray.
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Working cast with separated dies (Multiple pour system):
The final impression is poured twice to obtain two working casts: one of these casts is sectioned to obtain
the individual dies that are separated from that cast, while the other working cast is articulated on the
articulator.
Working cast with removable dies:
The final impression is poured for one time only to construct a working cast that involves removable dies.
Construction of a stone die (working cast with removable dies):
Dowel pins: these are ready-made metal pins which are used as a means of orienting the die(s) to the
original working cast, which allow the die(s) to be easily removed and accurately replaced into the working
cast. The dowel pin is tapered and cylindrical with one flat side for positive seating.
Interocclusal Record (Bite Registration) Objective of bite registration:
To transfer the relation between the upper and lower dental arches from the patient’s mouth to the
articulator we need bite registration. Proper inter-occlusal record is important to orient the die (s) of the
same arch to the opposing arch. When enough teeth are present in both dental arches we can transfer the
relation by hand articulation of the casts. i.e., no bite registration is needed in such cases, so we can
occlude the opposing casts by hand, and then we mount them on the articulator. If the remaining teeth
are insufficient to produce hand articulation of the casts, we have to record the bite by using either of the
followings:
1.
Pink base plate wax.
2.
Bite registration paste.
3.
Bite rim or occlusal rim.
Whatever the material used to record the relation between the upper and lower dental arches, we have to
guide the mandible to the required relation (centric or eccentric). So, the patient is asked to close and
guide him, put reference points, and then we put the record material and register the relation. The most
widely used material to record the relation is pink base plate wax. The procedure is by softening the wax
at first, then we ask the patient to bite on it, keeping in mind that we have to guide the mandible to the
reference points that we have marked to have the correct bite registration. Meanwhile, the patient is
asked to mold the wax at the lingual area by his tongue, while we adapt the wax on the labial and buccal
sides by our fingers. After complete setting of the wax, we remove it from the patient’s mouth, trim the
excess
wax,
and
attach
it
to
the
cast
and
transfer
it
to
the
articulator.
Bite rim: The bite rim is used in the following
cases:
1. Free end saddle.
2. When we need to restore the anterior teeth.
3. When we don’t have enough teeth to obtain the
centric relation.
Types of articulators:
The long–term successful restoration, particularly which of crown and bridges work is dependent on:
1- Proper management of the occlusion.
2- The maintenance of occlusal harmony.
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3- Avoid the creation of occlusal interferences.
Most single crowns and simple fixed partial dentures are fabricated on simple hinge articulators that have
limited ability to duplicate mandibular movements or not at all. While many of the inaccuracies produced
by this type of instrument may be corrected in the patient mouth using valuable chair time and the end
result is an occlusion that is less than optimal. Unfortunately, many of these inaccuracies are not
recognized and are allowed to remain in the mouth as occlusal interferences which frequently produced
symptoms of occlusal disease.
In dentistry we use:
aSimple hinge.
bSemi-adjustable.
cFully adjustable.
All restorative dentistry patient treatment (all fillings types, inlays and onlays) use semiadjustable articulator in the application of the basic principles of occlusion, the importance of
such instruments as an aid in providing the proper diagnosis and treatment of occlusion for these patients.
Hand – held casts can be a very useful aid to examination and planning, and ease of obtaining a stable
intercuspal position, but provide no information about excursive tooth contacts.
Some dentists to overcome the problems of occlusal interferences made occlusal reduction during the
different stages of checking, and that is not the solution of the problem because this reduce the occlusal
cutting efficiency (with anterior and posterior teeth), and if such reduction done with porcelain restoration
it multiple the problem due to the fact that the porcelain is a brittle material so the margins constructed
more rounded to overcome this disadvantage inconsequence more load would exerted on the prosthesis,
the muscles of mastication and the TMJ resulted in a more occlusal and TMJ diseases.
Waxing and investment and casting:
Construction of Dental Restoration:
1. Dental waxes.
2. Casting investment.
Dental waxes:
Dental waxes are hydrocarbons in nature (contain O2, H, and C) and have many applications in Dentistry.
Ideal requirements of pattern waxes:
1. Should be colored to be easy distinguished either from the die material or the tooth structure.
2. Should be cohesive and not adhesive.
3. Should soften without flaking.
4. Should soften at reasonable temperature and harden at mouth temperature.
5. Should have adequate flow to record the details of the prepared tooth.
6. Should burn-out completely with no residue.
-Blue inlay pattern wax Uses: to construct wax patterns for cast inlays, onlays, crowns and bridges.
-Blue inlay pattern wax Presentation forms:
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ab-
Usually presents as Blue or green sticks or rods.
Recently,presentsiinidifferenticolorsiandiformatsi(blocksioriinitins).
Casting Investment Casting investment:
Is composed of silica particles (SiO2) bonded together with different binding agents.
Requirements of ideal investment material:
1. Should be stable (not decompose) on heating (Refractory).
2. Should show a kind of expansion to compensate for metal shrinkage.
3. Able to wet the wax surfaces registering its details.
4. Easily manipulated, not expensive, not irritant and no release of toxic.
5. Should be porous to permit escape of gases.
6. Withstand the impact of molten metal.
7. Not adhere to the surface of cast metal.
8. Easy breakdown after casting.
Types of investment materials relative to the type of silica particles used:
a- Quartz-based investment.
b- Cristobalite- based investment Cristobalite-based investment provide higher rates of thermal
expansion (displasive transformation) than quartz-based investment does (when heated from 0600Co).
Types of investment materials relative to the type of binder used:
a- Gypsum-bonded investment .. Uses (CaSo4. 2H2O) binder.
b- Phosphate-bonded investment .. Uses magnesium ammonium phosphate.
c- Silica-bonded investment .. Uses silica gel binder in both types Tridymite could present as
impurity.
Gypsum-bonded Investment Uses: For casting metal alloys that melt below1000Co (i.e. gold alloys only)
because the investment decompose if heated above 700Co. Presentation: Presented as powder to be
mixed with regular tap water After mixing, the calcium sulfate hemihydrates dissolves in water and
changes into calcium sulfate dihydrates in the form of inter-meshed crystals having the silica particles in
between.
Phosphate-bonded Investment Uses: For casting metal-ceramic alloys and some base metal alloys (Can be
heated above 1000Co). Presentation: Presented as powder (containing ammonium diacid phosphate and
magnesium oxide) to be mixed with either water or colloidal silica solution. After mixing, the following
reaction occurs to form crystals of magnesium ammonium phosphate which bind the silica particles
together giving the investment its room temperature strength.
MgO + NH4 H2Po4 ---------------> Mg NH4 Po4 + H2O
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