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CH. 15 - PROVISIONAL RESTORATIONS

During the time between the preparation of the tooth and the placement of the final restoration, the tooth is protected

by a provisional restorationor commonly called a temporary restoration. A good provisional restoration should satisfy

the following requirements:

1. pulpal protection - restoration should prevent the conduction of temperature extremes

2. positional stability - should not allow the tooth to shift or extrude in any way

3. occlusal function - aids patient comfort, prevents tooth migration, and prevents neuromuscular imbalance4. easily cleaned - proper material and contour will allow proper hygiene

5. nonimpinging margins - or else inflammation will result

6. strength and retention - must not break or come off the tooth

7. esthetics - anterior teeth and premolars require good cosmetic results

I. TYPES OF PROVISIONAL RESTORATIONS

A. Prefabricated vs. Custom

- prefabricated forms can be used only for single-tooth restorations

- for fixed partial dentures, provisional restorations can be fabricated of several different kinds of resins and methods

B. Direct vs. Indirect Techniques

- the direct techniqueis done on the actual prepared teeth in the mouth

- the indirect techniqueis accomplished outside of the mouth on a cast made of quick-set plaster- the indirect technique is preferred over the direct technique for its accuracy and pulpal protection

- since polymethyl methacrylate shrinks 8% when it polymerizes, it is desirable to keep it on an indirect cast

- indirect technique protects the pulp from pulpal irritation or acute pulpal inflammation

II. RESINS FOR PROVISIONAL RESTORATIONS

- there are several resins used to make custom provisional restorations

- polymethyl methacrylate has been used the longest

- polyethyl methacrylate, polyvinylethyl methacrylate, bis-acryl composite resin, and visible light-cured (VLC)

urethane dimethacrylate have also come into common usage in recent years

II. TECHNIQUES FOR CUSTOM PROVISIONAL RESTORATIONS

- there are a variety of techniques for making a mold to form the outer surface of a custom provisional restoration

- both elastomeric and alginate overimpressions have been used to shape the provisional restoration

- an overimpression is made on the diagnostic cast, or in the mouth, before the tooth preparation is begun

- template formed from clear thermoplastic resin can also be used for this purpose; shaped using a cast & vacuum

A. Overimpression-Fabricated Provisional Crown

- alginate impression is popular because it is readily available in the dental operatory

- for later use, these impressions must be stored in a ziplock plastic bag, wrapped in a wet paper towel

- the tooth is prepared and another quadrant impression is taken in alginate; this is poured up in quick-set plaster

- the quadrant cast is trimmed and soft tissue areas are reduced as much as possible

- prepared tooth and adjacent areas on the quadrant cast are coated int alcote - tin foil substitute separating medium

- 12 drops of monomer are used for each tooth being restored; mix tooth acrylic resin: dappen dish w/ cement spatula

- seat the cast into the overimpression making sure the teeth are evenly aligned in the impression

- excessive force - can overseat the cast; while uneven force - can torque the case

- hold the cast in place with a large rubber band and place the assembly in a plaster bowl of hot tap water for 5 minutes

- place the assembly into a pressure pot if one is available; keep the pressureunder 20psi

- break the plaster cast off the provisional restoration

- acrylic burs or coase Moore discs are used to trim excess resin from the provisional restoration

- smooth the axial surfaces near the margins with a fine sandpaper disc

Fixed Prosthodontics

Burleson

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B. Provisional Cementation

- seat the provisional restoration and check the occlusion

- polish the restoration with pumice and then polishing compound on a muslin rag wheel

- undercontour the crown if it will be placed under an existing removable partial denture; does not touch clasp/rests

- the restoration should be cemented with temporary cement of moderate strength (zinc oxide-eugenol cement)

- 5-10% petrolatum is incorporated to slightly reduce the strength of the cement

- it is not necessary to keep ZOE cement dry while cementing; in fact, moisture will accelerate the hardening

C. Template-Fabricated FPD

- FPD provisional restorations should be in the form of a FPD rather than individual crowns

- this provides better cosmetic results in the anterior region and better strength in the posterior region

- to make a template, use a metal crown form or denture tooth in the space for the pontic of the FPD

- place a 5 by 5 inch sheet of 0.020-inch thick resin in the fram of the vacuum forming machine, shiny side down

- after approximately 30 sec. after pulling the hot sheet over the cast, turn off the vacuum and release the sheet

- trim the template: it should extend at least one tooth on either side of the prepared teeth

- after tooth preparation, take an alginate impression of the prepared quadrant and pour a quick-set plaster cast

- trim the quadrant cast and place alcote separating agent on the prepared abutment teeth and adjacent areas

- mix the acrylic resin (12 drops of monomer per tooth) and place the resin-filled template over the quadrant cast

- hold in place with rubber band, do not place the rubber band over the abutment teeth

- place the cast in hot water or pressure pot (20psi) for 5 minutes

- before removing the provional restoration from the cast, add resin to any voids or thin spots and place back in water

- placing the unpolymerized resin back into water will prevent monomer evaporation and prevent a frosted surface- remove and trim the proximal embrasures to premit proper emergence profile

Table 15-1 Characteristics of Resins used for Provisional Restorations

1. polymethyl methacrylate - has good marginal fit, transverse strength, polishability, and durability

- disadvantages: high exothermic heat increase, low abrasion resistance, free monomer toxic to pulp, shinkage

- brands: Jet (Lang dental), Duralay (Reliance Dental)

2. polyethyl methacrylate - good polishability, low exothermic heat increase, good strain resistance, low shrinkage

- disadvantages: surface hardness, durability, fracture toughness

- brands: Snap (Parkell biomaterals)

3. polyvinylethyl methacrylate - good polishability, low exothermic heat release, good abrasion, strain, flexible

- disadvantages: surface hardness, esthetics, fracture toughness

- brands: Trim (Harry Bosworth)

4. bis-acryl composite - good marginal fit, low exothermic heat increase, good abrasion, transverse, low shrinkage

- disadvantages: surface hardness, limited shade selection, limited polishability, brittle

- brands: Protemp (ESPE-Premier)

5. VLC urethane dimethacrylate - high surface hardness, good transverse, abrasion, working time, color stability

- disadvantages: marginal fit, less strain resistance, limited shade selection, expensive, brittle

- brands: Triad (Dentsply York)

Fixed Prosthodontics

Burleson

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