Provisional Crown and Bridge Materials and Techniques Seminar Quiz

DEFINITION An interim prosthesis is a fixed or removable dental prosthesis, , designed to enhance aesthetics, stabilization and/or function for a limited period of time,after which it is to be replaced by a definitive dental prosthesis REQUIREMENTS: 1- Biologic Requirements 2- Mechanical Requirements 3-Esthetic Requirements 1- BIOLOGIC REQUIREMENTS A-Pulp Protection. B-Periodontal Health C-Occlusal Compatibility and Tooth Position D-Prevention of Enamel Fracture 2-MECHANICAL REQUIREMENT A-Function: strong enough to resist the chewing forces the contact area can be over contoured to improve the strength B-Removal for reuse: Interim restorations often need to be reused and so should not be damaged when removed from the teeth. C-Displacement should be stable and not easily displaced 3-ESTHETIC REQUIREMENTS The temporary must have adequate contours, color, translucency and texture. This is especially important in anterior teeth. Materials and procedure for provisional restoration Currently Available Materials 1- poly methyl metacrylate ( PMMA) . 2- Poly ethyl methacrylate ( PEMA ) . 3- Microfilled composite. 4-Light-polymerized The mold cavity is created by two correlated parts: 1- Forming the external contour of the crown . 2- Forming the prepared tooth surfaces and (when present) the edentulous ridge area . *The terms external surface form (ESF) and tissue surface form (TSF) are suggested for these mold parts. 1- External Surface Form. Two general categories of ESFs: 1-custom , 2-preformed 1-Custom: a custom ESF is a negative reproduction of either the patients teeth before preparation or a modified diagnostic cast. The matrix or ESF can be fabricated by utilizing: 1. Irreversible Hydrocolloid 2. Putty Silicone 3. Thermoplastic sheet: A custom ESF can be produced from thermoplastic sheets, which are heated and adapted to a stone cast with vacuum or air pressure while the material is still pliable 2-Preformed: Various preformed crowns are available commercially. They can be thought of as ESFs rather than as finished restorations and thus must be lined with auto polymerizing resin include polycarbonate, cellulose acetate, aluminum, tin-silver, and nickel-chromium. These are available in a variety of tooth types and sizes. Materials from which preformed ESFs are made include: A- Polycarbonate: Polycarbonate has the most natural appearance of all the preformed materials. it rivals well as porcelain restoration in appearance. Although it is available in only a single shade, Polycarbonate ESFs are supplied in incisor, canine, and premolar tooth type. B-Cellulose Acetate : Cellulose acetate is a thin (0.2- to 0.3-mm), transparent material available in all tooth types and a range of sizes. Shades are entirely dependent on the auto polymerizing resin. The resin does not chemically or mechanically bond to the inside surface of the shell; therefore, after polymerization, the shell is peeled off and discarded to prevent staining at the interface. C-Aluminum and Tin-Silver: Are suitable for posterior teeth. The most crown forms have anatomically shaped occlusal and axial surfaces. The non anatomic cylindrical shells are inexpensive but must be modified to achieve acceptable occlusal and axial surfaces. D-Stainless Steel: Stainless steel shells are used primarily for children with extensively damaged primary teeth. In that application, they are not lined with resin but are trimmed, adapted with contouring pliers, and luted with a high-strength cement. 2-Tissue Surface Form (TSF) There are three categories of TSFs: 1-direct , 2-indirect, 3-direct-indirect 1-Direct technique Procedure 1- Before the tooth preparation make an alginate impression or silicon. (ESF) 2- Prepare the patient’s teeth in the usual manner. (TSF) 3-Lubricate the prepared teeth and the adjacent gingival margins with petroleum jelly or any suitably separating medium, and reseat the silicon index or the alginate impression with provisional restorative material in the dough stage on the tissue surface of the impression. 4-remove the restoration from teeth in intial polymerization to prevent locking into undercuts. (the final polymerization occur extraorally ) 5-Finish, polish, and cement the restoration Disadvantages of direct procedure: 1-potential tissue trauma from the polymerizing resin 2-poorer marginal fit. 3. consuming chair time but less in terms of visit number. 2-Indirect Technique Procedure: 1.Construct the impression from the patient mouth before preparation. (ESF), If the tooth or teeth to be restored has any obvious defect, it should be corrected on a study cast with red utility wax then the index may be constructed. In case of missing tooth artiftial tooth should be placed to match the missing tooth. 2 Upon completion of the preparations, make alginate impression for them and pour it with stone. (TSF) 3. Coat the cast with separating medium. 4. As the resin begins to lose its surface gloss and become slightly dull, fill the index then place it over the cast. 5. The interim restoration is then finished and polished . In this technique the interim restoration is constructed outside the mouth so it has the following advantages over the direct technique: 1-There is no contact of free monomer with the prepared tooth or gingiva, which might cause tissue damage or sensitization. 2-The prepared tooth is not subjected to heat created from the exothermic reaction of resin which might cause irreversible pulp damage. 3- The marginal fit of indirectly constructed restoration is better due to : (a) complete polymerization undisturbed on the stone cast. (b) separating the resin from the tooth causes distortion. 4-chair time reduced because the procedure is completed before patient visit 3-Indirect-direct Technique 1- The ESF is made from the diagnostic cast. If a thermoplastic sheet is used and the cast modified with wax, it should be molded over a stone duplicate of the cast rather than directly on the wax 2- Prepare the abutment teeth on diagnostic casts . The diagnostic preparation should be initial. 3-Coat the stone TSF with separating medium 4-apply the resin into the ESF and seated on the TSF. 5-Finish and clean the preformed ESF. 6-Prepare the patient’s teeth in the usual manner. 7-The remaining steps outline the (direct) procedure for lining, which is necessary to produce internal and marginal adaptation . 8-Apply a uniform coat of petrolatum on the prepared abutment teeth, gingival tissues, and outside of the ESF. Then fill the retainers with resin, and seat the restoration. 9-When the rubbery stage of polymerization is reached, remove it from the patient’s mouth and eliminate the excess resin , finishing , polishing . The indirect-direct advantages: 1- Chairside time is reduced. 2- Contact between the resin monomer and soft tissues is minimized compared to the direct procedure because bontic ridge areas do not normally require lining. Reference 1-Contemporary fixed prosthodontics fifth edition 2016 2-Fundamental of fixed prosthodontics fourth edition 2012