FERD - Provisionalization
May 2008, Volume 2, Issue 2
Published by AEGIS Communications
Provisional Restorations for Veneer Preparations
Elizabeth M. Bakeman, DDS
The function of provisional restorations when providing adhesively retained restorations closely parallels the function of permanent restorations, protecting the prepared tooth surfaces from the oral environment. However, fabricating, retaining, and removing provisional restorations during the course of providing adhesively retained porcelain veneers offer unique challenges. This article addresses these challenges and suggests possible techniques for successfully fabricating provisional restorations for veneers that will satisfy the phonetic, esthetic, functional, and retention criteria of the patient, the dentist, and the laboratory performing the fabrication of the definitive restorations.
The use of provisional restorations as an interim step when providing adhesively retained porcelain veneers serves numerous purposes. In situations where the tooth surfaces have been altered, provisional restorations protect the prepared surfaces from assault by the oral environment and minimize sensitivity. Prior to cementation, provisional restorations can be used as a tool to evaluate that uniform clearance has been allowed for the final restorative material. The provisional restorations also provide a template for directing treatment outcomes—esthetically, phonetically, and functionally. Lastly, segmental removal of the provisional restorations can provide a final confirmation that the definitive restorations indeed mirror the incisal edge position established during the transitional phase.
By definition, adhesively retained restorations do not rely on mechanical principals of resistance and retention form.1 In simplified terms, the modality utilized to retain porcelain veneers relies on the micromechanical interlocking and chemical bonding of the resin cement to both tooth structure and porcelain.2 Adhesively retained restorations have long been considered a viable option for the treatment of discolored, malformed, misshapen, or defective anterior teeth. The long-term success of adhesively retained porcelain veneer restorations clearly has been demonstrated in situations involving adherence to enamel.3,4 In situations where veneers are partially bonded to dentin, success rates are known to decrease.5 While the most optimal and least optimal clinical indications for adhesively retained restorations are apparent, many questions remain regarding situations that fall in the middle. The precise clinical impact of varying degrees of available enamel vs. dentin substrate, the long-term clinical effects of dentin bonding systems that exhibit significant in vitro shear bond strengths, and the influence of individual functional risks on the long-term prognosis of the final restorations are all questions that require further exploration.
Without the advantages of resistance and retention form, fabrication and retention of provisional restorations for veneer-type preparations present special challenges.6 Preparation design for adhesively retained restorations typically offers little, if any, mechanical retention. In addition, the color of the luting agent can have a significant impact on the esthetics of the provisional restorations due to the typically thin nature of these restorations.
Fabrication of Provisional Restorations for Veneers (Case #1)
A straightforward approach to fabricate provisional restorations for veneer preparations involves the use of a silicone matrixa developed from the diagnostic mock-up (Figure 1 and Figure 2).6,7 The silicone matrix is filled with a self-curing bisacryl materialb,c and seated intraorally over the prepared teeth. Once the material reaches an initial set, the matrix can be removed. In many instances the provisional restorations will be removed along with the silicone matrix (Figure 3). If this is the case, the restorations can be allowed to fully cure within the matrix extraorally. Bisacryl materials offer the advantage of limited exothermic reaction and minimal shrinkage upon curing. Once the restorations are fully cured, they can be gently teased from the matrix. For this reason it is advantageous to use a silicone matrix material that maintains its shape yet is pliable enough that it can be flexed during removal of the thin, delicate restorations. Stiffer silicone materials suitable for reduction guides,d in general, are too stiff for this purpose (Figure 4).
Upon removal from the silicone matrix, the provisional restoration should be inspected to ensure that uniform, adequate thickness has been achieved (Figure 5 and Figure 6). This step assures that the ceramist will be able to achieve the desired result based on the requirements of the proposed restorative material.
Undercuts or draw issues may prevent the removal of the provisional restorations at the time the silicone matrix is removed from the mouth. In this case, the restorations often can be gently teased with an incisofacial draw from the preparations and allowed to cure extraorally. A bisacryl material that has some level of flexibility at this stage is a helpful adjunct in allowing removal of the restorations. On occasion, the fused units will need to be sectioned into smaller segments in order to avoid fracture upon removal or insertion. Some practitioners avoid removing the provisional restorations from the preparations altogether at this stage and allow the restorations to cure directly on the teeth. This method necessitates trimming of the excess material intraorally (Figure 7). Additionally, the clinician does not have the advantage of measuring the thickness of the provisional restoration to ensure uniform thickness for the restorative material. While additional cementation protocols are avoided with this approach (ie, the slight polymerization shrinkage that occurs as the restorations cure serves to retain them), there is little assurance that the seal between the provisional restoration and the tooth structure is impervious from penetration by the oral environment.
Upon removal from the matrix, the restorations can be trimmed, shaped, and polished prior to cementation (Figure 8). Fine diamonds,e diamond-impregnated discs,f and acrylic burs specifically designed for trimming bisacryl materialsg are helpful in contouring the restorations. The occlusion is more easily evaluated and adjusted on the thin provisional veneers after the provisional restorations have been cemented to the prepared teeth.
The bisacryl materials are available in several different shades and can be custom stained for additional characterization. In addition, slight voids can be filled with coordinating light-cured materials or composite resin.
Whether creating provisional restorations for veneers, full-coverage crowns, or combination cases, the technique of using a silicone matrix is an effective approach. Preformed polymethyl methacrylate shells are useful when fabricating provisional restorations for traditional crown preparations where the preparations are circumferentially established at the gingival crest and the tooth surfaces are reduced by a millimeter or more. However, they are difficult to use with any predictability for veneer preparations that have varied marginal positions and minimal tooth reduction.
While there is no need for provisional restorations to function in minimizing sensitivity or preventing bacterial contamination of prepared tooth surfaces when an additive veneer approach is taken involving no preparation of the affected teeth, there still is a need for the provisional restorations to provide a template for directing treatment outcomes (ie, esthetically, phonetically, and functionally). An effective technique for the fabrication of provisional restorations for teeth that have no reduction of tooth structure involves spot etching individual teeth and the direct placement of composite resinh,i,j to achieve the desired outcome.
Luting Provisional Restorations (Case #1 cont.)
Once the provisional restorations have been trimmed and polished, a light-cured sealantk can be applied to the external surfaces (Figure 9). A water soluble lubricant is placed on the external surfaces to aid in removal of excess cement following cementation. Translucent resin cementsl,m appear to be well-suited for luting veneer provisional restorations, with or without spot etchingn of the facial surfaces of the prepared teeth. The decision to spot etch is not an exact science and currently is based on the practitioners’ individual experience. Indications for spot etching include preparations that do not break the interproximal contacts, provisional segments that span fewer than five teeth, and preparations that do not cover the incisal aspect of the teeth.
The need for spot etching decreases as increased numbers of units are fused together in the provisional restoration. Larger spans provide an increase in cross arch stabilization and, therefore, an increase in retention. Likewise, as preparations extend interproximally, or over the incisal edge, mechanical retention increases. How-ever, the benefits of extended preparation design in retaining the provisional restorations should never be a reason for extended preparations beyond those that are required to achieve the desired final result.8 Additional factors that the clinician may take into consideration when deciding upon luting protocols are the duration of time that the provisional restorations will need to be of service and any parafunctional activities of the patient; both factors will place higher demands on the luting agent.
Without etching or priming of the prepared tooth surfaces, the resin cement functions as a weak cohesive link between the tooth and the provisional restoration. With spot etching, the resin cement functions both cohesively and adhesively.
No matter which luting approach is utilized, the cement must provide retention sufficient enough that anterior guidance can be established without deleterious effects to the seal between the restoration and the tooth structure.9 If the restorations loosen during function, respectful of the diet limitations that the patient has been given, it should strongly be suspected that the anterior guidance is not in harmony with the patient’s functional pathways and it should be adjusted accordingly.10
Veneer thickness is frequently such that opaque cements lend a negative influence to the appearance of the provisional restorations. Translucent cements typically have high esthetic acceptance. Additionally, translucent cements do not negate the in-fluence of the underlying tooth structure and, therefore, function as a communication tool for the laboratory regarding the need for more opaque restorative materials in cases where shade masking is required.
Because adhesive protocols require a dry field in which to work, it is imperative that the patient provide meticulous home care of the provisional restorations in order to avoid tissue inflammation and subsequent bleeding sequela at the delivery appointment.11 The patient must be instructed in mechanical debridement specific to fused units, as well as the use of antimicrobial rinses to ensure optimal tissue health at the delivery appointment.12
Smile Design Approval (Case #1 cont.)
While provisional restorations provide an opportunity to fine-tune the functional requirements of the final restorations, they also facilitate a framework for development and acceptance of the esthetic components.13 A preoperative extraoral mock-up is only a design estimate that is created with the aid of the information generated from the preoperative records.14 Patients and clinicians must have the opportunity to evaluate the provisional restorations in the absence of the effects of local anesthetic and during function (Figure 10). If required, resinh,i,j can be added to increase length or contour of the provisional restorations. Material can be subtracted with the use of rotary instruments (ie, diamond burse and flexible discso) when contours or length are excessive (Figure 11). If significant alteration is made, the patient should be allowed additional time to test the restorations during function prior to final confirmation. The restorations should be modified until both the patient and the provider are pleased with the phonetic, esthetic, and functional results (Figure 12, Figure 13, Figure 14).15,16 An impressionp of the approved result allows for a three-dimensional transfer of information about tooth shapes and contours to the laboratory. Photographs of the approved provisional restorations also are necessary communication tools at this stage.
Confirmation (Case #1 cont. and Case #2)
Provisional restorations that have been retained with a resin cement typically require some degree of division prior to their removal. The bisacryl or resin provisional material can be segmented interproximally and facially with the use of diamond burs.e The provisional restorations are then torqued from the teeth with the use of a hand instrument (Figure 15).q In cases where the teeth have been spot etched, meticulous care must be employed in detecting and subsequently removing residual resin from the teeth.
The information gleaned from the preoperative photographs, the centric relation bite records, the face bow transfer, the impression, and photographs of the provisional restorations all work in concert to assure that the restorative objectives will be met (Figure 16 and Figure 17). That said, it is still recommended that just one half of the provisional restorations be removed at a time. Note: the midline should be used as a dividing point. This affords an opportunity to try in half of the final restorations against the contralateral provisional restorations. The length and labiolingual position of the incisal edge position can then be confirmed intraorally. In the majority of instances, this step is simply a verification tool for the clinician and the patient, in which case, photographs from the facial and occlusal vantage point are documented and included in the patient record. The final restorations should closely mirror the contours established with the provisional restorations (Figure 18, Figure 19, Figure 20).
The function of provisional restorations when providing adhesively retained restorations closely parallels the function of provisional restorations retained with cohesive protocols in assuring biologic, esthetic, and functional success of the final restorations. However, fabricating, retaining, and removing provisional restorations during the course of providing adhesively retained porcelain veneers offer unique challenges. More study is needed with regard to proven provisional protocols in situations that provide little, if any, mechanical retention.
The author wishes to thank Sandy Mosey, CDT, of Belmont, Michigan, and Lee Culp, CDT, of Sarasota, Florida, for fabricating the restorations featured in this article, as well as for their partnership, dedication, and continued commitment to excellence.
a Sil-Tech, Ivoclar Vivadent, Inc., Amherst, NY
b Luxatemp® Florescence, Zenith Dental, Englewood, NJ
c Protemp 3 Garant Temporization Material, 3M ESPE, St. Paul, MN
d Sil-Tech Super, Ivoclar Vivadent, Inc., Amherst, NY
e Medium/fine diamond burs, Brasseler USA, Savannah, GA
f Hyperflex, double-sided discs, Brasseler USA, Savannah, GA
g E-Cutter® acrylic burs, Brasseler USA, Savannah, GA
h 4Seasons, Ivoclar Vivadent, Inc., Amherst, NY
i Filtek Supreme Plus, 3M ESPE, St. Paul, MN
j Venus, Heraeus Kulzer, Inc., Armonk, NY
k Palaseal® , Heraeus Kulzer, Inc., Armonk, NY
l Variolink® II, Ivoclar Vivadent, Inc., Amherst, NY
m Choice, Bisco, Inc., Schaumburg, IL
n Etch-37, Bisco, Inc., Schaumburg, IL
o Sof-Lex Contouring and Polishing Discs, 3M ESPE, St. Paul, MN
p Take 1® , Kerr Corporation, Orange, CA
q Goldstein Crown Remover, Hu-Friedy, Chicago, IL
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About the Author
Elizabeth M. Bakeman, DDS
Grand Rapids, Michigan
Clinical Instructor, Kois Center for Advanced Dental Education