A Direct Technique for Fabricating Esthetic Anterior Fixed Provisional Restorations Using Polycarbonate Veneers
Fabrication of esthetic interim restorations by a chairside technique often challenges the clinician with regard to the required time and skills, as well as meeting the expectations of the patient. Autopolymerizing polymethyl methacrylate resin has been reported to be the most popular material for fabricating provisional restorations. However, this material does not routinely yield esthetic provisional restorations via a chairside technique. This article describes a simple technique to overcome some of the disadvantages of this material by using prefabricated polycarbonate facings backed with autopolymerizing acrylic resin. This technique can be used chairside for fabricating esthetic anterior interim restorations, utilizing the beneficial properties of both materials. It exploits the manufactured smooth-surface finish, superior esthetics, color stability, and durability of polycarbonate facings, as well as the marginal adaptation, strength, and low cost of autopolymerizing acrylic resin.
Interim restorations in fixed prosthodontics provide protection of the pulp, esthetics, function, space maintenance, and soft-tissue healing.1 Esthetics is one of the most important functions of an interim restoration, especially in the anterior region. Such a restoration not only satisfies a patient’s expectations but also makes the patient confident in the clinician.
Traditionally, autopolymerizing polymethyl methacrylate (PMMA) resin has been reported to be the most frequently used material of choice for interim restorations fabricated by direct and indirect techniques.2-5 The material has a long record of use, low cost, and good strength.3-5 Its marginal adaption has also been shown to be acceptable.6,7 However, this material has poor color stability, porosity, and poor surface texture,8 which could directly influence the esthetics. Achieving optimal esthetics with this material can be laborious and time-consuming. Consequently, alternatives such as polycarbonate crowns, denture teeth facings, bis-acrylic resin, and other composite resin materials have been suggested.9-18 Polycarbonate crowns are typically used for single-unit provisionals, denture teeth are laborious to trim, and bis-acrylic resin and other composite resins are more expensive than PMMA material.
Prefabricated polycarbonate crowns have long been employed in fixed prosthodontics to create interim restorations.13-18 They are color-stable, plastic materials that are made of a polycarbonate resin with microglass fibers, which provides durability, strength, and vitality.19,20 The crowns are easy to use and have the advantage of a manufactured smooth-surface finish, which can minimize the potential for plaque accumulation.15 However, their chairside use has been restricted to single-unit interim restorations.1,2 They fit poorly unless lined with resin and may require significant adjustments to achieve proper contours and occlusion.1,2
This article describes a simple, direct technique to fabricate an anterior fixed provisional restoration, using the beneficial properties of two materials: an esthetic polycarbonate facing/veneer and an autopolymerizing acrylic resin backing.
The technique described below is for chairside fabrication of a three-unit fixed provisional restoration for teeth Nos. 7 through 9 in a patient who presented with compromised metal-ceramic crowns requiring retreatment (Figure 1).
First, prepare a clear vacuum-formed matrix from the pretreatment diagnostic cast using a 0.020-inch thermoplastic material (Tray-Vac™ Complete, Buffalo Dental Mfg., www.buffalodental.com). If a patient presents with teeth that are misaligned, fractured, or show other tooth discrepancies, a diagnostic waxing is indicated for optimal shape of teeth. The vacuum-formed matrix should then be prepared over a duplicate cast of the wax-up.
Based on the diagnostic cast, the next step is to select the appropriate size of the polycarbonate crowns (3M ESPE, www.3MESPE.com). If the appropriate size is not available, select a crown with larger dimensions and adjust it later (Figure 2).
Then, carefully sever the facial surface from the rest of the crown using a diamond disc (Provisional Adjuster and Polishing Kit, Brasseler, www.brasselerusa.com). It is important to preserve as much proximal surfaces of the polycarbonate facing as possible (Figure 3.) Adjust the severed polycarbonate facings to conform to the shape and size of the planned restorations (Figure 4). The approximate thickness of the polycarbonate facing is usually around 1 mm (Figure 5).
Next, prepare the teeth using standard principles of tooth preparation. If previous crowns exist, section the crowns prior to removal and refine the teeth preparations accordingly (Figure 6).
Lubricate the facial surfaces of the polycarbonate facings with a light coat of petroleum jelly. This will ensure easy clean-up of any excess acrylic resin later. Should the clinician use petroleum jelly on teeth preparations for easy retrieval of the provisional restorations, the teeth preparations should be polished with pumice and water before cementation of the final crowns to avoid interaction with resin-containing cements.
The next step is to drill small holes on the lingual surface of the clear matrix to allow extrusion of excess autopolymerizing acrylic resin. Secure the polycarbonate facings to the inside of the clear matrix with the aid of a small bleb of rope wax (utility rope wax, Heraeus, www.heraeus-dental-us.com) (Figure 7). Confirm that the polycarbonate facings are secured in the matrix by inverting it a couple of times.
Choose the closest shade of autopolymerizing PMMA acrylic resin that matches the shade of the polycarbonate facings (Coldpac Tooth Acrylic, Yates Motloid, www.yates-motloid.com). Mix the appropriate amount of acrylic resin to fill the clear matrix and seat it directly on the prepared teeth in the mouth. Use an “on-off” action of the matrix until initial polymerization of the acrylic resin (Figure 8). After initial polymerization, remove the matrix and place it in warm water.1
After the definitive polymerization of the acrylic resin, peel out the clear matrix from the interim restoration and clean off any excess resin material or rope wax adhering to the facial surface of the restoration. Then carefully trim away any flash or excess material and contour the interim restoration with diamond and polishing discs (Provisional Adjuster and Polishing Kit, Brasseler).
After trimming, place the interim restoration in the mouth and evaluate the marginal adaptation, proximal contacts, and occlusion; make adjustments accordingly. If there is a discrepancy in color at the junction of the polycarbonate facing and the acrylic resin, remove the interim restoration from the mouth and lightly roughen this junction and the adjoining areas with a diamond rotary cutting instrument to place a roughened bevel.
Then, choose the appropriate shade of flowable composite resin (PermaFlo® flowable composite, Ultradent Products, Inc., www.ultradent.com). For better shear bond strength, apply a coat of methyl methacrylate monomer to the surface with a brush before application of the bonding agent.20 Add an appropriate amount of the flowable composite resin, contour, and then polymerize it for 20 seconds using a light-curing unit. Carefully trim away any excess material to blend the flowable composite material with the rest of the facial surface using standard trimming techniques (Provisional Adjuster and Polishing Kit, Brasseler). Polish the restoration with pumice and water using a wet rag wheel on a rotary instrument on slow speed.
Finally, return the polished provisional restoration (Figure 9) to the mouth and insert it using cement that is indicated for interim purposes (TempBond® NE™, Kerr Dental, www.kerrdental.com) (Figure 10).
Compared to denture teeth, prefabricated polycarbonate crowns are quicker and easier to trim because they are thin, hollow, and do not cause clogging of the burs.18 This makes them easy to use for a chairside technique. To save time, the clinician may choose to maintain an inventory of pre-trimmed polycarbonate facings of different sizes. The bond between the PMMA resin and polycarbonate crowns is known to be good.14-17 The bond between the flowable composite material used for modifying and repairing polycarbonate crowns also has been demonstrated to be effective.20
A disadvantage of this technique is the lack of shade selection options, as the polycarbonate crowns are generally available in a standard color. If a patient desires a close match of provisional restorations to adjacent teeth, then this technique is not recommended. A laboratory-fabricated provisional restoration through an indirect technique followed by custom characterizations may be needed in such situations. Also, if the size and shape of the polycarbonate facing does not conform to the shape documented by the vacuum-formed matrix, a color discrepancy at the junction of the polycarbonate facing and PMMA resin might be observed. This requires an additional step of correction using a flowable composite resin. Both of these disadvantages, however, can be overcome by proper case selection and attention to detail when using the technique. The only absolute contraindication to this technique is a patient who has a known allergy to methyl methacrylate monomer.
A direct technique for fabricating esthetic provisional restorations saves a clinician time and money. However, achieving optimal anterior esthetics by using some of the traditional chairside techniques and materials can be challenging. This article described a chairside technique for fabricating an esthetic provisional restoration that utilized the superior esthetic properties of a polycarbonate facing as well as the marginal integrity, strength, and low cost of an autopolymerizing acrylic resin backing. This technique may be an alternative option for maximizing the esthetics of an anterior provisional restoration that is fabricated chairside.
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About the Authors
Avinash S. Bidra, BDS, MS, FACP
Assistant Professor and Maxillofacial Prosthodontist
Department of Reconstructive Sciences
University of Connecticut Health Center
Anna Manzotti, DDS
Post-Graduate Prosthodontics Resident
Department of Reconstructive Sciences
University of Connecticut Health Center