Provisional Trimming: The Choice is Yours
Shari L. Becker, CDA, RDA, FADAA
When making a temporary crown or bridge, there are a number of choices on what instrumentation can be used to trim a provisional restoration. As techniques vary, basic guidelines based on a dental assistant’s instrument choice should be followed to trim margins, shape gingival and incisal embrasures, add anatomic contours, and achieve final finishing and polishing.
Custom temporaries can be fabricated with a variety of materials. The more popular include bis-acryl and methacrylate resins.1(p824) For trimming a temporary, the more popular selections include acrylic laboratory burs and discs.1(p520) Whether a disc, a bur, or a combination is used, it is important to use instruments that work best in the operators’ hands and are applicable to their specific needs.2
Acrylic Laboratory Burs
When selecting an acrylic laboratory bur, there are three main factors to take into account: shape, size, and blade design. There are a wide variety of laboratory burs on the market today; the more popular shapes include egg- and round-end tapered. These are offered by KOMET USA (www.kometusa.com), Axis Dental (www.axisdental.com), and other dental manufacturers. These basic shapes allow for a wide variety of angulations and uses. Size can vary depending on the needs of the operator (Figure 1). A smaller bur is used when a larger bur cannot reach into narrow areas or would damage surrounding areas by accidentally touching them. A larger bur is more efficient in material reduction, and it is easier to achieve smooth surfaces with it. In terms of blade design, three popular types are the standard cutter blade, the cross-cut blade, and the staggered-tooth blade design (Figure 2). Many of these blade designs vary from super coarse to extra fine, depending on the instrument and the manufacturer. Some of these laboratory burs are also designed to be non-clogging, which allows for more efficient and continuous cutting.
Like burs, there are many choices for discs. Because the shape of a disc is standard, three main factors that influence disc selection are size, design, and grit. The choice of size is a matter of preference for each operator. Diamond-coated wheels and sandpaper discs are both available in a wide variety of diameters (Figure 3). Many operators choose a variety of diameters to provide as much flexibility in terms of access as possible. There are many choices of design, and include rigid, semi-flexible, and very flexible for diamond discs. Another factor in selecting diamond-disc design is choosing single- or double-sided, serrated ends, full coated, partial or full perforation (Figure 4). When using a diamond or sandpaper disc, there are a choice of different grits (coarse, medium, fine, and extra fine), which can all be found in Composite Polishing Discs from KOMET USA and Sof-Lex™ discs (3M ESPE, www.solutions.3m.com) (Figure 5). Operators should find what size and design works best in their hands to meet their specific needs.
Whether trimming a single- or multiple-unit provisional, bulk trimming must be done first and usually starts with a coarse sandpaper disc or the egg- or round-end tapered laboratory bur. The idea is to remove the majority of excess bulk from the provisional. Once the bulk trimming is completed, detailed and fine trimming will follow.
If using sandpaper discs, a coarse disc or a medium-grade disc can be used for bulk reduction. If trimming a single unit, the egg-shape or round-end tapered acrylic bur may be used for margins and interproximal contacts. As there is little room for error around the margins, maintaining control of the handpiece is especially important here. The goal should be to create margins that are smooth and accurate to avoid future damage to the periodontium.3 If this is a multiple-unit temporary, a fine-point or flame-shaped laboratory bur can be used, which allows finer accessibility for bulk trimming at the interproximal margins (middle bur in Figure 1). This area may call for a diamond or sandpaper disc to access the interproximal space adequately to maintain appropriate shape and contour.
Gingival and Incisal Embrasures
When trimming any provisional, it is important to maintain and enhance anatomic integrity and esthetics. With gingival embrasures, over- or undercontouring creates the possibility of food impaction, gingival irritation, inflammation, overgrowth, or the creation of papilla spaces that could have irreversible consequences and hinder the final restorative results.4 The gingival embrasure contour has a direct relationship to the final margin. Having a basic understanding of emergence factors and anatomy, especially with implant provisionals, is critical. It is important to maintain marginal integrity while providing appropriate gingival embrasures to ensure minimal tissue response that will allow for a predictable outcome with the final restoration. A larger-diameter diamond disc is best to reach further interproximal areas (first disc in Figure 3). A medium sandpaper disc also may work well here, if care is taken not to over- or undercontour.
The shape of incisal embrasures can have a direct influence on esthetics and function. In an anterior segment, there should be a gradient in the depth of the incisal embrasures. The smallest embrasure should appear between the maxillary central incisors and grow incrementally deeper with each consecutive embrasure.5 The operator may need to modify embrasure depth to meet patient preference. A deeper embrasure contributes to a more oval tooth outline form. Because this is a fine adjustment, a small diamond disc (second disc in Figure 3) or small fine sandpaper disc would be advised to avoid overcontouring.
As the bulk trimming is completed, gingival embrasures refined and margins contoured, it is important to coordinate all aspects of tooth anatomy. Important elements include the emergence profile,6 gingival and incisal embrasures, interproximal contact zones, broad surface planes, and occlusal anatomy. The form of the contact point or area is influenced by the tooth morphology, width, and arrangement.1(p521) A small, tapered acrylic laboratory bur may be useful in creating lingual cingulum or occlusal contours (third bur in Figure 1). A round-end, tapered acrylic laboratory bur or medium sandpaper disc may serve well to create facial emergence contours. The use of a polishing disc also can add subtle anatomic contours to the facial of anterior provisionals. The diamond or sandpaper disc also can be used to enhance interproximal contour to give a more individualized appearance to a multiple-unit temporary.
Finishing and Polishing
Finishing—creating surface smoothness—can be achieved a number of ways. With many of the newer acrylic laboratory burs, the finer blade designs allow for a very refined and smooth result, with minimal or no finishing required. With the sandpaper discs, finishing is accomplished by using lesser coarse discs, gradually moving down to a fine or extra fine for a smooth finish.7 Polishing—achieving surface luster—can be accomplished using a variety of wheels and brushes with pastes or diamond-embedded points, cups, discs, brushes, or wheels (Figure 6). Some polishers are offered as a system (such as composite polishers with a diamond grit by KOMET USA) to achieve a high-gloss polish as the final result, while others offer more subtle polishing.
By using the appropriate selection of acrylic laboratory cutting burs, discs, or a combination of instruments, the fabrication of a single- or multi-unit custom provisional can be made easier.8 Used in conjunction with a basic understanding of esthetics and function, conformed and sealed margins, and appropriate contours, a smooth finish and polish should be the expectation to ensure a more predictable and successful result.
The author would like to thank Stephen R. Snow, DDS for providing the images shown in this article.
The author is a paid consultant for KOMET USA.
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2. Govoni M. Provisional restorations. Dental Economics Web site. Accessed June 8, 2009.
3. Donaldson D. Gingival recession associated with temporary crowns. J Periodontol. 1973;44(11):691-696.
4. McDonald TR. Contemporary temporization. Pennwell Dental Group. Accessed May 26, 2009.
5. Greenberg JR. Shaping anterior teeth for natural esthetics. Esthet Dent Update. 1992;3:86.
6. Chiche G, Pinault A. Esthetics of Anterior Fixed Prosthodontics. Carol Stream, Ill: Quintessence Publishing; 1994:124.
7. Rufenacht C. Fundamentals of Esthetics. Carol Stream, Ill: Quintessence Publishing; 1990:118.
8. McDonald TR. Excellence, Precision, Efficiency. The Single Tooth Provisional Restoration. The GAGD Explorer. Summer 2007:6.
About the Author
Shari L. Becker, CDA, RDA, FADAA
Editorial Board Member
Inside Dental Assisting
Snow Dental Care