Inside Dental Technology
Bar Modification for Improving Composite-Resin to Ridge Design
New prosthetic offerings including esthetic and functional solutions with complex restorations
The prosthetic product line offering from dental laboratories specializing in removable prosthodontics has dramatically expanded over the last several years. Removable prosthetic dental laboratories’ product lines now include complex restorations such as implant-retained and implant-supported overdentures. One of the new expanded prosthetic product services is milled implant-supported hybrid bars for which removable prosthetic dental technicians are seeing an increasing demand. There are many variables to take into consideration when planning and designing a complex implant-supported prosthesis. One variable that will be discussed is the ridge-to-resin or ridge-to-metal relationship. There are different designs for milled hybrid bars, and each must take into consideration the contour of the residual ridge in relation to the placement of denture teeth. In this article, the author will focus on the external finish lines for this type of milled bar and the methods for achieving a functional transition from residual ridge to prosthetic gingival base.
The implant-supported hybrid Montreal bar (NobelProcera™, www.nobelbiocare.com) case presented in this article was sent for processing and setup delivery on the Montreal bar. In Figure 1, the maxillary and mandibular milled titanium Montreal bars are seen in the oral environment. Note the extension of external finish lines to the residual ridge crest. The finish lines were extended too far labially and buccally, especially on the mandibular arch. Figure 2 shows the mandibular milled Montreal bar, and Figure 3 shows the maxillary in relation to the residual ridge of the oral environment. Note the labial and buccal extensions of titanium, and visualize the teeth plus acrylic resin in these areas. Figure 4 demonstrates the placement of external finish lines in relation to gingival acrylic resin. This ledge, as seen between both the maxillary and mandibular ridge crest and bar, needed to be re-designed to create a proper contour or bevel from the labial and buccal surface to the residual ridge. The Montreal bars were treated with a metal bonding interface (SR Link, Ivoclar Vivadent, www.ivoclarvivadent.com) (Figure 5). After the metal primer, an opaque was applied (anaxdent, www.anaxdent.com) in two stages, PO I and PO II. The first coat has a higher degree of opacity (PO II), and the second has a more pink gingival color (PO I). The gingival base was then invested and processed in a heat cure resin (SR Ivocap® Injection System, Ivoclar Vivadent). After processing and finishing, the problem with the external finish line became more evident. The relationship of the metal Montreal bar to the ridge created a definite food trap on the labial and buccal surfaces (Figure 6). It was necessary to redesign this ledge—as seen between both the maxillary and mandibular ridge crest and the bar—to create a proper contour or bevel from the labial and buccal surfaces to the residual ridge.
To achieve a proper contour, the titanium intaglio needed to be cut back to allow for a beveled tissue-to-tooth emergence profile, leaving the external finish line, as it created a concave intaglio instead of the desired convex acrylic or metal surface. The maxillary and mandibular titanium intaglio surfaces were cut back to the crest of the residual ridge to recreate a new external finish line. The ridge crest to the new external finish line allowed for a beveled gingival emergence to create the desired convex surface (Figure 7 and Figure 8). Figure 9 shows the intaglio of the Montreal bar before the metal was cut back. The labial aspect of acrylic resin was extended gingivally to help eliminate the food trap. The titanium bar was cut back and a new external finish line was created (Figure 10). The bar was opaqued in a two-step process (Figure 11). The exposed titanium was opaqued to mask out any graying effect from the metal (Figure 12 and Figure 13). Anaxgum (anaxdent) bonding agent was applied to the acrylic to create an interface for the composite to bond to acrylic. The gingival base was then built up with anaxgum composite on the master cast, filling in the space between the residual ridge and the cutback of acrylic/metal. A combination of dark and light pink composite was built up in layers and light cured.
Figure 14 is an in-situ or retracted intraoral photograph showing the elimination of a labial titanium ledge and a proper gingival contour. Figure 15 and Figure 16 show the right and left buccal view of composite-to-ridge relation. It is very important to allow space for Super Floss orthodontic floss (Oral-B, www.oralb.com) and Waterpik® (Waterpik, www.waterpik.com) to maintain proper gingival hygiene habits and prevent food or plaque accumulation. When characterizing the gingival base, note that the attached tissue just below the denture teeth has a blanched appearance compared to the unattached tissue closer to ridge crest, which is more vascular and has a darker pink or reddish tone. Figure 17 shows the finished maxillary hybrid with proper emergence gingival profile. Note the beveled peripheral border labial to the anterior implants. Figure 18 shows the occlusal view of the maxillary, while Figure 19 shows an occlusal view of the mandibular. Viewing the screw access holes makes it possible to visualize the ridge crest in relation to the metal and slight labial or buccal extension to the ridge crest.
In Figure 20 and Figure 21, the maxillary implant-supported bar is finished with the cutback shown in the anterior and left posterior areas. The titanium that opposes residual ridge and the composite, labial and buccal to ridge crest, are highly polished to create a proper transition from the acrylic resin and composite to the tissue. The finished mandibular intaglio with the metal modification is shown in Figure 22, with the finished lingual view of the maxillary in Figure 23 and the mandibular in Figure 24.
The esthetic and functional objective was to eliminate horizontal over-extensions of the bar—which would have created food traps—and to re-contour the borders to achieve a more ideal gingival emergence profile in relation to ridge crest. Ideally, this should be accomplished during the virtual design process, although sometimes problems with bar designs become evident during tooth setup or processing and need to be modified accordingly.
The author would like to thank and acknowledge Dr. Saj Jivraj and Dr. Hooman Zarrinkelk for collaborating on the case and this article.
About the Authors
Robert Kreyer, CDT
Custom Dental Prosthetics Inc.
Los Gatos, California
Saj Jivraj, DDS