May 1, 2003
by Jack Ringer, DDS
The use of laboratory fabricated resin materials for indirect restorations is not new and, in fact, the first commercially used indirect composite, Isosit, was first introduced in 1981.
Over the last decade or so, the introduction of several improved laboratory fabricated composite restorations has created a conservative, aesthetic and predictable treatment alternative for restoring teeth with moderate to large defects. Indirect composite restoration therapy may also be classified as Polyglass or Ceromer Restorative Dentistry (Table 1).
Polyglass/Ceromer inlay or onlay restorations have demonstrated their success due to their improved physical properties combined with the ability of the practitioner to bond the restoration to the tooth. Also, as the restoration is being fabricated indirectly, polymerization shrinkage is easily controlled and interproximal form and contacts are more accurately established. However, as with any therapy, there is a specific protocol that must be followed when placing Polyglass/Ceromer restorations in order for success to be predictable.
This article is going to cover the necessary steps, from tooth preparation through finishing that should be employed in order to attain predictable success in placing Polyglass/Ceromer inlay or onlay restorations.
Polyglass/Ceromer restorations rely on the bonding potential of the treated internal surfaces of the restoration to the prepared tooth utilizing bonding agents and resin cements for their retention. Therefore, the need for aggressive tooth preparation becomes unnecessary. As with the preparation guidelines for direct composites, the internal line angles for Polyglass/Ceromer restorations are rounded and smooth to maximize the bond of the restoration to the tooth and to minimize the potential for post-op sensitivity and stress fractures within the restoration. To minimize premature wear of the material and to optimize aesthetics, all external line angles should have a sharp butt joint or a hollow ground chamfer (Figs. 1 & 2). The cavosurface margins should not be in contact with the opposing cusps due to the increased susceptibility of wear or fracture of the restoration. This being so, the principals of parallelism, sharp internal line angles and “extension for prevention” used for traditional cast metal indirect restorations becomes unnecessary. The need for routinely onlaying cusps is lessened and only becomes necessary when there is a previously fractured or restored cusp. Our objective is to only “remove what is bad and keep what is good.”
Our final preparation is going to have divergent internal walls (approx. 15-20 degrees), round internal line angles, and butt joint or hollow ground chamfer external cavosurface margins. Typically, the prepared pulpal floor will be flat and at a depth of approximately 1.5mm. However, if onlaying a cusp is necessary, then the involved cusp should be reduced 1.5-2.0mm. occlusally and approximately 1.5mm facially or lingually; also with a butt joint or hollow ground chamfer margin (Fig. 2a).
It is recommended by this author, due to the small proportions of these restorations, that in order for the practitioner to gain optimum results, he or she must be working with magnification assistance and proper field illumination!
We need specific preparation burs to produce the ideal preparation for a Polyglass/Ceromer restoration, which may be different than those used for preparing cast metal restorations. The preparation burs are all diamonds with the exception of round carbide burs, which are used for the removal of previously placed amalgam or gold. The diameter of these burs is also small, as we want our preparation to be as conservative as possible. Therefore, as illustrated in Figure 3, the burs of choice for preparation would be course chamfer burs with diameters from 012-.018mm, e.g. Axis C856:012,014,018. The pulpal floor can be smoothed with an end-cutting bur, e.g. Axis M836:012.
In some instances, in trying to maintain a conservative preparation, undercuts or voids in the tooth may be present after the tooth is completely prepared. These areas should then be blocked out with the application of either glass-ionomer, flowable, or composite and then finished prior to impression taking (Fig. 4).
Impression protocol for Polyglass/Ceromer restorations should be the same as that used for most other indirect procedures. If the gingival margins are close or below the gingival tissue, retraction cord is placed. Triple tray impressions are very successful and convenient as they incorporate the bite, the preparation and the opposing arch. Polyvinyls, e.g. Examix, GC America or polyethers, e.g. Impregum, 3M/ESPE are all acceptable materials for recording impressions for Polyglass restorations. The illustrated case shows the use of Impregum Soft/Permadyne Garant, 3M/ESPE (Fig. 5).
Provisionals for Polyglass/Ceromer restorations, as with any dental procedure, should be made to be well fitting and aesthetically acceptable in a timely and cost effective manner. One technique which satisfies these requirements utilizes thermoplastic buttons, Advantage Dental (Fig. 6), provisional a resin material either dual-cure, e.g. Luxatemp Dual Cure, Zenith or auto-cure 3M/ESPE Protemp 3 (Fig. 7) and a provisional resin cement, e.g. Temp-Bond Clear, SDS/Kerr. Prior to preparation, a thermoplastic button is heated up until it is soft enough to mold around the involved tooth and extend onto the adjacent teeth (Figs. 6 & 6a). However, if the tooth to be prepared is already missing a cusp or cusps, then the deficient area should be built up with composite prior to placing the thermoplastic button. Once the material cools, it becomes hard and forms a stent for making the provisional inlay/ onlay. After the impression is taken, the selected shade of provisional resin material is placed in the stent and seated in the mouth. Once the material has set up, the stent and provisional are removed from the mouth. The provisional can then be adjusted and placed back in the mouth to confirm the fit and bite. The provisional restoration can now be luted with any provisional cement. This entire procedure can be performed by the dentist or delegated to an auxillary staff member (Fig. 8).
As there are several Polyglass /Ceromer systems available, it will be necessary to instruct the laboratory on exactly which type is to be used (Table 1). As with any aesthetic procedure, an accurate shade of the prepared tooth and of the final restoration should be illustrated, either by photography or color mapping. Any specific surface anatomy, occulsal and contact requirements, and opacity issues should also be conveyed to the laboratory technician. In the illustrated case a Sinfony, 3M/ ESPE restoration was manufactured by the laboratory (Figs. 9a, b & c). Another illustrated example was using Gradia, GC America (Figs. 10 & 10a). One can see that extremely beautiful and natural results can be achieved using these indirect composites systems (Fig. 11).
Bonding any of the Polyglass/ Ceromer restorations requires a specific protocol in order to insure predictable results. Materials typically required for this procedure are a dual-cure adhesive system and a dual-cure resin cement system. As with all bonding procedures, a clean and non-contaminated preparation site and the restoration itself are required. This can be easily achieved by cleaning the preparation site with any micro-abrasion system, e.g. Accu-Prep, Bisco. The final restoration is tried in to confirm the marginal adaptation and the bite.
Once this step is completed, a thin layer of the adhesive is applied to the clean internal surface of the restoration, air dried to thin and remove any solvents, and then light cured for 20 seconds. Following this, the preparation is then etched with 35% phosphoric acid for 15 seconds and thoroughly rinsed. To create the right moisture level to accept the dentin primer, the preparation is then exposed to a high volume evacuator
for approximately two seconds. This usually insures an even distribution of moisture on the dentin surface.
Visually, the dentin surface should now have a shiny appearance. A layer of adhesive containing a dentin primer is then applied vigorously for about 15 seconds to insure proper penetration of the monomer into the collagen network in order to form the hybrid layer. The tooth is then gently air dried to remove any solvents and then, if directed, light cured for 20 seconds. A second layer of adhesive is then applied and lightly air-dried followed by injecting a thin layer of the dual cure resin cement into the preparation covering all the involved surfaces.
Solo Plus Dual-Cure, SDS Kerr (Fig. 12) adhesive and Rely X ARC, 3M/ESPE (Fig. 13) dual-cure cement were used in the illustrated case. Recent studies have indicated that the acidity of the light cure only adhesive systems can cause a reduction in bond strength when used with a dual-cure cement.
Therefore, if the clinician desires optimum bond strength between the adhesive and the cement, than both components should be dual-cure materials (Tables 2 & 3). The restoration is now gently pushed into the preparation until completely seated. The bulk of excess cement is wiped away and then while applying positive pressure on the restoration to prevent any rebound, the tooth is then light cured from all sides in 40 second increments.
If prior to light curing, little excess cement was present on the margins, then an oxygen barrier material must be applied and additional light curing through this layer is necessary to insure that there is no air inhibited layer present at the external tooth/ restoration interfaces. It must be noted at this time, that materials are continually evolving with the intent of providing a simpler and more efficient protocol for bonding indirect restorations. Recently a new product; Unicem, 3M/ESPE (Fig. 14); was introduced that combines the etchant, dual-cure primer/adhesive and cement in a single capsule.
Following removal of the provisional and cleaning the preparation site, after mixing the cement in a titurator, it is injected into the tooth and the restoration is bonded to the tooth following the same protocol as described earlier. At this point in time there is no log term independent clinical research data supporting this product, however, anecdotal evidence shows a lot of promise for this product.
The finishing process for Polyglass/Ceromer restorations is the same as with other composite type restorations. Any bite adjustments and removal of any excess cement are made using either diamond or composite finishing burs.
Illustrated in Figures 3a & 3b are the burs of choice, which are football carbide burs, (Axis H379-023, 023F, and 023UF), along with long carbide finishing burs, (Axis H135-014 and H135-014F) or long diamond finishing burs, (Axis S135-014F and S135-014SF). Following this step, composite finishing wheels are used to polish the restoration, such as Axis PDQ Single Step Composite Polishing System (Fig. 3c).
Interproximally, finishing strips, e.g. Visionflex Diamond Strips, Brassler; Sof-Lex, 3M/ ESPE or Epitex, GC America are carefully used to remove any excess cement that may be present. However, it is necessary to avoid placing the abrasive surface of the finishing strip in the contact area, which could result in creating an unwanted open contact.
Upon completion, one finds that not only is the restoration intimately connected to the natural tooth, an extremely natural result is achieved (Fig. 11).
Dentists are continually faced with the dilemma of deciding what type of restoration and material they should use when restoring deficient tooth structure. It should be the goal of the dentist to provide a therapy that will be the least destructive to tooth structure, yet will have predictable longevity and acceptable aesthetics. Though Polyglass/ Ceromer restorations are relatively new and there are little long term studies about their longevity and predictability, there is mounting anecdotal evidence supporting the routine use of Polyglass/Ceromer inlay or onlay restorations. However, there is no question that Polyglass/Ceromer therapy meets or exceeds our requirements for a conservative and aesthetic restoration.
It is the opinion of this author that over the course of time, Polyglass/Ceromer restorations will become an integral treatment option in all contemporary aesthetic dental practices, thus insuring a more conservative, predictable and aesthetic result for our patients.
Dr. Jack Ringer is Assistant Professor, Loma Linda Dental School, Loma Linda, CA, and Faculty, Esthetic Professionals Educational Center, Woodland Hills, CA.
Oral Health welcomes this original article.
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