INTRODUCTION: THE PORCELAIN “REPAIR”
Repairing a broken porcelain (or porcelain-fused-to-metal) restoration is a clinical reality in every dentist’s practice. The traditional technique is to use composite resin to repair chipped porcelain. This is an attempt to use unlike materials to accomplish a long-term repair, but it rarely works.
Early “porcelain repair kits” used 37 percent phosphoric etch, silane primer, and adhesive and composite resin to repair chipped porcelain. This system did not work because 37 percent phosphoric acid cannot appreciably etch a porcelain surface. Without adequate micromechanical retention to affix the composite resin to the porcelain surface, any repair will likely not withstand the forces of mastication.
The use of hydrofluoric acid provides an adequate etched surface to create an improved micromechanical bond of composite to porcelain. However, the bond of composite to porcelain is not the only clinical problem. Another is the finishing and polishing of the porcelain-composite interface. Regardless of the finishing and polishing technique and materials used, the fine line of demarcation between the composite and porcelain is hard to eradicate.
If the broken restoration is a single unit, a complete remake may be the most predicable solution. But what about multiple-unit fixed bridgework? It may not be feasible economically or clinically to sacrifice a long-span restoration for one unit with a porcelain fracture. In esthetic cases, a clinically acceptable posterior bridge may not be the same shade as the one chosen for the anterior reconstruction. So, for these clinical problems, is there a long-term solution short of replacing the entire restoration?
REVENEERING EXISTING PORCELAIN RESTORATIONS
The patient in Figure 1 presented with the desire to remake his porcelain reconstruction. Some of the anterior units were fractured due to occlusal issues. The patient’s desire was to remake the restorations in the esthetic zone with a high value shade. The posterior bridgework was clinically acceptable, but the shade was much lower in value and hue than the desired anterior shade. Figure 2 shows a segment of this reconstruction, where an old single-unit crown was replaced and a veneer preparation was made into the existing anterior abutment of the posterior bridge immediately distal to it. The key to success with this procedure is the original thickness of porcelain on the existing bridge. The goal is to have little or no metal exposed. Tooth #27 and #28 are prepared for stacked porcelain veneer restorations (Fig. 3). The total thickness of the labial reduction of the natural tooth surface and porcelain surface is 0.5 mm facially and 1 mm incisally.
Figure 1: A smile in need of a remake. The patient requested a porcelain makeover of the esthetic zone with occlusal corrections to prevent future porcelain fracture. The posterior bridgework is clinically acceptable; however, the anterior abutments in the esthetic zone will require resurfacing to match the anterior units.
Figure 2: Preparations for porcelain veneers on tooth #27 and #28. The small metal exposures will not appreciably affect the bond of the veneers to the porcelain surface.
Figure 3: A 2x magnified facial view of the veneer preparations
Figure 4: A dentin desensitizer with antibacterial agent (AcquaSeal B, AcquaMed Technologies) is applied to cleanse the prepared tooth surface prior to the etching procedure.
Once preparations are complete, the natural tooth surface is treated with a dentin desensitizer that has an antibacterial component (AcquaSeal™ B [AcquaMed™ Technologies; West Chicago, Ill.]) (Fig. 4). The porcelain preparation is treated with hydrofluoric acid for 60 seconds (Fig. 5). This material can be caustic to the gingival tissues, so if tissue contact is anticipated, a light-cured “liquid dam” is applied for patient protection. Thirty-seven percent phosphoric acid is applied for a 15-second total etch to the prepared tooth surface (tooth #27) (Fig. 6). Thoroughly rinse both the tooth and porcelain surface with water for 60 seconds (Fig. 7). Figure 8 shows the natural tooth surface and porcelain surface after rinsing and air-drying. AcquaSeal B is reapplied to tooth #27 and the excess is removed using a high-volume suction. A moist, wet surface is left for the application of a hydrophilic bonding resin, and adhesive resin is applied in multiple applications to create a quality hybrid zone for bonding (Fig. 9).
Figure 5: Hydrofluoric acid is used to etch the porcelain preparation.
Figure 6: Phosphoric acid is used to etch the prepared tooth surface.
Figure 7: Both solutions are rinsed off with copious amounts of water.
Figure 8: Preparations prior to placement of adhesive resin
Without adequate micromechanical retention to affix the composite resin to the porcelain surface, any repair will likely not withstand the forces of mastication.
Following air thinning, the adhesive resin is light-cured (Fig. 10). Figure 11 shows the prepared surfaces after the adhesive resin has been placed and cured. The porcelain veneers are now ready for placement. A dual-cured resin cement is placed on the inside surface of the veneer restoration and the veneer is placed on the porcelain prepared surface (Fig. 12). A number 2 Keystone brush (Patterson Dental; El Segundo, Calif.) is used to remove excess resin cement prior to reaching a gel set (Fig. 13). The porcelain veneer restoration is then placed on tooth #27 (Fig. 14). The porcelain veneer on tooth #27 is stabilized using veneer stabilizers (Nash/Taylor Esthetic Instrument Kit [Hu-Friedy; Chicago, Ill.]) while the gel set is completed (Fig. 15). After using a scaler to remove marginal cement excess post gel set (Fig. 16), a cotton pledget is used to complete resin cleanup prior to light curing (Fig. 17).
Figure 9: Bonding resin is applied to both prepared surfaces.
Figure 10: Bonding resin is light-cured for 30 seconds.
Figure 11: Facial view of the prepared surfaces after curing of the adhesive resin. Note the shiny appearance of both the dentin and porcelain surfaces. This clinically shows the presence of the hybrid zone for bonding.
Figure 12: The porcelain veneer for tooth #28 is filled with resin cement and placed on the preparation.
Figure 13: The excess resin cement can be removed with a Keystone brush.
Figure 14: The restoration is placed on tooth #27.
Figure 15: The veneer is stabilized while the gel set is completed.
Figure 16: The excess can then be removed easily with a sharp scaler or explorer.
Figure 17: Before the final cure, any excess resin can be removed from the surface of the restoration with a cotton pledget.
It may not be feasible economically or clinically to sacrifice a long-span restoration for one unit with a porcelain fracture.
Figure 18 shows a cross section through a porcelain-fused-to-metal crown that was reveneered with porcelain to change the facial color to a brighter value, in order to match the adjacent restorations. Note the uniform thickness of resin cement and veneered porcelain. The bond of the porcelain veneer to the prepared porcelain surface is as strong as that bonded to dentin. Figure 19 shows the affected area in a full-arch, retracted view after placement of the esthetic anterior restorations. The previous bridge was retained, however the facial surface that was visible in the patient’s smile (tooth #28) was altered with a porcelain veneer to match the anterior restorations.
Figure 18: Cross section through a crown that had been veneered with porcelain. The distal abutment of this bridge had failed, necessitating removal. Note the uniform thickness of the remaining porcelain and the veneer restoration. The film thickness of the resin cement is also very uniform and micromechanically lutes the surfaces together.
Figure 19: A full-smile, retracted view after delivery of restorations on tooth #4–12 and #21–28. The veneers on tooth #4 and #5 are veneered to a long-span PFM bridge as well. Note how well these restorations blend in with the new anterior restorations.
This technique demonstrates how to repair existing porcelain restorations by bonding a porcelain veneer to the affected porcelain surface. By taking advantage of the strength of a porcelain-to-porcelain bond using resin cement technology, we can now make predictable porcelain repairs and resurface existing porcelain (and porcelain-fused-to-metal) crown & bridge restorations in a very predictable manner.