Article and Clinical Photos by Robert A. Lowe, DDS, FAGD,
FICD, FADI, FACD, FIADFE
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.
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).
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 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.
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.