Article and Clinical Photos by Robert A. Lowe, DDS, FAGD,
FICD, FADI, FACD, FIADFE
In the first part of this series on repairing an existing bridge ("Repair, Don't
Replace – Part 1"), a case was presented where a patient fractured the
facial ceramic of a maxillary central incisor on a six-unit porcelain-fused-to-metal
bridge. The facial fracture was stress related and did not involve the exposure of
the underlying metal substructure. A successful repair was made by creating a
veneer preparation into the ceramic and placing a new porcelain veneer on top
of the affected surface.
Now, what happens if the ceramic fracture is substantially larger and involves
the exposure of the underlying metal framework? The following case will demonstrate
how, in some circumstances, the remaining porcelain can be removed
from the metal and a "saddle crown" can be fabricated and cemented over the
existing bridge.
A patient presented with a porcelain fracture on an anterior
multiple-unit fixed bridge (Fig. 1). The fracture involved
the entire facial surface of tooth #7 and exposed the metal
framework at the disto-incisal angle. When viewed from
the lingual aspect (Fig. 2), the fracture extends down to
the porcelain-metal junction of the mostly metallic lingual
surface. Because of the occlusal forces placed on this tooth
in both protrusive and lateral excursions, it was decided to
prepare the remaining porcelain down to the metal understructure
and create a "saddle crown" to repair the defect.
The saddle crown consists of a facial and lingual surface
only. These surfaces are only joined proximally incisal to
the solder joint of the existing bridge. The preparation
is designed to create negative space for this "telescopic"
structure without compromising the structural integrity of
the bridgework below.
A round-ended, tapered, coarse diamond is used to prepare
the remaining porcelain and metal. Care must be
taken not to score the adjacent proximal ceramic surfaces
during the preparation phase (Figs. 3, 4). Also, be careful
not to create undercuts when preparing the cervical areas
of the preparation. In this case, it was a challenge to create
sufficient space on the lingual surface without prepping
away some of the existing metal framework. This should
be kept to an absolute minimum to avoid compromising
the strength of the existing bridge.
Figure 5 shows the incisal clearance created for the saddle
crown as the patient closes into centric occlusion. This clearance is checked in protrusive and lateral excursions
as well, to make sure adequate space has been provided.
The preparation is polished with a round-ended 30 micron
finishing diamond, followed by rubber polishing abrasives
to smooth the cut metal substructure and porcelain.
Next, a retraction cord (UltraPak® [Ultradent; South Jordan,
Utah]) is placed on the facial and lingual marginal
areas of the preparation (Figs. 6, 7). A two-cord technique
is used, first placing a #00 cord, then a #1 on top of it.
After a few minutes, the top cord is removed leaving
the #00 in the sulcus (Fig. 8). The master impression is
then made using a syringeable light-bodied and heavybodied
vinyl polysiloxane impression material (Honigum
[DMG America; Englewood, N.J.]) (Fig. 9).
A provisional restoration is then fabricated using a bisacrylic
provisional material (Luxatemp® [DMG America])
and is cemented with polycarboxylate cement (Fig. 10).
Digital photographs are provided to the ceramist to aid
in characterization.
Figure 11 is a facial view of the saddle crown on the laboratory
cast model. An incisal view of the master cast shows
the preparation design that basically strips the porcelain
down to the metal substructure on the facial and lingual,
and is "tied in" with a continuous mesial and distal proximal
finish line on the metal connectors of the preexisting
bridge (Fig. 12). A proximal view of the completed restoration
highlights the "saddle" design (Fig. 13). Interproximal
margins are in metal and are located incisal to the metal
connectors of the understructure. The lingual surface of
the restoration is made in metal to match the preexisting
bridge and limit the amount of lingual reduction (Fig. 14).
The completed saddle crown is tried in after removal of
the provisional restoration (Fig. 15). After verification of fit
and checking occlusion with articulating paper, the restoration
is ready for cementation. In this case, resin-modified
glass ionomer cement was used (Fig. 16). A 4-META-type
cement is also good to cement metal to metal if retention
is less than ideal. The cement is mixed according to the
manufacturer's instructions (Fig. 17) and pushed into place
on the preparation (Fig. 18). It is recommended to hold the restoration in place until the cement is completely set, as
hydraulic pressure can in some cases push the restoration
incisally as the cement sets.
Figure 19 is a lingual view of the cemented restoration.
The metal lingual surface of the saddle crown fits the adjacent
metal margin of the bridge like an inlay. Figure 20 is
a facial view of the completed saddle crown. Compare this
to Figure 21, which is a facial view of the previous bridge
prior to the fracture.
The esthetics of a repair made using a saddle crown makes
it an excellent alternative to replacing the entire multiunit
restoration. This solution works well in anterior and
posterior regions for pontics as well as abutments.
