Chairside - Glidewell Dental Labs

Figure 1: A preoperative view of tooth #7, part of a multiple-unit fixed
bridge that has sustained a porcelain fracture on the facial surface
Figure 2: An incisal view of the fractured abutment showing a porcelain
fracture down to metal on the disto-incisal angle
Figure 3: The fractured unit has been prepared using rotary diamond
instrumentation down to the metal understructure, then polished with a
fine diamond and rubber polishing abrasives. Care was taken not to disturb
the porcelain on the adjacent teeth and the metal covering the damaged
unit, especially the interproximal metal bridge connectors.
Figure 4: Lingual view showing the surface after preparation. The original
bridge had metal lingual surfaces, so preparation was made into the metal
to create space for the “saddle crown” on the functional surface. Some
of the metal was removed to tooth structure, but care was taken not to
remove so much as to compromise the integrity of the original 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
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