Introduction
A partial veneer crown is an extracoronal metal restoration that covers only part of the clinical crown, usually every surface except the buccal or labial wall. It keeps as much sound tooth as possible while still restoring the occlusal surface or holding a bridge.
Types
Related intracoronal castings: an inlay sits inside the crown without covering a cusp; an onlay covers one or more cusps.
Indications
- Back teeth that have lost a moderate amount of tissue, with an intact, well-supported buccal wall.
- Retainers for short-span bridges; restoring or changing the occlusal surface.
- Front teeth: rarely to restore damage, but as bridge retainers, to restore anterior guidance or to splint teeth.
Contraindications
- Short clinical crowns: too little retention.
- Long-span bridges.
- Endodontically treated teeth, especially front teeth: too little sound tooth.
- Active caries or periodontal disease; badly aligned abutments.
Preparing a three-quarter crown on an upper premolar
- Occlusal reduction: depth grooves, then at least 1.5 mm clearance on the functional (lingual) cusp and 1.0 mm on the buccal cusp and central groove.
- Axial reduction: guide grooves parallel to the long axis on the lingual surface and line angles; remove the tooth between them with a chamfer at the cervix; reduce the proximal walls, stopping short of breaking the buccal contact.
- Proximal grooves: with a tapered carbide bur parallel to the path of insertion, no deeper than 1 mm at the cervical end; walls flared toward the buccal.
- Bucco-occlusal contrabevel: a narrow bevel along the buccal cusp ridges removes unsupported enamel and protects the cusp from chipping.
- Occlusal offset: a V-shaped groove joining the proximal grooves along the buccal cusp, for rigidity.
- Finishing: round internal angles; check that there are no undercuts.
Impressions are taken with A-silicone, preferably one-step, two-layer. The wax pattern must be invested at once, because wax distorts as it relaxes.