The concept of a reduction coping is to create more space for the restoration after the laboratory receives the impression or cast of the prepared teeth. This additional space may be required to accomplish the goals of the case for esthetic or functional reasons.
The additional space allows for:
- Adequate space to make the tooth morphology changes requested.
- Increasing the thickness of the restorative material to improve its strength.
The coping can be fabricated out of:
- Cast metal
There can be a significant cost difference when a casting is made to due to the material and alloy expense, and the fabrication process. It may be worth considering the additional expense, as a cast metal coping will fit more precisely than one made from acrylic or resin.
Reduction copings are the most effective when the area of the tooth that needs to be reduced involves only the incisal edge, cusp tip, or one surface of the tooth. The modification of the preparation should never extend closer than 1mm to the finish line.
The coping is placed onto the tooth, and the amount of the tooth that extends through the opening is what will be reduced. A bur is used to reduce that portion of the tooth and slightly more, rounding all the edges and corners. This minimizes the chance that the restoration will not seat completely. Two examples where a reduction coping is most effective are:
- When there is an inadequate tooth reduction in incisal length to achieve the goals of the case.
- When the labial surface of one tooth protrudes further labial than the adjacent tooth or teeth, and the expectation is to have straight and aligned restorations. A reduction coping would be indicated for the protruded tooth in order to achieve the goal of the case, as the final outcome is significantly more predictable if all the restorations have a similar thickness.
The one surface on which it is difficult to use this process is the palatal aspect of the maxillary anterior teeth. It is difficult to replicate the palatal concavity that can be created in the laboratory using a reduction coping. If there is inadequate occlusal reduction, it may be necessary to re-prepare the teeth and take a new impression or modify the incisal edges of the mandibular anterior teeth to create more space.
Reduction copings can be used effectively in some cases to avoid rescheduling a patient to modify the preparations and re-impress. Consult your laboratory on a case-by-case basis to determine when it can be used to give the laboratory and clinician a more predictable outcome.