In making cores, I like to use material that has a sharp visual contrast with the remaining tooth structure, because I want to be certain that the margins of the preparation will allow the definitive restoration to be seated entirely on sound tooth structure and not on core material. The visual contrast allows for easy differentiation between tooth structure and core material. I often see new patients who have attractive posterior crowns and onlays with margins that cross the core material subgingivally (this often is apparent on radiographs). I believe that the practitioners who provided these restorations probably first placed tooth-colored cores and then could not distinguish the tooth/core material interface during preparation. This is easily understandable; modern esthetic materials allow dentists to place restorations that match so well as to make it difficult to differentiate occlusal, let alone subgingival interproximal, margins.

To avoid this, I purposely use a core material in a shade that is markedly different from that of the remaining tooth structure and offers a clear visual contrast. Many patients reveal the buccal surfaces of the posterior teeth (especially premolars) while smiling and prefer to have a more esthetic core during the interim period until the tooth can be prepared for a crown and esthetically temporized. In these situations, I place visual "markers" in the core material interproximally. This allows for enhanced visualization of the interface between tooth structure and core material.

THE TECHNIQUE
Remove any existing restoration and further prepare the tooth as is indicated for a routine core.

Choose a shade of core material or posterior resin-based composite that will provide maximum esthetic appeal and another shade that will contrast clearly with the remaining tooth structure. Use different shades of the same material to ensure bonding compatibility. White is a good contrasting shade in most instances.

After routine preparation, create the markers by placing 1 to 2 millimeters of the contrasting core material in the interproximal areas of the preparation (Figure) and cure it. Do not allow this material to be bonded on the facial supragingival aspect, because a white line on the buccal surface of the esthetic core will result. However, this actually can be beneficial if the buccal margin is subgingival.

View larger version (36K): [in this window] [in a new window]   Figure. The tooth preparation with core material "markers."

The tooth is relatively stable after undergoing this procedure, and esthetics are not compromised significantly. I often lighten the occlusion on any remaining cusp(s) to reduce the chance of further fracture during the interim period.

The patient is given another appointment for crown preparation. In that appointment, prepare the tooth routinely with margins on sound tooth structure. It will be less difficult to visualize the interface between tooth structure and core material because the markers contrast sharply with the tooth structure.

Depending on the size of the proximal boxes in the core preparation and the thickness of the shoulder or chamfer margin, the markers occasionally will be ground off during preparation. This is acceptable, however, because they can be seen during preparation and the clinician will be assured that the margin is on sound tooth structure even if the markers are reduced or eliminated.

CONCLUSION
This technique allows the patient to maintain relatively uncompromised esthetics during the interim period and provides the dentist with a predictable method of obtaining enhanced visualization of the interface between tooth structure and core material.

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