PREPARATION GUIDE
 
One of esthetic dentistry’s toughest challenges is to match the shade of different types of restorations’ to the adjacent teeth. Matching the colors and shades can be very difficult for the technician. Using pressed cores allows for even translucency of both restorations. In addition, older teeth often have greater translucency that the restoration must imitate.

According to Chiche,2 the ideal all-ceramic preparation should have:

A length of 2 mm to one third of the anatomic crown, no sharp incisal edges, and a flattened or rounded preparation tip.
The shoulder should be a rounded 90° angle with a flattened lingual wall to help with resistance form, and narrow interproximals compared to labial and lingual.
An ideal facial thickness is 1.3 mm to 1.5 mm (1 mm is the minimum), and an ideal lingual thickness is 1.5 mm with a definite concavity.
The taper should be 5° to 10° to achieve maximum surface area and for preparation support.
 

   
The Goldstein Crown Design Kit (Brasseler USA?) includes the tools necessary to meet the described specifications (Figure 2). In this case, preparation began with a measured amount of reduction through the use of a round 1.5 mm diameter diamond (no. 5801-016) (Figure 3). The cervical was reduced first (Figure 4) before the same diamond reduced the facial (Figure 5), the incisal edge, and finally around cervical of the lingual. A bulk reduction diamond (No. 5856-016 for smaller teeth or No. 5856-021 for larger teeth) (Figures 5 and 6) removed the remaining incisal, facial, and lingual enamel down to the 1.5 mm thickness. A football shaped diamond (No. 5379-023) provided lingual reduction (Figure 7).
   
   
High lip lines usually indicate the need for subgingival margins. A double cord retraction technique provided a safe subgingival result. After the initial supragingival preparation was complete, a purple zero Ultrapak? cord (Ultradent Products, Inc.) was gently inserted into the healthy sulcus. When inserting the cord, begin and end at the mid-facial with the two ends of the cord abutting each other. Allow the tissue to recede for 3 to 5 minutes before using a buld reduction diamond to lower the margins to the new tissue height. If further subgingival placement is needed, either:

Use an instrument to pull the tissue down; gently lower only the facial margins and do not infringe upon the biologic width, or
Use a Gingigel? #1 (Van R?) white cord (alumimpregnated) on the facial surface only. Place it from the mesiofacial to distofacial. Leave it for 3 to 5 minutes, wet it, remove it, and gently lower the margin with bulk reduction diamond.
A fine grit diamond was used to smooth and round all line angles and margins (No. 8856-016 or No. 8856-021). For the final finishing or the preparation, a tissue protective end cutting diamond (No. 10839-016) was used to remove any enamel prisms left on the margin because these may create stress and the porcelain will fracture when the margin is seated. A white stone (No. 649-420, Brasseler USA?) was used to give an extra smooth finish to the margins.
   

 
   
When the preparation was complete, a Gingigel? No. 1 white cord was placed circumferentially around the preparation to provide adequate retraction for the impression (Figure 8). Next, the Porcelain Veneer Kit (Brasseler USA?) was used for the veneer preparation; the kit included a depth cutter to provide the proper laminate thickness. Dentists disagree whether veneer preparation is necessary; the rule we use is based on whether a particular situation needs reduction.

Lingually inclined teeth and patients with spaced teeth may not require preparation, so “the most practical approach is to evaluate each patient, and indeed each tooth to be veneered.”5