It is essential to maintain the proper angulation when reducing the proximal walls of a tooth for a full crown.1 Overtapered or undercut proximal wall preparation may lead to loss of retention or resistance, thus compromising the quality of the crown. I describe a simple technique to help guide the angulation of proximal wall reduction for full-crown preparations.
First, cut a strip of baseplate wax about 15 millimeters long and 8 mm wide. Lay the wax strip on the buccal aspect of the diagnostic cast just apical to the free marginal gingiva. Determine the ideal angulation for reducing the proximal walls. Using a felt-tip marking pen with dark ink, draw one line on the wax strip that corresponds to the ideally angled mesial wall and one line that corresponds to the ideally angled distal wall in the final tooth preparation. This will make the lines easy to see when the wax strip is in the mouth. The lines should be at the approximate place at which the mesial and distal walls will be reduced on the tooth to be prepared.
Next, break proximal contact with the adjacent teeth with the use of a 169L high-speed friction-grip carbide bur. Place the wax strip on the lingual aspect of the tooth being prepared. Examine the lines on the wax strip through the interproximal space where contact has been broken (Figure
). Use the angulations of these lines to guide the reduction of the mesial and distal walls of the crown preparation.
