Marginal gap of crowns made with a phosphate-bonded investment and accelerated casting method

Numerous materials and methods have been used for complete crown fabrication. Conventional investing and casting procedures for phosphate-bonded investments require a 2- to 4-hour process before completion. Accelerated laboratory techniques have been used, but may not result in castings with equal marginal accuracy.

This study measured the marginal gap and determined the clinical acceptability of single castings invested in a phosphate-bonded investment with the use of conventional and accelerated methods.

Forty-four individual stone casts were poured from impressions made from a master die. Conventional and accelerated methods of investing and casting were followed in the fabrication of 44 single-unit castings. Twenty-two casts were used in each of the 2 groups. Each casting and its respective stone die were examined with a microscope at 4 predetermined sites. Perpendicular and 25-degree tilted measurements of marginal gap were documented for each. Evidence of marginal gap was then evaluated by t test.

Measurements recorded on the perpendicular and on a 25-degree tilt showed no statistically significant difference between conventional and accelerated groups. All gap measurements except one were within the range of clinical acceptability. The measurements revealed that conventional and accelerated perpendicular gap means were 13.2 and 13.6 microm, respectively, and the average tilted gap means were 31.6 and 32.2 microm, respectively.

A phosphate-bonded investment (Ceramigold) selected for an accelerated casting technique produced single castings within 30 minutes with marginal gaps comparable to those found that used conventional methods.