Effect of Phosphate-bonded Investment Materials and their Manipulation on the Marginal Fit of Cast-metal Crown Copings

This study evaluated the marginal fit of cast-metal crown copings fabricated while adhering to the manufacturers’ manipulation instructions for three phosphate-bonded investment materials, (1) Bellavest T®, (2) Castorit®-super C, and (3) Rema® cc, and when utilizing three modifications to their manipulation, and one modified application for Wirofine®, as practiced by a section of dental laboratory technologists in Nairobi, Kenya. Seventy fabricated crowns were seated on a metal die and four standardized photographs of each crown were taken to display the facial, palatal, mesial and distal aspects. The marginal fit was measured on each image using the ImageJ National Institutes of Health software. The results showed no significant differences in the marginal gap measurements of crowns fabricated according to the manufacturers’ instructions for Bellavest T®, Castorit®-super C, and Rema® cc, as well as the crowns fabricated from the modified manipulation of Bellavest T® and Rema® cc. The modified application and manipulation of Wirofine® and Castorit®-super C, respectively, yielded crowns with marginal gap measurements beyond the clinically acceptable range (<150 μm). Keywords: phosphate-bonded investment materials, marginal fit, cast-metal crown copings.