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

Abstract

Introduction: Dental practitioners are faced with the growing demand to provide fixed prostheses that offer long-term service to patients; prostheses that do not de-cement, create stagnation sites or develop marginal failure. The investment materials used in the laboratory stages of production of cast-metal crowns and retainers for fixed partial dentures, influence the dimensional fit of the resultant fixed dental prostheses. Objective: The main objective of this study was to determine the effect of four different phosphate-bonded investment material brands with various modifications to their manipulation, on the marginal fit of cast-metal crown copings. The study was conducted in Nairobi, Kenya, in the year 2020, at the Kenyatta National Hospital Dental Prosthetics Laboratory and at Prime Dental Studios, a privately-owned Dental Prosthetics Laboratory. Materials & Methods: This was a descriptive cross-sectional study, designed as a laboratory-based experiment. There were three control groups, and four experimental groups. Each of the seven groups had ten cast-metal crown copings fabricated using cobalt-chromium ingots. The groups of ten castings in the three control groups were fabricated according to the manufacturers’ instructions for investing, using Bellavest T®, Castorit®-super C, and Rema® cc, for the BV-mr, C-mr, and R-mr groups, respectively. The experimental group W-ma had a modified application of Wirofine®, manipulated according to the manufacturer’s instructions, but applied to invest cast-metal crown copings, instead of removable partial denture frameworks. The cast-metal crown copings in the BV/W-mm, C-mm and R-mm were fabricated after investment with the various investment materials, manipulated whilst utilizing modifications to the manipulation modalities that are in use by a section of dental laboratory technologists in Nairobi, Kenya. Each of the seventy cast-metal crown copings were photographed at four sites using a digital single-lens reflex camera with a macrolens. The photographs were magnified (x150%) in order to facilitate measurement of the marginal gaps in micro-metres, using the ImageJ National Institutes of Health (NIH) software. A sample size of 280 measurements was obtained. The continuous data was analysed using STATA software, version 16 with Kruskal Wallis H statistical tests followed by post-hoc (Dunn’s) tests being done to show relationships...