Quality of Gypsum Casts Comparing One-Stage and Two-Stage Pour Methods

Objectives: Clinical techniques described in dental textbooks often are derived empirically or are a result of a clinician’s experiences. Since the methodology is not based on rigorous scientific method, the techniques lack adequate scientific evidence. The goal of this study is to compare the one-stage pour method to the two-stage/instant inversion method of gypsum cast fabrication to determine if differences are produced in three key physical properties: detail reproduction, surface roughness, and surface porosity.
Methods: Custom trays were fabricated using Triad to take 20 Cavex alginate impressions of ANSI/ADA spec. 18 die, ten for each experimental group. Silky Rock was vacumixed and vibrated into impression, with only the one-stage pour being instantly inverted. Casts set for 30 minutes, removed, set overnight, and randomized. Detail Reproduction measurements were scored as rank 1-4 based on reproduction of 75µm & 50µm lines as seen under a stereographic microscope (5x & 10x). Entire die surface examined and porosities counted. Continued with surface roughness measurements via Mitutoyo profilomiter, 3 runs per sample yielding Ra values (µm).
Results: See Tables 1-3
Conclusions: One-stage pour method shows significantly better detail reproduction of the 50µm line of the ANSI/ADA spec. 18 die (p=.0272) as well as a less rough surface than the instant inversion casts (p=.0061). No significant difference with regards to 75µm line or porosity.