Effect of layer thickness setting on the adaptation of stereolithography apparatus-fabricated metal frameworks for removable partial dentures: An in vitro study

Abstract

Statement of problem. A staircase effect is noted in the fabrication of metal frameworks for removable partial dentures (RPDs) when using stereolithography apparatus (SLA). It affects the adaptation of the definitive metal framework depending on the layer thickness setting. However, studies on the effect of the layer thickness setting on the adaptation of metal frameworks are lacking. Purpose. The purpose of this in vitro study was to determine the optimal layer thickness through comparative analysis of the adaptation of SLA-fabricated metal frameworks with different layer thickness settings. Material and methods. A total of 15 metal RPD frameworks were SLA-fabricated by using 3 different layer thickness settings (16 mu m, 50 mu m, and 100 mu m). The adaptation of the frameworks was measured by using the silicone replica technique, sectioned at the canine, first molar, and second molar regions by using a guide. The thickness of the light-body silicone was measured with a digital microscope at 3 points in each of the 3 areas. The measurements of the adaptation were statistically analyzed using the nonparametric Kruskal-Wallis test and post hoc Mann-Whitney U test with Bonferroni correction. Results.The gaps measured in each area showed statistically significant differences in all 3 groups (P<.05). In the anterior, middle, and posterior areas, the 16-mu m metal framework group showed the narrowest gaps (207 +/- 46 mu m, 195 +/- 49 mu m, and 188 +/- 40 mu m, respectively). The 3 groups showed statistically significant differences in total gaps in the RPD frameworks relative to the layer thickness settings (P<.05); the total gap was lowest (197 +/- 42 mu m) for the 16-mu m group. Conclusions.For SLA, 50 mu m is the recommended layer thickness considering the effect of layer thickness settings on the adaptation of the RPD framework and the fabrication time.