Effect of Different Finish Line Designs on the Marginal and Internal Fit of Metal Copings Made by Selective Laser Melting Technology
Date of Award
Master of Science (MS)
Introduction: Marginal fit has been defined as the gap between the prepared tooth and the intaglio surface of the restoration. Internal gap is the perpendicular measurement from the internal surface of the casting to the axial wall of the preparation. Selective laser melting has been used for fabrication of metal copings such as Co-Cr base alloys and Au-Pt noble alloys. The purpose of this study was to determine the effect of different finish line designs on the marginal and internal fit of metal copings made from high noble, 25% noble and base alloys manufactured by SLM technology. Material and Methods: An ivorine right maxillary central incisor was prepared with three different finish line designs. Three preparations were scanned using a Trios scanner and a total of 90 dies were printed using DPR 10 Resin. Ninety metal copings were fabricated using 3 different types of alloys. Copings were cemented to the dies using resin cement. All specimens were sectioned buccolingually using a low speed diamond saw. Marginal and internal gaps were measured at 5 locations. Marginal and internal gap images were determined using an inverted bright field metallurgical microscope at x 100 magnification. A two-way multivariate analysis of variance (MANOVA) was conducted to determine overall significance followed by analysis of variance (ANOVA) for each dependent variable (α=0.05). Results: Overall, 2700 measurements were obtained for the study. The result of statistical analyses indicated that both alloy type and finish line had a significance influence on overall fit of the copings. For the internal fit, the alloy type had a significant effect (p<0.001), but the finish line had no statistically significant influence(p=0.337). For the marginal fit, both the alloy type and the finish line had a statistically significant effect, (p<0.001). There was no statistically significant interaction between variables. Conclusions: Finish line types did not significantly influence the internal fit between the copings and the dies, whereas alloy type did influence the fit between copings and dies. SLM-fabricated copings made with the Base Alloy (Co-Cr) on teeth prepared with deep chamfer finish lines demonstrated the best marginal fits when compared to the other groups.