In vitro comparison of marginal gap values of single and four unit metal-ceramic restorations manufactured by laser sintering procedure, before and after porcelain super-structure application

With advancing technology and increasing esthetic expectation, the use of porcelains with full ceramic and zirconia substructures increased. However, metal-ceramic restorationsare still the most frequently used restorations due to their high mechanical strength and lower costs. Although the traditional casting method was used in the production of metal-ceramic restorations, with the advancing technology, restorations manufactured with CAD/CAM methods and direct metal laser melting method are increasing. The aim of this study was to evaluate the marginal fit of the restoration before and after porcelain superstructure application of metal-ceramic crown produced with direct metal laser sintering method, with two kinds of Co-Cr metal powder, at two different thicknesses, at the single and four-unit restorations. Four-unit models (D) were produced with upper first premolar and upper second molar as abutment teeth; single-unit models (T) were produced as upper first molar. Two different metal powders; METO (M), BEGO (B) were used in this study Metal substructures were produced with 0,4 (4) and 0,5 (5) mm thicknesses by laser sinter method. 8 groups were obtained in total with these parameters (n=10). After the metal substructures were obtained, marginal discrepancy values were measured by using the silicone replica method and saved at the computer. Then porcelain was applied on metal substructures. Silicone replicas were obtanied from the samples that completed the porcelain process and marginal discrepancy values were measured. Kruskal Wallis test was used for comparison among groups. Bonferroni-corrected Dunn test was used to determine the group or groups that created intergroup differences. In the same group, Wilcoxon test was applied to determine the changes occurred after the infrastructure and superstructure. p<0.05 was considered statistically significant. According to the results, significant decrease was observed in BT5 and MT4 groups in mesial region between infrastructure and superstructure. There was significant decrease in BT5 and MT4 groups on distal surfaces. There was a statistically significant increase marginal discrepancy in the BT4, MT4 and MT5 groups on the occlusal surfaces. At molar teeth; there was a statistically significant increase in BD5 and MD4 groups on the mesial surfaces.. There was a statistically significant decrease in distal surfaces in BD4 group. A numerical decrease was found in the BD5 and MD4 groups. At premolar teeth; there was a statistically significant decrease was found in all groups between the substructure and porcelain at the mesial region. There was a statistically significant increase in the MD4 and MD5 groups between the substructure and porcelain in the distal regions. In BD4 and BD5 groups, numerical increase was found. A statistically significant increase was found in the BD4, BD5, MD4 groups on the occlusal surfaces of premolar teeth. MD5 group found a statistically significant decrease.