Selective Laser Sintering versus Selective Laser Melting and Computer Aided Design - Computer Aided Manufacturing in Double Crowns Retention.

Purpose This in vitro study aimed at ascertaining the retention forces for telescopic crowns fabricated with Selective Laser Manufacturing (SLM) and Selective Laser Sintering (SLS) additive technologies, and Computer Aided Design - Computer Aided Manufacturing (CAD-CAM) subtractive technology, by using suitable materials for each.Materials and Methods Full-factorial design was employed for experimental testing, considering the following three factors: (a) inner crown material ‒ technology (zirconia ‒ CAD-CAM; metal-alloy ‒ SLS; metal-alloy ‒ SLM); (b) tooth type (canine or molar); (c) wet vs. dry conditions (i.e. either with or without artificial saliva). The roughness of the inner crowns was analyzed through atomic force microscopy. Three-way analysis of variance (ANOVA) was applied for statistical analysis, followed by Tukey's post-hoc comparisons between the crown types.Results The retention force mean values were between 3.8 N (dry, SLM) and 14.8 N (artificial saliva, SLS), with statistically significant (p<0.001) differences between the three types of inner crowns and interaction with the tooth type. No significant interaction was found between crown or tooth types and the wet vs. dry testing conditions. The zirconia crowns' retention force was significantly (p<0.001) higher compared to similar SLM crowns, with 95% CI (3.62; 5.55) N for the differences. Zirconia was significantly (p<0.001) less retentive compared to similar SLS crowns, with 95% CI (-5.99; -4.06) N for the differences. The roughness decrease and subsequent loss of retention force was the largest in zirconia.Conclusions The SLS inner crowns showed the best retention, followed by zirconia and SLM inner crows.