CAD-CAM complete denture resins: Effect of relining on the shear bond strength

Objectives: The aim of this study was to compare the shear bond strength of relined CAD-CAM complete removable dental prosthesis (CRDP) resins with conventional heat-polymerized polymethylmethacrylate (PMMA) resin. Methods: A total of 96 resin specimens in identical dimensions of 10 mm x 10 mm x 11 mm were fabricated for four study groups [#1-Conventional heat-polymerized group: n=24 (ProBase); #2-Milled#1: n=24 (Ivobase); #3-Milled#2: n=24 (Ivotion); #4-3D-printed: n=24, (NextDent Denture 3D+)]. Twelve specimens in each group were sectioned in the middle to produce a 3 mm defect and then were relined using a conventional denture relining material. All specimens underwent thermocycling (5-55 degrees C) for 10,000 cycles. The shear bond tests were carried out in a universal testing machine. One-way ANOVA and Tukey's test were used for statistical analysis (p<0.05). The two-parameter Weibull distribution values were calculated. Results: Relined 3D-printed specimens had a significantly lower shear bond strength when compared with con-ventional (p=0.0003) and milled groups (Milled#1: p=0.0004; Milled#2: p<0.0001). There were no differences in the shear bond strengths between the milled and conventional groups. Weibull distribution presented the highest shape value for the non-relined Milled#1 (22.83) group and the lowest values for the 3D-printed relined group (4.001). Conclusion: The findings of this study conclude that the shear bond strength of the conventionally-relined 3D -printed resins used for fabricating CRDPs was inferior to the shear bond strength of conventionally-relined resins employed for manufacturing CRDPs using CAD-CAM milling and conventional heat-polymerization techniques. Clinical significance: When considering 3D-printing for the fabrication of CRDPs, it is recommended to employ it in clinical situations where a frequent need for denture relining is not expected.