Evaluation of the flexural strength and microhardness of provisional crown and bridge materials fabricated by different methods.

PURPOSE: The purpose of this study was to evaluate and compare the flexural strength and microhardness of provisional restorative materials fabricated utilizing rapid prototyping (RP), Computer Assisted Designing and Computer Assisted Milling (CAD-CAM) and conventional method.

MATERIALS AND METHODS: Twenty specimens of dimensions 25 mm × 2 mm × 2 mm (ADA-ANSI specification #27) were fabricated each using: (1) Three dimensional (3D) printed light-cured micro-hybrid filled composite by RP resin group, (2) a milled polymethyl methacrylate (CH) using CAD-CAM (CC resin group), and (3) a conventionally fabricated heat activated polymerized CH resin group. Flexural strength and microhardness were measured and values obtained were evaluated.

RESULTS: The measured mean flexural strength values (MegaPascals) were 79.54 (RP resin group), 104.20 (CC resin group), and 95.58 (CH resin group). The measured mean microhardness values (Knoop hardness number) were 32.77 (RP resin group), 25.33 (CC resin group), and 27.36 (CH resin group). The analysis of variance (ANOVA) test shows that there is statistically significant difference in the flexural strength values of the three groups ( P < 0.05). According to the pairwise comparison of Tukey's honest significant difference (HSD) test, flexural strength values of CC resin group and CH resin group were higher and statistically significant than those of the RP resin group ( P < 0.05). However, there was no significant difference between flexural strength values of CC resin and CH resin group ( P = 0.64). The difference in microhardness values of the three groups was statistically significant according to ANOVA as well as the intergroup comparison done using the Tukey's HSD ( post hoc ) test ( P < 0.05).

CONCLUSIONS: CC-based CH had the highest flexural strength whereas RP-based 3D printed and light cured micro-hybrid filled composite had the highest microhardness.