Fracture Strength of Interim CAD/CAM and Conventional Partial Fixed Dental Prostheses

To compare the fracture strength of three-unit provisional partial fixed dental prostheses (FDPs) fabricated by an indirect-direct technique from poly(methylmethacrylate) (PMMA) through digital and conventional workflows, and FDPs fabricated by a direct technique using Bisacryl (BisA) and externally reinforced BisA.

Forty partially edentulous typodonts with a missing mandibular left first molar and standard preparations on mandibular left second premolar and molar were used to fabricate three-unit provisional FDPs. Two materials and two techniques were used to fabricate a total of forty provisional FDPs: (1) BisA; (2) BisA reinforced with glass fiber strips [BisA-GFR]; (3) conventionally fabricated PMMA shell relined with PMMA [C-PMMA]; (4) CAD/CAM fabricated PMMA shell relined with PMMA [CAD/CAM-PMMA]. Provisional FDPs were then luted onto the preparations using a temporary cement. Specimens were mounted onto a chewing simulator; 20,000 cycles of 70 N forces were applied under 25°C distilled water. Specimens were then loaded to fracture using a universal testing machine (The Dillion Quantrol TC2i; Mecmesin) with a crosshead speed of 2 mm/min. One-way ANOVA, followed by Tukey post hoc test, was used to assess the effect of production technique on the fracture strength of the provisional FPDs (α = 0.5).

Mean fracture strengths recorded for the CAD/CAM-PMMA, C-PMMA, BisA, and BisA-GFR groups were 520 N, 448 N, 245 N, and 169 N, respectively. PMMA groups had significantly (p < 0.0001; F = 24.40) higher fracture strength compared to Bisacryl groups.

When high occlusal forces are expected, provisional FDPs fabricated with PMMA using the indirect-direct technique are recommended, irrespective of CAD/CAM or conventional workflow.