Comparative study of interim materials for direct fixed dental prostheses and their fabrication with CAD/CAM technique

Statement of problem. Prosthodontic treatment sometimes requires a long-term interim fixed dental prosthesis (FDP) until the definitive restoration can be cemented. However, some interim materials are weak and do not have an adequate marginal seal. Purpose. The purpose of this study was to compare the marginal fit and fracture strengths of interim FDPs fabricated by using a direct technique with different materials (Structur 3, Trim, and DuraLay) with interim prostheses (Telio CAD) made with a computer-aided design and computer-aided manufacturing (CAD/CAM) system. Material and methods. Seventy interim FDPs were fabricated by using different materials (Structur 3, Trim, DuraLay, and Telio CAD) on a metal master model. Resin-impregnated, light-polymerizing glass fiber (GrandTEC) was used to reinforce 10 interim FDPs per material fabricated with the direct technique. Interim FDPs were stored at 37 degrees C for 24 hours before thermocycling. Marginal fit was analyzed at 6 points in each interim FDP before and after thermocycling with either 2500 or 5000 cycles. After fracturing the interim FDPs with a universal testing machine, fracture strength, fragments separation, and fracture point were recorded. Marginal fit data were analyzed with 2-way repeated measure analysis of variance (ANOVA), fracture strength with 1-way ANOVA, and fragments separation and fracture point with the chi-square test at a 99% confidence interval. Results. All interim materials showed marginal discrepancies over time, but no significant differences were found among groups (P>.001), except in the marginal fit of interim FDPs reinforced with glass fiber (S3F), which showed the smallest marginal gap after 5000 cycles (P<.001). Reinforced interim FDPs (S3F, TMF, and DLF) and CAD/CAM FDPs (TCC) presented a fracture strength ranging between 471.3 +/- 62.4 N and 531.1 +/- 150.1 N (P>.001). Finally, significant differences were observed in the fracture point and frequency of separation (P<.001). Conclusions. Bis-acryl reinforced with glass fiber showed the least marginal discrepancy. No differences were found between the fracture strengths of interim FDPs fabricated with CAD/CAM system and interim FDPs reinforced with glass fiber. No significant difference in fracture strength was observed between interim FDPs reinforced with glass fiber and prostheses fabricated with CAD/CAM system. However, unreinforced interim FDPs showed the lowest fracture strength.