Fracture Strength of Composite Fiber-Reinforced Fixed Long-term Provisional Restorations

Objectives: To investigate the fracture strength of four-unit fixed long-term provisional restorations (FPR) in the posterior region made from different materials with and without composite fibre-reinforcement measures.
Methods: Sixteen dental models simulating the oral situation of two missing posterior teeth were fabricated. With a CAD/CAM workflow, an FPR was fabricated (BreCAM.HIPC (BRE)), which served as a master copy for a vacuum-formed template to manually produce the FPRs of all other subgroups. These were either FPRs made from a Methyl-methacrylate material (Top.lign professional) with (TOP_CF) and without (TOP) embedded Composite Polyethylene fibers (CF) for reinforcement. Further two composite materials were tested, both reinforced with CF (Protemp 4 (PRO_CF), Luxatemp Star (LUX_CF)). After temporary cementation (Temp Bond NE), all samples were either subjected to artificial aging (test groups: 1,600 thermo-cycles, 5-55°C, 240,000 chewing cycles, 50N) or were stored in a water bath (control groups: 55 days, 37°C). Then, all specimens were tested until fracture in a universal testing machine. Altogether, ten subgroups with eight specimens each were tested. For statistical analysis, the Mann-Whitney-Test and Kruskal-Wallis-Test were used.

Results: After artificial aging, mean fracture loads (N) were: LUX_CF: 182.9 ± 146.9, PRO_CF: 212.7 ± 148.3, TOP_CF: 273.1 ± 161.8, TOP: 275.8 ± 158.8 and BRE: 786.5 ± 293.6. For control groups, mean fracture loads were LUX_CF: 468.69 ± 204.7, TOP: 494.8 ± 183.5, PRO_CF: 529.0 ± 218.3, TOP_CF: 688.1 ± 305.8 and BRE: 1001.8 ± 327.9. BRE revealed the highest fracture strengths. Within the aged FPRs, a significant difference between BRE and all other groups (p<0.05) could be shown. Except for BRE (p>0.05), aging significantly reduced fracture strength in all other groups (p<0.05).
Conclusions: CAD/CAM FPRs showed higher resistance to fracture in comparison to conventional FPRs. No enhancement of fracture strength was observed with composite fibre-reinforcement.