Glass-fiber frameworks for fixed partial dentures: Laser-interferometrical in vitro analysis

Objectives: Laboratory tests confirmed superior physical properties of fiber-reinforced resin composites; however, clinical failures continue to be observed. This in vitro study introduces a new method to measure strain and fracture resistance in glass fiber-reinforced pontics. Method and materials: Thirty standardized pontics in five groups were fabricated. Pontics were reinforced with: glass fiber (group 1); glass-fiber bundle surrounded by glass-fiber mesh (group 2); glass fiber with glass-fiber mesh parallel to the pontic's occlusal surface (group 3); or glass-fiber mesh parallel to glass-fiber bundle (group 4). Unreinforced resin composite pontics served as controls (group 5). A laser interferometer measured inner strains (µm/mm) in sectioned pontics, occlusally loaded with 250 N and 450 N, with a universal testing machine. Inner strains were measured on three levels (1, 2, and 3). Specimens were then loaded to crack onset, and loads were recorded. Comparisons were made using analysis of variance. Kruskal-Wallis and Fisher's exact tests were used, respectively, for nonparametric and categorical data. Results: Group 3 showed significantly lower mean strain values than controls. No significant differences in maximal inner strain values or crack onset loads were recorded. The framework of Group 3 inhibited crack propagation significantly better than that in groups 2 and 5. Conclusion: Within the limitations of this study, speckle interferometry proved to be a promising method for analyzing strains of pontics under load. The tested framework designs in this study had only limited influence on load-to-crack onset. When strategically placed, a glass-fiber mesh prevented crack propagation.