Objectives: The objective of the study was to evaluate the effect of positioning the reinforcing fibers in the cavity of abutment tooth and its influence on the mechanical properties of fiber-reinforced composite (FRC) fixed dental prostheses (FDP) of cantilever design.
Methods: Caries free extracted human molars of similar size were selected and divided into two groups (n=6/group). A standard shape approximal inlay-type cavity (width:3.0,length:4.4,height:3.8mm) was prepared in mesial side of each tooth. Direct cantilever fiber-reinforced FDPs were fabricated to the prepared cavities. EverStick C&B (StickTech, Finland) glass fibers were incorporated in the cavity using the Filtek Supreme XT flow (3M ESPE, USA) to form framework for the FDP. Fibers were bonded with the Adpter Scotchbond Multi-Purpose Adhesive System (3M). The framework was veneered with the Filtek Supreme XT using a transparent mold. In the first group the FRC was positioned at the bottom of the cavity; in the second group close to the occlusal surface. Light curing was performed by using the Elipar S10 (3M) light curing unit for 40s for each of the layers. After water storage (7d, RT) the cantilever FDPs were loaded using a metal ball (Ø 5mm) positioned at the fissure of the pontic. Initial and final fracture load were determined by a bending test with a universal testing machine (LLOYD LRX, Lloyd Instruments, UK) using cross-head speed: 1.0mm/min. The results (N) were analyzed using t-test (p=0.05). Additionally, fracture types were registered.
Results:
Group | FRC, fibers at the bottom | FRC, fibers near to the surface |
Mean of the initial fracture load, N (SD) | 150.5 (53.0) | 249.5 (52.5) |
Mean of the final fracture load, N (SD) | 208.1 (61.4) | 283.6 (48.7) |
Fiber position had a statistically significant effect on both initial fracture load and final load bearing capacity of FDPs (p<0.05). In addition, FDPs where the fibers were at the bottom of the cavity tended to get an initial fracture to the connector during loading.
Conclusion: Based on this study cantilever fiber-reinforced FDPs seem to benefit of placing fibers close to the occlusal surface of the connector.