Effect of Fiber Orientation and Position on Fracture Resistance and Failure Mode of Cuspal Coverage Composite Restorations

Statement of Problem: Position and orientation of fiber may lead to increase load bearing capacity and prevent undesirable fractures in cuspal coverage composite restorations. The aim was to evaluate the effect of fiber position and orientation on fracture resistance and failure mode of composite cusp capping restorations. In this experimental study, MOD cavities with 2.5mm cuspal reduction were prepared in 50 human maxillary premolars. The teeth were divided into five groups (n=10) and all teeth were restored with packable composite resin (P60). In the first group no fibers were applied. In the second group one strip of fiber was inserted into resin composite in buccal to palatal direction. In the third group two strips of fiber were inserted in buccal to palatal and mesial to distal direction by crossing in central part of cavity. In the forth group, one strip was directed from mesiobuccal to distopalatal and the other from distobuccal to mesiopalatal line angle. In the fifth group, two strips of fiber were inserted in buccal to palatal direction with 1.5 mm distance. The teeth were stored in water for 7 days in room temperature and then thermocycled 500 times between 6±2 and 60±2 centigrade degrees. The specimens were subjected to compressive loading perpendicular to the occlusal surface. The necessary fracture loads were recorded in (KN) and the results were statistically analyzed by Mann-Whitney and ANOVA tests. Mode of fracture was analyzed by using Fisher test. Statistical analysis showed a significant increase of fracture load from control to the other four groups (p<0.05). There were statistically significant differences between second and third groups (p=0.034) as well as second and fifth groups (p=0.041). No significant differences were found between other pairs of groups. Also significant differences were observed in failure mode between composite restorations with and without fiber, except for second group (p<0.005). Fiber reinforced composites improve fracture resistance and failure mode of restorations with cusp capping. With increase use of fiber strips in special directions, fracture resistance will be rised.