Fracture resistance of injectable composite versus packable composite in class II cavities : An in vitro study /

Abstract

Restoration of posterior teeth has been always a demanding procedure for both the dentist and the patient. Class II cavities pose great risks on the tooth and the restorative material as well. Detrimental occlusal stresses constitute one of the main causes of composite failure which is bulk fracture. The complexity of the procedure is not only limited to restoring proper tooth contact, contours and anatomy but also to restore the physiologic fracture resistance while respecting biomechanical concepts. Manufacturers have claimed that the recently developed injectable composites will provide a time-efficient solution while providing sufficient mechanical properties to withstand stresses in such cavities. However, there is lack of evidence regarding the fracture resistance of injectable composites as compared to conventional packable composites. Therefore, the aim of this study was to investigate and compare between the fracture resistance of teeth with small and large class II cavities restored with injectable composite versus packable composite. Therefore, the study tested the effect of restorative material and cavity size on fracture resistance. In addition, the study evaluated the failure modes of both restorative materials. Accordingly, extracted maxillary premolar teeth were divided into five groups. The first group was control with intact teeth. Second group was small class II cavities restored with injectable composite and the third group was large class II cavities restored with injectable composite. Fourth group was small class II cavities restored with packable composite and the fifth group was large class II cavities restored with packable composite. Small cavities were box-only while large cavities were occluso-mesial. Teeth were molded in cylindrical acrylic blocks. Fracture resistance was assessed by a universal testing machine that loaded the teeth axially at the marginal ridges of the restorations and the cuspal inclines as well. The loading tip was a four millimeters diameter stainless steel ball and the loading rate was 1 mm/min. Teeth were loaded until the first sign of fracture and the load was recorded in Newtons. Finally, the mode of failure of the fractured specimens were analyzed under stereomicroscope whether restorable or non-restorable fracture. Fractures were considered restorable if they were coronal or 1 mm or less apical to the CEJ. Fractures were considered non-restorable if they were more than 1 mm apical to the CEJ. Regarding the results, there were no statistically significant differences between the fracture resistance of all five groups. Moreover, there were no statistically significant differences between the failure mode of all five groups where most of the fractures were restorable. Further laboratory and clinical studies are required to reach a consensus regarding the use of injectable composites in stress-bearing cavities.