Fracture resistance of weakened premolars restored with sonically-activated composite, bulk-filled and incrementally-filled composites (A comparative in vitro study)


Background: This study was conducted to assess the effect of sonic activation and bulk placement of resincomposite in comparison to horizontal incremental placement on the fracture resistance of weakened premolarteeth.Materials and method: Sixty sound human single-rooted maxillary premolars extracted for orthodontic purposes wereused in this study. Teeth were divided into six groups of ten teeth each: Group 1 (sound unprepared teeth as acontrol group), Group 2 (teeth prepared with MOD cavity and left unrestored), Group 3 (restored with SonicFill™composite), Group 4 (restored with Quixfil™ composite), Group 5 (restored with Tertic EvoCeram® Bulk Fill composite)and Group 6 (restored with Universal Tetric EvoCeram® composite using horizontal incremental layering technique).Standardized class II MOD cavity was prepared in all teeth except (group 1).After finishing the restorative procedureof each group according to the manufacturer's instructions, all teeth were stored in deionized distilled water in anincubator at 37°C for seven days.All specimens were subjected to compressive axial loading until fracturein auniversal testingmachine.Specimens were examined by a stereomicroscope at a magnification of (20X) to evaluatethe mode of fracture .Results: The results of this study revealed that the control group exhibited the highest fracture resistance compared toall prepared teeth groups (restored or unrestored) and the differences were statistically highly significant (P<0.01),except with group 3 (which was restored with SonicFill™ composite) where the difference was statistically significantonly (P < 0.05).Additionally the results of this study revealed that the prepared unrestored teeth (Group 2) exhibitedthe lowest fracture resistance compared to all restored groups and the differences were statistically highly significant(P<0.01). Meanwhile, among the restored teeth groups, teeth restored with SonicFill™ composite (group 3) exhibitedthe highest fracture resistance as compared with all other restored groups and the difference was statistically highlysignificant (P<0.01) .On the other hand, no statistically significant differences in fracture resistance were found amonggroups 4, 5 and 6, which were restored with Quixfil™ composite, Tetric EvoCeram® Bulk Fill composite and UniversalTetric EvoCeram® composite, respectively (P > 0.05). Group 3and Group 5 showed mostly mixed mode of failure,while Group 4 showed mostly adhesive mode of failure. On the other hand Group 6 teeth showed different modes offailure.Conclusions: SonicFill™ composite can be considered as a viable treatment modality for the restoration of weakenedmaxillary premolar teeth. On the other hand, the time-consuming incremental layering technique can be substitutedwith bulk filling, using bulk fill materials (Quixfil™ and Tetric EvoCeram® Bulk Fill) for reinforcement ofweakenedmaxillary premolars