Background: This in vitro study evaluated the fracture resistance of weakened endodontically treated premolars with class II MOD cavities restored with different composite restorations (Low-shrinkage Filtek P90, nanohybrid Filtek Z250 XT and SDR bulk fill). The type and mode of fracture were also assessed for all the experimental groups.Materials and Method: Fifty human adult maxillary premolar teeth were selected for this study. Standardized extensive class II MOD cavities with endodontic treatment were prepared for all teeth, except those that were saved as intact control. The teeth were divided into five groups of ten teeth each (n=10): (Group 1) intact control group, (Group 2) unrestored teeth with endodontic treatment, (Group 3) restored with (Filtek Z250 XT), (Group 4) restored with SDR bulk-fill flowable composite and (Group 5) restored with Filtek P90 composite. All specimens were subjected to compressive axial loading until fracture in a universal testing machine. The data were statistically analyzed using one-way ANOVA test and LSD test. Macroscopic fracture type were observed and classified into favorable and unfavorable. Specimens in group 3, 4 and 5 were examined by stereomicroscope at a magnification of 20× to evaluate the mode of failure into adhesive, cohesive or mixed.Results: The mean fracture load was (1.123 Kn) for group 1, (0.545 Kn) for group 2, (0.687 Kn) for group 3, (0.799 Kn) for group 4 and (0.672 Kn) for group 5. Using one way ANOVA test a highly significant difference (P < 0.01) were found among all groups. The use of bulk-fill flowable composite improved the fracture resistance significantly in comparison to silorane and non-significantly to Filtek Z250 XT. Filtek Z250 XT showed better improvement in fracture resistance but with no significant differences in comparison to Filtek P90 composite restorations. The type of failure was unfavorable for all the restored groups.Conclusion:All experimental composite restorations showed significant improvement in the resistance to cuspal fracture in comparison to unrestored one. However, under the conditions of this study, direct composite restorations should be considered as a valid interim restoration for weakened endodontically treated teeth before cuspal coverage can be provided.

Fracture resistance --- endodontically treated teeth --- Filtek Z250 XT --- SDR

Background: This in vitro study measure and compare the effect of light curing tip distance on the depthof cure by measuring vickers microhardness value on two recently launched bulk fill resin basedcomposites Tetric EvoCeram Bulk Fill and Surefil SDR Flow with 4 mm thickness in comparison to Filtek Z250Universal Restorative with 2 mm thickness. In addition, measure and compare the bottom to topmicrohardness ratio with different light curing tip distances.Materials and Method: One hundred fifty composite specimens were obtained from two cylindricalplastic molds the first one for bulk fill composites (Tetric EvoCeram Bulk Fill and Surefil SDR Flow) with 4 mmdiameter and 4 mm depth, the second one for Filtek Z250 Universal Restorative with 4 mm diameter and 2mm depth. Each spcimen was light-cured using WOODPECKER LED CURING LIGHT for 20 sec.Polymerization was performed with the light tip positioned in direct contact, 2 mm, 4 mm, 6 mm and 8mm distant from the top surface of the sample. After one day of storage in distilled water in a light proofcontainer at 37˚C, the hardness on the bottom and top surfaces of each specimen was tested using theDigital Micro Vickers Hardness Tester. Then the Data were analyzed statistically by ANOVA test, LSD testand t-test.Results: All experimental groups show top microhardness higher than bottom microhardness with highsignificant difference with all light tip distances. At 0 mm light tip distance all groups give the highestmicrohardness value. Filtek Z250 Universal Restorative shows accepted bottom to top microhardness ratioat all light tip distances. Surefil SDR Flow shows accepted bottom to top ratio only at 0, 2 and 4mm lighttip distances while Tetric EvoCeram Bulk Fill shows the bottom to top microhardness ratio less than theaccepted value with all light tip distances.Conclusion: From the results of this study we can conclude that the polymerization of bulk fill compositedepends greatly on the distance from light curing tip, Tetric EvoCeram Bulk Fill composite notrecommended to be used as bulk fill restoration in deep cavities and need further studies, while SurefilSDR Flow not recommended to be used in deep cavity when curing tip distance (6-8 mm), in addition wecan conclude that the thickness of the increments is more important than light curing tip distance

light cure tip distance --- depth of cure --- Tetric EvoCeram Bulk Fill composite --- Surefil SDR Flow