Hertzian Load-bearing Capacity of Hybrid and Nano-hybrid Resin Composites Stored Dry and Wet

Abstract Statement of Problem: Hertzian indentation test has been proven to be anefficient and reliable alternative upon Vickers hardness test. This methodhas been used to test dental ceramics, amalgams, glass ionomers and lutingcements.There is limited published information about the load-bearingcapacity of resin composites using Hertizian indentation test.Objectives: To investigate the load-bearing capacity of hybrid andnano-hybrid resin composites stored dry or wet up to 30 days, using Hertzianindentation test.Materials and Methods: Three resin composites were used: two nano-hybrids(Filtek Supreme, and Luna) and one hybrid, (Rok). A total of 108 disc-shapedspecimens (1mm thick x 10 mm diameter) were prepared using polyethylene mould.The specimens of each material were randomly divided into 6 groups of 6(n=6) and stored at 370C either in distilled water or dry for 1, 7 and 30 days.The specimens were tested using Hertzian jig aligned in the universaltesting machine. The specimen was placed on the top of a disc-shapedsubstrate. The load was applied at the center of each specimen and the loadat the first crack was recorded. Data were analyzed by ANOVA, Tukey’sandstudent’s t-test using SPSS version 18.0.Results: Three-way ANOVA showed a significant interaction between allthe factors (p = .0001). The load bearing capacity of almost all materialsreduced significantly in the wet condition in comparison with the drycondition (p = .0001). After seven days of immersion in distilled water,Filtek Supreme had significantly lower values than those of Rok and Luna,there was no significant differences between materials in the dry condition.Conclusions:In contrast to dry condition, the load-bearing capacity ofspecimens stored in distilled water decreased significantly over the 30 daysof immersion. The load bearing capacity of nano-hybrid composites testedin this study was shown to be comparable with that of the hybrid composite.key words: Hertzian Indentation, Load-bearing Capacity, Resin CompositesStatement of Problem: Hertzian indentation test has been proven to be anefficient and reliable alternative upon Vickers hardness test. This methodhas been used to test dental ceramics, amalgams, glass ionomers and lutingcements.There is limited published information about the load-bearingcapacity of resin composites using Hertizian indentation test.Objectives: To investigate the load-bearing capacity of hybrid andnano-hybrid resin composites stored dry or wet up to 30 days, using Hertzianindentation test.Materials and Methods: Three resin composites were used: two nano-hybrids(Filtek Supreme, and Luna) and one hybrid, (Rok). A total of 108 disc-shapedspecimens (1mm thick x 10 mm diameter) were prepared using polyethylene mould.The specimens of each material were randomly divided into 6 groups of 6(n=6) and stored at 370C either in distilled water or dry for 1, 7 and 30 days.The specimens were tested using Hertzian jig aligned in the universaltesting machine. The specimen was placed on the top of a disc-shapedsubstrate. The load was applied at the center of each specimen and the loadat the first crack was recorded. Data were analyzed by ANOVA, Tukey’sandstudent’s t-test using SPSS version 18.0.Results: Three-way ANOVA showed a significant interaction between allthe factors (p = .0001). The load bearing capacity of almost all materialsreduced significantly in the wet condition in comparison with the drycondition (p = .0001). After seven days of immersion in distilled water,Filtek Supreme had significantly lower values than those of Rok and Luna,there was no significant differences between materials in the dry condition.Conclusions:In contrast to dry condition, the load-bearing capacity ofspecimens stored in distilled water decreased significantly over the 30 daysof immersion. The load bearing capacity of nano-hybrid composites testedin this study was shown to be comparable with that of the hybrid composite.