ABSTRACT
Patients' demand for tooth-colored restoratives in the posterior region is increasing. Clinicians use universal nanohybrid resin composites for both anterior and posterior regions. There are few published reports comparing fracture toughness of nonohybrids and that of hybrid composite stored wet and dry
Objectives: To investigate the fracture toughness of three nanohybrids compared to that of a hybrid resin composite stored dry or wet up to 60 days, using four-point bending test
Materials and Methods: Four resin composites were used: three nanohybrids; Filtek Supreme [3M], Ice [SDI], TPH3 [Dentsply] and one hybrid Filtek P60 [3M]. For each material, 40 rectangular notched beam specimens were prepared with dimensions of 30 mm × 5mm × 2mm. The specimens were randomly divided into 4 groups [n = 10] and stored at 37[degree sign]C either in distilled water or dry for 1 and 60 days. The specimens were placed on the four-point test jig and subjected to force [N] using universal testing machine loaded at a crosshead speed of 0.5mm/min and maximum load at specimen failure was recorded and K[Ic] was calculated
Results: Three-way ANOVA showed a significant interaction between all the factors [all p < .0001]. Except for TPH3, all tested materials showed significantly higher K[Ic] when stored dry than stored wet [p < 0.05]. After 1 day of dry storage, Ice showed the highest K[Ic] [2.04 +/- 0.32] followed by Filtek P60 and the lowest was for Filtek Supreme [1.39 +/- 0.13]. The effect of time on fracture toughness was material dependent
Conclusions: Wet storage adversely affected the fracture toughness of almost all materials. Keeping the restoration dry in the mouth may increase their fracture toughness. Therefore, using a coating agent on the surface of restoration may protect them from early water uptake and increase their strength during a time period
ABSTRACT
Statement of Problem: Hertzian indentation test has been proven to be an efficient and reliable alternative upon Vickers hardness test. This method has been used to test dental ceramics, amalgams, glass ionomers and luting cements.There is limited published information about the load-bearing capacity of resin composites using Hertizian indentation test
Objectives: To investigate the load-bearing capacity of hybrid and nano-hybrid resin composites stored dry or wet up to 30 days, using Hertzian indentation 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-shaped specimens [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 37[degree]C either in distilled water or dry for 1, 7 and 30 days. The specimens were tested using Hertzian jig aligned in the universal testing machine. The specimen was placed on the top of a disc-shaped substrate. The load was applied at the center of each specimen and the load at the first crack was recorded. Data were analyzed by ANOVA, Tukey' sand student's t-test using SPSS version 18.0
Results: Three-way ANOVA showed a significant interaction between all the factors [p = .0001]. The load bearing capacity of almost all materials reduced significantly in the wet condition in comparison with the dry condition [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 of specimens stored in distilled water decreased significantly over the 30 days of immersion. The load bearing capacity of nano-hybrid composites tested in this study was shown to be comparable with that of the hybrid composite