Diametral tensile strength of resin composite on water storage
Objectives:The purpose of this investigation was to compare the diametral tensile strengths (DTS) of resin composite (RC) tooth restorative materials stored under wet and dry conditions, respectively. The hypothesis to be tested was that wet storage resulted in a significant reduction in DTS compared with dry storage. Methods: Cylindrical specimens (n = 2 x 60) of nominal dimensions 6 mm x 3mm (height) of 2 generic RCs, a densified material (DC), Spectrum TPH [Dentsply], and a microfilled material (MC), Durafill VS [Heraeus Kulzer], were exposed to a commercial light curing unit, Degulux Softstart [Dentsply], on both surfaces for 40 secs at 23 ±2oC. The control group (n = 2 x 30) was stored dry for 30 days while the remaining specimens were stored in deionised water at 37 ±2)oC for the same period. Compression across a diameter was carried out using a universal testing machine, H10KS [Tinius Olsen], at a constant crosshead speed of 0.75 ±0.25 mm/min. Wet storage specimens were surface dried before testing. All testing was at 23 ±2oC. Data were converted to DTS. A 2 x 2 analysis of variance was performed to investigate the effect of storage condition, material type, and material type by storage condition. The underlying assumptions of normality and constant variability were established by appropriate tests. Means and standard deviations were used for summarisation and significance was determined using P<0.05. Results: Mean (SD) DTS data were as follows (MPa): DC dry 54.7(7.0), wet 46.4(7.6); MC dry 38.3(5.2), wet 30.4(5.1). There was no significant interaction between material type and storage condition (P=0.867). Dry storage yielded a significantly greater mean DTS than wet conditions (P<0.001). Conclusion: Resin composite materials may deteriorate mechanically when stored for 30 days in water at 37oC.