SENB Fracture Toughness of Resin Composites after Storage in Water

Objectives: To determine the effect of storage in water at oral temperature for seven days on SENB fracture toughness of selected resin-composites using ASTM Standard D5045-99 (2007).  Methods: Seven SENB specimens each of resin-composites Esthet-X HD (EX; Dentsply/Caulk), 4-Seasons (FS; Ivoclar-Vivadent), Gradia Direct (GR; GC), Point 4 (PF; Kerr), and TPH3 (TP; Dentsply/Caulk) were fabricated in a custom-made metal mold (17.6x2.0x4.0mm; blade length approximately 2mm) to produce specimens having dimensions as per the ASTM Standard. Specimens were polymerized in 2mm increments (40-second light-activation/increment). Dimensions were measured with an electronic caliper at three equally-spaced positions and averaged to determine width (W), length (L), and thickness (B).  Crack-length (a) and crack-width (N) were measured using a stereomicroscope and digital camera both before and after fracture.  Specimens were stored in a water bath at 37±1°C for 1-day (control group) or 7-days (experimental group), and then fractured in three-point bending in air (33R4468 Instron universal testing machine; crosshead rate: 0.5mm/min, support span: 16mm). K_IC fracture toughness values were calculated and validated as described in ASTM Standard D-5045-99(2007).  Mean K_IC values in each group were compared using one-factor ANOVA and post hoc Student-Newman-Keuls tests (SNK; α=0.05).  A t-test was used to compare mean values of each product after storage for 1- and 7-days (α=0.05).  Results: Mean±StdDev K_IC values (MPa·m^1/2) were:

 

Storage duration	EX	FS	GR	PF	TP
1-day	1.22±0.09A	0.88±0.13C*	0.89±0.03C	1.01±0.03B	1.31±0.10A
7-days	1.21±0.12B	0.71±0.09E*	0.83±0.07D	0.96±0.08C	1.31±0.06A

Letters denote mean values in each row that are statistically different from each other (p<0.05)
* denotes mean values in each column that are statistically different from each other (p<0.05)

Conclusions: Mean K_IC values of the resin-composites tested were not statistically different after storage in water at oral temperature for 1-day versus 7-days except for product FS, where a decrease in fracture toughness was observed. Mean K_IC values of the resin-composites tested differed statistically within each test group. Funding: J. Dean Robertson Society, University of Oklahoma.