Influence of salivary enzymes and alkaline pH environment on fatigue behavior of resin composites.

OBJECTIVE

To evaluate the effect of enzymatic activity and alkaline medium on flexural strength and rotary fatigue resistance of direct and indirect resin composite restorative materials.

METHODS

Three direct resin composite materials Filtek Z100, Filtek Z250 and Filtek Silorane (3M ESPE), and two indirect resin composite materials; Sinfony (3M ESPE) and an experimental composite (Heraeus Kulzer) were used to fabricate bar-shaped specimens (2 x 2 x 25 mm; n=10) to determine the flexural strength (Fs) by means of a 3-point bending test according to ISO 4049. Additional specimens of the same dimensions (n=20) were used to prepare hour-glass shaped specimens which were immersed in distilled water for 48 hours, transferred to one of five aqueous media at 37 degrees C for 2 weeks; phosphate buffer, distilled water, 0.1N NaOH, 1 unit/ml Amylase, 0.1 unit/ml Esterase, and a group in 0.1N NaOH at 60 degrees C. Rotary fatigue resistance (RFR) was determined in a rotating-bending cantilever test with the highest stress located at the constriction of the hour glass. The rotary fatigue resistance tests were conducted according to the staircase approach (10(4) cycles, 1.0 Hz) and the mean RFR was calculated using logistic regression analysis.

RESULTS

NaOH produced a significant decrease in Fs of all materials. The effect of enzymatic biodegradation on Fs of Filtek Z100 and Filtek Z250 was found to be significant, however, for Silorane and indirect composites it was not significant. Except for NaOH the influence of the different aqueous solutions on RFR was not significant for all tested materials.