Effect of Water Immersion on Monomer and Strength of FRC

Effect of Water Immersion on  Monomer and Strength of FRC


*  Faculty of Dentistry, Universitas Gadjah Mada, Indonesia

**Faculty of Dentistry, University of Hong Kong, Hong Kong


Purpose: There is an interest in the use of fiber-reinforced composite (FRC) to support the concept of minimal invasive dentistry. The exposure of FRC to the oral environment causes detrimental effect of water sorption. With time water molecules will act as plasticizers and decrease the mechanical properties. Monomer system is the backbone of the dental composite  and residual monomer may dissolve in water.  Some released monomer are known to ellicit cytotoxic effets, and methyl methacrylate (MMA) is mentioned as cytotoxic.  This study investigated the effect of water immersion duration on monomer release and the compressive strength of fiber-reinforced composite.

Materials and Methods : Materials used were: E-glass fibre (Stick Tech, Finland), bis-GMA (Sigma-Aldrich, USA), MMA (ProSciTech, Australia), CQ (Esstech, USA) and CEMA (Esstech, USA). Fifteen specimens (2mm x 2mm x 25mm) with the composition of:  78.4%bis-GMA+19.6%MMA+1.0%CQ+1.0%CEMA were prepared and divided into 2 groups: compressive strength (12 specimens) and residual monomer (3 specimens). Each specimen had two fiber rovings of 25mm and placed in a mould,  and  light-cured with halogen light-curing unit on both sides for 3x40s. Specimens from each group were divided into three groups based on the water immersion durations  (1,14 and 21days) and immersed into 10ml distilled water of 37oC. The three residual monomer test specimens were analyzed using HPLC to test the concentration. All compressive strength test specimens were tested using UTM  (Torsee’s UTM, Tokyo Testing Machine Mfg.,Co., Ltd.Japan) for the strength.

Results: The data of MMA concentration was descriptively analyzed. It started on day1 (2352.96 µg/ml) followed by an increase on day14 (3567.15 µg/ml) and decreased on day21 (2427.19 µg/ml). Compressive strength showed an average (MPa) for day1 (93.84±8.30); day14 (67.83±4.82) and day 21 (51.08±2.10) respectively. Data from the compressive strength was analyzed by ANOVA, and it  proved a significant  decrease as the water immersion duration increases (p<0.05).

Conclusions: The duration of water immersion of e-glass FRC showed different effect on the concentration of released monomer and the compressive strength. Highest concentration of MMA concentration happened on day14 and followed by a decrease. As for the compressive strength, it decreased as the water immersion duration increased.



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