Effect of different thermo–light polymerization on flexural strength of two glass ionomer cements and a glass carbomer cement

Abstract

Statement of problemWhether polymerization lights can be used for heating glass ionomer cements (GICs) or glass carbomer (GCP) to improve their mechanical properties is not well established. PurposeThe purpose of this in vitro study was to assess the effect of thermo–light polymerization on the flexural strength (FS) of 2 GICs (Fuji IX GP Fast, Ketac Molar) and a GCP. Material and methodsSpecimens (n=10) were prepared in stainless steel molds (2×2×25 mm), compressed, exposed to 3 polymerization lights (500, 1000, 1200 mW/cm2) for 2 cycles of 40 seconds on each side, and stored in petroleum jelly (37°C, 24 hours). ResultsSignificant FS differences were detected among groups after different thermo–light polymerization regimens (F=50.926, df=11, P<.001). GCP showed the highest mean FS (∼5 times, P<.001) after thermo–light polymerization with power outputs of 1000 (127.1 ±25.8 MPa) and 1200 mW/cm2 (117.4 ±18.5 MPa), with no significance difference between them (P=.98), compared with 500 mW/cm2 (24.1 ±1.7 MPa). For Ketac Molar, compared with autopolymerization setting (15.5 ±3.1 MPa), a significant increase in mean FS (∼2.5 times) was only observed in specimens treated with 1200 mW/cm2 polymerization light (P=.03). For Fuji IX GP Fast, only the light with 1000 mW/cm2 output significantly increased the FS (98.9 ±23.4 MPa, P<.001) compared with the autopolymerization setting (34.9 ±6.4 MPa). ConclusionsThermo–light polymerization accelerated the development of FS in the tested GICs, potentially protecting against saliva contamination during the first 3 to 4 minutes after mixing GIC. Thermo–light polymerization of the glass carbomer with power outputs of 1000 and 1200 mW/cm2 also substantially increased FS. The clinical advantages of the findings should be validated by in vivo studies.