Effect of water on shear strength of glass ionomer cements for luting.

This study examined the effect of ambient water on the shear strength of glass ionomer cements for luting. Disk specimens were fabricated from four commercially available glass ionomer cements with different setting modes. At one hour after the start of mixing, the specimens were stored at 37 degrees C for 24 and 168 hours in dry condition or in deionized water. Shear strength was then determined using a punch tool. The shear strengths of both conventional cements were significantly greater for the specimens stored dry as compared to those kept in deionized water (p < 0.05). Conversely, resin-modified cement specimens stored dry had significantly lower strength compared to the specimens kept in deionized water (p < 0.05). This was because the ambient water surrounding the resin-modified glass ionomer cements helped increase the shear strength of the cements under the experimental conditions tested.

Correlation between the strength of glass ionomer cements and their bond strength to bovine teeth.

This study examined the possible correlation between the strength of glass ionomers and their adhesive strength to bovine teeth. The shear bond strengths of three different brands of glass ionomer mixed at four different P/L ratios to bovine teeth were measured 24 hours after the cement specimens were prepared. The correlation between shear bond strength and mechanical strength reported in our previous study was also examined. No significant (p > 0.05) increases in the bond strength to bovine teeth were found in any of the cements when the mixing ratio increased. The present study showed no significant (p > 0.05) correlation between mechanical strength of cement and its bond strength to bovine teeth. Rather than trying to increase the strength of the cement, it would be more effective to enhance the adhesive bond strength through procedures such as surface conditioning or cleaning of the tooth structure when glass ionomers are used as luting agents.