Calcium hydroxide, pH-neutralization and formulation of model self-adhesive resin cements

This study investigated the incorporation of calcium hydroxide (CH) and its effect on pH-neutralization and fundamental properties of model self-adhesive resin cements (SARCs).

Two-paste SARCs were obtained. Paste A: UDMA/Bis-GMA/TEGDMA/HEMA co-monomer, 25% phosphate monomer (GDMA-P), and 50% glass fillers; Paste B: UDMA/HEMA co-monomer, water, photoinitiators, and 60% glass fillers. CH was added at final concentrations of 0 (control), 0.25%, 0.5%, 1%, 2%, and 4%. Equal volumes of the pastes were mixed before testing. pH-neutralization of the eluate was followed during 24-h storage in distilled water. Other physico-chemical properties were evaluated only for the control and CH concentrations that neutralized the eluate. These evaluations included degree of CC conversion, film thickness, flexural strength/modulus, work-of-fracture, hardness, depth of cure, water sorption/solubility, and dentin bond strength. Statistical comparisons were conducted at a 5% significance level.

All CH concentrations above 0.25% caused pH increase of the eluate at 24h. The only CH concentrations leading to pH-neutralization were 2% and 4%. Compared with the control cement, the addition of 4% CH decreased the flexural strength, flexural modulus, work-of-fracture, CC conversion, and dentin bond strength. The cement with 2% CH had similar properties to the control cement, except for lower work-of-fracture and lower film thickness. Hardness, depth of cure, and water sorption were not affected by CH. The cement with 4% CH had lower solubility and film thickness than the other materials.

Incorporation of 2% CH to SARCs may lead to pH-neutralization without dramatically affecting other material properties.