Bonding strength of glass ionomers to dense synthetic hydroxyapatite and fluoroapatite ceramics

The bonding strength of two glass ionomers, a resin-modified and a conventional one, to dense synthetic hydroxyapatite (HA) and fluoroapatite (FA) ceramics was compared by measuring the shear strength between the ionomers and the apatites. Before the glass ionomers were applied on the apatites, the surfaces of HA and FA plates were either fine-polished or acid-etched after fine polishing. Commercially pure titanium (CP Ti) plates were used as a control. The effects of polyacrylic acid (PAA) surface preconditioning on bonding strength were also studied. The results show that the ionomers bind to HA significantly more strongly than to FA in all cases. The resin-modified material showed a significantly higher shear strength to apatites than the conventional one. Acid etching increased the shear strength significantly for the conventional glass ionomer to both HA and FA, and 25% PAA preconditioning increased the shear strength significantly for the resin-modified glass ionomer to both HA and FA. It was concluded that glass ionomers seemed to bind to apatite chemically, and the bonding strength was influenced by the cohesive strength of the ionomers and the surface roughness of the apatites. The dense synthetic apatites seemed to be good test materials for bonding evaluations of glass ionomers to mineral tissue.