Bond strength of composite to dentin treated by air abrasion

This study compared the bond strength of composite to dentin produced by an air-abrasive dentin pretreatment and acid etch only. Two hundred sixty extracted human molars were randomly divided into 13 groups (n = 20). An occlusal dentin surface with a defined smear layer was exposed. Dentin was conditioned either with 37% H3PO4 for 20 seconds, or an air-abrasion unit (KCP 1000, ADT) was used with 120 and 160 psi pressure and two different particle sizes, 50 and 27 microns. A combination of both treatments beginning with air abrasion was tested as well as dentin specimens without pretreatment. The dentin adhesive Syntac Single-Component was applied under dry and moist conditions. Composite cylinders with a bond diameter of 2.5 mm were bonded in two increments to the teeth. Specimens were stored for 24 hours at 37 degrees C in distilled water and then thermo-cycled for 1000 cycles (5/55 degrees C). Shear bond strength was tested using a Universal Testing Machine at 0.5 mm/min cross-head speed. Means and standard deviations in MPa were calculated. Analysis of variance and Bonferroni pairwise comparison tests were performed. Lowest bond strengths were obtained in specimens without conditioning the dentin. Air-abraded specimens showed a significantly higher bond strength than the before-mentioned groups. The comparison for acid-etched groups and air-abraded specimens revealed higher values for the abraded groups. Air abrasion with 160 psi pressure produced a significantly higher bond strength than 120 psi. There was no significant difference between the 27 and 50 microns particles. Air abrasion in combination with a self-priming bonding agent produced bond strength on dentin at least comparable to conditioning with 37% H3PO4.