Adhesive layer thickness of universal adhesives and influence of air-thinning on its thickness

Abstract

The purpose of this study was to compare the thickness of the adhesive layer of different universal adhesives on the flat dentin surface and Cl II prepared cavity and to evaluate the effect of air-thinning on the thickness of adhesive layer. To evaluate the adhesive layer thickness on the flat dentin surface, 40 extracted molars were prepared and cut below dentinoenamel junction to expose the dentin surface. Two groups of 20 teeth were divided according to the air-thinning procedure (air-thinning group(A), no air-thinning group(NA)). Then they are sub-divided to 4 groups of 5 teeth according to the type of adhesive used (All bond Universal (ABU), Single bond Universal (SBU), Tetric N bond Universal (TNU), Clearfil SE bond (SE)). Adhesives were mixed with Rhodamine B and applied to the flat dentin surface according to the manufacturer's instruction on air-thinning group. On no air-thinning group, air-thinning procedure was omitted. Flowable resin filling were done on the top of adhesive layer. Prepared tooth was sectioned to get 3 specimens from each tooth and thicknesses of adhesive layer were measured using confocal laser scanning microscope (CLSM). For the evaluation of the adhesive layer thickness on the cavity prepared teeth, Cl II cavity preparation was carried out on the extracted molar. For standardization, 40 replicas of the same cavity were made with epoxy resin. Groups were divided same as above, and bonding agent mixed with Rhodamine B was applied on the cavity and resin filling were done. Replicas were sectioned mesiodistally crossing the midline of the prepared cavity and the evaluation of the adhesive layer thickness on eight different locations of the cavity was carried out under CLSM. The results were statistically analyzed by ANOVA, Tukey’s test and t-test. The result showed that there was a significant difference on the thickness of adhesive layer on the flat dentin surface among the adhesives used (p<0.001) – ABU and TNU < SBU and SE on air-thinning group, ABU < TNU < SBU and SE on no air-thinning group. Air-thinning didn’t affect a significant difference on the thickness on SBU, TNU and SE (p>0.05) but there was a significant difference on ABU (p<0.05). On the Cl II prepared cavity, there was a significant difference between the adhesives used (p<0.001)-ABU and TNU < SBU and SE. There were significantly thicker adhesive layers on the line angles of the cavity (p<0.001). Air-thinning procedure didn’t affect the significant difference on the thickness on the Cl II prepared cavity (p>0.05). Within the limitation of this study, the adhesive layer thickness of universal adhesives depends on the type of adhesive used and the position on the cavity. Air-thinning procedure didn’t have a significant effect on the thickness of the adhesive layer on SBU, TNU and SE but have some effect on ABU on the flat dentin surface. On the Cl II prepared cavity, air-thinning produced no significant difference on the thickness.