Bond strength depends on characteristics of bonding surface and restorative technique. The majority of studies dealing with dentin bond strength were carried out on flat bonding surface, therefore, difference of bond strength between axial wall and pulpal wall is not clear yet. This study evaluated bonding difference between cavity walls in class I composite resin restoration with different filling techniques.

Twenty extracted caries-free human third molars were used. Cavities were prepared in 6 × 4 × 3 mm box-type and divided into four groups according to filling technique and bonding surface: Group I; bulk filling - pulpal wall, Group II; bulk filling - axial wall, Group III; incremental filling - pulpal wall, Group IV; incremental filling - axial wall.

Cavities were filled with Filtek Z250®(3M/ESPE., USA) and Clearfill SE bond®(Kuraray, Japan). After 24 hour-storage in 37℃ water, the resin bonded teeth were sectioned bucco-lingualy at the center of cavity.

Specimens were vertically sectioned into 1.0 × 1.0 mm thick serial sticks perpendicular to the bond surface using a low-speed diamond saw (Accutom 50, Struers, Copenhagen, Denmark) under water cooling. The trimmed specimens were then attached to the testing device and in turn, was placed in a universal testing machine (EZ test, Shimadzu Co., Kyoto, Japan) for micro-tensile testing at a cross-head speed of 1 mm/min. The results obtained were statistically analyzed using 2-way ANOVA and t-test at a significance level of 95%.

The results were as follows:

1. There was no significant difference between bulk filling and incremental filling.

2. There was no significant difference between pulpal wall and axial wall, either.

Within the limit of this study, it was concluded that microtensile bond strength was not affected by the filling technique and the site of cavity walls.

The purposes of this study were to examine the variability of adhesive thickness on the different site of the cavity wall when used total-etch system without filler and simplified self-etch system with filler and to evaluate the relationship between variable adhesive thickness and microtensile bond strength to the cavity wall.

A class I cavity in six human molars was prepared to expose all dentinal walls. Three teeth were bonded with a filled adhesive, Clearfil™ SE bond and the other three teeth were bonded with unfilled adhesives, Scotchbond™ Multi Purpose. Morphology and thickness of adhesive layer were examined using fluorescence microscope. Bonding agent thickness was measured at three points along the axial cavity wall, edge of cavity margin (rim), halfway down each cavity wall (hlf), internal angle of the cavity (ang). After reproducing the adhesive thickness at rim, hlf and ang, micro-tensile bond strength were evaluated.

For both bonding agents, adhesive thickness of ang was significantly thicker than that of rim and hlf (P < 0.05). As reproduced the adhesive thickness, microtensile bond strength was increased as adhesive thickness was increased in two bonding agents.

Adhesive thickness of internal angle of the cavity was significantly thicker than that of the cavity margin and the halfway cavity wall for both bonding agents. Microtensile bond strength of the thick adhesive layer at the internal angle of the cavity was higher than that of the thin adhesive layer at the cavity margin and the halfway cavity in the two bonding systems.