This study was carried out to design an ideal cavity for restoration of primary molars with adhesive composite resin. The materials used in this study were extracted primary molars from children, and class 1 cavities on the occlusal surface were prepared. An ideal cavity design was considered as being a bowl-shaped, flat floor cavity at an angle of 75°with the occlusal surface to the buccal and lingual walls. A box-shaped cavity was prepared for the control group.
The materials used in this study were Single Bond® as a bonding agent and AP-X® or Z-100® as a restoration material for the cavities. We determined the presence of microleakage in the cavity margin, the thickness of bonding agent, and the remaining monomer after the polymerized composite resin. After a thermal shock tester was used, the two kinds of cavity designs were compared for their adaptability. As a result, the following conclusions were obtained:
1. In the bowl-shaped cavity with a flat floor, teeth without microleakage amounted to 86.4% and this was more pronounced compared with the box-shaped cavity. When the areas of microleakage were found, they reached the cavity floor in both types of cavities.
2. In the bowl-shaped cavity with a flat floor, a thick layer of bonding agent was found in the corner and floor of the cavity after filling with AP-X®, and it was found also in the vertical wall of the dentin after Z 100® filling. Furthermore, in box-shaped cavity after AP-X® filling, the bonding agent layer was also found at the enamel wall. There was no difference between the two filling materials, concerning the thickness of bonding agent in the bowl-shaped cavity with a flat floor. There was, however, a tendency for the bonding agent to accumulate in the cavity corner in the box-shaped cavity with Z 100®.
3. Regardless of the cavity designs, the content of the remaining monomer after the cured composite resins was at a higher level in the walls of the cavity than on the center of the cavity. The level of the monomer on the wall of cavity was higher in the box-shaped cavity than in the bowl-shaped cavity with a flat floor. From these results, the bowl-shaped cavity with a flat floor appears to be an ideal cavity design for applying adhesive composite resin to primary molars.