Evaluation of the adaptation to cavity of Tokuyama Bond Force

Objectives: To evaluate the adaptation to step-form cavity of three adhesives including Tokuyama Bond Force. Methods: The step-form cavity (4-mm diameter/3-mm depth + 2-mm diameter/1.5-mm depth) was prepared with fresh bovine teeth by using a diamond bur. Tokuyama Bond Force (BF/Tokuyama Dental), S³ Bond (S3/Kuraray), and SE Bond (SE/Kuraray) were used. The adhesives were applied to the cavity walls following the manufacturer's instructions. Subsequently, resin composite (Estelite Flow Quick/Tokuyama Dental) was filled in the cavity and polymerized by light irradiation followed by Estelite Sigma (Tokuyama Dental). The specimens were kept in water at 37 ^oC for 24 hours. The specimens were cut along the symmetrical axis to expose the cross-section of teeth/adhesive. The cross-section was polished to a high gloss with diamond pastes (grit 6, 3, 1, 1/4 um) and observed by using laser microscope (VK9700/KEYENCE). Results: In BF, a uniform thin bonding layer was formed even around the corner and the edge part. The bonding layer is combined with resin composite and the cavity wall remarkably. In SE, the bonding layer is combined with resin composite and the cavity wall tightly. However, the bonding layer is thick especially around the corners. In S3, the bonding layer is thick especially around the corners. The slight abrasion in the bonding layer after being polished was observed.

Adhesives	Bonding layer thickness
	around the corner / um	at cavity floor / um
BF	11.6 - 13.3	10.7 - 12.3
S3	35.0 - 107.1	21.5 - 24.2
SE	326.0 - 600.6	58.9 - 163.3

Conclusion: BF showed excellent adaptability to the step-form cavity.