Interfacial Issues in Dentin Bonding

Objectives: Since Buonocore demonstrated phosphoric acid-etching pretreatment could increase the microscopic surface area, the adhesive dentistry has been developed by continuing progress in bonding technology and bonding materials. A large quantity of studies reported that the good immediate resin-dentin bonding strength decreased substantially after aging over time, which eventually led to the continuous failure of resin restoration over time. Efforts have been made to improve the bonding durability based on a widely accepted consensus that the critical barrier to further progress in dentin bonding is the incomplete infiltration. However, the durability of resin-dentin bonds remains the biggest challenge. The objective of the present study was to explore the interfacial issues in dentin bonding.
Methods: The crown part of Caries-free third molars was removed to expose a flat dentin surface and randomly divided into three groups to be subjected with different treatment, thus obtained the control group (wet bonding group), T1 group (modified ethanol-wet bonding group) and T2 group (bonding based on the hydrophobized demineralized dentin marix). Prepared specimens were bonded by Prime & Bond NT and reconstructed with resin composite. Samples were subjected to microtensile bond strength evaluation immediately or after 3-month aging, 12-month aging. TEM was used to characterize the hybrid layer.
Results: Microtensile bond strength evaluation showed that both T1 and T2 groups greatly improved the immediate bonding strength. During aging, the attenuation in bonding strength among the three groups was markedly different. The attenuation rate per month in the control group was up to 9.99%, in the T1 group was 3.26%, in the T2 group was reduced to 0.64%. TEM result showed that, the interface of the dentin collagen and the adhesive in the control group and T1 group was sharp and clear, while that in the T2 group was vague and with fuzzy transition.
Conclusions: Hydrophobizing the demineralized dentin matrix during bonding could substantially improved the bonding durability. Furthermore, it could be found that complete infiltration might be a necessary but not sufficient condition for bonding stability. The micro interfacial compatibility in the hybrid later was important to bonding durability.