Physicochemical and mechanical approaches to dentine/resin adhesive interface

The aim of this study is to determine the influence of different characteri stic parameters of the human dentine surface on the interaction between den tine and adhesive resin. The dentine surface of 21 freshly extracted teeth (from patients between the ages of 13 and 77 years old) was treated with To tal Etch (Vivadent etching gel) and characterised by three methods: Vickers microhardness (for mechanical characterisation); wettability (in order to characterise the dentine and adhesive interactions using the drop angle): o ptical and electron microscopy with image analysis (for microstructural cha racterisation). The average number and diameter of the tubules on the surfa ces were calculated. Then 21 stubs of Z100 restorative (3M dental products) were bonded on the dentine substrate of these teeth using Syntac Sprint (V ivadent). The shear bond strength (Instron universal testing machine) at a crosshead speed of 0.5 mm s (-1) was determined. Shear bond strength and mi crohardness increases with the age of the tooth. The shear bond strength de creases with the per cent surface area, and average number of tubules. The wettability angle increases with the number of tubules and the per cent sur face area of tubules. The results were analysed with the use of Sperman Ran k. The explanation of the wettability behaviour is very complicated and it is necessary to take into account the evolution of the resin adhesive visco sity over time. The originality in this work is that the physicochemical ch aracterisation and mechanical study were carried out on the same tooth. The fact that no significant statistical correlation is found between dentine, its specific parameters, and the shear bond strength can be explained by t he observation of fracture surfaces using SEM in combination with EDX analy sis. This shows some very heterogeneous fractures, from adhesive resin inte rfacial fracture to cohesive fractures in the adhesive resin or restorative composite resin. This work demonstrates that the dentine resin adhesive in terface is highly complex. It depends not only on the superficial parameter s of the dentine but also on the physicochemistry of the resin and the adhe rence test parameters.