The effect of dentine location and tubule orientation on the bond strengths between resin and dentine

This study determined the influence of dentine structure on the micro-tensi le bond strengths between resin and dentine of two different dentine adhesi ve systems (Single Bond, 3M Dental Products, St Paul, MN; MF-102 (experimen tal self-etching primer), GC Corporation, Tokyo, Japan). The study was sepa rated into two main parts: bond strength measurement and investigation of t he bonding interface. Twenty-two human premolars were used for the bond str ength measurement. Each tooth was cut vertically, separating the tooth into mesio-distal halves. One half of the tooth was used to bond to a surface p erpendicular to the dentinal tubules and other half to bond to a surface pa rallel to the tubules, For each half, six locations of dentine were bonded. Each material was used in accordance to the manufacturer's directions. Cyl indrical hourglass-shaped specimens of 1.2 mm diameter at the bonded interf ace were manufactured. The bonds were stressed in tension at a crosshead sp eed of 1 mm/min. Mean bond strengths were compared using LSD, one-way ANOVA , and Student's t-test. The fractured surfaces were examined under a scanni ng electron microscope, and the frequency of fracture modes was compared us ing the Kruskal-Wallis and Mann-Whitney U tests. For the investigation of t he bonded interface, four teeth were prepared by the same procedure used fo r the bond test specimens. The bonded interfaces were observed after an aci d-base treatment or fracturing across the bonded interface, prior to invest igation with a field-emission scanning electron microscope. For Single Bond , the bond strengths for mid-root dentine were significantly lower than for other locations (p < 0.05). For MF-102, there was no significant differenc e for all locations (p > 0.05). MF-102 bonded well to all locations of dent ine while Single Bond showed a porous zone at the base of the hybrid layer. The bonds were not influenced by tubule orientation. The results indicate that the bond for Single Bond may be affected by its ability to penetrate d emineralised dentine in different locations of a tooth. The self-etching pr imer of MF-102 produces a good bond and is independent of the position on t he tooth. (C) 1999 Elsevier Science Ltd. All rights reserved.