Effect Of MDP-containing Primers On The Short-and Long-term Enamel Bond Strengths

Objectives:The aim of this study was to investigate the effect of MDP-containing primers on short-and long-term enamel bond strengths.Methods:Thirty-two non-carious bovine mandibular incisors were extracted from8cows.4bovine incisors per cow were randomly divided into four groups due to the different pretreatments, each had1incisor. After the labial enamel surfaces were highly-polished, etched for15s, water-sprayed for30s and thoroughly air-dried, serving as control, the etched enamel surfaces were pretreated with three different experimental MDP-containing primers (Ex-1, Ex-2, Ex-3(Kuarary, Co. Japan)) for5s, water-sprayed for1min and thoroughly air-dried. Subsequently, Durafill Bond (Heraeus Kulzer, Hanau, Germany) was applied to the pre-treated enamel surfaces, gently air-dried, and light-cured for20s. Two2-mm increments of a composite resin Durafill VS (Heraeus Kulzer, Hanau, Germany) were placed, and light-cured for40s, respectively. After24-h tap water storage, the specimens were prepared into sticks of about0.9×0.9×8mm through the enamel-resin interface with a low-speed saw (Isomet1000, Buehler, USA). The micro-tensile bond strength (μTBS) tests were performed with a Micro Tensile Tester (Bisco, USA). The μTBS tests were performed in triplicate using4bovine incisors per cow (all12teeth) for short-term (24h) bond strength test. Another12teeth were stored at room temperature in tap water. All the specimens were subjected to μTBS-testing in the same way as those above-mentioned for the short-term test after1year’s storage. Four pieces of enamel surfaces from1cow were treated as above-mentioned, neither treated with Durafil Bond, nor placed with composite resin, for surfaces SEM observations. The other four1mm cross-section of enamel-resin flat pieces were obtained before the μTBS testing for the enamel-resin interface SEM observations. Specimens were immersed in0.1mol/1HCl for20s. All the SEM specimens were dried with a series of alcohol, gold-sputtered for SEM observations. For XPS analysis, another four pieces of enamel surfaces from1cow were treated in the same manners as those above-mentioned for the SEM observations.Results:The μTBS of control specimens was significantly lower than that of the three experimental groups (p<0.05). For both short-and long-term μTBS test, no significant different uTBS was found either among three tests of each group (p>0.05) or among the three experimental groups (p>0.05). The SEM findings revealed the different etching patterns caused by acid etching and MDP-containing primers. The XPS spectra of enamel treated with three MDP-containing primers were different in C1s region compared with the control group.Conclusion:The additional chemical bonding of MDP around HAp crystallites of the etched enamel substrate significantly increases the short-term(24h) enamel bond strengths and keeps it remained stable over a1yr storage period. The enamel etching pattern might be influence by chemical adsorption, ingredients and acidity of MDP-containing primers.