Study On The Synergic Mechanism Of Chemical Bonding With Micro-mechanic Interlocking At Resin-enamel Interface

Objectives:The aim of this study was to investigate how much chemical bonding coating contributes to the mechanical enamel bond strengths.Methods:4 non-carious bovine incisors per bull/cow were randomly divided into four groups, each had 1 incisor (each bull/cow had 4-8 incisors, all 8 bulls/cows,34 incisors). After the labial enamel surfaces were highly-polished, etched for 15 s, sprayed for 30 s, and thoroughly air-dried for 5 s, the etched enamel surfaces were primed with/ without one of the phosphoric acid esters (PAEs) (AquaPrime A+B, Merz; Xeno V, Dentsply; 40%MDP) for 5 s, thoroughly water-sprayed for 1 min, and totally air-dried. Subsequently, Heliobond (Ivoclar Vivadent) was applied, gently air-dried, light-cured for 20 s, and a Core Build-up composite resin (Bisco, USA) was placed in two 2-mm increments, and light-cured for 40 s, respectively. The acid-etched, unprimed enamel served as control. After 24-h water storage, the specimens were prepared into slabs of about 1×1×8 mm through the resin-enamel interface with a low-speed saw (Isomet 1000, Buehler, USA). The micro-tensile bond strength (μTBS) tests were performed with a micro-tensile tester (Bisco, USA). The above-mentioned tests were repeated five times, using the bovine incisors extracted from a bull/cow for an exprimental test, respectively. After another four bovine enamel surfaces were treated, applied with Heliobond and placed with composite resins as mentioned above, an bovine incisor was prepared into two disks of about lmm thickness perpendicularly through the resin-enamel interface with a low-speed saw. For the SEM observations of the resin-enamel interfaces, the sectioned surfaces of one disk from an incisor (all 4 disks) was immersed in 0.1mmol/l HCl for 30 s, and another 4 disks were not treated with HCl. Another five bovine enamel surfaces were treated as mentioned above, however, without application of Heliobond and composite resin, for SEM observations. Factorial design two-way ANOVA followed by post hoc LSD was used to statistically analyze the data.Results:Compared with the control, the acid-etched enamel primed with PAEs significantly increased theμTBS (P<0.01). However, MDP performed much better than AquaPrime and Xeno V (P<0.01). The latter two did not show any significant difference (P>0.05). The SEM findings revealed the different etching patterns caused by acid etching and PAEs.Conclusion:The chemical bonding/coating of PAEs at the enamel-resin interfaces could significantly increase the enamel bond strengths. However, it depends on the individual PAEs used.