The Effect Of Coating Time On Bonding Strength Of Different Adhesive Systems To Dentin

Objective: The aim of this study was to evaluate the effects of different coating time of three dental adhesive systems (Prime Bond NT, XenoIII,XenoV) on the microtensile bond strength (μTBS) to dentin, then optimize the process of clinic application and explore the mechanism.Methods: 65 noncarious human third molars from patients 18-30 years old were sectioned to absolutely expose flat dentin surface. All teeth were randomly separated into 13 experimental groups (n=5), group NT1～NT4, group XIII 1～XIII4, group XV1～XV4, and the control group C. Group NT1～4 were applied Prime Bond NT according to the manufacturer's instructions, coated one, two, three, four times respectively. Group XIII1～XIII4 was applied XenoIII and group XV1～XV4 was applied XenoV, applied one, two, three, four coats of adhesive respectively. Group C was applied no adhesive. Then 4mm thickness of composite (Ceram·X) was built up on it. After stored in physiological saline, the teeth were sectioned to obtain approximately 1mm×1mm beams for testing. 20 beams were prepared for each subgroup without microcrack. TheμTBS values of all specimens were tested, and fracturemodes were then determined using a stereomicroscope.Results:1. When applied Prime Bond NT, the meanμTBS values (in MPa) of four applied coats was significantly lower (p<0.05) than one, two, three applied coats, while there were no statistically significant differences (p>0.05) between them.2. When applied XenoIII ,the meanμTBS values (in MPa) of one and four applied coats was significantly lower (P<0.05) than two and three applied coats , while there were no statistically significant differences(P>0.05) between one and four, two and three applied coats3. When applied XenoV, the meanμTBS values (in MPa) of one and four applied coats was significantly lower (P<0.05) than coated two and three applied coats , while there were no statistically significant differences(P>0.05) between one and four, two and three applied coats.4. The maximum meanμTBS values (in MPa) of Prime Bond NT was 30MPa, significantly higher (p<0.05) than those of XenoIII and XenoV, while the maximum meanμTBS values (in MPa) of XenoIII was 22MPa and the maximum meanμTBS values (in MPa) of XenoV was 20MPa. There were no statistically significant differences between XenoIII and XenoV.5. Most of fracture modes were mixed failure. There was nosignificant difference among three fracture modes.Conclusion:1. The three dental adhesive systems (Prime Bond NT, XenoIII andXenoV) could offer effective bonding strengths to dentin. 2. Applied one coat of Prime Bond NT could get the maximum bonding strengths to dentin, while XenoIII and XenoV should be applied two coats. Addition of applied four coats of the three adhesives was found to decrease bonding strength to dentin.