Studies On The Bonding Properties Between Composite Resin And Dentin And Related Testing Methods

With the development of dental composite resin and bonding technique, composite resin has been applied more and more widely in clinic. The clinical effectivity of composite resin restoration is closely related to its bonding properties, including bond strength and marginal adaptation. In spite of the great improvement of dental adhesives and the resultant bond strength to dental hard tissue, poor marginal adaptation caused by the polymerization shrinkage of composite resin has not been completely eliminated. Thus, recent studies have focused on the improvement of the bonding properties such as marginal adaptation between restoration and tooth hard tissue and how to evaluate the bonding properties of these materials more objectively and roundly.This study consists of three experiments:In the first experiment: Micro-tensile testing is the most common method of testing bond strength between restoration and tooth hard tissue, which can more truly reflect the bond strength of adhesive to dentin. However, in previous experiments, bonding specimens were tested in dry condition, which has given rise to the question about its s significance. The objective of this experiment was to compare the microtensile bond strength of dentin bonded specimens measured in wet or dry conditions and analysis the possible reasons for the differences, and to provide experimental evidence for the standardization of the testing procedure. Methods: Six groups of conventional micro-tensile specimens (iBond, Adper Prompt, Clearfil SE Bond, Clearfil S3 Bond, Prime & Bond NT, Contax) were prepared, and the specimens of each group were randomly divided into 4 subgroups (moist, dry for 2h, 5h, 24h). All specimens were subjected to tensile bond strength test and the fractured surfaces were observed under SEM and the data were statistically analyzed. Results: The dry subgroups of all adhesives (except for iBond) showed higher bond strengths than moist subgroup (P<0.05), however the failure models of both dry and wet subgroups showed no different, mostly being adhesive failure. Conclusion: microtensile bond strength of moist specimens in vitro was low but more objective and reliable to evaluate the authentic bond effect of adhesive systems in vivo; micro-tensile specimen in the testing process should be keep moist.In the second experiment: Dye penetration detection was widely used to evaluate the marginal adaptation of restorations, but in this method only the leakage on the sectioned surface was observed. Micro-CT is a three-dimensional imaging instrument. So the purpose of this study was to investigate the possibility of using micro-CT to detect the marginal leakage of a restoration and to evaluate its advantages and disadvantages. Methods: Conventional class V composite resin restorations were done in extracted third molars and stained with silver nitrate solution. Then all teeth were sectioned longitudinally through the restoration and the silver penetration depth along the margin of the restoration was measured under microscope and micro-CT respectively. The sameness of the results from the two methods was statistically analysed. Some three-dimensional index of the leakage such as shape, depth, area and volume were detected using micro-CT. Results: (1) The silver penetration depths measured by the two methods were highly correlated and showed no significant difference by paired t test (r=1, P> 0.05); (2) In conventional microleakage method, the position of sectioning showed a significant influence on the results of leakage, presenting different leakage depths in different cut positions. Conclusions: Micro-CT can not only accurately demonstrate the three-dimensional shape of a microleakage, but also provide a qualitative and quantitative detection of the microleakage.In the third experiment: In an attempt to improve the marginal adaptation of restoration, many efforts have been made in the modification of adhesive restorative materials and clinical operations. In spite of this, the microleakage is still a problem in clinic. Objective: Using rebonding surface sealing technique to evaluate the immediate and long-term marginal sealing ability of using dental adhesives as surface sealants of bonding interface. Methods: Conventional class V composite resin restorations were done in extracted third molars and divided into two groups, one group being subjected to sealing with different dental adhesives (iBond, Clearfil SE Bond, Clearfil S3 Bond, Prime & Bond NT, Contax), another no any surface. Then the microleakage was detected immediately or after 5000 thermal cyclings in conventional method. Results: Five dental adhesives showed favorable immediate results in terms of sealing of bonded interface gap compared with the control group. After thermal cycling, the results of sealing treatment and control treatment showed no significant difference, both showing severe microleakage. Conclusions: The marginal leakage of a restoration can be reduced immediately after surface sealing with dental adhesive. However, these sealing showed poor resistance to thermal cycling.