The Experimental Study On Dentin Bonding Interface With Different Treatments

Objectives: The purpose of this study was to investigate and compare the thickness of hybrid layer, the depth of resin tag after acid etching and laser ablation under different conditions, and then explore the mechanism and optimum process to determine the best condition for application in clinical treatments.Methods: 45 recently extracted adolescent healthy permanent premolars were chosen, and their crowns were transversally sectioned to expose flat dentin surfaces absolutely. Then the samples were polished with silicon carbide paper of increasing grit. All the prepared 45 specimens were randomly devided into 9 groups from A to I. Groups A, B, C were treated with Nd: YAG laser as 0.75w, 15Hz; 1w, 15Hz; 1.25w, 15Hz respectively; Groups D, E, F were conditioned with 35% phosphoric acid for 5sec, 15sec and 30sec respectively, and the dentin surface was kept moist; Groups G, H, I were etched for 5sec, 15sec and 30sec respectively with 35% phosphoric acid, and the dentin surface was kept dry. After that, the specimens were immediately followed by application of the 1g/L Rhodamine B/Single Bond adhesive with a brush to dentin surface for 30 sec; photocured for 20 sec. A 2mm layer of composite was applied over the adhesive system layers. and photocured them for 40 sec. Subsequently, all the samples were split longitudinally through the restorations, and produced approximately 1mm width samples. Then polished the samples, observed and analysed the morphology changes of different groups via the laser scanning confocal microscope (LSCM).Results: Minimum hybridization formation was achieved when the dentin surfaces were conditioned with 35% phosphoric acid and then were kept dry. Which were only about 8μm. After treated with 1.25w, 15Hz Nd: YAG laser, the thickness of hybrid layer was about 31μm, four times of that in groups with dry bonding. When the dentin surfaces were conditioned with 35% phosphoric acid and then kept moist, the maximum hybridization about 43μm formation was achieved. There were significant differences among the 3 groups (P<0.05).There were no clear resin tags in dentinal tubules after conditioned with Nd: YAG laser.But all of the samples conditioned with 35% phosphoric acid could achieve resin tags traversing from the resin layer to the undemineralized dentin below, and the length of the resin tags were about 78～79μm when the dentin surfaces were kept moist, which were twice of that in the groups treated with dry bonding.Conclusions:1. The bonding system can infiltrate well into dentin bonding interface to achieve a quite ideal hybrid layer and resin tags in the groups treated with wet bonding.2. In the groups treated with dry bonding, only a little shorter resin tags and thinner hybrid layer can be observed, which demonstrates that dry bonding can not serve as an available method at dentin adhesion.3. Although pulse Nd: YAG laser can improve the efficiency of the dentin interface bonding mechanism, it seems not to be an approach on the efficiency of wet bonding.4. The pulse Nd: YAG laser can seal the dentin tuble efficiently, Which can be used to treat hypersensitive teeth and decrease the microleakage.