Remineralization Of Demineralized Dentin By A Universal Adhesive Doped With Amorphous Calcium Phosphate Assisted By Biomimetic Analogs

Objective:The purpose of this experiment is to add amorphous calcium phosphate（ACP）nanoparticles into a universal adhesive,and to simulate the clinical application of the adhesive with the aid of the biomimetic analogs polyacrylic acid（PAA）and sodium trimetaphosphate（STMP）.The universal adhesive was applied in etch-and-rinse mode to evaluate the performance of the adhesive after the addition of ACP and the stability of dentin bonding.The dentin remineralized after adhesive application was examined to determine the remineralization effect of demineralized dentin.In order to explore the most suitable ACP concentration to remineralize demineralized dentin without affecting the performance of the universal adhesive itself.Methods:128 human caries-free molars were stored in 0.5% chloramine T at 4°C for no more than three months.A slow-speed diamond saw was used to remove the crown enamel and expose the dentin under water-cooled conditions in the vertical direction of the long axis of the tooth.64 teeth were randomly selected and a 1 mm-thick disk of dentin was cut out along the enamel and cementum boundary above the long axis with the diamond saw,and the surrounding enamel was removed.Single bond universal（SBU）was selected as the control group.A universal adhesive containing ACP and a pretreatment agent containing biomimetic analogs（PAA and STMP）were prepared and the experiment was divided into four groups:（Group 1: control group;Group 2: 5% ACP group;Group 3: 10% ACP group;Group 4: 15% ACP group）.Testing whether there is a significant difference between the degree of conversion（DC）of the adhesive and the control group after the addition of ACP,and then the experimental samples were prepared.The dentin samples were acid etched using 37% phosphoric acid gel for 15 s,rinsed for more than 15 s to ensure that the phosphoric acid gel was rinsed off and blown dry.After application of pretreatment agent for 60 s,excess liquid was blotted away with filter paper,followed by application of adhesive for 20 s,blowing for 5 s,and light curing for 10 s.After accumulation of resin on the upper part of the dentin samples,half of the samples were used for immediate microtensile strength（μTBS）assessment,and the other half were cycled in a hot and cold cycle machine for 10000 cycles.part of the immediate and aged dentin samples were cut into rod-shaped microtensile specimens to test the μTBS,and the other Two sections of each tooth were selected close to the center of the tooth,and the immediate and aging nanoleakage was evaluated using Scanning Electron Microscopy.Microtensile strength and nanoleakage results were obtained using two-way ANOVA results.Adhesives was applied to the dentin discs and cured according to the previous method and placed directly into the simulated body fluid for remineralization,and the remineralization status of demineralized dentin was assessed by Attenuated Total Reflection-Fourier Transform Infrared Spectroscopy,microhardness machine,and Scanning Electron Microscopy analysis.Results:1.The DC of 15%ACP group was significantly different from that of the control group（P< 0.05）,but there was no significant difference between the other groups and the control group;There was significant difference in the immediate and aging μTBS between the15%ACP group and the control group（P < 0.05）,while there was no significant difference in the immediate and aging μTBS between the other experimental groups and the control group;There was no significant difference between the 15%ACP group and the control group,except that the nanoleakage after aging was significantly different from that before aging and that after aging（P < 0.05）.2.All experimental groups showed different remineralization results,with the increase of ACP concentration and remineralization time,the better the remineralization effect,among which the remineralization effect of 10% ACP and 15% ACP groups was close to that of healthy dentin.Conclusion:Universal adhesive containing ACP in etch-and-rinse mode can remineralize demineralized dentin with the aid of biomimetic analogs.According to the experimental results,without affecting the bonding performance of the universal adhesive SBU itself,the optimal concentration of ACP added is about 10%,and too much ACP concentration will affect the bonding strength of the adhesive and reduce the stability of the bonding interface.