Biomimetic Mineralized Hydrophilic Polyurethane Dentin Primers For The Induction Of Dentinal Tubule Occlusion

Objective:This experiment aimed to synthesize a biomimetic mineralized hydrophilic polyurethane dentin primer.We investigated the effects of its composition content and mineralization time on sealing dentinal tubules and inducing mineralization.Methods:We synthesized hydrophilic polyurethane by solution polymerization method using isophorone diisocyanate,polytetrahydrofuran ether diol 2000,and hydroxyethyl methacrylate as the main raw materials.Then we characterized it by Fourier infrared spectroscopy（FTIR）.Biomimetic mineralized hydrophilic polyurethane dentin primers（DDDEEKC-PU）were formulated with different concentrations of peptide DDDEEKC by incorporating hydrophilic polyurethane with different peptide DDDEEKC.We measured the degree of conversion of each group.Subsequently,each group of primers was applied to the acid-etched dentin disc surfaces and mineralized in simulated human fluids for 7,14,and 28 days,respectively.The ability of each group to induce mineralization and seal dentinal tubules was evaluated with the aid of X-ray diffraction,field emission scanning electron microscopy,Vickers hardness tester,and dentin permeability measurement devices.The results of degree of conversion were analyzed by One-way ANOVA.The results of Vickers hardness and dentin permeability were analyzed by Two-way ANOVA.Comparisons between the two groups were performed using Tukey-test,and the test significance level was α=0.05.Results:1.FTIR confirmed that hydrophilic PU has been synthesized.2.The degree of conversion of 0-PU,3-PU and 5-PU groups was similar to the commercial adhesive Single Bond Universal 2.But the rate of the 7-PU group was lower,about 48.47±3.82%.3.The results of dentin permeability showed that among the two factors,mineralization time（P<0.05）and DDDEEKC content（P<0.05）had an effect on the results,and there was also an interaction between them（P<0.05）.4.Field emission scanning electron microscopy of the dentin disc surface showed that the dentinal tubules were completely closed in the 5-PU and 7-PU groups after 14 days of mineralization.It was observed that after 28 days of mineralization,there was a large amount of lamellar mineralization fusing with each other on the surface of resin in the dentinal tubules of the 3-PU,5-PU and 7-PU groups.And in these groups,the gap between resin and tubules was filled completely.In the longitudinal section,new minerals appeared on the surface of the resin tag in the 5-PU and 7-PU groups,showing a "corn cob"-like morphology.But there was hydrolysis of the resin tag in the 7-PU group.5.After 7 days of mineralization,the changes of XRD peaks were not obvious in each group;after 14 and 28 days of mineralization,the characteristic peaks of hydroxyapatite appeared in each group,which confirmed the presence of nascent hydroxyapatite.And with the increase of peptide content,the value of each peak increased and the half-peak width decreased,indicating more crystalline formation and better crystal structure.6.Mineralization time（P<0.05）and DDDEEKC content（P<0.05）had significant effects on the microhardness of dentin surface,and there was an interaction between them（P<0.05）Conclusion:We have synthesized a hydrophilic biomimetic mineralized polyurethane primer,which can induce the formation of hydroxyapatite,occlude dentinal tubules and reduce dentin permeability.The mineralization effect of the 5-PU group is the best after 28 days of mineralization.