Polyamide-amine Containing Agarose Hydrogel Biomimetic Remineralization System Promoting Dentin Bonding

Objective:To investigate the biomimetic remineralization of demineralized dentin by establishing an agarose hydrogel remineralization system containing different concentrations of polyamide-amines and to examine the changes in dentin bond strength after biomimetic remineralization.Methods:Complete human third molars were selected and prepared into dentin discs with a thickness of 1 mm by precision cutting machine,and the dentin discs were polished and cleaned of surface debris by an automatic grinding machine and ultrasonic swabbing machine.The PAMAM agarose biomimetic remineralization system was prepared using Na F,Ca Cl2,Na2HPO4,and agarose powder with polyamide-amine（PAMAM）at concentrations of（3 mg/ml,5 mg/ml,and 10 mg/ml）,respectively.The prepared dentin discs were randomly divided into 5 groups.They were blank group A0 without acid etching;experimental group A1 with agarose remineralization system without PAMAM;and agarose remineralization system B1,B2,and B3 with 3 mg/ml,5 mg/ml,and 10 mg/ml PAMAM,respectively.20 dentin discs were prepared for each group.The dentin discs of the experimental group were acid etched by 35% phosphoric acid commonly used in clinical practice for 15 s and then rinsed for 30 s to prepare a demineralized dentin model.In the experimental group,the demineralized dentin underwent 10 cycles of mineralization and the properties of the products were examined by X-ray diffractometry and Fourier infrared spectroscopy,and the surface morphology of the remineralized dentin discs was observed by field emission scanning electron microscopy,and finally the Vickers microhardness of the samples was measured by Vickers hardness tester.Bonding to dentin samples using Filtek^TM Z350 XT nano-resin in a formal clinical procedure.Shear bond strength（SBS）tests were performed in a universal mechanical testing machine to examine the change in bond strength,and the fracture surfaces were observed and the microscopic morphology of the different fracture patterns was observed using field emission scanning electron microscopy.Results:1.It is known from experiments that the agarose biomimetic remineralization system containing the fourth generation of carboxy-terminal PAMAM can successfully remineralize demineralized dentin within 10 mineralization cycles.Compared with the agarose remineralization system without PAMAM,the remineralization system containing PAMAM accelerates the absorption of free calcium and phosphorus ions by the demineralized collagen fibrils,the effect of fixation and transformation,and strengthens the mechanical strength of demineralized dentin.2.The remineralized system containing the 5 mg/ml PAMAM group was found to be more remineralized than the 3 mg/ml PAMAM group by scanning electron microscopy,X-ray diffractometry,Fourier infrared spectroscopy and microhardness experiments.However,there was no statistical difference between the remineralization degree of the 5 mg/ml PAMAM group and the10 mg/ml PAMAM group.Therefore,in this experiment,the most suitable concentration of PAMAM in the remineralization solution was 5 mg/ml.3.Shear bond strength tests showed that the remineralized dentin can obtain higher bond strength and 5 mg/ml PAMAM remineralization solution is still the most suitable concentration.Conclusion:1.The agarose remineralization system containing PAMAM can achieve rapid biomimetic remineralization of demineralized dentin and restore the mechanical strength of dentin,and 5 mg/ml PAMAM is the most suitable concentration.2.Demineralized dentin showed better bond strength in resin bonding after treatment with this experimental remineralization system,and 5 mg/ml PAMAM was still the most suitable concentration.