The Research Of Polyamidoamine Drimer And Pamam/n-HAP On The Biomimetic Remineralization Of Demineralized Dentinal Tubules

Objective:The first experiment:The aim of this experiment was to observe the biomineralization and dentinal tubules occlusion abilities of generation 3.5carboxyl-terminated polyamidoamine dendrimer at different concentrations and evaluate the acid resistance of the remineralized dentin with different concentrations.The second experiment: Polyamide-amine / nano-hydroxyapatite(PAMAM / n-HAP),which owning the characteristics of organic and inorganic materials,was synthesized and characterized,then we observed its blocking effect on dentinal tubules.Methods: The first experiment: A total of 40 demineralized dentin models were prepared from 40 extracted sound human third molars.They were randomly divided into 4 groups(A,B,C and D).These models were treated with different concentrations of 3.5 carboxyl modified polyamide(PAMAM-COOH),and then immersed in artificial saliva for remineralization for 14 days.The combination of PAMAM-COOH molecule and dentin wasdetected by Fourier transform infrared spectroscopy(FTIR).The micrograph of the dentinal tubules was observed by scanning electron microscopy(SEM).The second experiment: PAMAM/n-HAP was prepared by “Pramanik aqueous-based chemical method” and characterized by transmission electron microscopy(TEM)and Fourier transform infrared spectroscopy(FTIR).The demineralized dentin models were prepared and divided into 4 groups(A,B,C,D),which were treated with deionized water,PAMAM/n-HAP,n-HAP,then soaked in artificial saliva(A,B,C)and deionized water(D)for 7 days for remineralization.The restorative effects of dentin tubules were evaluated by scanning electron microscopy(SEM),then the mechanical properties of demineralized dentin model were observed by microscopic hardness tester.Results: The first experiment: The results of FTIR showed that the G3.5PAMAM-COOH could combine with demineralized dentin tightly,and the samples of high concentration of PAMAM-COOH showed stronger characteristic peak.The results of SEM showed that the application of PAMAM-COOH can partly induced new mineral crystal to close dentin tubule,however,these new mineral crystals could not close dentin tubule completely.No significant differences could be observed in different samples of various concentrations.The second experiment: The results of FTIR showed characteristic strong vibration peak of PAMAM-COOH at 1244 cm-1 and 1650 cm-1,meanwhile,TEM showed 10 nm thick low contrast surface coating layer of nano hydroxyapatite,confirming the successful synthesis of PAMAM/n-HAP.The results of SEM showed that after the application of PAMAM/n-HAP,the diameter of the dentinal tubules can be effectively reduced.Besides the empty dentinal tubules can be closed and filled,obtaining good sealing effects.Inaddition,there are significant differences between the experimental group treated with PAMAM/n-HAP and other control group in mechanical properties.The results show that the application of PAMAM/n-HAP nanocomposite biomaterials can restore the mechanical properties to a certain degree.Conclusions:1.G3.5 PAMAM-COOH can be adsorbed to the surface of n-HAP.2.G3.5PAMAM-COOH can induce the sediment deposition in the demineralized dentin tubules to a certain extent,but the crystal shape is irregular and the sealing effect is not ideal.The experimental results showed no obvious differences between the samples which treated with different concentrations of G3.5 PAMAM-COOH(1000ppm,5000 ppm,and10000ppm).3.As a new type of nano composite biomaterial,PAMAM/n-HAP can effectively seal dentinal tubules with ideal depth of sealing,suggesting that PAMAM/n-HAP may become a new type of desensitizing materials or additive in clinical application.4.PAMAM/n-HAP can restore its mechanical properties to a certain extent by closing demineralized dentin tubules obtaining a certain degree of hardness.