Study On Photopolymerizable And Moisture-curable Polyurethanes For Dental Adhesive Applications

With the development of the minimally invasive concept of the stomatology,the photopolymerizable composite resin materials and the technology of adhesive have been widely used in the treatment of tooth defects.At present,the phenomenon of polymerization shrinkage in the composite resin due to light is still unavoidable,and there is always microleakage or nanoleakage at the bonding interface between the resin and the tooth structure.This defect of structure becomes a channel for the invasion of waters and microorganisms in the oral cavity,leading to degradation and destruction of the bonding interface,inducing complications such as secondary caries,and finally failure to repair.In fact,even if the polymerization volumetric shrinkage is close to 0%,marginal leakage would emerge after restorative materials had undergone a series of expansions and contractions from thermal and mechanical changes in the oral environment.On the other hand,as the key to the connection between the composite resin and the tooth structure,the adhesive plays a vital role for the more durable repaired in the composite resin.In order to improve the permeability of the adhesive to the dentinal tubules,a lot of hydrophilic monomers are often added to the dentin adhesive,which has certain water absorption after curing.The water absorption process is further aggravated,the integrity of the molecular chain of the binder is destroyed,and the hydrolysis is gradually.Studies have shown that the aging and degradation of the adhesive can also cause microleakage,which causes the cracking of composite resin.Therefore,how to reduce the polymerization shrinkage and water absorption of methacrylate composite resin and improve the durability of dentin-resin bonding is of great significance.The purpose of this paper is to study the prospect of polyurethane materials in resin-dentin bonding,and to prepare a photopolymerizable and moisture-curable polyurethanes for dental adhesive.The preventive effect on microleakage and the bonding strength of this polyurethane adhesive were examined,and the possible factors were clarified to provide new ideas and experimental basis for the improvement of dentin bonding materials,and the development of new materials.In the second chapter of this paper,four photopolymerizable polyurethane(PU)adhesives were prepared by adjusting the ratio of polyester and polyether polyol according to the solution polymerization method,and the structure of the synthesized product was characterized.The water absorption and dissolution values,mechanical properties and thermal stability of the materials were test.The optimum ratio of polyester and polyether polyols was selected by the comprehensive evaluation of various properties.The cytotoxicity in vitro test and microleakage prevention effect of the PU adhesive prepared at this ratio was initially evaluated.The results show that the tensile strength of PU adhesive can reach 18.46 MPa,and the maximum elongation at break is 51.2%.The water absorption and dissolution values of each group were significantly lower than the commercial control group.The initial degradation temperatures taken at 5% of mass loss can meet the requirements of oral temperature environment.The results of MTT assay test showed that the toxicity of PU adhesive on human dental pulp cells was not significantly different from the commercial control group.The microleakage test results show that the PU adhesive has better prevention effect on microleakage than the commercial control group.In the third chapter,according to the optimal ratio of the best polyester and polyether polyols selected in chapter 2,four kinds of photopolymerizable and moisture-curable(C=C and NCO)PU adhesive were prepared by adding different amounts of 2-Hydroxyethyl methacrylate(HEMA).The degree of double bond conversion,wettability and mechanical properties of the material were evaluated,and the adhesive with the best ratio of photopolymerizable and moisture-curable group was obtained.In addition,the properties of this C=C/NCO-PU adhesive in dentin bonding were evaluated.Finally,the vitro cytotoxicity of the adhesive is tested.The results showed that,the double bond conversion rate of the C=C/NCO-PU adhesive increased first and then stabilized with the increase of HEMA amount;The tensile strength and elongation at break of each group after 3 days of stored in water were increased.The tensile strength of the PU2 group were increased most among them;Microtensile strength of the C=C/NCO-PU adhesive after 30 days of stored in water is higher than the initial tensile strength;the maximum length of the resin tag can be up to 40 ?m by scanning electron microscopy;the microleakage test results showed that the C=C/NCO-PU adhesive has better prevention effect against microleakage than the commercial control group;The results of cytotoxicity in vitro test showed the C=C/NCO-PU adhesive has mild cytotoxicity.In the fourth chapter of the paper,the traditional acrylic resin--Bis-phenloA diglycidyl methacrylate(Bis-GMA)with good mechanical properties was introduced in order to improve the tensile strength of PU adhesives.A polyurethane/acrylate(Bis/PU)adhesive was prepared and the physicochemical properties,mechanical properties,bonding properties to dentin,biocompatibility and biological safety of the adhesive were comprehensively evaluated.The results showed that,the tensile strength is significantly improved when the mass ratio of Bis-GMA added is 10%.The results of microtensile test showed that the bonding strength to dentin of the Bis/PU adhesive is better than that of PU adhesive,and has better prevention effect against microleakage than the commercial control group.The results of biocompatibility test show that Bis/PU adhesive has mild toxicity,and has no short-term systemic toxicity and local tissue stimulation.In summary,the main three chapters content of this paper are continuous and progressive.The performance characteristics of polyurethane materials and their role in the dentin-resin bonding were evaluated according to the exploration of the proportion of reactants in polyurethane synthesis and the regulation of the photopolymerizable and moisture-curable group and the adding of traditional acrylic resin.The research of PU adhesives provided a new idea for improving the long-term stability of dentin bonding,and laid a solid foundation for the further development of new composite resins and dentin adhesives.