In-situ Experimental Study On The Failure Behavior Of Dentin Bonding System

The dentin-resin-zirconia bonding system is one of the most common restoration models in dental treatment.At present,most of the research on the repair of bonding systems only focuses on the improvement of the bonding strength of dentin,zirconia and other materials,and the improvement of the bonding performance of resin materials and adhesives.The clinically used repair methods usually combine the above two bonding methods,that is,resin materials are used as bonding transition bodies,and zirconia dentures are used to replace damaged teeth to build a tooth bonding system.Due to the multi-directional chewing force and the complexity of the oral medium environment,the failure mode of the dentin bonding system is complicated.In addition to the common failure modes such as adhesive cracking,dental materials and tooth structures themselves also have defects such as cracks and damage.Teeth diseases such as dental caries will also reduce the mechanical properties and bonding properties of the material,resulting in fracture or fatigue failure of the bonding system under complex load induction.This study takes the failure behavior and damage mechanism of the dentin bonding system as the research object,focusing on the fracture failure mechanism of the material based on the defect condition.Prefabricated indentation defects on the composite interface of dentin-resin and zirconia-resin with Vickers hardness tester,and built an in-situ mechanical test system integrating oral media environment and constant temperature control unit to carry out quasi-static and alternating simulation in oral environment Two types of experiments,and real-time observation of the crack evolution process in the indentation defect area with the aid of a microscope.The influence of material defects on the fracture failure of the bonding specimen was analyzed.The microscopic morphology of the bonding interface after crack propagation and cracking was analyzed with a scanning electron microscope to evaluate the cracking behavior and bonding performance of the interface.In the quasi-static compression experiment,the failure types of the bonding specimens are all failure of the adhesive on the zirconia-resin interface,and the bonding strength is 8.397±2.06(mean±SD)Mpa.Micro-zone defects can promote the fracture and damage of dental materials and dentin in the bonding system to a lesser extent,but this kind of damage effect has little effect under low load.It is confirmed that the significant gradient difference of the mechanical properties between the composite interface materials is the main reason for the low stress failure of the interface.The larger the gap between the mechanical properties of the materials,the lower the strength of the formed bonding surface.The bonding interface exhibits significant stage characteristics during load resistance,which is characterized by changes in cracking rate and adhesive cracking.In addition,it is found that the defects at the boundary position promote the interface cracking.The defects can promote the formation of a crack source at the bonding edge.Under the load,the crack source first induces cracking and gradually expands to both sides and inside,making the interface crack under low-stress.In the alternating load experiment,the load response of the dentin specimen showed significant segmentation characteristics.In the alternating load experiment with an amplitude of 60 N,the dentin bonding specimen did not fail in the week-long low-frequency experiment.During the experiment,the interface cracks and the morphology of the defect area evolved slowly,and they basically stagnate after stage ?.In the alternating load experiment with an amplitude of 90 N,all three materials were significantly damaged by the influence of prefabricated defects.In particular,the cracks on the surface of zirconia continued to expand and caused partial block shedding.The mode of crack expansion,chip formation and shedding is carried out,but the damage range is limited under the effect of simulated chewing force.The cracking width of the zirconia-resin interface continued to increase and cracked in a short experimental period,and the dentin-resin interface also cracked locally.When the amplitude load is much lower than the quasi-static load,it can achieve the same degree of material damage and interface cracking effect,indicating that the damage of the alternating load on the bonding specimen is significantly stronger than the quasi-static load,but the cracking mode and defect damage.There is no significant difference.It is proved once again that the difference between the Young's modulus and hardness of the composite interface,especially the zirconia-resin interface,is an important reason for the low stress failure of the interface.Compared with the effect of stress concentration effect,microcracks are more likely to induce fatigue crack nucleation and propagation under low stress under alternating load.