| With the continuous development of the types and properties of dental machinable ceramics,lithium silicate ceramics are increasingly used in the field of prosthodontics because of their excellent bearing capacity,good aesthetic properties and stable chemical properties.However,the characteristics of high hardness and brittleness increase the difficulty of processing them into dental restorations.Due to the limitation of restoration size,ceramics are processed by grinding with dental bur in clinic.In order to improve the machining efficiency and quality of ceramic restoration,more research must be taken toward this grinding process.In recent years,ultrasonic assisted grinding technology has become an efficient means to process hard and brittle materials in industry,so it is necessary to introduce it into the field of ceramic restoration processing.In this paper,taking the dental grinding of lithium silicate ceramics as the research object,the influences of material properties and process parameters on grinding force and machining quality are analyzed by finite element simulation and experimental methods,and the optimization effect and action mechanism after introducing ultrasonic vibration are studied.The main research contents and conclusions are as follows:(1)After the dental grinding experiments of the primary crystallized lithium silicate ceramics,it was found that the lithium silicate ceramic with 10% zirconia was easier to grind than that without zirconia,but the ground surface quality was slightly worse.In addition,the physical performance test results reveal that the inhibition of zirconia on the growth of lithium silicate crystal is the main reason for this phenomenon.(2)In order to study the behavior of grinding lithium silicate ceramics by dental bur more intuitively,the corresponding finite element simulation model was established in Abaqus.The material removal process and the variation of grinding forces under microstate were obtained by simulation.Furthermore,the influences of process parameters such as cutting depth,feed rate and rotation rate on grinding forces were analyzed using this simulation model.The accuracy of the simulation results was verified by experiments,which shows that this simulation method is helpful to evaluate and predict the efficiency and quality of grinding ceramics by dental bur.(3)The optimization effect and influence mechanism of ultrasonic vibration on dental grinding of the lithium silicate ceramic were studied by experiment and simulation.The results show that the introduction of axial ultrasonic vibration can effectively reduce the grinding forces,ground surface roughness and edge damage.In addition,the influence of cutting depth on ultrasonic optimization is the largest,followed by rotation rate and feed rate.Therefore,the ultrasonic assisted grinding method can further increase the cutting depth to shorten the machining time while improving the machining quality of lithium silicate ceramic restoration. |
