| Tooth is one of the most important organs of human beings.Dental pulp disease is a common dental disease caused by bacterial infection,external stimulation,trauma or immune response and so on.Root canal therapy,as the most effective and commonly used treatment of dental pulp disease and periapical disease,can effectively maintain the integrity of teeth and avoid bone loss or insufficient stability of dentures after tooth extraction.At present,it is widely used in clinical treatment.As the first step of root canal therapy,root canal preparation(RCP),the excessive force and temperature acting on the root canal during preparation will lead to the intraoperative injury of tooth root canal or the failure of surgical instruments,which will affect the treatment effect.In this paper,the cutting force and temperature in the process of root canal preparation are explored,and an in vitro root canal preparation experimental test platform is built.Taking the Nickel-Titanium(Ni-Ti)file as the research object,through the cutting theoretical analysis and heat transfer,the influence of file diameter,feed rate and root canal shape on force and temperature are revealed,which provides suggestions for the optimization of surgical parameters and the selection of file in root canal preparation.The specific work of this paper is as follows:The in vitro experimental platform of root canal preparation was established,and the influencing law and mechanism of different factors in the process of root canal preparation were analyzed.An in vitro substitution model of tooth root canal was established by using bovine anterior tibia;Based on Taguchi experimental method,a four factor three-level orthogonal experiment was designed to analyze the influence of single factor and multi factor interaction of file diameter,root canal curvature,feed rate and root canal width on cutting force and torque.The results show that root canal width is an important factor affecting cutting force,and root canal width and feed rate are important factors affecting torque.Among them,the increase of root canal width,feed speed,root canal curvature and the decrease of file diameter will lead to the decrease of valley cutting force and the increase of peak cutting force and torque.Based on the infinitesimal method and oblique cutting theory,a semi analytical model of cutting force using Ni-Ti file in root canal preparation was established.Due to the complex calculation of instantaneous cutting thickness caused by the changing posture of Ni-Ti file,a cutting simulation algorithm based on image Boolean Operation was proposed,which was aiming to obtain the variation of cutting thickness in the root canal preparation process.Then,the in vitro experiments of single factor were designed to verify the effectiveness of the cutting force model.Based on the model,the effects of different root canal curvature and preparation methods on the preparation effect were analyzed.Based on the thermal conduction theory,the temperature prediction model using Ni-Ti files for root canal preparation was established.Based on the First Law of Thermodynamics,taking the dentin cutting process using Ni-Ti files as the research object,considering the heat conduction,heat convection and heat radiation exchange between the root canal system and the outside environment,the governing equations of heat balance,boundary and initial conditions of Ni-Ti files and root canals were proposed.The effectiveness of the temperature model was verified by designing the single factor in vitro root canal preparation experiments.Based on the model,the effects of feed rate,spindle speed and cutting depth on the temperature distribution were explored.The proposed model can effectively be used to avoid the thermal damage on dentin,and provide guidance for the selection of surgical parameters for dentists. |
