Drilling Performances Of Cortical Bone And Design Of Reconfigurable Dental Drilling Guide

Implant denture can significantly improve the patient's masticatory capacity,and its retention and stability are much better than the traditional denture.Therefore,it has become the first choice by more and more patients.The first step of implant prosthesis is to prepare a cavity in the alveolar bone.However,chip clogging is one of the fundamental issues faced by the dentists during the drilling of cortical bone.The chip clogging can lead to significant increase in temperature,thrust force and torque,and can even cause the drill bit to break.To increase the success of implant denture and provide guidance for the dentists,it is therefore significant to explore the drilling mechanism of cortical bone and related techniques.However,the existing force model cannot effectively relate the chip clogging with the cutting parameters.In addition,dental surgical drilling guide is widely used for more accurate position of implant to obtain the desired outcome.Nevertheless,there are still some problems in the drilling guide,such as,the high cost and the long production period.Therefore,it is theoretically significant and clinically valuable to investigate the drilling performances of cortical bone and reconfigurable dental drilling guide.In order to solve the above problems,the simplified Johnson-Cook(J-C)constitutive model of cortical bone based on the automated ball indentation(ABI)technique and one-dimensional stress wave theory was established,and the drilling performances of cortical bone was investigated using experimental and numerical modeling methods.On this basis,the chip-evacuation force modeling was developed,and the critical depth of chip clogging was predicted.Finally,a reconfigurable drilling guide was proposed,which comprises drilling sleeves and a personalized substrate.The main researches are presented below.(1)The quasi-static and dymamic mechanical property parameters of the simplified J-C material model for the cortical bone were calibrated based on the ABI technique and one-dimensional stress wave theory.First,the area ratios of the microstructures were calculated through the graphics processing method.On this basis,the variation trend of the area ratio was explored along the longitudinal direction of the tibia.Secondly,ABI tests were performed to determine the micro-mechanical properties of the cortical bone and the effects of indenter size on the micro-mechanical properties at room temperature.The indentation morphology were examined with a scanning electron microscope(SEM).Thirdly,based on the graphics processing method and mixture rule,the mathematic model of the macroscopic mechanical property for the cortical bone was established.Afterwards,the quasi-static mechanical property parameters of the J-C model were calculated.Finally,the dynamic mechanical properties under high strain rate were examined according to the one-dimensional stress wave theory,and the parameters of the simplified J-C model were obtained.The results showed that the effects of indenter size on the bone strength were significant,and the bone strength calculated based on the ABI tests was much higher for the indenter with a smaller diameter.The main indentation defects are microcracks and material subsidence.Combining ABI technique and one-dimensional stress wave theory proved to be an effective tool to obtaining the parameters of the J-C model for the cortical bone.(2)Continuous and step-by-step drilling processes of the cortical bone were conducted to investigate the drilling performances based on the combination of numerical modeling and experimental analysis.First,by using the simplified J-C constitutive model,a three-dimensional(3D)finite element(FE)modeling for cortical bone drilling was developed based on the ABAQUS software,and a series of drilling tests was conducted.Secondly,the thrust force and torque experienced during bone drilling were examined based on the combination of finite element modeling and experimental methods.The experimental results showed a significant increase in the thrust force and torque owing to the chip clogging during the continuous drilling process while this increase was not observed in the simulations.Therefore,the FE model was not suitable for the simulation of continuous drilling of cortical bone.Conversely,the thrust force and torque during the step-by-step drilling process varied in a stable manner,and significant increase in the drilling force was not found in this drilling process.Additionally,the numerical results of the step-by-step drilling process were demonstrated to be consistent with the experimental ones.It can be concluded that the developed simulation model can be used to reflect the variation of the thrust force and torque during the step-by-step drilling process with high accuracy.The chip clogging can be reduced by the combination of higher rotational speed,lower feed rate and step-by-step drilling method,therefore,reduced drilling force and improved hole quality can be obtained under this drilling condition.(3)A force model for predicting the chip-evacuation force experienced during the drilling of cortical bone was developed based on the drill geometry.The force model was then used to estimate the critical depth of chip clogging.First,the chip-evacuation force model with two parameters was developed based on the formation mechanism of chip clogging.The parameters of the force model were obtained by using a nonlinear least-squares fit via a set of calibration tests.Secondly,the parameters of the force model were modeled as functions of drilling parameters through nonlinear-regression analysis.The importance of drilling parameters on the parameters of the force model was investigated via analysis of variance.Subsequently,the validity of the force model was analyzed by experimental results.Thirdly,based on the gradient of the chip-evacuation force,the critical depth of chip clogging was predicted.The coefficients of the prediction model of critical depth were then determined through nonlinear-regression analysis,and the prediction accuracy was assessed by the validation tests.Finally,the effects of drilling parameters on the chip-evacuation force and chip clogging were explored.The developed chip-evacuation force model proved to be an effective tool for predicting the chip-evacuation force,and the critical depth of chip clogging could be estimated accurately with a relative error less than 10%.The spindle speed and the feed both had significant effects on the chip-evacuation force and chip clogging.The prediction model of critical depth could provide a better approach to finding how a pecking cycle can be implemented,and then,it can assist the dentists in selecting drilling conditions.(4)Based on serialized and standardized drilling sleeves and a personalized substrate,a novel dental reconfigurable drilling guide is proposed,which is beneficial to ensure the accuracy of implant insertion.The drilling sleeves are installed in the substrate through transition fit and can be easily disassembled.First,the 3D model of mandible was reconstructed based on the CBCT data.Secondly,according to the implant planning from the dentist,the drilling sleeves were designed based on the diameter of special drills.The drilling sleeve was used in conjunction with the special drill.Thirdly,different substrates were designed through medical image processing software.Afterwards,the designed drilling sleeves and substrates were manufactured by means of computer numerical control machining and 3D printing,respectively.The reconfigurable drilling guide was formed by installing the serialized and standardized drilling sleeves in different substrates.Finally,the mandible solid models were fabricated through 3D printing,and the implant surgery were carried out in the mandible solid model after the drilling guide was worn on the corresponding model.The guide accuracy of the reconfigurable drilling guide can be analyzed by comparing the position and direction between the virtual and the real implants.The results were demonstrated that the drilling sleeve can be reused in different substrates for different surgical guides.Reusing the drilling sleeves economizes medical materials,and simultaneously achieves the prospective precision in implant placement.The works finished by this study are bebeficial to accurate calibration of the quasi-static mechanical property parameters of cortical bone.The predction model of the crtical depth for chip clogging and the reconfigurable drilling guide can not only be used to effectively control chip clogging during cortical bone drilling,but also satisfy the precision requirement in implant placement,and thus,the success rate of implant denture can be improved.Therefore,this research has important theoretical significance and clinical application value.