Finite Element Analysis Of 3D Printing Customized Titanium Plates For Mandibular Angle Fracture

[Background]Mandibular angle fracture is a common type of jaw fracture.The submandibular incision fully reveals the fracture section and the rigid internal fixation is a conventional surgical method.This method not only leaves scars on the face,but also easily damages the mandibular branch of the facial nerve.The intraoral approach to the surgical procedure with the cheeks reduces facial surgical scars,but the operation is complicated,and the operation time is long.In the 1970s,Champy proposed the theory of tension band.The method uses a single titanium plate to firm internal fixation along the outer oblique line of the mandible,which was completely adopted.Due to the application of intraoral incision facial scar was avoided and the facial appearance was acceptable.However,this method is regarded by many researchers as that it is only suitable for the mandibular angle fracture with favorable and mild displacement.For the mandibular fracture with unfavorable and severe displacement,fixation of lower mandibular margin was needed.In addition,it was also be found that the stability of the method is poor and leads to higher postoperative infections.Therefore,to expand the indication of tension band fixation and improve the stability of the fracture end of the titanium plate fixation need to be resolved.It is hypothesized to personalize the titanium plate by 3D printing.By using 3D printing,the parameters such as the thickness,width and length of the titanium plate are personalized,so that the titanium plate can increase the bone stability after the tension band fixation with sufficient strength.Furthermore,the bone outer surface which contact to the tension band is not flat,and the titanium plate is very difficult to be shaped.The tight fitting between the titanium plate and the bone surface affects the stability of the retention directly,and personalized titanium plate by 3D printing could achieve the tight fitting to the bone surface.Therefore,personalized titanium plate by 3D printing may expand the indications for tension band fixation surgery and is expected to solve the problem of instability after the fixing of tension band.[Objective]To analyze the stress distribution,stress and deformation of the mandibular and mandibular angle fractures under different occlusal conditions by using 3D printed personalized titanium plate to fix the mandibular angle fracture.It is sufficient to maintain the stability of the fracture and minimize the stress shielding rate.The suitable titanium plate size provides a reference for clinical treatment of mandibular angle fracture.[Methods]The DICOM format data of mandible collected by using CT scans was imported to MIMICS 3D modeling software to obtain the 3D reconstruction of the mandible.The same data was also introduced toreverse modeling software Geomagic Design X and Geomagic Studio,to complete mandibular solidification.After that the data was introduced to UG to design mandibular angle fracture with fracture fissure of 1 mm.A single small bone titanium plate was firmly fixed along the outer oblique line.According to the length of the fixed titanium plate,it is divided into two groups of 4 holes and 6 holes.According to the thickness of the titanium plate,it is divided into different groups with plate sickness of 0.2 mm,0.4 mm,0.6 mm,0.8 mm,1.0 mm,1.2 mm,1.4 mm,1.6 mm,1.8 mm and 2.0 mm group.There are 20 groups in total.According to the different healing time of fracture,it was divided into three different periods:fracture occurrence,fracture healing for 1 month and fracture healing for 3 months.According to the different occlusion,two cases of median occlusion and contralateral molar occlusion were simulated.They were introduced into the three-dimensional finite element analysis software Ansys Workbench to analyze the stress distribution and deformation of the mandibular and mandibular angle fractures,and calculate the stress shielding rate.Statistical analysis:The statistical software was used SPSS 21.0,and the measurement data was not satisfed the normality.Spearman grade correlation analysis was used to analyze the correlation between the two variables,and the difference was statistically significant according to the test level P<0.05.[Results]When the length,width,aperture,aperture spacing,bridge spacing,nail length and fracture healing time of titanium plate was the same,the maximum deformation value of the fractured layer became smaller and smaller with the increase of the thickness of the titanium plate,and the titanium plate of 1.0 mm thickness tends to be stable.When the length,width,thickness,aperture,aperture spacing,bridge spacing and nail length of titanium plate are the same,as the fracture healing progresses,the maximum deformation value of the fracture fault gradually decreases.When the length,width,aperture,aperture spacing,bridge spacing,nail length and fracture healing time of titanium plate are the same,with the increase of the thickness of the titanium plate,the stress value of the fractured layer is getting smaller and smaller,and the stress shielding rate of the titanium plate is getting larger and larger,and the stress shielding rate of the 0.2 mm thick titanium plate is the smallest.As the thickness of the titanium plate increases,the stress shielding rate increases gradually,and the stress shielding rate of the 2.0 mm thick titanium plate is the largest.When other conditions are the same,as the fracture healing progresses,the stress of the fracture fault gradually increases,and the stress shielding rate of the titanium plate gradually decreases.Statistical analysis showed that the maximum displacement was negatively correlated with the thickness,healing time and occlusion condition of titanium plate(P<0.05),but not with the length(P>0.05);the stress shielding rate was positively correlated with the thickness(P<0.05),and negatively correlated with the healing time(P>0.05).There was no significant correlation between stress shielding rate and occlusion condition and length(P>0.05).[Conclusion]The stability and stress shielding rate of 3D printing personalized titanium plate are related to the thickness of titanium plate and the time of fracture healing.The thinner the titanium plate is,the shorter the healing time is,the larger the maximum displacement is.The results show that the more unstable the titanium plate is,the more stable the maximum displacement is when the thickness of the titanium plate is 1.0 mm;On the premise that the aperture of titanium plate is 2.0 mm,the width is 4 mm,the spacing of holes is 6 mm and the spacing of bridges is 12 mm,the thicker the titanium plate is,the shorter the healing time is,and the greater the stress shielding rate is when the center occlusion occurs.When individually designed 3D printing titanium plate simulates mandibular angle fracture fixation,1.0 mm titanium plate can not only improve the bone stability after tension band fixation,but also minimize the stress shielding rate,which is expected to expand the indications of tension band fixation.