Study On The Thickness And Morphology Of Lingual Bone Of Impacted Mandibular Third Molar Based On CBCT And Simplant 3D Reconstruction

Objective:In the extraction of impacted mandibular third molar(M3M),the injury of lingual nerve and lingual tissue often leads to the complications of ipsilateral lingual numbness,bleeding,root displacement and adjacent tissue injury.As the only hard tissue barrier between M3 M and lingual soft tissue,M3 M lingual bone plays an important role in reducing the injury of uvula lingual tissue.In clinical practice,CBCT is often used to analyze the anatomical structure of M3 M lingual bone,so as to assess the risk of intraoperative injury.However,the measurement accuracy of lingual bone by CBCT is not high and the error is relatively large.Therefore,in this study,Cone beam CT(CBCT)and Simplant software were used.The previous large sample database was collated and analyzed,the thickness of lingual bone was quantitatively measured,the potential relationship between M3 M and lingual bone was explored,and the morphology of lingual bone was reconstructed in 3D to establish a visual 3D reconstruction model of lingual bone,which could provide a reference for the formulation of surgical plan for clinicians.Method: The imaging data of 200 patients meeting the experimental standards from the CBCT database of the imaging department of Hefei Stomatology Hospital during2020-2022 were collected,and the data scanned by CBCT were saved in DICOM format and imported into Simplant Pro11.4 software.In Simplant software,the lingual bone of impacted mandibular third molar was observed from three sections: Axial,Panoramic and Cross Sectional,and the thickness of lingual bone at the central crown site,the midpoint of the root and the apical location was measured with the built-in measuring ruler of Simplant.The possible related factors of impacted tooth inclination type,impacted tooth depth and lingual bone morphology were recorded.The Simplangt software was used to conduct three-dimensional reconstruction of lingual bone of different shapes,and the recorded data were statistically analyzed using SPSS22.0statistical software.The rank sum test was used to compare the thickness of lingual bone in the central crown area,the middle root point and the apical area of low impacted teeth.Logistic regression was used to analyze the correlation factors of lingual bone thickness.The result variable was whether the thickness of lingual bone was "high risk type".P < 0.05 indicates a significant correlation.Results:(1)The thickness of lingual bone at the midpoint of the root was(1.35±1.20)mm,and the thickness of lingual bone at the apical point of the root was(2.02±1.83)mm.However,when the impacted teeth were lower impacted,the thickness of lingual bone at the central crown site was(1.89±1.36)mm.(2)There were 101 cases(50.5%)of high risk type of lingual bone at the center of the root,and 90 cases(45%)of high risk type of bone at the root tip.(3)When the impacted teeth had multiple roots,the thickness of lingual bone at the midpoint of root was significantly thinner(P < 0.05).(4)In terms of inclination Angle of impacted teeth,when the impacted teeth were meso-impacted and horizontally impacted,the thickness of lingual bone at the root center and apex decreased significantly(P < 0.05).(5)After classification by the relationship between impacted mandibular third molar and mandibular rami,lingual bone thickness at different measurement sites decreased significantly when impacted teeth were class Ⅲ,and lingual bone thickness at root tip decreased significantly only when impacted teeth were class Ⅱ(P < 0.05).Conclusion: In the impacted mandibular third molar,the thickness of lingual bone at the midpoint of the root was significantly lower than that at the root tip,and the perforation and fracture of lingual bone were more likely.At the same time,root number,impacted tooth inclination Angle,impacted tooth type and other related factors all showed different degrees of influence on lingual bone thickness.In the extraction of impacted teeth,the above factors should be considered,and the injury of lingual nerve,lingual bone plate and surrounding soft tissue should be vigilant.