Research On The Anatomical Position Of Impacted Mandibular Third Molars At Different Ages

Objectives:In this study,the Buccal bone wall distance(BD),Lingual bone wall distance(LD)and Inferior alveolar nerve canal distance(INACD)of the third molars in different age groups were measured.To explore the relatively low risk tooth extraction age group and to provide anatomical guidance for clinical practice.Methods:1.Patients with completely impacted mandibular third molars collected from the department of Oral and Maxillofacial Surgery,Stomatological Hospital of Kunming Medical University from September 2018 to September 2019.They were scanned by NewTom CBCT(Quantitative Radiology s.r.1.Verona,Italy)in the department of Imaging,Stomatological Hospital of Kunming Medical University.The scanning parameters:110 kV,5?10 mA,voxel(The thickness of the scanning)0.3mm,exposure time 3.6s,scanning range from the top of the head to hyoid bone,and the CBCT data of patients were collected.2.From CBCT data using built-in software for DICOM data set,the data in DICOM format import SimplantPro 17.01 software,the patients are divided into five groups according to age(before the age of 20,20 to 29,30 to 39,40 to 49,50 years of age or older),using the software of image reconstruction of functional reconstruction of mandible and the image of mandibular third molar area,check the image,select the three landmark,dental crowns midpoint,pulp chamber vertex and root tip point measuring buccal bone wall distance,lingual bone wall distance,distance between tooth(root)and Inferior alveolar nerve,and clearly with fang root number(because the tooth germ root has not fully developed,the number of tooth roots was not included in the statistics.3.Inclusion criteria:(1)The third molars belong to complete bone impacted tooth.(2)CBCT images are clear and measurable.Exclusion criteria:(1)image quality cannot be used to measure cases.(2)mandibular third molars have fractures,cysts,tumors and other lesions.4.The SPSS 23.0 statistical software was used for database construction and statistical analysis.The measurement data were expressed as mean±standard deviation((?)),and the count was expressed as the number of cases(n).Pearson Correlation analysis and Significance(double-tail)analysis were used for the correlation analysis among the measurement indexes,and P<0.05 showed a significant correlation and P<0.01 showed a very significant correlation.Results:1.A total of 187 patients were included in this study,including 287 totally impacted mandibular third molars.According to the statistical results,there was no statistically significant difference between BD,LD,INACD and gender,left and right,tooth root numbers(P>0.05).2.According to the age group,the BD is the lowest in the group before 20 years old,and the difference is statistically significant(P<0.05),while the difference in other age groups is not statistically significant(P>0.05).The LD is the biggest in the group before 20 years old,and the difference was statistically significant(P<0.05),while the difference in LD among other age groups was not statistically significant(P>0.05).The INACD is the lowest in the 20-30 year old group,with a statistically significant difference(P<0.05)and the largest difference compared with people over 50 years old,while the other age groups had no statistically significant difference in INACD(P>0.05).3.The Correlation(Pearson correlation)and Significance(double-tailed)of BD,LD and INACD with age,number of root,left and right,and gender of the patients were analyzed.Age and the number of root were significantly correlated with the change of BD(P<0.01).Moreover,the number of double-root teeth increased faster.Age was significantly correlated with INACD change(P<0.05),and the Pearson coefficient was 0.135,indicating that the value of INACD also increased with age,but the slope was lower.Age and the number of roots were significantly correlated with LD(P<0.01),and Pearson correlation coefficients were-0.354 and-0.397.This indicates that LD is decreasing with age,and single tooth is decreasing faster(because the tooth germ root is not counted,and there are some gaps in single and double root data,the accuracy of this result will decrease to some extent).Conclusions:1.Before 20 years old,the thickness of lingual bone wall was the largest,in other words,the distance from the lingual nerve was relatively large,so from the perspective of anatomical distance,the risk of lingual nerve injury was relatively small when the tooth embryo was extracted.2.The group of 20-29 year old patients with totally impacted third molar,INACD is the smallest compared with other age groups.When the impacted third molar is extracted in this age group,extra care should be taken for the nerve injury of lower alveolar.3.Generally speaking,the BD is increases with age,and the increase range of the double-root teeth is faster.The INACD is increased with age,but at a smaller rate(with a lower slope).The LD is decreased with age,and the decrease of single tooth is faster.