CBCT Measurement And Analysis Of The Position Relationship Of Mandibular Impacted Third Molar

Aim: The purpose of this topic is to classify the impacted third molar(IMTM)under three-dimensional cone beam computed tomography(CBCT),measure the relationship between IMTM and surrounding tissues,try to quantify the existing classification and propose a new classification,and provide some help for clinical extraction of IMTM.Methods: A retrospective study was carried out on the patients who had undergone IMTM surgery and had examination in Changsha Stomatological Hospital from January 2018 to December 2022.IMTM was classified and counted according to Pell-Gregory classification and Winter classification,The horizontal distance(Proximal Distance,PD)between the center of the second molar’s distal plane tangent and the seco nd molar’s distal plane tangent and the mandibular ascending branch(Distal Distance,DD)were measured under,and the buccal lingual bone wall thickness at the midpoint of the IMTM’s crown,the midpoint of the enamel bone boundary and the midpoint of the root were measured,and the statistical analysis was performed using SPSS22.0 software.With the work side of sewing needle as a reference,analyze the relationship between different bone wall thickness(1.2mm),proximal and distal distances and their diff erences and gender and lateral differences to provide some reference for clinical removal of IMTM.Results:(1)According to Pell-Gregory ’s classification of jaw plane,the high position accounted for 18.6%,the middle position accounted for 55.5%,and the low position accounted for 25.9%;(2)According to ascending branch classification,Class Ⅰ accounts for13.6%,Class Ⅱ accounts for 43.9%,and Class Ⅲ accounts for 42.5%;(3)According to Winter’s classification,the near-middle,far-middle,54.1%,19.0%,1.0%,and 4.2%,respectively,are impacted.(4)The average thickness of IMTM buccal bone wall is 5.00 ± 1.89 mm,with an average of about 4 working end diameters of high-speed turbine locomotive needles,and the thickness of lingual bone wall is 2.05 ± 0.82 mm,with an average of about 2 needle diameters,with an average of 8.54 ±1.90 mm,an average of about 7 needle diameters,6.88 ± 3.40 m,an average of about 6 needle diameters,with a difference of 1.65 ± 4.05 mm,and an average of about 1.5 needle diameters.(5)The IMTM buccal and lingual bone wall thickness,near-middle distance,far-middle distance,and the difference between the near-far distance and the far-middle distance were tested with independent samples,and the data showed that: 1.The buccal and lingual bone wall thickness,near-middle distance,far-middle distance,and the difference between the near-far distance and the far-middle distance were statistically different from the gender(P<0.05);2.The thickness of the buccal and lingual bone wall,the distance between the proximal and the distal,the distance between the proximal and the distal,and the difference between the two sides were not statistically different.(6)The IMTM near-far difference classification is at most Class Ⅳ,followed by Class V,Class Ⅲ,Class Ⅱ,Class Ⅰ,Class VI and Class Ⅶ.Conclusion:(1)In Pell-Gregory ’s jaw plane classification,the most is the middle,the second is the low impaction,and the least is the high impaction.According to Winter classification,the statistics show that the proportion of horizontal impaction is the highest,while the proportion of far,middle and buccal lingual impaction is the lowest.(2)The thickness of the buccal bone plate is far greater than that of the lingual bone plate,so the operation of bone removal and tooth separation should be carried out at the buccal side as far as possible.There is no significant difference in the thickness of the lingual bone plate at the middle,middle and low levels,but the thickness of the lingual bone wall at different points is different,and the lingual bone wall at the middle of the crown is the thinnest.(3)Side has no effect on IMTM’s proximal and distal distance,the difference between proximal and distal distance,the thickn ess of buccal bone wall and lingual bone wall,but there is difference between sex.(4)In IMTM near-far difference classification,the maximum is Class Ⅳ and the minimum is Class Ⅶ.