Comparative Study On The Dental Jaws Of The Tibetan And Han Population With Curved Tomography

Objective:Using panoramic X-rays to measure the R/C values and mandibular angle values of the permanent teeth of Tibetan and Han men and women of different genders,establish the reference values of the R/C and mandibular angles of Tibetan permanent teeth and analyze the R/C and mandibular angles of different genders and different ethnic groups.The relationship between the mandibular angle,further explore whether the R/C value and the mandibular angle value are different between different ethnic groups,and provide a reference for clinical diagnosis and treatment.Methods:Select the PRGs taken from December 1,2018 to June 31,2020 in the Department of Stomatology,People's Hospital of Xigaze,and select individuals that meet the research criteria.Screening criteria: Less than 40 years old;Permanent teeth;No missing teeth(except 18,28,38,48);Exclusion criteria for complete root development:craniofacial abnormalities;A history of trauma in orthodontic orthognathic treatment;Significant short root anomaly;The incised end of the crown of permanent teeth had a large area of prosthesis or obvious wear.There was obvious loss of periodontal attachment.The reference point of measurement on curved sectional radiograph is not clear.In this study,a total of 200 patients' panoramic X-rays were examined,including 100 for Tibetans,50 for men and 50 for women;100 for Han,and50 for men and 50 for women.The R/C value of permanent teeth(except the third molars)in the panoramic film was measured by the improved Lind crown-root ratio measurement method.The details are as follows: First,the midpoint of the horizontal line connecting the mesial and distal alveolar ridges of the tooth is selected as the dividing point for measuring the clinical crown-to-root ratio,and then use CAD software to measure the teeth,connect the mesial and distal alveolar ridge levels of the teeth,and set the midpoint of the line as the crown-root dividing point(m);for incisors,incisors and molars The tangent line or the straight line connecting the cheek tip is used as the reference line(a);For canines and premolars,the straight line perpendicular to the long axis of the canine cusp or the cheek cusp of the premolar is the reference line(a);the longest root is selected for the two teeth,and the palatal root is removed for the three teeth Select the longest buccal root,and then draw a straight line parallel to the reference line a through the root apex point as the root apex reference line(b);the vertical distance from point m to the root apex reference line b is the root length(L1);m The vertical distance from the point to the cutting end or the tip reference line a is the crown length(L2),and then the root-to-shoot ratio(R/C)= L1/L2 is calculated.The angle of the mandible is measured by the intersection of the tangent line of the lower edge of the mandible and the tangent line of the posterior edge of the ascending branch of the mandible.Results:(1)The R/C of the Tibetans with the same name in the same dental arch were higher than those of the Han,and the differences were statistically significant(P<0.05).(2)The R/C of Tibetan and Han are different in the order of the size of the upper arch and the lower arch.The lower jaw of Tibetans is: 5>3>6>4>7>2>1;the upper jaw is: 3>5>4>6>7>2>1,the second mandibular premolar is the largest,followed by the upper canine,and the lower jaw The incisor is the smallest.The lower jaw of the Han nationality is 6>5>3>4>7>2>1;the upper jaw of the Han nationality is:3>5>4>2>6>1>7,the mandibular first molar is the largest,followed by the upper canine,and the upper jaw is the second Molar teeth are the smallest.(3)There are only gender differences in R/C of individual teeth between Tibetans and Hans..(4)The mandibular angle value of Han women was greater than that of Tibetan women,and it was statistically significant(P<0.05).There was no statistical difference in mandibular angle values between Tibetan and Han men.Conclusion:There are significant differences in the R/C values of permanent teeth between Tibetan and Han populations and the mandibular angle values of Tibetan women and Han women.