Study On The Difference Of Crown And Root Morphology Of Central Incisors With Different Bone Types,Compensation Degree And Gender

Objective:Using CBCT to study the differences of crown and root morphology of central incisors with different bone types,compensation degree of central incisors and sex.Methods and Materials:The CBCT of 276 orthodontic patients aged 15-21 years from January 2018 to January 2021 were collected in Stomatology Hospital of Shandong University.When studying the difference of crown and root morphology of incisors in different skeletal types,according to the Wits value,the samples were divided into three groups:class Ⅰ(-2mm≤Wits≤2mm),class Ⅱ(Wits>2mm)and class Ⅲ(Wits<-2mm).Based on the PP-MP value,the samples were divided into low angle group(PP-MP<21°),average angle group(21°℃PP-MP≤28°)and high angle group(PP-MP>28°).According to the axial angle of upper and lower central incisors,the samples were divided into upper central incisor lip tilt group(U1-PP>118°),normal group(110°<U1-PP≤118°),tongue tilt group(U1-PP<110°),lower central incisor lip tilt group(L1-MP>98°),normal group(88°≤L1-MP≤98°)and tongue tilt group(L1-MP<88°).When studying the difference of crown and root morphology of incisors in different genders,the samples were divided into male and female groups.In CBCT images,the upper boundary of the visual field includes at least the whole skull base,and the lower boundary contains at least the submental point.The acquired CBCT was imported into Dolphin 11.8 software to synthesize the lateral cephalogram.Fixed point,measured CBCT image and CBCT synthesized lateral cephalogram,and the measurement results of jaw and dental landmarks were obtained.CBCT measurement items include:U1CA1,U1CA2,U1AC(differential value between U1CA1 and U1CA2),L1CA1,L1CA2 and L1AC(differential value between L1CA1 and L1CA2);CBCT measurement items include PP-MP,Wits,U1-PP and Ll-MP.The measurement results were analyzed by single factor analysis of variance(ANOVA):three groups of sagittal skeletal facial types(in high,average and low angle samples),vertical skeletal facial types(in classⅠ,Ⅱ and Ⅲ samples),different degrees of compensation of maxillary and mandibular central incisors and the difference of CA and CA of central incisors in male and female groups.Tukey LSD analysis was used to compare the differences between the two groups.Independent sample t-test was used to test the difference of CA and CA of central incisor in male and female groups.P<0.05 is that the difference between groups is statistically significant.Result:1.Skeletal facial type1.1 sagittal skeletal facial type groupIn low,average and high angle samples,U1CA1,U1CA2,U1AC(1/3apical curvature of upper central incisor),There was no significant difference in L1CA1,L1CA2 and L1 AC among skeletal class Ⅰ,class Ⅱ and class Ⅲ.1.2 Vertical skeletal facial group1.2.1 skeletal class Ⅰ samplesIn skeletal class Ⅰ samples,there was no significant difference in U1CA1,U1CA2,U1AC,L1CA1,L1CA2 and L1AC among low angle,average angle and high angle groups(P>0.05).1.2.2 skeletal class Ⅱ samplesAmong the class Ⅱ samples,there was significant difference in U1CA1 between the low angle group and the average angle group(P<0.05).U1CA1=1.54±4.19° in low angle group.U1CA1=-0.42 ±3.94°in the average angle group.The position of the root relative to the crown in the class Ⅱ low angle group was closer to the lingual side than that in the average angle group.There was no significant difference in U1CA1 between high angle group,low angle group and average angle group(P>0.05).There was no significant difference in U1CA2,U1AC,L1CA1,L1CA2 and L1AC among low angle,average angle and high angle groups.1.2.3 skeletal class Ⅲ samplesIn class Ⅲ samples,there was significant difference in U1AC between low angle group and high angle group(P<0.05).U1AC=-0.81±2.08°in low angle group.U1AC=-2.21±2.57°in high an gle group.The degree of buccal curvature of the root tip of the upper central incisor in the class Ⅲ low angle group was less than that in the high angle group.There was no significant difference in U1AC between the average angle group and the low and high angle groups(P>0.05).There was no significant difference in U1CA1,U1CA2,L1CA1,L1CA2 and L1AC among low angle,average angle and high angle groups(P>0.05).2.Compensation degree of central incisor2.1 degree of compensation of upper and middle incisorsThere were significant differences in U1CA1 and U1AC between lip tilt group and normal lip tilt group(P<0.05).The measured value was the highest in the lingual tilt group(U1CA1=1.39±3.89°,U1AC=-0.17±2.06°),the second in the normal group(U1CA1=-0.20±3.76°,U1AC=-1.80±1.99°),and the lowest in the labial tilt group(U1CA1=-0.58±4.46°,U1AC=-2.17±2.53“).There was no significant difference in U1CA1 and U1AC between normal group and lip inclination group(P>0.05).There was no significant difference in U1CA2 among tongue tilt group,normal group and lip tilt group(P>0.05).3.GenderThere was significant difference in L1CA1 and L1CA2 between male and female(P<0.05).The measured values of male group(L1CA1=2.98±3.15°,L1CA2=3.89±2.97°)and female group(L1CA1=1.75±3.10°,L1CA2=2.88±2.85°).Compared with female group,the crown position of male group was closer to the lingual side of root position and 1/3 root middle and 1/3 root neck,but there was no significant difference in 1/3 apical curvature central incisor between males and females.There was no significant difference in U1CA1,U1CA2 and U1AC between males and females.Conclusion:1.The Collum angle of central incisor and 1/3 apical curvature of central incisor had no correlation with sagittal skeletal surface type,but had weak correlation with vertical skeletal facial type.2.When the upper central incisor tongue tilted,the 1/3 root tip of the upper central incisor changed the original direction of growth and development,relatively to the lingual side.There is no correlation between the crown and root morphology of the main body of the upper central incisor(above the 1/3 root tip)and the degree of compensation of the central incisor.the reason for the change of the overall morphology of the upper central incisor is the different 1/3 apical curvature of the upper central incisor.There was a significant difference between the main body and the whole crown and root morphology of the lower central incisor in the tongue inclination group and the lip inclination group,but there was no significant difference in the 1/3 apical curvature of the lower central incisor.3.There was no significant difference in Collum angle and the 1/3 apical curvature of upper central between male and female.Compared with female,the crown position of male is more tongue inclined relative to the root of Central incisors.