| Background and ObjectivesAs the supporting bone of dental arch,the basal bone arch is the boundary of tooth movement during orthodontic treatment.Previous studies mostly focused on the buccal boundary of the basal bone arch contours,and rarely involved the overall basal bone arch contours including the lingual side and the retromolar region.In addition,compared with the researches on skeletal Class I and skeletal Class Ⅱ malocclusion,there are few explorations on the bimaxillary basal bone arches characteristics of patients with skeletal Class Ⅲ malocclusion.Futhermore,few analysis has been found on the relationship between the vertical skeletal pattern and bimaxillary basal bone arches matching in patients with skeletal Class Ⅲmalocclusion.Objectives of this study were to depict bimaxillary basal bone arch contours and its main variations among young adults using the generalized procrustes analysis(GPA),and to demonstrate width matching of the two jaws,exploring change trends of the basal bone arches variations among young adults using principal analysis(PCA).Bimaxillary basal bone arches contours of patients with skeletal Class Ⅲ malocclusion were revealed by GPA and two factors(Vertical 1 and Vertical 2)from 18 vertical cephalometric measurements were extracted using factor analysis(FA).A structural equation modeling(SEM)was constructed,exploring the correlation between two factors representing the vertical skeletal pattern and width mismatching of the bimaxillary rear basal bone arches(the second molar region and the retromolar region)of patients with skeletal Class Ⅲ malocclusion.Sensitive cephalometric measurements indicating width mismatching of bimaxillary basal bones arches were found by loadings of FA.Materials and MethodsIn this retrospective cross-sectional study,firstly cone-beam computed tomography(CBCT)pretreatment images of 100 subjects(50 males,50 females,male:skeletal Class Ⅰ 16 cases,skeletal Class Ⅱ 12 cases,and skeletal Class Ⅲ 22 cases;female:skeletal Class Ⅰ 15 cases,skeletal Class Ⅱ 13 cases,and skeletal Class Ⅲ 22 cases)were included.100 pairs of bimaxillary basal arch contours were obtained which were inner cortical contours through the furcation of the upper and lower first molar on the plane parallel to the mandibular occlusal plane.The mean bimaxillary basal bone arch contours of 100 subjects were illustrated using GPA,and the width difference of the basal bone at different dental positions were calculated.The width differences of bimaxillary basal bones were used to represent the mismatching of basal bones.PCA was used to clarify main sites and trends of variations of basal arches among 100 subjects.After analysis of basal bone arch contours and variation trends among young adults,we further explored basal bone arches contours and the relationship of its width mismatching with the vertical skeletal pattern of patients with skeletal Class Ⅲ.96 patients(45 males and 51 females)with skeletal Class Ⅲ bone were selected and added.GPA was used to demonstrate the mean basal bone arches contours of patients with skeletal Class Ⅲ in different genders,and the width difference of bimaxillary basal bones at different dental positions were calculated.CBCT images were used to synthesize cephalograms automatically,and FA was used to extract two main factors(Vertical 1 and Vertical 2)from 18 vertical cephalometric measurements.A SEM was established to reveal the correlation between two factors representing the vertical skeletal pattern and the width mismatching of bimaxillary rear basal bones arches of patients with skeletal Class Ⅲ.We explored sensitive cephalometric measurements indicating width mismatching of bimaxillary basal bone arches in skeletal Class Ⅲ patients according to the loading value of measurement variables in the factors.ResultsGPA results of 100 patients with skeletal Class I,skeletal Class Ⅱ,and skeletal Class Ⅲmalocclusion showed that the width mismatching of the bimaxillary basal bone arches was mainly at the second molar segment(male,maxillary basal bone width 65.49 mm,mandibular basal bone width 68.62 mm;female,62.85 mm in maxilla,68.23 mm in mandible)and the retromolar region(male,64.54 mm in maxilla,71.80 mm in mandible;female,62.20 mm in maxilla,71.38 mm in mandible).The upper basal bone width at the second molar(P<0.001),the retromolar region(P<0.001)and width difference(P=0.009)at the second molar segment were different statistically between genders.When 2 mm ideal overjet was set,the maxillary basal bone arch was about 2 mm wider than that of the mandible on both sides from the incisor to the first molar.Width mismatching occurred at the second molar and the retromolar region,and the maxillary width was smaller than that of the mandible.The results of PCA showed that the variation of basal arch contours among young adults mainly occurred at the posterior segment.GPA results of 96 subjects with skeletal Class Ⅲ showed that the width mismatching of bimaxillary basal bone arches was also present at the second molar segment(width difference:male-4.29 ± 4.32 mm;female-5.55 ± 4.43 mm)and the retromolar region(male-8.49 ± 5.11 mm;width difference:female-8.93±5.25 mm).Results of FA showed that in factor 1,which accounted for 41.81%explanation of male cephalometric measurements,Sum of Angles(0.9477),∠MP-SN(0.9408),N-Me/S-Go(0.8975),∠MP-FH(0.8959),∠N-Go-Me(0.8939),and∠PP-MP(0.8157)had larger loadings(>0.8100).In the female factor 1(43.74%explanation),Sum of Angle(0.9489),N-Me/S-Go(0.9342),∠N-Go-Me(0.9185),∠MP-SN(0.9098),∠MP-FH(0.8817)and ∠PP-MP(0.8307)had larger loadings(>0.8300).In factor2,the loading value of ANS-Me was the largest for both men and women.SEM results showed a positive correlation between the vertical skeletal pattern and the width mismatching of bimaxillary rear basal bone arches in both genders of skeletal Class Ⅲpatients,which was mainly reflected in the positive influence of the vertical factor 1(P<0.000,B=3.985)and the vertical factor 2(P<0.001,B=2.470)of male cephalometric measurements on the width mismatching at the retromolar region.For female,factor 1 had a significant positive influence on the width mismatching of the bimaxillary basal bone arches at the second molar(P<0.001,B=5.535)and the retromolar region(P=0.016,B=3.427),and factor 2 was also positively correlated with the width mismatching at the rear segment of bimaxillary.Conclusions(1)The contours of bimaxillary basal bone arches of male and female were basically matched from the incisor to the first molar,and the width mismatching of bimaxillary basal bone arches was mainly found at the second molar and the retromolar region.The feature was same in both genders.(2)The bimaxillary basal bone arches are wider and longer in male than in female.(3)The vertical skeletal pattern of skeletal Class Ⅲ patients is correlated with the width mismatching of bimaxillary rear basal bone arches.For both male and female,the more inclined they were to the low-angle skeletal pattern,the larger width mismatching occurred at the rear segments of bimaxillary basal bone arches,and the greater width difference occurred.(4)Sum of Angle,∠MP-SN,N-Me/S-Go of male and Sum of Angle,N-Me/S-Go,∠N-Go-Me of female can indicate the posterior width mismatching of bimaxillary basal bones in skeletal Class Ⅲ patients clinically as sensitive cephalometric parameters to some extent. |
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