| Objective: In this study,different developmental stages of maxillary second molars were used as the indicator to observe the three-dimensional characteristics and trends of distal available space of maxillary first molars at different developmental stages in adolescent with skeletal class Ⅱ.The purpose of this study is to provide reference for the prediction of the growth potential of distal available space of maxillary molars,the selection of treatment time and the formulation of treatment plan for classⅡ adolescents in practice.Materials and methods: Adolescent patients(aged 8-14 years old)with skeletal class Ⅱ average angle(78.0°<SNA<86.0°,ANB>6.0°,ANB>5.0°,29<MP-SN< 40°,22 °<MP-FH<32°)in Dalian Stomatology Hospital were selected.All patients were scanned by the same cone beam projection computed tomography(CBCT)system in the radiology department of our hospital.According to the lateral cephalogram,103 patients were selected.According to the different calcification development stages of the right maxillary second molars,103 cases were divided into the following four groups: Group T1: tooth crown was completely formed and root was not formed(23 cases,male:10cases,8.42±0.43 years old,female:13 cases,8.20±0.46 years old),Group T2: tooth root began to form(23 cases,male:10 cases,10.48±1.11 years old,females:13 cases,10.36±0.63 years old),Group T3: root formation 1/2(29 cases,male:13 cases,12.29±0.66 years old,female:16 cases,12.27±0.88 years old),Group T4: root formation3/4 and apical foramen unclosed(28 cases,male:13 cases,12.56±0.79 years old,female:15 cases,12.89±1.21 years old).The CBCT data of all patients were imported into Invivo Dental 6.0 software to construct CBCT three-dimensional images,and the three-dimensional changes of the distal available space of the right maxillary first molars in T1,T2,T3 and T4 were measured and analyzed:(1)Length measurement:Measure the distance from the distal point of the root to the distal point of the maxillary tubercle at 3mm,6mm and 9mm above of the maxillary first molar CEJ(cementoenamel junction)in the sagittal plane,marked as L3,L6,L9,respectively;(2)Width measurement: In the sagittal plane,the distance between the inner side of the buccalpalatal bone cortical plate at 2mm,4mm,6mm,8mm,8mm,10 mm,12mm and 14 mm from the farthest point of the maxillary first molar CEJ was measured,marked as W2,W4,W6,W8,W10,W12,W14,respectively;(3)Height measurement: the distances between the top of the alveolar ridge and the baseline 10 mm from CEJ,at 2 mm,4 mm,6 mm,8 mm,10 mm,12 mm and 14 mm from the maxillary first molar CEJ were measured in the sagittal plane,marked as H2,H4,H6,H8,H10,H12,H14,respectively.All data were imported into SPSS 26.0 statistical software and tested for normal distribution and homogeneity of variance.If the data conforms to the normal distribution and the homogeneity of variance,the independent samples t-test was used for the comparison between the two adjacent groups,if the data did not conform to a normal distribution,a nonparametric test was performed.P<0.05 was statistically different,and P<0.01 was statistically significantly different.Results:(1)Length: there was no gender difference in length measurements(P>0.05);there were statistical differences in the changes of L3,L6,L9 in T1-T2,T2-T3 and T3-T4 stage(P<0.05);the growth of L3 in T1-T2 stage was the largest,amounting to 2.3 mm;the growth of L3,L6,L9 in T1-T2 stage was greater than that in T2-T3 and T3-T4 stage.The growth of L3 and L9 in T2-T3 stage was greater than that in T3-T4 stage.(2)Width: The width measurements were greater in men than in women(P<0.05);both males and females increased in T1-T2 and T2-T3 stage,there were statistical differences in the growth of W2,W4,W6,W8,W10 in T1-T2 stage in the male group,and W4,W6,W8 in T1-T2 stage in the female group,and W8,W10 in T2-T3 stage in the male group,and W8,W10,W12 in T2-T3 stage in the female group(P<0.05);W4,W6,W8 decreased in the male group in T3-T4 stage,among which the decrease of W6 was statistically different(P<0.05);the width of all female groups decreased in T3-T4 stage,among which the decrease of W2,W4,W6 was statistically different(P<0.05).(3)Height: there was no gender difference in height measurements(P>0.05);the growth of H12 in T2-T3 stage was 0.99 mm,which was statistically different(P<0.05);the growth of H10,H12,H14 in T3-T4 stage was 2.18 mm,2.01 mm,1.60 mm respectively,which were statistically significantly different(P<0.01).Conclusion:(1)The length of distal available space of maxillary first molar in class Ⅱ adolescents changed in all stages from T1 to T4,but the growth in length decreased sequentially from T1-T2,T2-T3 to T3-T4 stages;suggests that the sagittal growth potential of distal available space of maxillary first molar may decrease with the development of the second molar.(2)There was gender difference in the width of distal available space of maxillary first molars in class Ⅱ adolescents,which is larger in males than in females.The width increased in both T1-T2 and T2-T3 stages,with a greater increase in T1-T2 stage;the increase of W8,W10 in T1-T2 and T2-T3 stage were greater and statistically different in male group,the increases of W8 in T1-T2 stage and W10,W12 in T2-T3 stage were greater and statistically different in female group;while in T3-T4 stage,except W10 and W12 in male group,the width of males and females all decreased.(3)The height of the distal available space of the maxillary first molar in class Ⅱ adolescents was increased significantly in T3-T4 stage,which may related to the development of second molar roots and the eruption of the second molar.(4)In clinical practice,three-dimensional direction growth potential of the distal available space of the maxillary molars may can be judged according to the development stage of maxillary second molars in adolescents,to make a reasonable treatment plan and ensure that the teeth move in a safe range. |
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