Growth And Development Of Dental Arch And Basal Arch In Children With Skeletal Class Ⅲ Malocclusion

Objective:To study the growth and development of dental arch and basal arch in skeletal class Ⅲ malocclusion,and provide theoretical basis for the early treatment of skeletal class Ⅲ malocclusion.Methods:From October 2019 to February 2022,84 patients with skeletal Class Ⅲmalocclusion were randomly selected,with an average age of 8.60±2.17 years old,including 50 males(8.73±2.16)years old and 34 females(8.45±2.21)years old.Cranial positioning X-rays were taken on the volunteers,and lateral cephalometric films were obtained,imported into Uceph software(China),and related indicators were measured.Correlation analysis was performed on the data of bone arch length and width;after CBCT scanning was performed on volunteers,CBCT was converted into DICOM format,imported into Mimics 21.0 software for 3D digital model reconstruction,and the length and width of dental arch and basal arch were measured.SPSS25.0 software was used for statistical analysis of the dental arch and basal arch at different occlusal developmental stages,and the independent sample t test was used to analyze the differences in the length and width of the dental arch and basal arch of different genders.Pearson correlation analysis was used between the related indexes of lateral cranial radiograph and dental arch and basal arch.When P<0.05,the difference was statistically significant.Results:(1)Growth and development trend of dental arch in patients with skeletal class Ⅲ malocclusion at the replacement stage:At the age of 5～7,male maxillary arch U4L was higher than that of female(P<0.05).At the age of 7～9,male mandibular arch L4L was higher than that of female(P<0.05).At the age of 9～11,male L4L was higher than that of female.The difference was statistically significant(P<0.05);The width of dental arch grew and changed fastest at 7-9 and 9-11 years old,especially the width of the posterior segment of dental arch.The U6W of female was larger than that of male at 5-7 years old,and the difference was statistically significant(P<0.05).The U6W of male was larger than that of female at 7-9 years old,and the difference was statistically significant(P<0.05);At the age of 5～7,the male maxillary abutal arch length was more than that of female in U4BL,U5BL and U3BL,respectively(P<0.05).At the age of 7～9,the male maxillary abutal arch length was more than that of female in U4BL,the difference was statistically significant(P<0.05).From 9 to 11 years old,female maxillary basal arch U3BL was higher than male,and the difference was statistically significant(P<0.05);The width of basal arch grew and developed rapidly during 7-9,9-11 years old.The U4BW,U6BW and L4BW of male maxillary basal arch were significantly higher than those of female(P<0.05).(2)After averaging the coordinates of the upper and lower dental arches and the basal arch of the four age groups,the fourth power polynomial f(x)=ax4+bx3+cx2+dx+e was used to measure the teeth of the four age groups.The fixed point mean coordinates of the dental arch and the basal arch were fitted,and the regression coefficient R2 of the obtained maxillary and mandibular dental arches and the upper and lower mandibular basal arch fitting curves were all greater than 0.98,and the fitting effect was good;(3)There was a correlation between the skeletal class Ⅲ malocclusion and the related indexes of the lateral cranial radiograph.There was no correlation between dental arch and basal arch and SNB,SN-MP,FH-MP,FHI%,SNA and PTM-S(P>0.05),but was positively correlated with Go-Co,Pcd-S,Go-Po and Ptm-A(P<0.05),and negatively correlated with OP-FH(P<0.05).Conclusion:(1)The length of dental arch and basal arch in patients with skeletal classⅢ malocclusion gradually increased with age,and the length of dental arch grew fastest in 7-9 and 9-11 years old.The width of dental arch grew fastest at 7-9 and 9-11 years old,especially the width of posterior dental arch.The basal arch length grew and developed rapidly during 9-11,11-13 years old.The basal arch width changed rapidly during 7-9,9-11 years of age;(2)The growth and development trend of the mandibular arch and the basal arch are similar,but the growth and development of the upper and lower j aw are not coordinated;(3)For the treatment of patients with skeletal class Ⅲ malocclusion,clinical treatment can be carried out by changing Pcd-S,Ptm-A and OP-FH.In the early treatment process,the growth of the upper jaw can be promoted by growth and development,and the position of the mandible can be changed according to the growth and development,and the plane of the posterior occlusion can be controlled well,so as to form normal overbite and overlay as far as possible.