Association Between The Developmental Stages Of Mandibular Third Molars And The Growth Of Bimaxillary In Male Adolescents

ObjectivesThe aim of this study is to explore whether the growth and development stage can be accurately judged by the developmental stage of mandibular third molar,by analyzing the correlation among the developmental stage of mandibular third molar,chronological age,cervical bone age and three dimentional growth of maxillary and mandibular bone in adolescent males.Thus we may provide a new method to predict the growth and development potential of bimaxillary bones.Materials and MethodsAccording to the inclusion criteria,CBCT image datas of initial visit patients from October 2020 to December 2020 were included in the Department of Orthodontics,Hospital of Stomatology,Shandong University.A total of 235 male patients,aged from 9 to 18 years,with no obvious abnormalities in growth and development,were enrolled.Dolphin 11.8 software was applied to observances and measurements:1,head position correction,3d reference planes establishment,measurment of maxillary mandibular width and palatal vault depth.2,The development stage of the left mandibular third molar was identified by the method of Nolla.3,The images of C1～C4 cervical vertebrals were acquired through CBCT synthesized cephalogram,and cervical vertebral maturation(CVM)was determined according to McNamara et al.4,The effective maxillary length,maxillary body length,mandibular body length,mandibular ramus height and effective mandibular length were obtained by referring to McNamara and Jarabak methods.5,The maturity stages of the palatal sutures were determined according to the morphological characteristics staging method(MPS)recommended by Guyan et al.These datasets were imported into SPSS software and Spearman correlation coefficient test was used to study the correlation between the development stage of the third mandibular molars and above mentioned indicators,with P<0.01 as the statistical standard.One-way analysis of variance(ANOVA)was used to compare and analyze the differences of three-dimensional growth of maxilla and mandible between groups according to Nolla staging method of the third mandibular molars,with P<0.05 as the statistical standard.Results1.There was a significant positive linear correlation between chronological age and the stage of the mandibular third molar in male adolescents.The Spearman correlation coefficient was 0.859,(P<0.01),indicating a strong correlation between the two indexes.There is also a linear regression correlation between them,R=0.882,(P<0.01).The regression equation was Y(age)=7.88+1.04x(dental age),R2=0.776.2.Spearman’s correlation coefficient between the stages of mandibular third molar and cervical vertebral maturity stage was 0.823,(P<0.01),indicating a strong correlation between the two items.Most of the samples whose mandibular third molars are in NI1 and NI2 stage were in CS1-3 stage(92.3%).Most of the samples whose mandibular third molars are in NI3～5 stage were in CS2～4 stage,and the proportion of CS3～4 stage was increasing with the development of mandibular third molar.In the group NI6,samples of CS3～4 stage still accounted for the highest proportion,and the proportion of CS5 stage reached 24.2%.From group NI7,the proportion of CS4 gradually decreased,and the proportion of CS5～6 increased correspondingly.From group NI8,CS6 stage accounted for the most.3.Spearman’s correlation coefficient between the stages of mandibular third molar and palatal suture stages was 0.739,(P<0.01),indicating a moderate to strong correlation between the two items.In group NI1～2,MPS1 accounted for 76.9%of the total.In group NI3～5,people in MPS2～3 accounted for the largest proportion(87.9%),but a very small proportion of 4S1 stage(4.04%)began to appear.In group NI6,people in MPS2～3 still accounted for the highest proportion,but people in MPS4s1 stage accounted for nearly 20%,and MPS4s2 stage began to appear(6.1%).From the beginning of NI7 stage,stage 4S1 always accounted for the largest proportion.4.Max-max’,PNS-A,PVD and Co-A all showed an increasing trend with the development of mandibular third molars.The maximum increase of maxillary basal width appeared in stage NI2～3 and NI5～6,with an increase of 2.45mm and 1.31mm respectively,and the width remained nearly unchanged after the NI6 stage.The growth peak of the sagittal length of maxilla was 3.86mm from NI3 to NI5,accounting for 69.05%of the total recorded growth,and remained at the same level after NI7.Palatal vault depth increased by 1.54mm between NI2 and NI3,and then increased slowly until NI9.Effective maxillary length Co-A increased significantly from stage 2 to stage 4,(P<0.05),with an increase of 3.91mm,accounting for 44.43%of the total recorded increment.After that,the effective maxillary length increased steadily until NI7 with low velocity.5.Go-Go’,Ar-Go,Go-Me and Co-Gn showed an overall increasing trend with the development of mandibular third molars.The growth peak of mandibular width Go-Go’appeared in NI 2～3 and NI 6～7,and basically remained stable after NI7.The height of mandibular ramus increased at a steady rate during NI 2～5 stages,and accelerated from NI 5 stages.The maximum increase was observed during NI 6～7 stages(4.5mm),accounting for 43.27%of the total recorded increase.The mandibular body length showed two growth peaks(P<0.05)at the NI2～3 stage and the NI6～8 stage,with a total increase of 8.24mm,accounting for 81.50%of the total increase.The effective mandibular length Co-Gn showed an increasing trend in general,and showed two significant increases(P<0.05)at the NI2～3 stage and the NI6～7 stage(5.57mm and 4.96mm,respectively),accounting for 31.19%and 27.77%of the total increase.1.The development stage of the mandibular third molars of male adolescents not only has a significant positive correlation with age and cervical bone age,but also has a strong correlation with the maturity stage of the palatal suture.In NI3～5 stages,MPS2 and 3 stages accounted for the largest proportion,more than 90%.2.The development stage of the mandibular third molars of male adolescents is correlated with the growth of maxilla,and the corresponding relationship between the rapid growth stages of maxilla length,width and height and Nolla stage is different to some extent.The width and vertical vault of maxilla increased rapidly at NI2～3 stage,and then slowed down.The sagittal growth spurt of maxilla started at NI3～5,and slowed down significantly after NI5.3.The development stage of mandibular third molars of male adolescents were correlated with the growth peak of mandible.The growth peak of mandible corresponds to NI2～3 and NI6～7 of mandibular third molars.In conclusion,Nolla staging of mandibular third molars can be used as an alternative or alternative method to evaluate the developmental stage of maxillofacial growth and to predict the potential of mandibular growth and development,and can be used in clinical diagnosis and curative effect prediction.