Relationship Between Dental Crowding,Basal Bone Form,and Tooth Mass In Female Adults With Different Vertical Skeletal Patterns

Objective:To explore the relationship between dental crowding,basal bone form,and tooth mass in female adults with different vertical skeletal patterns.Materials and methods:The sample comprised 130 female adults,with skeletal class I malocclusion,aged(22.70±5.10)years.According to the Frankfort-mandibular plane angle(FMA),the samples were divided into 40 hypodivergent cases(FMA<22°),aged(22.63±4.44)years,50 normodivergent cases(22°≤FMA≤28°),aged(23.32±5.70)years,and 40 hyperdivergent cases(FMA>28°),aged(22.00±44.97)years.The arch length required and arch length available were measured on the initial dental casts.The amount of crowding was assessed by subtracting the arch length available from the arch length required.The sample was divided into the crowded group(crowding≥3mm)and noncrowded group(-3mm<crowding<3mm)based on the amount of crowding.The tomography data were imported into Mimics 21.0 software.The axial planes of the maxillary and mandibular base bone were defined as the planes parallel to the functional occlusal plane through the mesiobuccal root apex of the upper right first molar and the superior border of the right mental foramen,respectively.The basal bone length was measured on the axial plane of the base bone.The coronal measuring plane,perpendicular to the Frankfort horizontal plane and median sagittal plane,passing the buccal groove of the maxillary right first molar.The maxillary basal bone width was measured at mesiobuccal root apex and root bifurcation levels,and the mandibular basal bone width was measured at mesial root apex and root bifurcation levels,respectively.All measurements were randomly remeasured twice by the same examiner.The data was transported into SPSS 22.0.An independent sample t-test was used for intergroup comparison and the relationship between different measurements was investigated using the Pearson correlation coefficient.The significance level was fixed at P<0.05.Results:1.In the hypodivergent and normodivergent groups,for the upper dental arch,the maxillary base bone exhibited statistically significantly smaller in the crowded group compared with the noncrowded group(P<0.05),and the dental crowding was inversely correlated with the maxillary base bone size(r=-0.546～-0.402,P<0.05);as for the lower dental arch,the mandibular basal bone length exhibited statistically significantly smaller in the crowded group compared with the noncrowded group(P<0.05),and the dental crowding was inversely correlated with the basal bone length(r=-0.769--0.329,P<0.05),while the basal bone width showed no relationship(P>0.05).In the hyperdivergent group,for the upper dental arch,the maxillary base bone exhibited statistically significantly smaller in the crowded group compared with the noncrowded group(P<0.05),and the dental crowding was inversely correlated with the maxillary base bone size(r=-0.413～-0.332,P<0.05);as for the lower dental arch,the mandibular basal bone length and the root bifurcation level width exhibited statistically significantly smaller in the crowded group compared with the noncrowded group(P<0.05),and the dental crowding was inversely correlated with the basal bone length and the root bifurcation level width(r=-0.366～-0.346,P<0.05).2.Among the three vertical skeletal patterns,there was no significant difference in tooth mass between the crowded group and noncrowded group(P>0.05),and there was no significant correlation between dental crowding and tooth mass(P>0.05).Conclusion:1.In female adults of skeletal class I malocclusion with hypodivergent and normodivergent patterns,decreased basal bone length and width constitute significant factors associated with upper arch crowding,while the severity of lower arch crowding is mainly related to the basal bone length and has no significant correlation with basal bone width.In hyperdivergent subjects,dental crowding is closely related to the size of the base bone.2.The dental crowding is not correlated with tooth mass in female adults of skeletal class I malocclusion.