Crown-root Morphology Of Maxillary Lateral Incisors:A Cone-Beam Computed Tomography Study On Patient With Palatally Canine Impacted

Objective:Two different etiologic factors and theories have been proposed for maxillary palatally impacted canines as detailed in several reviews,which are guidance theory and genetic theory.Briefly,it is commonly thought that are associated with hypoplastic or missing lateral incisors.The purpose of this research was to investigate crown-root morphology of maxillary lateral incisors on patient with palatally canine impacted,and the relationships among palatally impacted canines and the dimension of the maxillary lateral incisors by using the cone-beam computed tomography technique(CBCT).Besides,the aim of this research was to identify the etiologic factors associated with palatally impacted canines comparing with buccally impacted canines.Methods:An experimental group of 24 patients with 27 palatally displaced canines(7 from boys,17 from girls;mean age of the subjects,13.6 years;age range,11-17 years)was selected from the records of patients referred to a radiology practice specializing in cone-beam volumetric tomography imaging.The control group 1 was age-and sex matched with 30 subjects with 37 buccally impacted canines(10 from boys,20 from girls;mean age of the subjects,13.9 years;age range,11-17 years).Another group as the control group 2 was age-and sex matched with 30 normal subjects with 60 canines(9 from boys,21 from girls;mean age of the subjects,13.3 years;age range,11-17 years).All subjects were from orthodontic clinic in the Stomatological Hospital Affiliated to Luzhou Medical College from September 1,2011 to February 1,2014.Digital cone-beam volumetric tomography images were reoriented and reconstructed into several radiographic images;and the volumetric images were reoriented with the long axis of the lateral incisor vertical and then reconstructed into images of a sagittal slice through the maxillary lateral incisors and 4 axial slices across the maxillary lateral incisor.The linear variables of the maxillary lateral incisors were measured by using digital measurement tools.The widths of the maxillary lateral incisor roots were registered at the cementoenamel junction level,4 mm apical to the cementoenamel junction level and 8mm apical to the cementoenamel junction level.The widths of the maxillary lateral incisor crowns were registered at the crown 4 mm to the cementoenamel junction level.The anatomically correct buccolingual and mesiodistal widths were measured at the 4 axial slice levels.The lengths of the lateral incisor were measured on the sagittal slice image.An independentt test was used to test for differences between the groups.All data were expressed by M±SD,analyzed by Students's T test(P<0.05),indicated statistical significance.Results:1.There were statistical differences in the tooth lengths,the lengths of the crown,buccolingual and mesiodistal widths at the cementoenamel junction level,mesiodistal widths of the crown,buccolingual widths at the level of 4 mm apical to the cementoenamel junction of the experimental group compared with those of the control group 1(P<0.05).Then the differences in the tooth lengths,buccolingual and mesiodistal widths at the cementoenamel junction level,mesiodistal widths of the crown were significant(P<0.01).2.There were statistical differences in the tooth lengths,the lengths of the crown,the lengths of the root,buccolingual and mesiodistal widths at the cementoenamel junction level,buccolingual and mesiodistal widths of the crown,buccolingual widths at the level of 4 mm apical to the cementoenamel junction,buccolingual widths at the level of 8 mm apical to the cementoenamel junction of the experimental group compared with those of the control group 2(P<0.05).Then the differences in the tooth lengths,the lengths of the root,buccolingual widths at the level of 4 mm apical to the cementoenamel junction were significant(P<0.01).3.There were statistical differences in the lengths of the root,mesiodistal widths at the cementoenamel junction level of the control group 1 compared with those of the control group 2(P<0.05).Conclusion:The palatally displaced canines were associated with small lateral incisors.The crown-root dimensions of maxillary lateral incisors adjacent to palatally impacted canines were smaller compared with those adjacent to bucally impacted canines and normal canines.