Analysis Of Related Factors Of “Black Triangle” Occurred Between Upper Central Incisors During Adult Orthodontic Alignment Stage

Objective: The related data of CBCT images and models of adult orthodontic patients before treatment were measured.Screen the related factors of “black triangle” between upper central incisors through statistical analysis of adult orthodontic patients during the alignment stage.Methods: 60 subjects were selected from those who sought orthodontic treatment for the first time in the Orthodontic Department in Hospital of Stomatology,Hebei Medical University,from 2012 to 2016.They were divided into two groups: 30 patients who developed “black triangle” between upper central incisors during their orthodontics alignment stage were included in the experimental group and 30 patients who did not have “black triangle”between upper central incisors were included in the control group.The median age of the experimental group and the control group were 24.00 and 18.00 years old,respectively.CBCT image data and plaster models of all subjects were collected before treatment.Apply InvivoDental 5.1.3 software for three-dimensional reconstruction and measurement of anterior teeth and alveolar bone.Cephalograms were measured for all subjects with WinCeph8.0 software and record models were measured by the electronic digital calipers.CBCT measurement items include: the ratio between crown length and root length of upper central incisors(CL/RL),the vertical distance from the alveolar crest to the contact point between maxillary central incisors(BC-CP),the vertical distance from the alveolar crest to proximal cementoenamel junction(pCEJ)between maxillary central incisors(BC-pCEJ),the vertical distance from the contact point between upper central incisors to the maxillary incisal edge(CP-IE),the horizontal distance between mesial pCEJ of uppercentral incisors(p RCEJ-pLCEJ),the angle between two long axes of upper central incisors(RD).If the roots were convergent,the record would be negative,adversely,if the roots were divergent,the record would be positive.The ratio between the vertical distance from pCEJ to the long axis of the central incisor and the vertical distance from contact point to the long axis of the central incisor(a/b),the ratio between maximum crown width and maximum crown length of upper central incisors(W/L),the angle between upper central incisal edges(U1-R),embrasure area between upper central incisors(Si),the alveolar bone height between upper central incisors(H),the alveolar bone thickness at the level of 2mm under the bone crest(L2),the alveolar bone thickness at the level of 4mm under the bone crest(L4),the alveolar bone thickness at the level of 6mm under the bone crest(L6)and alveolar bone thickness at the apical level(LRa).The cephalometric measurement items include: U1-SN,U1-NA(mm)and U1-NA(°)reflect the inclination and location of the maxillary central incisors,MP-SN,MP-FH and S-Go/N-Me reflect the vertical development of the craniofacial skeleton.Model measurement items include: upper anterior teeth irregularity index(UIRR),the overlap of upper central incisors(Overlap),anterior overbite(OB)and overjet(OJ).All the above items were analyzed with SPSS 21.0 statistical software.Compare two groups of measuring items by using two sample t test or Wilcoxon rank sum test or chi square test.Test standard: ?=0.05.Finally,find out the risk factors for clinical guidance with Logistic regression analysis.Results:1 Comparison of initial age,gender and whether or not they were treated with extraction in orthodontic treatment between experimental group and control groupThe median age of experimental group was 24.00 years old.The interquartile range of age of control group was 9.5 years old.There was significant difference between two groups(P<0.01),the experimental groupand the control group had no significant difference in gender distribution(P>0.05),there is no significant difference in the proportion of patients with tooth extraction in two groups(P>0.05).2 Comparison of occlusal status before treatment between experimental group and control groupIn the experimental group,the IRR index of the maxillary anterior teeth was 10.40±4.71 mm.The IRR index of the control group was 7.31±3.47 mm.There was significant difference between two groups(P<0.01).U1-SN,U1-NA(°),U1-NA(mm),U1-R,the overlap,overbite and overjet of upper incisors,MP-SN,MP-FH and S-Go/N-Me was not statistically significant in two groups(P>0.05).3 Comparison of anatomical and physiological factors before treatment between experimental group and control groupThe vertical distance BC-CP in the experimental group was6.49±0.71 mm and it was 5.39±0.61 mm in the control group.There was significant difference between two groups(P<0.01).The vertical distance CP-IE in the experimental group was 3.48±0.71 mm and it was 4.06±0.79 mm in the control group.There was significant difference between two groups(P<0.01).The median of embrasure area in the experimental group was2.85mm~2 and the interquartile range of that was 1.91mm~2.The median of embrasure area in the control group was 1.64mm~2 and the interquartile range of that was 0.79mm~2.There was significant difference between two groups(P<0.01).The distance BC-pCEJ and p RCEJ-pLCEJ,CL/RL,RD,a/b,W/L,the thickness and height of alveolar bone between upper central incisors were not statistically significant in two groups(P>0.05).4 Logistic regression analysis showed that the appearance of the “black triangle” was significantly correlated with the initial age,the vertical distance BC-CP,and embrasure area.Conclusions: The initial age of orthodontic treatment,the vertical distance from alveolar crest to contact point between maxillary central incisors and the embrasure area were risk factors of “black triangle” between uppercentral incisors during adult orthodontic alignment stage.