Quantitative Study Of The Relationship Between The Incisive Canal And Maxillary Central Incisors By X-ray Images

ObjectiveThe sagittal position of the maxillary central incisors determines the aesthetic appearance of orthodontic patients.In orthodontic clinical diagnosis and treatment,in order to improve the profile and solve protrusion,patients with bimaxillary protrusion need to be treated with extracting four premolars and maximum anchorage retracting the upper and lower anterior teeth.Traditional orthodontic treatment can make the maxillary central incisors retract 5.78mm,and the miniscrew anchorage can increase the maximum retraction of the maxillary central incisors to 8mm,but in the process of retraction of the maxillary anterior teeth,a few maxillary central incisors will invade an important anatomical structure of the maxilla,the incisive canal,which leads to complications such as root resorption and loose teeth.The purpose of this study was to study the positional relationship between the incisive canal and the maxillary central incisors through the cephalometrical film and cone beam computed tomography(CBCT),in order to provide reference for clinical treatment and subsequent research,and to compare the positional relationship between the incisive canal and the maxillary central incisors by using the cephalometrical film and the CBCT image,so as to provides a reference for the orthodontic patient’s diagnose and the design of the treatment plan.MethodsSeventy-six adults undergoing orthodontic treatment patients who had been photographed on the cephalometrical film and the CBCT image were selected.The U1-SN angle,maxillary central incisors and PP plane angle al were measured using the cephalometrical film;the length of the incisive canal L,the angle of the incisive canal long axis and the PP plane a2,the maxillary central incisors axis and PP plane angle β3 and the maxillary central incisors apex distance RR were measured on the CBCT image;three measurement levels were defined on the CBCT image,the measurement level paralleling to PP plane includes:nasopalatine foramen level(N),root tip level(R),incisive foramen level(Ⅰ),and then measuring the N level incisive canal lip side alveolar bone plate thickness NT,R level incisive canal lip side alveolar bone plate thickness RT,I level incisive canal lip side alveolar bone plate thickness IT,N level incisive canal width NW,R level incisive canal width RW,I level incisive canal width IW,R level URl to incisive canal distance RRD,R level UL1 to incisive canal distance RLD,I level UR1 to incisive canal distance IRD,I level UL1 to incisive canal distance ILD.All statistics were expressed as mean±standard deviation,using a paired sample t test to detect differences between the two samples,and Pearson correlation analysis was used to examine the correlation between the samples.Results1.U1-SN has a significant positive correlation with the angle of maxillary central incisors axis and PP plane(cephalometrical film)β1(P<0.01);U1-SN has a significant positive correlation with the angle of maxillary central incisors axis and PP plane(CBCT)α3(P<0.01);The angle of maxillary central incisors axis and PP plane(cephalometrical film)al has a significant positive correlation with the angle of maxillary central incisors axis and PP plane(CBCT)α3(P<0.01);The angle of long axis of the incisive canal and PP plane α2 was positively correlated with the angle of maxillary central incisors axis and the PP plane angle(CBCT)α3(P<0.05).2.R level UR1 to incisive canal distance(3.57±1.41mm)should be significantly greater than I level UR1 to incisive canal distance(2.41 ±1.18mm),(P<0.05);The same R level UL1 to incisive canal distance(3.48±1.48 mm)was also significantly greater than the I level UL1 to incisive canal distance(2.40±1.25 mm),(P<0.05).3.There was no significant difference between the R level of UR1 to the incisive canal distance(3.57±1.41mm)and the R level of UL1 to the incisive canal distance(3.48±1.48mm)(P>0.05);There was no significant difference between the I level of UR1 to the incisive canal distance(2.41±1.18mm)and I level of UL1 to incisive canal distance(2.40±1.25mm)(P>0.05).4.N level incisive canal width(2.67±1.04mm)is smaller than R level incisive canal width(2.89±0.91mm),(P<0.05);R level incisive canal width(2.89±0.91mm)is less than I level incisive canal width(3.60±0.87 mm),(P<0.05).5.N-level incisive canal lip-side alveolar bone plate thickness(8.17±1.83mm)was significantly larger than R-level incisive canal lip-side alveolar bone plate thickness(7.96±1.68mm),(P<0.05);there was no significant difference between the N-level incisive canal lip-side alveolar bone plate thickness(8.17±1.83mm)and the I-level incisive canal lip-side alveolar bone plate thickness(7.98±1.61 mm),(P>0.05);there was no significant difference between the R-level incisive canal lip-side alveolar bone plate thickness(7.96±1.68mm)and the I-level incisive canal lip-side alveolar bone plate thickness(7.98±1.61 mm),(P>0.05).Conclusionl.In this study the average distance from the apex of the U1 to the incisive canal is only 3.5mm;the I-level average distance from the root of the U1 to the incisive canal is only 2.4mm.It may cause the resorption of the tip of root and the lateral side of root when the maxillary anter:ior teeth are retracted.2.In this study,the width of the incisive canal,N level(2.67 mm)<R level(2.89 mm)<I level(3.60 mm);and the distance between the UR1 and UL1 root tips was only 5.98 mm.When the maxillary anterior teeth are retracted with the teeth intrusion,it may cause the resorption of the mesial surface of the root.3.1n this study,the thickness of the alveolar bone plate of the N-level,R-level,and I-level incisive canal was about 8.0 mm.In the literature,the maximum labial-palatal diameter of the maxillary central incisors roots was 5.8 mm,which shows that the clearance of the maxillary central incisors roots in the alveolar bone is small and a controlled teeth movement should be taken during the teeth retraction.