The Dental-facial Morphology Research Of Patients With Congenitally Missing One Mandibular Incisor

Background:The incidence of congenitally absent teeth is on the rise in current society.Itcauses some problems as aesthetic,function and even mental health.with growingeconomy,increasing life-stress,and demand of better living-standard,the problemscaused by congenitally absent teeth are accentuated and the voice that people wish tochange the imbalance caused by congenitally differences is increasing.The incidenceof congenitally missing mandibular incisor is high in our country and it has greatimportance to the patients as the position of missing tooth.This thesis was to figureout the characteristic of congenitally missing one mandibular permanent incisorthrough the study on dental-facial morphology and extraction treatment of thesepatients in orthodontics.Objective:The part1was to explore the dental-facial morphology of patients withcongenitally missing one mandibular permanent incisor through examining theocclusion and facial morphology feature.The part2was to explore the influence of thedental-facial morphology of patients with congenitally missing one mandibularpermanent incisor after extraction orthodontic treatment through comparing thedental-facial morphology before and after treatment.Methods:The part1compared the craniofacial and occlusion feature between27cases of congenitally missing one mandibular permanent incisor patients and normalpeople,with methods of cephalometrics and model analysis,and analysed the data withSPSS17.0software.The part2compared the dental-facial morphology of12cases of congenitallymissing one mandibular permanent incisor before and after extraction orthodontictreatment with the method that was extraction of two first premolar in maxillarydental arch and non-extraction in mandibular dental arch.The data was analysed withSPSS17.0software.Results:Part1:Among the27cases of congenitally missing one mandibular incisor therewere9male cases,with ratio33.3%;18female cases,with ratio66.7%and the ratio ofmale to female is1:2.There were17cases of lateral incisor absence,with ratio63.0%;10cases of central incisor absence,with ratio37.0%.The constituent ratio ofskeletal type was:skeletal type I51.9%,skeletal type II44.4%,skeletal type Ⅲ3.7%;The constituent ratio of vertical skeletal type was:matched average51.9%,high-angle18.5%,low-angle29.6%;The constituent ratio of occlusion wasclass I51.9%,classⅡ33.3%,classⅢ14.8%;Among the27patients the incidence ofmalocclusion type was74.1%deep overbite,88.9%deep overjet,63.0%dentalcrowding,14.8%space;The patients’ Bolton index of the anterior teeth was65.4%,andthe whole teeth was85.0%.Both of them were smaller than normal people.There wasno significant difference in all Cephalometric measurements between gender(p＞0.05)．Comparing to normal range,in craniofacial defection Y axis angle was largerwith significant statistical difference (p<0.01),SNB was smaller and ANB was largerwith statistical difference (p<0.05);The smaller protrusion of mandibular incisor andlower lip was found,and L1-NB(mm),LLP(mm) diminished.Part2:The treatment of the12patients with congenitally missing one mandibularpermanent incisor was well;In all Cephalometric measurements,comparing withpretreatment craniofacial defection Y axis angle was larger with significant statisticaldifference (p<0.01);U1-SN diminished,U1-NA(mm) diminished and U1-L1was larger with significant statistical difference (p<0.01);ULP(mm) diminished withsignificant statistical difference (p<0.01).ConclusionIn the situation of congenitally missing one mandibular incisor patients,femalehad higher incidence than male,and the lateral incisor was easier absence than centralincisor;Most of the patients was skeletal type I with comparatively increasing skeletaltype Ⅱ,the vertical type showed mainly matched average type,the chief type of thefirst molar relationship was Class I,and the main malocclusion type was deepoverjet,deep overbite and dental crowding.There was no gender difference incraniofacial development of the patients who lacked one mandibular incisor.Thepatients who were congenitally missing one mandibular incisor showed a deficiencyof anterior alveolar bone,a clockwise rotation of mandibular bone,a deficientprotrusion of mandibular incisor and lower lip.Extraction treatment could improve theocclusion and facial morphology.