The Study Of Lower Premolar Position In Different Facial Types Patients Of ClassⅠby CBCT

Objectives1.To explore if there are correlations between the the position of thelower first and second premolars in ClassⅠpatients.To provide atheoretical basis for orthodontic diagnosis,to provide the perfect treatmentplan and precisely adjustment for position of the tooth.2.To test the null hypothesis that there are no difference between thelower first premolar and the lower second premolar with the same verticaltype.3.To establish the standard of lower premolars position in lower jawwith different vertical types of AngleⅠpatients.MethodsA sample of120patients were chosen from the patients who came theaffiliated hospital stomatology,chongqing medical university to acceptorthodontic treatment firstly.The FMA angle as a standard was used to select40short face type，40average face type，and40long face type patients，aged from15to30old years.All patients were taken photos byCBCT(cone-beam computed tomography，CBCT).120patients image were 3D reconstructed and lower premolar index were measured by CBCTassociated soft InvivoDental5.1.All data was analysed by SPSS17.0.Results1.The angle between right mandibular first premolar tooth long axis andthe buccal cortical bone of the low-angle group is greater than of theaverage-angle group; The angle between right mandibular first premolartooth long axis and the buccal cortical bone of the average angle group isgreater than of the high-angle group.There was statistically significantdifference among the three groups(P <0.01).2.The distance from right mandibular first premolar apical to the buccalcortical bone、the distance from apical to the lower edge of the mandibular、the rotation angle of the apical in buccal side and the rotation distance of theapical in buccal side、 the apical maximum movable distance of thelow-angle group is greater than of the high-angle group,the same upperindex of high-angle group is greater than of the average angle group.Therewas statistically significant difference among the three groups(P <0.01).3.The angle between the right mandibular second premolar tooth longaxis and the buccal cortical bone、the distance from apical to the buccalcortical bone、the rotation angle of the apical in buccal side of the low-anglegroup is greater than of the high-angle group.There was statisticallysignificant difference among the three groups (P <0.05).4.In the high-angle group, the angle between the tooth long axis and the buccal cortical bone、the distance from apical to the buccal cortical bone、the rotation angle of the apical in buccal side and the rotation distance of theapical in buccal side of the second premolar is larger than of the firstpremolar, the difference was statistically significant (P <0.01). The anglebetween tooth long axis and the lingual cortical bone、the distance from theapical to the lingual bone cortical、the distance from apical to the lower edgeof the mandibular of the first premolar is greater than of the second premolar,the difference was statistically significant (P <0.01).The rotation angle andthe rotation distance of the apical in lingual side of the first premolar isgreater than of the second premolar, the difference was statisticallysignificant (P <0.05).5.In the average-angle group, the distance from the apical to the buccalcortical bone、the rotation angle and the rotation distance of the apical inbuccal side of the second premolar is greater than of the first premolar, thedifference was significance (P <0.01). The angle between the tooth long axisand the buccal cortical bone of the second premolar is greater than of the firstpremolars, the difference was statistically significant (P <0.05). The anglebetween the tooth long axis and the lingual cortical bone, the distance fromapical to the lingual bone cortical of the first premolar is greater than of thesecond premolar, the difference was statistically significant (P <0.01). Therotation angle of the apical in lingual side of the first premolar is greater thanof the second premolar, the difference was statistically significant (P <0.05). 6.In low-angle group, the angle between the tooth long axis and thelingual cortical bone、the distance from apical to the buccal cortical bone、the distance from apical to the lingual bone cortical、the rotation angle andthe rotation distance of the apical in buccal side, the rotation angle and therotation distance of the apical in lingual side of the first premolar is greaterthan of the second premolar, the difference was statistically significant (P<0.01).Conclusions1.CBCT can show maxillofacial hard tissue structures accurately,CBCT is high valuable in the oral clinically.2. The position of lower premolar in different facial types is statisticallysignificant difference,the orthodontist in the treatment should pay closeattention to the buccal movable space of the high-angle group and theaverage-angle group.The orthodontist should pay attention to therelationship of apical and alveolar bone when they use the torque.3. There is statistically significant difference between the first premolarand the second premolar in the same facial types. The orthodontist shouldpay attention to the average-angle group patients’ the first premolar apicalbuccal movable space.