A Study About The Effect Of The Change In Position Of Incisors Before And After Orthodontic Treatment On The Profile Aesthetics Based On Genders And Antero-Posterior Jaw Relationships

Objective To investigate the morphological characteristics,change laws and compensatory mechanisms for people of different genders and antero-posterior jaw relationships,the aesthetic samples were selected and then analyzed by cephalometric measurement of their soft and hard tissue indexes before and after orthodontic treatment,with a view to provide references for diagnosis of clinical orthodontic and design of esthetical position of incisors.Methods In this retrospective study,the selected 85 adult aesthetic samples were divided into male,female groups and Class Ⅰ,Ⅱ,Ⅲ groups according to genders and antero-posterior jaw relationships.The cephalometric measurement of incisors,alveolar bone,chin and other related soft and hard tissue indexes were performed on the lateral cephalometric films.Using SPSS26.0 software.The multiple linear regression was used to analyze the changes of soft and hard tissues before and after orthodontic treatment,then to find the esthetical position of incisors and the reference values of soft tissue.The LSD multiple comparisons was used to investigate the compensatory mechanisms of incisors,alveolar bone and chin in class Ⅰ,Ⅱ and Ⅲgroups.Results 1,The mandibular plane angle(20.63°～23.55°),interincisor angle(119.86°～124.83°),upper lip inclination(58.42°～64.27°),lower lip inclination(44.94°～50.71°)and Z angle(69.02°～72.25°)were significantly smaller in the aesthetic males than aesthetic females,while the mandibular symphysis inclination(87.64°～92.47°),lower incisor inclination(97.02°～103.00°),MIA(9.02°～12.23°)and LIA-LI-Pog angle(21.04°～24.32°)were significantly greater than aesthetic females,and the upper lip was located 0.10mm-1.29mm behind the E line and the lower lip was located 0.04mm-1.04mm in front of the E line,which was more protrude than aesthetic females.2.For males,the amount of change in mandibular symphysis inclination significantly negatively predicted the amount of change in Z angle(P=0.016);the amount of change in upper incisor inclination positively predicted the change in upper lip protrusion distance(P=0.001).For females,the change of interincisor angle was a highly significant positive predictor of Z-angle change(P=0.006),a significant negative predictor of upper labial protuberance change(P=0.001)and lower labial protuberance change(P=0.017);mandibular symphysis inclination change was a highly significant negative predictor of Z-angle change(P=0.005)and a significant positive predictor of lower labial protuberance change(P=(P=0.001);the change in upper incisor protrusion distance significantly predicted the change in upper lip protrusion distance positively(P=0.012)and negatively predicted the change in upper lip inclination angle significantly(P<0.001).3.The lower alveolar inclination angle and the chin-inferior alveolar intersection angle were significantly reduced after orthodontic treatment in Class Ⅰ,Ⅱ,and Ⅲ.The lower incisor inclination angle was significantly reduced in Class Ⅱ andⅢ after orthodontic treatment,while the difference in lower incisor inclination angle was not significant in Class Ⅰ after orthodontic treatment.4.The differences in chin inclination,chin morphology ratio and lower incisor-inferior alveolar intersection angle were not significant in the Class Ⅰ,Ⅱ andⅢ before and after orthodontic treatment.Conclusion 1,Aesthetic males had a smaller mandibular plane angle,more labially inclined incisors and more anteriorly protruding lips compared with aesthetic females.2,The change of upper incisor inclination has a significant effect on the soft tissue lateral profile of males,the change of upper incisor protrusion distance has a significant effect on the soft tissue lateral profile of females,and the change of mandibular symphysis inclination and interincisor angle has a significant effect on the soft tissue lateral profile of both males and females.3,For Class Ⅰ patients,the lower incisors should be kept relatively upright in alveolar bone and mandibular plane after orthodontic treatment;for Class Ⅱ patients,the lower incisors should be lingually inclined in the orthodontic treatment,but still retains its certain proclination;while for Class Ⅲ patients,the lower incisors should be appropriately labially inclined according to the width of the alveolar bone for further compensation.4.There was no significant compensory phenomenon of the chin in Class Ⅰ,Ⅱand Ⅲ before and after orthodontic treatment,and there was no significant correlation between the lower incisors inclination relative to the alveolar bone neither in differernt antero-posterior jaw relationships nor receiving orthodontic treatment.