Craniomaxillofacial Changes Following The Extraction Of Premolars Inpatients With Bimaxillary Protrusion

Bimaxillary protrusion is a condition characterized by protrusive and proclined upperand lower incisors and an increased procumbency of the lips. Because of the negativeperception of protruding lips and protrusive dentitions often leads such patients to seekorthodontic care to decrease protrusion and improve profile. The present trend to treatBimaxillary Protrusion is extraction of the4premolars, followed by anterior toothretraction to obtain the desired dental and soft-tissue profile changes. Extraction treatmentwill not only change the patient’s pofile but also the whole craniofacial. Previous studiesof pofile and airway change with bimaxillary protrusion have used per-and posttreatmentlateral cephalograms to analyz the linear and angular of pofile and upper airway. However,the effects of growth have seldom been take into account.The study intends to use Hasseland Farman improved method to determine the growth and development of cervicalstaging of patients.These simples were divided into2groups as adult, adolescent. The aimof this clinical study was to investigate the influence of retraction of anterior teeth afterextraction of four premolars in adults and adolescents with bimaxillary protrusion.And usefrontal photographs of women, to measure the changes in the facial dimensions betweenpretreatment and posttreatment. The correlation between facial dimensions and arch widthwere also investigated. ObjectiveThis retrospective study aims to compare the craniofacial changes in adults andadolescents with bimaxillary protrusion after extraction treatment, and analyzed therelationship between anterior teeth and lip positions and the relationship between Frontalfacial and arch width.MethodsExperiment1: A sample of122patients (81adults,41adolescents) was chosen fromthe files of previously treated patients at the Fourth Military Medical UniversityStomatology Hospital, Department of Orthodontics.Pretreatment and posttreatmentcephalometric radiographs were traced and analyzed using “Onyx2.6” software.Pretreatment and posttreatment variables were compared using t-test, and the relationshipbetween anterior teeth and lip positions was analyzed using Pearson correlationcoefficient.Experiment2: Cephalometric radiographs of68patientswith bimaxillary protrusion(41adults,27adolescents) were used to evaluate the sagittal upper airway dimensions.Pre-and posttreatment radiographs were loaded into “Onyx2.6” software. All linear andangular of upper airway in both groups were measured and analyzed. T-tests were used tocompare the groups changes.Experiment3: Frontal facial photographs of56bimaxillary protrusion women wereimported in the photoshop cs3software. All linear were measured by e-ruler10.0software.Dental model plasters were sent to CAD/CAM for construction of digital3D virtualmodels. And measure by using the meshlab1.32software. T-tests were used to comparethe mean differences in the changes of variables between pre-and posttreatment.Pearson’scorrelation coefficients were calculated for dependent variables as a function ofindependent variables. Stepwise multiple regression analysis was used to evaluate futurealterations of dependent variablesResults1. Compare the hard tissue and soft tissue of adult and adolescent patients withbimaxillary protrusion showed:(1) All linear and angular measurement of hard tissue before treatment were not significantly different between the two groups.The Pog-Pog ’,G-Sn-Pog’, FH-N’-Pog ’ in adult greater than adolescent patients.But after treatment SNBwas greater in adolescent patients;(2)The SNA、SNB、U1-A、L1-Apog、H angle、Pog-Pog’、Sn-H line、Ls-SnPog、Li-SnPog’、 G-Sn-Pog’、 FH-N’-Pog’showed significantlydecrease,and U1-L1、Ls1u–Ls、Cm-Sn-Ul showed significantly increase after treatmentin the adult patients;(3)The SNA、ANB、U1-A、L1-APog、H angle、Li-SnPog’、A-N’-Pogshowed significantly decrease,and U1-L1、 Ls1u–Ls、Li1l-Li、Cm-Sn-Ul showedsignificantly increase after treatment of adolescent patients;(4) The changes of Prn-Sn，Cm-Sn-Ul、 Pog-Pog’、 G-Sn-Pog’、FH-N’-Pog’ adolescent patients were greater thanthe adult;(5)A1mm retraction of the maxillary incisor would produce a0.402mmretraction of the upper lip, a1mm retraction of the mandibular incisor would produce0.456mm retraction of the lower lip of adult patients. And a1mm retraction of themaxillary incisor would produce a0.876mm retraction of the upper lip, a1mm retractionof the mandibular incisor would produce0.715mm retraction of the lower lip ofadolescent patients.2. The compairsion of the sagittal upper airway dimensions between the adult andadolescent patients showed:(1) Pretreatment and posttreatment measurement data hadsignificantly different in the PNS-B、 PNS-Ad1、 PNS-Ad2between adult andadolescent.Before treatment the C3-RGn、Hy-H1of adult were greater;(2) The changes ofC3-RGn、Hy-H1、Hy-H2of adolescent patients were greater than the adult;(3) There wassignificant decrease in PNS-adl、PSP—SPPW、U—MPW of adult patients,and significantincrease in Hy-H1of adolescent patients.3.(1) At the end of treatment, maxillary and mandibular intercanine widths were notsignificantly differences. The maxillary and mandibular interpermolar and intermolarwidth decreased significantly;(2) Significant correlations existed between the horizontalchange of Stomion and WA5-B53.ConclusionsThe responsion of the adult and adolescent patients with bimaxillary protrusion aredifferences. The procline of upper and lower incisors were decreased significantly, but no statistically significant changes were found between the maxillary and the mandible inadult group. But to adolescent patients the hard and soft tissue profile changes producedby orthodontic treatment may either enhance or compensate the effects produced bygrowth. Large incisor retraction may lead to a narrowing of the upper airway inbimaxillary protrusion adult patients.And no statistically significant airway volumechanges were found in adolescent patients. There were significant correlations existedbetween the horizontal change of Stomion and maxillary interpermolar width, but it isunreliable.Since the mechanobiological response of the upper airway should be taken intoconsideration during large incisor retraction, as the pursuit of large incisor retraction maylead to a narrowing of the upper airway in bimaxillary protrusion adult patients.