The Effect Of The Upper Airway Volume After Retracting Anterior Teeth By Strong Anchorage In Skeletal Class?Adult Patients With Bimaxillary Protrusion:A CBCT Study

Purpose:To evaluate the changes of the air volume of nasopharynx,palatopharynx,glossopharynx and total airway volume in skeletal Class ? bimaxillary protrusion adult patients with different vertical types by using cone-beam computed tomography(CBCT).Provide a reference for the treatment of clinical operators.Method:Patients with skeletal Class ? bimaxillary protrusions who underwent orthodontic treatment and treated by maximum anchorage from the Affiliated Stomatological Hospital of Nanchang University from January 2015 to December2018 were collected.According to the inclusion criteria and exclusion criteria,21 samples were selected.All the patients were treated with extraction of four first premolars and retraction of anterior teeth using implant anchorage.The subjects were divided into high angle group(FMA>28°),average angle group(22°?FMA?28°)and low angle group((FMA<28°)according to the FMA,7 cases in each group.Cone-beam CT scans were performed before and after treatment for all patients and the CBCT data were used for craniofacial superimposition and reconstruction of the upper airway by Invivo dental 5.0 software.Then airway items(NPV?NPM?PPV?PPM?GPV?GPM?TV)and teeth movements items(?U6M??U6B??L6M??L6B??U1??L1)were measured.Besides,the cephalometric radiographs were performed before and after treatment for all patients and the craniofacial iteams(SNA,SNB,ANB,FMA,IMPA,U1 SN,U1L1,HMP,HC3,HFH)were measured by Winceph 8.0.Each items was measured 3 times and averaged.After that,the difference between pretreatment and posttreatment airway volume(?NPV??PPV??GPV??TV)and the difference of craniofacial iteams(?SNA??SNB??ANB??FMA??IMPA??U1-SN??U1-L1??HMP??HC3??HFH)werecalculated.All data were entered into SPSS 18.0 software for paired t-test,one-way ANOVA,and Pearson correlation coefficient,P<0.05 for statistical significance.Results:1.There was no significant difference about the airway volume change after orthodontic treatment in three groups(P>0.05)2.The decrease of ANB and FMA was statistically significant in the high angle group(P<0.05).In the average angle and the low angle,the decrease of U1-SN and the increase of U1-L1 were statistically significant(P <0.05).3.Comparison of the varies of cephalometric measurements among three groups showed that there was no significant difference between the high angle group and the average angle group(P>0.05).The difference about ?ANB,?FMA,?U1-SN was statistically significant between the high angle group and the low angle group(P<0.05).The difference between?PPV,?GPV and ?TV in the mean angle group was statistically significant compared with low angle group(P<0.05).4.There was a significant correlation among ?GPV and ?HMP(r=-0.579),?TV and ?HMP(r=-0.543),?TV and ?L6B(r=-0.618).The comparison of the three groups was moderately negative.Conclusions:The upper airway volume were found no significant difference in skeletal Class ? adult patients with bimaxillary protrusion after using maximum anchorage.The change of the airway volume is related to the amount of buccal movement of the mandibular first molars and the perpendicular distance from hyoid bone to mandibular plane.