Effects Of Premolar Extraction On Upper Airway Morphology In The ClassⅠHyperdivergent Patients

Objective:The study was designed to observe the effects of premolar extraction on upper airway morphology in the ClassⅠhyperdivergent patients by comparing the pretreatment and postreatment upper airway morphology.In order to offer a more reliable theoretical basis for making the clinical orthodontic treatment plan.Methods:Sample selection: There were 13 extraction and 13 non-extraction orthodontic patients with ClassⅠhyperdivergent malocclusion who have finished the orthodontic treatment in the Department of Orthodontics,Hospital of Stomatology,Hebei Medical University from 2009 to 2016 selected.Inclusion criteria : Cervical morphology showed no growth potential.The molars showed ClassⅠocclusion,0°≤ANB≤5°;SN-MP>40°or FH-MP>32°.Except of the third molar,all had whole permanent dentitions with no congenitally missing teeth;no chronic rhinitis,no sleep apnea,no history of respiratory diseases,no previous orthodontic treatment history,no tonsil and adenoid operation history;no craniofacial deformity,no mouth opening deformity,no temporomandibular joint disease history;good health.The date of the pretreatment and posttreatment cephalometrics were complete,recognizable and clear.Sample grouping: The study included 13 patients without four premolars extracted(4 boys,9 girls,with a minimum age of 14 years and a maximum age of 26 years,with a mean pretreatment age of 17.62±3.45 years)and 13 patients with four premolars extracted(3 boys,10 girls,with a minimum age of 14 years and a maximum age of 24 years,with a mean pretreatment age of16.85±3.51 years).All patients had been treated with straight wire appliance(SWA).The mean treatment times were 19±5.63 months for thenon-extraction group and 27.69±7.57 months for the extraction group.The treatment goals were to get a Class I molar and canine relationships and normal overbite and overjet with well-interdigitated teeth at the last of the treatment.Cephalometrics: All cephalometrics of the subjects were taken before and after treatment by the same technician of CRANEX?D panoramic X-ray.All the patients were asked to relax,to breath calmly and not to swallow in the intercuspal position and natural head position.Whole of the cephalometrics were measured with the WinCeph 8.06 software by the same researcher and corrected the mangnification before the measurement.Each measurement was measured three times and then calculated the average values.Statistical analysis:SPSS 21.0 software was used to make the statistical analysis.The value is 0.05 as a standard test.Results:1 The results of measurement of cephalometric analysis before and after treatment1.1 The results of measurement of cephalometric analysis before and after treatment in the non-extraction group1.1.1 Cephalometric analysis of the upper airway before and after orthodontic treatment in the non-extraction groupThe PNS-Ba,PNS-UPW,SPP-SPPW,U-MPW,Mc1-Mc2,V-LPW,PNS-V,length of the soft palate increased after treatment;PNS-R,PAS,C3-RGn,thickness of the soft palate decreased after treatment.There were no significant differences between the pretreatment and posttreatment measurements(P> 0.05).1.1.2 Cephalometric analysis of the hyoid and tongue before and after orthodontic treatment in the non-extraction groupThe sagittal and vertical position changes of the hyoid and the thickness and length changes of the tongue showed no significant differences between the pretreatment and posttreatment(P> 0.05).1.1.3 Cephalometric analysis of the soft and hard tissues before and after orthodontic treatment in the non-extraction groupThe sagittal and vertical position changes of the mandible and maxilla showed no significant differences between the pretreatment and posttreatment(P> 0.05).The U1-NA(mm),L1-NB(mm)increased and the U1-L1 decreased after treatment and also showed significant differences in all the measurements(P< 0.05),but there were no significant differences in the other measurements between the pretreatment and posttreatment(P> 0.05).1.2 The results of measurement of cephalometric analysis before and after treatment in the extraction group1.2.1 Cephalometric analysis of the upper airway before and after orthodontic treatment in the extraction groupThe PNS-R,SPP-SPPW,PNS-V,length of the soft palate increased after treatment;PNS-Ba,PNS-UPW,U-MPW,Mc1-Mc2,PAS,V-LPW,C3-RGn,thickness of the soft palate decreased after treatment.There were no significant differences between the pretreatment and posttreatment measurements(P> 0.05).1.2.2 Cephalometric analysis of the hyoid and tongue before and after orthodontic treatment in the extraction groupThe sagittal and vertical position changes of the hyoid and the thickness and length changes of the tongue showed no significant differences between the pretreatment and posttreatment(P> 0.05).1.2.3 Cephalometric analysis of the soft and hard tissues before and after orthodontic treatment in the extraction groupThe sagittal position changes of the mandible and maxilla showed no significant differences between the pretreatment and posttreatment(P>0.05).But the vertical position changes of the MP-FH decreased after treatment and also showed significant differences between the pretreatment and posttreatment measurements(P< 0.05).The U1-SN,U1-NA(°),U1-NA(mm),L1-MP,L1-NB(°),L1-NB(mm)decreased and the U1-L1 increased after treatment and showed significantdifferences in all the measurements(P< 0.05),but there were no significant differences in the other measurements between the pretreatment and posttreatment(P> 0.05).2 Comparison of the changes in the measurements between the non-extraction group and the extraction groupFor the between-treatment groups outcomes,the changes of U1-SN in non-extraction group and the extraction group before and after the treatment were 1.43±5.46°,-8.65±3.81°;the U1-NA(°)were 1.19±6.25°,-7.28±5.46°;the U1-NA(mm)were 1.13±1.76 mm,-3.60±2.66mm;the L1-MP were3.43±7.08°,-6.77±6.17°;the L1-NB(°)were 3.63±6.08°,-7.34±6.36°;the L1-NB(mm)were 1.67±1.96 mm,-2.62±1.90mm;and U1-L1 were-5.14±8.48°,15.18±7.32°.There were significant differences in these measurements between the non-extraction group and the extraction group(P<0.05).The change of the airway sagittal diameter and the hyoid position before and after treatment had no significant difference between the two groups(P> 0.05).Conclusions:Extraction of four premolars for the treatment of the ClassⅠhyperdivergent patients does not affect the upper airway dimensions.