| Objective:This paper is aim to analysis whether the different extraction patterns would make difference in the dentofacial vertical dimention of the hyperdivergent anterior openbite subjects through contrasting the measurements pre and post orthodontic treatment based on the lateral cephalometric radiographs and provide advices to our clinical treatment.Methods:Choose 24 hyperdivergent open-bite subjects who already finished the orthodontic treatment from all the cases treated between 2008-2013 at the Department of Orthodontics,Shenyang Stomatological Hospital,38°<SN-MP < 54°,32°<FH-MP<47°.To ruduce errors,all the cases had Angle ? molar relationship.All the 24 cases had a 0-4.2mm open bite,in the anterior of the arch,there are at least four teeth cannot touch each other in vertical dimension.As to the patients who had habits of tongue-thrust swallowing and mouth breathing,we should advice the patients to break the bad habits at first.To observe the mesial movement of the first molars,all the cases had mild to moderate crowding from 1 to 5mm in both maxillar and mandible.The dental arch width ratio between the upper and lower arch are coordinate and the anterior Bolton tooth ratio are normal.All the cases had no TMJ syndrome before the treatment.Divided the 24 cases into two groups according to the different extractions patterns.The first premolar extractions are group E4(2 male and 10 female,pre-treatment age :16.89±3.26)and the second premolar extractions are group E5(12female,pre-treatment age:16.89±4.81).All the patients treated with 0.022-inch slot system straight wire appliance(SWA),and closed the extraction space by sliding techniques.All the subjects had Class ? molar relationship after the orthodontic treatment.All the cases had no use of the occlusal block and intraoral auxiliary arch such as MEAW,and no use of the extraoral traction appliance(e.g.High-pulled headgear)and intraoral anchorage(e.g.Mini-implant anchorage,Nance appliance and TPA).The lateral cephalometric radiographs were took pre and post the orthodontic treatment by the same X ray system,and all the lateral cephalometric radiographs were traced and measured by one orthodontist.This study includes 12 dentoalveolar measurements and 15 skeletal measurements.The measurements are statistically analysised by SPSS 17.0 software.To determine the changes due to the treatment and to compare differences between the two groups,paired t-test and independent t-test were performed,respectively,and significance was predetermined at P <0.05.Results: a.The measurements have no significant difference between the two groups before treatment(P>0.05);b.After treatment,all the anterior open bite patients get normal overbite,Group E4 has 3.27±0.94 mm increment of the overbite(P<0.001),the Group E5 has 3.59±1.34mm(P<0.001);c.In each group,the anterior lower facial height and anterior total facial height are both increased,the average increment of Group E4 are 3.01±2.41 mm and 3.17±3.06 mm,respectively,Group E5 are 2.90±2.01 mm and 3.56±3.65 mm,all the data have statistical significance(P<0.05);d.there is no significant difference in mandibular plane angle in each group(P>0.05);e.Group2 showed more mesial movement of the maxillary and mandibular first molars and less retraction of the maxillary and mandibular central incisors than group 1(P <0.05);f.Other measurements are clinical insignificant between the two groups(P>0.05).Conclusion:1.Both the two extraction patterns cannot make the mandible rotate counterclockwise and decrease the lower anterior facial height,so it is unreliable to control facial height of hyperdivergent anterior open bite malocclusions through extracting posterior 2.In these patients,premolar enucleation decisions should be based on the dental arch space discrepancy,facial convexity,molar relationship,andthe condition of teeth and so on. |
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