Preliminary Study On The Correction Mechanism Of Myobrace Appliance For Children With Anterior Crossbite

Background:Anterior crossbite is a common malocclusion of children,which affects the growth and development of teeth,the function of the jaws,the aesthetic appearance of the face,and the mental health.Early treatment is particularly important because the anterior crossbite have a tendency to aggravate.Myobrace is an emerging functional appliance that can improve perioral muscle activity,correct abnormal muscle strength,and provide good conditions for growth of alveolar bone and jaws in growing children.At present,there are some controversies about the correction effects and mechanism of Myobrace.There are few studies on the treatment of anterior crossbite with the appliance and as a kind of functional appliance,whether it could affect the position of the jaws and affect the width of the upper airway is still controversy,and its mechanism is still unclear.Objective:To study the changes of the jaws,alveolar bone,width of upper airway space and hyoid bone position after treatment with Myobrace in the children who are in the growth period and have anterior crossbite,and to explore the correction mechanism of the Myobrace functional appliance on the anterior crossbite,then provides a reference for the clinical application of Myobrace.Method:According to the inclusion criteria,10 patients with anterior crossbite and treated with Myobrace functional appliance were selected as the treatment group,aged 6.8±1.62 years.The patients in the treatment group were treated with Myobrace appliance for lh/d and all night,and the tongue was trained for 10min/d.The lateral cephalometric films were taken before the treatment and 12 months later.Another 10 patients with untreated anterior crossbite were selected as the control group,aged 6.5± 1.65 years old.The lateral cephalometric films were taken at the initial visit and 12 months later.The measurements include 17 hard tissue measurement items and 5 soft tissue measurement items.All the measurement data of the treatment group were compared before and after the treatment and compared with the control group.All the results of comparisons were statistically analyzed.The statistical analysis software was SPSS 23.0,and the test level was a=0.05.Results:1.The position of maxilla(SNA,ANB),the length of the upper and lower jaws(A’-Ptm’,Co’-Po’)and the mandibular plane angle(MP-SN,MP-FH)increased in the treatment group.The inclination of lower incisors(L1-MP)decreased,the changes above were statistically significant compared with the pre-treatment data(P<0.05),but compared with the control group,only the changes of MP-SN,MP-FH and L1-MP were statistically significant(P<0.05).There was no significant difference before and after treatment in the position of mandible(SNB),the position of chin(PRL-Po),the inclination of upper incisors(UI-SN),Wits appraisal,the protrusion of upper and lower lips(Ls-E,Li-E)(P>0.05),and no significant difference was observed between the two groups(P>0.05)2.In the sagittal position of the hyoid bone,the increase of C3H before and after treatment was statistically significant(P<0.05),and the difference was not significant after comparison with the control group(P<0.05);the vertical position of the hyoid bone(MPH,HH1,FHL-H)was not statistically different before and after treatment(P>0.05),and there was no difference between the treatment group and the control group(P>0.05).3.The width of upper airway(SPPS,MPS,IPS)increased in the treatment group,compared with the control group,the superior-posterior airway space(SPPS)increased after treatment,and the difference was significant(P<0.05)while there was no significant difference in the change of the middle airway space(MPS)and the inferior airway space(IPS)(P>0.05).Conclusion:1.Myobrace appliance is an effective orthodontic tool for children with anterior crossbite in early growth and development period.Its main functions are as follows:(1)the retroclination of the lower incisors;(2)the clockwise rotation of the mandible.It indicates that the Myobrace appliance is mainly used for the correction of the anterior crossbite by the retroclination of the lower incisors and the clockwise rotation of the mandible.2.After the treatment,the sagittal position of the hyoid bone and the maxilla moved forward,and length of the maxilla is increased,indicating that the tongue muscle training may cause changes in the position of the hyoid bone and the forward movement of the maxilla.However,the changes above were not statistically significant compared with the control group,which may be related to the limitations of sample size and follow-up time.The accuracy of this hypothesis needs to be verified by further studies.3.The upper part of the upper airway is widened after the treatment,suggesting that the Myobrace appliance has an effect on the width of upper airway,which may be related to the growth of the maxilla during the treatment,but the change of the maxilla is not significant compared with the control group,the mechanism of upper airway width change still needs further study and discussion.