The Effect Of Functional Mandibular Advancement On Temporomandibular Joint And The Evaluation Of Long-term Dentoskeletal Stability In Adolecence—A Systematic Review And Meta-analysis

Background and purpose: Skeletal class Ⅱ malocclusion is commonly seen in clinical work.According to epidemiologic research,the incidence of skeletal class II malocclusion is about 20.05% in China.During clinical examination,class Ⅱ molar and canine relationship,along with deep overbite and deep overjet are always observed,and patients always have convex facial profile.The most common cause is mandibular retrognathism.For adolecent patients with mandibular retrognathism,it is a widely used method to use functional mandibular advancer to guide the mandible to a more forward position to make full use of potential growth.However,there is in dispute in the academic community whether this treatment will have adverse effects on TMJ and whether it has long-term stability.Therefore,the aim of this study is to use evidence-based medicine（EBM）to investigate whether functional mandibular advancement（FMA）will have adverse effect on the temporomandibular joint（TMJ）and whether the dentoskeletal effects will remain stable in long term,so that the early treatment can be applied more effectively in adolescent skeletal Class II patients.Methods: Pubmed,EMBASE,Cochrane,Scopus and Web of Science databases were used for electronic searching of the related literatures about functional mandibular advancement used in adolescent patients with class II malocclusion of mandibular retrognathism.The studies about the two following aspects will be eligible for this study:（1）the status of temporomandibular joint（TMJ）and its related symptoms and signs after treatment,and there existed comparison with the TMJ status before treatment（part 1）;（2）patients who were observed for at least one year after treatment,and the dental effects（measured by overjet）and skeletal effects（evaluated by ANB angle）of functional mandibular advancement were evaluated（part 2）.On the preliminary screening,the titles and abstracts were checked thoroughly by two researchers independently.According to the inclusion and exclusion criteria,further screening of the literature would be promoted.According to the guideline on Cochrane Handbook,Cochrane Collaboration risk of bias tool was used to evaluate the quality of the included randomized controlled trails（RCT）,and Risk of Bias In Non-randomized Studies of Interventions（ROBINS-I）tool was used to assess the quality of included non-randomized studies of the effects of interventions（NRSI）.If the results showed great difference,this assessment would be evaluated by the third researcher.The studies deemed to be of low quality would be extracted.Then the extraction of the characteristics of the included studies would be completed,and Review Manager 5.3 software would be used to make forest plots.Finally,statistical analysis would be carried out.Publication bias analysis was performed for studies that met the inclusion criteria.Sensitivity and subgroup analysis were used to measure the sources of heterogeneity and explain the possible impact on the results if there existed high heterogeneity in statistical analysis.Results: 1.In part 1 of this study,the effects of mandibular advancement on temporomandibular joint in adolescence were reviewed in 18 articles,including 5randomized controlled trials,8 non-randomized studies of the effects of interventions and 5 systematic reviews.In part 2 of this study,the evaluation of the long-term stability of the mandibular advancement in adolescence reviewed a total of 8randomized controlled trials and 4 non-randomized studies of the effects of interventions.2.In part 1 of this study,a total of 579 samples were included,temporomandibular joint morphological changes,muscle dysfunction,temporomandibular joint disc position changes,temporomandibular joint noise,maxillofacial pain and temporomandibular joint pain were used as outcome indicators,and a total of 80 patients developed temporomandibular joint discomfort during treatment,but the TMJ symptoms in these patients were relieved or disappeared during the follow-up period.3.In part 2 of this study,a total of 589 samples were included.ANB angle was used to evaluate skeletal stability,and overjet was used as dental index to evaluate stability.A total of 12 articles can be used to evaluate the long-term skeletal stability after mandibular advancement,and 7 articles can be used to evaluate the long-term dental stability of after mandibular advancement.4.In part 1of this study,the results showed that functional mandibular advancement had no adverse effects on temporomandibular joint [I~2=27%,OR=0.54,95%CI（0.33,0.87）,P= 0.01].5.In part 2 of this study,the results of statistical analysis indicated thathe overall skeletal effect is stable [I~2=0%,MD=-0.53,95%CI（-0.82,-0.24）,P = 0.0003],however occlusal effect showed slight relapse [I~2=76%,MD=-0.88,95%CI（-1.42,-0.35）,P = 0.001].Conclusion: 1.TMJ symptoms may occur during the functional oral appliance wearing,but the symptoms will release or disappear during follow-up period.2.Less convinced evidence indicate that slightly previous TMD will be improved after treatment.3.There is TMJ disc anterior displacement observed during treatment,but most of them will return to the normal position later.4.Moderate evidence support that FMA will not induce or aggravate TMD.5.After treatment,there is no significant skeletal relapse observed.But there existed slight occlusal relapse measured by overjet and sagittal molar relationship.6.The reason of the relapse of overjet and saggital molar relationship is:（1）the susceptible relapse after correction in individuals,（2）the growing of maxillary anterior dentoalveolar and the growing of dentition,（3）the inclination of retroclined mandibular incisors is easy to relapse.