Clinical Study On Factors Influencing Disturbed Eruption Of Mandibular Second Molar In Orthodontic Treatment

[Objective] To investigate and analyze related factors of mandibular second molar disturbed eruption in orthodontic treatment, and provide clinical guidance for orthodontic treatment.[Materials and Methods]Part one:355 patients with early permanent dentition (aged 10-12 years) were included in the study. All subjects presented with mandibular second molars unerupted before orthodontic treatment, and mandibular second molar eruption completely without treatment. Posttreatment and undergoing panoramic radiographs and plaster model were collected. Incidence and malocclusion types in orthodontic treatment of mandibular second molar disturbed eruption were observed.Part two:36 patients without disturbed eruption of mandibular second molars in orthodontic treatment (mean age 12.96+1.04 years old), male 16 cases, female 20 cases; and 36 cases had disturbed eruption of mandibular second molars in orthodontic treatment (mean age 12.87+1.11 years). Male 16 cases, female 20 cases were selected. The cephalometric radiographs of patients before and after treatment, panoramic radiographs and record mode were collected. Analyze the relativity between mandibular second molar incidence and mandibular third molar tooth germ, vertical facial types, sagittal facial types, anterior dental arch crowding, posterior arch crowding and mandibular first molar antedisplacement by the chi square test and two Logistic regression analysis.[Results]l.The incidence of orthodontic treatment in mandibular second molars dislocation was 59.72% and lingual dislocation rate is the highest, reaching 41.03%. No significant differences was found in gender. (P>0.05).2.Mandibular second molars dislocation in patients with angle class Ⅰ, class Ⅱ and class Ⅲ accounted for 36.79% and 46.23% and 16.98%. No significant differences was found in malocclusion types. (P> 0.05).3.Correlation analysis indicated that orthodontic treatment with extraction of teeth and distance of mandibular first molar moved forward were negatively correlative with mandibular second molar dislocation. (P< 0.05).[Conclusion]1.High rate of mandibular second molars dislocation in orthodontic treatment was noted in the study, which is 59.72%; so that orthodontists might pay more attention to mandibular second molar in treatment plan and operation. No significant differences was found in gender and malocclusion types.2.Correlation analysis indicated that orthodontic treatment with extraction of teeth and distance of mandibular first molar moved forward were negatively correlative with mandibular second molar dislocation3.High rate of mandibular second molars dislocation in orthodontic treatment suggested that orthodontic treatment after mandibular second molar eruption might be an option to shorten and simplify the treatment process.4. In early permanent dentition cases (mandibular second molars unerupted),it is necessary to pay close attention to the mandibular second molar eruption situation, and start treatment of mandibular second molars in time.