| BackgroundThe eruption of mandibular third molars and their management continues to be a subject of debate that interest various clinicians.The third molars are the last teeth developed in the human oral cavity.With the improvement of quality of life and diet,the masticatory muscles,jaw and the other chewing organs may appear unbalanced degeneration.Hence,the third molar will remain impacted easily.The third molars are the most common impacted teeth that can be seen in adults and their eruption is a complicated multifactorial process because of their development,position and formation.Compared with any other teeth,the impaction rate of the third molars could vary from 9.5% to 39%(mandible>maxilla,Class?malocclusion>Class ?malocclusion).Therefore,the clinicians are difficult to predict the eruption of the third molars.The differences of the third molars eruption vary considerably among different population,especially for orthodontic patients whose the magnitude of teeth and bones are inconsistent.In addition,they show a higher impaction rate for the third molars.It is believed that the main cause of high impaction rate of mandibular third molars is the lack of retromolar space and the bad initial angulation.Impacted third molars adversely affect the adjacent second molars as reflected in disruption of the periodontal ligament,root resorption,caries,influence on dental arch crowding and infection from plaque accumulation.Consequently,prophylactic extraction of impacted third molars have been recommended by numerous clinicians.Class?malocclusion is quite common disorder in clinic.According to patients' different kinds of situations,such as age and patients' complaints,anteroposterior discrepancy of bimaxilary,the stability of TMJ,etc.Class?malocclusion can be treated by combined surgical and orthodontic treatment or dental camouflage to dissimulate the skeletal and facial profile discrepancy.If the crowding of arch is severe and the arch length is deficient,the orthodontics tend to prefer premolars extraction.If the maxillary tuberosity develops well and the crowding of arch is not severe,we may adopt non-extraction therapy involves the backward movement of maxillary dentition and the forward movement of mandibular dentition.The mechanisms of different premolar extraction patterns may have a significant effect on the eruption of mandibular third molar.Compared with non-extraction therapy,mesial displacement of the mandibular molar could develop the retromolar space for the third molar's eruption with premolar extraction.Patients with Class?malocclusion have bilateral Class?molar relationship and the position of the upper and lower first molars are stable relatively.But for the patients with Class II malocclusion whose mandibular molar protraction had been used to correct the molar relationship due to their Class?molar relationship previously.Besides,the effect of different extraction patterns on the eruption of mandibular third molars in adult patients with Class?malocclusion is rarely reported in the literature.The purposes of this study were to investigate the changes in the angulation and retromolar space of mandibular third molars with different extraction patterns and to predict the eruption of mandibular third molars.The study of the influence of orthodontic treatment on mandibular third molars eruption will contribute to understanding the impacted factors of the third molar better,consequently help to provide the clinic managements and a new theoretical foundation for the third molars.ObjectiveThe aim of the present study was to compare the changes in the angulation and retromolar space of mandibular third molars in adult patients with Class?malocclusion orthodontically treated with different extraction patterns,which may help to predict the eruption of mandibular third molars.The results of this study may provide the theoretical basis and a guidance in choosing the suitable treatment.MethodsIn this study,90 adult patients(male 45,female 45)with Class?malocclusion were chosen from the Department of Stomatology,The Second Affiliated Hospital Of Guangzhou Medical University,between 2006 and 2016.A total 170 mandibular third molars,all the patients had passed through the peak of growth and development(CVS4~6),aged from 18~24,average age was 20.72±1.93,the average duration of the treatment was 2.04±0.37 years.All the patients with Class?malocclusion(bilateral Class?molar relationship)and an average angle type(MP-FH=31.1±5.6).In addition,all the patients were treated with MBT straight wire appliance system and closing space in 2-step technique.No attachments to reinforce the anchorage and the extraction space that had been closed fully after treatment in extraction group.The panoramic radiographs were made before and after treatment.All subjects were divided into three groups: non-extraction group(30 patients,58 mandibular third molars);first premolar extraction group(30 patients,58 mandibular third molars);second premolar retraction group(30 patients,54 mandibular third molars).The radiographs were obtained by a single experienced operator with the same machine.All the panoramic radiographs were inputted into Winceph8.0 software to measure the angulation and retromolar space of mandibular third molars by the same doctor in 3 weeks.Compared and analyzed the changes in the angulation and retromolar space of mandibular third molars by SPSS18.0 software.Finally attempted to predict the eruption of mandibular third molars and compare the changes in the possibility of mandibular third molars eruption by “Olive-Basford's method”.Results1.The gender ratios and the average age showed no significant differences before the treatment in each group(P>0.05).2.The measurements for the left or right sides of mandibular third molars showed no significant differences before the treatment in each group(P>0.05).3.The angulation of mandibular first molars showed no significant difference before and after the treatment(P>0.05).The angular changes of mandibular third molars in the first premolar extraction group and the second premolar retraction group both showed significant differences(P<0.001),while there was no significant difference in the non-extraction group(P>0.05).4.The angular changes of mandibular first molars showed no significant differences among each group before and after the treatment(P>0.05).The angular changes of mandibular third molars showed significant differences(P<0.001)among each group before and after the treatment.The differences of M3-MP angular(pretreatment-posttreatment)in both the first premolar extraction group and the second premolar retraction group were less than that in the non-extraction group,while the other measurements differences were greater than that in non-extraction group.5.There were more retromolar spaces of the mandible after the treatment in both the first premolar extraction group and the second premolar extraction group(P<0.001),while the non-extraction group experienced slightly decrease with no significant difference after treatment(P>0.05).The changes of mesiodistal width of the lower third molar showed no significant difference before and after treatment in each group(P>0.05).6.The changes of retromolar space of the mandible showed significant differences before and after treatment among each group(P<0.001).The differences of the retromolar space of the mandible before and after treatment in the non-extraction group were greater than that in the first premolar extraction group,while the first premolar extraction group were greater than that in the second premolar extraction group.The changes of mesiodistal width of the lower third molar showed no significant differences before and after treatment among each group(P>0.05).7.Evaluated the possibility of eruption of the mandibular third molars before and after treatment by “Olive-Basford's method”(AB/CD).The value of AB/CD showed no significant difference in the non-extraction group before and after treatment(P>0.05).The possibility of eruption of the mandibular third molars was significant increased both in the first premolar extraction group and the second premolar extraction group(P<0.001).The differences were statistical significance between the three groups(P<0.001).The differences of the value of AB/CD before and after treatment in the non-extraction group were greater than that in the first premolar extraction group,while the first premolar extraction group were greater than that in the second premolar extraction group.Conclusion1.There was no significant change of the angulation of the mandibular first molars before and after treatment.The position of the mandibular first molars was relatively stable.2.The angulation of the mandibular third molars in adult patients with Class?malocclusion treated with non-extraction therapy underwent slightly mesial inclination with no significant change after treatment.The mandibular third molars were more upright with the first premolar or the second premolar extraction therapy.The improvement of the angulation of the mandibular third molars in the first premolar or the second premolar extraction therapy was better than that in the non-extraction therapy.Besides,there were no statistical significances between the three groups.3.There was significant increase of the retromolar space of the mandible in adult patients with Class?malocclusion treated with the first or second premolar extraction therapy,while the non-extraction therapy experienced slightly decrease with no statistical significance after treatment.The maximum amount of change was the second premolar extraction therapy,followed by the first premolar extraction therapy,and finally the non-extraction therapy.4.The possibility of eruption of the mandibular third molars was improved obviously with the extraction therapy,especially the second premolar extraction therapy was more pronounced than that with first premolar extraction,while the non-extraction therapy showed no difference before and after treatment.But in the end of the treatment,there was quite a bit of patient with extraction therapy underwent the impaction or growth of mandibular third molar.However,an improvement in the opportunity of eruption does not necessarily mean that third molars would erupt in the future.In that case,the long-term observation was needed.The treatment for asymptomatic needed to be considered carefully about its indication.In a word,pathology free third molar impaction should be temporary observation instead of prophylactic removal. |
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