The Research On The Second Retromolar Space In Bimaxillary Protrusion Adults By CBCT

Bimaxillary protrusion is a serious malocclusion, which greatly affects the patients’ appearance, as the development of the society and people s living standards, more and more patients especially adult patients are becoming more and more thirsty for treatment. The incidence of the bimaxillary protrusion in Chinese is higher than the White and the Japanese population. Treatments of bimaxillary protrusion include orthodontic camouflage and orthognathic surgery. Orthodontists usually extract four first premolars to retract the anterior teeth so as to improve the profile with strong anchorage. As the development of orthodontic technology and the change of treatment idea, orthodontists pay more attention to some problems of the extraction, at the same time, they are beginning to search for some methods and possibilities to reduce the necessity of extraction, and how to retract the anterior teeth? Which spaces can be utilized in the dental arch? Many scholars have begun to focus on the second retromolar space. However, it is not clear whether the space can be utilized in retracting the anterior teeth, how much can be used, the three-dimensional structures of the space, the relationship between the spaces and the malocclusion. Some research have been carried on these problems by lateral cephalograms and orthopantomograms, but these images can’t show the space clearly in three-dimensional directions, Cone beam computed tomography(CBCT) is well suited for imaging the craniofacial area. It provides clear images of highly contrasted structures and is extremely useful for evaluating bone. Some medical scholars made some meaningful research on human tissue by CBCT, but the CBCT research on the second retromolar space have not been reported. As a result, we are trying to use CBCT to study the second retromolar space to provide reference for clinical treatment.Objective:The purpose of this study is to analyse the difference of the second retromolar space in bimaxillary protrusion of adults with different vertical facial types so as to help orthodontists to make individualized diagnosis and programs for the bimaxillary protrusion patients.Materials and Methods:According to the inclusion criterion of the study,30bimaxillary protrusion patients were selected randomly, every patients needed the lateral cephalogram. the FMA angle was used to selected10high-angle patients,10average-angle patients, and10low-angle patients, aged18to32years. CBCT scan was used in selecting the mandibular functional occlusal plane as the reference plane.Some parameters including the mandibular ramus length, the mandibular body length, the mandibular second retromolar space, the maxillary length and the maxillary second retromolar space were measured on CBCT. All data were analyzed using variance by SPSS15.0software.Results:1. There was no significant difference between the maxillary retromolar space and the maxillary length in the different vertical facial types. however, the mandibular retromolar space in low-angle group is longer than the average-angle group, and the average-angle group is longer than the high-angle group.2. The length of the retromolar space in the third molar group is longer than non-third molar group.3. The retromolar space has no significant difference between different genders.4. The mandibular body length and the mandibular ramus in high-angle group is shorter than the average-angle group, the average-angle group is shorter than the low-angle group.Conclusion:1. In the different vertical facial types, the maxillary retromolar space has no significant difference, and the mandibular retromolar space has negative correlation with the facial angle. So in clinical treatment, we should take mandibular plane angle into account when using the second retromolar space.2. The retromolar space of the mandible is longer than the maxilla in the different vertical facial types.3. The third molars have a positive effect on the length of the retromolar space, the mandible and the maxilla. We should make the third molar into account when treating the bimaxillary protrusion. 4. The gender has no significant relationship with the second retromolar space.