Analysis Of Bolton Index For Maxillary First Premolars Extraction Cases

Investigate the impact of bilateral maxillary first premolar extraction on Bolton ratios post-orthodontic treatment. 125 patients with maxillary anterior teeth crowded or protrusion, without obvious crowding or protrusion of lower anterior teeth nor obvious skeletal malocclusion were included. Before orthodontic treatment, the overall and anterior Bolton ratio was within the mean ± 1 standard deviation. Digital models simulated bilateral maxillary first premolar extraction, prioritizing posterior ideal occlusion over gap closure, established normal anterior overbite and ideal posterior occlusion; When there were conflict between closing gap and establishing ideal occlusion relationship, prioritized the latter. We measured the overall and posterior Bolton ratio before and after orthodontic treatment, as well as the possible size of gap after orthodontic treatment with good occlusion of the posterior teeth. In the case of ideal occlusion relationship, it was observed that about 27.2% of the samples had gaps in the posterior segment after simulated orthodontic treatment, and the gaps were located in the mesial or distal region of the maxillary second premolar, with an average size of 2.03 ± 1.17mm. After orthodontic treatment, there was a significant difference in both overall and posterior Bolton ratio between those with and without residual gaps in the ideal occlusal relationship, and a regression equation was provided for predicting residual space. Patients with pretreatment-standard Bolton ratios may retain posterior maxillary gaps after bilateral maxillary first premolar extraction and stable occlusion, emphasizing the need for posterior Bolton ratio-occlusion balance in clinical space management.