Objective: To investigate the effects of tooth extraction on dental arch width and alveolar bone width.
目的：研究拔牙矫治对牙弓宽度和基骨宽度的影响。
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Conclusion: We use L as arch length and H as chord length to bend syringe needle that is used to posterior superior alveolar nerve block anesthesia by intraoral injection. The success rate is 98%.
Results: After treatment, in maxilla the arch width and alveolar bone width between canines were in creased(P<0.01), those were decreased between second premolars(P<0.01 ).