A Retrospective Study of Factors Contributing to Anchorage Loss in Upper Premolar Extraction Cases

Background: Anchorage control is one of the components in the treatment of extraction cases. However, what determines more or less anchorage loss is still an unanswered question. Aim: The purpose of this study was to investigate the most important factors contributing to the anchorage loss of maxillary first molars in premolar extraction cases. Materials and Methods: The study included 726 upper premolar extraction cases, including 214 male patients and 512 female patients, and the mean age was 14.4 +/- 4.5 years old (range: 9-45). Factors including physiological characteristics, treatment mechanics, and cephalometric variables were collected and their influences on the angulation changes of maxillary first molars were analyzed. Results: The mean angulation change of maxillary first molar after treatment was 2.81 degrees(mesial tipping). The change of UM/PP showed a statistically significant difference in different sex (male 3.84 degrees +/- 5.26 degrees vs female 2.38 degrees +/- 5.10 degrees), age (adult -0.05 degrees +/- 4.73 degrees vs teenager 3.46 degrees +/- 5.07 degrees), and molar relationship (Class II 3.28 degrees +/- 5.15 degrees vs Class I 2.36 degrees +/- 5.19 degrees). There are six variables accounted in the regression analysis (R = 0.608, R-2 = 37.0%). Among them, the pre-treatment molar tipping (Standardized Coefficients: -0.65) and the pre-treatment incisor/molar height ratio (Standardized Coefficients: -0.27) were the most important factors influencing anchorage loss during treatment. Conclusion: Compared with treatment-related factors, the patient's physiological characteristics play a more important role in anchorage loss. The pre-treatment angulation of the maxillary first molar is the most influential factor in changes to maxillary molar angulation, which are often predisposing anchorage loss.