Factors associated with failure of miniscrew-assisted rapid maxillary expansion in adults: a retrospective cohort study

Miniscrew-assisted rapid maxillary expansion (MARME) is widely used to correct transverse maxillary deficiency in adults, yet treatment failure is not uncommon, and existing predictive approaches often rely on cone-beam computed tomography, which entails additional radiation exposure. This study aimed to identify factors associated with MARME failure in adults using routine orthodontic diagnostic records. This retrospective study included 109 adults (≥ 18 years) with transverse maxillary deficiency who were treated with MARME and classified into the success ( n = 82) or failure ( n = 27) group based on radiographic evidence of midpalatal suture separation. Age, sex, and 16 dentoskeletal variables from lateral cephalograms and panoramic radiographs were screened by univariate logistic regression, and a final multivariable model was constructed using Hosmer’s purposeful selection. A simplified scoring model based on risk factors was also developed. In the final multivariable model, male sex, a saddle angle greater than 124.0°, a U6-to-palatal plane distance greater than 25.5 mm, and a root projection beyond the sinus floor ratio greater than 0.5 on panoramic radiographs were significantly associated with MARME failure. Palatal length was retained as a potential confounder but did not reach statistical significance ( p = 0.208). The multivariable and simplified scoring models showed apparent areas under the curve of 0.871 and 0.860, respectively. The predicted probability of failure remained approximately 10% or less with up to two risk factors but increased more markedly with three or more risk factors. Male sex, a larger saddle angle, a greater U6-to-palatal plane distance, and a higher root projection beyond the sinus floor ratio were independently associated with MARME failure. Palatal length was retained as a potential confounder but was not statistically significant. The scoring model using routine diagnostic records may serve as an adjunct to risk assessment.