Introduction: To optimize long-term stability, it is ideal to ensure dental positions that are in balance with surrounding structures, such as maintaining the relationship of the maxillary first molar and the infrazygomatic crest (MICR). Our objective is to emphasize the importance of the MICR in both, untreated normal individuals followed longitudinally in a pilot study whose records were obtained from the Bolton-Brush Growth Study Center, Case Western University, Ohio, and in a series of patients treated with upper premolar extractions, analyzing the long-term stability. We also included a patient treated with surgery-first protocol and extractions, all performed in the same orthodontic clinic. Methods: The MICR was analyzed using lateral cephalograms. The first group consisted of twelve untreated class I patients, with records at 12 and 18 years of age. The second group, including twelve class II patients treated with upper premolar extractions, with records at the beginning and end of treatment. Data was analyzed with the Wilcoxon test. Results: In untreated patients, MICR evolves with a mesialization of the first molar, which is statistically significant. The treatment allowed to maintain the MICR in class II patients, by not distalizing the molars. In the class III patient, the maxillary advancement surgery altered the MICR, although a stable occlusion was achieved. Conclusions: Correct MICR favors treatment stability, improving the prognosis against possible relapse. However, there is lack of studies analyzing changes in occlusal load transfer, and possible repercussion in patients whose relationship is altered by maxillary advancement surgery.
(Rev Esp Ortod. 2017;47(3):125-135)