Efficacy of intraarch mechanics using differential moments for achieving anchorage control in extraction cases

A prospective survey was conducted to test the hypothesis that maximum anchorage can be achieved in the maxillary arch by controlling forces and moments using intraarch mechanics while retracting canines into first premolar extraction sites. The sample consisted of 24 patients (mean age 18 years, 9 months) who required the extraction of two maxillary first premolars, with or without extractions in the mandibular arch. Movements of the first molars, canines, and incisors were evaluated with 6 cephalometric variables and 10 study model variables. T tests were used to assess differences between pretreatment and postretraction tooth positions. Cephalometrically, the maxillary first molars (left and right sides combined) moved mesially ONLY 0.7 mm (SD 0.43; p < 0.008). All other cephalometric variables showed no significant differences between the two time points. From the study models, the molars moved mesially ONLY 0.5 mm on both the right and left sides (right side SD = 0.43 and left side SD = 0.38; p < 0.005), while the canines were retracted on average 5.8 mm on the right side and 5.6 mm on the left. The molars and canines showed significant mesiopalatal and distolingual rotations, respectively. Many of the study model and cephalometric variables were significantly correlated to one another. This study questions the need to use adjunctive appliances, which directs a distal force to the posterior teeth, if horizontal molar anchorage control is a treatment objective. By controlling forces and moments, using intraarch mechanics while retracting maxillary canines into first premolar extraction sites, minimal molar anchorage loss occurred.