ASSOCIATIONS BETWEEN INITIAL, POSTTREATMEAT, AND POSTRETENTION ALIGNMENT OF MAXILLARY ANTERIOR TEETH

Contradictory findings from studies on pretreatment malalignment as a risk factor for relapse of maxillary incisor alignment may be due to i nappropriate sample selection and measurement technique. In an attempt to clarify the issue, 745 sets of study models made before CTI) and a fter (T2) orthodontic treatment and at long-term out of retention (T3) were screened. On the basis of the configuration of the maxillary ant erior teeth on the T3 study models, three groups were established: one with significant spacing (group 1, n = 30); one with significant irre gularity (group 2, n = 49); and one with perfect alignment (group 3, n = 28). The occlusal surfaces of the 321 maxillary study models at T1, T2, and T3 were photocopied and the tooth anatomic contact points dig itized. An algorithm was used to fit the dental arch to the digitized points. Amount of incisor rotation and anatomic contact point displace ment of the maxillary anterior teeth relative to the dental arch were computer generated. Interdental spaces in the maxillary anterior segme nt, as well as overjet and overbite, were measured manually. Nonstruct ural data were collected from the charts. Logistic regression analyses revealed that irregularity was associated with greater anatomic conta ct displacement and with greater incisor rotation both at T1 and T2 (P < 0.01). Similar analyses also revealed that spacing was associated w ith greater interdental spaces at T1 and T2 (P < 0.01). Correlation an alyses revealed that the pattern of pretreatment rotational displaceme nt has a strong tendency to repeat itself after retention (P < 0.001), as opposed to the pattern of contact point displacement and interdent al spacing.