Efficacy of swm appliance in the expression of first-, second- and third-order information in Class I and Class II.

Background: To assess the efficacy of a multibracket appliance-Straight-wire Mirabella (SWM) prescription-in terms of achieving the ideal first-, second- and third-order values proposed by Andrews.

Material and Methods: A total sample of 46 Caucasian subjects was divided into two groups: 23 with class I malocclusion (Group 1), and 23 with class II malocclusion (Group 2). The treatment protocol involved fixed multibracket appliances-SWM prescription-for both groups, with the addition of class II elastics for Group 2. Values for ΔU1-PP, ΔIMPA, in-out, tip and torque were measured on digital scans, and the results obtained were compared with the ideal values proposed by Andrews.

Results: Statistically significant differences were revealed between the entire sample and Andrews' values for: in-out on upper lateral incisors and upper canines; tip on the upper first premolars, upper second premolars, upper first molars and upper canines; and torque on the lower central incisors, lower lateral incisors, lower canines and lower first premolars. However, comparison of Groups 1 and 2 revealed statistically significant differences only at the lower lateral incisors. The use of class II elastics influenced ΔIMPA values, but not ΔU1-PP.

Conclusions: The efficacy of the multibracket appliance-SWM prescription-in expressing first- second- and, to a lesser extent, third-order information was demonstrated in both class I and class II malocclusions. Class II elastics only influenced the third-order expression on the lower lateral incisors and the ΔIMPA. Key words: Straight wire fixed appliances, prescription efficacy, Class I malocclusions, Class II malocclusions.