Aim: To assess and differentiate the effects on mandibular incisors and molars during leveling of the curve of Spee in patients treated with either continuous archwires or utility archwires. Subjects and Materials: Two groups of patients, in whom either round/rectangular continuous archwires with a slight reverse curve of Spee (n = 28) or utility archwires (n = 19) were used to level the curve of Spee, were studied. Mandibular study casts and lateral cephalometric radiographs were taken prior to treatment (T1) and after the curve of Spee was leveled (T2). The casts were used to measure arch dimensions, and the cephalometric superimpositions were used to measure mandibular incisor and mandibular molar movements relative to a coordinate system. Results: In the continuous archwire group, the
mandibular incisors proclined, with the incisal edge moving downward and forward, while the mandibular molars extruded and tipped, with the root apices moving further forward than the mesiobuccal cusp tip. The utility archwire group demonstrated intrusion and retroclination of the mandibular incisors, while the mandibular molar mesiobuccal cusp tipped by moving distally and extruding. Conclusion: The two techniques had different effects on the mandibular incisors and molars during leveling of the curve of Spee, which needs to be considered when defining specific treatment objectives for a patient. World J Orthod 2002;3:159-165.