The aim of the present study was to compare the effectiveness of two alignment sequences with thermal activated archwires with different Af temperatures applied for the correction of mandibular anterior crowding

A parallel randomized clinical trial was conducted involving 42 patients ages 15 to 25 years (mean: 19.5 years) who required orthodontic treatment including the correction of mandibular anterior crowding. Eligibility criteria were no active caries, exemplary hygiene, non- extraction in the lower arch and no significant tooth size or shape abnormalities. Outcome: The primary outcome was the degree of crowding measured on plaster casts using Little's Irregularity Index. The secondary outcome was crowding survival time until the occurrence of correction in a six-month period. Randomization: The patients were randomly allocated to the different groups using sealed opaque envelopes. Blinding: The patients were blinded to the group to which they were allocated. Intervention: Patients were treatment with a pre-adjusted appliance (0.022 in- Roth prescription). Two nickel-titanium alignment and leveling sequences were employed - NiTi archwire: 0.012 in and 0.019 X 0.025 in; and thermal activated NiTi archwires: 0.018 in and 0.016 X 0.022 in with different austenite finish temperatures (37ºC and 35ºC), which formed the different study groups.

Inclusion Criteria:

• Moderate mandibular anterior crowding (crowding: 4 to 6 mm) according to Little's Irregularity Index
• Presence of all teeth in lower arch through to the second molars, no indication for extractions in the lower arch
• No need for therapeutic interventions (use of inter-maxillary elastic bands, inter-dental wear, open NiTi spine, active lip bumper)
• Absence of systemic conditions that could affect tooth movements
• Absence of significant tooth size or shape abnormalities
• No history of trauma and no history of root resorption or alveolar bone loss.

Exclusion Criteria:

• Severe mandibular anterior crowding (crowding: up to 7 mm) according to Little's Irregularity Index
• Absence of any teeth in lower arch through to the second molars
• Indication for extractions in the lower arch
• Need for therapeutic interventions (use of inter-maxillary elastic bands, inter-dental wear, open NiTi spine, active lip bumper)
• Presence of systemic conditions that could affect tooth movements
• Presence of significant tooth size or shape abnormalities
• History of trauma and history of root resorption or alveolar bone loss.