Changes in Andrews' fifth key of occlusion (interproximal contacts) before and after orthodontic treatment.

This study aimed to assess the changes in interproximal contacts before and after orthodontic treatment using the OXIS classification. OXIS refers to the types of contacts that is open (O), point contact (X), straight contact (I), and curved contact (S), and thus the acronym "OXIS". Interproximal contact data of 30 orthodontic patients were obtained at three time points: T0, at the beginning of treatment; T1, at the end of fixed appliance treatment; and T2, one-year post-treatment. For the maxillary second molar-first molar contact, the most common contact at T0, was the "S" pattern (41.6%) which increased to 61.6% at T1 and reduced to 48.3% at T2. For the maxillary first molar-second premolar contact, maxillary second premolar-first premolar contact, and maxillary first premolar-canine contact, the most common contact at T0 was the "I" pattern (58.3%, 46.5% and 43.3%, respectively), which increased to 88.3%, 93.3% and 73.3%, respectively at T1 and decreased to 80%, 88.3% and 71.6%, respectively at T2. For the maxillary canine-lateral incisor contact and lateral-central incisor contact, the most common contact at T0 was the "O" pattern (45% and 33.3%) while it was the "X" pattern at T1 (63.3% and 80%) and T2 (58.3% and 80%). A similar observation was made for the posterior mandibular and anterior teeth. There was statistical significance for most of the changes in the mandibular contacts (p ˂ 0.05). Interproximal contacts change significantly from T0 to T1. Broader contacts were normal at T1 and T2 in the posterior segments. At T2, changes in the interproximal contacts were observed in the posterior segments, and substantial evidence was available, particularly for the mandibular arch.