The Clinical Evaluation of Two Different Film Thicknesses of Clear Overlay Retainer.

Inclusion Criteria: * Patients after active orthodontic treatment; * Must be healthy without systemic and oral diseases; * The central incisors, canines and first molars of both upper and lower arches must be existed; * Agreed to the trial and signed informed consent forms, either by themselves, or their parents. Exclusion Criteria: * Oral habits such as bruxism and clenching, * Do not accept this type of retainers