The aims of this study were to compare health related quality of life, comforts degrees，retention effectiveness, and failure rates as well as survival times between two clear overlay retainers with different thicknesses, thus to provide basis information regarding appropriate selections of the thickness of clear overlay retainers.

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