Patients who have severe crowding that required four premolars extraction will be treated in this study. The effects of clear aligners therapy on oral health related quality of life (OHRQoL) in comparison with vestibular fixed appliances using the validated OHIP-14 tool during orthodontic treatment. So the aim of the study was to compare the changes in OHRQoL between patients receiving clear aligners or fixed appliances during the first year of the orthodontic treatment.

There are two groups:

First group (Experimental): the patients in this group will be treated using clear aligners.

Second group (Control): the patients in this group will be treated using fixed appliances.

For years, orthodontists and dentists have used removable appliances for orthodontic treatment. Today, with the CAD/CAM technology, clear aligners treat a broader range of cases with greater precision. They consists of a series of plastic aligners that are intended to replace conventional wire and bracket technology for many orthodontic cases. Each custom manufactured aligner exerts gentle, continuous forces to move teeth incrementally from their original state to a final, treated state. Each aligner is worn for about two weeks, then replaced by the next in the series until the final position is achieved.

Inclusion Criteria:

• Class I malocclusion with severe crowding (more than 5 mm of tooth-size-arch-length-discrepancy).
• Good oral hygiene and periodontal health.
• No congenitally missing or extracted teeth (except for the third molars).
• No history of previous trauma to the maxillofacial region or surgical interventions.

Exclusion Criteria:

• Previous orthodontic treatment.
• Subject with psychological abnormalities.
• Subject with systemic diseases.
• Subject has known allergy to latex and plastic