36 participants who have mild crowding from the Orthodontic Department at University of Damascus Dental School will be randomly assigned into two groups.

1. In the experimental group, patients will be treated using single aligner appliance in order to align their crowding teeth.
2. Control group will undergo typical orthodontic treatment using an MBT-prescription of metallic brackets.

Most adult patients do not prefer traditional fixed appliances for aesthetic reasons, long treatment duration, and relatively difficult oral care. The current study came in order to evaluate the Efficiency of a new single aligner appliance that is both aesthetic and economical.

Inclusion Criteria:

1. Adults patients aged between (16 - 28) years.
2. Class I malocclusion with Mild crowding (1 - 4) mm in the anterior region of the mandibular dental arch
3. All lower teeth are existed (except for third molars).
4. No congenitally missing or extracted teeth (except for third molars)
5. Patients have not undergone previous orthodontic treatment.
6. Patient with good oral hygiene (Plaque Index less than 1).
7. With no severe skeletal discrepancy.

Exclusion Criteria:

1. Bimaxillary dentoalveolar severe protrusion.
2. Any systemic diseases affect teeth movement.
3. Bad oral hygiene.
4. Patient lack of commitment toward follow-up appointments.