Table 1 Inclusion and exclusion criteria in two groups

Inclusion criteria

1. completed orthodontic treatment with SL or CL brackets, and not receive orthodontic treatment before

2. panoramic radiograph before and after treatment

3. completed root growth of the maxillary incisors before treatment

4. no evidence of EARR of the maxillary incisors on the pretreatment panoramic radiograph

5. no severely dilacerated incisor roots

6. class I molar relationship before treatment and extract four first premolar

7. No root canal teeth, prosthesis

Exclusion criteria

1. impacted teeth

2. trauma before and during orthodontic treatment

3. caries or periodontal disease

4. other systemic diseases, such as lip\palatal cleft