Inclusion Criteria:  Chronological age ranges from 11 years to 13 years. Skeletal Class II malocclusion with a deficient mandible (SNB ≤ 76°). Horizontal growth pattern (MP/SN ≤ 39°). Angle Class II division 1 malocclusion with at least 5 mm overjet. Mandibular arch crowding less than 5 mm. The patients have to be in the prepubertal growth stage (cervical maturational stage 3 or 4) when applying orthopedic force. Patients with good oral hygiene, and a healthy periodontal condition.  Exclusion Criteria:  Patients who underwent previous orthodontic treatment. Patients with previous craniofacial surgeries, chronic diseases, syndromes, or growth problems that may affect bone. Any signs or symptoms of para-functional habits or previous history of temporomandibular disorders. Extracted or missing upper permanent teeth (except for third molars).