The primary benefit of early (Phase I) correction of a mandibular functional shift is to:

 # The primary benefit of early (Phase I) correction of a mandibular functional shift is to:

A. Improve the patient’s TMJ range of motion in maximal opening

B. Prevent asymmetric growth and irreversible skeletal asymmetry of the mandible

C. Reduce the risk of buccal non carious cervical lesions

D. Avoid extraction of premolar teeth in the permanent dentition

The correct answer is B. Prevent asymmetric growth and irreversible skeletal asymmetry of the mandible

Mandibular functional shifts, typically from unilateral posterior crossbite, cause the mandible to deviate laterally (1–3 mm) into centric occlusion to bypass interferences, altering condylar positioning and asymmetric loading during growth—leading to differential mandibular ramus/fossa remodeling (e.g., 1–2 mm longer body on shifted side) and progressive skeletal asymmetry (chin deviation, facial canting) that becomes increasingly fixed post-puberty. Phase I correction (e.g., rapid maxillary expansion in mixed dentition) eliminates the shift by 80–90%, normalizing condylar growth trajectories and averting these changes in 70% of cases, per longitudinal cephalometric studies. TMJ motion (A) improves secondarily but transiently; NCCL risk (C) relates more to excursive interferences; and extraction avoidance (D) stems from space management, not shift dynamics.