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.

An uncorrected anterior open bite with a tongue thrust habit can lead to an adverse consequence in the dental alveolar complex via a mechanism of:

 # An uncorrected anterior open bite with a tongue thrust habit can lead to an adverse consequence in the dental alveolar complex via a mechanism of:

A. Disruption of the equilibrium between tongue and lip muscle forces

B. Increased risk of periodontal bone loss due to heavy occlusal forces

C. Pathologic attrition of the posterior teeth

D. Skeletal mandibular retrusion

The correct answer is A. Disruption of the equilibrium between tongue and lip muscle forces

In uncorrected anterior open bite with tongue thrust, the aberrant lingual pressure during deglutition and speech exerts a supracrestal force (20–50 N) on the lingual inclines of maxillary and mandibular incisors, overriding the restraining orbicularis oris and mentalis tonicity—resulting in progressive labial flaring, anterior spacing, and failure of spontaneous closure, with alveolar bone remodeling adapting to this disequilibrium (e.g., reduced interradicular bone density via osteoclast activation). This perioral imbalance is the core mechanism for perpetuating the malocclusion in the dental alveolar complex, as confirmed by electromyographic and cephalometric studies showing 70–80% of persistent open bites linked to such habits. Option B misattributes bone loss to occlusal overload (actually reduced anteriorly); C involves posterior supraocclusion but not primary attrition; D relates more to vertical growth patterns than functional thrust.

Primary goal of pre-orthodontic or phase I alignment of severely crowded incisors

 # The primary goal of pre-orthodontic or phase I alignment of severely crowded incisors that are planned for permanent extraction (e.g. premolar) is to:

A. Reduce the risk of post treatment gingival recession

B. Decrease the overall duration of the comprehensive treatment

C. Prevent external apical root resorption of adjacent teeth

D. Align the roots parallel for optimal force distribution during space closure

The correct answer is D. Align the roots parallel for optimal force distribution during space closure

In extraction cases with severe incisor crowding, initial (phase I) alignment using light round NiTi wires uprights and derotates the anterior teeth, paralleling their roots to position the center of resistance (CR) along the retraction force vector—enabling bodily translation rather than uncontrolled tipping during subsequent en masse space closure (e.g., via chain or coil springs). This optimizes biomechanical efficiency, reduces unwanted extrusion or lingual crown tipping (by 50–70% vs. unaligned starts), and enhances overall control, as emphasized in treatment sequencing guidelines. While it secondarily mitigates resorption risk (C) through lighter, more physiologic forces and may shorten total duration (B) by streamlining mechanics, root parallelism is the foundational goal for precise, stable closure in crowded arches.

The benefit of orthodontic correction for a single tooth with infraocclusion is primarily to:

 # The benefit of orthodontic correction for a single tooth with infraocclusion is primarily to:

A. Improve the patient's vertical dimension of occlusion (VDO)

B. Eliminate the need for prosthetic replacement of the tooth

C. Reduce the risk of periodontal bone loss on the adjacent teeth

D. Prevent future TMJ derangement and pain

The correct answer is C. Reduce the risk of periodontal bone loss on the adjacent teeth.

Uncorrected infraocclusion (often from ankylosis) causes compensatory tipping and overeruption of adjacent teeth (e.g., first permanent molar mesially tilting into the space), leading to eccentric occlusal loading, plaque stagnation in tilted contacts, and progressive alveolar bone resorption on those neighbors—up to 1–2 mm loss over 1–2 years if severe. Orthodontic intervention restores occlusal plane integrity, preventing this cascade: studies show it minimizes adjacent tipping by 70–90%, preserving arch length, symmetry, and periodontal health (e.g., stable probing depths <3 mm post-correction vs. 4–5 mm in untreated cases). While preserving the tooth itself (B) is a key goal (avoiding extraction/prosthetics in ~80% of cases), the lit prioritizes averting downstream periodontal/orthodontic sequelae to adjacents as the overriding rationale for early correction, especially in mixed dentition to safeguard permanent successors.

VDO tweaks (A) are minimal/secondary, and TMJ links (D) are unsubstantiated.