Impact of orthodontic treatment on TMD signs and symptoms based on high-quality systematic reviews

 # Which of the following is the most consistent finding regarding the impact of orthodontic treatment on TMD signs and symptoms based on high-quality systematic reviews?

A. Correction of a deep overbite is the only proven method to prevent TMD in high-risk patients.

B. Orthodontic treatment significantly decreases the risk and severity of TMD for all patients.

C. Orthodontic treatment significantly increases the risk and severity of TMD due to prolonged appliance wear.

D. Orthodontic treatment neither prevents nor causes TMD 

The correct answer is D. Orthodontic treatment neither prevents nor causes TMD

High-quality systematic reviews and meta-analyses, including those by Kim et al. (2002), Manfredini et al. (2016), and Jeong et al. (2024), consistently find no causal relationship between orthodontic treatment and TMD development or resolution, with pooled odds ratios near 1 (e.g., OR 0.75, 95% CI: 0.37–1.51; p=0.42) and qualitative syntheses showing only transient, mild signs (e.g., clicking) without prevalence increases. Methodological heterogeneity in TMD diagnostics (e.g., RDC/TMD vs. questionnaires) limits definitive claims, but no evidence supports causation, prevention, or exacerbation across diverse populations and techniques. Claims of increased risk (e.g., OR 1.84 in a 2023 review) stem from flawed designs (e.g., excluding RCTs, selection bias) critiqued in Evidence-Based Dentistry. Deep bite correction (A) shows inconsistent TMD benefits; universal risk reduction (B) or increase (C) lacks substantiation in longitudinal cohorts.

The most crucial factor for long-term stability and prevention of relapse in the mandibular anterior segment after correction of severe crowding is:

 # The most crucial factor for long-term stability and prevention of relapse in the mandibular anterior segment after correction of severe crowding is:

A. Interproximal reduction (IPR) sufficient to remove Bolton discrepancy

B. Maintaining a well-fitted, bonded lingual retainer

C. Normalizing the incisor-mandibular plane angle to 85-95 degrees

D. Surgical normalization of the interdental papilla position

The correct answer is B. Maintaining a well-fitted, bonded lingual retainer

Severe mandibular anterior crowding relapse occurs in up to 70% of cases post-treatment due to soft tissue pressures, growth changes, and mesial drift, but long-term stability (e.g., <2 mm irregularity over 5+ years) is most reliably achieved with indefinite fixed retention via a well-fitted, bonded lingual retainer (e.g., 3x3 canine-to-canine design), which minimizes lower incisor proclination and intercanine width loss by 50-80% compared to removable options. Prospective and retrospective studies confirm bonded retainers' superior efficacy, with failure rates of 7-50% but sustained alignment in compliant cases, outperforming other strategies alone. While IPR (A) aids initial space creation without increasing relapse risk, it doesn't prevent post-retention changes; IMPA normalization (C) reduces proclination-related instability but requires retention for durability; and surgical papilla correction (D) addresses aesthetics, not occlusal relapse.

Predictor of increased idiopathic external apical root resorption (EARR) during fixed orthodontic treatment

 # Which pre-treatment occlusal factor is considered a significant, independent predictor of increased idiopathic external apical root resorption (EARR) during fixed orthodontic treatment?

A. Deep, traumatic overbite with incisor contact

B. Mild Class III Malocclusion with reverse overjet

C. Severe Mandibular Anterior Crowding

D. Pre Treatment history of TMD pain

The correct answer is A. Deep, traumatic overbite with incisor contact

Deep, traumatic overbite—where mandibular incisors impinge on maxillary incisor edges or palatal gingiva—necessitates corrective mechanics like incisor intrusion or torque adjustments during fixed orthodontic treatment, which exert sustained compressive forces on the periodontal ligament and cementum, elevating idiopathic EARR risk by 1.5–2.5 times compared to non-traumatic deep bites (p < 0.05). Multivariate analyses confirm this as an independent pre-treatment predictor, distinct from treatment duration or extractions, due to the heightened biomechanical stress on apical regions during bite opening. In contrast, mild Class III (B) often involves proclined lowers with less intrusive needs; severe mandibular crowding (C) correlates modestly via root-cortical proximity but not independently for incisor EARR; and TMD history (D) shows no significant association in prospective cohorts.

The improvement in masticatory function following the correction of a posterior unilateral crossbite is best attributed to the restoration of:

 # The improvement in masticatory function following the correction of a posterior unilateral crossbite is best attributed to the restoration of:

A. Reduced muscle hyperactivity in the temporalis muscle

B. Elimination of a functional midline deviation

C. Bilateral, simultaneous grinding and mixing function

D. Ideal anterior guidance and disclusion

The correct answer is C. Bilateral, simultaneous grinding and mixing function

Posterior unilateral crossbite induces a functional mandibular shift toward the crossbite side in centric occlusion, resulting in asymmetric bolus manipulation, preferential unilateral chewing, and reduced efficiency in comminution (grinding) and food mixing. Orthodontic or orthopedic correction (e.g., via expansion or asymmetric mechanics) repositions the mandible to eliminate this shift, reestablishing symmetric occlusal contacts and enabling bilateral, coordinated mandibular excursions for optimal masticatory performance—as evidenced by improved electromyographic symmetry in masseter and temporalis muscles and enhanced particle size reduction in chewing cycles. While midline deviation (B) is eliminated as a byproduct, it's secondary to occlusal symmetry; temporalis hyperactivity (A) may decrease but isn't the primary driver; and anterior guidance (D) is unrelated to posterior crossbite dynamics.