Correction of a severe anterior open bite in an adult through combined orthodontic and orthognathic surgery

 # Correction of a severe anterior open bite (greater or equal to 4 mm) in an adult through combined orthodontic and orthognathic surgery (e.g. Le Fort I impaction) primarily improves masticatory function by:

A. Increasing the number of simultaneous bilateral posterior occlusal contacts

B. Increasing the vertical dimension of occlusion

C. Eliminating the need for tongue-thrust habit adaptation

D. Preventing future TMJ derangement and pain

The correct answer is A. Increasing the number of simultaneous bilateral posterior occlusal contacts

Severe anterior open bite in adults often stems from vertical maxillary excess, leading to reduced or eccentric posterior occlusal contacts due to mandibular posturing or supraeruption, which impairs efficient bolus grinding and mixing during mastication (e.g., 20-40% lower chewing cycles for particle size reduction pre-treatment). Combined orthodontic-orthognathic intervention, such as Le Fort I impaction with mandibular autorotation, closes the anterior gap while enhancing posterior coupling—typically increasing functional contact points by 2-3 pairs per quadrant—as confirmed by pre/post-surgical occlusal analyses and electromyographic studies showing 30-50% gains in masticatory efficiency. This restores symmetric force distribution and excursion freedom, outperforming habit correction (C, adjunctive at best) or VDO changes (B, actually decreased here); TMJ benefits (D) are secondary and inconsistent.

Adverse consequences of an uncorrected deep overbite (Class II Div 2)

 # Adverse consequences of an uncorrected deep overbite (Class II Div 2) are most directly related to the biomechanical factor of:

A. Lack of freedom in centric relation to centric occlusion slide

B. Inability to achieve canine-protected occlusion

C. Increased horizontal components of force on posterior teeth

D. Traumatic contact leading to gingival impingement or pathologic wear

The correct answer is D. Traumatic contact leading to gingival impingement or pathologic wear

In uncorrected Class II Division 2 malocclusion, the deep overbite (>5 mm typically) with retroclined maxillary central incisors positions the mandibular incisors to make direct, forceful contact with the palatal gingiva, mucosa, or incisal edges of the maxillary incisors during closure and excursions, imposing high compressive and shear stresses that biomechanically precipitate gingival recession (up to 2-3 mm loss), periodontal attachment breakdown, and localized enamel abrasion. Finite element analyses quantify these forces as 2-4 times normal vertical loading on anterior units, directly linking to the most prevalent adverse sequelae like palatal impingement and wear patterns. Options A and B relate more to condylar positioning or lateral guidance deficits in other Class II variants; C pertains to protrusive overload in open bite or Div 1 cases.

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.