Relapse due to late anterior mandibular crowding

 # A key finding from long-term stability studies following orthodontic treatment is that late anterior mandibular crowding is often independent of the pre-treatment malocclusion. This relapse is primarily attributed to:

A. A continued, anteriorly-directed component of natural craniofacial growth

B. The patient's failure to wear a maxillary removable retainer

C. Improper arch form used during the alignment phase

D. A rebound effect from temporary root resorption during treatment

The correct answer is A. A continued, anteriorly-directed component of natural craniofacial growth

Long-term stability studies, including serial cephalometric analyses by Björk and Skieller, demonstrate that late mandibular anterior crowding (developing or worsening 5–10+ years post-treatment) arises from physiologic late mandibular growth—a forward (anteriorly directed) rotation and elongation of the chin relative to the stable incisor apices, which displaces the lower incisors lingually against lip and tongue pressures, reducing arch perimeter by 1–2 mm on average. This process is largely independent of initial malocclusion severity or treatment modality (e.g., extraction vs. non-extraction), occurring in 60–80% of cases regardless of pre-treatment alignment, as confirmed in cohorts like the University of Washington Post-Retention Study (Little et al.). Patient compliance with maxillary retainers (B) influences upper arch stability but not lower growth; improper arch form (C) affects short-term relapse; and root resorption (D) shows no causal link to late crowding. Indefinite lower retention remains essential to mitigate this growth-driven tendency.

Dental Health Component of Index of Orthodontic Treatment needs (DHC of IOTN)

 # From a public health perspective, the Dental Health Component (DHC) grade 4 of the IOTN classifies conditions where the adverse consequences are severe enough to require treatment for health reasons. Which Grade 4 sub-criterion is most directly linked to the risk of dental trauma?

A. 4a: Increased overjet 6 mm to 9 mm with incompetent lips

B. 4h: Extensive hypodontia requiring restorative dentistry

C. 4i: Submerged deciduous teeth

D. 4e: Severe skeletal discrepancy requiring surgery

The correct answer is A. 4a: Increased overjet 6 mm to 9 mm with incompetent lips

In the IOTN DHC, grade 4a specifically addresses increased overjet of 6–9 mm, which significantly elevates the risk of traumatic dental injuries to the maxillary incisors (relative risk ~2.8–4.0 compared to normal overjet <3 mm), as proclined incisors are more protrusive and vulnerable to impacts. Incompetent lips exacerbate this by failing to provide protective coverage, further increasing exposure—though standard IOTN 4a criteria focus on overjet magnitude alone, with lip incompetence noted in grade 3a for moderate cases. Public health guidelines prioritize this sub-criterion for early intervention due to its direct link to injury incidence (e.g., 20–30% higher in affected children), unlike hypodontia (B, 4g/4h: restorative needs without trauma risk), submerged teeth (C, typically 5s: ankylosis-related eruption issues), or severe skeletal discrepancies (D, often 4p or 5a: functional/surgical needs but indirect trauma association via secondary malocclusions).

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.