• 9.1 Aetiology
• 9.2 Occlusal features
• 9.3 Assessment and treatment planning in Class II division 1
• 9.4 Early treatment
• 9.5 Management of increased overjet with Class I/mild Class II skeletal pattern
• 9.6 Management of increased overjet with moderate to severe Class II skeletal pattern
• 9.7 Retention

Viva Questions - Chapter 9: Class II Division 1 (Mitchell's Introduction to Orthodontics)

Section 9.1 - Aetiology

• Skeletal Class II base - most commonly due to a retrognathic mandible (short mandibular body, posteriorly positioned condyles)
• Less commonly, a prognathic maxilla
• Increased vertical skeletal divergence (hyperdivergent pattern) may worsen the overjet
• Reduced lower anterior face height may also be seen in some cases

• Proclined upper incisors due to: digit sucking habits, tongue thrust, incompetent lips
• Lower labial segment retroclined by a deep traumatic overbite
• Premature loss of lower deciduous canines causing lower labial segment retroclination

• Lip incompetence - when the lips are apart at rest, the lower lip frequently lies behind the upper incisors. This allows the upper incisors to procline further while the lower incisors are restrained, worsening overjet.
• Digit sucking habits - sustained thumb/finger sucking beyond age 7-8 years proclines upper incisors, retrolines lower incisors, may create anterior open bite, and narrows the upper arch
• Endogenous tongue thrust (true adaptive) generally follows the malocclusion; primary tongue thrust is rare

1. Primes the upper labial segment labially (proclined upper incisors)
2. Retrolines lower incisors
3. Prevents normal vertical development anteriorly (anterior open bite)
4. Creates a posterior cross-bite due to buccinator pressure narrowing the upper arch
5. If habit ceases before age 7-8, spontaneous improvement often occurs; after that, orthodontic treatment is usually needed

Section 9.2 - Occlusal Features / Objectives

• Increased overjet (>4 mm; can be 10-12 mm in severe cases)
• Class II incisor relationship
• Class II molar relationship (usually)
• Overbite is often increased (deep) and may be traumatic (lower incisors occluding on palatal mucosa)
• Upper arch may be narrow with upper canines buccally displaced
• Lower arch crowding is common
• Lip incompetence

1. Reduce and eliminate the increased overjet
2. Correct the incisor relationship to Class I
3. Correct the molar relationship to Class I (or at least a cuspal Class II)
4. Eliminate any deep traumatic overbite
5. Align teeth within both arches
6. Achieve a stable result that does not relapse

Section 9.3 - Treatment Planning

• Skeletal pattern: mild/moderate vs. severe Class II discrepancy
• Dental age/growth remaining: treatment in growing patients allows use of functional appliances; adults may need orthognathic surgery
• Vertical skeletal pattern: hyperdivergent patients are poor candidates for functional appliances; headgear with high-pull may be needed
• Overjet magnitude: small overjet can be managed with URA or fixed appliance alone; large overjet needs functional appliance or surgery
• Space requirements: presence of crowding affects whether extractions are needed
• Patient compliance: functional appliances are compliance-dependent
• Lip competence: incompetent lips worsen prognosis for stability

• Early treatment does not produce significantly better long-term outcomes than late treatment
• Early treatment increases the overall duration of active treatment
• Some benefit in trauma prevention from early overjet reduction may justify early intervention in selected cases (overjet >9 mm)

• Mild skeletal discrepancy (Class I or mild Class II skeletal pattern)
• Overjet that can be reduced by tipping upper incisors palatally
• Sufficient space (e.g., after extractions)
• Cooperative patient It uses a Roberts retractor (palatal spring) to tip upper incisors. It is a tipping appliance only - it cannot produce bodily movement or torque.

• Restraint of maxillary forward growth (~27% of overjet reduction)
• Enhanced/redirected mandibular growth (~some forward positioning)
• Dental tipping: retroclination of upper incisors and proclination of lower incisors

• Twin Block (most widely used, "gold standard") - two separate blocks, upper and lower, with inclined planes
• Frankel appliance (FR-2)
• Clark's Twin Block
• Harvold activator
• Medium Opening Activator (MOA)
• Bionator
• Herbst appliance (fixed functional)
• Forsus appliance (fixed functional)

• Restraint of maxillary forward growth (dental and skeletal)
• Increase in mandibular length (controversial - approximately 1-2 mm extra growth vs. untreated controls)
• Anterior repositioning of the mandible
• Retroclination of upper incisors
• Proclination of lower incisors (a risk of over-proclination)
• Mesial movement of lower buccal segments
• Distal tipping of upper buccal segments
• Dental changes account for approximately 60-70% of overjet reduction; skeletal changes 30-40%

• Cervical-pull headgear (most common): force directed downward and backward, retracts and extrudes upper molars. Useful in cases with reduced lower anterior face height.
• High-pull headgear: force directed upward and backward. Used in hyperdivergent patients to intrude and retract upper molars without extrusion. Also used to control vertical growth.
• Headgear provides skeletal anchorage (restrains maxillary growth) and can distalize upper molars to create space.
• Major limitation is compliance; also significant safety concerns (eye/facial injuries from rebound if not using safety mechanisms).

1. After functional appliance - to detail the occlusion, align teeth, achieve correct torque of incisors, and close any residual spaces
2. Alone (camouflage) in mild/moderate skeletal Class II with acceptable facial profile - usually involving upper premolar extractions + retraction of upper labial segment with sliding mechanics
3. Pre-surgical orthodontics in severe skeletal Class II patients to be combined with orthognathic surgery

• Upper first premolars (most common) - to provide space for upper labial segment retraction
• Occasionally upper second premolars if there is less crowding
• Lower arch extractions depend on crowding and anchorage requirements
• In a growing patient with functional appliance treatment, lower extractions may not be needed
• "4 premolars out" (all four first premolars) may be used if there is crowding in both arches

• Severe skeletal Class II discrepancy (ANB > 5-6 degrees) not amenable to growth modification
• Adult patient - no growth remaining
• Hyperdivergent pattern making functional appliances ineffective
• Significant facial asymmetry
• When camouflage treatment would compromise the dental or periodontal health
• Patient desire for improvement in facial profile (not just dental alignment) Surgery: usually bilateral sagittal split osteotomy (BSSO) of the mandible to advance it, sometimes combined with Le Fort I maxillary setback.

Section 9.4 - Early Treatment

Section 9.5 - Increased Overjet with Mild Skeletal Discrepancy

1. Extract upper first premolars (and lower first premolars if lower crowding present)
2. Use a fixed appliance to retract the upper labial segment using sliding mechanics (e.g., retraction on rectangular archwires using elastic chain or coil spring)
3. Control anchorage carefully (TPA, headgear, or TADs if needed)
4. Achieve Class I incisor relationship and Class I molar (or Class II molar if only upper extractions)
5. Detail the occlusion
6. Retention

Section 9.6 - Increased Overjet with Moderate to Severe Skeletal Class II

• Phase 1: Twin Block functional appliance to advance the mandible and reduce the overjet to approximately 3-4 mm, while correcting the molar relationship
• Phase 2: Following functional appliance treatment, extract upper first premolars (and lower premolars as needed), place fixed appliances, detail the occlusion
• Retention with Hawley retainer/vacuum formed retainer
• Explain that roughly 30-40% of improvement is skeletal (mandibular growth stimulation) and 60-70% is dental tipping

Section 9.7 - Retention

• Corrected overjet can relapse if labial musculature remains incompetent (lip seal not established)
• Lower incisor proclination from functional appliance can relapse
• Mandibular growth may cease while maxillary growth continues, worsening the skeletal pattern again
• Retention should be worn full-time initially, then nights only

• Upper Hawley retainer - standard; allows some occlusal settling
• Vacuum-formed (Essix) retainer - full coverage; good for alignment retention
• Fixed bonded retainer (lower 3-3 or 4-4) if lower incisors were proclined
• Functional appliance itself can be used as a night-time retainer in the short-term post-treatment

Bonus / Crossover Questions

• Allows upper incisors to continue procline
• Prevents lower incisor proclination (keeps lower labial segment back)
• Acts as a "self-perpetuating" mechanism worsening the overjet
• After treatment, the lower lip should lie in front of or at the level of the upper incisors for stability

Note: These questions are based on the confirmed contents of Chapter 9 ("Class II Division 1") from An Introduction to Orthodontics by Laura Mitchell (Oxford University Press, multiple editions including 4th 2013 and 5th 2019). The book is not available in the institutional library, so answers draw on the confirmed chapter structure plus established orthodontic knowledge consistent with Mitchell's approach.