Vertical Discrepancies

The Vertical Paradigm

• Core rule: everything in orthodontics is extrusive, vertical control is the organising idea
• Low angle (square jaw, deep bite) → molar extrusion + mandibular translation
• High angle (open-bite tendency) → molar intrusion + mandibular autorotation
• High angle: never run Cl II elastics, only short Cl II and anterior trapezoid
• Easiest: low-angle / deep-bite / dental
• Hardest: high-angle / open-bite / dental

Diagnosis: Facial Pattern & Long Face

• Dental vs skeletal: localise & quantify; dentoalveolar compensation can mask severe skeletal discrepancy
• Long-face Type I, environmental: mouth breathing, open-mouth posture (adenoids / tonsils / deviated septum)
• Long-face Type II, genetic: short upper lip, VME (excessive downward maxillary growth)
• Long-face Type III: short ramus height, antigonial notch, steep MP, backward (clockwise) rotation
• Hyperdivergent: FMA >28°, SN-MP >32°; dolichofacial; open-bite tendency; low bite force
• Hypodivergent: FMA <25°, SN-MP <32°; brachycephalic; deep overbite; strong masseter

Cephalometric Toolkit, Vertical

Y-axis (S-Gn / FH)

59° ± 6<53 counter-CW / brachycephalic; >65 clockwise / dolicho

FMA (FH–MP)

<25° hypo; >28° hyperhyperdivergent MP >30° = long-face syndrome (33.3)

SN-MP

<32° hypo; >32° hypercorroborates FMA

MMPA (Mx–Mn planes)

27° ± 4>27° open-bite tendency; <27° deep-bite tendency (Millett)

Jarabak ratio (PFH/AFH)

posterior at fault → skeletalanterior at fault → postural

NSBa / Saddle angle

>135° vertical growth~118° brachycephalic

LAFH (% total face)

35% normal<35% decreased; >35% increased

Anterior Open Bite: Definition & Prevalence

• Definition (Carabelli/Sato): incisors fail to overlap vertically; occlusal planes do not meet at incisor level
• Peak age: most common 8–10 y in the mixed dentition
• Prevalence: ~4% of schoolchildren and adolescents
• Self-correction: ~50% of 3-year-olds show AOB; most resolve once sucking habits cease
• Sustained AOB in permanent dentition is not self-correcting

Etiology: Local vs General Factors

Classification of Open Bite

• False/dental: teeth proclined, osseous bases normal, not beyond canines
• True/skeletal: alveolar processes deformed, dolicho/hyperdivergent, increased lower facial third
• By zone: anterior / posterior / complete
• Anterior subtypes: dental (eruption impediment) vs skeletal (posterior facial growth)
• Early Tx types (23.1): Type I simple dental · Type II combined · Type III dentoskeletal
• Severity: incomplete / simple / complex / compound

Cephalometric Differential Diagnosis

• Localise with MP/PP angle (~30° in normal occlusion; occlusal plane bisects it equally)
• Normal molars + incisor under-eruption → anterior dental cause only
• Over-eruption maxillary molars → posterior maxillary cause
• Over-eruption mandibular molars → posterior mandibular cause
• Low ODI (< 67°) = open-bite tendency; low APDI (< 77°) = Class II frame
• Hyperdivergent signs: steep MP, large gonial angle, short ramus, antegonial notch

Sato Model: Posterior Discrepancy

• Prime cause: molar over-eruption + mesial tipping alters the posterior occlusal plane (POP)
• Born Class II → normal vertical molar increase → POP flattens → forward mandibular rotation → Class I
• Insufficient vertical → mandible cannot rotate forward → opens (Class II high-angle AOB)
• Excessive vertical → strong forward rotation → prognathism with AOB (Class III)
• POP steeper → backward mandibular rotation; POP flatter → forward rotation + TMJ decompression

Closure Mechanics I: Principles

• Extrusion closes fast (~1 mm/month) but is UNSTABLE; leave arch 2–4 months after closure
• Posterior intrusion is slower but more stable; scissor effect: 1 mm posterior bite block → >3 mm anterior opening
• In-block extrusion bend: 0.5–1 mm step; force 800–1000 g; pain + root-resorption risk
• Individual extrusion: 30–40 g per upper incisor, 20 g per lower incisor
• Bypass arches (NiTi/TMA 0.012–0.020"): 1–2 mm/month, no tip/torque control
• Vertical-pull chin cup (VCC): growth control in the high-angle open bite, restrains vertical growth & drives forward autorotation, prevents molar extrusion, ~12 h/day ± posterior bite block

Closure Mechanics II: Appliances

MEAW Approach

• Wire: 0.016 × 0.022" Elgiloy in 0.018 slot; L-loops at every interproximal space
• Tip-back bends: 2–3° per tooth, cumulate to 15–20°; upright buccal segments; control POP
• Elastics: 3/16", 6 oz, ANTERIOR ONLY, never in molar zone (molar elastics cause over-eruption)
• Extract third molars in ALL AOB cases (never premolars, Sato: no P1 extractions in ~40 y)
• Class II elastics abandoned: move anterior back + posterior forward, oppose desired forward mandibular adaptation

Course Emphasis: Detorque, Don't Extrude

• Close by detorquing, not extrusion: lower incisor extrusion + upper incisor detorque + posterior intrusion
• Pitts technique: high-torque brackets inverted on 1 & 2 to close AOB without extruding incisors
• Cleats behind lower incisors to improve tongue posture and control torque
• Lingual arch (lower) to prevent molar extrusion
• AOB splint (acrylic + mini-screws TAD anchorage) for reliable molar intrusion

Surgery & Stability

• Le Fort I maxillary impaction → mandibular autorotation; bite closes in hours
• Indications: AOB > 6 mm + high MP + weak chin → impaction + BSSO
• AOB surgical relapse: highest at 42.9%, because occlusal planes not corrected, molars not leveled
• Non-surgical stability: correct the vertical dimension; results hold at 10–16 y follow-up
• Pre-surgical prep: heavy arches, surgical hooks; models every 6 months during presurgical Tx
• Stability key: upright the buccal segment (~15° → 4.5 mm space/side); short retainer 3–6 months

Deep Bite: Definition & Norms

• Overbite norm: 2–3 mm; percentage more accurate (crown-length variation)
• Nanda: 25–40% acceptable if TMJ function sound
• Neff: 20% ideal; 33.3: 5–20% normal range
• Deep curve of Spee: hallmark of dental deep bite
• Freeway space: 2–4 mm, must be preserved after bite opening

Deep Bite Classification

• Dental (simple): teeth/alveolar only, acquired, deep curve of Spee, normal vertical skeleton
• Skeletal (complex): basal malrelationship, hereditary, two-step occlusion, high relapse
• Skeletal signs: reduced LAFH, long PFH, small gonial angle, short broad symphysis
• Brachy pattern: counterclockwise mandible rotation, convergent facial planes
• Dental cause: molar infraocclusion and/or incisor over-eruption (or combination)
• Cl II Div 2: most frequent clinical association with deep bite

Neuromuscular Basis & Consequences

• Posterior vertical chain: masseter, temporalis, internal pterygoid, anteriorly positioned & strong → deep bite
• Mechanism: strong anterior position depresses dentition, blocks posterior eruption
• Periodontal: occlusal overload, traumatic overbite, circumscribed radiolucencies (Roque)
• TMJ: condyles forced backward/upward in fossa, clenching, disc displacement, headache
• Incisal consequences: labial migration, wear of mandibular incisors, maxillary anterior spacing

Cephalometric Localisation

• Key comparison: palatal-plane/OP angle vs mandibular-plane/OP angle
• PP/OP > MP/OP: maxillary incisor over-eruption or maxillary molar intrusion
• PP/OP < MP/OP: mandibular incisor over-eruption or mandibular molar intrusion
• Low-angle signs: decreased MP angle, large ramus, small gonial angle (FMA < 25°, SN-MP < 32°)
• Jarabak ratio: PFH/AFH, posterior fault → skeletal; anterior fault → postural

Treatment Principles: Four Levers

Force Specifications

Intrusion Appliances I

• Anterior bite plane / Hawley: disoccludes posteriors → passive eruption; scissor effect 1 mm extrusion = 2–3 mm bite opening
• Bite turbos: resin on palatal upper incisors, comfortable, hygienic; 6.5 oz elastics q24 h
• Growth-direction rule: favourable hypodivergent; contraindicated hyperdivergent
• Cl II Div 2: turbos procline retroclined incisors (reversing incline plane)
• Utility arch (Ricketts 2×4): 45° tip-back + negative torque ~10–15° → pure incisor intrusion

Intrusion Appliances II

• Burstone segmented arch: 0.018×0.022 SS, ~3 mm helix anterior to molar tube, pure anterior intrusion
• Reverse-curve / anti-Spee (Gregoret): negative torque seats apices in trabecular bone → intrusion without proclination
• Round reverse-curve: 300–400 g continuous, suits brachycephalic, intrudes + proclines (no root control)
• Intrusion arch with loops: 5–7 mm vertical loop, 20 g/tooth, 2–3 months; negative torque essential
• Lip bumper: corrects curve of Spee, distalises/uprights molars, lip dysfunction cases

TAD Intrusion & Alexander Discipline

Best lower incisor intrusion

TMA 17×25 + loop tied between incisorsstable, less tipping, less resorption

Force: intermittent light

15–30 g/toothcontinuous → resorption risk

Sydney Intrusion Spring (SIS)

~400 g at 5 mm activationzygomatic plate anchorage

Alexander/Werneck prescription

0.018" slot, 0.017×0.025 SSposterior anchorage unit key

TAD lower intrusion

1.5 × 8 mm between canines–incisorspower chain to pretorqued wire

Distal jet / Beneslider

palatal TADs — 1 mm/monthPAOO: 1 mm/week

Decision Pearls & Stability

• Extraction controversy (Viazis): premolar extraction lingualises remaining teeth → deepens bite, avoid
• Bite plane: favourable hypodivergent (0.5 mm posterior clearance); contraindicated hyperdivergent
• Skeletal deep bite: high relapse, hereditary pattern; combined surgical–orthodontic if severe adult
• Stability: correct CR = CO at end of treatment; lower inter-canine width must not be expanded

Retention & Stability of Vertical Correction

• Intrusion is more stable than extrusion, prefer upper incisor intrusion over extrusion; decide based on VME
• Real retainer = correcting the vertical dimension / occlusal plane (Sato), not an appliance
• Anterior open bite is the least stable correction; greater skeletal contribution → poorer prognosis
• Habit / airway / myofunctional follow-through essential: break digit-sucking / tongue-thrust first; screen airway
• Leave the arch passive after closure; avoid jiggling forces (root resorption risk)

Decision Framework: Master Gate