Level II Unit A Summary--integrated

Unit A - Part 1 : Malocclusion: what is it and why should we treat it?

Describe ideal occlusion regarding tooth relationship to the line of occlusion.

Angle’s Description of “line of occlusion” Lecture, Contemporary Orthodontics (sixth edition) TOC

• Angle used specific suffixes to identify tooth positions:
  • Bucco-version
  • Linguo-version
  • Labio-version
  • Torsio-version (rotation)
• The line of occlusion is a smooth (catenary) curve passing through the central fossa of each upper molar and across the cingulum of the upper canine and incisor teeth. The same line runs along the buccal cusps and incisal edges of the lower teeth, thus specifying the occlusal as well as interarch relationships once the molar position is established.¹
• In the upper and lower arches, this line represents the engagement between the arches, sitting on approximately 138 occlusal contact points.²
• The Angle classification has four classes: normal occlusion, Class I malocclusion, Class II malocclusion, and Class III malocclusion. Normal occlusion and Class I malocclusion share the same molar relationship but differ in the arrangement of the teeth relative to the line of occlusion. The line of occlusion may or may not be correct in Class II and Class III malocclusion.¹

Describe ideal occlusion in transverse, antero-posterior, and vertical planes.

Ideal Occlusion in the A-P Plane Lecture, Contemporary Orthodontics 6e

Image: Antero-posterior (sagittal) occlusal relationship of the molars.¹

• Posterior Occlusion in the anterio-posterior plan is defined by the molar relationship.
  • Divided into 4 classes (Angle’s):
    • Class I (normal occlusion): Mesiobuccal cusp of maxillary fist molar occludes in the buccal groove of the lower first molar
    • Class I Malocclusion: Molar relationships remain the same but differ in the arrangement of teeth relative to the line of occlusion.
    • Class II Malocclusion: Lower molar distally positioned relative to upper molar, line of occlusion not specified
      • Class II Division 1: Proclined maxillary incisors (increased overjet); associated with convex profile and lip incompetence
      • Class II Division 2: Retroclined maxillary incisors + proclined lateral incisors; associated with a deep bite
    • Class III: Lower molar mesially positioned relative to upper molar, line of occlusion not specified
• Anterior occlusion in the anterio-posterior plane is defined by overjet
  • Overjet: the horizontal overlap of the incisors
    • Normally the incisors are in contact, with the upper incisors ahead of the lower by only the thickness of their incisal edges (i.e., overjet of 2 to 3 mm is the normal relationship).
    • If the lower incisors are in front of the upper incisors, the condition is called reverse overjet or anterior crossbite.³
    • Image: Overjet — the horizontal overlap of the incisors.

Ideal Occlusion in the Transverse Plane

• Occlusion in the transverse plane is dictated by the location of the posterior teeth.
• Normal transverse occlusion is: Upper teeth buccal to lower teeth (i.e. BULL Rule )
• The most common major deviation from the transverse dental relationship is lingual posterior crossbite
• Lingual posterior cross bite: upper teeth lingual to the lower teeth

Ideal Occlusion in the Vertical Plane

• Ideal Occlusion in the vertical plane is measure by overbite
• Overbite is defined as the vertical overlap of the incisors
  • Normally the lower incisal edges contact the lingual surface of the upper incisors at or above the cingulum
    • there is normally a 1 - 2 mm overbite
  • In open bite, there is no vertical overlap and the vertical separation of the incisors is measured to quantify its severity

List dental characteristics for the Angle classification and discuss its advantages.

Lecture, Contemporary Orthodontics 6e, Ch.1

Dental characteristics the classification is based on

• Molar relationship — the mesiobuccal cusp of the upper first molar sits in the buccal groove of the lower first molar; the distobuccal cusp sits in the embrasure between the lower 6 and 7.⁴
• Palatal cusp — the upper palatal cusp should sit in the main (central) fossa of the lower first molar.⁴
• Position relative to the line of occlusion — whether the remaining teeth follow the smooth catenary curve or show versions/rotations away from it.¹
• Angle used specific suffixes to describe individual tooth positions: bucco-version, linguo-version, labio-version, and torsio-version (rotation).³

Advantages of the Angle system

• Simple and quick — it reduces a complex three-dimensional relationship to a small number of molar-based groups.³
• Universally understood shorthand — it remains in everyday use and provides a common language for clinical communication of general malocclusion groups between practitioners.³

Limitations of Angle's method

• Subjective and lacking quantification — there is no measurement in millimeters of severity.³
• Considers only the antero-posterior plane — it ignores the transverse and vertical planes of space.³
• Ignores soft tissue, which is the focus of the modern soft-tissue paradigm.³
• It classifies the dentition but does not, by itself, distinguish a dental from a skeletal cause.⁴

Describe functional, health, and psychosocial reasons for treatment.

Lecture

Primary Objectives for Orthodontics

1. Reduce psychosocial handicap — often the most important reason; particularly relevant for Class II patients with large overjets who may experience social impacts such as bullying.⁵
2. Improve oral function — includes preventing instabilities or amending conditions related to the temporomandibular joint (TMJ).⁵
3. Adjunct to disease control (not to treat disease) — while malocclusion (e.g. anterior crossbites) does not cause caries or periodontal disease, it makes cleaning harder, so patients are more prone to lesions without meticulous hygiene.⁵

Describe realistic goals for orthodontic treatment and their evolution.

Lecture The modern objectives for orthodontic treatments fall under the “Soft Tissue Paradigm”

• Treatment goals of the soft tissue Paradigm
  • Normal soft tissue proportions and adaptations
  • Functional occlusion is a secondary goal

Historically the angle paradigm for ideal dental occlusion was to have an ideal dental occlusion and skeletal relationships. This goal has shifted to the soft tissue paradigm in the modern era because a patients appearance is often much more of concern to them and functional occlusion can still occur even if the scheme is not ideal.

Feature	Angle Paradigm	Soft Tissue Paradigm
Primary goal of treatment	Ideal dental occlusion	Ideal soft tissue proportions and adaptation
Secondary goal of treatment	Jaw relationships	Functional occlusion
Hard vs soft tissue relationship	Ideal skeletal/dental produces ideal soft tissue	Ideal soft tissue defines ideal skeletal/dental
Diagnostic emphasis	Dental casts, cephalometric x-rays	Clinical examination of soft tissues
Treatment approach	Obtain ideal dental and skeletal relationships, and the soft tissues will be OK	Determine ideal soft tissue relationships, and then place the jaws and teeth as needed to obtain them

Modern Patient Perception

Patients often identify themselves by their profile in the mirror rather than molar relationships. Modern standards favor fuller profiles (e.g., the “Angelina Jolie era”) over the straight or concave profiles favored in the past.

Discuss treatment need versus demand in the current environment.

Treatment Need 01 - Malocclusion Definition and Prevalence The key points to remember from modern population studies of malocclusion:

• About half the population have well-aligned teeth or slight irregularity, while about 15% have irregularity severe enough that either major expansion of the dental arches or extraction of a permanent tooth in each quadrant of the arch is likely to be needed if the teeth are to be aligned.

• With increasing age, incisor irregularity gets worse and the number of people with ideal alignment decreases.

• 15% of the US population are Class II, and about half of these individuals have overjet severe enough to predispose them to problems in social interactions.

• Open bite is much more prevalent and deep bite less prevalent in African-Americans.

• Class III and reverse overjet are much more prevalent in those of Asian descent.

• Other racial / ethnic differences are modest and unimportant.

Treatment Demand and Patient Demographics Lecture

Treatment need is the clinician’s judgement that a malocclusion warrants correction; treatment demand is whether the patient actually seeks (and accepts) that care. The two diverge widely.

Image: Treatment categories — normal, malocclusion with no treatment, and malocclusion with treatment.	Image: Distribution of who seeks orthodontic treatment across Class I, II, III and normal occlusion.

The perception gap

• 65% of the population have malocclusion.⁶
• Dentists feel that 55% need treatment.⁶
• Patients (lay people) feel that only 35% need treatment.⁶
• ~50% would accept treatment if it were provided at no cost.⁶
• ~5% would not accept treatment even if it were free.⁶

Do lay people not recognise problems, or value treatment differently?

Lay people can discriminate between good and bad teeth. The gap arises because they place a different value on the benefit of treatment relative to its cost, not because they fail to see the problem.⁶

Image: Perception of treatment benefit — dentists 55%, lay people 35%, would accept if no cost 50%.⁶

Treatment utilisation

• Range: only 5–40% of people with malocclusion actually receive treatment.⁶
• Many factors influence the decision, socioeconomic status being a major one. In some areas (e.g. Oahu) up to 75% of treatment may be government-funded.⁶
• 100% free treatment risks low compliance; poor hygiene can produce white-spot lesions around brackets, for which the clinician may be held responsible.⁶

Socioeconomic factors — median family income

Income tracks closely with who gets care. Reported US median family income:⁶

• 2010: all other races $59,914vs.Hispanicorigin$36,771
• 2010–2012: all other races $55,626vs.Hispanicorigin$37,035

Increasing adult demand

Older patients are increasingly likely to want orthodontic treatment now — driven by reasons such as job advancement and the desire to “trade up”, and because treatment has become more socially acceptable (the exact reason remains debated).⁶

Unit A - Part 2 The etiology of Malocclusion: Definition and rational

Categorize known causes of malocclusion and their relative prevalence.

02 - Known Causes of Malocclusion, Lecture There are four major factors in the etiology of malocclusion :

1. Hereditary factors
2. Interference with normal development
3. Trauma
4. Disturbance in normal function

Most malocclusion has no known specific cause

Only about 5% of malocclusions are attributable to a specific known cause; the remaining ~95% result from a complex, poorly understood interaction of inherited and environmental influences. From a broad perspective, only about one-third of the population has normal occlusion while two-thirds have some degree of malocclusion.⁷

Image: Categories of known causes of malocclusion.	Image: Known (~5%) versus unknown (~95%) causes of malocclusion.

Hereditary Factors

Recent Development

Fragments of prehistoric jaws show mostly good development, so malocclusion may be a modern problem.⁷

• Evolutionary trend towards a decrease in teeth and jaw size.⁷
• Interracial mixing (out-breeding) does NOT produce a multiplicative increase in malocclusion — the effects of interracial crosses appear to be more additive than multiplicative (the Hawaiian melting-pot studies of Chung et al.).⁷
• Familial patterns of malocclusion, like the Hapsburg jaw, are real and can run across generations.⁷
• Up to 50% may be the maximum contribution to malocclusion by hereditary factors; the environmental contribution is likely at least as large as the genetic one.⁸

Interference with normal development

Interferences with Pre-Natal Development

• Genetic and environmental insults in utero
  • Fetal alcohol syndrome
  • Teratogens like thalidomide
  • Zika Virus
  • Treacher collins syndrome
  • Even birth trauma to the mandible is possible but more rare
  • Intra-uterine molding
• Pre-Natal interferences with the Dentiion
  • hyper and hypo dontia

Anything affecting things like neural crest cell migration or neural plate closure

Interference with Post-Natal Development

• Look at it through the soft tissue theory of growth: scarring from an injury is more likely to affect development than the hard-tissue injury itself.⁹
• Fracture of the condylar process has a 75% chance of normal growth and a 25% chance that it produces asymmetry.⁹
  • That 25% is normally due to soft tissue scarring around the TM joint that restricts translation, so the normal soft tissues cannot pull the mandible forward on that side as the rest of the face grows.⁹
  • Clinically this means there is little advantage to open surgical reduction of a child’s condylar fracture — the added scarring could make things worse. Conservative management with early mobilisation is preferred.⁹

Effects of Trauma on the dentition

• Trauma can effect the occlusal balancing forces
  • for example :
    • a young child crawling around on the floor bites down on an electrical cord, the result is likely to be a severe burn at the corner of the mouth, as in the girl shown in image 1. As it heals and scars down, pressure against the teeth creates a marked asymmetry in the mandibular dental arch, and makes normal arch form almost impossible to maintain.

The reverse effect is seen when cheek tissues are lost (image 2). Then unopposed pressure by the tongue tips the teeth facially.

Image 1: Scarring as this burn heals will distort dental arch form.9	Image 2: Loss of cheek tissue to a tropical infection has led to buccal displacement of the teeth.9

Direct Trauma to the teeth

• This can also lead to malocclusion.⁹
  • If a tooth is lost the adjacent teeth tend to drift into its space and normal alignment is lost unless space is maintained.⁹
  • Trauma to a primary tooth can displace the underlying permanent tooth bud — disturbing enamel formation (a crown defect) or, after the crown is complete, causing dilaceration (distortion of root form).⁹

Disturbances in function

• See thumb sucking and tongue thrusting below — these act through the equilibrium theory of tooth position.

Identify malocclusions linked to inherited jaw proportions and provide supporting evidence.

Lecture, Contemporary Orthodontics 6e, Ch.5

The two types most likely to be due to inherited jaw proportions are mandibular prognathism (Class III) and the long-face pattern.⁸

Twin studies show that up to 50% of malocclusions have origins in hereditary factors.⁸

• Certain types of malocclusion do run in families. Research methodologies: twin studies, family studies, and dog (breeding) studies.⁸
• Twin studies (Hughes et al.): the hereditary component for spacing/tooth position within the arches was 69–89%, ~53% for overbite, but only ~28% for overjet — so overjet has a much larger environmental component.⁸
• Harris and Johnson (Bolton-Brush study): heritability of skeletal (craniofacial) characteristics is high, but that of dental (occlusal) characteristics is low — and with age, skeletal heritability rises while dental heritability falls.⁸
• Brazilian study (55 families, >2000 individuals): heritability of mandibular prognathism is high (≈0.32, autosomal dominant with incomplete penetrance), with the long-face pattern the second most likely deformity to run in families.⁸
• The classic dog-breeding (Stockard) experiments once seemed to prove independent inheritance of jaw vs tooth size causes malocclusion — but they were misleading because many small breeds carry the achondroplasia gene, which explains most of the deformities seen.⁸

The Habsburg Dynasty

The Habsburg dynasty maintained a protrusive Class III (“Habsburg”) jaw for over 200 years through inbreeding to keep power within the family — demonstrating that genetic influence is very strong in Class III patients and often visible across generations.⁸

Image: Inherited facial disproportion.	Image: Class II trend — deficient chin and large overjet.
Image: Habsburg portrait showing the inherited prognathic jaw.	Image: Habsburg jaw recurring across generations.

Explain how mandibular trauma affects future growth.

Lecture, Contemporary Orthodontics 6e, Ch.5

• The condylar neck is particularly vulnerable to childhood falls; the condyle regenerates well in ~75% of cases (no growth deficit), but in ~25% there is a growth deficit.⁹
• The mechanism of deficit is not the loss of cartilage itself, but soft-tissue scarring around the TM joint that restricts translation — the normal soft tissues then cannot carry the mandible forward on that side, so growth lags (the soft-tissue/functional-matrix theory of growth).⁹
• Mandibular translation is required for growth — opening on a hinge is not enough. Ankylosis fuses across the TM joint → restricts motion → inhibits growth.⁹
• Resulting clinical signs:
  • Mandible shifts toward the affected/fractured side (the condyle is no longer under the traction of the lateral pterygoid).⁹
  • Occlusal cant — as the mandible shifts, compensatory extrusion occurs on the opposite side to maintain contact.⁹
  • Retrusive (deficient) chin — the mandible cannot grow antero-posteriorly.⁹
• Management of ankylosis: remove the ankylosed joint and replace it with a costochondral (rib) graft, because the rib is a “growth site” that grows by endochondral ossification at a rate similar to the condyle.⁹

Image: Adult monkey collapses on the condylectomy side after unilateral condyle removal.	Image: Mandibular shift and occlusal cant following condylar injury.
Image: Fracture of the condyle in early childhood.	Image: Resulting retrusive chin.
Image: Ankylosis resulting from scarring.	Image: Costochondral (rib) graft used to reconstruct the joint as a growth site.

Identify the magnitude and duration of force required for tooth movement (e.g., thumb sucking habits).

Lecture, OrthoInstruction: Equilibrium Theory, Contemporary Orthodontics 6e, Ch.5

Magnitude of force

• Very little force is required — even a few grams, if maintained long enough, can move a tooth. There is essentially no (or a very low) magnitude threshold; the eruption experiments use a force of only ~3 g.¹⁰
• The supporting structures (PDL + alveolar bone) are built to withstand heavy forces of short duration (mastication): the PDL fluid acts as a shock absorber and the bone bends. Only if pressure is maintained long enough to squeeze out the fluid (a few seconds) is there an effect on the soft tissues — and then it hurts and the force is released. Therefore it is duration, not magnitude, that determines tooth movement.¹⁰

Force-level eruption experiment (Force A / B / C, ~3 g)

• Force A (below eruption level): no change — the tooth continues to erupt.¹¹
• Force B (equal to eruption level): eruption is blocked while force is applied, but resumes once removed.¹¹
• Force C (beyond eruption level): achieves intrusion; once removed, a “catch-up” eruption occurs, ending at the same point as Force B.¹¹

Image: Tooth movement versus pressure in the PDL — low threshold.	Image: Force experiment setup.
Image: Eruption (microns) over time with force on/off cycles.	Image: Force A/B/C eruption response.

Thumb-sucking presentation

• Sucking habits during the primary dentition years have little if any long-term effect.⁹
• The classic presentation of a habitual thumb sucker is :
  • protruding upper incisors
  • anterior open bite
  • maxillary constriction causing the child to shift into a unilateral posterior crossbite
    • the negative pressure of sucking actually isn’t responsible for this, its because the tongue is depressed ! so it shifts the balance of the upper teeth as usually the tongue is supposed to be pushing back on them
  • A little more forward growth of the maxilla is also possible
  • lingually positioned lower incisors

Variation

There can be considerable variation in which teeth are affected and how much.⁹

Duration of force

• This relates back to equilibrium theory (Level I): how much the teeth are displaced correlates with the number of hours per day of the habit, not the magnitude of pressure.¹²
• The duration threshold for tooth movement is about 4–8 hours per day (≈6 hours). Evidence: removable-appliance wear (must be worn ~4–8 h/day to work) and Davidovitch’s animal work showing second messengers (cyclic AMP) appear after ~4 hours.¹²
• Intermittent-force findings (rabbit incisor eruption):¹³
  • 50% of the time → effect similar to continuous force
  • 25% of the time → intermediate effect (individual variation)
  • 10% of the time → little or no effect
• Therefore a habit practised 12 hours a day (50% of the time) has the same clinical effect as if it were practised the full 24 hours — directly relevant to thumb-sucking, where it is the night-long thumb that matters.¹³
• A large open bite (e.g. 7 mm) is usually the result of a high-pressure, long-duration thumb-sucking habit rather than tongue posture alone.¹³ Image: Intermittent light force and the eruption of the rabbit incisor as a function of duration.¹³

Image: Intermittent force versus continuous force on eruption.	Image: Effect of force duration (% of time) on eruption.

Describe the maturation of oral function and swallowing patterns from infancy to adulthood.

Lecture, OrthoInstruction: Equilibrium Theory, Contemporary Orthodontics 6e, Ch.5

• For most patients the position of the tongue is more an adaptation to the position of the teeth than the cause of their displacement.¹⁴
• Tongue-thrust swallowing has too short a duration to affect tooth position — tongue pressure during a typical swallow lasts approximately 1 second, and a few hundred swallows per day total only a few minutes (well below the ~4–6 h threshold).¹⁴

Maturation of the swallow

• The mature/adult swallow appears in some children as early as age 3, is present in the majority by about age 6, and is never achieved in 10–15% of a typical population.¹⁴
• This is not a “retained infantile swallow” — only brain-damaged children retain a truly infantile swallow (posterior tongue not involved). The label is incorrect.¹⁴
• During the transition, a child passes through a stage of lip activity, separation of the posterior teeth, and forward protrusion of the tongue — which is also the description of the classic tongue-thrust swallow. A sucking habit, anterior open bite, or incisor protrusion delays this transition because the child must place the tongue forward to form an anterior seal during swallowing.¹⁴

Two circumstances for tongue-thrust swallow today

• Younger children with normal occlusion — a transitional stage of normal maturation.¹⁴
• Individuals of any age with displaced incisors — a large overjet (often) and anterior open bite (nearly always) conditions the patient to place the tongue between the anterior teeth to seal the mouth.¹⁴

Discuss myofunctional therapy for tongue thrusting and its validity for anterior open bite.

Lecture, OrthoInstruction: Equilibrium Theory

• No validity — the tongue thrust is most likely an adaptation to the anterior open bite, not the cause of it.¹⁴
• At every age above 6, the number of children with a tongue-thrust swallow is about 10 times greater than the number with anterior open bite — if it were an etiologic agent, it would be a very weak one.¹⁴
• Tongue-posture training (“hold your tongue back”) is generally ineffective because the instinct for an anterior seal is physiological, and the swallow itself is too brief to matter.¹⁴
• Crib appliance: a “crib” can be used to block the tongue, but success depends on the patient having enough vertical growth to close the bite; otherwise it becomes a surgical case.³

Describe the role of nasal obstruction in malocclusion etiology.

Lecture, OrthoInstruction: Equilibrium Theory, Contemporary Orthodontics 6e, Ch.5

Mechanism concept

• The mode of respiration alters postural relationships of the head, jaw and tongue, which changes resting pressures against the dentition (resting pressures are the long-duration pressures that matter for equilibrium).¹⁵
• Long-face mechanism: postural changes from nasal obstruction create a muscle/tongue imbalance — the mandible rotates down and back, producing an atresic (narrow) upper arch and a long, open-bite face (the “adenoid facies”).¹⁶

Don't equate lips-apart with mouth breathing

Total nasal obstruction is very rare; the clinical question is how much partial obstruction matters. Observers tend to equate lip separation at rest with mouth breathing, but this is incorrect — one can breathe entirely through the nose while the lips are apart.¹⁵

Evidence: Linder-Aronson and Vig experiments

• Linder-Aronson (Sweden): children needing adenoidectomy had longer faces on average (mandible rotated down/back). After surgery they shifted toward nasal breathing, the mandibular plane angle decreased, and they tended to return toward normal facial proportions (incomplete recovery); the nasopharyngeal cavity and upper-arch/molar region enlarged and incisors protruded as tongue posture changed.¹⁶
• Vig (UNC, nasal-mask/plethysmograph): measured the nasal/oral ratio in long-face vs normal adolescents. Both groups were predominantly nasal breathers; a minority of long-face children had <40% nasal breathing, but none of the normal children did.¹⁷
• Head-position experiment: abruptly blocking the nose causes a reflex — the head tilts up, the mandible drops, and the tongue drops to open an oral airway; posture returns to normal once the obstruction is removed.¹⁷

Conclusion

• Partial nasal obstruction tends to increase face height in humans.¹⁶
• But impaired nasal respiration is a risk factor, not the major determinant, of the long-face pattern. The threshold percentage of mouth breathing needed to affect growth is unknown — so routine adenoidectomy/tonsillectomy purely to improve facial growth is rarely justified.¹⁷

Image: Adenoid facies — long, narrow face with anterior open bite.	Image: Change in cervicocranial angle with induced oral respiration.

Image: Nasal-oral ratio in long-face versus normal adolescents (Vig / Linder-Aronson data).¹⁷

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Footnotes

1. Contemporary Orthodontics 6e, Ch.1 — Angle classification and line of occlusion ↩ ↩² ↩³ ↩⁴

2. L3 Level II Unit A — The Line of Occlusion (~138 contact points) ↩

3. L3 Level II Unit A — Lecture ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸

4. palatal cusp characteristics ↩ ↩² ↩³

5. L3 Level II Unit A — Primary Objectives of Orthodontics ↩ ↩² ↩³

6. L3 Level II Unit A — Treatment Demand and Patient Demographics ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹²

7. Contemporary Orthodontics 6e, Ch.5 — Specific causes and ~5% known causes ↩ ↩² ↩³ ↩⁴ ↩⁵

8. dog studies) ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹

9. Contemporary Orthodontics 6e, Ch.5 — Specific causes: trauma, condylar fracture, dental disturbances ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹² ↩¹³ ↩¹⁴ ↩¹⁵ ↩¹⁶ ↩¹⁷ ↩¹⁸

10. OrthoInstruction — Magnitude of force (low threshold, PDL shock absorber) ↩ ↩²

11. C eruption experiment (~3 g) ↩ ↩² ↩³

12. day) for tooth movement ↩ ↩²

13. 10% of time; 12 h ≈ 24 h) ↩ ↩² ↩³ ↩⁴

14. OrthoInstruction — Swallow maturation, ~1 s tongue contact, tongue thrust as adaptation ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰

15. OrthoInstruction — Respiratory mode, posture and resting pressures ↩ ↩²

16. OrthoInstruction — Linder-Aronson adenoidectomy data and long-face mechanism ↩ ↩² ↩³

17. oral ratio; partial obstruction as risk factor ↩ ↩² ↩³ ↩⁴