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Etiology of Malocclusion
Polygenetic
Multifactorial
Investigation:…
Etiology of Malocclusion
- Polygenetic
- Multifactorial
- Investigation: monozygotic vs dizygotic (independent is genetic) more diff = more genetic contribution
1| Equilibrium theory: Force
Soft tissue
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Jaw
Hypo2: Red bite force = red LAFH
- Refuted, only in CP cases
Hypo1: Inc usage = inc size
- Refuted by stagnant inter-canine width
- But genetic drift toward smaller by diet
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Habits
Sucking (Y)
Effect dental:
- Upper incisor procline
- Lower incisor retrocline
Effect skeletal:
- Backward mand rotation
- Max constriction (lower tongue/cheek)
Tongue (Y/N)
Observed in:
- Transition infantile -> adult swallow (6y/o)
- Displaced incisors -> achieve oral seal
Types of tongue thrust:
- Sustained forward posture (>6hr)
- Infantile swallow (<6hr)
Mouth breathe (N)
Extent: Contribute but not etiology
Cause: Enlarge adenoid, nasal block, allergy
4| Specific causes
Genetic
Acromegaly & Hemimandibular hypertrophy
- Acromegaly cause: Ant pituitary excess GH, excess Mnd growth Cl III
Embryological Dev (<1%)
- Teratogens Aspirin, smoke, alcohol)
- Retinoic acid thalidomide
- Intrauterine moulding (Pierre Robin seq)
Genetic disorders
- Cleidocranial dysplasia
- Craniosynotosis
- Treacher Collins syndrome
- Hemifacial microsomia
- Cleft lip and palate (30% syndromic, 70% polygenic/multifactorial)
Skeletal: growth disturbances
- Childhood jaw fracture (if scarring 5% of px)
- RA affecting growth
Soft tissue: muscular dysfunction
- In utero cause
- Birth injury
- Motor nerve damage
- Excessive muscle contraction (eg. torticollis)
- Decrease in tonicity (eg. CP, weakness mandible drops, supraerruption post, AOB)
Dental: disturbance
Congenitally missing
- eg. retained primaries, poor LT prog. space/drift of perm
- Hypodontia genetic
Malformed & supernumerary
- Size mismatch: micro/maco, spacing/crowding
- Supernumerary: Impede eruption, median diastema, crowding
Eruption interference
- Ankylosis of primary molars
Ecotopic erruption 6s
- Path too M, impacted against Es
- Damage E roots, early loss
- Impaction of #5s
Early loss of primary #4/5
- Mesial drift of #6, space loss
- Impaction/displacement of successor
- Localized molar Cl II/III
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Ectopic erruption of #3 (Environmental)
- Buccal 15% assoc with overcrowding 85%
- Palatal 85% assoc with sufficient space 83%
- Factor #1 Long path of eruption (22mm from orbit floor)
- Factor #2 Pegshape/small #2 fails to guide
- Transposition (exchange places genetic between #4)
Early loss of primary #3 (More severe than loss of Es)
- Distal Palatal drift of incisor, space loss
- Impaction/discplacement of successor
- Midline deviation
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Genetics
- OJ/OB/Molar relationship/soft tissue/skeletal
- NOT: occlusal rltns / dental problems
- Minor role: Arch width and length
Skeletal problems
- Geneitc
- Embryological defects
- Trauma
- Fx
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