Aetiology of malocclusion Flashcards
What are Andrew’s six keys?
Crown angulation (tip)
Molar relationships
Rotations
Contact points/spacing
Curve of spee
Crown inclination (torque)
Name some aetiologys of skeletal relationships
When do we accept the skeletal pattern or modify it?
This is dependent on a number of factors, the patient’s concerns, the severity of the discrepancy, their age and their motivation.
What are the soft tissues?
*Lips
*Cheeks
*Tongue
*Masticatory musculature
*Periodontal Tissues
*Fraenal attachments
What is Proffit’s equilibrium theory?
- The dentition erupts into a position of equilibrium with the surrounding soft tissue environment.
- Any alteration in the factors involved in equilibrium may cause an alteration in the tooth position until a new equilibrium is established.
- The forces of the tongue on the inside of the teeth and lips and cheeks on the outside of the teeth are balanced. When we carry out orthodontic treatment we apply forces to the teeth which changes the equilibrium and the teeth move.
- It states that the duration of any applied force is more important than the magnitude of the force. Meaning that if we move teeth out of equilibrium zone, then the lighter but longer duration forces will result in the teeth moving back, and relapse is a strong possibility.
What do we assess orthodontically when looking at a patients lips?
*Resting lip line – vertical position- are they acting higher or lower on the upper incisors?
*Lip competence – the ability to get a lip seal, does the patient strain to achieve competence?
*Growth of the lips - how old is the patient, are they going to grow more?
*Lower lip trap - discussed in more detail in Class II div I cases
*Lip contour - are they thin, are they full?,is one thicker than the other?
*Ideal occlusion - resting lower lip covers between a third and a half of the labial surface of the upper central incisors in the A-P and vertical position to aid stability (Ballard 1967)
What are the average lip lengths? (M&F)
*20mm female
*22mm male
How does lip competence change with age?
It improves with age
When is the majority of lip growth?
Through pubertal spurt
9 – 13yrs in females *9 – 15yrs in males
What can a large tongue cause in terms of malocclusions?
Procline lower incisors and may also result in spacing.
Retracting the incisors will encroach on tongue’s space and they will be in an unstable position.
What is an endogenous tongue thrust? Aetiology?
Swallowing activity accompanied by a thrusting behaviour
Very Rare (~1%)
? in-built neuromuscular defect e.g. cerebal palsy, Down’s syndrome.
Name some features of endogenous tongue thrust
*Bimaxillary proclination
*Tongue thrust associated with lip incompetence or only very mild incompetence
*Presence of a large part of the tongue between the teeth at all times
*Reversed curve of Spee in both arches
*A marked lisp
State the percentages of digit sucking in a) infancy and b) 12 years
In infancy, up to 50% may have a sucking habit
At age 12 years, 2% of the population have the habit
How does the habit of digit sucking alter dentition/soft tissues?
The habit alters the intrinsic soft tissue pressures, this alters the forces which were in equilibrium and tooth position may alter.
- Proclination of upper incisors
- Retroclination of lower incisors
- AOB
-Differential eruption of teeth
-AOB may be asymmetric - Maxillary constriction
-Lower tongue position
-Increased buccinator activity
-Potential unilateral crossbite
Name some dental factors of malocclusion
*Variations in tooth number
*Abnormalities in tooth position
*Abnormalities in tooth form
What is dentoalveolar disproportion
Occurs where there is a discrepancy between the size and/or number of the teeth, and the size of the dental arches, or the space within that arch to accommodate the teeth, resulting in crowding or spacing
Name some aetiology’s of crowding
*Size of the teeth
- Number of the teeth
- Position of the teeth
- Reduced size of dental arch
Insufficient space within an arch:
- Retained primary teeth or early loss of primary teeth
What is hypodontia
The developmental absence of one or more teeth (excluding 3rd molars)
What is oligodontia?
Absence of 6 or more teeth
What is anodontia?
Absence of all teeth
Name the incidences of hypodontia
<1% primary dentition
*4-6% permanent dentition (Polder 2004)
*2% 2s - May be associated with ectopic 3s
*3% all 5s
What is the aetiology of hypodontia?
Hypodontia is associated with the environment; however, the majority of cases are thought to be genetic with a familial pattern. This is under extensive research.
Name some syndromic associations of hypodontia
Ectodermal dysplasia – X link recessive, affects the skin, sweat glands, nails, teeth.
Cleft lip and palate
Down Syndrome
Holoprosencephaly – solitary midline maxillary central incisor, facial clefts, Cyclopia, autosomal recessive
What are some local factors of hypodontia?
● Irradiation of the jaws in early life.
●Microdontia associated with chemotherapy.
How is hypodontia managed?
Multidisciplinary clinics - Paediatric, Restorative and Orthodontics
Simple cases can be managed in specialist practice with the GDP providing the restorative care.
What are supernumerary teeth?
A tooth that has developed in addition to the normal series of teeth.
What is the aetiology/associations of supernumerary teeth?
Aetiology: unknown, however, theories include an offshoot of the dental lamina or the development of a tertiary dentition.
*Some craniofacial syndromes are associated with an increased incidence of supernumerary teeth: Cleft lip and palate, Cleido-cranial dysostosis, Gardner syndrome.
What is the incidence of supernumerary teeth?
3% of the Caucasian population in the permanent dentition
In the primary dentition, the incidence < 1%.
M: F 2:1
Maxilla : Mandible 5:1
What are the classifications of supernumerary teeth?
Supplemental, Conical, Tuberculate, Odontome
Name the characteristics, incidence and management of supplemental numerary teeth
Duplication of a tooth within a series
*Found erupted distal to the last standing tooth in that series.
*Usually erupt, causing crowding.
Incidence: 7% of supernumeraries
Management: depends on the malocclusion, will be managed often in a joint clinic with paeds/restorative and orthodontics
Name the characteristics, incidence and management of conical numerary teeth
*Small peg-shaped tooth, often occurring in the maxillary midline (mesiodens), and often erupt.
*If they erupt into the line of the arch, they can cause crowding.
Incidence: 75% of supernumeraries
Management: if erupted extract with GDP, if unerupted and no clinical reason to remove then monitor
Name the characteristics, incidence and management of tuberculate numerary teeth
*‘Barrel-shaped’; lack of root development
*Often occur in pairs, most commonly palatal to the maxillary incisors, preventing their eruption.
*Can indirectly contribute to development of a malocclusion.
*If adjacent teeth drift into the space, can result in crowding of the unerupted tooth.
Incidence: 12% of supernumeraries
Management: depends on its effect on the dentition
- removal, maintain space, expose & bond of impacted central incisor if indicated
Name the two kinds of odontome numerary teeth
Complex: haphazard arrangement of dental tissue most commonly anterior maxilla
Compound: discrete tooth like structures (denticles) usually located in the premolar/ molar region x4 more common than complex odontomes
Define ectopic teeth
Teeth that fail to erupt in the correct position within the dental arch
When do maxillary canines normally erupt?
At what age can they normally be palpated from?
11-12 years old
Palpated from 9 years old
When do mandibular canines normally erupt?
9-10 years old
What’s the estimated impaction incidence of maxillary canines?
0.8-2.8% (Shah et al., 1978)
1.7% estimated (Ericson and Kurol, 1986)
What’s the estimated impaction incidence of mandibular canines?
0.35%
Is canine impaction more common in males or females?
2x more common females
What % of canine impaction is bilateral?
8%
Give % of impaction of canines either buccal or palatal
palatal 85%
buccal in 15%
Name some causes of early loss in primary teeth
- Caries (any teeth)
- Trauma (usually anterior teeth)
- Impacted upper first permanent molars (second primary molars)
What considerations do we need to have when extracting primary teeth?
*Primary teeth are nature’s space maintainers.
*Early loss of primary teeth can impact the developing occlusion ie space loss resulting in crowding and centreline shifts.
What are space maintainers?
A fixed or removeable appliance which acts to preserve the space created by the early loss of a tooth
Why may a primary tooth be retained?
*Successor developmentally absent
*Successor ectopic
*Local abnormality in alveolar development (infra-occlusion)
*Failure of permanent successor to resorb primary tooth
What is infraocclusion?
What is it’s aetiology? What is the incidence? Pathogensis?
Where the tooth fails to maintain its position in the developing occlusion
Aetiogy- idiopathic, genetic, trauma, absence of a successor
Incidence- 8-14% in 6-11 yr olds; occurs Mandible>Maxilla; Es>Ds affected
Pathogensis: ankylosis occurs during reparative phase of tooth resorption and tooth fails to erupt
Name the classifications of infraocclusion
Mild - level of infraocclusion above contact point
Moderate - within contact point
Severe - below contact point
What are balancing XLA’s?
A balancing extraction is a tooth from the opposite side of the same arch, designed to minimise centerline shift.
What are compensating XLA’s?
*Compensation means extraction of a tooth from the opposing quadrant to the enforced extraction.
*Designed to minimise occlusal interference by allowing teeth to maintain occlusal relationships as they drift.
*More difficult to justify compensation than balance, especially when it would involve removal of a tooth from an intact arch.
Name some methods of orthodontically creating space to relieve crowding
*Increase arch length: molar distal movement (headgear or temporary anchorage device) / incisor forward movement (if retroclined)
*Recently the Enmass retraction or distalisation of the upper arch on non-extraction base using TADs has been widely used in the literature.
*Arch expansion (removable or fixed appliance)(However, excessive lower arch expansion or proclination of the lower incisors should generally be avoided as this is inherently unstable.)
*Interproximal enamel reduction
*Utilisation of the Leeway space.
*Extraction: which teeth? - use space analysis to aid treatment planning
What is bimaxillary proclination?
Bimaxillary proclination is where both the upper and lower incisors are proclined, and the proclined upper incisors will automatically have an increased overjet even if the lower incisors occlude with the middle third of the palatal surface of the upper incisors.
