Aetiology of Malocclusion Flashcards
What are the 3 general etiological factors of malocclusion?
- skeletal
- shape
- size
- relative position of upper and lower jaws
- muscular
- form and function of muscles
- lips, cheek, tongue
- dentoalveolar
- size of teeth in relation to size of jaws
What is the cranial base angle measured from?
- attachment of the maxillary complex to the anterior cranial base
- articulation of the mandible with the posterior cranial base
What are possible aetiologies of skeletal variation?
- genetic
- strong hereditary component
- especially class III
- environmental
- masticatory muscles
- mouth breathing
- head posture
How are lateral cephalograms analysed?
- hand traced onto paper
- digitised using a computer
What is SNA on a lateral cephalogram?
- maxilla and anterior cranial base angle
- average class I value = 81 degrees
S = sella turcica
N = nasion
A = maxilla
What is SNB on a lateral cephalogram?
- mandible and anterior cranial base angle
- average class I value = 78 degrees
S = sella turcica
N = nasion
B = mandible
What is ANB on a lateral cephalogram?
- angle formed by the maxilla, anion and mandible
- average class I value = 3 degrees
What are the possible aetiologies of a class II skeletal relationship?
- mandibular deficiency
- mandible too small
- most common
- posteriorly positioned mandible
- set back due to obtuse cranial base
- normal sized mandible
- larger maxilla
- maxillary protrusion
- not common
- teeth erupt into post normal occlusion
- class II
How do the cephalometric values of a class II skeletal relationship compare to a class I?
- SNA usually average
- 81 degrees
- increased if maxilla is prognathic
- SNB usually decreased
- <78 degrees
- ANB increased
- > 5 degrees
What are the possible aetiologies of a class III skeletal relationship?
- mandible placed anterior relative to maxilla
- sue to acute cranial base angle
- maxillary deficiency
- maxilla too small
- most common
- paranasal hollowing visible
- larger mandible
- teeth erupt into pre-normal occlusion
- class III
How do the cephalometric values of a class III skeletal relationship compare to a class I?
- SNA usually decreased
- <81 degrees
- if maxilla is deficient
- SNB usually average
- 78 degrees
- increased if mandible prognathic
- ANB decreased
- <1 degree or negative
What planes are used to assess vertical jaw relationship?
- Frankfort place
- lower orbital rim to superior border of external auditor meatus
- mandibular plane
- lower border of mandible
- should meet at external occipital protuberance
What clinical values are used to asses vertical jaw relationship?
- upper anterior face height
- brow ridge (labella) to base of nose
- lower anterior face height
- base of nose (sub nasal) to inferior aspect of chin (menton)
What is the average ratio of lower anterior face height to total anterior face height?
- 50% clinically
- 55% cephalometrically
What is the averrable value of the Frankfort mandibular plane angle?
27 degrees
What are the characteristic signs and measurements of a long facial type?
- LAFH-TAFH >55%
- FMPA >31 degrees
- step inclined mandibular plane
- backward mandibular growth rotation
- anterior open bite tendency
Hat are the characteristic signs and measurements of a short facial type?
- LAFH-TAFH <55%
- FMPA <23 degrees
- tendency to parallelism of jaws
- forward mandibular growth rotation
- deep overbite tendency
What are arch width discrepancies?
- disproportion of maxillary and mandibular dental arches
- causes unilateral or bilateral buccal segment cross-bites
- often exaggerated by antero-posterior discrepancies
What is mandibular displacement?
- mandible forced to deviate to one side to achieve intercuspation
- occurs where interarch width discrepancies causes upper and lower posterior teeth to meet cusp to cusp
What are the possible causes of facial asymmetries?
- dental
- displacement of normal mandible due to unilateral cross bite
- true mandibular asymmetry
- hemi-mandibular hyperplasia/elongation
- condylar hyperplasia
- hemi-facial microsomia
What is dente-alveolar disproportion?
- discrepancy between size of teeth and jaws
- crowding
- small jaws and normally sized teeth
- large teeth (macrodontia)
- spacing
- large jaws and normally sized teeth
- small teeth (microdontia)
- more common
What is the definition of a local cause of malocclusion?
localised problem or abnormality within either arch, usually confined to one, two or several teeth producing a malocclusion
- tend to get worse over time
- scope for interceptive treatment
Provide examples of local causes of malocclusion
- variation in tooth number
- variation in tooth size of form
- abnormalities of tooth position
- local soft tissue abnormalities
- local pathology
In what ways can variation in tooth number present?
- supernumerary teeth
- hypodontia
- retained primary teeth
- early loss of primary teeth
- unscheduled loss of permanent teeth
Where are supernumerary teeth most commonly found
- anterior maxilla
What are the four types of supernumerary teeth?
- conical
- small peg shaped
- slender and pointed
- mostly in upper incisor region, close to midline
- usually present individually or in pairs
- often erupt, can extract
- tend not to prevent eruption but can displace adjacent teeth
- tuberculate
- round, barrel shape
- often paired
- mostly in upper incisor region
- tend not to erupt
- usually extracted
- can cause eruption failure in permanent incisors
- develop in the cingulum area
- supplemental
- normal morphology
- in addition to adjacent teeth
- usually upper laterals or lower incisors
- often extracted
- decision based on form and position
- odontome
- collection of toothlike substances
- disorganised form
- compound
- discreet denticles - complex
- disorganised mass of dentine, pulp and enamel
What is hypodontia?
- developmental absence of one or more teeth
- commonly upper laterals and second premolars
- strong genetic component
- can be accompanied by microdontia
When should retained primary teeth be investigated?
when there is a difference of more than 6 months between the shedding of contra-lateral teeth
Why may primary teeth be retained?
- absent successor
- ectopic sucessor
- infra occluded primary molars
- ankylosed
- common in Es, even with permanent successor
- may require extraction
- dentally delayed development
- pathology/supernumerary
How should retained primary teeth be managed when there is no permanent successor?
- maintain primary tooth as long as possible
- if good prognosis - extract deciduous tooth early
- encourages space closure in crowded cases
- early orthodontic referral
What are infraoccluded primary molars?
- primary teeth retained and permanent teeth erupt past
- tooth fails to achieve occlusal relation ship
- temporary ankylosis
- percussion sounds like clicking
- extraction
- difficult to keep clean so often become carious
What can cause early loss of primary teeth?
- trauma
- periapical pathology
- caries
- resorption by successor
What can occur as a result of early loss of primary teeth?
- localisation of crowding
- influenced by:
- tooth extracted
- when extracted
- inherent crowding
- influenced by:
What is a balancing extraction?
- extracting a tooth from opposite side of the same arch
- minimise midline shift
What is a compensating extraction?
- extracting a tooth from opposing arch on same side
- maintain occlusal relationship
What extractions should be considered for early loss of different kinds of primary teeth?
- incisors
- little impact
- no compensating or balancing extractions
- canines
- unilateral loss in crowded arch can shift centre line
- mesial drift of buccal segments
- consider balancing extraction
- molars
- increased space loss with Es compared to Ds
- more space loss in upper than lower
- 6s drift medially into space for 5s
What factors can influence the impact of loss of 6s?
- age at loss
- important for lower
- if late, often poor space closure
- if early, distal drift of 5s - in lower arch should be at time of bifurcation development in 7s
- important for lower
- crowding
- rapid space loss possible in upper arch
- good result in lower arch
- malocclusion
What are the consequences of unscheduled loss of a central incisor and how should it be managed?
- depends on timing of loss
- early results in drifting of adjacent teeth
- late results in long term space
- ideally maintain space
- reimplant
- simple denture
- plan how to deal with space longer term
- definitive prosthesis
- if lateral incisor drifts to fill space
- reopen space for prosthesis
- build up lateral
What is macrodontia?
- larger than average tooth
- localised or generalised
- problems:
- crowding
- asymmetry
- aesthetics
- management:
- can be slimmed down but limited by pulp chamber
- extraction and replacement with prosthesis
What is microdontia?
- smaller than average tooth
- localised or generalised
- peg incisors
- leads to spacing
- strong genetic link
- also link with hypodontia
What abnormal forms of teeth can present?
- peg laterals
- dens in dente
- germinated/fused teeth
- talon cusps
- dilaceration
- accessory cysts and ridges
What teeth are most commonly ectopic?
- third molars
- upper canines
- check for palpable buccal canine bulge from 9 years
- due to long path of eruption
- associated with peg laterals
- higher incidence in class II, div 2 incisor relationships
- buccal placement associated with crowding
- managed with extraction of 3, surgical exposure or extraction
- first permanent molars
- reversible before age of 8
- caries risk
- indicated by crowding, mesial path of eruption and abnormal E
- managed with separator, extraction of E, distalisation of 6
- upper centrals
- possibly due to supernumerary or trauma to primary predecessor
- tuberculate or odontome
- ankylosis of primary tooth, displacement of tooth germ
- possibly due to supernumerary or trauma to primary predecessor
What are transpositions of teeth?
- interchange in the position of two teeth
- true
- teeth swap place entirely - pseudo
- apices in correct position
- true
- most common teeth:
- upper canines and first premolar
- lower canines and incisors
- management:
- accept
- extract
- correct
What local soft tissue abnormalities can cause malocclusion?
- digit sucking
- proclined upper incisors
- retroclined lower incisors
- anterior open bite
- fraenum
- labial frenum can cause median diastema
- tongue thrusting
- anterior open bite
- common cause of relapse after treatment
What local pathology can cause malocclusion?
- caries
- cysts
- displacement of teeth
- cyst renucleated to manage
- tumours
