aetiology of malocclusion Flashcards
What areas is the aetiology of malocclusion concerned with?
Skeletal pattern
Soft tissues
Dental causes
What is the skeletal pattern?
Relationship of upper and lower dental bases
Antero-posterior (class I, II, III- side profile- A point should be in front of B point by 2-4mm)
Vertical (equal facial thirds by Ricketts, lower anterior face height is 55% of total and Frankfurt mandibular plane angles- average should intersect at occiput of 27.5 degrees +/- 5)
Transverse (asymmetries from right to left- enlargement/reduction of one side of face, can show crossbite)
Why might someone have a class II skeletal pattern?
Maxillary protrusion
Mandibular retrusion (retrognathia)
OR BOTH
More likely due to mandibular retrusion (86%)
Why might someone have a class III skeletal pattern?
Maxillary retrusion (hypoplasia) 34%
Mandibular protrusion (prognathia) 40%
OR BOTH 26%
What are the facial third landmarks?
Trichion to globella
Globella to subnasale
Subnasale to soft tissue menton
What are the Frankfort mandibular plane landmarks?
Frankfort- external auditory meatus (tragus of ear) to lower border of orbit
Mandibular- gonion (angle of mandible) to menton (tip of mandible/chin)
What does the Frankfort mandibular plane angle show?
It crosses behind the occiput- low angle, reduced face height, deep bite
If crosses in front of the occiput- high angle, increased face height- AOB
What soft tissues play a role in malocclusion?
Lips and cheek (zone of equilibrium, dentition stable between cheek/lip pressure and tongue pressure)
Tongue (large can procline incisors and cause lateral OB
Habits (dummy/digit sucking can cause AOB and prevent eruption of anterior teeth)
Labial frenum (normal/abnormal, low may cause diastema?
What are the forces playing a role in causing a stable dentition?
Tongue- <5g, 10g
Lip/cheek- 5g, 5g
PDL- shock absorber
How do the lips support the dentition?
Length- can have short upper lip, vertical maxillary excess leading to gummy smile
Form- competent (lips meet at rest, lower Iip should rest on lower third of upper incisor)/incompetent (80% of kids can have it temporarily)
Lip line- relationship of lower lip to upper incisor (normal, low, high)
What is tongue thrust?
Adaptive- eg. thumb sucking, tongue postures forwards to achieve seal and allow effective swallow
Endogenous- rare- eg. lisp, bimaxillary proclination (incomplete OB, AOB)
What are the effects of digit sucking?
Reduced over bite/AOB
proclines upper incisors
Retroclined lower incisors
Posterior crossbite
Severity depends on duration of habit (>4-6hrs leads to malocclusion)
How can you examine a labial fraenum?
Put under tension by pulling the lip up, if the palatal mucosa at the diastema blanches can have fraenectomy
What are the dental causes of malocclusion?
Tooth/tissue ratio
No of teeth
Abnormal form/position
Path of closure
Pathology
What is the tooth/tissue ratio?
CROWDING
AKA dentoalveolar disproportion- overlap of teeth due to insufficient space, (mild/moderate/severe)
More common in females in both arches
Genetic (intermixing, evolution etc), environmental (diet)
40% increase over last 100000 years due to reduction in jaw size and decrease in tooth wear patterns
SPACING
Mild/moderate/severe, generalised/localised, eg. midline diastema
Not common in UK
What is the severity scale of crowding/spacing measurements?
Mild- 1-4mm
Moderate- 4-8mm
Severe- 8+mm
How can the no of teeth affect occlusion?
Missing teeth (anodontia/hypodontia) teeth often smaller so spacing
Supernumerary teeth (4 types) occurs in 2%, multifactorial
Supplemental teeth
Interference w normal timing
What is the severity scale of hypodontia?
Mild/moderate/severe
Severe- 6+ missing, congenital, doesn’t include third molars
Eg. Ectodermal dysplasia
What is the prevalence of missing teeth?
3-7%
6.4% in general population
Most common in Africa
1.4x higher in females
Most to least common missing teeth-
Lower wisdom
Upper wisdom
Lower 5s
Upper 2s
Lower incisors
Mild- 81%
Moderate- 14%
Severe- 3%
What are the 4 types of supernumerary teeth?
Conical (mesiodens)
Tuberculate
Supplemental
Odontomes (complex and compound) compound is 4x more common than complex
What are conical teeth?
AKA mesiodens
Usually between upper 1s
Peg shaped
Usually high and inverted but within long axis and normal root
Often erupts and displaces other teeth
What are tuberculate teeth?
Barrel shaped
12% of supernumeraries
Don’t usually erupt
Prevents eruption of other teeth
Usually palatal of central incisor
What are supplemental teeth?
7% of supernumeraries
Duplicate of another tooth
Usually maxillary incisor
Looks normal
Occurs at end of series
Can cause crowding
Can block eruption
Can cause pathology such as cysts and therefore resorption also
What is interference w normal timing?
Premature loss of teeth (primary/permanent)- if C can cause centre line shift, if E can make 6 move mesially
Retention of primary (can deflect permanents) extract early where necessary
Delayed eruption of permanent (usually variation but should consider if due to impeded eruption supernumary etc)
What are infra-occluded teeth?
AKA submerging 
Tooth fails to continue to erupt vertically so lies below occlusal plane
8-14%
10x more common in mandible
Due to missing permanent teeth or ankylosed primary teeth
What does ankylosed mean?
Fused to the bone
ankylosed Es, can be associated w missing permanents
Extract early if possible as may become surgical extraction
What is the abnormal form of teeth?
1 standard deviation above or below
MACRODONTIA
Fusion- 2 tooth buds fuse
Gamination- 2 crowns and single root
MICRODONTIA
Peg shaped laterals usually
Due to missing teeth often
What is the abnormal position of teeth?
TRANSPOSITION
positional interchange of 2 teeth
-true transposition- complete swap
-pseudotransposition- rare 0.33%, usually unilateral and maxillary, tipped into wrong position but roots correct
IMPACTION
What is the path of closure?
Lateral displacement
Forward displacement
-instanding tooth/class III incisors
What is an instanding tooth?
One tooth in crossbite
What are pathological causes of malocclusion?
Cysts (dentigerous cyst)
Trauma (dilaceration)
Tumours
What is a dentigerous cyst?
Develops in bone over tooth that hasn’t erupted
What is dilceration?
Deviation or bend in the linear relationship of the tooth crown to root
Usually upper 1s
Usually trauma w primaries
