Aetiology of Malocclusion Flashcards
What are the Equilibrium effects on dentition?
- Duration more important than magnitude (6h threshold)
- Long-lasting pressure from tongue, lips, cheeks at rest, gingival and PDL fibres
- Masticatory forces and soft tissue pressures during swallowing should not have major influence
What are examples of Equilibrium Effects on Dentition
- Prolonged thumbsucking
- Forward resting tongue posture
- Macroglossia
- Incompetent lips
Vertical effects: Periodontal ligament (eruption) and the opposing tooth, tongue interposed between teeth
Transverse: Tongue vs cheek
How does muscles affect jaw growth?
Bone formation at point of muscle attachments (dependent on the activity of muscles)
E.g. Enlargement of mandibular gonial angles in patients with hypertrophy of mandibular elevator muscles
Musculature is part of soft tissue matrix, which growth carries the jaws down and forward
influenced by genetics
What is the relationship between masticatory function and dental arch size?
Unclear whether masticatory effort influences size of dental arches
What is the relationship between bite force and dental eruption?
Different biting force is an effect and not cause of facial pattern (Deep or open bite)
Except: Rare muscle dystrophy or weakness syndrome: downward and backward mandibular rotation + excessive eruption of posterior teeth
Dental Effects of Sucking Habits
- Thumb displaces upper incisors labially and lower incisors lingually → Increased OJ
- Thumb interferes with incisor eruption → AOB
- Mandible positioned downward to accommodate thumb → Excessive eruption of posterior teeth
- 1mm of posterior bite opening leads to 2mm of anterior bite opening
- Constriction of maxillary arch
Sucking habits cause maxillary arch constriction because?
- Lowered tongue → Reduced pressure on lingual surfaces of upper posterior teeth
- Increased cheek pressures at buccinator muscle contracts (greatest at corners of mouth)
When is tongue thrust swallow seen?
- Transitional stage in normal maturation till age 6
- Individuals with displaced incisors: Adaptation to achieve anterior oral seal
BUT sustained forward resting tongue posture: can cause a malocclusion affects vertical and horizontal position of teeth
Possible Dental Effects of Mouth breathing
- Supraeruption of posterior teeth unless compensated by downward and backward rotation of ramus
- Increase in face height, AOB and increased OJ
- Increased pressure from stretched cheeks may contract maxillary arch
- Classic adenoid face: Narrow width dimensions, protruding teeth and lips separated at rest
Skeletal Causes of Incisor Class II Div 1 Malocclusion
- Protrusive maxilla
- Retrognathic mandible
- Combination
- Can be exacerbated by a downward and backward mandibular growth rotation
- Can occur in Class I skeletal pattern in presence of other factors
Soft Tissue Causes of Incisor Class II Div I Malocclusion
- Lower lip trap → Lower incisor retroclination and upper incisor proclination
- Active lower lip + low lip line → Retroclination of lower incisors
- Forward resting tongue posture and lip incompetence or short upper lip → Upper incisor proclination
Worse if sustained for more than 6 hours
Habits Causing Incisor Class II Div I Malocclusion
NNS if more than 6h per day
Proclination of upper incisors + retroclination of lower incisors
Dental Causes of Incisor Class II Div I Malocclusion
Maxillary crowding → Labial displacement/proclination of upper incisors
Skeletal Causes of Incisor Class II Div 2 Malocclusion
- Mild Class II Skeletal Pattern
- Reduced vertical dimensions:
- Horizontal palatal plane
- Upward and forward mandibular rotation → Reduces severity of Class II Skeletal pattern - Can occur in Class 1 skeletal pattern in presence of other factors
Soft Tissue Causes of Incisor Class II Div 2 Malocclusions
- Mediated by skeletal pattern
- High lower lip line (due to reduced lower anterior facial height) → Upper incisor retroclination
- Active muscular lips → Bimaxillary retroclination
Dental Characteristics of Incisor Class II Div 2 Malocclusion?
- Increased inter-incisal angle → Lack of occlusal stop → Continued overeruption of incisors
- Crowding of U/L incisors secondary to retroclination
- Scissorbite due to relative positions and width of the arches
Skeletal Causes of Incisor Class III Malocclusions
- Mandibular prognathia
- Increased mandibular length
- More anteriorly positioned glenoid fossa
- Maxillary retrusion
- Maxillary hypoplasia
- True retrusion due to reduced anterior cranial base length
- Combination
Can be exacerbated by upward and forward mandibular growth rotation
Dental Causes of Incisor Class III Malocclusions
- Labial displacement/ proclination of lower incisors
- Palatal displacement/ retroclination of upper incisors
- Functional shift (Pseudo-Class III Malocclusion) secondary to an occlusal interference
Dental Characteristics of Class III Malocclusions
- Mandibular buccal crossbite due to relative positions and widths of arches
- Maxillary constriction can lead to secondary crowding
Skeletal Causes of AOB
- Vertical facial growth: Downward and backward mandibular growth rotation
- Failure of anterior teeth eruption to compensate for increased inter-occlusal distance between maxilla and mandible
- Condylar degenerative diseases
- Arrested condylar growth secondary to trauma
Soft Tissue/Habits Causing AOB
- Forward resting tongue posture
- NNS hinders eruption of incisors
- Mouth breathing (Not very significant)
Dental causes of AOB
- Bimaxillary proclination
- Ankylosis secondary to trauma
- Impaction/ectopic eruption
- Alveolar cleft (associated with cleft lip and palate)
Causes of Deep Overbite
- Reduced vertical dimensions (Upward and forward mandibular rotation)
- Active lip musculature or high lower lip line
- Bimaxillary retroclination
- Over-eruption of anterior teeth
5.Posterior bite collapse
Skeletal causes of Posterior Open Bite
- Long face skeletal pattern (AOB extends posteriorly)
- Unilateral condylar hyperplasia
- Hemimandibular hyperplasia
- Unilateral idiopathic condylar resorption
Soft Tissue Causes of POB
- Macroglossia
- Lateral tongue spread
Dental Causes of POB
- Ankylosis
- Primary failure of eruption
- Impeded eruption of tooth
- Mesial tipping of molars
Skeletal Causes of Posterior Crossbite
- True transverse discrepancy
- Relative transverse discrepancy
- Mandibular buccal crossbites in SK Class III
- Scissor bite in SK Class II
- True skeletal asymmetry
Skeletal Asymmetry that is unilateral excessive growth
- Unilateral condylar hyperplasia
- Hemimandibular elongation
- Hemimandibular hyperplasia
Skeletal Asymmetry that is unilateral deficient growth
- Hemimandibular hypoplasia
- Unilateral deficient condylar growth (Trauma or infection)
- Unilateral idiopathic condylar resorption
Causes of Skeletal Asymmetry
- Childhood fractures of jaw
- Rheumatoid arthritis e,g, hemifacial microsomia (asymmetric mandibular deficiency)
Dental Causes for Posterior Crossbites
- A lateral functional shift secondary to occlusal interference or arch width discrepancy
- Localised displacement
- Rotation or inclination of tooth
Soft Tissue Causes of POB
- Non-nutritive sucking
- Macroglossia
- Mouthbreathing
Other causes of Posterior Crossbite
Cleft palate: Transverse growth restricted by scar tissue of cleft repair
Causes of Crowding and Spacing
Tooth size and arch length discrepancy
- Arch width and length genetically determined ?
- Anomalies in dental development: Size, shape, number of teeth
- Environment: Premature loss of primary or permanent tooth
Problems with Hypodontia
- Retained primary teeth with poor long-term prognosis
- Spacing and drifting of teeth
- Lack of alveolar bone development
Problems with Macrodontia
Crowding and displacement or impaction
Problems with Microdontia
Spacing and drifting of teeth
What is a mismatch in size between upper and lower teeth that may disrupt normal occlusion called?
Anterior Bolton ratio or Overall Bolton ratio
Problems with supernumerary teeth?
- Impede eruption
- Deflect eruption path → Rotation or displacement
- Median diastema
- No effect
Problems with early loss of primary second molars?
- Mesial drifting and tipping of first molars → Space loss
- Localised molar class II or III relationships
- Impaction/displacement of successor
Problems with early loss of primary canines
- Distal drift and lingual collapse of incisors → Space loss
- Impaction/displacement of successor
- Midline deviations
Problems with early loss of primary 1st molar
KIV midline deviations
Causes of late lower incisor crowding
- Late mandibular growth
- Forward
- Downward or upward rotation - Lack of interproximal attrition in modern diet
Causes of Bimaxillary Proclination
- Tooth size arch length discrepancy
- Lacks of lip tonicity or forward tongue resting posture
- Ethnic origin
Causes of Spacing
- Generalised/Localised microdontia
- Hypodontia (Congenital or early removal)
- Pathologic tooth migration
- Median diastema
Physiologic development of Median Diastema
Frenal attachment attaches to the incisive papilla in early mixed dentition
Migrates labially to labial mucosa during normal development
Diastema closes as lateral and canines erupt
Persistence of Median Diastema
- Hypodontia/Microdontia of lateral
- Thick frenal attachment
- Frenal attachment at close proximity to interdental papilla
- Supernumerary teeth (mesiodens)
- Digit sucking habit
- Forward resting tongue posture
Definition of Displacement
Abnormal position of tooth germ
Causes of Displaced teeth
- Space deficiency
- Retained primary tooth
- Supernumerary teeth or cysts
- Habits
