Occlusion and Malocclusion Flashcards
Mention the 2 ways by which an ideal occlusion can be defined
Static (morphological)
Functional
What was the key to normal occlusion according to Edward Angle?
- Relative anteroposterior position of the first permanent molars
- Good cuspal interdigitation to provide mutual support for the teeth in function
How is mutual protection of the teeth achieved?
- Disclusion of posterior teeth during lateral and protrusive movements, due to canine guidance/group function and incisal guidance
- Multiple, simultaneous and bilateral contacts of the posterior teeth in ICP, with the incisor teeth slightly out of contact therefore protecting them
- ICP coincident with centric relation but with some limited freedom of movement for the mandible to move slightly forwards in the sagittal and horizontal planes from ICP
Define Malocclusion
Malocclusion can be defined as an appreciable deviation from the ideal, and which can be considered aesthetically and functionally unsatisfactory
Explain Andrews’s six keys of Occlusion (Very IMP)
- Molar relationship - the distal surface of the distal marginal ridge of the upper 1st permanent molar occludes with the mesial surface of the mesial marginal ridge of the lower 2nd molar.
- Crown angulation or mesio-distal tip - gingival portion of the long axis of each tooth crown is distal to the occlusal portion of that axis
- Crown inclination - for the upper incisors, the occlusal portion of the crown’s labial surface is labial to the gingival portion. In all other crowns, the occlusal portion of the labial or buccal surface is lingual to the gingival portion
- Rotations - should be absent
- Spacing - should be absent between the dental arches
- Occlusal plane - should be flat
What is a Class I occlusion?
The position of the dental arches is normal, with the molars in normal occlusion
What is a Class II malocclusion?
Relation of the dental arches is abnormal, with the mandibular teeth occluding distal to normal
What are the 2 subdivisions of a Class II malocclusion?
Class II Division 1 - upper incisors are protruding
Class II Division 2 - upper incisors are lingually inclined
What is a Class III malocclusion?
Dental arches are also abnormal; all mandibular teeth occlude more mesial than normal
What are the main aetiologies of malocclusion?
- Evolutionary trends
- Genetic factors
- Environmental factors which may be further divided into: physiological, habitual and pathological factors
What are some physiological factors that may affect occlusion?
- Soft tissue envelope - influence of the tongue, cheeks and lips on the position of teeth
- Mouth breathing - leads to a longer face and smaller mandible, common in pre-adolescent children
- Muscular activity - low muscle tone in conditions such as muscular dystrophy and cerebral palsy; result is a downward and backward growth rotation of the mandible, increased lower face height and AOB
- Lower lip resting behind the upper incisors, thus causing them to become more proclined leading to an increased overjet (LIP TRAP)
- Hyperactive mentalis muscle leading to retroclination of the lower incisors (STRAP-LIKE LOWER LIP)
- High lower lip position = retroclination of upper incisors (Class 2 div 2)
- Adults with an increased anterior face height have a reduced bite force and a different muscle fibre composition in the masseter
What is a habit that can affect occlusion? What are the changes that can be observed?
Dummy and digit sucking can influence the developing dental arches and occlusion.
The following changes can occur:
- Increased maxillary arch length and prognathism
- Narrowing of maxillary arch and widening of mandibular arch width
- Posterior crossbite
- Maxillary incisor proclination, spacing and increased overjet
- Reduced overbite
- Anterior open bite
- Class II buccal segments
During digit sucking, the tongue is pushed down and away from the upper arch causing increased pressure from the cheeks and absence of tooth contact –> posterior crossbite
Which pathological conditions can contribute to malocclusion?
- Childhood fractures of the jaws
- Juvenile rheumatoid arthritis
- Excessive growth hormone
- Periodontal disease
- Dentoalveolar trauma
- Early loss of primary teeth
What are the benefits of orthodontic treatment?
- Resistance to caries and periodontal disease
- Improved masticatory efficiency
- Prevention or cure of TMJ dysfunction
- Improvement in speech
- Prevention of trauma
- Psychological benefits
What are some risks of orthodontic treatment?
- Enamel decalcification
- Enamel fracture
- Root resorption (mostly external)
- Pain and damage to the pulp
- Gingivitis
- Alveolar bone loss
- Oral ulceration
- Allergic reaction
- Headgear injury
- Facial aesthetics
- TMJ dysfunction
- Relapse (lower incisor crowding, rotations, spacing)
- Failure of treatment
Risk factors for external root resorption: Unusually shaped roots, history of dentoalveolar trauma, excessive orthodontic force, movement of teeth without occlusal contact, intrusive forces, reduction of large overjets by moving the anterior teeth distally, pushing apices of teeth into cortical bone
