Occlusion Flashcards
What are the 2 mandibular movements?
Rotation and translation/ lateral translation
Describe the rotation movement of the mandible
The resting position- lips together, teeth not touching.
Condyle and disc remain within articular fossa.
Also known as hinge movement- imaginary terminal hinge axis through the centers of the condoles- the lines around which the condoles rotate
Which instrument is used to record the terminal hinge axis?
Face bow
- records the terminal hinge axis and the distance between condyles
Describe translation of the condyles
From mouth closed to maximum opening of the mouth
Lateral pterygoid contracts, articular diosc and condyle begin to move, travelling forward and downwards along and over the incline of the articular eminence (may also travel laterally).
What is Posselts envelope?
The extreme mandibular movements (according to sagittal plane)
What are the 6 positions recorded in posselts envelope?
ICP - maximum interdigitation of teeth
E (edge to edge) - mandible pushed forward until incisal edges touch (no hinge movement, just translation)
Pr (protrusion) - reverse overjet, no posterior tooth contacts and eventually no tooth contacts
T (maximum opening) - full translation of condyle
R (returned axis position) - no tooth contacts, most superior posterior position of condyle in fossa
RCP (returned contact position) - first tooth contact when in returned axis position
What is the relationship between ICP and RCP in 90% of the population?
1mm
Describe lateral translation
Also known as Bennet movement
Contraction of one lateral pterygoid causing mandible to move to opposite side.
Movement happens on non-working side - condyle moves forwards and inwards.
Working side condyle moves in lateral posterior direction
What is a mutually protected occlusion?
Canine guidance - strong roots to withstand forces.
No posterior contacts when mandible moves towards working side.
Posterior teeth are not designed to absorb lateral forces, therefore interference may cause occlusal trauma and undesirable tooth movements. This may also prevent musculature rest in dynamic movements which can cause TMD/ pain/ enlargement.
How thick is articulating paper?
40 microns
Shimstock = 20um
When should you mark the tooth contacts with articulating paper?
Before prep/ removing restoration
After placement of crown/ restoration
Describe the ICP contacts?
Lingual cusps of upper molars contact the fossa of lower molar
Bucal cusp of lower molar contracts fossa of upper molar (these are the functional cusps)
Maxillary molars positioned more buccaly
What is the normal measurement of overbite?
2-4mm
What is the difference between overjet and overbite?
Overjet- horizontal overlap
Overbite- vertical overlap
Define crossbite
Condition where one or more teeth may be abnormally malposityioned buccal or lingual or labial with reference to opposing teeth.
Can be posterior/ anterior and unilateral/ bilateral
What is group function?
Multiple teeth in contact when mandible moves to working side (bilateral group function often seen in toothwear- need to alter OVD when providing restorations)
In an ideal occlusion, which teeth should contact in protrusion movements?
Only incisors and canines
Otherwise- protrusive interference.
What are some clinical signs of bruxism?
Toothwear
Fractured restorations
Tooth mobility (in absence of periodontal disease)
Muscle pain and fatigue
Headache/ earache
Pain and stiffness around TMJ
What are the 4 types of toothwear?
Abrasion
Attrition
Erosion
Abfraction
Define occlusal trauma
Injury resulting in changes within the attachment apparatus- PDL, supporting alveolar bone and cementum as a result of occlusal forces.
Primary- intact periodontium
Secondary- reduced periodontium
Fremitus- palpable or visible movement of tooth when subjected to occlusal forces (feel incisor as patient taps teeth in ICP)
When examining the occlusion of a patient, what should be assessed?
Incisor relationship
Guidance
Overjet/ overbite
ICP contacts
Working/ non-working side/ progressive contacts
Pathology
What is an advantage of a semi-adjustable articulator
Condyle is on the lower jaw- anatomically correct
Can use with average values set
Can see full range of mandibular movements for occlusal diagnosis and evaluation
What instrument is used on clinic in order to accurately mount casts?
To mount maxillary cast - Facebow transfer- records relationship of maxilla to the hinge axis of rotation of the mandible.
To mount mandibular cast - Interocclusal jaw registration (can use ICP or RCP)
What are the 2 bony landmarks when using a facebow transfer?
Infraoribital foremen- 43mm apical to incisal edge of 12.
External auditory meats - earpieces, near to position of condyle
Which materials can be used to record ICP?
Wax or paste
Record block if free end saddles and casts cannot be hand articulated.
Recording ICP may result in an increased OVD, how is this avoided?
Thin layer of material
Ensure cusp tips are visible through wax/ registration paste
What is meant by a re-organised approach and what position is this recorded in?
Measure in RCP - planning to provide restorations to a different occlusion (define this occlusion before work is start, must be tolerated by patient).
Slide forward jaw along returned arc of closure (between R and RCP) to a more acceptable OVD (before ICP).
Note: RCP and ICP are the same in 10%
What is meant by conformative approach?
The provision of restorations in harmony with existing jaw relationships - no change in OVD, occlusal contacts remain unaltered.
When is a conformative approach NOT used?
Need increased vertical height for restorations
Tooth/ teeth significantly out of position
Significant change in aesthetics
History of occlusal related failure/ fracture of existing restorations
Why is the returned arc important?
It is controlled by the closure of TMJ and is not influenced by the teeth
Reproducible
Useful for edentulous patients
Which 4 factors can cause tooth mobility?
Traumatic occlusion
Parafunction
Trauma
Periodontal disease
Dental abscess
What is centric occlusion
ICP
What is centric relation
RCP
most reproducible relationship (retried arc- irrelevant to tooth position)
What is the average FWS in pt sitting upright?
2-3mm
What is a border position of the mandible?
Maximum movement of the mandible in any plane/ direction
Irrespective of tooth positioning
What is the bennet angle?
The path of the non-working condole in the horizontal plane during lateral excursion
