occlusion Flashcards
What movement of the jaw does each muscle of mastication do
Temporalis (T)
-Elevates and retracts the mandible
-Assists in rotation
Lateral Pterygoid
-positions disc in closing (superior - SLP)
-Protrudes and depresses mandible and causes lateral movement (inferior - ILP)
Medial Pterygoid (MP)
-Elevates the mandible
-Lateral movement and protrusion
Masseter (SMA)
-Elevates and protracts the mandible
-Assists in lateral movement
what are the mandibular movements
Rotation
Translation
Lateral translation
Describe what the mouth is like in the resting position of the TMJ
the mouth slightly open, lips together and the teeth not in contact (resting vertical dimension). The space between the teeth is the free-way space
The mouth is slightly open, up to 20mm
What happens with TMJ when it moves to resting position
When the mouth is opened just a small amount (20mm) the condyle hinges within the articular fossa. There is no downwards or forwards movement (no protrusion)
What is the terminal hinge axis
The imaginary horizontal axis connecting the condyles around which the. mandible performs pure rotation
What happens during hinge movements of the TMJ
Rotation of the condylar heads around an imaginary horizontal line through the rotational centers of the condyles
What does the facebow record
the relationship of the the maxilla to the terminal hinge axis of rotation of the mandible
Distance between the condyles
It allows a maxillary cast to be placed in an equivalent relationship on the articulator
What heppens during translation movement of the mandible
Lateral pterygoid contracts
Articular disc and condyle begin to move
Travels downwards and forwards along the incline of the articular eminence, In this position a thin portion of the disc maintains the position betewen the articulating surface of the mandibular condyle and the articular eminence
May also travel laterally (laterotrusive movement)
What happens during the rotation movement of the mandible
Small amount of mouth opening (up to 20mm)
Condyle and disc remains within the articular fossa
No downwards or forwards movement
Also known as “hinge movement”
What is posselts envolpe
Describes the Extremes of mandibular movement
Border movements of the mandible in the Sagittal Plane
What does:
ICP
E
Pr
T
R
RCP
stand for
ICP = Intercuspal position
E = Edge to Edge
Pr = Protrusion
T = Maximum opening
R = Retruded Axis Position
RCP = Retruded contact position
What is happening in the ICP position
Tooth position regardless of the condylar position
The comfortable bite
Best fit of the teeth
Maximum interdigitation of the teeth
Can be called centric occlusion (CO)
What is happening during the E position
Tooth position sliding forward from the ICP
Teeth slide forward from ICP guiding on palatal surfaces of anterior teeth
Incisal edges of upper and lower incisors touch
What is happening during the Pr position
Condyle moves forwards and downwards on articular eminence
Only incisors +/- canines touch
No posterior tooth contacts
Eventually no tooth contacts
What is happening during the T position
No tooth contacts
Mouth wide open
Full translation of the condyle over the articular eminence
What is happening during
the R position
No tooth contacts
Most superior anterior position of the condylar head in the fossa
where the Terminal hinge axis is
What is happening during the RCP position
First tooth contact when the mandible is in retruded axis position
ICP is approximately 1mm anterior to RCP in 90% of the population
What is the returded arc of closure and where does it lie on posselts envelope
Retruded arc of closure is the arc of opening and closing made by the mandible whilst the condyles are rotating about the terminal hinge axis
Between R and RCP
What is the difference between RCP and ICP and how does the mandible move to the positions
ICP is approximately 1mm anterior to RCP in 90% of the population
RCP and ICP not coincident so the mandible slides forward to achieve ICP
What is lateral translation and what is it also known as
Movement resulting from contraction from one of the lateral pterygoids
Bennet movement
What is the bennet angle and what is it formed from
The path of the nonworking condyle in the horizontal plane during lateral excursion
formed by the sagittal plane and the path of the mandibular condyle during lateral movement when viewed in a horizontal plane
In the frontal view of posselts envelope what are the divets caused by
Divets are a result of canine guidance
What is meant by a mutually protected occlusion
when the mandible is moving laterally the long strong canines of the upper and lower jaw ensure that that the posterior teeth do not touch when the mandible is sliding to the side. This protects them from lateral forces
When examining the occlusion wha are the 2 types
Dynamic
Static
What equipment is good for checking occlusion
Millers forceps and articulating paper
When do you mark tooth contacts
Before
Preparing a tooth
Removing a restoration
After
Placement of a crown
Placement of a restoration
What is classified under static occlusion
Incisor Relationship
Molar relationship
Overjet/Overbite
Cross bites
Open bites
Individual tooth contacts
RCP – ICP slide (freedom in centric)
In ICP contact what is meant by functional and non functional cusps
Functional Cusps
-Cusps that occlude with the opposing teeth in the intercuspal position
The lingual cusps of the upper posterior teeth and the buccal cusps of the lower posterior teeth
Non Functional Cusps
-Cusps that do not occlude with the opposing teeth in the intercuspal position
The buccal cusps of the upper posterior teeth and the lingual cusps of the lower posterior teeth
What are the functional and non-functional casps on the mandible
The buccal cusps are the functional cusps with the non-functional cusps being on the lingual side
What are the functional and non-functional casps on the axilla
The palatal cusps are the functional cusps on the madnible with hte buccal cusps being the non-functional
What is the fossa on teeth and what happens during ICP
Depression or concavity on tooth surface
Functional cusp of a tooth contacts the fossa of the opposing tooth during ICP
What are the ICP contacts
The palatal cusp of an upper molar contacts the fossa of a lower molar
The buccal cusp of a lower molar contacts the fossa of an upper molar
What problems can arrise in static occlusion
Incisor relationship (Angles classification)
Overbite (The vertical overlap of the incisors)
Overjet (Relationship between the upper and lower teeth in a horizontal plane)
Crossbite (a condition where one or more teeth may be abnormally malpositioned buccal or lingually or labially with reference to opposing teeth)
Open bite (Anterior Open Bite,Lack of vertical overlap of anterior teeth when posterior teeth in full occlusion
Posterior/Lateral Open Bite
Failure of contact between the posterior teeth when the teeth are in full occlusion)
What is dynamic occlusion
the contacts between the teeth when the mandible is moving
What is canine guidance
When a mandible moves laterally to the working side there should only be contact between the canines
What is meant by group function
When multiple teeth are in contact during lateral movement of mandible
Bilateral group function seen in toothwear
What happens during protusion movement
Condyle moves forwards and downwards on articular eminence
Only incisors +/- canines touch
No posterior tooth contacts
What is meant by occlusal interference
Undesirable tooth contacts that may produce mandibular deviation during closure to ICP or may hinder smooth passage to and from ICP (Schillingberg 1997)
What types of occlusal interference is there
Working side
Non-worling side
protrusive
What is working side interference
Occurs when there is underdesireable contact between the maxillary and mandibular posterior teeth on the same side of the arches as the direction in which the mandible has moved
If that contact is heavy enough to disocclude anterior teeth, it is interference
What is non-working side interference
Occurs when there is undersireable occlusal contact between maxillary and mandibular teeth on
the side of the arches opposite the direction in which the mandible has moved in a lateral way
What is protrusion interference
any posterior contact during protrusion
Why would you want to avoid posterior contacts
Teeth are designed to absorb heavy forces in the direction of the long axis of the tooth
Most teeth are not designed to absorb significant lateral forces generated by occlusal interferences
Musculature gets a rest as less activity if not undesirable posterior contacts so muscles wont get any rest in occlusal interference
Occlusal trauma and undesirable tooth movement
What are the 2 types of bruxism
Eccentric
The parafunctional grinding of teeth
An oral habit consisting of involuntary rhythmic or spasmodic or functional gnashing, grinding or clenching of teeth in other than chewing movements of the mandible which may lead to occlusal trauma
Centric
Clenching: The pressing and clamping of the jaws and teeth together. Frequently associated with acute nervous tension or physical effort
What are the clinical signs of bruxism
Toothwear
Fractured restorations
Tooth migration
Tooth mobility (Often in absence of periodontal disease)
Muscle pain and fatigue
Headache
Earache
Pain and stiffness in the TMJ and surrounding muscles
On a articulation cast what angles are the bennet angle and Condylar Guidance Angle set at
Bennet Angle set at 15
Condylar Guidance Angle set at 30
When recording a face bow registration:
What would you do first and where
Mark the Anterior Reference Point
-on the patient’s right side using the Reference Plane Locator and Marker
It is the approximate position of the infraorbital foramen
When recording a face bow registration:
What do you do with the bite fork
Apply bite registaryion paste but not too thickly
with bite fork arm to the right and locating notch facing up, make sure notch is at the midline
Then Firmly seat to record cusp tips of maxillary teeth and check that it is parallel with the patients’ coronal and horizontal planes
After taking the facebow off a patient what have you recorded and what is next
The relationship of the maxilla to the hinge axis of rotation of the mandible
We can now mount the maxillary cast in an equivalent relationship on the articulator
How do you mount a facebow onto a lower cast
An interocclusal registration can be used to mount the mandibular cast in relation to maxillary cast already mounted on the articulator using the facebow transfer
When mounting face bow onto lower cast what are the two choices of interocclusal registration you can use
- Intercuspal Position (ICP)
-Conformative Approach
2.Retruded Contact Position (RCP)
-Reorganised Approach
When mounted on the cast for interocclusal registration what are the various ways to get into ICP position and why
No material
-Plenty of tooth contacts. ICP is obvious to technician
Wax
-ICP is not obvious to technician (make sure to not use too much should only be a thin bit with cusp tips visible, dont want increased OVD)
Paste
-ICP is not obvious to technician (make sure to not use too much should only be a thin bit with cusp tips visible, ont want increased OVD)
Record block
-Free end saddles. Casts cannot be hand articulated
When would it be considered an unorganised approach of interocclusal registration
You haven’t assessed the occlusion before starting restoration(s)
You change the occlusion with your restoration(s)
You haven’t planned where your ICP will be and what the related jaw relationship is
You provide an occlusion which does not conform to the previously well tolerated one
What is meant by conformative appraoch when doing interocclusal registration
the provision of restorations in harmony with the existing jaw relationships
This means that the occlusion of the new restoration is provided in such a way that the occlusal contacts of the other teeth remain unaltered
When do you not use the conformative approach when doing interocclusal registration
An increase in vertical height is needed to make space for restorations
Tooth/teeth significantly out of position (ie overerupted, tilted or rotated)
A significant change in appearance is wanted
There is a history of occlusally related failure or fracture of existing restorations
Why use reorganised approach when doing interocclusal registration
ICP is non-existent or no use
You need space to place restorations
RAP is a reproducible position of the mandible independent of the teeth
