Occlusion Flashcards
Where are the functional cusps located in the maxillary and mandibular posterior teeth?
Maxillary: palatal
Mandibular: buccal
(beware in cross bite situations it is the opposite)
Where does the DB cusp of the mandible sit?
Central fossa of maxillary molars
Where does the MP cusp of the maxilla sit?
Central fossa of mandibular molars
Where does the palatal cusp of maxillary bicuspid contact?
MR of mandibular bicuspid and 1st molar
What is the definition of centric stops?
Where the mandibular teeth contact the maxillary teeth in complete intercuspation, holding the teeth in a stable position
Where do the supporting cusps contact?
- The opposing inclines leading to the fossae; ideally with a buccal and lingual contact for each cusp
- Also the SC has at least one mesial or distal contact with opposing marginal, triangular, transverse or oblique ridge
What is the definition of tripdism?
A supporting cusp in occlusion is held in firm position with at least three contacts
Explain the process of incisor guidance?
During protrusion the mandibular incisal edges glide down the palatal inclines of the maxillary incisors, with many teeth involved
In what direction does the working side condylar head move during lateral excursion?
Laterally, this movement is immediate and non-progressive
How is the condylar angle formed? and What is its average value?
- From the downward movement of the non working condyle to the horizontal plane
- 30
How is the Bennett’s angle formed?
- Angle is formed by the medial movement of the non-working condyle to the vertical plane
Explain the process of the Bennett’s movement? And how far it will move?
The working side condyle moves laterally in the direction of lateral excursion and slightly downwards
- This bodily laterals shift of the mandible is bennett’s movement
- Average at 1.5mm
What is the definition of centric relation?
Position of the mandible to the maxilla, with the intra-articular disc in place, when the head of the condyle is against the most superior part of the distal facing incline of the glenoid fossa
What are the 6 main factors that help decide which articulator to use?
- Intended use
- Patient’s occlusion
- Availability of equipment
- Operator skill
- Technician skill
- Expense
Why use an articulator?
- It simulates the maxillary and mandibular relationship of the patient
- To mount both casts, giving the registered relationship of the teeth
- Study dynamic occlusion
- Diagnostic aid
- Aid development of restorations
What important rule must we follow when using articulators?
Ensure that what is presented on the articulator is identical to what the patient experiences in their mouth
What is a face bow?
A caliper like device used to record the spatial relationship of the maxillary arch to the TMJ and another reference plane
What does a face bow allow us to understand?
- The transfer of the TMJ relationship to the articulator
- The maxillary cast will have the same relationship to the opening axis of the articulator, as the maxillary arch had to the TMJ
Which anterior reference point does an Hanau FB use?
Orbitale
Which anterior reference point does an Whip mix FB use?
Nasion
What does a facebow record?
- The distance from the centrically related horizontal axis of rotation of the joints to the upper teeth
- The relationship between the axis-orbital plane (Frankfort plane)
- The distance between condyles
Name the 2 forms of facebow registration?
Arbitrary and Kinematic
What armamentarium is needed for the arbitrary facebow?
- Ear plug
- Anterior reference pointer
- Intercondylar distance scale
- Finger lock screw
- Centre lock wheel
- Sight
- Bite fork
- Reference point locator
Name the 2 types of arbitrary facebow?
Earpiece and Facia
What type of anterior reference point does earpiece facebow use?
Orbitale
- located suing the denar reference point locator
Nasion
Where is the caliper of the facia face bow positioned?
- 13mm anterior to the auditory meatus on the cantho-tragal line
- this locates the true hinge axis within a 5mm margin of error
What is the definition of the true hinge axis?
- The condylar hinge axis is an imaginary line passing through the centre of the condyles when the mandible rotates in the sagittal plane
- This rotation is within 5-12 degree, when axis of rotation coincides with centric relation called THA
How to place the average face bow on a patient?
- Attach the softened beauty wax on fork
- Place fork against incisal and occlusal surfaces of maxillary teeth
- Ensure the midlines are coincident
- Important that the tips of the cusps and the incisal edges do not touch the fork
What movement occurs in the superior synovial cavity?
Retraction
Protraction
Lateral excursion
(Superior = sliding)
What movements occur in the inferior synovial cavity?
Rotational movement (opening and closing of the mouth) InferioR = rotational
What memory trick to remember for superior and inferior synovial cavity?
Superior = sliding
InferioR = rotational
Name the functional cusps of the maxilla and mandible?
Maxillary palatal
Mandibular buccal
What is the function of the tripoding contact of the molar teeth and where do they contact?
Buccal cusp of maxillary teeth is outside the mandibular opposite tooth, and the palatal cusp of maxillary teeth are the functional cusp as they sit in the central fossa of the mandibular opposite tooth, gives centric holding and tripoding contact and the transfer of occlusal forces
How do the functional cusps change for a crossbite?
In a crossbite situation the Maxillary buccal and the mandibular lingual cusps will be the functional cusps – ensure to check occlusion before starting any restoration
How do individual supporting cusps contact each other?
In ICP, the contact is not at the tip or the deepest part of the fossa. The actual point of contact is called a centric stop
How do molars present a tripoding contact with the opposing molar?
Buccal aspect of mandibular tooth contacts the palatal facing cusp of maxillary molar and the palatal facing incline of the buccal cusp (DB) contact the facing slope of the palatal cusp, and another contact at the marginal ridge
What is the function of tripoding contact?
Stability
What is the definition of incisal guidance?
In protrusion the mandibular incisal edges glide down along the palatal inclines of the maxillary incisors, a poor guidance can lead to non-axial forces causing trauma to the tooth
What is the definition of mutually protected occlusion and give examples on how this can be shown?
- Anterior teeth protect the posterior from cutting forces
- Posterior teeth protect the anterior teeth from grinding forces
- During lateral excursion, only the anterior teeth contact, creating the space called the Christensen’s phenomenon
- During static occlusion, the posterior teeth protect the anterior teeth from the bulk load of pressure
What occurs if the disc of the TMJ becomes displaced?
It changes tooth contacts and mandibular movements
What is the size of the condylar angle?
30 degrees, measured in the horizontal plane
What is the definition of the working side?
The side the mandible is moving towards