8. Lower occlusion rim Flashcards
What does the lower occlusion rim determine? (3)
- Determining vertical dimension.
- Recording centric relation.
- Mounting lower cast.
Define physiologic rest position: (4)
- Mandibular position, head is upright
- Elevator and depressor muscles = equilibrium in tonic contraction (muscle tonus)
- condyles = neutral, unstrained
- no tooth contacts
Condyle location in physiologic rest position?
in front and below their position at centric relation
physiologic rest position mandible position? (2)
2-4mm below MI
-AKA interocclusal rest space
Define vertical dimension:
Distance b/w 2 selected anatomic or marked points, one on a fixed and one on a movable member (usually one on the tip of the nose and the other upon the chin)
Two types of vertical dimension?
- Occlusal vertical dimension.
* Rest vertical dimension.
Define occlusal vertical dimension:
distance measured between two points when the occluding members are in contact
Define rest vertical dimension
Distance between two selected points measured when the mandible is in the physiologic rest position
Formula for interocclusal rest space?
RVD – OVD = interocclusal rest space
What reference is taken to determine vertical dimension for dentures? why?
physiologic rest position, because it doesn’t change so much throughout the patient’s life
Determining vertical dimension with alveolar ridges? (2)
- measure distance between alveolar ridges
- get ridge to be parallel
Determining vertical dimension with facial proportions? (2)
- Willis: distance pupil-corner of mouth = base of nose-chin
- Mc gee: Distance glabella - base of nose = base of noce to chin
Willis facial proportion?
distance from pupil-corner of mouth = base of nose-chin
Mc gee facial proportion?
Distance glabella - base of nose = base of nose to chin
What technology can we use to determine vertical dimension? (2)
Electromyography and kinesiography
Determining vertical dimension with lateral teleradiography?
- Angle ANS-centroid-supragonion = 47o (Slavicek)
Phonetic methods to determine VD? (2)
- Silverman- 2mm space for “S” sound
- Gollis - 4mm space for “M” sound (while saying emma)
The main way to determine vertical dimension?
subtract 2-4mm from physiologic rest position
Secondary method for assessing vertical dimension? (3)
Deglutition assessment:
- when swallowing the mandible is at occlusal VD
- constant height throughout life
How do we alternatively check VD? (4)
- lower occlusion rim is set at RVD (instead of OVD)
- lower cast mounted at +2-3mm pin (interocclusal rest space)
- Pin put at 0 again
- inaccurate unless kinematic facebow used
Resorption with incorrect vertical dimension? (2)
- high VD = ridge resoprtion long term
- low VD = accelerated anterior ridge resorption (due to antero-rotation of mandible)
What happens if the VD is too high? (7)
- rims hit eachother when talking
- mucosa sores
- pain (muscles and joint)
- bone resorption
- long face appearance
- full mouth sensations
- higher ridge resoption
What happens if the VD is too low? (3)
- bone resorption (b/c antero-rotation of mandible)
- facidity and wrinkles around mouth
- bites own cheeks and lips b/c lack of muscle tone
What do we use to get occlusal records? how thick? how do we fix it?
- Aluwax (soft, sticky)
- 1mm thick rectangles over the lower
- fixed with hot wax knife
Why do we aim for centric relation for dentures? (4)
- More stability is achieved for the dentures.
- Less ridge resorption (even load distribution).
- Healthier position for stomatognatic system.
- That ́s the reference that we have.
Why is the lower occlusion rim split into 2? (2)
- space for tongue - it pushes forward
- patient tends to bite with anterior teeth, moving mandible forward
What does the thickness of the aluwax record end up becoming
0.5mm from 1mm intially
How do we guide the patient into CR? (2)
- press chin down with thumbs
- use rest of fingers to push angle of mandible up and forwards
How do we heat aluwax?
45 degrees for 30 seconds
The aluwax record is taken in what position? (3)
centric relation
- back 45 degrees
- head and neck hyper extended
When mounting the lower cast what do we set the articulator to? (4)
- incisal pin at 1mm
- centric lock closed
- PCPI 45degrees
- articulator upside down
Do we take three CR records and check them with a split-cast?
no because we would need three record bases and occlusion rims
What type of rest vertical dimension do edentulous patients usually have?
Lowered rest VD
What type of occlusal vertical dimension do edentulous patients usually have?
They dont have an occlusal vertical dimension
What vertical dimensions can we restore with complete dentures and with what refences? why? (4)
- Restore OVD and RVD
- Don’t have dental refernces
- Reference to be taken: Physiologic rest position because it doesn’t change throughout life
What is the usual vertical rest dimension?
2-4mm
What are the consequences of a low VD?
edentulous face
What are the consequences of a high VD?
difficulty in joining the lips
Clinical procedure to determine VD ?
- Remove occlusal rims from mouth of patient
- Mark the tip of the nose and chin
- ask patient to open mouth for 2 mins
What is the clinical procedure to determine VD after tiring out muscles? (4)
- Ask patient to close mouth slowly relaxed
- minimal lip pressure
- upright position
- head not on headrest
- measure distance between drawn points & calculate avg
- Ask patient to swallow a few times
- check difference between rest VD and OVD = 2-4mm (interocclusal rest space)
How do we alter VD when placing the occlusal rims in the patients mouth? (4)
- No changes on upper rim (info would be lost)
- Modify lower rim until it touches upper tim evenly
- When biting at CR patient must be at estimated OVD
- at rest there should be a space between upper and lower rims 2-4mm
If you put too much pressure while guiding the patient into CR which muscle protectively contracts?
Lateral pterygoid
