Jaw Relations and Articulation Flashcards
What are non-contact relationships?
Movement governed by muscles of mastication and articular surfaces of TMJ
Where is the axis of rotation in non-contact relationships?
Condylar heads
What is the path followed by any point on mandible while rotating called?
Retruded arc of Closure
What does opening of the mouth beyond 20mm cause?
Protrusion by translation and further rotation of both condyles establishing posterior guidance
What is the inter-occlusal distance?
When muscles of mastication are at rest the space between the teeth is the inter-occlusal distance
Describe the intercuspal position (ICP)
Relation of upper and lower jaws when teeth are in maximum intercuspation
Describe the retruded contact point (RCP)
The most posterior position achievable by the mandible, usually 1mm distal to ICP
What is protrusion?
Movement of mandible governed by palatal slopes of anterior teeth where posterior teeth separate from anterior
What is lateral excursion?
Jaw working from side to side (side mandible moves to is working side and side moving away from is non-working side)
Describe canine guidance lateral excursions
Separation of teeth by contact of canines on working side only
What is group function lateral excursions
Contact of premolars and canines on working side only
Name 3 parameters of jaw movement
- TMJ
- Teeth
- Muscles of mastication
What is the maximum envelope of movement?
Total mandibular movement which is limited by boarder positions and described by Posselt in 1952
Describe the influence of contact relations of removable partial denture design - If the patient has an ICP
Reproduce this and set teeth to harmonise with existing occlusion - Conformative approach to occlusion
Describe the influence of contact relations of removable partial denture design - If the patient has no ICP
Make denture occlusion correspond to RCP so new ICP = RCP - Reorganized approach to occlusion
How may a patient’s mandibular movement be traced?
Electromagnetic techniques
What is the function of articulating study casts?
Allow a design to avoid premature occlusion on any denture component
What is the primary rule of articulated study casts?
Must maintain tooth-tooth ICP
Name 2 ways study casts may be articulated
- Hand alone if there is enough teeth present to do this
2. Wax registration rims if ICP not easily located by hand
What allows study casts to be held reliably in ICP?
Articulators
What is a surveyor?
A simple mechanical parallelometer with a vertical arm which can be brought against teeth or ridges of a cast to identify parallel surfaces and points of maximum contour
Name 4 purposes of surveying study casts
- Identify optimum path of insertion
- Design, material and position of clasps
- Allow blocking out of unwanted undercuts
- Measure and mark correct position and depth of undercut
Describe the initial survey
Always with the occlusal plane at right angles to the vertical because this is the most likely direction of displacement during function
What is the function of blocking out unwanted undercuts?
Duplicate models can be made on which a prosthesis is constructed and subsequently seated upon and withdrawn from
What is a survey line?
A mark around a tooth indicating its greatest circumfrence in any one position relative to the vertical
What are undercut areas?
Areas below the survey line
