Tooth borne dentures Flashcards
Primary imps
- required for
- tray selection
Using ‘off the peg’ impression trays
Needed for planning, design, construction of special trays
Tray selection - should be 4mm between flange of tray and buccal surfaces of teeth
Articulators are used to…
To position the maxillary and mandibular casts in a particular relationship
Articulator designs
Different designs available
- hinge articulator
- average value (movement) articulator
- Arcon (semi adjustable)
- non-arcon (semi adjustable)
- fully adjustable
Semi-adjustable articulators
Produce a simulation of anatomical relationships and movements, good occlusal function
What is needed as well as an articulator
Facebow and occlusal records
Surveying
Parallelometer Identifies parallel surfaces and points of maximum contour Clinician should survey cast Helps decide pre-prosthetic treatment Several attachments
Surveying - analysing rod
Place against teeth & ridges
Identify undercut areas and parallel surfaces
Doesn’t mark cast
Surveying - graphite marker
Moved round teeth and ridges
Marks position of maximum convexity (survey line) separating non-undercut from undercut area
Tip of marker should be level with gingival margin
If not, false survey line produced
Undercut gauge
Measure extent of undercut
0.25mm, 0.50mm, 0.75mm
Allows correct positioning of retentive clasp arms
Trimming knife
To eliminate unwanted undercuts on master cast
Wax added and excess removed
Gives surface parallel to path of insertion
Duplicate cast made
Guide planes
2 or more parallel axial surfaces Limit path of insertion Improve stability Can occur naturally on teeth Trimming knife can be used to prepare guide planes on wax patterns
Path of insertion
The path followed by a denture from its first contact with teeth until fully seated
Coincides with path of withdrawal
May or may not coincide with path of displacement
May be single path or multiple paths of insertion
4 stages of surveying procedure
Preliminary visual assessment – eyeballing cast
Initial Survey
Analysis
Final Survey
Initial survey
Cast positioned in occlusal plane horizontal
Identify undercuts that could provide retention
Analysis of horizontal plane or tilted cast
Need to consider
- appearance
- interference
- retention
A system of design
Saddles Support Retention Bracing and reciprocation Connector Indirect retention Review of completed design
What are saddles and what are they made from
The part of the denture that rests on covers the edentulous areas and carries the artificial teeth and gingiva
Acrylic or framework of metal overlaid by acrylic
Concerns about saddles
Design of occlusal surface Base extension Design of polished surface Material for impression surface Junction between saddle and abutment tooth
Design of occlusal surface of saddles
Important to position artificial teeth to produce even contact in intercuspal position & occlusal balance
Material for the impression surface (saddles)
Metal or acrylic
Acrylic – can add to, advantage with bone resorption in distal extension saddle
What is support in relation to an RPD
Resistance to vertical forces directed towards the mucosa
Planning support is dependent on
Root area of abutment teeth
Extent of the saddles
Expected forces on the saddles
Components for tooth support
Occlusal rests
Cingulum rests
Incisal rests
Overdenture abutment teeth
Other functions of rests
Distribution of horizontal force
Maintaining components in correct position
Protecting the denture/abutment tooth junction
Providing indirect retention
Reciprocation
Preventing over eruption
Improving occlusal contact
Retention is
Components which resist displacement of denture
Retention is achieved by
Using clasps which engage undercuts
Muscular control
Physical forces from coverage of mucosa by denture
Path of insertion
Categories of clasps
Occlusally approaching Gingivally approaching I bar clasp Other variations -ring clasp (occlusally approaching) -L or T shaped (gingivally approaching)
RPI system
Combination of occlusal rest (R), distal guide plane (P) and gingivally approaching I bar (I)
Used mainly with mandibular distal extension saddles
Connectors
Major and minor
Join together the components of a denture
Minor – join the small components e.g. rests, clasps to saddles or major connectors
Keep number to minimum to keep design simple.
Major – links saddles and unifies structure of denture
Also provides bracing and support by distributing functional loads widely to teeth and mucosa (maxillary)
Also provides indirect retention by contacting surfaces and palatal coverage