Clinical Techniques of RPDs (1) Flashcards
Describe treatment planning for RPDs following diagnosis
- Pain relief
- Initial prosthodontics
- Surgery / periodontal / orthodontics / restorative dentistry
- Definitive prosthodontics
Describe the clinical stages of RPD production
- Preliminary impressions
- Recording occlusal relationship for articulation of study casts
- Master impressions for working casts
- Castings trial / altered cast impressions
- Trial protheses
- Insertion
- Review
Why must study casts be articulated and surveyed?
To allow RPD design and custom impression trays to be made
Name 4 things which should be recorded in a preliminary impression
- All surfaces of all teeth
- All of the palate back to junction of hard and soft palate
- Bounded saddle areas to full depth of sulci
- Distal extension saddle areas to hamular notch (upper) and retromolar pad (lower) to full functional width and depth of sulci
Describe 5 features of a tray used to take an impression
- Rigid in use
- Sufficient extension to support impression of all structures
- Incorporate occlusal stops
- Have a robust, preferably integral handle
- Capable of withstanding autoclave sterilisation if reusable
What are box trays designed for?
To be used where teeth are present
Describe why alginate impressions in rigid stock trays are useful
- Give accurate impressions for good quality casts
- Prepare satisfactory design, assess occlusion and enable custom impression trays to be constructed
Name 3 places where dead space is likely to occur
- Saddles
- Palate
- Reflection of sulci
What is the best way to prevent dead space ruining an impression?
Adapt the tray
Explain how a tray is adapted to remove dead space
- Thermoplastic impression compound added to tray
- Hot wax knife removes excess impression compound or teeth indent
- Alginate places over the compound and impression taken normally
Describe how to take a lower impression
- Stand in front of patient while seating tray
- Half close mouth
- Tongue up and forward to touch the upper lip
Give 4 steps of disinfecting alginate impressions
- Rinse with cold water for 30 secs
- Immerse Perform for 10 mins
- Rinse in water and remove excess
- Wrap in damp gauze, plastic bag and label as disinfected
What is Immerse Perform?
Persulphate compound - Organic acids
Describe 6 things which may be included on prescription to the laboratory with alginate impression for a RPD
- Patient details
- Registration rims (+/-)
- Impression material to be used for master impressions
- Trays (+/-)
- RPD Design
- Date to be ready for
What is the function of articulating study casts when designing RPDs?
Avoid premature occlusion on prosthesis
Name 3 parts of prosthesis on which premature occlusion may occur
- Occlusal rests
- Clasp shoulders
- Major / Minor connectors
Describe 3 ways to articulate study casts
By hand - Sufficient natural teeth allows casts to be held in ICP
Registration rims - Insufficient teeth present
Rigid wax sheet
Describe the process of recording ICP with registration rims
- Registration rims produced in labs in places of saddles
- Tried and trimmed in mouth until no interference from wax rims while patient closes into ICP
- Registration material applied on top of registration rims
- Patient bites into ICP and material will record ICP to allow articulation
Name 2 times there is no requirement to articulate prior to designing an RPD
- Opposing arch is edentulous
2. No tooth-tooth ICP contacts
Describe the sequential design for RPDs
- Study casts (articulated and surveyed)
- Classification
- PoI
- Saddles
- Support
- Connectors
- Retention (direct and indirect)
- Reciprocation and bracing
Why are tooth modifications necessary?
Design of an RPD often dictates teeth need to be altered prior to master impression
Name 4 types of tooth modification
- Rest seat preparation
- Guide planes
- Survey line reduction
- Augmentation of undercuts
Describe 2 functions of a rest seat preparation
- Provide more suitably inclined surface for occlusal rest to direct force down long axis of the tooth
- Provide space between occlusal surface of upper and lower teeth to allow rest of adequate thickness and strength
Describe the ideal dimensions of an occlusal rest
About on half of the bucco-lingual cusp-cusp width and one third of mesiodistal width of tooth
What are guide planes?
Two or more vertically parallel surfaces
Name 4 functions of guide planes
- Provide horizontal stability
- Increase retention
- Provide reciprocation
- Prevent clasp deformation
What type of bur is used to prepare guide planes?
Cylindrical straight bur
Describe unfavourable survey lines with regards to RPD design
- High survey line leads to premature occlusal contact
- It also reduces space available for a clasp
- Removal of tooth tissue at bulbosity reduces height of survey line
- Composite addition can augment the undercut
