Pros Paper 2020 Flashcards
What structures/anatomic features should you record in the preliminary impression for a patient with a partially dentate lower arch with only the anterior teeth remaining?
(5 marks)
- Tooth surfaces
- Border extension, alveolar ridge, and full functional depth of buccal, lingual and labial sulci.
- Anatomical landmarks such as hard palate and distal extension extended back to 2/3 of the retromolar pad
- Surface detail (check for voids)
b) Why and how should you modify the stock tray prior to taking the impression? (5 marks)
Use red impression composition, to improve the extension/fit of stock trays in areas where it is poorly extended - the vault of the palate, distal extension saddles, long bounded saddles.
You would do this by moulding the red compound to the appropriate shape on the tray and submerging in a water bath (55-570) and then inert into the mouth.
Describe the jaw relationship to which you would restore a patient requiring a partial denture when using the conformative approach to occlusal rehabilitation? (3 marks)
- If a patient has an ICP: then reproduce this and set teeth to harmonise with the existing occlusion, (confirmative approach)
- ICP is the relation of the upper and lower jaws when the teeth are in maximum intercuspation
- This is the most comfortable position to bite hard and a good start position to assess occlusal relationships
Why should study casts be articulated prior to designing removable partial dentures? (5 marks)
It is to avoid causing premature occlusion on the denture components.
• Identify optimum path of insertion – for appearance, for retention, to avoid interference of tissue undercuts, identify guide planes.
• The design, material and position of clasps
• The initial survey is always with the occlusal plane at right angles to the vertical i.e. cast horizontal because this is the most likely direction of
displacement during function.
State the jaw relationship that is recorded when restoring the occlusion using the reorganized approach? (2 marks)
If the patient has no ICP the denture is made for occlusion to correspond to RCP eg.
ICP=RCP and this is known as the reorganised approach to occlusion
- RCP stands for retruded contact position and is the most posterior position achievable by the mandible, usually 1-1.5mm distal to ICP
a) What do you understand by the terms ‘path of insertion (POI)’ and the ‘path of displacement’ regarding partial dentures? (4 marks)
• The POI is the path followed by denture from first contact with teeth until fully seated
• always coincides with path of withdrawal
• may or may not coincide with path of displacement (which is assumed to be at right
angles to the occlusal plane)
• Path of displacement is the direction in which the prostheses is displaced/dislodged from its position during function
b) Explain THREE possible benefits that a patient may gain in changing the POI from a vertical one. (6 marks)
• can improve aesthetics
• can improve retention
• avoid interferences from large
undercuts
a) Guide planes are often prescribed when constructing partial dentures. Describe how and where a guide plane is prepared on a premolar tooth when using a vertical POI. (3 marks)
- Guide planes provide a definite path of insertion
- To prepare you require two or more vertical parallel surfaces
- And is prepared using a straight bur at maximum bulbosity of the survey line
- So in this case, survey the premolar and take a 2mm square vertical to
- the parallel surfaces at the maximum bulbosity using a straight bur
b) What advantages may patients gain from having an RPD with guide planes? (5 marks)
- They may improve aesthetics by utilizing anterior undercuts
- Increases retention because of parallelism
- Displacement is limited to path of insertion, which protects clasp deformation
- Provides horizontal stability (bracing) and provides reciprocation
- Protects tooth tissue junction by preventing food impaction
- Contributes to distribution of occlusal force throughout the arch
Which lower distal extension saddle denture design feature dictates using a vertical POI? (2 marks)
- Stability is compromised by lack of posterior abutments therefore tend to rotate more and produce a torquing force if the principal abutments are locked into the denture.
- Slightly shorter guide planes are used in distal extension cases to minimise this torquing action.
What may be the most appropriate impression material for master impressions for partial dentures in a patient with a history of periodontal disease, suggest some specific clinical conditions that would justify your choice. (5 marks)
- Alginate rather than typical PVS
- Allows ensure easier removal
- Provides better tolerance/acceptability for patient
- Better for presence of gross undercuts (tilted teeth)
- Large interdental spaces between contiguous teeth
- Periodontally involved (gross recession production long teeth/mobile teeth)
Describe possible faults that may occur in such an impression (alginate) (5 marks)
- Not accurate enough to make prosthesis from (high permanent deformation)
- Easily torn, so might have to take multiple impressions
- Dimensionally unstable – must be poured immediately can’t be repoured
- Poorer quality of surface stone detail in poured cast
- Does not bond to tray – adhesives needed so likely the tray and impression
- separated if not applied correctly
a) What properties are required of a well-designed major connector? (6 marks)
- Must be rigid
- Be a shape well tolerated by the patient
- Should not impinge upon gingival margins
- Clear of anterior ruggae occlusal rest
- Should not create stagnation areas
- Provide support where required
b) If your prescription is for an upper mid-palatal strap/plate tooth supported connector what are the minimum dimensions required for it and explain your reasoning. (4 marks)
- the minimum dimensions for a mid palatal plate is 0.5 x 15mm
- Palatal plate must be 0.5mm thick so it is rigid with broad coverage for support
a) Why are rest seats often prepared on teeth for which occlusal rests are prescribed? (4 marks)
• Provide more suitably inclined bearing surface for the occlusal rest than those existing on the natural teeth (floor of rest should be perpendicular to the long axis of the
tooth) and to provide a shape of surface giving a desirable amount of bracing (saucer-shaped without sharp angles).
• Provide space between the occlusal surface of the upper and lower teeth to allow a rest of adequate thickness and strength to be used.
