Blocking out and duplicating Flashcards
What is blocking out?
The preparation of the master/definitive part dentate cast, for the construction of a RPS
What is the definition of ‘blocking out’ in a dental context?
To prevent a part of the removable prosthesis entering an area that it should not enter
- A rigid connector should not and cannot enter undercut areas
- Clasp arms should only engage undercuts to s depth suitable for the metal they are made from
- Undercuts can be found on teeth and soft tissues
In relation to survey lines what should you block out? (3 points)
Only block out:
- In relation to the path of insertion and removal
- Between high and low survey lined where a connector is boing placed
- From undercut gauge mark to low survey line where a clasp is being placed
If you do not block out, the need to adjust at chairside is likely. What is the problem with this?
Need to trim as best as possible so will have to guestimate
- This can inevitably provide a poor denture fit and function
If you block out in plaster then what can the RPD be processed in?
In heat cure acrylic
If you block out in wax then what can the RPD be processed in?
Processed in self-cure acrylic
One option for dental cast preparation is on the master cast block out the undercuts to the path of insertion & removal using wax & chisel on the surveyor. What are the advantages of this? (2 points)
Accuracy of the prosthesis which can be checked on the master cast both in laboratory and at chairside
- The master cast is not destroyed/broken at processing stage
One option for dental cast preparation is on the master cast block out the undercuts to the path of insertion & removal using wax & chisel on the surveyor. This will be duplicated in ‘refractory’ material for a CoCr framework. Duplicated again to give a stone ‘working cast’. The PMMA can be processed on the working cast and delivered on the master cast. What are the disadvantages of this? (3 points)
Another duplication and possible error
- Requires more stages and time
- Not always possible to fit onto master cast which is rigid compared to oral mucosa
One option for dental cast preparation is it can be utilised for a PMMA denture base not a Co/Cr. Block out undercuts with dental plaster on the surveyor using the chisel tool. The trial and processing is undertaken on this master cast (hence it can be destroyed or teeth broken off). What are the advantages of this option? (2 points)
Requires less stages and time
- However there is technique and skill in blocking out in plaster
One option for dental cast preparation is it can be utilised for a PMMA denture base not a Co/Cr. Block out undercuts with dental plaster on the surveyor using the chisel tool. The trial and processing is undertaken on this master cast (hence it can be destroyed or teeth broken off). What are the disadvantages of this option? (2 points)
The master cast cannot always be ‘in tack’ after processing
- Teeth may break off the master cast which usually are the abutment teeth and the ones important when fitting RPD at chairside to confirm it
What do you need to prepare in upper casts? (3 points)
Block out in areas that the RPD requires the undercuts to be blocked out
- ‘Pindams’ (towards the front) kept back (5mm) from gingival margins
- Post dam is the posterior seal but in front of the soft palate
What is post dam?
The posterior periphery of an upper denture in the palate and in front of the palatine fovea (i.e. on the hard palate for an RPD)
- (when used for complete dentures it it placed on the border of the hard an d soft palate and still in front of the palatine fovea)
What is a pin dam?
A mush shallower groove than the post dam
- Anterior aspect of the finished edge of an RPD aids in ensuring flush fitting and deflection of food material not slipping under the denture
What is it important to ensure when preparing for clasps?
Important to ensure that the retentive end of the clasp is the only part that engages the undercut
An example of duplicating material is reversible hydrocolloid. Give some info about this?
Agar/agar
- Reusable up to 10 times as it keeps its elasticity
- Like alginate impressions it suffers from inhibition and syneresis
- Short shelf life
