Sectional models and veneers Flashcards
what type of model are indirect restorations produced on?
Sectional model
What do sectional models allow?
The die to be separate
Removable component while maintaining the die in the correct position in relation to the other teeth
What are the sectional models produced in?
In a hard material such as class IV die stone epoxy resin or equivalent that can withstand production process without loss of accuracy
What are the advantages/disadvantages of pinned systems?
Technically difficult to use - lots can go wrong
Accurate
Time consuming to produce - expensive
What are the advantages/disadvantages of tray systems?
Quick
Simple
Cheap
Less accurate
How are sectional models produced?
Impressions trimmed to leave 2-3mm of gingivae - sulcus and palate not needed, minimises any inaccuracies
Centre marked to allow ease of positioning
Surface tesnion reducing solution to allow the die material to flow readily into the detail of impression material
Plastic tray is the base containing locating grooves and retaining lugs
Vacuum mixed die stone is vibrated into the impression material after drying the silicone surface and tray filled
The impression is turned on to a base aligned and left to set
Once set impression is removed
Model is left to dry before sectioning and ditching
What is the sectioning process?
Dies required are sectioned from the remainder of the model
This allows access to the margin and for the restoration to be seen from all aspects
The sections are made by making parallel cuts which allows all sections to be removed
Margins of the die and the adjacent teeth may be damaged easily by the blade
What is the ditching process?
The removal of the gingival tissue around the die
This allows margin to be seen and accessed clearly a round bur is used to remove the material - easy to damage the margin
What is die hardener used for? and why use it?
To increase the abrasion resistance of die stone,
This prevents material being abraded when using a blade near the margin - necessary for epoxy resin models
What is a die spacer used for
Allows room for the luting agent
It is a thin layer of the varnish added to the surface of the prep, restoration placed over the top
If not dont there would be no room for the cement between the tooth and restoration
How thick is the layer of die spacer
50 nanometers
What are the 2 materials that veneers are made from?
Lithium disilicate or leucite containing feldspathic
What is the production process for sintering ceramics?
Ceramic particles packed together on a refractory model to desired shape
Ceramic fired to 900degrees
Ceramic is trimmed, glazed and stained
Refractory is removed and veneer fitted to original model
Where are errors made in the sintering of cermic production?
The die must be duplicated which requires another stage of production and the associated errors
A technique referred to as platinum foil technique where a foil shell is created and used to support the ceramic particles in the furnace
What are the sintering production problems?
Feather margins
Duplication of die in refractory material may produce error
Refractory/ceramic compatibility is sensitive
Removing refractory from finished restoration
Fitting restoration to the original die
