Unit 308 Flashcards
Prosthodontics is…
the restoration or replacement of damanged or missing teeth by the use of artificially constructed devices.
When teeth have been damaged and cannot be restored by fillings they are restored by..
inlays, crowns, veeners
when teeth have been extracted they are usually replaced with…
dentures, bridges, implants
who contructs the artificial devices?
Dental Technician
Why is getting the occlusion correct so important with prosthodontics?
The musculature surrounding the temporomandibular joint especially the lateral pterygloid muscles will become strained if patient does not bite in their correct occlusion.
What materials are used to record an accurate copy of the patients mouth?
Impressions
What properties should impression materials have?
- easy to mix
- cost-effective
- adequate working time before setting
- relatively short setting time
-record tooth details accurately - stable and elastic
What kind of patients can we use non-elastic impression materials on?
edentulous
Alginate is what type of impression material?
irreversible hydrocolloid
What are the 2 main reasons alginate is commonly used?
easy to mix and relatively cheap
Can alginate impressions be used to make the working model for a crown, bridge, veener or inlay construction?
NO
What is the reason alginate cannot be used to make the working model?
it is not accurate enough
What is alginate powder made of?
calcium salt, alginate salt and filler
what temperature should the water be when mixing alginate?
room temperature
what is spatulating?
folding the powder into the water and vigorously spreading it against the bowl side.
The working time of alginate is determined by?
the temperature of the mixing water used
What does chromogenic materials mean?
materials that change colour in response to some stimulus e.g. mixing and setting stages.
Dimensional changes of alginate in the presence/absence of water.
Left in water - impression expands
Left out of water - impression shrinks
Addition silicone impression material is what type of material?
Elastomer
Why is addiction silicone impression material used?
Highly accurate when set
How is the impression material produced in regards to the tubs of heavy bodied putty with liquid or paste activator?
chemical reaction
What can cause addition silicone impression material to be affected (setting times and mixing)?
Some types of rubber PPE gloves
What types of gloves are advised to be worn when mixing addition silicone impression materials by hand?
vinyl gloves
Are silicone impressions affected by temperature?
NO
What material is light bodied material used with?
Addition silicone impression
What technqiue is best to use for a very accurate impression - adition silicone imp?
two stage technique
- condensation cured silicones
What is the average setting time for silicone impressions?
4 minutes or more
Advantages of silicone impressions:
- dimensionally stable in the presence of moisture
- mixing techniques prevent the formation of air bubbles
- excellent elasticity, strength and accuracy
- suitable for all types of prosthodontics
Disadvanatges of silicone impressions:
- more complicated n time consuming
- expensive materials
-uncomfortable for patient
-paste materials are sticky prior to setting
Do polyethers materials create very accurate impressions?
YES
An example of polyethers impression material:
impregum
What is the impression material polyethers presented as?
2 pastes in different colours
How is polyethers material mixed?
waxed paper pad and collected into special syringes for administration to the prepared tooth.
remaining material is loaded onto an impression tray
What type of material is polyethers?
elastomer
Polyethers impression material has a similar setting time to silicones but set more stiffly how are they usually removed from the mouth?
sharp displacing action from the mouth
Main disadvantage of polyethers material:
slightly less dimensionally stable when moist compared to silicones.
How is a disinfectant bath made for impressions?
10% sodium hypochlorite with water
products such as proforma
How long should an impression be left in a disinfectant bath?
10 minutes
Alginate impressions are packaged how?
covered with a wet gauze and sealed in an air tight bag
Elastomer impressions are packaged how?
Blown dry using the tripe syringe and sealed in an air tight bag.
Wash imps before placing in disinfectant and after.
Impressions must be stored at what temperature?
room temperature
Alginate impressions must remain…
moist at all times
What shape is an impression tray?
horse shoe shape
edentulous patients would need what type of tray?
edentulous tray
dentate patients would need what type of tray?
boxed tray
What is the reason behind impression trays having holes in them?
impression materials are not adhesive to plastic or metal
so the holes enable the material to lock itself into the tray.
The impression trays that are made in numerous sizes for adults and children are called?
stock trays
The trays made in acrylic by the technician are called?
special trays
What are the trays called that record a partial section of both dental arches and occlusion in one impression?
triple trays
fixed prosthodontics means…
tooth restorations or replacements that are cemented within or onto a tooth.
The 4 fixed prosthodontics are:
- crown
-bridge
-veener
-inlay
The material used for each prosthodontics is decided on:
- the tooth involved
- aesthetics
- is the material temporary or permanent
- occlusion does the patient bite in an unusual way
Temporary crowns and bridges can be constructed at the chairside using :
stock crown forms
preoperative impressions to construct them
How much of a tooths surface does a crown cover?
3/4
The usual method of making crowns is sending them of to the lab to construct however this can take up to 2 weeks, what are the quicker alternatives of a constructing a permanent crown?
- 3 dimensional imaging techniques - scan n construct on the same day
- new comp materials e.g. luxacrown construct crowns at the chairside
What materials are used to take impressions for a crown?
- alginate impression of the opposing arch
- occlusal registration - bite registation putty + catalyst
- elastomer impression
When is the face bow technique carried out?
when several crowns are being constructed on the same arch
What burs are used when preparing a tooth for a crown?
(friction grip)Long tapered diamond bur
Why is gingival retraction cord used?
To allow the impression material to flow into the crevice and accurately record the prepared tooth margins.
What is retraction cord soaked in?
astringent solution - adrenaline or alum
What are Beebee crown shears used for?
short beaked shears used for cutting and shaping the margins of temporary crowns.
What are crown formers used to do?
plastic or polycarbonate tooth shaped formers - variety of sizes and available for each tooth shape
Luting cement - self cure resin
chemical bonding between tooth and prosthesis
double syringe mix
Luting cement - light cure resin
light cure bonding between tooth and prosthesis
double syringe mix
Luting cement - dual cure resin
combination of self cure and light cure bonding between tooth and prosthesis
double syringe mix
Luting cement - polyester resin
chemically adhesive and inert in saliva
waxed pad and spatula
Luting cement - glass ionomer
chemically adhesive to tooth and inner surface of prosthesis
waxed pad and spatula
Luting cement - zinc polycarboxylate
chemically adhesive to tooth and inner surface of prosthesis
glass slab and spatula
Luting cement - zinc phosphate
mechanically adhesive to rough inner surface of prosthesis and surface of tooth
glass slab and spatula
A fixed prosthesis is permanently cemented onto the tooth using a…
luting cement
Porcelain jacket crown
anterior teeth only
good aesthetics
All ceramic crown
modern version of PJC
constructed of stronger ceramic materials e.g. zirconia
posterior n anterior
require less tooth preparation than a conventional bonded crown e.g emax
Porcelain bonded crown
consist of substructure of metal for strength with a buccal or labial face of porcelain for better aesthetics
They appear less opalescent than the all ceramic crowns
Full gold crown
made of yellow gold or mixture of precious or non precious metals
STRONGEST of all crowns
ideal for posterior teeth and patients with a heavy bite
Over time a tooth that has a root filling can become brittle and fracture, the tooth will need additional support, this is achieved by..
Post crown
A post crown consists of..
a metallic post and core structure that is then shaped to hold a conventional crown.
In a post crown what are the metallic posts constructed from?
preformed posts e.g. paraposts or dentatus posts
The post and core are handmade by the technician + crown
What instrument is the root filling removed with when preparing for a post crown?
gates glidden drill
A suitable material for core construction is:
hardened glass ionomer cements such as Vitremer.
Glass fibre posts are cemented into the post hole using self adhesive resin cements before a core is constructed using bulk fill composite material e.g filpost and relyx fibre post.
Why are temporary crowns placed whilst the permanent crown is being constructed?
maintain appearance
prevent sensitivity
maintain the correct space between adjacent teeth
maintain the correct occlusion between opposing teeth
Temporary crowns placed using a prefabricated product are made by…
fitting a crown form over the prepared tooth
Is it true handmade and prefabricated temp crowns can be successfully used for posterior teeth?
YES
Trimmed prefabricated crowns are cemented using..
temp bond