Dental Amalgam Flashcards
What are cavity varnishes?
are natural rosins (such as copal, colophony or sandarac resin) or synthetic resins (polystyrene) dissolved in a solvent (alcohol, ether, chloroform or acetone)
applied to walls and floor of the cavity using a brush
What is the purpose of varnishes?
bridge the gap between the dentine and restorative material - decrease post-operative sensitivity and decrease microorganism
What materials were use in varnishes?
gold and amalgam
What is the mechanical mixing of amalgam known as?
trituration
What is the tray lined with in amalgamators?
aluminium foil
Why is the amalgamator lined with aluminium foil?
in the event of a mercury spillage, the aluminium foil will retain the mercury and react with it (it will not vaporise)
- reduce mercury vapour
What happens if you overtrituration the amalgam?
too wet and hot after mixing and is difficult to remove from the capsule
leads to…
excessive expansion
reduced strength
What happens if you undertrituration?
dry crumbly mix (not reacted enough)
low strength
poor corrosion resistance
How do you put amalgam into teh cavity?
incrementally, in layers
bring mercury to the top then remove
How do you want to condense amalgam?
laterally and axially
How do you prevent bonding the amalgam to the band?
apply a thin layer of Vaseline
Do you carve towards or away from the marginal ridge?
away
What is burnish?
plastic deformation of a surface due to sliding contact with another object. Burnishing smears the texture of a rough surface rendering it shiny
Why is it important to polish amalgam?
amalgam is rough at a microscopic level, with pits that retain food debris ad acids
improves marginal adaptation of material - extend life of retoration
easier to clean
What reaction can occur if amalgam is not polished?
galvanic activity on the surface leading to corrosion in extreme cases
What speed and bur would you use for polishing amalgam?
slow speed polishing burs
brown and green
After polishing, how do you finish an amalgam restoration?
use a mix of zinc oxide powder and alcohol in a rubber cup or on a brush for a final high-lustre polish
Is elemental mercury toxic?
yes, highly toxic
When is more mercury vapour released, what temperature?
over 80dc
What are teh adverse effects of amalgam?
enamel discolouration
amalgam tattoo
lichenoid reaction
galvanic cell
Why does enamel discolour with amalgam?
due to dentine structure being permeable
particularly when the restoration has been in situ for some time
corrosion by-products migrate into dentinal tubules
Why can an amalgam tattoo form?
some fine particles of the material can migrate into the soft tissue
benign lesion
may mimic melanoma
diagnosis confirmed by biopsy
What can cause the lichenoid reaction?
not uncommon
believed to be caused by electrochemical reactions and a Type IV hypersensitivity reaction
use a different material
What is a galvanic cell?
2 dissimilar metals and saliva
mild electric shock or a silver paper experienced
effects reduce with time
