Extra Qs Flashcards
What materials are used to make a normal denture, a Flexi denture and the teeth
- normal = PMMA
- flexi = nylon
- teeth = acrylic
What is diametral tensile strength (DTS)
-How much force applied to a brittle material before it breaks, taking the diameter and height into account. Pulling
How does the DTS compare for amalgam, composite and glass ionomer cement
- Amalgam and composite are very similar
- GIC is a lot less so is used for temporary fillings so can easily be removed. Fluoride leaches out
How long does it take for amalgam to set
24 hours to fully set
Consequences of filling material shrinking. What technique can be used to prevent this
- Causes staining, secondary caries, hypersensitivity
- Incramental technique. (layer by layer) However cannot be used if the setting time is long as would take ages
What temperature rise of filling material will damage the pulp
10 degrees
Is there a larger temperature rise in light or chemically activated composite
light activated
How does the WT, ST, technique sensitivity, porosity, and shrinkage compare with chemical and light activated composites
-Chemically activated = more technique sensitive as gooey, long setting time of 4-5 mins, lower temperature rise, more porosity so weaker, more shrinkage.
[It is made of a base and a catalyst]
-light = infinite working time. Setting time is 60s
How the width of the light tip affects the curing time. What other factors can affect the curing depth
Smaller tip = more intense = more cured
-Also depends on the the distance between the light and filling, and the angle
What is shear bond strength
- the ability for a filling to bond to dentine or enamel
- the strength required to shear off from the tooth
- shear force is like scissors sliding past each other
How is amalgam and composite bonded to dentine/ enamel
- Amalgum=mechanical strength. No bonding strength
- Composite= complex (chemical and mechanical)
The 3 ways that the bond can shear
- Adhesive failure: fails directly at interface. True evaluation of bond. What we want
- Cohesive failure: Some material has stuck onto the tooth surface. Or some tooth has been taken away with it
- Mixed: cohesive and adhesive
Higher strength will last longer
How the shear bond strength compares with composite and GIC
- composite = stronger. It needs an adhesive to stick
- GIC = weaker. Used for temporary fillings so can be easily removed. It naturally sticks, no adhesive added
Modern light curing units use which part of the electromagnetic spectrum to activate light cured composite materials
visible light
The apparatus use in the laboratory to measure the temperature change during the setting reaction is known as what
Calorimeter
