Flashcards in Dental Materials Deck (293)
What 2 forms can GICs come in?
Encapsulated or hand mix (liquid/powder)
Why is encapsulated preferable?
Mixed for you
Can out straight into mouth
How can self mix go wrong?
Too much powder or liquid will set slower/faster and alter consistency and binding properties
What are GICs used for?
Cement and fillings
What forms can zinc oxide eugenol and calcium hydroxide come in?
2 paste (temp-bond, Dycal) or liquid/powder
How are 2 paste ZOE and calcium hydroxide cements mixed?
Equal amount of both
15s mix time till creamy, no streaks
5-6 min set time
How is liquid/powder ZOE and calcium hydroxide cement mixed?
2 spoons power : 3 drops liquid
Add in powder small amount at time till right consistency
Clean spatula, put powder on spatula and roll towards you until sausage shaped
1-1:30min mix time
4-5 min set time
How is alginate mixed?
Powder fluffed - mix ingredients, remove clumps
Scoop in bowl, add room temp water
Mix for 30s, spread against side to remove air bubbles and thoroughly mix
1-2 min set time depending on temp - warm water sets faster
What 3 forms are most dental materials in unset?
1. Power and liquid
2. 2 paste
3. 1 paste
What 2 forms do most dental materials cure to?
2. Rubbery, elastic material
Describe dis/advantages of powder/liquid materials
Depends on what using material for
Alginate is v easy, cements more difficult to incorporate all powder into liquid in short time
Need to avoid incorporating air into material
What are the dis/advantages of 2 paste materials?
Difficult to mix to give homogenous resulting mass
Need to avoid incorporating air while hand mixing
What are the dis/advantages of 1 paste materials?
Can be difficult to pack into cavity if v viscous
What are the dis/advantages of delivery gun/pentamix materials?
Easy to mix
Tips cannot be reused
Could two air while filling impression tray
What are the 3 methods of setting dental materials?
2. Root temp.
3. Light cure unit
Compare the physico-mechanical properties of the 3 cure types of materials
1. Heat: optimum physico-mechanical properties (dentures) but not feasible for chairside
2. RT: compromised compared to heat set - denture repair material
3. Light: physico-mechanical properties between RT and heat set - composite
What are the 5 ideal properties of dental materials?
2. Mechanically stable
3. Chemically resistant
4. Dimensionally stable
5. Minimal thermal and electrical conductivity
What are the 11 generic groups of dental materials?
3. Soft liners and tissue conditioners
5. Resin composites
6. Bonding agent
7. Casting materials
8. Investment and die materials
11. Dental alloys/amalgam
What 5 factors influence selection of material?
1. Patient history
2. Age of patient/dentition
3. Patient compliance
4. Location of tooth
5. Depth of cavity
Compare the important factors for ant. and post. restorations
Ant: colour match, natural looking in all lighting conditions, compressive strength not necessity
Post: high compressive strength, aesthetics not necessity
If a carious cavity extends to the pulp what is required when restoring?
Cavity liner to act as thermal insulator so tooth not sensitive to heat changes
What is Grassman's law?
Three parameters of colour:
1. Dominant wavelength (hue)
2. Excitation purity: saturation of colour; intensity 0-1
3. Luminous reflectance: brightness (100) or darkness (0)
Why is colour important in DMs?
Wavelength material reflects may change w/ age thus colour may change
What is the importance of surface finish of a restoration?
When light reflects off a solid some reflects from surface and some reflects from body of solid
Surface reflection dilutes colour: rough surface is much lighter than smooth surface of same material thus colour of restoration could become much lighter w/ wear
What are metameric colours?
Colours that appear the same under 1 light source but different under another
What is the significance of metanerism in dentistry?
Need to match restoration colour to natural colour in light corresponding to that of use
What is fluorescence?
Phenomenon observed when material absorbs colour of one wavelength and emits colour of another wavelength
Why is fluorescence important in DMs?
Teeth emit fluorescent light (look whiter under fluorescent light) so materials need to look natural
Some porcelains contain fluorescing agents to mimic natural appearance
Define opacity, translucency, transparency
Opacity: selective absorbance of light
Transparency: no interaction w/ light, complete transmission
Translucency: mixture of absorption, refraction, transmission