Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
63 Cards in this Set
- Front
- Back
|
What is stress? |
force per unit cross sectional area |
|
|
What is strain? |
ratio of the change in length to the original length |
|
|
What is a typical biting force? |
500-700N |
|
|
What sort of retention is used for amalgam & what needs to be incorporated into the cavity design? |
Mechanical retention - undercuts are required |
|
|
What is creep? |
Gradual dimensional changes due to repetitive forces |
|
|
What is the elastic limit? |
The max stress that can be applied without permanent deformation |
|
|
Name 2 non elastic impression materials |
impression compound & impression paste |
|
|
What are the components of impression compound? |
wax, stearic acid, pigments, resins, filler |
|
|
What are the components of alginate? |
Sodium alginate, calcium sulfate, trisodium phosphate, fillers, flavourings |
|
|
What is the setting reaction of alginate? |
sodium alginate reactions calcium sulfate to produce calcium alginate & sodium sulfate |
|
|
What slows the setting reaction of alginate? |
The sodium alginate reacts with the trisodium phosphate first & then reacts with the calcium sulphate to begin the setting reaction |
|
|
Name 2 types of elastomers |
polyether & addition silicones |
|
|
What does the shark fin test measure? |
How much an impression material will flow under pressure |
|
|
What is tear strength? |
The amount of stress a material will withstand before fracturing |
|
|
What can decrease the setting time of gypsum? |
more powder, increased spatulation, increased impurities, increased temperature |
|
|
What is the setting process of gypsum? |
Hemihydrate dissolves in water producing dihydrate, dihydrate crystals come into contact & push apart causing some expansion |
|
|
What are the components of acrylic? |
methacrylate monomer, PMMA particles, plasticiser, pigments, co polymer, inhibitor |
|
|
What is the most common heat schedule used for heat cured PMMA? |
72C for at least 16 hours |
|
|
What can happen is PMMA is under cured? |
Get free monomer which can be an irritant |
|
|
What is the issues if there is porosity in acrylic? |
affects strength, affects appearance, rough surface, absorbs saliva |
|
|
What is the softening temperature of acrylic? |
75C |
|
|
What is the purpose of copper in amalgam? |
Increases strength & hardness |
|
|
What are the different available particle types in amalgam? |
lathe cut & spherical |
|
|
What is the setting reaction of amalgam? |
silver-tin reacts with mercury to form silver-mercury & tin-mercury |
|
|
What factors can decrease amalgam strength? |
Undermixing, too low condensation pressure, slow rate of packing, too much mercury present after condensation, corrosion |
|
|
What additional setting reaction occurs in copper enriched amalgam? |
silver-copper reacts with gamma 2 to produce gamma 1 & copper-tin |
|
|
What are the different filler particles than you can get in composite? |
quartz, silica, borosilicate glass, lithium aluminium silicate, barium aluminium silicate |
|
|
What is the main resin used in composite? |
Bis GMA |
|
|
What is the purpose of camphoquinone in composite? |
It is activated by blue light & produced the free radicals required to initiate the addition polymerisation of Bis-GMA |
|
|
What is the light range required for curing composite? |
430-490nm |
|
|
What is the most common material used to etch enamel? |
37% phosphoric acid |
|
|
What does acid etching do to the enamel & why is it carried out? |
Acid roughens the surface of the enamel to allow for micro mechanical interlocking of resin filling materials. It also improves the wettability of enamel |
|
|
What is the smear layer & how thick is? |
It is a layer of organic debris left after preparing a cavity - its is 0.5-5 microns thick |
|
|
What is used to remove the smear layer? |
dentine conditioner - usually phosphoric acid |
|
|
Why is dentine primer a bifunctional molecule? |
It needs to have a hydrophilic end to bond to the dentine & a hydrophobic end to bond to the resin |
|
|
What are the acids used in GI? |
polyacrylic acid & tartaric acid |
|
|
What is present in the base of GI? |
silica, alumina, calcium fluoride, aluminium fluoride, sodium fluoride, aluminium phosphate |
|
|
What is anhydrous GI? |
Acid is freeze dried & added to powder & liquid is distilled water |
|
|
What are the 3 stages of the setting reaction of GI? |
dissolution, gelation, hardening |
|
|
What happens in each stage of the GI setting reaction? |
Dissolution - H+ attack glass particles leaving silica gel around the unreacted glass Gelation - calcium ions cross link to from calcium polyacrylate (initial set) Hardening - formation of aluminium polyacrylate |
|
|
What are the uses of GI? |
temporary restoration, fissure sealants, dressing, luting cement, orthodontic cement, base or lining, restoring primary teeth |
|
|
In GI, what does tartaric acid do? |
Speeds up the setting reaction |
|
|
What is the difference between a cavity liner & base? |
A base is a thick mix of material used to replace the dentine & minimise the amount of filling material used, a liner is a thin layer of material placed over exposed dentine only |
|
|
What is the purpose of a cavity liner? |
To provide pulpal protection & to promote pulpal healing |
|
|
What are the main problems with zinc phosphate cement as a liner material? |
Its initial pH is 2 & it has an exothermic setting reaction |
|
|
What is cold working? |
Work carried out on metal a lower temperature than the recrystallising temperature |
|
|
What are the effects of cold working? |
higher elastic limit, higher hardness, higher ultimate tensile strength, lower ductility, lower impact strength, lower corrosion resistance |
|
|
What makes stainless steel corrosion resistant? |
The chromium oxide layer |
|
|
In relation to metals, what is slip? |
When dislocations collect at grain boundaries |
|
|
Name 3 materials that can be used as a temporary restoration |
bis-acryl composite, polymethylmethacrylate, polyethylmethancylate |
|
|
What are the ideal properties of a provisional restoration material? |
easy handling, easy to remove, absence of toxicity, high mechanical strength, chemical stability in oral environment, reliable margin integrity, good aesthetics |
|
|
What is the ideal film thickness of a luting agent? |
25 microns or less |
|
|
What types of material can be used a luting agents? |
zinc phosphate, zinc polycarboxylate, GIC, RMGIC, composite resin based |
|
|
What are some problems with zinc phosphate as a lung agent? |
low initial pH, exothermic setting reaction, full set takes 24 hours, doesn't bond to tooth or restoration, brittle, opaque |
|
|
What is the main difference between GI luting cement & GI restorative material? |
The size of the glass particles in the cement is smaller than in the restorative material - less than 20 microns |
|
|
How does GI cement bond to the tooth? |
Through ion exchange with the calcium in enamel & dentine & through hydrogen bonding with the collagen in dentine |
|
|
What needs to be done to the restoration if cementing with GI and what does it allow? |
The restoration needs to be sandblasted to allow for micro mechanical retention |
|
|
What is the hydrophilic monomer in RMGIC? |
HEMA |
|
|
Why is RMGIC cement not the material of choice for luting a conventional porcelain crown? |
The HEMA can expand in a wet environment so the crown may crack |
|
|
What additional material is required if bonding a porcelain restoration & why? |
silane coupling agent - composite can't bond directly to the porcelain surface so the silane is required to bridge the 2 different material - it bonds to both |
|
|
What materials can be used as a metal bonding agent? |
MDP & 4-META |
|
|
What component of temporary luting cement makes the structure weaker? |
wax |
|
|
When should temporary cement containing eugenol be avoided & why? |
If the definitive restoration is going to be cemented with a resin cement because eugenol interferes with composite resin polymerisation |
