Applied Dental Materials Flashcards
What hazards are associated with bisohenol A resin ?
Caused some oestrogen like effects in mice
Bisohenol a is ingredient in composites but not nowadays
Can be a breakdown product of bis gma or bis dma
No evidence that bisohenol a is harmful to humans
What hazards are associated with methyl methacrylate ?
Monomer in acrylic resin can penetrate gloves in minutes
What types of adverse reactions to gloves can occur ?
Contact dermatitis, anaphylaxis, sensitisation, respiratory symptoms
What hazards are associated with light curing units ?
High intensity light curing units
Some white light units emit UVA light (not diode lights)
What is gypsum ?
Calcium sulphate dihydrate
CaSo4.2H2O
What controls the setting expansion of gypsum ?
Potassium sulphate
Sodium chloride
Borax
What controls the setting time of gypsum ?
Potassium sulphate Sodium chloride Borax Potassium citrate Gypsum 20%
What effect does additional water have on gypsum ?
Extends the setting time but produces a weaker mix
What effect does increased spatulation have on gypsum ?
Decreases setting time but increases expansion
What is calcium sulphate hemihydrate type 2 ?
Beta
(CaSo4)2.H2O
Plaster of Paris
What are the properties of type 2 calcium sulphate hemi hydrate ?
Water to powder ratio is 40-50/100 initial set time is 5-10 mins Linear expansion is 0.2-0.3% Compressive strength is 24mpa Tensile strength is 0.6 mpa
What is the setting reaction of calcium sulphate hemihydrate ?
(CaSo4)2H2O + 3H2O —–> 2caSo4.2H2O heat
Hemihydrate in suspension
Heavily saturated calcium sulphate
Ions form on nucleus of crystallisation
What is type 3 calcium sulphate hemihydrate ?
Dental stone
Alpha
What are the properties of type 3 calcium sulphate hemihydrate ?
Water to powder ratio is 25-35/100 initial set time is 5-20 mins Linear expansion is 0.1-0.2% Compressive strength is 70mpa Tensile strength is 15mpa
What is type 4 calcium sulphate hemihydrate?
Alpha modified, die stone, largest crystal size
What are the properties of die stone?
Water to powder ratio is 25-35 initial set time is 5-20 mins Linear expansion is 0.1-0.2% Compressive strength is 75mpa Tensile strength is 20mpa
What are the advantages of die stone ?
Good colour contrast
Reasonable strength
Economical
Good working time
What are the disadvantages of die stone ?
Brittleness
Abrasion
What are the advantages of electroplating ?
Accurate Hard Inexpensive Good abrasion resistance Difficult to damage
What are the disadvantages of electroplating ?
Time consuming (18hrs)
Cyanide
Bad colour contrast
Poor wax adaptation
What is the composition of the copper electrolyte used for electroplating ?
Copper sulphate 200g
Absolute alcohol 2ml
Sulphuric acid 30 ml
Distiller water 1000ml
What is the composition of the silver electrolyte used for electroplating ?
Silver cyanide 36g
Potassium carbonate 45g
Potassium cyanide 60g
Water 1000ml
Give an example of a diluent resin
TEGDMA
What is the filler in a resin based composite ?
SiO2
What is the function of the filler in a composite ?
Control shrinkage and coefficient of thermal expansion
Aesthetics
Mechanical properties
What other fillers may be in a composite ?
Barium or strontium
Ground up composite
What is the purpose of a silane in composites ?
Coupling agent
Bond filer particles to resin
What is the initiator in composites?
Camphorquinone
Starts polymerisation reaction
What is the activator for composites ?
Blue light 470 nm
I hat is the purpose of the activator in composites ?
Stimulate initiator to release free radicals
What is the inhibitor in composite resins ?
Hydroquinone
What is the shrinkage of composites ?
3 %
How does filler loading affect thermal expansion and shrinkage ?
Decreases as filler loading increases
What are the effects of water sorption on composites ?
Warpage, discolouration, reduced mechanical properties
Where does water go if it enters a composite restoration ?
Into the resin
In voids
In the resin filler interface
What affects the depth of cure of composite ?
Oxygen inhibition
Shade
What are the components of a denting bonding system ?
Enchant
Primer
Sealer
What Is the purpose of an enchant ?
Remove pellicle, open tubules
What Is the purpose of the primer ?
Forms bond, reactive groups bond to dentine and free mma groups available to bond to resin
What is silorane ?
Cyclic monomer from oxirane and siloxanes
What is the advantage of silorane ?
Reduces polymerisation shrinkage of composite to
