DMS Flashcards
stages of acrylic polymerisation
activation
- of initiator to provide free radicals
initiation
- free radicals break C=C bond in monomer and transfer free radicals
propagation
- growing polymer chain
termination
- of polymerisation
what types of porosity can occur from the polymerisation reaction of PMMA?
gaseous porosity
contraction porosity
granular porosity
How can gaseous porosity occur when making acrylic resin?
monomer boiling (100 degrees C)
occurs in bulkier parts
gas bubbles form under resin
how to avoid gaseous porosity (PMMA)
Cure slowly
How can contraction porosity occur when making acrylic resin?
too much monomer used
insufficient excess material
insufficient clamp pressure
how can granular porosity occur when making acrylic resin?
too little monomer used
How does porosity of acrylic resin affect the denture properties?
affects strength
affects appearance
rough sensation to tongue
absorbs saliva
- poor hygiene
What are the components of composite resin
filler particles - glass
resin
monomer
camphorquinone
low weight dimethacryalates
silane coupling agent
function of camphorquinone in composite resin
photoinitiator
activated by blue light
produces radical molecules
- initiates free radical addition polymerisation leading to changes in resin properties
effects of adding filler particles to composite
improved mechanical properties
lower thermal expansion
lower polymerisation shrinkage
less heat of polymerisation
improves aesthetics
some are radiopaque
define ‘depth of dure’
the depth to which the composite resin polymerises sufficiently
components of a total etch dentine bonding agent
dentine conditioner
- 35% phosphoric acid
primer
- adhesive part of agent
- has a hydrophobic/hydrophillic molecule
adhesive
- resin that penetrates into surface of dentine attaching to the primers hydrophobic surface
what is dental amalgam
an alloy formed by the reaction of
- mercury (liquid)
- silver, tin, copper and other metals (powder)
properties of y1 amalgam
good corrosion resistance
properties of y2 amalgam
weak and poor corrosion resistance
why was zinc originally added to amalgam?
scavenger during production
preferentially oxidises and slag formed/removed
why is zinc free amalgam now preferred?
interacts with blood and saliva
results in H2 bubbled formed within amalgam
- pressure build up causes expansion
- downward pressure leads to pulpal pain
- upwards pressure - restoration proud of surface
what is creep?
when a material experiences repeated low level stress levels *below elastic limit)
causes material to flow resulting in permanent deformation
benefits of copper enriched amalgam
higher early strength
less creep
higher corrosion resistance
increased durability of margins
give an example of a non-gamma 2 amalgam
permite
advantages of amalgam
strong
hard
durable
radiopaque
user friendly
disadvantages of amalgam
corrosion
leakage
- does not bond
poor aesthetics
mercury
- perceived toxicity
- environmental impact
downsides of zinc phosphate cement
low initial pH of 2
- can cause pulpal irritation
- can take 24 hours to return to normal pH
exothermic setting reaction
not adhesive to tooth or restoration
not cariostatic
24 hour set
brittle
opaque
downsides of zinc polycarboxylate cement
difficult to mix
difficult to manipulate
soluble in oral environment at lower pH
opaque
lower modulus and compressive strength than zinc phosphate
how does GIC/RMGIC differ from GI/RMGI filling material?
smaller glass particle size to allow for suitable film thickness
how does GIC bond to tooth surface?
ion exchange with calcium in enamel and dentine
hydrogen bonding with collagen in dentine
advantages of GIC
low shrinkage
long term stability
relatively insoluble once set
aesthetically better than traditional dental cement
fluoride releasing
cheap
self adhesive to tooth substance
advantages of RMGIC
incorporation of resin improves material properties
shorter setting time
longer working time
higher compressive and tensile strengths
decreased solubility
higher bond strength to tooth
potential problems with RMGI
HEMA is cytotoxic
- residual monomer may irritate/damage pulp
HEMA swells in wet environment
- can cause conventional porcelain crown to fracture
- cannot be used to cement posts as may split root
no bond to indirect restoration
downsides of composite luting agents
technique sensitive
dual cured physical properties reduced by 25% if they are not light cured
advantages of composite luting agents
bette physical properties
lower solubility
better aesthetics
function of silane coupling agent when bonding to porcelain
acts as a surface wetting agent
strong oxide bond between oxide groups on porcelain surface and silane
C=C bond on silane coupling agent reacts with composite resin luting agent
What do you need to do to porcelain prior to cementing it as a restoration?
etched with HF
add silane coupling agent
- as surface is still not hydrophobic after etching
How are metals etched?
by sandblasting
materials used for bonding to non-precious metals
MDP and 4-META
Features of self adhesive composite resin
metal coupling agent is incorporated into composite resin to simplify bonding process
- MDP is used in Panavia
anaerobic self cure material
good film thickness
downsides of self adhesive composite resin
moisture sensitive
expensive
properties of a temporary cement
soft for easy removal
- some do not set at all
- prep must be physically retentive
Why should eugenol containing cements now be used to cement a provisional restoration where the permanent restoration will be cemented with a resin cement?
residual eugenol may interfere with the setting of this type of luting agent
limitations of sandblasting
roughens surface but doesn’t give the undercut surface of etching
- chemical bond required to strengthen bond
Ideal luting agents for an MCC?
GIC
RMGIC
Ideal luting agent for a metal post?
GIC
ideal luting agents for a fibre post?
- dual cure composite and dentine bonding agent
- self adhesive composite
ideal luting agent for a veneer?
light cure composite + dentine bonding agent
ideal luting agent for an adhesive bridge
anaerobic cure composite
ideal luting agents for a zirconia crown
- GIC
- RMGIC
- dual cure composite + DBA
- anaerobic cure composite
- self adhesive composite
ideal luting agents for a composite inlay?
- dual cure composite + DBA
- self adhesive composite
ideal luting agents for a porcelain inlay?
- dual cure composite + DBA
- self adhesive composite
ideal luting agents for a gold restoration?
- GIC
- RMGIC
constituents of temporary cements
supplied as two paste systems
- base and catalyst/accelerator
- base contains ZnO, starch and mineral oil
- accelerator contains resins, eugenol or ortho-EBA and carnauba wax
GIC uses
filling material
core build up
- prior to restoration with crown
lining
- underneath permanent fillings
luting
- cementing indirect restorations
Components of GIC
acid
- Polyacrylic acid
- tartaric acid
base (powder)
- silica
- alumina
- calcium fluoride
- aluminium phosphate
- sodium fluoride
Outline the 3 phases of GIC setting reaction
dissolution
- acid into solution
- H+ ions attack glass surface
- leaves silica gel around unreacted glass
gelation
- calcium ion cross linking with poly acid
hardening
- aluminium ion crosslinking
downsides of glass ionomer filling material
poor tensile strength
lower compressive strength than composite
poorer wear resistance than composite
lower hardness
higher solubility than composite
Benefits of gIC
similar thermal expansion to dentine
no contraction on setting
fluoride release
stable chemical bond to enamel and dentine
low micro leakage
Resin modified glass ionomer uses
dressing
fissure sealant
temporary Endodontics access cavity filling
luting
orthodontic cement
restoration of deciduous and permanent teeth
base or lining
