resin based materials and fissure sealants e lec Flashcards
understand dental metals as an adhesive and as a protective varnish layer
what is the ideal material to replace teeth
a material like itself
what are some metallic materials
amalgam
and gold
what are the disadvantages of amalgam or gold
they are not aesthetic
give examples of ceramic materials
feldspatic ceramic( dental porcelain)
what is the disadvantage of dental porcelain
have to damage natural tooth
example of the polymer based systems
resin based materials
how are fissure sealants activated
light/chemical activation
how are dental composites activated
light/chemical activation
how are polyacid modified resins activated
light/chemical activation
how is resin modified polyalkenoate activated
light/chemical activation
how is glass polyalkenoate activated
chemical activation
what else are glass polyalkeontes also called
glass ionomers
or glass ionomer cements GIC
what are the three phases of reacted set material
silica gel
polymer
ionomer glass
how does the setting reaction occur
the starting materials are poly acid and an ionomer glass- a powder and a liquid
what is the liquid
usually water
what is the chemical reaction
acid + base = salt + water
what are acidic polymers called
poly acids
what is it called when poly acids react with poly bases
poly salts
poly salts can be used to make
cohesive solid material called glass polyalkeonates cements (GPAC)
what are the specifics of the GPAC reaction
initially the acid dissolves forming a vicious aqueous liquid with the glass dispersed into it
Hydrogen ions which have dissassociate from the polyacid are available to displace cations on the surface of the glass these then migrate away with some ion species reacting with the negatively charged polymer ions( fluoride) crosslinking them to become long polymer chains or polysalts.
what happens to the modified glass surface
silica gel
when will the material reach full strength
one week
how long do we have to wait to polish the restoration
a week
during the period where the material is strengthening what can it cause
CRACKS IN the surface of the material
how can we stop cracks in the surface of the material
applying varnish or petroleum jelly
what does the reaction also release
fluoride which forms fluoroapatite crystals which is greater acid resistance
how was secondary caries prevented
by fluoride being released by poly alkeonates
what are other schools of thought about fluorine being released from polyalkenoate
However, some now doubt whether there is enough fluoride release to be of statistical benefit. Other schools of thought are that the glass polyalkenoate can act as a fluorine “sponge” absorbing fluoride during treatments, say with tooth paste or mouth wash, then releasing it over a prolonged period afterwards
what do polyalkenoates also react with
calcium ions on the tooth surface and therefore has a direct link with the tooth
what is the disadvantage of polyalkenoates
their wear resistance is poor - do not make good materials if used alone
they are too opaque where excellent aesthetics are required eg incisal edges
what class restorations are poly alkenoates used for
class III and V restorations
what are the advantages of poly alkenoates
sometimes can be used on the tooth without any preparation The material can also be used a luting cement (adhesive) for fixed prosthetics.
also can be used as an intermediate under amalgam or composite
what attempts have been used to strengthen poly alienates
by binding silver to the poly alkenoates which strengthens it but also castes a grey shadow
also a copolymer of polyvinylphosphonic acid and polyacrylic acid, these form an improved matrix.
what two copolymers can strengthen the poly alkenoate glass
polyvinylphosphonic acid and polyacrylic acid
what is special about the filler
it is inert
why is a filler used if its not a primary ingredient in the reaction
because the polymers used shrink by a large margin
It reduces swelling due to water absorption, the polymers are highly crosslinked leading to the formation of voids into which water can ingress.
what could the shrinkage of the polymer lead to
cracking of the teeth and also tooth/cusp failure
if we add glass to the poly alkenoate what will happen
it will reduce the thermal expansion and stop fracturing the tooth in extreme cases - could reduce sensitivity due to the fact the fluid in the dentinal tubules stopped moving
what things increase by adding fillers
strength
aesthetics \
youngs modulus
wear resistance
what is the conventional filler size
5-10 micrometers in diameter,
what is the size of the microfilled composite
0.04micrometres
hybrid materials have around % volume of filler
78-85%
what does bis-GMA mean
bisphenol glycidyl methacrylate
what does UDMA mean
urethane dimethacrylate
what materials are used to dental composite
bis-GMA and UDMA
what does bis-GMA and UDMA commonly mixed with
triethyleneglycol dimethacrylate (TEGMA)
why is bis-GMA and UDMA controversial
skin sensitivity and linked to carcinogenic
why can bis-GMA and UDMA still be used in dental composites
they are used in small amounts and polymerised in to a highly crosslinked polymer chain which is quite different.
what is the polymer matrix cured with
the blue light activation
what is the issue if the cavity is overfilled with the polymer matrix
the blue light will only travel a few mm so it will lead to a soggy bottom formation in the bottom of the cavity
what are the benefits of the blue light
Not only that blue light sources age and there may be a need to increase exposure at the end of the bulbs life. will build up your Dental composite restoration incrementally to avoid the problems; this will also help reduce the over all effect of shrinkage which potentially could fracture a tooth
what are the issues with dental composites
hydrophobic meaning you need to dry the tooth
it doesn’t bond to teeth as well- series of bonding systems that aim to interface tooth and composite
what do bonding agents rely on
a pre treatment
what is the smear layer
when you cut into dentine and causes debris to spread over the surface blocking the dentinal tubules
what is used to remove the smear layer
phosphoric acid
what forms if the bonding material is successful
the formation of tags which can enter the dentinal tubules
what binds the filler and the matrix
silaine coupling agent
what does silaine coupling agent bind
the filler and the matrix
what range is the blue light wavelength
420-450 nm
what’s special about resin modified polyalkenoate
it has carbon carbon double bond which can be broken meaning that addition polymerisation
what are poly acid modified resins called
compomers
how does poly acid modified resins work
once the material is placed, small amounts of water will be absorbed from the patients saliva causing disassociation at the acid groups. This in turn starts a reaction with the glass which has been replaced with an ionomer glass thus there is a small background acid base reaction which is very much secondary.
is there a need for a bonding system in poly acid modified resins
no - as no initial chemical reaction with the tooth
what are fissure sealants
preventative materials
what are fissure sealants used for
to protect vulnerable tissues in the occlusal surfaces from acid producing bacteria
what age group will fissure sealants be applied to
paediatric patients
