8 - Glass Ionomers Flashcards
glass ionomer consist of?
early glass ionomers for restorations were what?
consist of ion-cross-linked polymer matricer surrounding glass reinforcing filler particles
-early ones based on solution of polyacylic acid liquid mixed with complex alumino-silicate powder containing calcium and fluoride
in glass ionomer what does the acidic liquid solution do?
what happens to the calcium ions?
what happens during next 24-72 hours after this?
- it dossolved portions of the periphery silicate glass particle, this releases Ca, Al, F, Si, and other ions
- calcium ion chelated by ionized carboxyl side group on polyacrylic acid polymer chain, cross linking the hcains and producing an amorphous polymer gel (chelation is bonding of organic molecule to a central metal atom at two or more points)
- during next 24-72h the Ca ion replaced by slowly reactiong aluminium ions to produce a more highly cross linked matrix that is mechanically stronger
during the maturation with Al ion cross linking, what 2 things participate to make an inorganic comatrix that is best described as a hydrated silicate?
silicon ions and unbound water
how do set glass ionomers compare to composites?
have modest properties compated to composites but have relatively good adhesions
-release fluoride from matrix that gets incorportated into neighboring tooth structure to inhibit caries (VERY NICE. I LIKE)
what were original GIC a hybrid of?
what was the earliest commercial product named using?
- hybrid of silicate and polycarboxylate cements
- GI used the aluminosilicate powder from silicates and the polyacrylic acid liquid from polycarboxylates
- named using the acronym for this hybrid, called aluminosilicate polyacrylic acid (ASPA)
how was the original polyacyllic acid modified?
what on earth is the MIRACLE MIX?
- copolymeriztion with other acids
- power particles were reduced in size and mixed with other reinforcing particles
- amalgam alloy particles were admixed in some formulations to produce an amalgam substitute called MIRACLE MIX
- this was an amalgam substitue but inferior to amalgam, its matrix sucked, and had crap strength
- to try and help they put in siliver pallidium, called this CERMET
so the early GI’s werent too good, hwo did they change around the 90s?
what restorations are RMGI recommended for?
started using alternative filler particles and/or matrix setting reactions to make them more composite like
- these are called hybird or RMGI
- usually light ucred
- they are more composite like but still undergo acid base rxn during setting
- reccomended for class 5, can be used for classs 1 and 2 in primary teeth
the most recent GI materials are?
what are compomers and how are their mechanical properties?
- polyacid-modified resin composites/compomers (PARC)
- similar to RMGI BUT dont have water
(bc this prevents premature setting to ensure setting is only bc of polymerization)
- basically compomers = polymer based composites that take advantage of fluoride releasing behavior of glass ionomers
- mechanical properties of these bad boys are better thatn GI and RMGI
why use GI?
are they better than composire?
- use because chemical adhesion and they release fluoride
- not much evidence saying theyre better than composites
what type of systems before setting are GI? how do they flow?
-in contrast what are resin bonding agents like?
How does GI bond (mechanically or chemically?) Is one more important than the other (TEST QUESTION)
- most GI are aqueous systems and wet tooth structure well because they are hydryophilic,, they have high viscosities dont flow and adapt into tight spaces well
- resin bonding agents are hydrophobic and have been formulated for use with hydrophilic primers to facilitate wetting, flow, and bonding
- bonding of GI achieved in part by mechanical retention and in part by chemical chelation (mech bonding more important, b/c of this chemical bonding only matters when micro mechanical bonding is hard to achieve)
what is the fluoride ion release proportional to and when is it highest?
has a critical level of fluoride release been defined clinically?
is the absence of 2ndary caries evidence for a fluoride ion effect?
proportional to the concentration available for diffusion across the concentration gradient
- fluoride release is usually high for the first few days and then decreases in time
- a critical level of fluoride release has never been defined clinically
is the absence of 2ndary caries evidence for a fluoride ion effect? NO
esthetic problems with GI?
should you use these bad boys in high caries risk areas?
Does fluoride release from GI remain steday over time?
esthetic problems result in replacement or repair in much less thatn 10 years after placement
so fluroide release might not be a major advantage if other factors dont favor long term service
BUT GI seem very well suited for a high caries risk area
No, F release decreases after 2 days
biocompatibility?
has it been a concern with GI?
- was a concern with traditional GI because they were very acidic when mixed, could result in post op sensitivity and pulpal irritation
- as the rxn goes the pH goes form 1->4-5, once rxn done pH=~7
- the potential pulpal effects of the low pH limited to areas immediately adjacent to the material, this is because the acid groups are attached to polymer molecules with limited diffusibility
remaining dentin thickness - how thiCK does it have to be before you PROTECT it with unset glasss ionomer materials?
what happens when the fluid filled dentinal tubules are in direct contact with setting cement? (2 things)
less than 0.5mm, protect with a calcium hydroxide liner
- high ionic concentration in the unset glass ionomer cause dentinal fluid to rapidly diffuse outward into cement, this puts tension on pressure receptors in pulp, causing sensitivity or pain
2- unset components like H ion move into tubules, towards pulp, this causes chemical irritation when RDT inaduquate
-tubule fluid content is inadequate to buffer the acid before it reaches the pulp
risk of post op sensitivity when comparing RMGI to traditional GI?
MUCH LESS in RMGI
