GLASS IONOMER CEMENTS

By Dr.Swathi Pai on Tuesday 29 April 2008 with 0 comments




Introduced in 1971 in England by Wilson and Kent

Powder- Aluminosilicate glass prepared with fluoride fluxes. Type II restorative material is coarser than the type I luting agents

Liquid- Aqueous solution of various polyacids, commonly polyacrylic or copolymers of acrylic and maleic acid or acrylic and itaconic acid; Itaconic acid reduces the viscosity of the liquid; Tartaric acid improves the working and setting properties


Powder/liquid ratio is 3 to 1 by weight

The cement bonds to the inorganic component (calcium) by hydrogen bonding followed by metal ion bridges Fluoride is available 1-3 mm from the restoration


Formulations

Hydrous- polyacid in the liquid, highest viscosity, highest pH, fastest initial set, lowest solubility,most biocompatible

Anhydrous- polyacid is freeze dried in the powder; just add H20; lowest pH, slowest initial set, some biocompatability problems

Semihydrous- polyacid in powder and liquid; intermediate viscosity and pH (example Ketac Cem Maxicap and most encapsulated systems)


Clinical failures result from

-loss of restoration- poor adhesion from too dry a mix

-inadequate isolation or improper preparation of the tooth

-cracking or craze pattern- dehydration during setting phase

-increased opacity- moisture contamination during setting phase


Proposed nomenclature for glass-ionomer dental cements and related materials (Ref. Mclean, Nicholson, Wilson ,Quintes Int Vol. 25, No. 9/1994):

Glass-ionomer cement- A cement that consists of a basic glass and an acidic polymer which sets by

an acid-base reaction

Glass-ionomer hybrid materials- There are two classes of this material basically separated by their

ability to cure in the dark (acid/base reaction)

Resin-modified glass ionomer- Has sufficient acid and base to allow the reaction to take

place within a reasonable time (Vitremere, Fuji II LC)

Polyacid-modified composite resin- Correct ingredients are present (glass & acid) but in insufficient amounts to promote acid-base cure in the dark (Variglass, Dyract)

ADVANTAGES

DISADVANTAGES

tooth colored

adheres chemically to enamel & dentin (ionic bond)

CTE similar to tooth

high fluoride release

anticariogenic & antimicrobial

rechargeable

less shrinkage than composite

biocompatible

no bonding agent required

resistant to staining

technique sensitive

sticky, difficult to sculpt

short working time

delayed set

poor polish

moisture sensitive

weak for stress bearing areas

poor abrasion resistance

low tensile and fracture toughness

only average esthetics


RECOMMENDED USES

-cervical lesions: Class V restorations in adults

-high caries risk patients

Category: Conservative and Endodontics Notes

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