Cements 3 Flashcards
Uses of glass ionomer cements
- cavity base/lining
- luting
- filling
GIC is a development of what?
- polycarboxylates
- change zinc oxide to glass particles
How is GIC a lining/base?
- under amalgam or composite
- sandwich technique for composite
Luting with GIC is used in which departments?
- prosthodontics
- orthodontics
How is GIC used for fillings?
- use product specifically designed for restorative purposes
- ISO standards type I and II
- class V, III and I and I in deciduous teeth
GIC are also called what?
polyalkenoates
Composition of GIC
- hand mix or encapsulated
- powder is aluminosilicate glass made from aluminium oxide, silicon oxide and calcium fluoride
- liquid is aqueous solution of polyacid, originally acrylic acid but also maleic, itaconic or copolymers
- more recently polyvinyl phosphoric acid (much stronger)
- or anhydrous cements (powder containing freeze dried acid) and water
GIC setting reaction
acid +base _> salt and water
- MO.SiO2 + H2A -> MA + SiO2 + H2O
GIC setting is complex. Gove the 3 overlapping steps
- dissolution (acid and glass particles react)
- gelation (crosslinking due to calcium ions reacting with polyacid)
- hardening (crosslinking due to aluminium ions reacting with polyacid)
Initial setting and maturation of GIC
- water exposure can effect setting - dilutes acid
- can lead to weak cement (chalky appearance)
- need to protect - varnishes sold by manufacturers
- dentine bonding agents often used - may leave a ledge (need to deal with it to prevent biofilm formation)
What acid is often added to GICs?
Why?
- tartaric acid
- helps break down glass particle surface
- reacts with aluminium ions
- extends WT - only calcium ions reacting with glass
- once tartaric acid used up, aluminium ions reacts with glass
- GICs have better WTs and STs
Structure of GIC
- final cement has a cored structure
- glass particles surrounded by polyacid matrix
What properties are effected by porosity?
- method of mixing
- cement viscosity
How does method of mixing influence porosity?
- hand mixing is difficult to accurately proportion components
- mechanical means it’s already proportioned by manufacturers
Cement viscosity - how does that affect porosity?
- luting cements have lower viscosity
- restorative cements have higher
Ketac-Cem is a … cement whereas Ketac-Molar is a … cement
- luting
- restorative
For lower viscosity GICs, like … and …, which mixing process is used? Why?
- liners and bases
- hand mixing - mechanical mixing causes bubbles to form like froth
For higher viscosity GICs like for …, what mixing is used? Why?
- restorations
- mechanical mixing
- not significant difference ijn porosity and less technique sensitive
GICs are strong/brittle
Explain
- brittle
- low tensile and compressive strength (stronger in compression)
- weak in thin sections
- porosity significantly effects properties
- limit of applications
GICs are radiolucent/opaque.
Explain
- originally low to no radio-opacity
- radio-opacifiers added but until recently compromised appearance
- glasses containing Sr, Zr not common so radio-opacity improved
Are GICs moisture sensitive?
- requires protection during setting
- and if other procedures require a dry field
- dessication can cause fracture of the GIC
Are GICs biocompatible?
- acids used tend to be weak acids with large molecular weight
- some concerns with release of aluminium ions - possible link to neurological conditions
Thermal properties of GICss
- thermal insulator
- similar coefficient of thermal expansion to dentine
- low instance of marginal staining (compared to composite)
- doesn’t shrink of setting, adheres to enamel and dentine
Adhesion of GIC to enamel and dentine
- chemically bonds to enamel and dentine
- similar to polycarboxylates - COO- group bonds to calcium ions
- bond strength is low but sufficient for erosion cavities
- limit of bond strength primarily due to low GIC tensile strength
How to improve bond strength of GIC?
- acid etching
- citric acid is too strong and demineralises dentine
- polyacrylic acid removes debris without demineralising
GIC can bond strongly to what?
- metals and alloys
- makes it a good luting agent
Aesthetics of GICs
- range of shades available - not as wide as composite
- difficult to colour match - GIC will change shade as it sets
- ratio of aluminium to calcium important - more aluminium, means less tooth-like
Solubility of GIC
- care needed in setting or if dry field needed in another procedure
- once set GICs have good stability in aqueous environment
- are susceptible to erosion in low pits
Fluoride release from GICs
- initial burst release
- decreases over time
Fluoride recharge in GICs
- fluoride can be reloaded into the material
- fluoride released similar to initial performance
- many potential sources (tap water, toothpaste, gels)
Is fluoride release from GIC beneficial?
- no clear evidence it is
- possible benefits for high caries risk and poor dexterity patients
Uses of GIC
- filling (specific restorative ones, for Class I and II in deciduous, III and V)
- sandwich technique
- liner/base
- luting
- orthodontics (bands, brackets)
Differences in GICs for luting than those for restoration
- similar
- smaller glass particles for a thin film
- thinner mix for this thin film
- vary Al/Ca for rapid setting
- add BaO for radio-opacity
- stronger
- adhesion is tooth and stainless steel
- fluoride release
- moisture sensitive
Explain ART
- atraumatic restorative therapy/treatment
- GIC formulations altered to allow treatment in economically developing world
- don’t need complex equipment to place
- compositions prioritise strength over appearance
Explain metal additions to GICs
- called cermets
- additions to increase strength
- compromised appearance
- clinical performance was poor so discontinued
GICs have been developed for cores - what is the compromise?
- mechanical properties over appearance
Explain resin additions to GICs
- add monomers to improve matrix phase
- add photo-initiators to improve setting time
- reduce moisture sensitivity in setting
- improve mechanical properties
