Glass ionomer/ Resin modified glass ionomer Flashcards
Glass Ionomer setting Reaction
Reaction between silicate glass powder and polyacrylic acid
Acid base reaction
Water is necessary for the reaction - technique sensitive, too much water causes the material to be opaque and lack strength, if water is lost during setting - cracking and crazing occurs
if a material does not have this reaction it is not a true glass ionomer - you have to mix something
properties of GI
co efficient of thermal expansion similar to tooth structure
flouride release
bonds to tooth structure
low thermal conductivity
biocompatible
*not as esthetic as composite*
low resistance to wear
low strength
Adhesion - GI chemically bonds to tooth structure
Bond strength is low bu durable
ion exchange process
polyacrylic acid displaces surface phosphate. Calcium enters the hydroxyapatite structuer and forms a calcium polyacrylate salt
calcium and aluminum phosphates and polyacrylates are formed at the tooth/GI interface
Secondary bond occurs w/collagen w/in the dentin via hydrogen bonding
Adhesion
the bond is improved by preconditioning
polyacrylic acid is common conditioner
conditioning- use a less ionized acid to remove the smear layer. The restorative material will form a chemical bond
etching - stronger acid. etching involves the subsurface. restorative material will form a micromechanical bond
biocompatability
larger molecular wieght of polyacrylic acid prevents entry into dentinal tubules
low pH - use a liner (example: calcium hydroxide) if there is less than .5 mm remaining dentin thickness
flouride release
released w/o affecting the physical properties of the material
initial fluoride release is high, but release diminishes over time
GI can be “recharged” with a topical fluoride treatment
Indications for GI as a restorative material
restoration of deciduous teeth
restoration of permanent teeth - anterior proximal areas (class III), smooth surface areas (class V)
Contraindications for Glass Ionomer as a Restorative Material
restorations where there is a high load
large preparations
cores buildup where there is little tooth remaining
where esthetics are of concern
considerations in restorative procedures
after placement and setting remove excess around the margins with a scaler
premature finishing can cause damage to the cement matrix
wait at least 3 mins before finishing to avoid damage to the surface
ideally wait 24 hours to finish the restoration
plan these restorations early in the treatment plan so that polishing can be completed at a subsequent patient visit
contamination w/ saliva can disrupt the matrix & damage the surface
desiccation of the restorating can cause crazing
Resin Modified Glass Ionomer (RMGI)
Liquid - polyacrylic acid copolymer, methacrylate, photo initiator
powder - fluoroalumino silicate glass powder, photo sensitizer
reaction - acid base reaction, polymerization of the resin, if not supplied in two components it is not a glass ionomer
*things in bold are added - HAVE TO MIX - otherwise not a glass ionomer
Stages in RMGI Reaction
acid-base reaction - begins w/ mixing, during this time the matrix is susceptible to damage by too much water
light activation - takes place at the end of placement, completed w/in 10 sec of light activation
Advantages of RMGI
flouride release
early strength
limited moisture sensitivity
can be finished immediately
adhesive
disadvantages of RMGI
polymerization shrinkage
swelling of the material due to moisture uptake
must be fully light cured for optimal properties - depth of cure
Comparison of RMGI to GI
RMGI
improved esthetics
water sensitivity is reduced
slightly less fluoride release
slight increase in thermal expansion
increased polymerization shrinkage
can be recharged w/fluoride (GI can also be recharged)
Indications for RMGI
Restoration of anterior proximal and smooth surface restorations
sandwich technique
restoration of deciduous teeth
blocking out of undercuts for indirect restorations
lining of cavity preparations
Contraindications for RMGI
where esthetics is a concern
direct placement over pulp tissue
core build ups where more than 50% of the tooth structure is missing
Indications for glass ionomer as a liner
direct pulp cap over the pulp capping material - protection of calcium hydroxide or MTA
sandwich technique - open sandwich (glass ionomer is exposed to the environment), closed sandwich (glass ionomer does not come into contact with the oral cavity)
Higher powder to liquid ratio
increased compressive strength
limited polyacrylic acid available - decreased ability to form chemical bonds
decreased retention
shortens mixing time
lower powder to liquid ratio
properties decline
compomer
polyacid modified composite resin
setting reaction is light activated
bond to tooth structure the same way as composite resin
comparing various restoratives
bonding to enamel
enamel is acellular, inorganic
etching for 15 sec w/ 30 - 40% phosphoric acid creates irregularities in which bonding resin can form resin tags
enamel bonds of resin to enamel can range from 20 - 50 MPa
Bonding to Dentin
dentin in organic - collagen
dentin contains tubules that connect with the pulp
dentin is wet
smear layer is present after preparation
bond strength is higher to superficial dentin than to deep dentin or cervical dentin
margins placed on dentin exhibit greater microleakage compared to enamel margins
minimize marginal gap formation, marginal leakage
meticulous technique - precise bonding technique exactly following manufacturer’s instructions, isolated field - no contamination
incremental placement of composite
sandwich technique
open sandwich technique
glass ionomer extends and is visible at the gingival cavosurface margin
RMGI extends to the external margin
closed sandwich technique
glass ionomer does not extend to the cavosurface margin
margins are resin composite
RMGI is not present at any margin
Bottom Line
preps with enamel margins will exhibit little marginal leakage as compared to margins on dentin (apical to the CEJ)
consider an RMGI sandwich technique when the cervical margin is on dentin (no enamel at the cervical cavosurface margin)
RMGI should be used in thin layers to limit the possibility of a restoration fracture
Fuji II LC
RMGI used for the gingival floor
activate the capsule - push in the green plunger, activate in the applicator one click
mix in the amalgamator 11 sec
4 mesial and distal lesions into dentin
prepare distal box w/ gingival floor margin in enamel, prepare mesial box w/ gingival tissue which should result in a gingival margin w/ no enamel
condition the dentin in the box that will have the RMGI - 10% polyacrylic acid
extrude a SMALL amt of the RMGI in the mesial box, pust the material lightly to place, remove the buccal, lingual and occlusal margins, cure 20 secs, material will also chemical cure, clean any excess
RMGI layer should be 1.0-1.2mm in thickness, should not be used to build up to the proximal contact
should be at least 2.0 mm thickness of composite over the RMGI
