Glass ionomer/ Resin modified glass ionomer

Question 1

Glass Ionomer setting Reaction

Answer 1

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

Question 2

properties of GI

Answer 2

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

Question 3

Adhesion - GI chemically bonds to tooth structure

Answer 3

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

Question 4

Adhesion

Answer 4

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

Question 5

biocompatability

Answer 5

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

Question 6

flouride release

Answer 6

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

Question 7

Indications for GI as a restorative material

Answer 7

restoration of deciduous teeth

restoration of permanent teeth - anterior proximal areas (class III), smooth surface areas (class V)

Question 8

Contraindications for Glass Ionomer as a Restorative Material

Answer 8

restorations where there is a high load

large preparations

cores buildup where there is little tooth remaining

where esthetics are of concern

Question 9

considerations in restorative procedures

Answer 9

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

Question 10

Resin Modified Glass Ionomer (RMGI)

Answer 10

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

Question 11

Stages in RMGI Reaction

Answer 11

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

Question 12

Advantages of RMGI

Answer 12

flouride release

early strength

limited moisture sensitivity

can be finished immediately

adhesive

Question 13

disadvantages of RMGI

Answer 13

polymerization shrinkage

swelling of the material due to moisture uptake

must be fully light cured for optimal properties - depth of cure

Question 14

Comparison of RMGI to GI

Answer 14

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)

Question 15

Indications for RMGI

Answer 15

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

Question 16

Contraindications for RMGI

Answer 16

where esthetics is a concern

direct placement over pulp tissue

core build ups where more than 50% of the tooth structure is missing

Question 17

Indications for glass ionomer as a liner

Answer 17

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)

Question 18

Higher powder to liquid ratio

Answer 18

increased compressive strength

limited polyacrylic acid available - decreased ability to form chemical bonds

decreased retention

shortens mixing time

Question 19

lower powder to liquid ratio

Answer 19

properties decline

Question 20

compomer

Answer 20

polyacid modified composite resin

setting reaction is light activated

bond to tooth structure the same way as composite resin

Question 21

comparing various restoratives

Answer 21

Question 22

bonding to enamel

Answer 22

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

Question 23

Bonding to Dentin

Answer 23

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

Question 24

minimize marginal gap formation, marginal leakage

Answer 24

meticulous technique - precise bonding technique exactly following manufacturer’s instructions, isolated field - no contamination

incremental placement of composite

sandwich technique

Question 25

open sandwich technique

Answer 25

glass ionomer extends and is visible at the gingival cavosurface margin

RMGI extends to the external margin

Question 26

closed sandwich technique

Answer 26

glass ionomer does not extend to the cavosurface margin

margins are resin composite

RMGI is not present at any margin

Question 27

Bottom Line

Answer 27

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

Question 28

Fuji II LC

Answer 28

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

Question 29

4 mesial and distal lesions into dentin

Answer 29

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