Zoe cement-karan
Transcript of Zoe cement-karan
-KARAN HIRAL MEHTABDS II YEARDSCDS
•Have been used extensively in dentistry since 1890’s
•Vary widely in properties based on the use
•Low strength cements
•Least irritating of all dental cements
•Known to have an obtundant effect on exposed dentin
•To improve strength many modified ZOE cements have been
introduced
•in vitro, eugenol from ZOE fixes cells, depresses cell
respiration, and reduces nerve transmission with direct
contact
•Effect of eugenol are dose dependent
•Diffusion through dentin dilutes eugenol by several orders of
magnitude
•ZOE may form a temporary seal against bacterial invasion
Applications of ZOE in dentistry:-
1. Endodontic sealers
2. Root end filling materials
3. Periodontal coating
4. Inelastic impression materials
5. Cavity base
6. Temporary restorations
7. Luting agent
Type I ZOE cement:-
•These are meant for short term luting
•Lacks strength and long-term durability and is used
for temporary cementation of provisional coverage
•Permanent restorations are also sometimes
cemented for a short period for the patient to try it.
•Low strength allows easy removal of the restoration
without damage
Type I ZOE cement is further classified as:
1. Class I – setting cement2. Class II – non-setting cement
Type II ZOE cement:-
•They are meant for long term cementation of
permanent restorations
•They are considered somewhat inferior to other
cements
•Has reinforcing agents added and is used for the
permanent cementation of cast restorations or
appliances (modified ZOE cements)
Type III ZOE cement:-
•They are used for the interim period when a
tooth is under going treatment or until it is
ready for a permanent restoration
•Can also be used as bases under permanent
restoration
Type IV ZOE cement:-
•Low strength materials
•Used as liners
Available as:-
Powder and liquid
Two paste system
*Eugenol is 4-allyl-2-methoxy phenol
Setting reaction and microstructure are the same as that of the zinc oxide eugenol impression pastes.
First reaction:-Hydrolysis of zinc oxide
The reaction proceeds as a typical acid-base reaction
The chelate formed is an amorphous gel that tends to crystallize imparting strength to the set mass
Structure of set cement:-
The set cement consists of a matrix of zinc
eugenolate in which particles of zinc oxide are
embedded.
Compressive strength:-
•Relatively week cements
•Strength depends on its use
•Compressive strength ranges from 5 to 55 Mpa
•Lowest are the cavity liners (minimum 5 Mpa)
Type I 6 to 28 Mpa ISO-maximum of 35 MPaType II 45 to 55 Mpa ISO-minimum of 35 MPa
Factors that increase the strength:-
1. Smaller particle size
2. Reinforcing with alumina-EBA or polymers
Tensile strength: Ranges from 0.32 to 5.3 Mpa
Modulus of elasticity: Ranges from 0.22 to 0.54. Important property for
cements intended for use as bases
Thermal conductivity: 3.98 [Cal. Sec-1 cm-2 (oC/cm)-1] X 10-4
Their thermal insulating properties are excellent and are
approximately the same as human dentin. The thermal
conductivity of zinc oxide-eugenol is in the range of insulators like
cork and asbestos.
Coefficient of thermal expansion: 35 X 10-6/ 0C
•Solubility of set cement is highest among the cements
(0.4 to 1.5% wt)
•Solubility is reduced by increasing the P/L ratio
•They disintegrate in oral fluids
•This break down is due to hydrolysis of the zinc eugenolate matrix
to form zinc hydroxide and eugenol
This property is important for those cements used for luting of
restorations (type I and type II)
The film thickness of ZOE cements (ISO maximum of 25
micrometer) is generally higher than other cements.
Do not adhere well to enamel or dentin
The set cement is opaque
•pH: 6.6 to 8.0
•Effect on pulp: least irritating of all cements. Pulpal response is
mild
•Bacteriostatic property: inhibits the growth of bacteria
•Obtundant property: has an anodyne or soothing effect on the
pulp in deep cavities, reducing pain.
Reasons why ZOE cements are not often used for final cementation of crowns and other fixed dental prosthesis:-1. Does not adhere well to enamel or dentin2. Low strength3. High solubility
•Powder to liquid ratio- 4:1 to 6:1 by wt.
•Bottles are shaken gently
•Measured quantities of powder and liquid are dispensed on to a cool glass slab
•Bulk of powder is incorporated into the liquid
•Mix in circular manner
•Zinc oxide eugenol exhibits pseudothickening
•Smaller increments are then added to complete the mix
•For temporary restorations a thick putty-like consistency is recommended
•ZOE cement instruments are cleaned using oil of orange.
Equal measurements of each paste is mixed to get a uniform colour
Setting time is 4 to 10 minutes
ZOE cements set quicker in mouth due to heat
and moisture
Factors affecting setting time
The complete reaction between zinc oxide and euginol takes about 12 hours. This is too slow.
1. Manufacture: the most active ZnO powders are those formed from
zinc salts like Zn(OH) and ZnCO3 by heating at 3000oC
2. Particle size: smaller zinc oxide particles set faster
3. Accelerators: Alcohol, glacial acetic acid and water
4. Heat: Heating the glass slab, slows the reaction
5. Retarders: glycol and glycerine
6. P/L ratio: higher the ratio, faster the set
Modified ZOE cements:-
EBA-alumina modified cements
Polymer reinforced
•Available as: white powder and pinkish liquid
•Its greater strength allows its use as an intermediate
filling material and as a base
•A part of liquid is substituted by orthoethoxy benzoic
acid (EBA)
•Alumina is added to powder
•The popularity of these cements as a retrograde filling
material is increasing because of high cost of MTA
1. Long term cementation
2. Temporary and intermediate restorations
3. Root end filling material
Zinc oxide : 60-75%
Fused Quartz or alumina : 20-35%
Hydrogenated Rosin : 6%
EBA : 62.5%
Eugenol : 37.5%
•More easier to handle
•Improved carvability
•Compressive strength: 55 to 60 MPa (8000 psi)
•Tensile strength : 4.1 Mpa (600 psi)
•Modulus of elasticity: 2.5 Gpa (0.36 psi X 106)
•Film thickness: 25 micrometer
•Solubility and disintegration in water is 0.05% wt. Despite their low
solubility, these cements disintegrated and wore more quickly
clinically when compared to the polymer modified zinc oxide
cement
•Effect on pulp: relatively mild to pulp
•Adhesion: Adhere well to tooth structure
•Modifications take the form of resins added to the powder
or the liquid
•Aim is to increase the strength and reduce the solubility
•Resin modified cements are among the strongest of the zinc
oxide-eugenol based cements
•High strength and low wear make them ideal intermediate
restorative material
•It can last as long as 1 year
1. Luting agent
2. As base
3. As temporary filling materials
Zinc oxide : 70%
Finely divided natural or synthetic resins
Eugenol
Acetic acid : accelerator
Thymol : antimicrobial
The zinc oxide powder is surface treated. The combination
of surface treatment and polymer reinforcement results in
good strength, improved abrasion resistance and
toughness.
Setting reaction:-
The reaction is similar to ZOE cements. Acidic resins if
present may react with ZnO and strengthen the matrix
•Improved mechanical properties
•Compressive strength: 48 MPa (7000 psi)
•Tensile strength : 4.1 Mpa (600 psi)
•Modulus of elasticity: 2.5 Gpa
•Film thickness: 32 micrometer
•Solubility and disintegration in water is 0.03% wt
•Effect on pulp: moderate effect which is same as
unmodified ZOE cements
•Improved abrasion resistance and toughness
Factors affecting setting time:-
1. Low powder-liquid ratio increases setting time
2. Moisture: accelerates setting time
3. Cooling the glass slab slows the setting time
•ZOE is very popular as an endodontic sealer.
•Rickert’s and Grossman’s formula are the popular traditional formulations
•These are used with gutta percha in endodontic therapy to seal canals
•Some materials are used as therapeutic sealers and are formulated with ingredients
such as iodoform, paraformaldehyde or trioxymethylene which have therapeutic
value
•Some contain antibiotics such as tetracyclines or steroids as antiinflammatory
agents.
•Some formulations can also be used as pulp capping
•Endodontic sealers also contain radiopaque materials such as barium sulphate,
bismuth sulphate, bismuth salts or silver powder.
GROSSMAN'S FORMULA
POWDER LIQUID
Zinc oxide 42% Eugenol
Staybelite resin 27%
Bismuth subcarbonate 15%
Barium Sulphate 15%
Sodium borate anhydrate 1%
1.CRAIG’S RESTORATIVE DENTAL MATERIALS BY CRAIG
2.SCIENCE OF DENTAL MATERIALS BY PHILIPS
3.BASIC DENTAL MATERIALS BY MANAPPALLIL
4.SKINNER’S SCIENCE OF DENTAL MATERIALS BY SKINNER’S
5.INTERNET