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Zinc Phosphate Cement one of oldest cement (Properties (No mechanical…
Zinc Phosphate Cement
one of oldest cement
Classification
depend on use
Type 1 (Fine grain)
=> for lute casting (definitive) and prosthesis
class 1 hardening
--> hardening time: 2 mins
class 2 normal hardening
--> 4.5-8.5 mins
Type 2 (Middle grain)
=> for lute provisional crown and cavity liners
class 1 fast hardening
--> hardening time: 2 mins
class 2 normal hardening
--> 4.5-8.5 mins
Properties
Hardening time and Viscosity
Viscosity change with time and temperature
Hardening time ↑
physical factors
change grain thickness
↓ water concentration/ ↑ powder
↓ temperature
chemical factor
retarders
metallic oxides neutralized
orthophosphoric acid
No mechanical physical properties
Good Thermal isolation
Solubility
powder/ liquid ratio
Poor Electrical insulation
=> if have metal filling, change to ionomer glass for cement
No Shrink Hardening
Mechanical
Toughness
--> lower than dentine, much lower than enamel
Compression resistance
--> good. if P/L ↓, compression resistance ↓
Pulling resistance <<< compression resistance
Bonding
wet tooth and restoration
--> flow through inter surface irregularities
no chemical adhesion but mechanical adherence
Chemical and Biological
initial stage pH: 2-4
--> depend on ratio, more fluid, more acid
--> may irritate pulp, germicidal effect
=> pulp protection (residual dentine), should not in deep cavity
hardening stage pH: 7
--> ↑ after 1-2 days
Composition and Hardening
Powder
zinc oxide: 90%
magnesium oxide: 10%
Liquid
orthophosphoric acid
water
buffer to
stabilize acid pH
slow reaction
increase working time
zinc oxide
aluminum oxide
Hardening
zinc orthophosphate network
=> hopeite on surface
exothermic
--> use cold glass tile to prevent
Handling/ Indications
Indications
lute onlay, inlays, crowns, orthodontic bands
high resistance cavity liner
Not for deep cavity
Not for provisional filling
Handling
P/L:
cavity line: 3.5/1
lute material: 2.5/1
mixing time: about 60/120 sec
phylum behavior
before use, cool the glass tile til it reach 5 ℃
--> never freeze the tile
placed into crown and bring to patient
don't add liquid