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CROWN AND
BRIDGE CEMENT
BY:-SURBHI BHARDWAJBDS II
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Alternate name Zinc Phosphate cement
Zinc Oxyphosphate Cement
Zinc Cement
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HISTORYThe earliest formulation as reported byRollins(1879),Gaylord(1889),Ames(1893 &Fleck(1902) were variously based on syrup oforthophosphoric acid or unstable mix of
metaphosphoric acid & sodiummetaphospate in solution.
Later cements with 50% sol. of o-phosphoric
acid was used but problem revolved aroundthe control of setting reaction but by the timeFlecks (1902) paper these problems hadbeen solved.
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The importance of densifying &deactivating the ZnO powder to moderatethe reaction was recognized & it was also
found that satisfactory cements could beproduced only if aluminum wasincorporated into the o-phosphoric acid
solutionThe basic science underlying this empiricalfinding was elucidated only in 1970
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Definition According to Boucher zinc phosphate
cement is defined as material used forcementation of inlays, crowns, bridges, and
orthodontic appliances and occasionally asa temporary restoration. It is prepared bymixing zinc oxide and magnesium oxidepowders with a liquid consisting principally
of phosphoric acid, water, and buffers.
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TYPES Type I(fine grain) - Used for the
permanent cementation of castrestorations such as crowns, inlays,
onlays, and bridges. This materialcreates the very thin film layer that isnecessary for accurate seating ofcastings.
Type II(medium grain) -Recommendedfor use as an insulating base for deepcavity preparations
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dispensing
As powderliquid system
As singlecomponent
NOTE-A capsulated system which is mechanically mixedhas been marketed
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Composition of powderZINC OXIDE-
90.2%(Reactiveingredient)
MgO-8.2%(To reduce temp.
of calcination)
SILICA-1.4%(inactive filler)
BITHMUS OXIDE-.1%
(imparts strength tofreshly mixedcement)
BaO/CaO- .1%(modifiers)
Colour pigmentsin trace amount
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Composition of liquid 38.2%
Reactive ingredientPhosphoric
acid
16.2% buffer
Aluminumphosphate &zinc phos.
Zinc 7.1%
Moderator
Water
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manipulation
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cement formingreaction
ZnO Alumino-phosphoric
acid complex
Zinc aluminophosphate ge
Heat
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properties
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1.BIOLOGICAL PROPERTY It is recognized as pulpal irritant
Probable cause is free phosphoric acidpresent at the time of placement ofcement
Pulp should be covered with pulpcapping agents
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RHEOLOGICAL
PROPERTIES
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1.WORKING AND SETTING TIME
MATERIAL ADA no. 96 Commercial product
TYPE I 2.5-8 mins 5.5 mins
TYPE II --- 3-4mins
FACTORS AFFECTING
# Powder liquid ratio
# Rate of powder incorporation# Temperature of mixing slab# Spatulation time# Water content
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2.CONSISTENCY
luting
standard
base
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3.RETENTION Non-adhesive to tooth structure or
surface of casting
MECHANICAL adhesion (factors
affecting)
#Rough surface on tooth & restoration
#Film thicknes & consistency of material
#Strength of luting cement
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3.SOULBILITY &DISINTEGRATION Measured by wt. loss when a disc of
cement is suspended in distilled waterfor 24hr.
ADA req. for type I is max. 0.2%
FACTORS AFFECTING
#P/L ratio
#Initial wetting of cement mix
#Solvent & its pH
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Mechanical propertiesPROPERTIES TYPE I TYPE II
Compressive strength 80-100 MPa(ADA>75MPa)
100-170MPa(ADA>103.5)
Tensile strength 5.5MPa 5-14MPa(brittle)
MOE 14,000MPa 22,000MPaFilm thickness 25-30 mc mt. 30-35 mc mt.
STRENGTH OF CEMENT IS INFLUENCED BY
#Initial powder & liquid composition
#P/L ratio#Time#Handeling of the cement during placement
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Thermal property Have adequate thermal insulating
property.
Used as base under metallic restoration
Optical propertySet cement is opaque
Hence,cant be used for ant. restoration
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uses Primarily used as permanent
cementation material to fix performedrestorations
To fix orthodontic bands Thermal insulating base
Temporary or intermediate restorative
material
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Advantages disadvantages Good compressive
strength
Easy manipulation
process Sets sharply to
relative hard mass
Low cost production
Long history ofclinical success
Pulpal irritation
Lack ofanticariogenic & anti
bacterial action Lack of chemical
adhesion to toothstructure
Soluble in oral fluids Non-aesthetic
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modifications
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HYDROPHOSPHATE CEMENT The phosphoric acid is freeze dried &
converted to solid form, these solid acidphosphates are blended with phosphate ofZn,Ca & other metals as well as the oxides ofthese metals with water
Liquid used id distilled water Acidity is same as of conventional Zn-P
cement Other properties inferior then that of
conventional one Used as luting cement & thermal insulating
bases
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FLUORIDE CEMENYS Some zinc phosphate cement contain 1-
3% of stannous fluorides & they areparticularly used for orthodontic
cementation Have low strength & high solubility
because of dissolution of fluoridecontaining material
But ant cariogenic property is not sogood as leaching of fluoride ionsdecrease in 1-2days
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Copper cement/Silvercement/germicidal cement Ag salts or Cu oxides are sometimes added to powder of
zinc phosphate cement to impart antibacterial /antisepticproperty
Silver cement generally contain few % of salt such as silverphosphate. Silver salts darkens on exposure in the mouth
Cement is black when cupric oxide is added,red if cuprousoxide is added white if cuprous iodide is added & green ifcupric silicate is added
Cement is used in rare cases such as rampant caries ofdeciduous teeth
They are seldom used currently because there clinicalbehavior doesnt seem superior to any other temporary
restorative material & their toxic reaction to the pulp isgenerally recognized
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CONCLUSION
Zinc phosphate is oldest and mostwidely used dental material and isconsidered as gold standard cement
because of its long clinical success.
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