1 INTRODUCTION The term cement has been applied to powder / liquid materials which are mixed to a paste consistency. The word luting is defined as the use of a moldable substance to seal joints and cement two substances together. Various cements are used for luting for example zinc phosphate, zinc silicophosphate, zinc polycarboxylate, glass ionomer, and zinc oxide eugenol and resin cements. The clinical success of fixed prosthesis is heavily dependant on the cementation process. For a restoration to accomplish its purpose, it must stay in place on the tooth. No cements that are compatible with living tooth structure and the biologic environment of the oral cavity possess adequate adhesive properties to hold a restoration in place solely through adhesion. Although the establishment of optimal resistance and retention forms in the tooth preparation are of primary importance, a dental cement must be used as a barrier against microbial leakage, sealing the interface between the tooth and restoration and holding them together through some form of surface attachment.
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INTRODUCTION
The term cement has been applied to powder / liquid materials which are
mixed to a paste consistency. The word luting is defined as the use of a moldable
substance to seal joints and cement two substances together. Various cements are used
for luting for example zinc phosphate, zinc silicophosphate, zinc polycarboxylate,
glass ionomer, and zinc oxide eugenol and resin cements. The clinical success of
fixed prosthesis is heavily dependant on the cementation process.
For a restoration to accomplish its purpose, it must stay in place on the tooth.
No cements that are compatible with living tooth structure and the biologic
environment of the oral cavity possess adequate adhesive properties to hold a
restoration in place solely through adhesion.
Although the establishment of optimal resistance and retention forms in the
tooth preparation are of primary importance, a dental cement must be used as a barrier
against microbial leakage, sealing the interface between the tooth and restoration and
holding them together through some form of surface attachment.
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PRINCIPLES OF CEMENTATION
Dental treatments necessitate attachment of indirect restorations and
appliances to the teeth by means of a cement. These include metal, resin, metal-resin,
metal ceramic, and ceramic restorations, provisional or interim restorations; laminate
veneers for anterior teeth; orthodontic appliances, and pins and posts used for
retention of restorations. The word luting is often used to describe the use of a
moldable substance to seal a space or to cement two components together;.
The properties of various cements differ from each other. Hence, the choice
cement is mandated to a large degree by the functional and biologic demands of the
particular clinical situation. If optimal performance is to be attained, the physical and
biologic properties, and the handling characteristic, such as the working and setting
times and ease of removing excess materials, must be considered in selecting a
cement for a specific task.
CHARACTERISTICS OF ABUTMENT – PROSTHESIS INTERFACE.
When two relatively flat surfaces are brought into contact, analogous to a
fixed prosthesis being placed on a prepared tooth, a space exists between the
substrates on a microscopic scale.
Typical prepared surfaces on a microscopic scale are rough, that is, there are
peaks and valleys. When two surfaces are placed against each other, there are only
point contacts along the peaks. The areas that are not in contact then become open
space. The space created is substantial in terms of oral fluid flow and bacterial
invasion. One of the main purposes of a cement is to fill this space completely. One
can seal the space by placing a soft material, such as an elastomer, between the two
surfaces that can conform under pressure to the “roughness”.
The current approach is to use the technology of adhesives. Adhesive bonding
involves the placement of a third material, often called a cement that flows within the
rough surface and sets to a solid form within a few minutes. The solid matter not only
seals the space but also retains the prosthesis. Materials used for this application are
classified as Type I cements. If the third material is not fluid enough or is
incompatible with the surfaces, voids can develop around deep, narrow valleys and
undermine the effectiveness of the cement.
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BONDING MECHANISM
Non adhesive luting
Originally the luting agent served primarily to fill the gap and prevent entrance
of fluids. Zinc phosphate for example exhibits no adhesion on the molecular level. It
holds the restoration in place by engaging small irregularities on the surface of both
tooth and the restoration. The nearly parallel opposing walls of a correctly prepared
tooth make it impossible to remove the restoration without shearing or crushing the
minute projections of cement extending into recesses in the surfaces.
Micromechanical bonding
Resin cements have tensile strengths in the range of 30 -40 MPa, which is
approximately five times that of zinc phosphate cement. When used on pitted
surfaces, they can provide effective micromechanical bonding. The tensile strengths
of such bonds can sometimes exceed the cohesive strength of enamel. This allows the
use of less extensive tooth preparation for restorations such as ceramic veneers and
resin bonded fixed partial dentures.
The deep irregularities necessary for micromechanical bonding can be
produced on enamel surfaces by etching with phosphoric acid solution or gel, on
ceramics by etching with hydrofluoric acid and on metals by electrolytic etching,
chemical etching, sandblasting or by incorporating salt crystals into preliminary resin
pattern.
Molecular Adhesion
Molecular Adhesion involves physical forces (bipolar, Vander Waals) and
chemical bonds (ionic and covalent) between molecules of two different substances.
Newer cements, such as polycarboxylate and glass ionomers, possess some adhesive
capabilities, although this is limited by their relatively low cohesive strength. They
still depend primarily on nearly parallel walls in the preparation to retain restorations.
Limited success has been achieved in attempts to develop resin cements and
coupling agents that will exhibit strong, durable molecular adhesion to tooth structure,
base metals and ceramics. Noble metal alloys are not suited for direct molecular
bonding. However, a thin layer of silane can be bonded to a gold alloy with special
equipment (Silicoater, Kulzer, Irvine or Rocatec, ESPE-Premier) to serve as a
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coupling agent by bonding chemically to resin cements. Equally effective is a layer of
tin electroplated onto gold alloy.
By applying a silane coupler to roughened porcelain, shear bond strengths in
excess of the cohesive strength of the porcelain have been achieved. However such
bonds tend to become weaker after thermo cycling in water. At this time, molecular
adhesion should be looked upon only as a way to enhance mechanical and
micromechanical retention and reduce micro leakage, rather than as an independent
bonding mechanism.
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DISLODGEMENT OF PROSTHESIS
Fixed prostheses can debond because of biologic or physical reasons or a
combination of the two. Recurrent caries results from a biologic origin. Disintegration
of the cements can result from fracture or erosion of the cement. For brittle
prostheses, such as glass-ceramic crowns, fracture of the prosthesis also occurs
because of physical factors, including intraoral forces, flaws within the crown
surfaces, and voids within the cement layer.
In the oral environment cementation agents are immersed in an aqueous
solution. In this environment the cement layer near the margin can dissolve and erode
leaving a space. This space can be susceptible to plaque accumulation and recurrent
caries; therefore, the margin should be protected with a coating (if possible) to allow
continuous setting of the cement.
There are two basic modes of failure associated with cements: cohesive
fracture of the cement and separation along the interfaces. Because the cement layer is
the weakest link of the entire assembly, one should favor higher strength cements to
enhance retention and prevent prosthesis dislodgement by providing a firm support
base against applied forces.
Several factors have an influence on the retention of these fixed prostheses.
First, the film thickness beneath the prosthesis should be thin. It is believed
that a thinner film has fewer internal flaws compared with a thicker one.
Second, the cement should have high strength values. Generally, greater forces
are required to dislodge appliances cemented with cements that have higher tensile
strength than with cements of low tensile strength. It is also well established that the
stresses developed during mastication are exceedingly complex. Undoubtedly,
properties other than tensile strength may be involved. These include compressive and
shear strength of the cement, fracture toughness, and film thickness.
Third, the dimensional changes occurring in the cement during setting should
be minimized. Sources include gain or loss of water and differences in the coefficients
of thermal expansion among the tooth, the prosthesis, and the cement.
It is, therefore, important to isolate the cement immediately after removal of
the excess. Fourth, a cement with the potential of chemically bonding to the tooth and
prosthetic surfaces or bond- enhancing intermediate layers may be used to reduce the
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potential of separation at the interface and maximize the effect of the inherent strength
on the retention.
When a mechanical undercut is the mechanism of retention, the failure often
occurs along the interfaces. If chemical bonding is involved, the failure often occurs
cohesively through the cement itself. The prosthesis becomes loose only when the
cement fractures or dissolves.
IDEAL PROPERTIES OF LUTING CEMENT
Described by McLean and Wilson
1. Low viscosity and film thickness
2. Long working time with rapid set at mouth temperature
3. Good resistance to aqueous or acid attack
4. High compressive and tensile strength
5. Resistance to plastic deformation
6. Adhesion to tooth structure and restoration
7. Cariostatic
8. Biologically compatible with pulp
9. Translucency
10. Radio opacity
CHOICE OF LUTING AGENT
An ideal luting agent is one which has a long working time, adheres well to
both tooth structure and cast alloys, provides a good seal, is non toxic to pulp, has
adequate strength properties, is compressible into thin layers, has a low viscosity and
solubility and exhibits good working and setting characteristics. In addition any
excess can be easily removed. Unfortunately, no such product exists.
Zinc phosphate cement
Is probably still the luting agent of choice. Cavity varnish can be used to
protect against pulp irritation from phosphoric acid and appears to have little effect on
the amount of retention of the cemented restoration.
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Zinc polycarboxylate cement
This agent is recommended on retentive preparation when minimal pulp
irritation is important.
Glass ionomer cement
This has become a popular cement for luting cast restoration. It has good
working properties and because of its fluoride content, it may prevent recurrent
caries.
Resin modified glass ionomer cement
Currently among the most popular luting agents, Resin modified glass
ionomer cements have low solubility, adhesion and low micro leakage. The
popularity it mainly due to perceived benefit of reduced post cementation sensitivity.
Adhesive resin
Long-term evaluations of these materials are not yet available, so they cannot
be recommended for routine use. Laboratory testing yields high retention strength
values, but there is concern that stresses caused by polymerization shrinkage,
magnified in thin films, leads to marginal leakage. Adhesive resin may be indicated
when a casting has become displaced through lack of retention.
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ZINC PHOSPHATE CEMENT
Zinc phosphate cement is the oldest of the cementation agents and thus has the
longest track record. It serves as a standard by which newer systems can be compared.
It is a traditional crown and bridge cement used for the alloy restorations. It is
supplied as a powder and liquid, both of which are carefully compounded to react
with one another during mixing to develop a mass of cement possessing desirable
physical properties.
Composition
Powder
The principal ingredient of the zinc phosphate cement is zinc oxide.
Magnesium oxide, silicon dioxide, bismuth trioxide, and other minor ingredients are
used in some products to alter the working characteristics and final properties of the
mixed cement.
Zinc oxide (ZnO) 90.2
Magnesium oxide (MgO) 8.2
Silicon dioxide (SiO2) 1.4
Bismuth trioxide (Bi2O3) 0.1
Miscellaneous (BaO, Ba2So4, CaO) 0.1
The magnesium oxide, usually in quantities of about 10%, are added to the
zinc oxide to reduce the temperature of the calcinations process.
The silicon dioxide is inactive filler in the powder and during manufacture
aids in the calcinations process.
Although bismuth is believed to impart smoothness to the freshly mixed
cement mass, in large amounts it may also lengthen the setting time.
Tannin fluoride may be added to provide a source of fluoride ions in some
products.
The ingredients of the powder are heated together at temperatures ranging
from 1000º to 1300º C for 4 to 8 hours or longer, depending on the temperature.
Calcinations results in a fused or a sintered mass. The mass is then ground and
pulverized to a fine powder, which is sieved to recover selected particle sizes. The
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degree of calcination, fineness of the particle size, and composition determine the
reactivity of the powder with the liquid.
The powder particle size influences the setting rate. Generally the smaller the
particle size, the faster the set of the cement.
Liquid
Adding aluminum and sometimes zinc, or their compounds, to a solution of
orthophosphoric acid, produces zinc phosphate cement liquids. Although the original
acid solution contains about 85% phosphoric acid and is a syrupy fluid, the resulting
cement liquid usually contains about one third water
H3PO4 (free acid) 38.2
H3PO4 (combined with aluminum and zinc) 16.2
Aluminum (Al) 2.5
Zinc (Zn) 7.1
Water (H2O) 36.0
The partial neutralization of phosphoric acid by aluminum and zinc tempers
the reactivity of the liquid and is described as buffering. The reduced rate of the
reaction helps establish a smooth, non-granular, workable cement mass during the
mixing procedure. Both partial neutralizing or buffering and dilution adjust the zinc
phosphate cement liquid so it reacts with its powder to produce a cement mass with
proper setting time and mechanical qualities.
The composition of the liquid should be preserved to ensure a consistent
reaction, as water is critical to the reaction. Changes in composition and reaction rate
may occur either because of self-degradation or by water evaporation from the liquid.
Self-degradation of the liquid is best detected by clouding of the liquid over time.
Setting Reaction
When the powder is mixed with the liquid the phosphoric acid attacks the
surface of the particles and releases zinc ions into the liquid. The aluminum, which
already forms a complex with the phosphoric acid, reacts with zinc and yields a zinc
aluminophosphate gel on the surface of the remaining portion of the particles. Thus
the set cement is a cored structure consisting primarily of unreacted zinc oxide
particles embedded in a cohesive amorphous matrix of zinc aluminophosphate. The
set zinc phosphate cement is amorphous and is extremely porous.
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The surface of alkaline powder is dissolved by the acid liquid, resulting in an
exothermic reaction.
Manipulation
The manner in which the reaction between zinc phosphate cement powder and
liquid is permitted to occur determines to a large extent the working characteristics
and properties of the cement mass. Incorporate the proper amount of powder into the
liquid slowly on a cool slab (about 21 º C) to attain the desired consistency of the
cement.
Powder Liquid Ratio
Reducing the powder liquid ratio can increase working and setting times. This
procedure is however not acceptable means of extending setting time because it
impairs the physical properties and results in a lower initial pH of the cement. The
powder liquid ratio is 1.4gm/0.5ml.
Rate Of Powder Incorporation
Introduction of small quantity of powder into the liquid for the first few
increments increases working and setting times by reducing the amount of heat
generated and permits more powder to be incorporated into the mix.
Care Of The Liquid
When zinc phosphate cement is exposed to a humid atmosphere it will absorb
water, whereas exposure to dry air tends to result in a loss of water. The addition of
water causes more rapid reaction with the powder, resulting in a shorter setting time.
A loss of water from the liquid results in a lengthened setting time. Therefore keep the
bottle tightly closed when not dispensing the material. Polyethylene squeeze bottles
do not require removal of a dropper and therefore eliminate the tendency for gain or
loss of water from the liquid.
Mixing Slab
A properly cooled thick glass slab will dissipate the heat of the reaction. The
mixing slab temperature should be low enough to effectively cool the cement mass
but must not be below the dew point unless the frozen slab technique is used. A
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temperature of 18º to 24º C is indicated when room humidity permits. The moisture
condensation on a slab cooled below dew point contaminates the mix, diluting the
liquid and shortening the setting time. The ability of the mixing slab to be cooled and
yet be free of moisture greatly influences proper control of the reaction rate of zinc
phosphate cement.
Mixing Procedure
By incorporating small portions of the powder into the liquid, minimal heat is
liberated and easily dissipated. The heat of the reaction is most effectively dissipated
when the cement is mixed over a large area of the cooled slab. Use a relatively long
narrow bladed stainless steel spatula to spread the cement across this large area to
control the temperature of the mass and its setting time.
During neutralization of the liquid by the powder, the temperature of the
mixing site is inversely proportional to the time consumed in mixing. Thus a large
volume of the powder is carried to the liquid all at once rather than spatulated over a
large area of the slab for a sufficient time, the temperature at the site of the reaction
becomes higher.
This temperature rise speeds the reaction and hinders control over the
consistency.
During the middle of the mixing period, larger amounts of powder may be
incorporated to further saturate the liquid with the newly forming complex zinc
phosphates. The quantity of the unreacted acid is less at this time because of the prior
neutralization gained from initially adding small increments of powder. The amount
of heat liberated will likewise be less, and it can be dissipated adequately by the
cooled slab.
Finally smaller increments of powder are again incorporated, so the desired
ultimate consistency of the cement is not exceeded.
Thus the mixing procedure begins and ends with small increments, first to
achieve slow neutralization of the liquid with the attendant control of the reaction and
last to gain a critical consistency.
Depending on the product 60 to 90 seconds of mixing appears adequate to
accomplish a proper zinc phosphate cementing mass.
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Contact With Moisture
The area near the cement must be kept dry while the powder and liquid is
mixed, during insertion into the mouth and during hardening. If the cement is allowed
to harden in the presence of saliva some of the phosphoric acid is leaked out and the
surface of the cement will be dull and easily dissolved by oral fluids.
After the cement sets it should not be allowed to dry. Drying of the cement
results in shrinkage and crazing of the surface. A coating of varnish should minimize
dehydration as well as prevent premature contact with oral fluids.
Working Time And Setting Time
Working time is the time measured from the start of the mixing during which
the viscosity (consistency) of the mix is low enough to flow readily under pressure to
form a thin film. Adequate working time is expressed between 2.5 to 8 minutes at a
body temperature of 37˚ C. The first 60 to 90 seconds are consumed by mixing the
powder and liquid.
Setting time is the time elapsed from the start of the mixing until the point of
the needle no longer penetrates the cement as the needle is lowered onto the surface.
Practically, it is the time at which the zinc phosphate cement flash (excess) should be
removed from the margins of the restoration. The setting time can be measured with a
4.5 N (1 pound) Gillmore needle at a temperature of 37º C and relative humidity of
100%. A reasonable setting time for zinc phosphate cement is between 5 to 9 minutes,
as specified in ADA specification no. 8.
Frozen Slab Method
The frozen slab method is a way to substantially increase the working time (4-
11 minutes) of the mix on the slab and shorten the setting time (20 to 40% less) of the
mix after placement into the mouth.
In this method, a glass slab is cooled in a refrigerator at 6º C or in a freezer at
–10ºC .
No attempt is made to prevent moisture from condensing on the slab when it is
brought to room temperature. A mix of cement is made on the cold slab by adding the
powder until the correct consistency is reached. The amount of powder incorporated
with the frozen slab method is 50% to 75% more than with the normal procedures.
The compressive strength and tensile strength prepared by the frozen slab method are
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not significantly different from those prepared for normal mixes, however, because
incorporation of condensed moisture into the mix in the frozen slab method
counteracts the higher powder liquid ratio. This method has been advocated for
cementation of bridges with multiple pins.
Mechanical Interlocking
Whenever an inlay is seated in a prepared cavity the surfaces of both the inlay
and the tooth have slight roughness and serrations into which the cement is forced.
Film thickness is a factor for retention. Thinner the cement better is the cementing
action. Zinc phosphate cements are irritating to the pulp. Although the pH of the
cement approaches neutral at 24 hours. Thinner mixes are more acidic and remain so
for a longer period of time than the standard mixes.
Berk, H. Stanely said that thin mix Zinc phosphate cements have more pulp
response than thick mix because Zinc phosphate cements is pushed into dentinal
tubules and it destroys the odontoblast right in place. The application of a cavity
varnish to a cut tooth structure can act as a barrier to the penetration of the acid.
A recent animal study involving cementation of crowns reported pulp response
to none when a cavity varnish was applied to the teeth prior to cementation of crowns.
With respect to the effect of retention, Fetton showed a coat of varnish to have no
influence in crown retention.
Molta JP said that cavity varnish has been shown to reduce the retention of
cemented pins and decrease tensile bond between two opposed dentinal surface when
Zinc phosphate cement is used for luting.
Characteristics Properties
Physical and biologic properties
Two physical properties of the cement that are relevant to the retention of the
fixed prostheses are the mechanical properties and the solubility’s. The prosthesis can
get dislodged if the underlying cement is stressed beyond its strength. High solubility
can induce loss of the cement needed for the retention and may create plaque retention
sites.
Zinc phosphate cement when properly manipulated exhibits a compressive
strength of 104MPa and a diametral tensile strength of 5.5 MPa.
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Zinc phosphate cement has a modulus of elasticity of approximately 13 GPa.
Thus it is quite stiff and should be resistant to elastic deformation even when it is
employed for cementation of restorations that are subjected to high masticatory stress.
A reduction in the powder liquid ratio of the mix produces a markedly weaker
cement.
A loss or gain in the water content of the liquid reduces the compressive and
tensile strengths of the cement.
Retention
Whenever a casting is seated in the prepared tooth, the surfaces of both the
casting and the tooth structure have slight roughness and irregularities into which the
plastic cement is forced. Such extensions many times act as undercuts in providing
retention of the inlay.
The thickness of the film between the casting and the tooth is also a factor in
the retention. The thinner the film, the better is the cementing action.
Solubility and disintegration
The premature contact of the incompletely set cement with water results in
dissolution and leaching of that surface. Prolonged contact even of well-hardened
cement, with moisture demonstrates that some erosion and extraction of soluble
material does occur from the cement.
Even the filling cement mixes show considerable loss of material in the mouth
over a period of time, indicating that zinc phosphate can be regarded only as a
temporary filling material. Wear abrasion and attack of food decomposition products
accelerate the disintegration of zinc phosphate cements. Greater resistance to
disintegration is achieved by increasing the powder liquid ratio. A thicker mix of
cement exhibits less solubility than a thinner mix.
Dimensional stability
Zinc phosphate cement exhibits shrinkage on hardening. The normal
dimensional change when properly mixed cement is brought into contact with water
after it has set is that of slight initial expansion, apparently from water absorption.
This expansion is then followed by slight shrinkage on the order of 0.04% to 0.06% in
7 days.
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Consistency and film thickness
Two arbitrary consistencies of the cement are used based on their use.
Inlay seating or luting and cement base or filling. A third consistency which
lies midway between inlay seating and the cement base, is band seating consistency
used for retention of orthodontic bands.
The inlay seating consistency is used to retain alloy restorations. Although the
unhardened zinc phosphate cement is somewhat tenacious, the retaining action in its
hardened state is one of mechanical interlocking between the surface irregularities of
the tooth and the restoration.
The film thickness of the zinc phosphate cement greatly determines the
adaptation of the casting to the tooth and also determines the strength of the retention
bond.
The maximum film thickness is 25μ m. the heavier the consistency; the greater
the film thickness and the less complete the seating of the restoration.
The ultimate film thickness that a well-mixed, non-granular cement attains
depends first on the particle size of the powder and second on the concentration of the
liquid.
The film thickness also varies with the amount of force and the manner in
which this force is applied to a casting during cementation.
An increased amount of powder incorporated into the liquid will increase the
consistency of the cement mass.
The operator must frequently test each mass as the end of mixing time
approaches. The final consistency will be fluid, yet will string up from the slab on the
spatula about 2-3cm as the spatula is lifted away from the mass.
A heavy putty like consistency of zinc phosphate cement is used as a thermal
and chemical insulating barrier over thin dentin and a high strength base.
Viscosity
The consistency of cements can be quantified by measuring viscosity. A small
but significant increase in viscosity is seen at higher temperatures. A rapid increase in
viscosity demonstrates that restorations should be cemented promptly after
completion of the mixing to take advantage of the lower viscosity of the cement.
Delays in cementation can result in considerably thick film and insufficient seating of
the restoration.
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Acidity
During the formation of zinc phosphate cement, the union of zinc oxide
powder with phosphoric acid liquid is accompanied by a change in pH. In the early
stages the pH increases rapidly, with a standard mix reaching the pH of 4.2 within 3
minutes after mixing has started. At the end of one hour this value increases to about
6 and is nearly neutral at 48 hours.
Investigations have shown that the initial acidity of zinc phosphate cement at
the time of placement into the tooth may excite pulpal response, especially where only
a thin layer of dentin exists, between cement and pulp.
Thermal and electrical conductivity
One of the primary uses of zinc phosphate cement is an insulating base under
metallic restorations.
Applications
Zinc phosphate cement is used most commonly for luting permanent metal
restorations and as abase.
Other applications include cementation of orthodontic bands and the use of
cement as a provisional restoration.
Advantages
1. Adequate strength to maintain the restoration
2. Relatively good manufacturer properties
3. Mixed easily and that they set sharply to a relatively strong mass from a fluid
consistency.
Disadvantages
1. Irritating effect on the pulp
2. Lack of anticariogenic properties
3. Lack of adhesion to the tooth
4. Vulnerability to acid attack
5. Brittleness
6. Solubility in acid fluids.
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Reaction Of Pulp To Cement
The phosphoric acid in Zinc phosphate cement can be the cause of the pulpal
reaction.
The closer it approaches the pulp, the greater is the intensity of the response.
Also the ratio of powder to liquid is important consideration. A thick mix of Zinc
phosphate cement used as a base will generate a moderate localized response, whereas
a thin mix used to cement on a crown that is placed under great pressure by patients
biting on a tongue blade can cause a very severe reaction.
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ZINC SILICOPHOSPHATE CEMENT
They are also called as Zinc silicate, Silicate zinc cement.
Zinc silicophosphate cement is a hybrid resulting from the combination of zinc
phosphate cement and silicate powders.
Types Of Zinc Silicophosphate Cements
According to ADA no –28 (1969) there are three types
Type I – as a cementing media
Type II – temporary posterior filling material
Type III – dual purpose cementing media and temporary posterior filling material.
Properties
Zinc silicophosphate cements (ZSP) consist of mixture of silicate glass, a
small percentage of zinc oxide powder and phosphoric acid.
They are used as luting agents for restorations and orthodontic bands,
intermediate restorations and as die material.
Its strength is somewhat superior to that of zinc phosphate cement, and the
major difference is that Zinc silicophosphate cement appears somewhat translucent
and releases fluoride by virtue of silicate glass.
Clinical observation has shown that silicophosphate is less soluble in the
mouth than zinc phosphate cement. The fluoride content should give some
antocariogenic action. Therefore it is recommended for cementation of restoration in
patients with high caries rate.
The flow property of the mix is not as good as zinc phosphate cement, leading
to higher film thickness. The cement does not bound to tooth structure; hence
retention is by mechanical interlocking.
Esthetically it is superior to the more opaque zinc phosphate cement for
cementation of ceramic restorations.
The use of Zinc silicophosphate cement is declining, as practitioners have
choice of other more esthetically pleasing materials such as resin and glass ionomer
cements.
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Advantages
1. Zinc silicophosphate cements have a better strength and toughness than zinc