LUTING AGENTS

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.
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.

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.

MECHANISM OF RETENTION
A prosthesis can be retained by mechanical or chemical
means or a combination of mechanical and chemical factors.
Surfaces are rough, and the cement fills the roughness of both
surfaces. The entire interface region then appears continuous,
and the cement layer can resist shear stress acting along the
interface. This situation represents a typical mechanical
retention, and the strength of retention depends on the strength
of the cement, which resists applied forces that may act to
dislodge a prosthesis. For certain situations, mechanical
retention alone is insufficient, and incomplete wetting can also
leave voids on the surface that may allow an influx of oral fluids.
Because of these deficiencies, chemical bonding as a means of
retention is the ultimate goal. Theoretically, chemical bonds
can resist interfacial separation and thus improve retention

Aqueous cements based on polyacrylic acids do provide chemical
bonding through the use of acrylic acids. Resin based cements
using some specialty functional groups also have exhibited
chemical bonding.
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 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.
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 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
Low viscosity and film thickness
Long working time with rapid set at mouth temperature
Good resistance to aqueous or acid attack
High compressive and tensile strength
Resistance to plastic deformation
Adhesion to tooth structure and restoration
Cariostatic
Biologically compatible with pulp
Translucency
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
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.
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 is 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.

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.
According to ADA sp. No. 8
type I – fine grained for luting
type II – medium grained for luting and filling

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 – principal ingredient of zinc phosphate
cement
Magnesium oxide (MgO) 8.2 – reduces temperature of
calcination process
Silicon dioxide (SiO2) 1.4 -- inactive filler in the powder and
during manufacture aids in the calcinations process.

Bismuth trioxide (Bi2O3) 0.1 -- bismuth is believed to impart
smoothness to the freshly mixed cement mass, in large
amounts it may also lengthen the setting time.
Miscellaneous (BaO, Ba2So4, CaO) 0.1
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 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

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 – reacts with zinc oxide
H3PO4 (combined with aluminum and zinc) 16.2 – buffer,
reduces the rate of the reaction
Aluminum (Al) 2.5
Zinc (Zn) 7.1
Water (H2O) 36.0 – controls the rate of the reaction

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.
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 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.

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) Gill more 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
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. 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.
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.

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.

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.
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
Adequate strength to maintain the restoration
Relatively good manufacturer properties
Mixed easily and that they set sharply to a relatively strong
mass from a fluid consistency.
Disadvantages
Irritating effect on the pulp
Lack of anticariogenic properties
Lack of adhesion to the tooth
Vulnerability to acid attack
Brittleness
Solubility in acid fluids.
Trade names
Modem Tenacin
Flecks zinc cement
De Trey zinc cement improved

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 anticariogenic 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.

Reaction of pulp to cement
Zinc phosphate 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.

Advantages
Zinc silicophosphate cements have a better strength and
toughness than zinc phosphate cements
Shows considerable fluoride release hence anticariogenic
Translucent
Under clinical conditions lower solubility and better bonding
Best suited to cement of ortho bars and restoration on non-
vital teeth.
Disadvantages
Less satisfactory mixing
Higher film thickness
Greater pulpal irritation
Trade names
Flourathin and Lucent ( type I)

ZINC POLYCARBOXYLATE CEMENT
In the quest for an adhesive cement that can bond strongly to the
tooth structure, Zinc polycarboxylate cement was the first cement
system that developed an adhesive bond to tooth structure in
1960.

Composition
Zinc polycarboxylate cement or zinc polyacrylate cements are
supplied as a powder and liquid or as a powder that is mixed
with water.
Powder
Zinc oxide and magnesium oxide that have been sintered and
ground to reduce the reactivity of zinc oxide.
Stannic acid may be substituted for magnesium oxide.
Other oxides such as bismuth and aluminum can be added.
The powder may also contain small quantities of stannous
fluoride, which modify setting time and enhance manipulative
properties. It is an important additive because it increases
strength. However, the fluoride released from this cement is
only a fraction.
The cement powder that is mixed with water contains 15 % to
18% polyacrylic acid coated on the oxide particles.

Liquid
A water solution of polyacrylic acid.
Most commercial liquids are supplied as 32% to 42% solution
of polyacrylic acid having molecular weight of 25,000 to
50,000. The manufactures control the viscosity of the cement
liquid by varying the molecular weight of the polymer or by
adjusting the pH by adding sodium hydroxide.
Itaconic and tartaric may be present to stabilize the liquid,
which can gel on extended storage.
Setting reaction
The setting reaction of this cement involves particle surface
dissolution by acid that releases zinc, magnesium, and tin
ions, which bind to the polymer chain via the carboxyl groups.
These ions react with carboxyl groups of adjacent polyacid
chains so that a cross-linked salt is formed as the cement
sets.

The hardened cement consists of an amorphous gel matrix in
which unreacted particles are dispersed. The microstructure
resembles that of zinc phosphate cement in appearance.
Water settable versions of this cement are available. The
polyacid is a freeze-dried powder that is then mixed with the
cement powder. The liquid is water or a weak solution of
NaH2PO4. However the setting reaction is the same whether
the polyacid is freeze dried and subsequently mixed with water
or if the conventional aqueous solution of polyacid is used as
the liquid.

Manipulation
Mixing
The cement liquids are quite viscous. The viscosity is a function
of the molecular weight and the concentration of the polyacrylic
acid thereby varies. Generally the powder liquid ratio is 1.5
parts of powder to 1 part of liquid by weight. The consistency of
the mix is creamy compared with that of zinc phosphate
cements. The mixed cement is pseudoplastic that is the
viscosity decreases as the shear rate increases, or in other
terms, the flow increases as spatulation increases or as force is
placed on the material. The correct consistency is found in a
mix that is viscous but that will flow back under its own weight
when drawn up with a spatula.
The cement liquid should be mixed on a surface that does not
absorb liquid. A glass slab affords the advantage over paper
pads supplied by the manufacturers because once it is cooled it
maintains the temperature longer.

The cool slab and powder provides for longer working time, but
under no circumstances should the liquid be cooled in a
refrigerator.
Mix polyacrylate cements within 30 to 60 seconds, with half to all
of the powder incorporated at once to provide the maximum
length of working time 2.5 to 6 minutes. Working time can be
extended to 10-15 minutes by using a cool slab chilled to 4˚C.
The liquid should not be dispensed before the time when the mix
is to be made. It loses water to the atmosphere rapidly and this
results in marked increase in viscosity.
Use the mixed cement only as long as it appears glossy on the
surface. Once the surface becomes dull, the cement develops
stringiness and the film thickness becomes too great to seat a
casting completely.
If good bonding to tooth structure is to be achieved, the cement
must be placed on the tooth surface before it loses its glossy
appearance. The glossy appearance indicates a sufficient number
of free carboxylic acid groups on the surface of the mixture that
are vital for bonding to tooth structure.

Surface penetration and retention
Despite the adhesion of the cement to tooth structure,
polycarboxylate cements are not superior to zinc phosphate
cement in the retention of cast noble metal restorations.
A comparable force is required to remove gold inlays cemented
either with zinc phosphate cement or with polycarboxylate
cement. Examination of fractured surfaces shows that failure
usually occurs at the cement –tooth interface with zinc phosphate
cement.
In the case of polycarboxylate cements, the failure occurs usually
at the cement metal interface.
The cement does not bond to the metal in the chemically
contaminated condition. Thus it is essential that this contaminated
surface on the casting be removed to improve wettability and the
mechanical bond at the cement metal interface. The surface can
be carefully abraded with a small stone, or it can be sandblasted
with high-pressure air and alumina abrasives.

Because this type of cement affords an opportunity to obtain
adhesion to tooth structure, a clean cavity surface is necessary
to ensure intimate contact and interaction between cement
and the tooth. A recommended procedure is to apply a 10%
polyacrylic acid solution for 10 to 15 seconds followed by
rinsing with water.
Removal of excess cement
During setting the polycarboxylate cement passes through a
rubbery stage that makes the removal of the excess cement
quite difficult. The excess cement that has extruded beyond
the margins of the casting should not be removed while the
cement is in this stage, because some of the cement may be
pulled out from beneath the margins leaving a void. The
excess should be removed when the cement becomes hard.
The outer surface of the prosthesis should be coated with a
separating medium like petroleum jelly, to prevent excess from
adhering. Another approach is to start removing excess
cement as soon as seating is completed.

Properties
Viscosity
The initial viscosity of zinc polycarboxylate cement is higher than
zinc phosphate cements and a delay of 2 minutes in cementation
reverses the situation.
Film thickness
When polycarboxylate cements are mixed they appear to be
much viscous than zinc phosphate cement. Since zinc
polycarboxylate cement is pseudoplastic cement it undergoes
thinning at an increase shear rate. Clinically, this means that the
action of spatulation and seating with a vibratory action will
reduce the viscosity and yield a film thickness of 25-μ m or less.

Working time and setting time
The working time for polycarboxylate cement is much shorter
than phosphate cement that is 2.5 minutes. Lowering the
temperature of the reaction can increase the working time that
may be necessary for fixed bridges. Unfortunately, the
temperature of the cool slab can cause the polyacrylic acid to
thicken. The increased viscosity makes the mixing procedure
more difficult. It has been suggested that only the powder
should be refrigerated before mixing.
The setting time ranges from 6 to 9 minutes.
Mechanical properties
The compressive strength of polycarboxylate cement is 55 Mpa.
The diametrical tensile strength is slightly higher than that of
zinc phosphate cement.
Its modulus of elasticity is less than half.

Brown stated that an increse in the compressive and tensile
strength of polycarboxylate cement can be obtained with the
addtion of stainless steel powder or fibers .
Zinc polycarboxylate cement is not as brittle as zinc phosphate
cement.
Thus it is more difficult to remove the excess after the cement
has set.
Solubility
The solubility of the cement in water is low, but when it is
exposed to organic acids with a pH of 4.5 or less, the solubility
markedly increases.
Also a reduction in the powder liquid ratio results in
significantly higher solubility and disintegration rate in the oral
cavity.

Bond strength
An interesting feature of polyacrylate cement is it’s bonding to
enamel and dentin, which is attributed to the ability of the
carboxylate groups in the polymer molecule to chelate to
calcium. The bond strength to enamel has been reported to be
from 3.4 to 13 MPa and to that of dentin is 2.1 MPa. Optimum
bonding requires clean tooth surface. Sand blasting or
electrolytic etching of the gold alloy surface is necessary to
achieve optimum bonding.
Dimensional stability
The zinc polyacrylate cement shows a linear contraction when
setting at 37 C. The amount of contraction varies from 1 % for
a wet specimen at 1 day to 6 % for a dry specimen at 14 days.
These contractions are more pronounced than those observed
for zinc phosphate cements and start earlier.

Acidity
Zinc polyacrylate cements are slightly more acidic than zinc
phosphate cements when first mixed but the acid is only weakly
dissociated, and penetration of the highly molecular weight
polymer molecules toward pulpal tissue is minimal.
Mortiner noted that film thickness is thicker than zinc phosphate
cement.
According to Wilson and Paddon the cement remains much less
brittle and is tougher than silicate, zinc phosphate and glass
ionomer cement.
Abelson said that the retention of full crown was similar to zinc
phosphate.
Applications
Zinc polyacrylate cements are used primarily for luting permanent
alloy restorations and as bases. Theses cements have also been
used in orthodontics for cementation of bands.

Advantages
Biocompatibility with the pulp is excellent.
Postoperative sensitivity is negligible when used as a luting
agent
Adhesion to tooth and alloy
Easy manipulation.
Disadvantages
Need for accurate proportioning required for optimal properties
Greater viscoelasticity
Shorter working time
Low compressive strength
More critical manipulation.
Trade names
Dertelon (Premier dental products)
PCA (S.S. White)
Cermaco (Johnson & Johnson)

GLASS IONOMER CEMENT
Glass ionomer is the generic name of a group of materials that
use silicate glass powder and an aqueous solution of polyacrylic
acid. The material acquires its name from its formulation of a
glass powder and an ionomeric acid that contains carboxyl
groups. It is also referred to as polyalkeonate cement.
Originally, the cement was designed for the esthetic restoration
of anterior teeth and it was recommended for use in restoring
teeth with class III and V cavity preparations. Also because the
cement produces a truly adhesive bond to tooth structure.

Types of Glass ionomer cement
Type I
Luting applications
Powder liquid ratio is generally 1.5 : 1
Grain size 15 µm or less
High early resistance to water contamination
Radiopaque for easy detection of excess
Limited extension of working time thru chilling glass slab.
Type II
Restorative material
Powder liquid ratio 3:1
Must protect for 24 hours for best results
Reduced fluoride content to improve translucency

Type III
Liner and base.
Powder liquid ratio varies according to use
Lining requires 1.5:1 powder liquid ratio for easy manipulation
Base requires 3:1 or greater for strength
Light activated varieties available
Type IV
Metal modified glass ionomer cement
Miracle mix
Cermet cement
Light curable versions of GIC are also available. (HEMA added
to liquid)
Hybrid glass ionomer resin modified

Composition
Powder
The glass ionomer powder is an acid soluble calcium
fluroaluminosilicate glass.
The raw materials are fused to a uniform glass by heating them
to a temperature of 1100˚ C to 1500 ˚C. Lanthanum, strontium,
barium or zinc oxide additions provide radiopacity.
The glass is ground into a powder having particles in the range
20 to 50 μm.
SiO2 29.0 %
Al2O3 16.6 %
AlF3 5.3 %
CaF2 34.3 %
AlPO4 9.8 %
Fluoride is an essential constituent of glass ionomer cement. It
lowers the temperature of fusion, increases the strength and
improves the working characteristics of the cement paste.

Liquid
The liquid for GIC was aqueous solutions of polyacrylic acid in
a concentration of about 50 %. The liquid was quite viscous
and tended to gel over time.
The acid is form of a copolymer with itaconic, maleic, or
tricaboxylic acid. Theses acids tend to increase the reactivity
of the liquid, decreases the viscosity, and reduce the tendency
for gelation.
The copolymeric acids used in modern glass ionomer liquids
are more irregularly arranged than in the homopolymer of
acrylic acid. This configuration reduces hydrogen bonding
between acid molecules and thus reduces the degree of
gelling.
Tartaric acid present in the liquid improves the handling
characteristics and increases the working time however it
shortens the setting time.

One of the glass ionomer formulations consist of freeze dried acid
powder and glass powder in one bottle and water or water with
tartaric acid in another bottle as the liquid component. When the
powders are mixed with water, the acid dissolves to reconstitute
the liquid acid. The chemical reaction then proceeds in the same
manner as that demonstrated by the powder liquid system. This is
usually done to extend the working time. These cements have a
longer working time with a shorter setting time. They are referred
to as water settable GIC’s or as anhydrous GIC’s.
Simmons and Murray et al say that compressive strength has
been found to be significantly increased with the addition of silver
alloy powder.
McLean showed that a simple matrix of metal powder and
alumino silicate glass ionomer powder failed to form a sufficient
bond at metal/ polyacrylate interface. The glass ionomer cement
is capable of establishing a bond with the dentin substrate before
development start, but the composite start only after stress is
started

Chemistry of setting
Glass ionomer cement is an acid base reaction cement as defined
by Wilson and Wygant.
When the powder and liquid are mixed to form a paste, the surface
of the glass particles is attacked by the acid. Calcium, aluminium,
sodium and fluorine ions are leached into the aqueous medium.
The polyacrylic acid chains are cross-linked by the calcium ions and
form a solid mass. Within the next 24 hours a new phase forms in
which aluminum ions become bound within the cement mix. This
leads to more rigid cement. Sodium and fluorine ions do not
participate in the cross linking of the cement. Some of the sodium
ions may replace the hydrogen ions of carboxylic group, where as
the rest combines with fluorine ions, forming sodium fluoride
uniformly dispersed within the set cement. During the maturing
process, the cross-linked phase is also hydrated by the same water
used as the medium.

The unreacted portion of glass particles are sheathed by silica gel
that develops during removal of the cations from the surface of
the particles. Thus, the set cement consists of an agglomeration
of unreacted powder particles surrounded by a silica gel in an
amorphous matrix of hydrated calcium and aluminum polysalts.
Role of water in the setting process
Water is a most important constituent of the cement liquid. It
serves as the reaction medium initially, and then it slowly hydrates
the cross linked matrix, thereby increasing the material strength.
During the initial reaction period, this water can readily be
removed by desiccation and is called loosely bound water. As the
setting continues, the same water hydrates the matrix and cannot
be removed by desiccation and is then called tightly bound water.
This hydration is critical in yielding a stable gel structure and
building the strength of the cement.

If freshly mixed cements are kept from the ambient air, the
loosely held water will slowly become tightly bound water over
time. This phenomenon results in cement that is stronger and less
susceptible to moisture.
If the same mixes are exposed to ambient air without any
covering, the surfaces will craze and crack as a result of
desiccation. Any contamination by water that occurs at this stage
can cause dissolution of the matrix forming cations and anions to
the surrounding areas. This process results in weak and more
soluble cement. Although the dissolution susceptibility tends to
decrease over time, the minimum time at which the danger of
cracking from the exposure to air no longer exists has not been
established. The ionomer cement must be protected against water
changes in the structure during placement and for a few weeks
after placement if possible.

Manipulations
To achieve a long lasting restoration several conditions need to be
satisfied like appropriate cavity surface preparation to achieve the
bonding, proper mixing to obtain a workable mixture.
Surface preparation
Clean surfaces are essential to promote adhesion. A pumice wash
can be used to remove the smear layer that is produced during
cavity preparation. On the other hand organic acids such as
polyacrylic acids of various concentrations can remove the smear
layer but still leave the collagenous tubule plug in place. These
plugs inhibit the penetration of the cement constituents and affect
the hydrodynamic fluid pressure within dentin.
One workable method is to apply a 10 % of polyacrylic acid
solution to the surface for 10 to 15 seconds, followed by a 30
second water rinse. The smear layer will be removed but the
tubules remain plugged. This procedure of removing the smear

The purpose of pumice debridement is to remove the fluoride rich
layer surface that may compromise the surface conditioning
process.
After conditioning and rinsing of the preparation, the surface should
be dried but it should not be unduly desiccated. It must remain
clean because any further contamination by saliva or blood impairs
bonding of the cement.
Preparation of the material
Glass ionomer cements mixed with carboxylic acid liquids have a
powder liquid ratio of 1.3: 1 or 1.35: 1, but it is the range of 1.25
to 1.5 g of powder per 1 ml of liquid.
The powder and liquid are dispensed on a paper or a glass slab. A
cool dry glass slab may be used to slow down the reaction and
extend the working time .The slab should not be used if the
temperature is below dew point, that is, at temperatures that
enhance moisture condensation on the glass slab that can alter the
acid water balance needed for a proper reaction.

By waiting for a few minutes, the temperature of the slab will rise
sufficiently until water vapor no longer condenses on its surface.
The powder and liquid should not be dispensed onto the slab until
just before the mixing procedure is to be started. Prolonged
exposure to the office atmosphere alters the precise acid water
ratio of the liquid. The powder is divided into two equal portions.
The first portion is incorporated into the liquid with a stiff spatula
before the second portion is added. The mixing time is 30 to 60
seconds. At this time the mix should have a glossy surface. The
shiny surface indicates the presence of polyacid that has not
participated in the setting reaction. The residual acid ensures
adhesive bonding to the tooth. If the mixing process is prolonged,
a dull surface develops, and adhesion will not be achieved.
Encapsulated products are typically mixed for 10 seconds in a
mechanical mixer and dispensed directly onto the tooth and
restoration.

The cement must be used immediately because the working time
after mixing is about 2 minutes at room temperature. An
extension of the working time to 9 minutes can be achieved by
mixing on a cool slab, (3˚ C), but because a reduction in
compressive strength and modulus of elasticity is observed, this
technique is not recommended. Do not use the cement once a
skin forms on the surface or when the viscosity increases.
Glass ionomer cements are very sensitive to contact with water
during setting. The field must be isolated completely. Once the
cement has achieved its initial set (7 minutes), coat the cement
margins with the coating agents supplied with the cement.
It is important to prevent excess cement from spreading to the
tooth structure or to the prosthesis. This cement is particularly
susceptible to attack by water during setting. Therefore, the
accessible margins of the restoration should be coated to protect
the cement from premature exposure to moisture.

Properties
Film thickness
The glass ionomer cement is capable of forming films of 25μm or
less.
Working time and setting time
The working time ranges from about 3 to 5 minutes the water
settable cements tend to have somewhat longer working time.
The setting time is usually between 5 to 9 minutes. The water
added cements have a more rapid initial set than those that use the
polyacid liquid.
Both working time and setting time can be determined by
indentation tests.
The oscillating rheometer of Wilson gives more information and is a
better measure of working time. Its dynamic nature is closer to the
clinical than is static indentation test.

Strength
The 24-hour compressive strength of Glass ionomer cements
ranges from 90 to 230 MPa and is greater than that of zinc
phosphate cement.
Tensile strength is similar to those of zinc phosphate cement.
Glass ionomer cements show brittle failure in diametral
compression tests.
The elastic modulus of glass ionomer cements is less than that of
zinc phosphate but more than that of zinc polycarboxylate cement.
The rigidity of glass ionomer cements is improved by the glass
particles and the iononic nature of the bonding between polymer
chains.
Bond strength
Glass ionomer cements bond to dentin with values of tensile bond
strength reported between 1 and 3 MPa. The bond strength of
glass ionomer cements to dentin is somewhat lower than that of
zinc polyacrylate cement, perhaps because of the sensitivity of
glass ionomer cements to moisture during setting.

The bond strength has been improved by treating the dentin with
an acidic conditioner followed by an application of a dilute aqueous
solution of ferric chloride.
Glass ionomer cements bond well to enamel, stainless steel, and tin
oxide plated platinum and gold alloy.
Solubility
The solubility in water for the first 24 hours is high. It is important
that the cement should be protected from any moisture
contamination during this period. After the cement has been
allowed to mature fully, it becomes one of the most resistant of the
nonresin cements to solubility and disintegration in the oral cavity.
Biologic properties
The glass ionomer cements bond adhesively to tooth structure and
they inhibit infiltration of oral fluids at the cement tooth interface.
This particular property plus the less irritating nature of the acid
should reduce the frequency of postoperative sensitivity.

There are several factors contributing to the irritant nature. One is
the pH and the length of time that this acidity persists.
Another factor may be the viscosity. The pH relate to the thinner
mixes used for cementation and do not apply to the higher
powder liquid ratio.
Glass ionomer luting cements may cause prolonged
hypersensitivity, varying form mild to severe, micro leakage has
been suggested as an explanation, but a recent study showed no
increase in bacterial counts 56 days after cementation of crowns
with a glass ionomer cements. These cements may be
bacteriostatic or bactericidal because of fluoride release.
Graver says that post-cemented micro leakage is the cause of
tooth sensitivity.
Smith D.C. states the cause of post cemented sensitivity as
bacterial invasion, hydraulic pressure, acidity in the early setting
stage and wash out of thin mix.
Taywn stated that the higher the powder liquid ratio the greater is
the thermal diffusivity.

Adhesion
Glass ionomer has the property of permanent adhesion to
untreated enamel and dentin under moist conditions of the mouth.
It reacts with the smear layer on cut dentin (more for a filling
material than for a luting agent). Glass ionomer also bonds to
other reactive polar substrates such as the base metals.
Bonding is of a chemical rather than a micro mechanical
nature. Therefore, no acid etching or surface roughening
procedures is deprecated. About 80% of maximum bond strength
is developed in 15 minutes but strength slowly increases for several
days after that.
Mechanism of adhesion to enamel and dentine
Chemically, tooth material consists of apatite, which makes
up 98% of enamel and 70% of dentin by weight and collagen,
which is found in dentin alone. The bond of glass ionomer cements
is better to enamel than to dentine, because bonding to apatite is
the principal mode of adhesion.

Beech proposed that the interaction between apatite and
polyacrylic acid produced polyacrylate ions, which then formed
strong ionic bonds with the surface calcium ions of apatite in
enamel and dentine.
Wilson suggested that initially, when the cement paste is applied
to tooth material and is fluid, wetting and initial adhesion is by
hydrogen bonding provided by free carboxyl groups present in the
fresh paste. As the cement ages, the hydrogen bonds are
progressively replaced by ionic bonds. The cations coming either
from the cement or the hydroxyapatite. Polymeric polar chains of
polyacid are essential for the achievement of adhesion. Their role
is thought to be one of bridging the interface between the cement
and the substrate.
Wilson et al postulated that during absorption polyacrylate
entered the molecular surface of hydroxyapatite, displacing and
replacing the surface phosphate. Also calcium ions are displaced
from hydoxypatite along with phosphate during this ionic
exchange.

Therefore, an intermediate layer of calcium and aluminium
phosphates and polyacrylates would form at the interface
between the cement and apatite.
Chain length is also an important factor in adhesion. The
polymer chains capable of bridging gaps between the cement
body and substrate.
Collagen contains both amino and carboxylic acid groups, so
adhesion could be due to hydrogen bonding or cationic bridges.
However, recent absorption studies show that polyacrylic acid and
polyacrylate are not absorbed on collagen.
Cements based on polyacrylic acid appear to bond more
strongly than those based on copolymers of acrylic acid with
itaconic or maleic acids. Evidence is only accumulating that bond
strength to tooth substances depends on the nature of the
polyacid used.
If it were proved, then the molecular configuration of the
polyacid would become an important factor in controlling
adhesion.

Improving adhesion
When the cement tooth bonds fractures, it is by cohesive
failure within the cement rather than adhesive failure at the
interface. Therefore, the strength of the bond is limited by the
cohesive strength of the cement used. The smear layer is
considered to be beneficial. However, salivary contamination of a
freshly prepared dentine surface reduces bond strength, but
whether this was because of its water contact or contamination of
the dentin surface is uncertain.
Surface conditioning
A number of research workers have sought to improve
adhesion of glass ionomer cements. One way that is common to
nearly all adhesive technologies is by pretreatment of the
surface.
Mclean and Wilson first used the term surface conditioning for this
treatment in order to differentiate it from acid etching.

Surface conditioning is needed in order to eliminate the wide
variation found in the structures of the tooth surfaces following
cutting. Rough tooth surfaces are contraindicated. In general,
the smoother the surface, the stronger is the bond. Good
interfacial contact is important for adhesion. Smoothening is
necessary to prevent air entrapment and to minimize sites where
stress concentration could occur.
Fluoride release
Both enamel and cementum can absorb fluoride. Fluoride
is incorporated within the mineral structure as fluoridated hydroxy
apatite. Fluoride is released in the early life of the restoration and
it gradually decreases over a period.
Fluoride is released for at least 18 months. Thickly mixed
cements released more fluoride because they contain
proportionately more glasses and therefore more fluoride. Not all
the fluoride is available for release. It is released as sodium
fluoride and is restricted by the sodium and the calcium content of
the glass and not by the total fluoride content of the glass.

Sodium fluoride is released preferentially from the matrix rather
than the filler. The rate of release is proportional to the inverse of
the square root of time.
Aluminum ions are also released, temporarily and ceases once the
cement has fully hardened. Aluminum ions absorbed by enamel
confer acid resistance upon the tooth.
Action of fluoride in prevention of caries
The anticaries effect can be due to the uptake of fluoride
ions by enamel apatite at hydroxyl sites, and high fluoride level at
enamel surfaces increases resistance to plaque acids. Surface
energy of apatite is decreased, therefore, the dental plaque does
not adhere to tooth enamel surfaces.

Reaction of cement on pulp
Several reasons have been postulated as to why Glass ionomer
cement does not have the same damaging effect on the pulp than
Zinc phosphate cement.
First being the polycarboxylic acid used is much weaker than
phosphoric acid.
Second, the acid is a polymer, means that it will have a much
higher molecular weight and this will limit diffusion along the
dentinal tubules towards the pulp.
Thirdly, there is a strong electrostatic attraction between hydrogen
ions and negatively charged polymer chain and dissociation will
less readily take place than with simple anions.

Applications
Glass ionomer cements are primarily used for permanent cement,
as a base, and as a class V filling material.
The cement has been evaluated as a pit and fissure sealant and
an endodontic sealer.
Glass ionomer cements are being used clinically for cementation
of orthodontic bands because of their ability to minimize
decalcification of enamel by means of fluoride release.

HYBRID IONOMER CEMENTS
Self cured and light cured ionomers (or resin modified glass
ionomers) are available for cementation.
Composition
One self-cured hybrid ionomer cement powder contains a
radiopaque, fluroaluminosilicate glass and a micro encapsulated
potassium persulfate and ascorbic acid catalyst system.
The liquid is an aqueous solution of polycarboxylic acid modified
with pendant methacrylate groups. It also contains 2 –
hydroxyethylmethacrylate (HEMA) and tartaric acid.
Another self-cured cement contains a mixture of
fluroaluminosilicate and borosilicate glasses in the powder. Its liquid
is a complex monomer containing carboxylic acid groups that can
undergo an acid base reaction with glass and vinyl groups that can
polymerize when chemically activated.

A light cured hybrid ionomer cement contains fluroaluminosilicate
glass powder and a copolymer of acrylic and maleic acids, HEMA,
water, camphoroquinone and an activator in the liquid.
Setting reaction
Setting of hybrid ionomer cements usually results from an acid
base glass ionomer reaction and self-cured or light cured
polymerization of the pendant methacrylate groups. Some
cements are only light cured.
Manipulation
The powder is fluffed before dispensing. The liquid is dispensed
by keeping the vial vertical to the mixing pad. The powder liquid
ration is 1.6 g of powder to 1.0 g of liquid, and the powder is
incorporated into the liquid within 30 seconds to give a mousse
like consistency. The working time is 2.5 minutes. The cement is
applied to a clean dry tooth that is not desiccated. Some products
recommend the use of a conditioner for enhanced bonding to

The compressive and tensile strengths of hybrid ionomer cement
are similar to glass ionomer cements.
The fracture toughness is higher than that of other water based
cements but lower than composite cements.
The bond strength to moist dentin ranges from 10 to 14 MPa and is
much higher than that of most water based cements.
Hybrid ionomer cement have very low solubility when tested by
lactic acid erosion. Water sorption is higher than resin cements.
Fluoride release is similar to glass ionomer cements. The early pH
is about 3.5 and gradually rises.
Applications
Self cured hybrid ionomer cement are indicated for permanent
cementation of porcelain fuse to metal crowns, bridges, metal
inlays, onlays, and crowns, post cementation and luting of
orthodontic appliances.
Additional uses include adhesive liners for amalgam, bases,
provisional restorations and cementation of specific ceramic
restorations.

ZINC OXIDE EUGENOL CEMENT
This material has been used to a wide range applications in
dentistry including its use as an impression material for edentulous
arches, a surgical dressing, a bite registration paste, a temporary
filling material, root canal filling, a cementing medium, and as a
temporary relining material for dentures.
ZOE cement is one of the least irritating of all the dental materials
and provides an excellent seal against leakage.
Types
According to ADA specification 30
Type I ZOE cement –temporary cementation
Type II ZOE cements –permanent cementation of restorations or
appliances fabricated outside of the mouth
Type III ZOE cements –temporary restoration and thermal
insulating bases
Type IV ZOE cements – cavity liner

Composition
Tube no 1 (base)
Zinc oxide 87-- should be finely divided and it should contain
only a slight amount of water.
Fixed vegetable or mineral oil 13-- plasticizer and aids in off
setting the action of the eugenol as an irritant.
Tube no 2 (catalyst)
Oil of cloves or eugenol 12--Oil of cloves, which contains 70 %
to 85% eugenol, is sometimes used in preference to eugenol
because it reduces the burning sensation experienced by patients
when it contacts the soft tissues.
Gum or polymerized resin 50 -- facilitates the speed of the
reaction, and it yields a smoother, more homogenous product.
Filler (silica type) 20

Lanolin 3-- inert powder (such as kaolin, talc, diatomaceous
earth) may be added to one or both of the original pastes.
Resinous balsam 10-- Canada balsam and Peru balsam are often
used to increase flow and improve mixing properties.
Accelerator solution and color 5-- soluble salts that may act as
accelerators. Chemicals commonly used are zinc acetate, calcium
chloride, primary alcohols and glacial acetic acid. The accelerator
can be incorporated in either one or both pastes.
Chemistry
The setting mechanism for ZOE material consists of zinc oxide
hydrolysis and a subsequent reaction between zinc hydroxide and
eugenol to form a chelate.

Water is needed to initiate the reaction and it is also a by-product
of the reaction. This type of reaction is called autocatalytic. This is
the reason why the reaction proceeds more rapidly in a humid
environment. The setting reaction is accelerated by the presence
of zinc acetate dihydrate, which is more soluble than zinc
hydroxide and which can supply zinc ions more rapidly. Acetic acid
is a more catalyst for setting reaction than is water, because it
increases the formation rate of zinc hydroxide. High atmospheric
temperature also accelerates the setting reaction.
The free eugenol cement of the set cement is probably extremely
low. It appears to be much higher than it actually is, because the
chelate hydrolyzes readily, forming free eugenol and zinc ions.

Manipulation
The mixing of the two pastes is generally accomplished on an oil
impervious paper, although a glass-mixing slab can be used. The
proper proportion of the two pastes is generally achieved by
squeezing two strips of the paste of the same length, one from
each tube, onto the mixing slab. A flexible stainless steel spatula
is satisfactory for the mixing. The two strips are combined with
the first sweep of the spatula, and the mixing is continued for
approximately 1 minute until a uniform color is observed.
Cements intended for final cementation of restorations carry
manufacturers directions and measuring devices that are
important to use, because of the deceptive flow qualities of these
cements, adding powder until the operator feels the mix is of
suitable consistency for cementing a restoration will lead to a
cement deficient in powder and a lowered strength in the set
cement.

Properties
Setting time
The initial setting time may vary between 3 to 6 minutes.
The final setting time is the time at which the material is hard
enough to resist penetration under a load. It can occur within 10
minutes for type I pastes and 15 minutes for type II. The actual
setting time is shorter when the setting occurs in the mouth.
Film thickness
The film thickness should not be more than 25 μm for cements
used for permanent cementation and not more than 40μ m for
cements used for temporary cementation.
Disintegration
A maximum value of 2.5% is acceptable for provisional cementing
materials but a value of 1.5 % is required for the other cements.

Compressive strength
A maximum value of 35MPa is required for cements intended for
temporary cementation.
A minimum of 35 Mpa is required for cements intended for
permanent cementation.
The strength of the cement for temporary cementation is selected
in relation to the retentive characteristics of the restoration and
the expected problems of removing the restoration when the time
arrives.
Provisional cementation
On many occasions, cementing a restoration provisionally is
advised not that the patient and dentist can assess its appearance
and function over a longer time than a single visit. However, this
trial cementation should be managed cautiously. On one hand,
removing the restoration for definitive cementation may be
difficult, even when temporary ZnOE is used.

To avoid this problem, the provisional cement can be mixed with
little petroleum or silicone grease and applied only to margins of
restoration to seal them while allowing subsequent removal
without difficulty.
On the other hand, a provisionally cemented restoration may
come loose during function.
If a single unit is displaced, it can be embarrassing or
uncomfortable for the patient.
If one abutment of a FPD becomes loose, the consequences can
be more severe.
If the patient does not promptly return for recementation caries
may develop very rapidly. Provisional cementation should not be
undertaken unless the patient is given clear instructions about the
objective of the procedures, the intended duration of the trial
cementation and the importance of returning if an abutment
loosens.

Temporary cementation
Unmodified ZOE cements are used as a luting material for
provisional restorations in crown and bridge prosthodontics.
Unmodified cements are available in the compressive strengths of
1.4MPa to 21MPa. Studies proved that luting cements with a
compressive strength of 15 to 24 MPa was the most appropriate
cement based on retention; taste; ease of removal; ease of
cleaning.
Non-eugenol paste
One of the chief disadvantages of the ZOE pastes is the possible
stinging or burning sensation caused by eugenol when it contacts
soft tissues. Furthermore the ZOE reaction is never completed,
with the result that the free eugenol may leach out. Some patients
find the taste of eugenol extremely disagreeable and in patients
who wear a surgical pack for several weeks; a chronic gastric
disturbance may result.

A material similar to ZOE reaction product can be formed by a
saponification reaction to produce an insoluble soap, if the zinc
oxide is reacted with a carboxylic acid.
The reaction is ZnO + 2RCOOH→ (RCOO) 2Zn + H2O
Almost any carboxylic acid reacts with zinc oxide, but only a few
such acids provide compounds of dental interest.
Orthoethoxybenzoic acid, (EBA), is used in this regard.
The carboxylic acid is not necessarily a liquid. Powdered acids can
be dissolved or dispersed in a liquid carrying agent, such as ethyl
alcohol.
The non-eugenol cements do not adhere well to preformed metal
crowns as the eugenol containing cements, and they are slower
setting.
The non-eugenol cements however do not soften provisional
acrylic crowns.

RESIN BASED CEMENT
Resin luting cements have been in existence since the 1950’s. The
early formulations were lightly filled methyl methacrylate resins.
Because of their high polymerization shrinkage, tendency for pulpal
irritation, penchant for micro leakage and poor handling
characteristics, these resins had only limited use.
However , with the development of composite direct filling resins
with improved properties acceptance to acid etch and potential to
bond to dentin, a variety of resin cements have become available.
ISO 4049 describes three classes of composites for polymer based
filling, restoration and luting materials
Class 1 – self cured materials
Class 2 – light cured materials
Class 3 – dual cured materials

Requirements based on ISO 4049
Class 1,2,3: maximum film thickness 50μ m
Class 1,3: minimum-working time 60 seconds
Class 1,3: maximum setting time 10 minutes
Class 2: depth cure 0.5mm (opaque) 1.5mm (others)
Class 1,2, 3: water sorption 40 μg/mm³
Class 1,2,3: solubility 7.5μ g/mm³
Composition
The basic composition of the most modern resin based cements is
similar to that of resin based composite filling material. The resin
cement consists of a resin matrix (bis-GMA or diurethane
methacrylate) with inorganic fillers that are bonded to the matrix
via coating with an organosilane coupling agent. The filler particle
provides strength. The fillers are those used in composites (silica or
glass particles, 10 to 15μ m in diameter) and the colloidal silica is
that used in micro filled resins. The resin matrix binds them
together and bonds them to the tooth structure. Because most of a
prepared tooth surface is dentin.

Monomers with functional groups that have been used to induce
bonding to dentin are often incorporated in these resin cements.
They have organophosphates, hydroxyethyl methacrylate (HEMA),
and the 4-methacyrlethyl-trimellitic anhydride (4-META) system.
Bonding of the cement to enamel can be attained through the
acid tech technique.
Polymerization can be achieved by the conventional peroxide
amine induction system or by light activation. Some cements are
autopolymerising for use under light blocking metallic restorations,
while others are either entirely photo cured or dual cured (light
activated) for use under translucent ceramic veneers and inlays.
In dual cured cements, a catalyst is mixed into the cement so that
it will eventually harden within shadowed recesses after a rapid
initial hardening is achieved with a curing light.

Dual cured cements come in a base catalyst form and must be
mixed before use.
Light cured composites are photo initiated in the presence of a
camphoroquinone amine system. They provide a wide selection of
shades, tints and opaquers.
Properties
Resin based cements are virtually insoluble in oral fluids.
They are formulated to provide the handling characteristics
required for the particular application for e.g., cements
recommended for cementation of indirect restorations have a film
thickness of 25μ m or less.
With respect to bonding to dentin, the so-called adhesive
cements, which incorporate the phosphonate, HEMA or 4-META
adhesion systems, generally develop reasonably good bond
strengths to dentin. Bonding to tooth structure may be more
critical for resin based cements than for some other types of
cement, because they possess no anticariogenicity potential.

These cements differ from restorative composites primarily in their
lower filler content and lower viscosity. Resin cements are virtually
insoluble and are much stronger than conventional cements. It is
their high tensile strength that makes them useful for
micromechanically bonding etched ceramic veneers and pitted
partial denture retainers to etched enamel on tooth preparations
that would not be retentive enough to succeed with conventional
cements.
Biologic properties
Resin based cements, just like composite cements are irritating to
the pulp. Thus, pulp protection via a calcium hydroxide or glass
ionomer liner is important when one is cementing an indirect
restoration that involves bonding to dentin.

Manipulation
The chemically activated versions of theses cements are supplied
as two component systems a powder and a liquid or two pastes.
The peroxide initiator is contained in one component and the amine
activator is contained in the other. The two components are
combined by mixing on a treated paper pad for 20 to 30 seconds.
The time of excess removal is critical. If it is done while the cement
is in a rubbery state, the cement may be pulled from beneath the
margin of the restoration, leaving a void that increases the risk of
plaque buildup and secondary caries.
Removal of the excess cement is difficult if it is delayed until the
cement has polymerized. It is best to remove the excess cement
immediately after the restoration is seated.

Light cured cements are single component systems just as are the
light cured filling resins. They are widely used for cementation of
porcelain and glass ceramic restorations and for direct bonding of
ceramic orthodontic brackets. The time of exposure to the light
that is needed for polymerization of the resin cement is
dependant on the light transmitted through the ceramic
restoration and the layer of polymeric cement. However the time
of exposure to the light should never be less than 40 seconds.
The dual cure cements are two component systems and require
mixing that is similar to that for the chemically activated systems.
The chemical activation is slow and provides extended working
time until the cement is exposed to the curing light, at which
point the cement solidifies rapidly. It then continues to gain
strength over an extended period because of the chemically
activated polymerization.

Disadvantages
Excessive cement film thickness
Marginal leakage because of setting shrinkage
Severe pulpal reactions when applied to cut vital dentin
Dentin bonding agents have been reported to reduce pulpal
response, presumably by sealing the dentinal tubules and
reducing micro leakage. Adhesive resin was found to produce
better marginal seal than zinc phosphate cement.
Composite resin system
Three types of composite resin materials are available for use in
indirect techniques: microfilled resins, small particle composite
resins and hybrid resins. All show excellent wear resistance, but
small particle composite resins and hybrid resins can be etched to
produce micromechanical retention. They can also be silanted to
increase the bond strength further. One manufacturer of a
reinforced microfilled resin inlay/ onlay system provides a special
bonding agent to increase the bond strength of its material.

Resin bonded bridges
Theses prosthesis are widely employed as alternatives to metal
ceramic bridges.
In this procedure, the preparation of the abutment teeth is minimal
and is confined to enamel of the lingual surface and proximal
surfaces. The tissue surfaces of the abutments are roughened by
electrochemical etching or other means and the surfaces of the
prepared tooth enamel are acid etched to provide mechanical
retention areas for the resin cements.
Glass ceramic restorations
These restorations are often translucent and require specific shades
of cementation agent to maximize their esthetic appearance.
Resin cements have been the cementation agents of choice
recently for all ceramic inlays, crowns and bridges because of their
ability to reduce fracture of the ceramic structures. To achieve the
best retention, the undersurface of the glass ceramic restorations is
usually etched and a silane coating is applied before cementation.

Resin metal bonding
Bonding composites to the metal framework of a bridge and
denture acrylic to a partial denture framework can be improved by
the use of silica coating. Presently there are three methods of
applying silica to either noble or base metal alloys.
One method applies pyrogenic silica using a propane flame.
Other method is to use heat in an oven or ceramic blasting to coat
the restoration or appliance. Bond strengths of composites to silica
coated Au-Pd-Cr-Be alloys from 16 to 22 MPa. Silica coating of
noble alloys eliminates the need for tin-plating these alloys to
improve adhesion of composites. The bond strength of denture
acrylics to Ni-Cr-Be alloys range from 7 to 23 MPa when alloy is
treated with a silica coating or primed with adhesive resin cement.
Liquid cements based on thiosulfates have recently become
available for treatment of alloys. Recently, metal primers based on
thiophosphate chemistry have been introduced as a treatment for
resin metal bonding.

COMPOMERS
Compomer is the resin based cement indicated for cementation of
cast alloy crowns and bridges, porcelain fused to metal crown and
bridges and gold cast inlays and onlays.
Cementation of all ceramic crowns, inlays onlays and veneers The
cement should not be used as a core or filling material.
Compomers are also known as poly acid modified composites.
Composition
The cement powder contains strontium aluminum fluorosilicate
glass, sodium fluoride and self and light cured initiators. The liquid
contains polymerizable methacrylate / carboxylic acid monomer,
multifunctional acrylate / phosphate monomer, diacrylate monomer
and water.
Setting reaction
Setting is the result of self and light cured polymerization. Once the
cement comes into contact oral fluids an acid - base reaction may

occur. The carboxylic acid groups contribute to the adhesive
capability of the cement.
Manipulation
Dry the tooth to be cemented but do not desiccate. The powder
liquid ratio is 2 scoops to 2 drops. Tumble the powder before
dispensing. Mix the powder and the liquid rapidly for 30 seconds.
Place the mixed cement in the crown only and then seat the crown.
A gel state is reached after 1 minute, at which time the excess
cement is removed with floss and a scaler. Light cure the exposed
margins to stabilize the restoration. Setting occurs 3 minutes after
start of mix. Once set, compomer cement is very hard.
Properties
Compomer cement has higher values of retention, bond strength,
compressive strength, flexural strength and fracture toughness. The
cement has low solubility and sustained fluoride release.

CEMENTATION PROCEDURE
The permanent cementation of the restoration is the final clinical
procedure that marks the success of our efforts.
Our interest is that the permanent cementation should be
performed without long periods of temporary cementation.
Otherwise the patient may be exposed to a series of unpleasant
complications such as separation of the teeth, difficulty in
achieving a satisfactory level of oral hygiene, problems in removal
of the restoration, and the possibility of infiltration because the
thickness of the temporary cement is without doubt greater than
the thickness of the permanent cement and is much less fluid.
In immediate cementations the conditions of the healthy
periodontium are ideal and especially in conditions of complete
visibility of the entire preparation, cases in which the provisional
restoration has been constructed properly, the only practice we
follow is one of isolating the area, cleaning the preparation and
protecting the prepared surface of vital teeth.

Isolation
The performance of all luting agents is degraded if the material is
contaminated with water, blood, or saliva. Therefore the
restoration and the tooth must be carefully cleaned and dried
after the try in procedure, although excessive drying of the tooth
must be avoided to prevent damage to the odontoblasts. The
casting is best prepared by air- brading the fitting surface with
50µm alumina. This should be done carefully to avoid abrading
the polished surfaces or margins. Alternative cleaning methods
include steam cleaning, ultrasonic and organic solvents.
Before initiation of cement mixing, isolating the area of
cementation and cleaning and drying the tooth is mandatory.
However the tooth should never be excessively desiccated. Over
drying the prepared tooth will lead to postoperative sensitivity.
Saliva control
Depending on the location of the preparation in the dental arch,
several techniques can be used to create the necessary dry filed
of operation.

In areas where only supragingival margins are present, moisture
control with a rubber dam is probably the most appropriate
method. However, in most instances a rubber dam cannot be used
and absorbent cotton rolls must be placed at the source of the
saliva; an evacuator must be placed where the saliva pools. In the
maxillary arch, placing a single cotton roll in the vestibule
immediately buccal to the preparation and a saliva evacuator in
the opposing lingual sulcus is generally sufficient.
When working on a maxillary second or third molar, multiple
cotton rolls must be placed immediately buccal to the preparation
and slightly anterior to block off the parotid duct. if a maxillary roll
does not stay in position but slips down, it can be retained with a
finger or the mouth mirror.
An alternative to multiple cotton rolls is placement of one long roll
“horseshoe fashion” in the maxillary and mandibular muccobuccal
folds.

The use of moisture absorbent cards is another method for
controlling saliva flow. These cards are pressed paper wafers
covered with a reflective foil on one side. The paper side is placed
against the dried buccal tissue and adheres to it. In addition two
cotton rolls should be placed in the maxillary and mandibular
vestibules to control saliva and displace the cheek laterally.
Svedopter and Speejector – for isolation and evacuation of the
mandibular teeth, the metal saliva ejector with attached tongue
deflector is excellent. By adding facial and lingual cotton rolls,
excellent tongue control and isolation is provided.

Excessive forces are not necessary to make crowns seat during
the phase of cementation. If the space for the cement has been
provided by the use of die spacer, it is not necessary to exert a
great deal force, which can determine a permanent alteration of
the integrity of the marginal fit. It should be kept in mind that the
cementation load should not exceed 5-7 kg.

• The technique used is
known as the brush
technique and
consists of the
application of a small
quantity of cement on
the incisal edge of the
preparation using a
brush for the
application.

• The interior of the
crown in the area of
the margins is
painted with a small
quantity of cement,
and the crown is
placed along its path
of insertion.

• The insertional technique is
as follows: the crown is
inserted slowly to about one
half the distances; it is then
withdrawn by a few
millimeters and is reinserted
to almost the full extent of
its length. The process is
then repeated. We use a
slight up and down
movement along this path to
assist the layering of the
cement. When the operator
no longer feels any
resistance, the crown is
pushed to the finish line and
thus to its final seating. It is
necessary to avoid rotational
movements to find the
correct seating position. This
can be damaging if porcelain
margins are present.

• Once the crown has been
inserted the patient is
provided with an occlusal
support and is asked to
close to maintain the
position of the crown
during the setting of the
cement.
• In professional practice
we prefer to cement one
crown at a time, or at the
most two adjacent
crowns.

Once the cement has hardened we follow this procedure: after
immersion of the P.K. Thomas no. 2 waxing instrument in a
silicone lubricant we enter the junctional area and remove the
excess cement by following the anatomy of that area. We prefer
to use this instrument because it has a rounded tip and a
curvature that are ideal for following the anatomic contour. We
place it against the coronal surface and insert it in the gingival
sulcus in the junctional area. By applying light pressure we follow
the junction and remove the cement. The purpose of this cement
is this technique is to remove the cement following the contour
without causing scratches in the area of crown margin. The same
procedure is repeated on the lingual surface and on the
interproximal surfaces, and because of the instrument curvature;
it results as being efficient and easy to perform.

Some cements like polycarboxylate or resin, tend to pull away
from the margins if excess removal is performed too early.
Dental floss with a small knot in it can be used to remove any
irritating residual cement interproximally and from the gingival
sulcus. The sulcus should contain no cement. After the excess
has been removed. The occlusion can be checked once more
with Mylar shim stock.
Cements take at least 24 hours to develop their final strength.
Therefore the patient should be cautioned to chew carefully for
a day or two.

POST-CEMENTATION
Aqueous – based cements continue to mature over time
well after they have passed the defined setting time. If they are
allowed to mature in an isolated environment, that is, free of
contamination from surrounding moisture and free from loss of
water through evaporation, the cements will acquire additional
strength and become more resistant to dissolution. It is
recommended that coats of varnish or a bonding agent should
be placed around the margin before the patient is discharged.
An appointment is generally scheduled within a week or 10 days
after cementation. The prosthodontist should check carefully
that the gingival sulcus remains clear of any residual cement.
The presence of “polished” facets on the contacting surfaces of
the cast restorations at post cementation appointments should
lead to a careful reassessment and correction of the occlusion.
If any minor shift in tooth position has occurred, occlusal
adjustment may be necessary.

LUTING OF VENEERS
All ceramic restorations may be cemented with zinc phosphate,
glass ionomer or dual polymerizing resin cement. The cement
comes in four shades (A2, C2, B1 & B3) permitting some influence
on the final shade of translucent restorations. This not only
provides better retention and colour control but it makes the
ceramic material less fragile than if it were cemented with non
resin cement.
Clean the prepared tooth with non fluoride pumice and try in the
porcelain veneers. Verify the marginal fit. A drop of water or
glycerin will help the veneer stay in place. The restoration should
be internally clean, etched and silaned. Remove any organic
debris with ethanol or acetone.

Acid etch the internal surface of the restoration with hydrofluoric
acid (for feldspathic porcelain etching time is 5 minutes). The gel
is carefully rinsed under running water (this hydrofluoric acid acts
as an organic solvent and helps to remove any residual
investment)
Dry the ceramic with oil free air. The silane coupling agent is
applied to internal surface of restorations. Dispense one drop of
silane primer and drop of silane activator into dappen dish. Stir
the liquid in the dish for 10-15 seconds with a brush. Apply to
etched porcelain for 1 min and air dry after it.
These silane coupling agents are organosilones which help to form
covalent bonds (methacrylate group) with the resin when it is
polymerized. Alternate to it titanates and zirconates can also be
used as coupling agents.
Etch the enamel surface with 37% phosphoric acid rinsed for 20
seconds and air dry the tooth.

The bonding agent is then applied to the tooth for 30 seconds
with a brush and compressed air is used for 5-10 seconds to
remove the excess adhesive
Polymerize the adhesive for 20 seconds with a light source.
Dispense equal amounts of base and catalyst from dual cure
resin. Mix for 10-20 seconds with plastic mixing stick. Apply a
thin layer of cement to the internal surface of the crown. Seat the
crown and remove excess cement from the marginal areas with
an explorer and clean brush. Continue polymerizing for an
additional 45-60 seconds, directing the light from the lingual
(through the tooth) so that shrinkage will occur toward the tooth.
Then direct the light from the labial (through the veneer). When
light activation is not utilized, allow 6 minutes for auto
polymerization.
Once the luting agent is polymerized trim the excess cement and
check the occlusion. Final finishing procedures can be
accomplished with porcelain polishing agents.

LUTING OF CERAMIC RESTORATIONS WITH RESIN BASED
CEMENTS
The crown should be cleaned, etched and silaned. Remove any
organic debris with ethanol or acetone, followed by placing the
restoration in an ultrasonic cleaner. Further cleaning can be
accomplished by applying liquid phosphoric acid etchant. The
crown is silaned with a silane coupling agent. Dispense one drop
of silane primer and one drop of silane activator into a dappen
dish. Stir the liquid in the dish for 10 -15 seconds with a brush.
Apply it to the internal surface of the crown; avoid application on
the external surface of the crown by covering the outside of the
crown with wax. Rinse the crown and dry it with compressed air.
Clean the tooth preparation with a rubber cup and flour of
pumice. Then wash and air dry. Etch the enamel for 30 seconds.
Rinse and air dry the tooth.

Apply bond adhesive over the entire preparation with a brush.
Thin the bonding agent with compressed air for 15 seconds.
Polymerize the adhesive.
Dispense equal amount of base from the syringe and catalyst
from the tube. Mix for 10 -20 seconds with a flat ended plastic
mixing stick. Apply a thin layer of cement to the internal surface
of the crown. Seat the crown and remove the excess to avoid
ditching the cement at the margin.
Aim the light cure at the marginal areas from facial, lingual and
occlusal directions for 40 -60 seconds.

CONCLUSION
Luting agents possess varied, complex chemistries that affect their
physical properties, longevity and suitability in clinical situations.
It appears a single adhesive will not suffice in modern day
practice. To date, no adhesive can completely compensate for the
shortcomings of the preparation retention and resistance forms or
ill fitting, low strength restorations. Prosthdontics must be aware
of the virtues and shortcomings of each cement type and select
them appropriately.

Review of literature
Edwin. V in 1951 in his study on mechanism of dental structure
said that the dental cements act as a bond by keying action.
Roughness of interface between the inlay and the tooth area
involved (pitch or taper between opposing walls of cavity) thickness
of the bond.
John E. Johnston 1954 did a evaluation of an acrylic cement for
one year. He concluded that acrylic cement is more difficult to
remove then ZnPO4 from cervically, a complete dehydrated surface
is desirable, ability to with stand expansion and contraction due to
temperature charge is not determined yet if the marginal cement is
removed and before polymerization, leaking will occur.
R.W.Phillips (1968) in his article ZNO and Eugenol cements for
permanent restoration in his conclusion was ZNOE was inferior to
ZnPO4 in terms of compressive strength.

Wendi A. Levine (1969) did an evaluation of film thickness of
resin luting agents. Most of the commercially available resin
luting cements have films thin enough to allow to successful
placement of etched cast metal retainer. Restorative resins which
have grater film thickness are unsatisfactory for use as luting
agents.
W.A. Richter (1970) did a study on predictability of retentive
values of dental cements. He concluded that by comparing the
tensile strength of ZnPO4 , hydrophosphate and ZOE are equal
and carboxylate is at least one third stronger. In retentive
evaluation the carboxylate, ZnPO4 and Hydrophosphate cements
are equal and ZOE is ½ as retentive.
Oilo G(1978) – The influence of surface roughness on the
retentive ability of two dental luting cements.

Two series of brass cones and two series of dentine posts
with varying surface roughness were produced. Maximum
roughness value and arithmetical mean roughness were recorded
for each cone. A tensile stress was applied until the crown and
cone separated. The retentive force is relation to retentive area
was measured. The results showed that the retentive ability of
both cements increased with increasing surface roughness. The
increase in retention was greater for bras than for dentine.
Dorothy McComb (1982) did a comparison of glass ionomer
cement with other cement of retention of castings. She concluded
that G.I. have the greater retentive strength and Zinc Phosphate
has the weakest strength.
Michael L. Myers (1983) conducted a study on marginal leakage
of contemporary cementing agents, he concluded that the least
amount of leakage were shown by ZnPO4, than followed by glass
ionomer cement with protective varnish and last is
polycarboxylate.

Gudbrand Oilo (1984) did a clinical study of two luting cements
used on student treated patient. In his 6 to 18 months
observation there was no difference in both ZnPO4 and
Polycarboxylate cement, both cement was seen equally suitable
as a luting material.
W.R. Lacefield (1985) did a study of tensile bond strength of a
glass ionomer cement, he concluded that the tensile bond
strength of G.I. cement to enamel was significantly greater than
to dentin (etched with phosphoric and citric acid has no
significantly effect on temporary bond strength.
G.L.Button (1985) in his article on surface preparation and shear
bond strength of the casting cement interface accounted that air
blasting with 60 μm aluminium oxide particles provided the
surface roughness and topography with the greatest resistance to
shear stress.

Antony H.L. Tjan (1987) did a comparison of effect of various
cementation methods on the retention of prefabricated posts
according to his study the post cemented with composite recorded
the greatest retention, then the ZnPO4 and glass ionomer.
C.L. Davidson (1991) made a study on destructive stresses in
adhesive luting cements. He said that nature and magnitude of
the stress development, depend greatly on the formulation and
film thickness of the luting cement. The thicker the layer, the
faster the stress development in the G.I. and slower in the
composite. The contraction stress has a detrimental effect on the
corrosive strength of the glass ionomer and on the adhesive
strength of the composite.
R.E. Kerby (1991) compared physical properties of stainless steel
and silver reinforced G.I. Cement, he suggested that the stainless
steel reinforced G.I. cement possess strength properties that
should lead to a stronger, more # resistant restorative when
compared with the presently available one.

LUTING AGENTS

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