Indian Dental Academy: will be one of the most relevant and exciting training center with best faculty and flexible training programs for dental professionals who wish to advance in their dental practice,Offers certified courses in Dental implants,Orthodontics,Endodontics,Cosmetic Dentistry, Prosthetic Dentistry, Periodontics and General Dentistry.

1. LUTING AGENT
I. Introduction
Numerous 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,
orthodontic appliances; and pins and posts used for retention of
restorations.
The term LUTING is often used in textbooks to describe the use of a
moldable substance to seal space or to cement two components together.
These different applications make varying demands on manipulative
properties, working and setting times, resistance to mechanical breakdown,
and to dissolution. Thus some materials are better suited to some
applications than others. Because one type of cement is unlikely to perform
satisfactorily under all conditions, specific cements must be selected and
developed for each applications.
II. Basic considerations:
The discrepancies of fit arising during the fabrication process for the
inlay or crown, the preparation of the tooth leaves a rough and debris
covered surfaces. The cement lute then must have the ability to wet the
tooth and restoration, flow into the irregularities on the surfaces it is
joining and fill in and seal the gaps between the restorations and the tooth.
Because an exposed cement line at the restorations margin is
inevitable – especially with todays restorative materials the cement must
1

2. also have adequate resistance to dissolution in the oral environment. It
must also develop an adequately strong bond through mechanic
interlocking and adhesion. High strength in tension, shear, and
compression are required, as well as good fracture toughness to resist
stresses at the restoration tooth interface.
Good manipulation properties including adequate working and
setting time are essential for successful use. The manipulation, including
dispensation of the ingredients, should allow for some margin of error in
practice. The material must be biologically acceptable.
As the literature says the oldest established and most widely used
types of dental cements.
1. Zinc phosphate and
2. Zinc oxide-Eugenol were developed in the late nineteenth century
and early twentieth century. Although they have undergone
considerable technical improvement, in principle they have
remained almost unchanged for 50 years. most clinical techniques
and evaluation criteria are based on long experience with these
materials significant research on new cements has been carried out
only in the last 25 years.
The advent of acrylic resins led to the development of fine grained
cold curing polymethyl methacrylate cements in the Mid 1950’s. Such
materials did not become popular for routine cementation. More recently,
cements based on the BIS-GMA monomer of Bowen have become
available in powder to liquid (filler monomer) form and two paste forms.
All these materials set by polymerization mechanisms, so the handling
2

3. qualities are different and generally less satisfactory than conventional
cements. Another problem with resin cements that has limited their use is
the potential tissue reaction to residual monomers in the set material.
None of the foregoing cements shows significant adhesion to clean
enamel and dentin. The need for good wetting and bonding and low
toxicity led to the development of cements based on the reaction of
polymerize organic acids and metal ions in the mid 1960s by Smith. The
early carboxylate (or polycarboxylate) cements were based on zinc oxide
and an aqueous solution of polyacrylic acid or its co-polymers later work
by Wilson and cowoskers resulted in the glass ionomer cements that utilize
non-leachable glasses rather than zinc oxide. Development in this area still
proceeding.
As a result of the research of the last few years there are now
available cements of four basic types, classified according to the matrix
forming species.
1. Phosphate bonded.
2. Phenolate bonded
3. Carboxylate bonded and
4. Methacrylate (resin) bonded
Within each category are several classes and this multiplicity
together with the choice of several brands of material in each class, has
lead to confusion among clinicians as to which type of cement is most
suitable to a given situation. Although there are national (ADA, ANSI,
BSI, ASA) and international (ISO, FDI) standards for cements, these are of
limited value in predicting clinical durability. Another difficulty is that
3

4. reports in the literature are often based on the testing of one or two brands
of a cement type, and the results are then assumed to apply to all such
cements. It is therefore appropriate to briefly review the characteristics of
the available cements.
III. Types of cement
1. Phosphate based cements.
a. Zinc phosphate cement: It is the oldest of the cementation agents
having a widest range of application and terms is the one that has
the longest track record. It serves as a standard by which newer
systems can be compared. It consists of powder and liquid in two
separate bottles.
Composition and chemistry: the main ingredients of the powder are:
a. Zinc oxide (90%).
b. Magnesium oxide (10%).
The ingredients of powder are sintered at temperature between
1000°C and 1400°C into a cake that is subsequently ground into five
powders. The powder particle size influences setting rate. Generally, the
smaller the particle size, the faster the set of the cement.
The liquid, contain phosphoric acid, water aluminium phosphate and
in some instances, zinc phosphate. The water content of most liquids is
33%±5%. The water controls the ionization of the acid, which in terms
influences the rate of the liquid powder (acid base) reaction.
It is obvious that because water is critical to the reaction, the
composition of the liquid should be preserved to ensure a consistent
4

5. reaction. Changes in composition and reaction rates may occur either
because of self degradation or by water evaporation from the liquid. This
means that changes in the composition can affect the reaction. Self
degradation effects are best detected as a clouding of liquid over time.
Properties: the long persistence of zinc phosphate cements in clinical
practice indicates that reasonable performance is obtained. Although the
properties are far from ideal they are usually regarded as a standard against
which to compare newer cements. The principal reasons for their
satisfactory performance under routine conditions are that they can be
easily manipulated and that they set sharply to a relatively strong mass
from a fluid consistency.
At standard luting consistency the powder to liquid ratio is 2.5 to 3.5
(g per ml). The cementing mix flows readily under pressure to a film
thickness between 20 and 40 mm, which is adequate to seat most types of
restorations as in practice the space between the restoration and the tooth
may range upto as much as 100 mm. The film thickness achieved in
specific clinical situations is a function of the rheology of the cement and
the geometry of the surface being cemented.
At the recommended powder to liquid ratio, the compressive
strength of the set zinc phosphate cement is 80+0110 MPa after 24 hours.
The strength is strongly and almost linearly dependent on powder to liquid
ratio. The tensile strength is much lower than the compressive strength, 5
to 7 MPa and the cement shows brittle characteristics.
The modulus of elasticity (stiffness) is about 13 GPa. According to
the standard method, the solubility and disintegration in distilled water
5

6. after 23 hours may range from 0.04% to 3.3%, for inferior material the
standard limit is 0.2%.
The comparative evaluation a cement solubility under clinical
conditions has shown significant loss, but conflicting results. Dissolution
contributes to marginal leakage around restorations and bacterial
penetration.
At room temperature (21 to 27°C) the working time for most brands
at luting consistency is 3 to 6 minutes the setting time is 5 to 14 achieved
by use of a cold (frozen) mixing slab, which permits upto an approximately
50% increase in the amount of powder, improving both strength and
resistance to dissolution. The cement has been found to contract about
0.5% linear giving rise to slits at the tooth cement and cement restoration
interface.
Retention: Setting of the zinc phosphate cement does not involve any
reaction with surrounding hard tissues or other restorative materials.
Therefore primary bonding occurs by mechanical interlocking at interfaces
and not by chemical interactions.
Prologic effects: the freshly mixed zinc phosphate is highly acidic with a
pH of 1.6 two minutes after mixing. Even after setting at 1 hr the pH may
still be below 4. after 24 hrs the pH reaches 6 to 7.
One material that has a low acid content and incorporates calcium
hydroxide has little effect on the pulp when used as a lining. Very thin
mixes will also lead to etching of the enamel. The etching may assist
mechanical interlocking to the adjacent substrates.
6

7. Advantages and disadvantages:
The main advantages of the zinc phosphate cements are that they
can be mixed easily and that they set sharply to a relatively strong mass
from a fluid consistency. unless the mix is extremely thin (for instance,
with a very low powder to liquid ratio) the set cement has a strength that is
adequate for clinical service, so their manipulation is less critical than with
other cements.
However, then distinct disadvantages include pulp irritation, lack of
antibacterial action, brittleness, lack of adhesion, and solubility in acid
fluids.
Modified zinc phosphate cements
Fluoridated cements: Some phosphate cements contains fluoride in the
form of stannous or other fluorides.
- Which have low strength and higher solubility rate.
- They used in orthodontic bracket cementation.
Copper cements: they come improves oxide (red) or cupric oxide (oxides)
or copper salts added to the zinc oxide powder.
- They have germicidal action.
Silicophosphate cements: These materials that are combination of zinc
phosphate and silicate cements have been available for many years.
The principal applications have been for the cementation of fixed
restorations especially porcelain, because of their translucence.
7

8. - They are germicidal as they contain little amount of mercury
or silver compounds.
Composition and setting: the powder in these materials consists of a
combination of silicate glass and zinc oxide, the silicate glass contains 13
to 25% fluoride. The liquid is similar to silicate liquids containing about
50% H3PO4; 4% Zn and 2% Al the set cement seems likely to consist of
unreacted and zinc oxide particles bonded together by an alumino
phosphate gel containing zinc, Ca, Aluminium and Flouride ions.
Properties: Powder to liquid ratio is 2.1 to 3.2g per ml.
 Flow properties of the mix are not as good as per Zinc Phosphate
contents, leading to a higher film thickness in practice.
 Compressive strength to set cement is 135 to 175 Mpa better than
Zinc phosphate.
 Tensile strength is 7 Mpa.
 These materials appear to be tougher and more abrasion resistant
from phosphate cements.
 Solubility in distilled water after 7 days is higher than for Zinc
phosphate cements, but under clinical conditions it is less so.
Biological effects: The set cement is much more translucent than the
opaque Zinc phosphate. Thus it has been used for the cementation of
porcelain restorations.
8

9.  Because of the acidity of the mix and the prolonged low
PH (410.5) after setting. Hence pulp protection is necessary on all
vital reduced teeth.
Advantages and Disadvantages: The silicophosphate cements have better
strength and toughness properties than the Zinc phospate cements, show
considerable flouride release, transulcence and, under clinical conditions,
lower solubility and better bording.
Disadvantages include less satisfactory mixing and rheologic properties,
leading to higher film thickness in practice and greater potential for pupal
irritation. They are but suited to cementation of orthodontic bands and
restorations on non vital teeth. Inauguration
PHENOLATE – BASED CEMENTS
There are three main types of cements under this classification:
1) The simple Zinc oxide – Eugenol.
2) Reinforced Zinc oxide – Eugenol.
3) EBA cements.
1) Zinc oxide – Eugenol cement:
Compositon and setting: The basic combination of Zinc oxide and
Eugenol finds it principal applications in the temperory filling of teeth, and
as a cavity lining in deep davities.
 The powder is Zinc oxide, with additives such as silica,
may be present. Upto 1% Zinc acitate, chloride, sulfate, or other salts
may be present in accelerate the setting.
9

10.  The liquid is purified Eugenol in some cases, oil of cloves
(85% Eugenol).
 It may contain about 1% of acetic acid or alcohol to
accelerate setting together with small amounts of water.
 The cement sits by a chelation reaction between two basic
components involving the formation of Zinc eugenolate. However, the
reaction is reversible, the Zinc Eugenolate being easily hydrolyzed by
moisture Eugenol and Zinc hydroxide. Thus the cement disintegrates
rapidly when exposed to oral conditions.
Properties: The material is easy to mix but requires a long spatulation
time at least 90 seconds.
 Because of work nature of binding agent, the compressive
strength is low, ranging from 7 Mpa (luting consistency) to 40 Mpa
(filling consistencyA).
 Tensile strength is much lower.
 The solubility of the set cement in distilled water is high
when exposed directly to oral conditions, the material maintains good
sealing characteristics despite a volumetric shrinkage of 0.9% and a
thermal expansion of 35x10-6
/degree C.
Biologic effects: The presence of Eugenol in the set cement under clinical
conditions appears to lead to an anodyne and abundant effect on the pulp in
deep cavities.
10

11.  The seating capacity and antibacterial action appears to
facilitate pulpal healing.
Reinforced Zinc oxide – Eugenol cements
Composition and setting: These materials contain 10 to 40% of finely
divided natural or synthetic resins added to or coated on to the powder
particles. Additional accelerator (Zinc acetate, chloride, or acetic acid)
may be present as well as antimicrobial agents such as thymol or 8-
hydroxyghinoline.
Properties:
• Working time is about 5 mts. and setting 7 to 9 mts. Lly to
Zinc phosphate.
• Compressive strength – 35 to 55 mpa and
• Tensile strength – 4 MPa and
• Modulus of elasticity is – 2 to 3000 Gpa.
• The mechanical properties are reduced by impression in
water, resulting in loss of Eugenol. This tendency seems less
pronounced with the polymer – reinforced materials.
Biological Effects: There may be irritation to connective tissue.
Advantages and disadvantages:
Advantages – Main advantage is the minimum reaction to the pulp.
• Good sealing properties
11

12. • The strength is adequate as a lining material and for luting
single restorations and retains with good retention form.
Disadvantages - Main is hydrolic break down when exposed to oral fluids.
• The inflammatory reaction is soft tissues and potential
allergic response.
EBA and other chelate cements
 In order to further improve on the basic Zinc-oxide
 Eugenol system. Many workers have investigated
mixtues of zinc and other oxides with other liquid chelating agents.
Composition and setting: The Zinc oxide contains 20 to 30%
Aluminium oxide or other mineral fillers; polymeric reinforcing agents,
such as polymethyl methacrycate.
- The liquid consists of 50 to 60% EBA with the reminder
Eugenol.
In order to obtain optimal properties it is important to use as high a
powder – liquid ratio as possible i.e., 3.5g per ml.
Properties:
 The working and setting times range between 7 and 15 mts. The
film thickness is in the range 40-70mm.
 Compressive strength is 50-70 Mpa.
 Tensile strength is 6 to 7 Mpa.
12

13.  Modulus of elasticity – 5 Gpa.
 The EBA cements show viscoelastic properties with very
low strength, and large plastic deformation at slow (0.1 mm/ mint) rates
of deformation and at mouth temperature (37°C). This says its retention
values for crown is low than Zinc phosphate cements.
 When exposed to moisture, greater oral dissolution occurs
than for other cements.
Advantages and Disadvantages:
Advantages:
• The principal advantages of the EBA cements are their easy
mixing.
• Long working time.
• Good flow and low irritation to the pulp.
Disadvantages:
- Main is critical proportioning.
- Hydrolic break down in oral fluids.
- Liability to plastic deformation.
- Poorer retention than Zinc phospate cement.
POLYCARBOXYLATE – BASED CEMENTS
Zinc polycarboxylate cements: These cements were developed in late
1960’s as an adhesive dental cement in the search for a material that would
combine the strength properties of the phosphate system in the Biologic
13

14. acceptability of Zinc oxide Eugenol materials. These materials have gone
through several stages of development since their acception and progress is
continuing.
Compositon and chemistry: The polycarboxylate cements are liquid
systems.
 The liquid is an aqueous solution of polyacrylic acid or a
copolymer of acrylic acid with other unsaturated carboxylic acids, such
as itaconic acid.
 The molecular net of the polyacids ranges from 30,00 to
50,000. The acid concentration may vary to some degree from one
cement to another but usually is about 40%.
 The composition and manufacturing procedure for the
powder are similar to those of Zinc phosphate cement. The powders
mainly zinc oxide with some Magnesium oxide. Stannic oxide may be
substituted for magnesium oxide. Other oxides, such as bismuth and
Aluminium, can be added. The powder may also contain small
quantities of stannous flourides, which modify setting time and enhance
manipulative properties. It is an important additive because it increases
strength. However, the flouride released from this cement is only a
fraction (15% to 70%) of the amount released from Silicophosphate and
glass ionomer cements.
 The setting reaction of this cement involves particle
surface dissolution by the acid that releases zinc magnesium, and tin
ions, which bind to the polymer chain via the carboxyl groups, as given
below. These ions react with carboxyl groups, as adjacent polyacid
14

15. 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 disposed. The microstructure resembles that of
Zinc phosphate cement in appearance.
STRUCTURE OF THE CHEMICAL
The role of carboxylate functional groups in polycarboxylate cements:
A  Yielding matrix through cross linking by zinc ions.
B  Bonding to tooth structure through Calcium hydroxide).
- 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.
Bonding to tooth structure: The outstanding characteristics of this cement
are that it bonds chemically to the tooth structure. The mechanism is not
clear but as shown in above diagrams, the polyacrylic acid is believed to
react via the carboxyl groups with calcium of Hydroxyapitite. (In reference
to GIC, the inorganic component and the homogeneity of enamel are
greater than those of dentin. Thus, the bond strength to enamel is greater
than that to dentin.
Properties: For luting consistency the recommended powder to liquid ratio
is 1.5 1(2t/wt). About the film thickness, the freshly mixed mix is in
spatulation and seating of a restoration, it exhibits shear thinking. Thus,
contrary to the subjective impression that the correct mix for a Zinc
15

16. polycarbohydrate cement is much thicker than a luting zinc phosphate mix.
Under presssure mix tends to thicken more quickly than the zinc
polycarboxylate mix.
 One of the most common errors made with
polycarboxylate cements is to make a mix that appears to be a fluid as a
zinc phospate mix; this will result in the use of low powder-to-liquid
ratio with consequent poor properties in the cement. Measuring devices
for these material will ensure correct proportions.
 The working time is 2.5 to 3.5 minutes at room
temperature and the setting time is 6 to 9 mts at 37C, the water mix
materials tending to give slightly longer setting times. As with other
cements, working time can be substantially increased by mixing the
material on a cold slab and by refrigerating the powder. The liquid
should not be chilled as this encourages gelation due to hydrogen
bonding.
 At cement consistency the compressive strength from 55
to 85 MPa.
 Tensile strength 8 to 12 MPa.
In general these cements have somewhat lower compressive
strengths than zinc phosphate cements but are significantly stronger in
tension. The cement gains strength rapidly after the initial setting period;
the strength at 1 hr. is about 80% of the 24 hr. value. These data indicate a
slow continuance of the setting reaction tending towards greater rigidity
and more brittle behaviour. However, the cement remains much less brittle
16

17. and is tougher than silicate, since phosphate, or glass ionomer cement,
through less so than a resin cement.
The solubility of the present day cements in distilled water, when
determined by a specification weight loss method, ranges from less than
0.1% to 0.6%. The latter high value relates particularly to cements that
contain stannous fluoride. Effective fluoride release can be obtained
without substantial effects on the mechanical properties of the cement.
Significant fluoride intake by neighbouring enamel occurs. As with zinc
phosphate cements, the solubility is much higher in organic acid solutions,
especially at lower PH and if the acid has chelating powers.
Few recent clinical studies of solubility gave conflicting results, two
studies conducted by Mitchem and Osborne in 1978 respectively showing
lower results than zinc phosphate and the other the reverse. Both studies
agreed in finding the zinc silicophosphate both the least loss of the cement
tested. In vivo evaluation of marginal leakage showed similar results for
the two types of cement and whose results for an EBA alumina cement.
Thus these all suggests that polycarboxylate cement has adequate clinic
performance.
The polycarboxylate cements display good adhesion to enamel, and
to a lesser extend, to dentin as well as to the various alloys. Adequate
fluidity of the mix and sufficient available carboxyl groups are necessary
for interfacial interaction as well as a surface free of contaminants and void
defects. Bonding to both or alloy surface is reduced if contaminated with
saliva.
Biologic effects: The effect of Zinc polycarboxylate cements on soft and
calcified tissues found to be molding Macrons investigators like Smita
17

18. D.C. in 1971. The effect on the pulp is less than Zinc oxide Eugenol. The
general biocompatibility of these materials seems excellent this appears to
be primarily due to the low intrinsic toxicity the mild effect on the pulp and
other tissues is also due to the rapid rise of the PH of the cement towards
neutrality; localization of the polyacrylic acid and limitation diffusion try
its molecular size and acid ion bonding to dentinal fluid ca and proteins;
and the minimal movement of fluid in the dential tubules in response to the
cement the presence of stannous fluoride does not appear to affect the mild
respnse.
-It gives anticariogenic properties in fluorides containing cements.
Advantages and Disadvantages:
• The main advantages of these materials are the low irritancy
adhesion to tooth substance and alloys.
• Easy manipulation and strength, solubility and film thickness
properties comparable to those of zinc phosphate cements.
• The need for accurate proportioning for optimal properties and thus
more critical manipulation.
• The lower compressive strength and greater viscoelasticity from
zinc phosphate cements, the short working time of some materials and
the need for clean surfaces to utilize the adhesion potential.
Removal of excess cement
During setting, the polycarboxylate cement passes through a
rubbery stage that makes the removal of the excess cement quite difficult.
18

19. The excess cement that has extruded beyond the margins of the casting
should not be removed while the cement is in this stage, because there is
danger that some of the cement may be pulled out from beneath the
margins, leaving a void. The excess should not be removed until the
cement becomes hard. The outer surface of the prosthesis must be coated
carefully with a separating medium such as petroleum jelly to prevent
excess cement from adhering.
- Care should be taken not to allow the medium to touch the
margin of the prosthesis. Another approach is to start removing excess
cement as soon as seating is completed. The goal of these two method
is to avoid removing the excess during th rubbery stage.
GLASS IONOMER CEMENT:
Type I GIC is designed for cementation of castings.
Compositon and setting: These materials were formulated by bringing
together the silicate and poly acrylate system. Originally the use of silicate
glasses in the zinc polycarboxylate cements was envisaged that the
available material were insufficiently reactive. Wilson and Kent and their
coworkers in 1975 developed glasses that were ion – leachable by aqueous
polyacrylic acid and its acid copolymers. The powder in these materials is
a fine ground calcium aluminium fluoro-silicate glass with a particle sized
of around 40 cm for the filling materials and less than 25cm for the luting
materials. The liquid is a 50% aqueous solution of a polyacrylic – Itaconic
acid or other poly carboxylic acid copolymer containing about 5% tartaric
acid. On mixing the acids react with the glass leaching ca and aluminium
ions from the surface which cross-link the polyacid molecules into a set. A
recent material has the polyacid contained in the powder and the liquid is a
19

20. solution of the tartaric acid. This contributes to easier mixing and better
stability.
Properties: The powder to liquid ratio for luting is about 1:3:1 for the
conventional types of glass ionomes cement. Best results on a chilled seas.
The slow ratio of hardening initially during formation of the calcium
polysalt before al cross linking becomes effective means that the cement is
sensitive to moisture and more soluble during the early stages of its
hardening. The gel can also craze if allowed to dry out. Thus, it is essential
to protect exposed margins until sufficient strength has developed
• The setting time is 8 to 9 mts. somewhat shorter than with zinc
phosphate cements.
• The film thickness less than 30 cm was also comparable and was
adequate to seat castings satisfactorily.
• Over 24 hours the compressive strength increased to 900 to 1400
Mpa.
• Tensile strength to 60 to 80 Mpa.
- The modulus of elasticity was about 7 Mpa.
A glass ionomer cement showed superior retention of gold inlays
and onlays compared with a phosphate and a silicophospate cement.
- The solubility of the cements in water was about 1% and this
was increased in artificial saliva and lactic acid.
20

21. Good resistance to dissolution was observed under clinical
conditions. However, the initial slow set and moisture sensitivity may
contribute to leakage.
Varnish protection is desirable.
These cements have potential for adhesion to enamel, dentin and
alloys in a similar manner to the polycarboxylate. In vitro the adhesion is
variable and affected by surface conditions. Slight and variable marginal
leakage in tests of cemented restorations has been reported.
Biologic effects: Evidence fro in vitro testing and clinical experience with
the restorative form of the glass ionomer cements suggest the tissue
response would be similar to the zinc polycarboxylate cements. However,
there is only limited data on the luting cements. Paterson and Watts
observed pulp necrosis in rat molars after application to exposures.
However parmajer et. al. found little pulp irritation from one commercial
cement in cavities in monkey teeth after 3 months. Likewise Reisbick in
1980, in a clinical study, found in slight sensitivity on cementing but no
evidence of hypersensitivity after 6 months. However, some cases o
postoperative sensitivity have been reported and this may be due to
mismanipulation and marginal leakage of bacteria.
Advantages and disadvantages:
Advantages: The glass ionomer cement materials include easy mixing,
high strength and stiffness, leachable fluoride, good resistance to acid
dissolution, and potential adhesive characteristics.
21

22. Disadvantages: It includes initial slow setting and moisture sensitivity,
variable adhesive characteristics, radiolucency, and possible pulp
sensitivity.
Precautions should be taken to protect the pulp when cementing
restorations with glass ionomer cements. The priologic considerations take
precedence over other matters, such as the potential for adhesion that
ensures a strong bond to tooth structure. The smear layer on the cut surface
of the cavity preparation should not be removed but should be left intact to
act as a barrier to the penetration of the tubules by the acid component of
the cement. All deep areas of the preparation should be protected by a thin
layer of a hard setting calcium hydroxide cement.
Methacrylate (Resin) based cements:
A variety of Resin-based comments have now become available
because of the development of the direct filling resin with improved
properties, the acid etch technique for attaching resins to enamel, and
molecules with a potential to bond to dentin conditioned with organic or
inorganic acid.
Acrylic cements:
For many years powder to liquid cold curing acrylic cements have
been available. These materials have been used for the cementation of
restorations, of temporary crowns, and also as core materials. The powder
in these materials is a finely divided methyl-methacrylate polymer or
copolymer containing benzoyl peroxide as initiations. Mineral filler and
pigments may also be present. The liquid is a methyl methacrylate
monomer containing an amine accelerator. The material sits by
22

23. polymerization of the monomer, which concurrently dissolves and softens
the polymer particles. The set mass consists of the new polymer matrix
uniting the undissolved but swollen original larger polymer beads or
particles.
These cements are stronger and less soluble than other cements but
display low rigidity and visco-elastic properties. They have no effective
bond to tooth structure in the presence of moisture and tins permit marginal
leakage although they may show better bonding than other cements to resin
facings and polycarbonate crowns. Pulp reaction on vital dentin from
monomer in the unset material, and residual monomer in the set material
are biologic concerns. Other problems include the short working time and
the difficulty in removing excess materials from margins.
Bis-GMA type cements:
The materials of more recent development are based on the
BISGMA system and thus are combinations of an aromatic dimethacrylate
with other monomers. Such materials have been supplied as two viscous
liquid or two pastes. The material that has been widest explanation and
investigation is a powder to liquid combination.
The powder is a finely divided borosilicate glass of average particle
size of 15mm. The particles are silam treated to improve bonding and
contain an organic peroxide initiator. The liquid is based on the reaction
product of the diglycidyl either of bis-phenol A and methacrylic acid.
Which is diluted with a low viscosity monomer such as ethylene glycol
demethacrylate. An amine Accelerators is also present. On mixing the
polymerization of the monomer mixture occurs, leading to a highly cross
linked composite resin structure. The material is easily mixed to a fluid
23

24. consistency and is used in conjunction with an etching solution of 50%
citric acid to clean the tooth surface and promote adaptation and bonding.
The mix rapidly increases in viscosity and working time is short.
When set, the material has higher bending and compressive
strengths than other cements. The modulus of elasticity was found to be
less than for zinc phosphate, but the plastic strain at fracture and toughness
much higher. Sections of cemented casting, revealed spaces at the tooth
resin interfaces, presumably due to polymerization contraction. Although
bonding was improved by citric acid treatment, it appeared to be
attributable to penetration of resin into the tubules, a phenomenon that has
also been observed by Vongiduklakis and Smith.
Although the strength and resistance to dissolution of this type of
material is superior to any other type of cement, these biologic and
practical questions common to other types of resin cement have limited its
use on vital teeth. Poorer retention for full crowns than for other types of
cement was observed by Chan et al in 1975. These problems also include
short working time, difficulty in seating castings and difficulty in removing
excess material. They may be best suited to long term temporary
concentration of a loose fitting casting when restoration care is delayed.
Factors affecting the clinical performance of cements:
The correct seating of a restoration is important to occlusal function,
esthetics and durability of the cement, especially in relation to securing the
thinnest set cement time between restoration and tooth.
Another factor that influence the material situation is the taper and
marginal geometry of the restoration.
24

25. 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. As shown is Fig 1
typical prepared surfaces on a microscopic scale are rough that is there are
peats and valleys. When two surfaces are placed against each other, there
are only point contacts along the peaks (Fig2). 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 purpose of a
cement is to fill this space completely. On 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 surfaces
and set to a solid from within a few minutes (Fig 3). The solid matter not
only seals the space but also retains the prosthesis. If the third material is
not fluid enough or is incompatible with the surfaces, voids can develop
around deep, narrow valleys (Fig 4) and undermine the effectiveness of the
cement.
Figure 1 Figure 2
Figure 3 Figure 4
Procedure for cementation of prosthesis: to be effective cement must be
fluid and be able to flow into continuous film of 25mm thick or less
25

26. without fragmentation. The procedure consists of placing the cements on
the internal surface of the prosthesis and extending slightly over the
margin, seating it on the preparation, and removing the excess cement at an
appropriate time. Cementation of a single crown as an example is described
with (Fig 5a).
Placement of cement: The cement paste should coat the entire inner
surface of the crown and extend slightly beyond the margin. It should fill
about half of the interior crown volume (Fig 5b). the clinician should make
certain that the occlusal aspect of the tooth preparation is free of voids to
ensure that there is no air entrapment in the critical area during the early
age of the seating.
Seating: The important factors in seating the cemented restoration include
the rheology of the cement, the working time, the final film thickness and
the geometry of the gap through which the excess cement.
They may be suited to longterm temporary cementation of a loose
filling casting when restoration care is delayed must escape. The cement
should have a fluid consistency and along working time. The mix should
also wet tooth and restriction surface readily. In these respects, fluid
hydrophilic materials appear desirable. The flow or rheologic
characteristics of the cement mix are a function of the pressure and gap
size. The correct mixes of zinc phosphate, polycarboxylate, and EBA
cements flow on to low film thickness with moderate pressure under
practical conditions.
The data of Hoard et al using a model full crown die system showed
that the most fluid cement (zinc oxide eugenol) generated least hydraulic
26

27. pressures duirng seating followed by polycarboxylate with zinc phosphate
exhibiting greatest peak and residual hydraulic pressure.
Both Eames and associates and Hembree and Coworkers have
confirmed that venting is a satisfactory method of achieving minimal film
thickness under crowns. In addition to venting, provision of a 30mm relief
space or etching away the interior of the casting have been suggested.
Eames et al found better seating of full crowns using 10 and 20°
convergence angles and recommended the most satisfactory technique for
allowing escape of cement to be a die relief method.
Moderate finger pressure should be used to displace excess cement
and to seat the crown or other prosthesis on the preparation. An
alternatively method is to use a vibrational instrument to facilitate the
seating of the prosthesis without creating excess pressure. After the
marginal gap area is evaluated for closure with an explorer the patient may
be asked to complete the seating by biting on a soft piece of wood which is
static method and a round stick rolling on the crown which is called as
dynamic method. During this stage, the last increment of excess cement is
expelled through the space between the prosthesis and the tooth. As the
prosthesis reaches its final position on the preparation. The space for
expelling the excess cement becomes smaller, making the seating more
difficult (Fig 5c). variable that can facilitate scaling include using a cement
of lower viscosity, increasing the taper and decreasing the height of the
crown preparation (Fig 5d) vibration, and introducing escape vents on the
occlusal aspect of the prosthesis (Fig 5e), increasing the degree of taper can
compromise retention, monomer the escape vents can be filled with gold
foil or cast gold plugs. If the occlusal surface contacts the axial wall of the
tooth during insertion, air pockets may be introduced (Fig 5f).
27

28. Removal of Excess cement:
The excess cement aluminates around the marginal area at the
completion of seating. Its removal depends on the properties of the cement
used. If the cement sets to a brittle state and does not adhere to the
surrounding surfaces, the tooth and the prosthesis, it is best removed after it
sets. This applies to zinc phosphate, silicophasphate, and ZoE cements. For
glass ionomer cements, polycarboxylate cements and resin based cements
that are potentially capable of adhering both chemically and physically to
the surrounding surfaces the protocol of excess cement removal varies.
One can coat the surrounding surface with a separating medium such as
petroleum jelly, thereby inhibiting the materials adherence to the surfaces,
and remove the excess after the cement sets. Another technique involves
the removal of excess cement as soon as the seating is completed, thus
preventing the material from adhering to the adjacent surfaces.
Post cementation
Aqueous based cements continue to nature over time well after they
have passed the defined setting time. If they are allowed to nature is 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 resistance to dissolution. It is
recommended that coats of varnish or a bonding agent should be placed
around the margin before the patient is discharged.
Mechanism of retention:
A prosthesis can be retained by mechanical or chemical means or a
combination of mechanical 6 mechanical factors.
28

29. As we know the retention of crowns, bridges is a function not only
of the mechanical properties of the luting agent but also the design of the
tooth preparation and the restoration. There factors influence the stress
distribution within the interposed cement layer, the efficiency of bonding
of the cement to both of the surfaces being joined, and the durability of the
cement that include its long-term resistance to mechanical breakdown and
dissolution.
Analysis of the stress distribution in the restored tooth indicate that
compressive shear and tensile forces are all generated in the cement layer.
Craig and Farah recommended that a cement with a high tensile
strength should be used for the cementation of crowns as shear stresses in
the marginal area can exceed the strength of low strength cements. For the
support of restorations, the tensile strength was again found to be
important, but the most important property was the elastic modulus of the
cements (stiffness). As previously noted, except for the resin cements, zinc
polycarboxylates tend to display the greatest tensile strength, but have
lower modulus and compressive strength than zinc phosphate cements. The
silicophosphate and glass ionomer cements tend to be superior in the latter
property to both these cements, but are better materials of lower tensile
strength, the EBA and resistance to plastic deformation.
Theoretically, chemical bonds can be resist interfacial separation
and thus improve retention. Aqueous cement based on polyacrylic acids to
provide chemical bonding through the use of acrylic acids. Resin based
cements using some specialty functional groups also have exhibited
chemical bonding. Cavity varnish reduces retention for all cements.
Improved mechanical and adhesives retention is obtained for all cements
29

30. by careful clearing of the preparation to remove residual temporary cement
and all residues including cutting debris. Such cleansing may include
mechanical treatment (premier slurry) and chemical agents such as
detergent cleaners and EDTA. Such agents have yet to be fully optimized,
however, similarly the interior of restorations should be cleansed by sand
blasting or etching.
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 with in 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 (Fig 7). This space can be susceptible to
plaque accumulation and recurrent caries; therefore, the margin should be
protected with a coating (if possible) to allow continues setting of the
cement. There are two basic modes of failure associated with cements.
Cohesive fracture of the cement (Fig 8a) and separation along the interface
(Fig 8 b). 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.
To summuries the factors of retention of fixed prosthesis.
30

31. 1. The film thickness beneath the prosthesis
should be be thin. It is believed that a thinner film has fewer internal
flows compared with a thicken one.
2. The cement should have high strength values.
3. The dimensional changes occurring in the
cement during setting should be minimized, hence isolate the cement
immediately after removal of the excess.
4. 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
further often occurs along the interfaces. If chemical bonding is involved,
the failure often occurs cohesively through the cement itself. The
prosthesis become loose only when the cement fracturer or dissolves.
Fig: Failure modes of the interface, A) Clearage through the cement
layer. This is unlikely because of the dimension of the cement involved. B)
The most likely failure that occurs at the cement prosthesis and cement
tooth interfaces. Remnants of the cement often remain on the opposing
surfaces.
31

32. Summary
It is evident that none of the materials available to use at present is
free from deficiencies in the required clinical characteristics such as
biocompatibility, ease of manipulation, satisfactory sealing and retentive
properties, and long term stability. Thus, a proportion of clinical failure is
inevitable. This incidence can minimized by proper selection and
manipulation of the cement as previously outlined, however, the two
principal modes of failure for the cement lute (namely, dissolution,
including erosion and disintegration, and mechanical breakdown) are both
dependent on the clinical situation as well as on the intrinsic properties of
the cement. Factors within the control of the clinician, such as the desing of
the preparation, the fit of the restoration the manipulation of the cement,
the seating of the restoration and the finishing of the margins are some of
the important determinants of success.
A more rational approach to cement selection manipulation and
cementation procedures can give us improved postoperative results and
greater average longevity of the restoration. However the development of
new and improved cement systems with higher strength and stiffness and
lower oral dissolution is required. Adhesive and anticariogenic properties
are also desirable. More research is needed on cement performance in
clinical practice for both simple and complex restorative procedure to
develop a predicture correlation between laboratory measurements and
clinical performance. Improved laboratory and clinical characterization of
cements should lead us to the goal of an adhesive biocompatible cement
that will last as long as the restoration.
32

33. CONTENTS
1. Introduction
2. Basic Consideration
3. Types of cement
4. Factors affecting the clinical performance of cements
a. Characteristics of abutment prosthesis interface
b. Procedure for concentration of prosthesis
c. Placement of cement
d. Seating
e. Removal of excess cement
f. Post cementation
g. Mechanism of retention
h. Dislodgement of prosthesis
5. Summary
33