DENTAL MATERIALS Dr Waseem Mushtaha Al Azhar University Gaza Lama El Banna

1. Dental Cements for Bonding
Application
Dr. Waseem Bahjat Mushtaha
Specialized in prosthodontics

2. Types of cements
Zinc phosphate cement
Zinc silicophosphate cement
Zinc polycarboxylate cement
Glass Ionomer cement
Zinc Oxide- Eugenol cement
Resin-based cement

3. Zinc phosphate cement
General description:
Zinc phosphate is the oldest of the
cementation agents and thus is the one that
has the longest track record. It consists of
powder and liquid in two separate bottles.

4. Zinc phosphate cement

6. Composition
1(Powder:
Zinc oxide (90%(
Magnesium oxide (10%(.
The ingredients of the powder are sintered at
temperatures between 1000C and 1400 into a cake
that is subsequently ground into fine powders. The
powder particle size influences setting rate.
Generally, the smaller the particles size, the faster
the set of the cement.

7. b) Liquids:
Phosphoric acid, water, aluminum phosphate, and in
some instances, zinc phosphate. The water content
of most liquids is 33% ± 5%
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 the zinc and
yields a zinc aluminophosphate cement is a core
structure consisting primarily of unreacted zinc
oxide particles embedded in a cohesive amorphous
matrix of zinc aluminophosphate.

8. Factors Influencing Working and
Setting Time
1(Powder : liquid ratio:
Working and setting times can be increased by
reducing the powder: liquid (P:L) ratio. This
procedure, however, is not acceptable means of
extending setting time because it impairs the
physical properties and results in a lower initial
PH of the cement. The reduction in compressive
strength, along with the decrease in the P:L ratio.
The initial PH of the mixture also decreases with
increasing P:L ratio.

9. 2(Rate of powder incorporation:
Introduction of small quantity of the 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. Therefore, it is the
recommended procedure for zinc phosphate
cement.

10. 3(Spatulation time:
Operators who prolong the spatulation time
are effectively destroying the matrix that
was forming. Fragmentation of the matrix
means extra time is needed to rebuild the
bulk of the matrix.

11. 4(Temperature of mixing slab:
The most effecting method of controlling the
working and setting times is to regulate the
temperature of the mixing slab. Cooling the
slab markedly retards the chemical reaction
between the powder and the liquid so that
matrix formation is retarded. This permits
incorporation of the optimum amount of
powder into the liquid without the mix
developing an unduly high viscosity.

12. Physical and Biological properties
Two physical properties of the cement that are
relevant to the retention of fixed prostheses
are the mechanical properties and the
solubilities. The prosthesis can become
dislodged if the underlying cement is
stressed beyond its strength. High solubility
can induce loss of the cement needed for
retention and may create plaque retention
sites.

13. Zinc phosphate cements, when properly
manipulated, exhibit a compressive strength
of (103.5MPa) and a diametral tensile
strength of (5.5MPa) . Zinc phosphate
cement has a modulus of elasticity
approximately (13GPa). 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.

14. The recommended P:L ratio for this zinc
phosphate cement is about 1.4g to 0.5 ml.
the increase in strength attained by addition
of powder in excess of the recommended
amount is modest as compared with the
reduction incurred by decreasing the
amount of powder in the mix. A reduction
in P:L 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.

15. Zinc phosphate cements show relatively low
solubility in water when they are tested in
accordance with ADA specification.
Retention:
Setting of the zinc phosphate cement does not
involve any reaction with surrounding hard
tissue or other restorative materials.
Therefore, primary bonding occurs by
mechanical interlocking at interface and not
by chemical interaction.

16. Biologic properties
As might be expected from the presence of the
phosphoric acid, the acidity of the cement is quite
high at the time when a prosthesis is placed on a
prepared tooth. Two minutes after the start of the
mixing, the PH of zinc phosphate cement is
approximately 2. The PH then increases rapidly
but still is only about 5.5 at 24 hours. The PH is
lower and remains lower for a longer period when
thin mixes are employed.

17. Zinc phosphate cement probably occurs
during the first few hours after insertion.
However, studies of zinc phosphate cements
prepared with liquids containing radioactive
phosphoric acid indicate that in some teeth
the acid from the cement can penetrate a
dentin thickness as great as 1.5 mm. Thus,
if the underlying dentin is not protected
against the infiltration of acid via the
dentinal tubules, pulpal injury may occur.

18. Manipulation
1(It is probably not necessary to use
measuring device for proportioning the
powder and liquid, because the desired
consistency may vary to some degree with
the clinical situation. However , the
maximum amount of powder possible for
the operation and should be used to insure
minimum solubility and maximum strength.

19. 2(A cool mixing slab should be employed.
The cool slab prolongs the working and the
setting times and permits the operator to
incorporate the maximum amount of the
powder before the matrix formation
proceeds to the point at which the mixture
stiffens. The liquid should not be dispensed
onto the slab until mixing is to be initiated,
because water will be lost to the air by
evaporation.

20. 3(Mixing is initiated by addition of a small amount of
powder. Small quantities are incorporated initially with
brisk spatulation. A considerable area of the mixing slab
should be used. A good rule to follow is to spatulate each
increment for 15 seconds before adding another increment.
The mixing time is not unduly critical. Completion of the
mix usually requires approximately 1 minute and 30
seconds. As stated previously, the appropriate consistency
varies according to the purpose for which the cement is to
be used. However, the desired consistency is always
attained by adding more powder and never by allowing a
thin mix to stiffen. For a fixed partial denture, additional
time required to apply the cement. Therefore, a slightly
decreased viscosity should be used.

21. 4(The casting should be seated immediately with a
vibratory action if possible, before matrix
formation occurs. After the casting has been
seated, it should be held under pressure until the
cement sets to minimize the air spaces. The field
of operation should be kept dry during the entire
procedure.
5(Excessive cement can be removed after it has set.
It is recommended that a layer of varnish or other
nonpermeable coating should be applied to the
margin.
The purpose of the varnish coating is to allow the
cement more time to mature and develop an
increased resistance to dissolution in oral fluid.

22. Mixing of zinc phosphate cement

23. Zinc silicophosphate cement
Zinc silicophosphate cement (ZSP) cements consist of a
mixture of silicate glass, a small percentage of zinc oxide
powder, and phosphoric acid. The clinical indications for
this cement are similar to those of zinc phosphate cement.
Its strength is somewhat superior, the other major
difference is that set ZSP cement appears somewhat
translucent and releases fluoride by virtue of the silicate
glass. Aesthetically, it is superior to the more opaque zinc
phosphate cement for cementation of ceramic restorations.
The use of ZSP cement is declining, as practitioners have
choices of other more esthetically pleasing materials, such
as resin and glass ionomer cements.

24. Zinc polycarboxylate cement
a) Basic components: primary zinc oxide, small
quantities of magnesium oxide.
b) Acidic component: polyacrylic acid, which may
be supplied:
1(As a viscous aqueous solution of concentration
30-40%
2(As a dry powder, blended with the basic
components.
c) additionally, some products contain stannous
fluoride

25. Polycarboxylate cement

26. Manipulation
a) Polyacrylic acid solutions are more viscous
than the liquidus of other cements, which
affects the ease of mixing of the material.
b) If the cement is being used to secure
adhesion to enamel and dentin, it is
important that the tooth surface should be
clean and saliva-free

27. c) The cement should be applied to the tooth
as soon as possible after mixing, otherwise
poor adhesion may result. If a cement mix
begins to “cobweb” on manipulation, it
should be discarded. There is a continuous
increase in cement viscosity during
manipulation of the material
d) Polycarboxylate cement will adhere to
instruments, particularly those made of
stainless steel.

28. Thus:
1(It is useful to use alcohol as a release agent
for the mixing spatula.
2(Instruments should be cleaned before the
cement sets on them.
3(If cement does inadvertently adhere to a
spatula, most of it can be chipped off quite
easily. The remaining material can be
removed in boiling sodium hydroxide
solution.

29. Setting reaction
This involves the formation of a salt, zinc
polyacrylate. The set material is a cored structure
containing a considerable quantity of unreacted
zinc oxide.
Setting time:
a) This depends on the composition and method of
manufacture of the powder and liquid.
b) A faster setting time is achieve at higher
temperatures.

30. Properties
a) These cements have very little irritant
effect on the pulp.
b) Low thermal diffusivity
c) Chemical properties: these cements are
more soluble than zinc phosphate materials.
Some products may also absorb water,
which can cause the material to become soft
and gel-like.

31. d) Zinc polycarboxylate cements are almost as
strong as phosphate materials in
compressive and stronger in tension
e) The set cement is very opaque because of
the large quantity of unreacted zinc oxide
that is present.
f) Biological properties is similar to those of
zinc phosphate cement

32. Adhesion properties:
The polyacrylic acid is believed to react via
the carboxyl groups with calcium of
hydroxyapatite.

33. Zinc Oxide- Eugenol cement
Composition:
a) powder:
Zinc oxide
Magnesium oxide may be present in small
quantities, it reacts with eugenol in a similar
manner to zinc oxide
Zinc acetate in quantities up to 1% as
accelerators for the setting reaction

34. b) liquid:
Eugenol, the major constituent of oil of cloves
Olive oil, up to 15%
Sometimes acetic acid, to act as an accelerator
Manipulation:
These cements are mixed by adding the powder in
small increments to the liquid, until a thick
consistency is obtained. A powder/liquid ratio of
between 4/1 and 6/1 by weight will give a material
of the required properties, with experience, a
suitable consistency can be recognized without
weighing the materials. As a rule, a thin glass slab
and stainless steel spatula are used.

35. Zinc oxide eugenol

36. Setting reaction
a) Chemical reaction, to form a compound called zinc
eugenolate
b) Absorption of the eugenol by the zinc oxide may also
occur.
Other factors to be noted:
a) The setting reaction between pure zinc oxide and pure
eugenol will not occur in the absence of water. Thus, a
mixture of zinc oxide and eugenol, without added
accelerators, can be kept in a desiccator for several days
without undergoing much change.
b) The set materials contains both some unreacted zinc oxide
and eugenol.

37. Setting time
This depends on:
a) powder:
Particles size a fine powder will have a greater surface area
exposed to the eugenol so can react more quickly.
b) Accelerating additive
c) powder/liquid ratio: a thicker mix gives a faster setting
material.
d) Exposure to moisture on mixing or the addition of water
will accelerate the reaction.
e) Increase in temperature also causes faster setting

38. Types of Zinc Oxide- Eugenol
cement
Type 1:
ZOE cement has a PH of 7 and is
biocompatible with the pulp . The strength
of temporary cement must be low to permit
removal of the restoration without trauma to
the teeth.

39. Type 2
On is based on the addition of alumina to the
powder and ortho-ethoxybenzoic acid to the
eugenol liquid, and the second based on the
use of a polymer.
The compressive strength improved ZOE
cements but overall the mechanical
properties are inferior to those of other
cements.

40. Zinc oxide and eugenol past

41. Resin based cement
General description:
A varietly of resin-based cements have now become
available because of the development of the direct-
filling resins with improve properties, the acid-
etch technique for attaching resins to enamel, and
molecules with a potential to bond to dentin
conditioned with organic or in organic acid. Some
are designed for general used and other for
specific uses such as attachment for orthodontic
brackets or resin bonded bridge.

42. Resin based cement

43. Glass-ionomer
(Glass polyalkenoate(
1(Presentation:
Traditional form : powder and liquid.
Preproportioned capsules.
Water settable cement : the polyacrylic acid is
freeze-dried and added to the powder. In
such a case the liquid may be distilled water
or a diluted solution of tartaric acid.

44. Composition
The powder is of the same composition as that
of silicate cement
N.B Barium is added to give radiopacity.
The liquid is the same composition as that of
the polycarboxylate cement.

45. Setting reaction
The setting reaction is an acid base reaction
that undergoes the following stages on
mixing the powder with liquid:
1(Dissolution.
2(Migration
3(Reaction and precipitation

46. Dissolution
Dissolution of the surface glass particles by the acid
i.e H+ attack to release cations (Ca++ , AL+++) and
fluoride ions . Between 20% to 30% of the glass is
decomposed by the acid attack.
Migration
Migration of the surface ions Ca++, Al+++ and fluoride
ions complex into the liquid. The divalent Ca++
ions will migrate first followed by the trivalent Al+
++ ions. The sodium ions form silica gel on the
surface of the particles.

47. Reaction and precipitation:
The migrated Ca++ ions will react first with the
carboxylic group of the acid to form the cross
linked carboxylic salt gel leading to the initial set.
This is followed by the reaction of the slowly
migrate trivalent Al+++ ions. The later reaction
takes longer time and results into a stronger cross
linked cement.
The precipitation process of the carboxylic gel salts
is a continuous process and may take 24 hours.
Therefore, the setting material should be protected
against premature exposure to saliva as it affects
the setting and the surface hardness.

48. The microscopic of the set material
The set material is a composite cored structure
consisting of unreacted glass cores
surrounded by silica gel embedded in a
matrix of cross linked poly salt hydrogel of
calcium and aluminum. Aluminum
fluoracarboxylate salts constitute the main
bulk of the matrix and provides the final
strength.

49. Types of glass ionomer cement
There are three types of GIC based on their
formulations and their potential uses. These are
designated as follows:
Type I : for luting applications.
Type II : as a restorative material.
Type III : for use as a liner or based. Light-curable
versions of GIC are also available.
Type IV: fissure sealants.
Type V: orthodontic cements.
Type VI: core build up.

52. Properties
Biological properties:
a) The glass ionomer cements have a mild
effect on the pulp. In case of deep cavities,
calcium hydroxide lining must be used
under glass ionomer cement.
b) Anticariogenic effect: these cements have
the potential for inhibiting secondary caries
due to the presence of fluoride.

53. Solubility and disintegration
Glass ionomer cements are susceptible to
attack by water during its setting. Therefore,
it is necessary to coat the restoration
immediately by varnish to protect the
cement from premature exposure to the
saliva. Value of solubility and disintegration
of the glass ionomer cements in water after
24 hours immersion is about 1.5% by
weight.

54. Film thickness
The film thickness of the glass ionomer
cement is about 25 microns which is similar
to that of zinc phosphate cement.

55. Mechanical properties
Compressive strength properties:
The 24 hours compressive strength of glass ionomer
cements ranges from 90-240 MPa. A glass
ionomer cement as a filling material showed an
increase in strength from 160 to 280 MPa between
24 hours and one year. The strength of the glass
ionomer cements improves more rapidly when the
cement is protected from moisture during the first
24 hours after filling.

56. Tensile strength:
It is a brittle material. Its tensile strength ranges from
14-24 MPa.
Bond strength:
The glass ionomer cements bond chemically to tooth
structure by the reaction of carboxylic group of
polyacrlyic acid with the calcium and phosphate
content of tooth structure. The bond strength of
glass ionomer cement to tooth structure is lower
than of the polycarboxylate cements because of
the sensitivity of the glass ionomer cements to
moisture during setting. To obtain a good bond to
dentin, the surface must be treated with a
conditioner to remove any smear layer which
interfere with bonding.

57. Optical properties:
They are translucent. Therefore, they can be
used in anterior restoration in low stress-
bearing area.

58. Modifications of glass ionomer
cement
Modifications have been made in order to
improve the mechanical properties, abrasion
resistance, and optical properties of glass
ionomers.

59. Metal modified glass ionomer
Trials have been made to incorporate
amalgam alloy powder with the glass
powder in order to increase wear resistance
and flexure strength. E.g (miracle mixture)
such attempt was not successful because it
did not increase the wear resistance.

60. Metal modified glass ionomer

61. Cermet glass ionomers
Fine precious metals such as silver, gold , palladium were
sintered with the glass ionomer powder. Silver is the most
commonly used by sintering it adheres intimately to the glass
particles. The strength and wear resistance were improved
markedly.
Glass cermets can be used as:
1(Core build up restorations or as
2(A restoration for class I and II in deciduous teeth.
They have higher abrasion resistance higher flexure strength
and higher fracture toughness than the conventional glass
ionomers. Because of the metal content, they are opaque.
They have lower fluoride release than conventional glass
ionomers.

62. Ketac silver

63. Light cured glass ionomers ( resin
modified glass inomer or hybrid
ionomer(
They were first used as lining materials under
composite resin, then they gained a wide
acceptance as anterior restorative, specially class
V cavities.
These materials undergo setting reaction through two
mechanisms
a) Dual cure:
i- the conventional acid-base reaction which takes
place when the powder and liquid are mixed

64. Light cured glass ionomers

65. ii) Polymerization reaction of the resin
component i.e. free radical reaction when
light is applied to the cement.
Resin modified glass ionomer is usually
supplied as a powder and liquid, the powder
is radiopaque ion leachable fluroalumino-
silicate glass while the liquid is a modified
polyacid with methacrylate end group, the
HEMA ( Hydroxyethyl methacrylate) which
is usually added to the liquid. The acid base
reaction play a significant part of the
reaction over the curing reaction.

66. b) Triple cure:
To ensure effective polymerization of the
resin part in deep cavities, the formulated
cement will set through three reactions:
i) Conventional acid – base reaction.
ii) Light cure polymerization of the resin.
iii) Chemical cure polymerization of the resin

67. Compomer ( polyacid modified resin
compsite materials(
These are supplied as one paste system and
not as power and liquid. They are
considered as intermediate restoratives
between glass ionomers and composite
materials. They are a mechanical mixture of
glass ionomer particles and composite
materials. The light curing reaction plays a
significant part of the reaction over the
acid-base reaction. The later being minimal.

68. Light curing glass ionomers have the
following advantages over the conventional
types:
i) Better optical properties.
ii) Less sensitivity to moisture after setting
iii) Superior mechanical properties.
They are used as anterior restorative
materials.
N.B. polyacide modified resin composite
materials are more related to composite
resin rather than glass ionomer materials.

69. Cavity varnish and liners
Varnishes and liners are used for coating the
freshly out tooth structure of the prepared
cavity.
The cavity varnish: is natural gum such as
copal, rosin or a synthetic resin dissolve in
an organic solvent such as acetone,
chloroform or an ether.

70. The cavity varnish is applied to the cavity
preparation with a brush or cotton pedget,
the solvent is allowed to evapoate leaving a
thin coating resin film on the surface. This
process may be repeated two to three times
to give a uniform resin layer.
The cavity liner is a liquid in which calcium
hydroxide and some zinc oxide are
suspended in a solution of natural or
synthetic resin.

71. Varnish

72. Application
1(To seal the dentinal tubules and prevent penetration of
chemicals into the pulp.
2(To act as a temporary protection against the loss of
constituents from the surface of a filling material. Cavity
varnishes are used as a surface coat over glass ionomer
restoration.
3(To seal the dentinal tubules under amalgum restorations
and prevent penetration of metallic ions into enamel and
dentin thus reducing discoloration of the teeth, around
amalgum restorations. A film of varnish under a metallic
restoration is not an effective thermal insulator.

73. Calcium hydroxide cements
This material is supplied as two pastes in two
collapsable tubes. One paste consists of a
mixture of calcium hydroxide, zinc oxide
and sulphonamide, the other paste consists
of glycol salicylate, titanium dioxide and
calcium sulphate. Light activated calcium
hydroxide cements have become available.

74. Calcium hydroxide

75. Properties
1(The freshly mixed cement is alkaline with
a PH of 11-12. it has the ability to stimulate
the pulp to lay down secondary dentin.
Thos characteristic is utilized in very deep
carious lesions where calcium hydroxide
cement is used as a pulp capping agent. i.e.
it can be placed adjacent to the pulp and it
is capable of destroying micro-organisms
found in carious lesions.

76. 2(Solubility and disintegration : the calcium
hydroxide is highly soluable since it is
dissolved if left at the cavity wall and
margin, this will lead to increase marginal
leakage.
3(The compressive strength of calcium
hydroxide liner is very low about 5 PMa.
Therefore in deep cavities a thin sublining
of a calcium hydroxide cement and then a
base of zinc phosphate cement should be
placed before condensation of amalgam.