This document discusses the constituents and classification of composite restorative materials. It is composed of principal and diluent monomers, inorganic fillers, silane coupling agents, polymerization inhibitors, initiators, ultraviolet stabilizers, and optical modifiers. The inorganic fillers improve mechanical properties, reduce shrinkage, and provide aesthetics and radiopacity. Composites are classified based on filler particle size, from traditional macrofill composites containing large 8-12 micron particles to microfilled and hybrid composites with smaller particles.

1. Composite restorative materials
Dr. Waseem Bahjat Mushtaha
Specialized in prosthodontics

2. Composite restorative materials
The term of composite material may be defined as a
compound of two or more distinctly different materials
with properties that are superior or intermediate to those of
individual constituents. Examples of natural composite
materials are tooth enamel and dentin. In enamel, enamelin
represent the organic matrix, where as in dentin the matrix
consist of collagen. In both of these “composite” the filler
particles consist of hydroxyapatite crystals. The difference
in the properties of these two tissues is associated in part
with difference in the matrix: filler ratio.

3. Constituents of composites
1(Principal monomers.
2(Diluent monomers
3(Inorganic fillers
4(Silane coupling agent
5(Polymerization inhibitors.
6(initiator/activator components
7(Ultraviolet stabilizers.
8(Optical modifiers

4. 1(Principal (higher molecular
weight) monomers.
Many composites are based on an aromatic
dimethacrylate system, the monomer being the reaction
product of bisphenol-A and glycidyl methacrylate,
often called (BIS-GMA) or Bowen’s resin. This highly
viscous monomer can undergo free radical addition
polymerization to give a rigid cross-linked polymer.
Some products use alternative monomer which are
described as urethan dimethacrylates (UEDMA). The
properties of composites based on these latter
monomers are in general similar to those of materials
containing Bowen’s resin.

5. 2(Diluent(lower molecular weight)
monomers
These monomers added to the composite
formulation due to:
1(To reduce the viscosity of the material.
2(Enable proper blending with the inorganic
constituents.
3(To facilitate clinical manipulation.

6. The monomer of choice may be:
a) Monofunctional monomer, ethylene glycol
methyl methacrylate (EGDMA(.
b) Difunctional monomers, ethylene glycol
dimethacrylate (TEGDMA(.
Greater quantities of diluent monomer caused:
1(Lower viscosity. (advantage(
2(Greater shrinkage on polymerization
(disadvantage(.

7. N.B. Difunctional monomers are usually uses
rather than monofunctional monomers
due to:
1(They have less shrinkage on polymerization
2(They give a more cross-linked structure,
which is harder and stronger, and has a lower
coefficient of thermal expansion.
3(They give polymers with lower water
absorption.

8. 3(Inorganic fillers
a) Incorporation of filler particles into a resin
matrix will improves the properties of the
matrix material (if the filler particles are
well bonded to the matrix(:
1(Improvement in mechanical properties
(compressive strength, modulus of elasticity
and hardness(

9. 2(Reduction in coefficient of thermal expansion
3(Contribution to the aesthetics; glass particles are
able to modify the optical appearance and match
the color of the surrounding tooth material.
4(Reduction in the shrinkage on setting.
5(Less heat released in polymerization
6(The composite is radio-opaque if barium or
strontium glasses are used.
N.B. (it contributes the composite easier to polish(

10. b) Filler particles are most commonly produced by grinding
or milling quartz or glasses to produce particles ranging
in size 0.1 to 100µm. Silica particles of colloidal size
(approximately 0.04), referred to collectively as the
microfiller, are obtained pyrolytic process. During
pyrolytic process, the silicon atoms are present in low
molecular-weight compounds, such as SiCl4, that are
typically polymerized by burning SiCl4 in an O2 and H2
atmosphere. During this process, macromolecules
consisting of SiO2 are formed, these particles
called pyrogenic (born in fire) silica particles.
These macromolecules are of colloidal size and
constitute the filler particles.

11. c) Composites often are classified on the basis of
the average size of the major filler component.
In addition to the filler volume level, the size, size
distribution, index or refraction, radiopacity, and
hardness are also important factors in determining
the properties and the clinical application of the
resulting composites.

12. d) To incorporate a maximum amount of filler into
a resin matrix, a distribution of particle size is
necessary. It is obvious that if a single particle
size is used, even with close packing, a space
will exist between particles. Smaller particles
can fill these spaces and, by extending this
process, a continuous distribution of particles
can afford maximum filler loading. Most
composites also contain some colloidal silica.
Inorganic filler particles generally account for
between 30 and 70 vol% or 50 to 85 wt% of the
composite.

13. The amount of filler that can be incorporated in to the resin
matrix generally is affected by the relative filler surface
area. Colloidal silica particles have large total areas,
thus, even small amount of filler particles have a large
total surface area that can form polar bonds with
monomer molecules and thicken the resin. Microfillers,
because of their large surface area, are frequently added
to composite formulations in amounts of less than 5 wt%
to modify the past viscosity, thereby reducing the risk
for sedimentation of the ground particles. The
microfillers also enhance filler packing. So the
microfilled composites, colloidal silica is the only
inorganic filler.

14. e) To ensure acceptable aesthetics of a composite
restoration, the translucency of the filler must be
similar to that tooth structure. To ensure
acceptable translucency the index of refraction
of the filler much closely match that of the resin.
For BIS -GMA and TEGDMA, the refractive
indices are about 1.55 and 1.46, respectively,
and a mixture of the two components in equal
proportions a refractive index of about 1.5. most
of the glasses and quartz that are used for fillers
have refractive indices of approximately 1.5,
which is adequate to achieve sufficient
translucency.

15. f) Quartz has been used extensively as a filler,
particularly in the first generation of composites.
It has the advantage of being chemically inert
but its also extremely hard, making it difficult to
grind into fine particles. Thus, quartz containing
composites are more difficult to polish and may
cause more abrasion of opposing teeth or
restorations.

16. 4(Silane coupling agents
It is important, for reinforcement of the
polymer by the filler to occur, that the two
constituents should be bonded together. To
achieve this, the filler is usually treated with
a vinyl silane compound.

17. 5(Polymerization inhibitors
Since dimethacrylate monomer will
polymerize on the storage, an inhibitor is
necessary. Hydroquinone has been widely
used but was responsible for causing
discoloration of the material so atypical
inhibitor is butylated hydroxytoludene that
used in concentration of 0.01 wt%.

18. 6(initiator/activator components
1(Chemical activation. Benzoyl peroxide
initiator and tertiary amine activators, or
sulphanic acid type initiators may be
employed of the tertiary amines, N,N-
dimethyl-p-toluidine was used as activator,
but now N,N- dihydroxymethyl-p-toluidine
is widely used.

19. 2(Ultraviolet. activation: composites containing
benzoin methyl ether were developed. On
application of u.v. light of appropriate
wavelength, energy is absorbed and free radicals
are generated to initiate polymerization. This
system has now been superseded by visible light
curing due to:
a) Limited depth of polymerization
b) Layering techniques attempting to overcome
c) Potential harmful effects such as skin cancer
and eye damage.

20. 3(Visible light activation: composites have
been developed which contain an α- diketone
and an amine. On application of visible light
of wavelength 460-485 nm, free radical are
generated. Visible light-cured materials are
now very widely used.

21. 7(Ultraviolet stabilizers
To prevent discoloration with age of
composites, compounds are incorporated
which improves color stability. (example 2-
hydroxy-4- methoxybenzophenone.

22. 8(Optical modifiers
To match the appearance of teeth, dental
composites must have visual coloration
(shading) and translucency that can simulate
tooth structure. Shading is a achieved by adding
different pigments. These pigments often
consist of different metal oxides that are added
in minute amounts. Example titanium dioxide
and aluminum oxide (0.001 to 0.007 wt%(

23. Classification of resin-based
composites
1(Traditional composition (macrofill(.
2(Microfilled composite.
3(Small particle-filled composite.
4(Hybrid composite.

24. 1(Traditional composition
(macrofill(.
This was the first type of resin composite marketed for filling front teeth. As the
name implies, the particles in a macrofill are fairly large. Crystalline quartz
was ground into a fine powder containing particles 8 to 12 microns in
diameter. As mentioned the acrylic matrix in a composite tends to shrink on
setting. Excessive shrinkage in a filling material is undesirable because it
would either leave a gap between the tooth surface and the filling material, or,
if well bonded, would cause cracks in the tooth structure as the filling
contracts during setting. The inclusion of glass particles reduces this problem
because they reduce the volume of acrylic, and act as a mechanical "skeletal
structure" within the composite to help maintain the original volume of the
filling. The advantage of large particle size is that more of them can be
incorporated into the mixture without making it too stiff to work with.
Macrofills are 70% to 80% glass by weight

25. Unfortunately, macrofill composites have two undesirable
qualities:
1(Due to large particle size, macrofills are not very
polishable. The relatively soft acrylic polymer polishes
below the level of the glass particles, which constantly
pop out of the surface leaving holes in their place. This
leads to a surface which, on a microscopic level, looks
like a series of craters interspersed with boulders.
2(Large particles are relatively easily dislodged from the
surface of the restoration during function exposing the
relatively soft acrylic polymer which wears away
exposing more filler particles which again pop out ad
infinitum. This tendency to abrade away makes
macrofils unsuitable for posterior restorations

26. The first macrofill appeared on the market in the mid
1960's. Most older dentists affectionately
remember it by its brand name, Adaptic. Adaptic
had the additional disadvantage of containing no
radiopaque materials which made it hard to
distinguish from decay on x-rays (composites
using quartz as a filler are radiolucent. Their
radiopacity is less than that of dentin(.

27. 2(Microfilled composite
Microfill composites use particles of very small size
as a filler, about .04-.5 microns in diameter. The
very small end of this range is called a colloidal
silica and is produced by "burning" silica
compounds in an oxygen and hydrogen
atmosphere to form macromolecular structures
which fall into this size range. This type of
composite was invented to overcome the esthetic
liabilities of the macrofills. Microfill composites
polish beautifully and can be formulated to be
quite translucent.

28. Unfortunately, the smaller the particle size, the fewer
of them you can stuff into the composite because
it becomes too stiff to work with. A smaller
particle has a relatively greater surface area in
relationship to its volume than a bigger one. In
order to include many small particles in a
composite mixture, their total surface area
increases. As friction is a function of involved
surface area, the increased surface increases
internal friction and makes the composite so stiff
that it cannot be manipulated. According to
Phillips Science of Dental Materials, "Colloidal
silica particles, because of their extremely small
size, have extremely large surface areas ranging
from 50 to 400 square meters per gram."

29. Therefore, due to its relatively low filler
content, this type of composite is weaker
than composites with larger particle size,
and has a relatively greater shrinkage
during setting. Microfills are only 35 to 50
percent by weight filler particles. Microfills
are used for small fillings in front teeth.
They are also used for direct veneer on
front teeth because of their superior
polishability.

30. Microfill composites have three main
disadvantages.
1(Due to the relatively low density of filler
particles, microfills are not as strong as
composites with larger particle size, especially on
the incisal edges of front teeth where the bulk of
material is likely to be fairly small.
2(Also due to low density of filler particles,
microfills are more prone to shrinkage while
setting, and this limits their use in large, bulky
fillings.
3(Due to the relatively high level of acrylic matrix
material, microfills tend to be quite translucent
which gives them an overall tendency to cast a
slightly gray hue.

31. Microfill composites are not generally used
for posterior fillings because of the
relatively unfilled nature of the material.
The relatively large amount of acrylic
matrix wears too much when subjected to
the stresses of grinding and chewing

32. 3(Small particle-filled composites
Inorganic fillers are ground to a size smaller than
those used in traditional composites.
The average filler size of these materials range from
1 to 5µm, but the distribution of sizes is fairly
broad. This broad particle-size distribution
facilitates a high filler loading, and small particle-
filled composites generally contain more inorganic
filler (80 wt% and 60 to 65 vol%) than traditional
composites. This is particularly true of those
designated for posterior restorations.

33. Some small particle-filled composites use quartz
particles as fillers, but most incorporate glasses
that contain heavy metals. The matrix resin of
theses materials is similar to that of traditional
and microfilled composite materials. The filler
consist of silan-coated ground particles. Colloidal
silica is usually added in amounts of about 5 wt%
to adjust the paste viscosity.

34. This category of composites exhibits the most
superior physical and mechanical properties The
compressive strength and elastic modulus of small
particle-filled composites exceed those of both
traditional and microfilled composites. The tensile
strength of small particle-filled composites is
double that of the microfilled materials and 1.5
times greater than that of the traditional
composites. The coefficient of thermal expansion
is less than that of other composites. Wear
resistance is improved. Polymerization shrinkage
is less than of traditional resins

35. Those materials filled with glass-containing heavy
metals are radiopacity is an important property
for materials used for restoration of posterior
teeth to facilitate the diagnosis of recurrent caries.

36. Clinical consideration of small
particle-filled composites:
Due to improved strength of these composites
and higher filler loading, they are indicated
for applications in which large stresses and
abrasion might be encountered, such as in
Class I and Class II sites.
The smooth surfaces are not as good as
microfilled materials (disadvantage(

37. 4(Hybrid composite
1(There are two kinds of filler particles in the
hybrid composites. Most modern hybrid filler
consist of colloidal silica and ground particles of
glasses containing heavy metals constituting a
filler content of approximately 75 to 80 wt%. The
glasses have an average particle size of about 0.6
to 1.0 µm. In atypical size distribution, 75% of
the ground particles are smaller than 1.0 µm.

38. Colloidal silica represent 10 to 20 wt% of total filler
content. In this instance, the microfillers also
contribute significantly to the properties. The
smaller filler particles, as well as the greater
amount of microfillers, increase the surface area.
Thus, the overall filler loading is not as high as it
is for some of the small particle-filled composites.
2(The hybrid composite is evident polish compared
with that for the traditional and small particle-
filled composites.

39. 3(Physical and mechanical properties for
these systems generally range between
those of the traditional and small particle-
filled composites. The properties superior to
those of the microfilled composites.
4(Because the ground particles contain heavy
metal species, they have radiopacities
greater than of the enamel.

40. Clinical consideration of hybrid
composites
Because of their surface smoothness and
reasonably good strength, these composites are
widely used for anterior restorations, including
Class IV sites. Although the mechanical
properties generally are somewhat inferior to
those of small particle-filled composites, the
hybrid composites are widely employed for
stress-bearing restorations.

41. Flowable composites
This composite restorative is formulated with a range of particle sizes
about the same as hybrid composites. The amount of filler is reduced
and the amount of unfilled resin matrix material is increased. This
makes for a very loose mix. It is delivered into a cavity using a
syringe. It flows freely over the inside surface of the cavity
preparation. This material has made it possible to fill small cavities in
the tops of teeth without a shot since the area of decay is often small
enough to be removed with little or no sensation in the tooth, and the
flowable composite will bond even if there are no undercuts in the
cavity preparation. Flowable composites are often used to seal the
dentin of a tooth prior to placing the filling material. Due to the low
level of filler particles, flowable composites are more prone to
shrinkage, so they are generally not used by themselves to fill large
cavities..

42. Flowable composites

44. Light sources
The following component of light-cure device:
1(A quartz-halogen bulb.
2(A transformer and control circuitry.
3(Appropriate light filters
4(A switch
5(A timer device
6(A curing tip: this is vary from around 5mm in
diameter up to 7 mm or more for curing larger
surfaces as in posterior composites.

45. Light curing unit

46. Chemically activated materials
a) The two pastes should be mixed in the correct
proportion (equal volumes(.
b) Contamination of one paste by the other should be
avoided.
c) As far as possible, avoid incorporation of air during
mixing.
d) During mixing of some products, tints can be added to
permit color matching between composite and tooth.
e) The mixed materials should be placed in the cavity
without delay.

47. Composite ( chemical activation(

48. Light cured materials
a) In general, most commercially available light
sources will polymerize most light curing
materials.
b) Under-curing must be avoided at all costs. This
gives a material with a hard outer “skin” and soft
material at the base of the cavity.
c) Under-curing may result if the light source is
not sufficiently close to the surface of the
material being polymerized.

49. d) Over-curing is not harmful. This may be a
wise precaution if using a light with a
material from a different manufacture.
e) Darker shades of material absorb more
light so require longer curing times.
f) In some instances, may begin to polymerize
if exposed to strong ambient light.

50. Composite (light cure(

51. Finishing procedures
a) If surface finishing is required, this probably best
achieved by:
1(Contouring the material with a diamond stone or
tungsten carbide bur.
2(Polishing with a composite finishing system
comprising mildly abrasive pasts and discs.
b) Surface glazes are supplied with some materials
(there are unfilled polymers). why?

52. Finishing burs

53. Applications
1(Anterior restoration.
2(Posterior restoration : alternative to dental
amalgam.
3(Used as core build-up materials.
4(Luting of resin-bonded bridge system.
5(Inlay materials.
6(Polymeric crown and bridge materials
7(Laminate veneer system.

56. Repair of composite
Composites may be repaired by placing new
material over the old composite. This is a useful
procedure for correcting defects or altering
contours on existing restorations. The procedure
for adding new material differs depending on
whether the restoration is freshly polymerized or
an older restoration.

57. When a restoration has just been placed and
polymerized, it may still have an oxygen-
inhibited layer of resin on the surface. Additions
can be made directly to this layer, because this
represents, in essence, an excellent boning
substrate. Even after the restoration has been
polished, a defect such as porosity can still be
repaired by adding more material. A restoration
than has just been cured and polished may still
have more than 50% of unreacted methacrylate
groups to copolymerize with the newly added
material.

58. As the restoration ages, fewer and fewer unreacted
methacrylate group remain, and greater cross-
linking reduces the ability of fresh monomer to
penetrate in to the matrix. The strength of the bond
between the original material and the added resin
decreases in direct proportion to the time that has
elapsed between polymerization and addition of
the new resin. In addition, polished surfaces
expose filler surfaces that are free from silan
coating. Thus, the filler surface area does not
chemically bond to the new composite layer, so
the strength of repaired composite is less than half
the strength of the original material.

59. Critique of composites
1(Biological consideration: pulp irritation, plaque can
accumulate on a rough composite surface (How?). less
of this problem(.
2(Bonding. Composite are not adhesive to enamel and
dentin (How can solve this problem?(.
3(solubility: very low.
4(Mechanical properties: generally good (compared
between all types of composites?(.
5(Aesthetics : though initial aesthetics of composites can
be good, the resin may discolor over a period time. And
the accumulation of plaque can cause discolaration.

60. 6(Thermal properties:
A- Composites have less thermal expansion
than unfilled resins. (why?(
B- Composites are good thermal insulators.
7(Dimensional change on setting: this is
comparatively small for polymers prepared
from difunctional monomers, and which
heavily filled.

61. 8(With some composites it is difficult to
obtain a smooth surface finish by abrading
and polishing techniques. Also, abrasive
wear in service roughens the material,
because the polymer phase wear more
rapidly than harder ceramic material.
However , materials with microfine fillers
can take and retain a smooth surface finish.
9(Most composite are radio-opaque.