Dental Materials

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Transcript Dental Materials

Composites, Glass Ionomers, and
Compomers
Chapter 6
Direct-Placement Materials
 Direct-placement materials are those that
can be placed directly into the cavity
preparation or bonded directly onto the
tooth surface.
 Esthetic materials are tooth-colored
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Composite resin
Glass ionomer cement
Resin-modified glass ionomer (hybrid ionomer)
Compomer
Composite Resin
 A composite is a mixture of two or more
materials that has properties superior to any
single component.
 Composite resins are tooth-colored.
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They can be used in both anterior and posterior
teeth.
 Composite resin is composed mainly of
organic resin matrix and inorganic fillers
joined together by a silane coupling agent.
Copyright © 2011 by Saunders, an imprint of Elsevier Inc.
Composite Resin (cont’d)
 Composite resins are joined together by a
silane coupling agent that sticks the particles
to the matrix.
 Also added are initiators and accelerators
that cause the material to set.
 Pigments give the material color.
Resin Components
 The most commonly used resin for the
matrix of composites is bis-GMA.
 Another is urethane dimethacrylate.
 These resins are thick liquids made up of two
or more organic molecules.
 To reduce viscosity and allow the loading of
filler particles, a low molecular weight
monomer is added.
Filler Particles
 Filler particles are added to the organic
resins to make them stronger.
 Fillers are also added to control handling
characteristics.
 Fillers help to reduce shrinkage.
 Fillers used in composite resins are made up
of inorganic particles such as quartz, silica,
and glass.
Filler Particles (cont’d)
 The higher the filler content, the stronger the
material will be.
 One important factor to keep in mind when
choosing a composite resin material is the
size of the filler particles.
 Particle size will affect the wear resistance
and polish-ability of the material.
Particle Size
 The amount of filler in the resin and the
amount of resin between the particles are
related to how the material wears.
 Large filler particles tend to get plucked from
the resin matrix at the surface when the
restoration is under function.
 Larger particles cause the finished
restoration to appear dull or rough.
Particle Size (cont’d)
 Smaller particles are not as easily pulled
from the resin and therefore cause fewer
voids that contribute to wear.
 Smaller particles are packed more closely
together, thereby exposing less of the resin
matrix to wear.
 The smaller the particles, the smoother is the
surface.
Coupling Agent
 To provide a stronger bond between the
organic fillers and the resin matrix, a
coupling agent is used.
 This coupling agent is silane, which reacts
with the surface of the inorganic filler.
 Good adhesion of the two is necessary to
minimize loss of filler particles and reduce
wear.
Pigments
 Pigments are inorganic materials that are
added in various amounts to approximate
the basic shades of tooth enamel.
 To get an accurate color match, a shade
guide is used.
Polymerization
 Polymerization is the chemical reaction that
occurs when low molecular weight molecules
called monomers join together to form longchain, high molecular weight molecules
called polymers.
 Chemicals that cause the polymerization
reaction to begin are initiators and
activators.
Types of Composites
 Three types of composite materials are used
in dentistry.
 Each composite material has its advantages
and disadvantages:
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Chemical cure
Light cure
Dual cure
Chemical Cure
 Chemically cured composite resins, also
called self-cured composite resins, represent
a two-paste system.
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They are supplied in jars or syringes.
 One paste is called the base; the other is
called the catalyst.
 Equal parts of the two are dispensed and
mixed together.
Chemical Cure (cont’d)
 With this type of system, the operator has a
limited amount of working time before the
material starts to set.
 When the materials are mixed together, it is
important that they be spatulated to a
homogenous mixture to allow a thorough
cure.
 Air is introduced during the mixing process;
this may cause voids in the restoration.
Light Cure
 Light-cured composite materials are the
most common type of composite used in
dentistry.
 The operator has ample working time to
manipulate the material to its desired form.
 The material is set with the use of a curing
light in the blue wavelength.
 Care must be taken with the operatory light
so that it does not begin to set the material
prematurely.
Dual Cure
 Dual-cured composite resins utilize both
visible light and chemical reactions to cure
the material.
 These resins are available in a two-paste
system or may be dispensed from a syringe.
 The initial set is made by the curing light,
and the chemical reaction finishes the
process.
Types of Filled Materials
 Composite resins have steadily improved in
quality over the years.
 Filler particle size has decreased, the number
of filler particles has increased, and
polymerization shrinkage has decreased.
 Fillers are available in three classifications:
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Macrofilled
Microfilled
Hybrid
Macrofilled Materials
 First generation of composite resin material
 Conventional composite containing the largest of the
filler particles
 Provides greater strength
 Duller, rougher surface
 Absorbs stains more easily
Microfilled Materials
 Developed to overcome the problems
associated with the larger particle size
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Contain much smaller particles
Not as strong as macrofilled materials
Polish to a glossy finish
Do not absorb stains as easily
Hybrid
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Contain both macro and micro particles
Easily polished
Greater strength than microfilled products
High wear resistance
Microhybrids, which are a combination of
small particles and microfine particles, are
considered the newest generation.
Flowable Composites
 Flowable composites are low-viscosity, light-
cured resins that are lightly filled.
 These composites flow readily and can be
delivered directly into the preparation by
small needles on syringes.
 These typically are utilized in conservativetype procedures.
Pit and Fissure Sealants
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Low-viscosity resins that vary in filler size
Used to prevent caries
Contain little or no filler
Similar to flowable composites
Physical Properties
 Important physical properties of composites
include the following:
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Biocompatibility
Strength
Wear
Polymerization
Shrinkage
Thermal conductivity
Water sorption
Radiopacity
Biocompatibility
 Newly placed composite resins can release
chemicals that, in deep cavity preparations,
could pass through the dentinal tubules into
the pulp, causing inflammation.
 When the tubules are sealed by dentin
bonding agents and/or a base is placed,
sensitivity is reduced or eliminated.
Strength
 Composites with larger filler particles
(macrofilled) are stronger in both tensile and
compression than are microfilled materials.
 Macrofilled materials still are not as strong
as amalgam, but they are stronger than glass
ionomers.
Wear
 Composites wear faster than amalgams.
 Recent improvements in material are closing
that gap in strength.
Polymerization Shrinkage
 Term refers to the shrinkage that occurs
when the composite resin is cured
 The matrix, when cured, usually shrinks
away from the cavity walls.
 Material cures toward the center of the bulk
of material, which pulls the material away
from the interface.
 Curing in small increments (1 to 2 mm)
decreases shrinkage.
Thermal Conductivity
 Composite resin has a thermal conductivity
close to that of natural tooth structure.
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It is much lower than that of metal.
 Composite resin is a biologically protective
material for the pulp.
Coefficient of Thermal Expansion
 Ideally the coefficient of thermal expansion
(CTE) of the filling material would be the
same as that of the tooth structure.
 In the case of composite, the CTE is greater
and will have a greater change in dimension
than will the adjacent tooth structure.
 This can result in debonding and leakage of
the restoration.
Elastic Modulus
 The elastic modulus (also referred to as the
e-modulus, or Young’s modulus) is the
stiffness of the composite and is determined
by the amount of filler.
 The greater the volume of the filler, the
stiffer (higher elastic modulus) and more
wear resistant is the restoration.
Water Sorption
 The resin matrix absorbs water from the oral
cavity.
 The greater the resin content, the more water
is absorbed.
 Microfills and flowables have greater water
sorption.
 Water softens the resin matrix, which
gradually degrades the material.
Radiopacity
 Metals such as lithium, barium, or strontium
are added to the filler to make the restoration
more opaque when viewed on a radiograph.
 Older materials did not have these fillers,
and most appear radiolucent.
Selection of Materials
 Several criteria can be used to determine the
best material to use in a particular situation.
 In the anterior teeth (non–stress-bearing
areas), selection is usually based on color
matching and ability to finish to a natural,
glossy appearance.
 Stress-bearing areas use the stronger hybrid
or microhybrid materials.
Shade Guides
 Many manufacturers include a shade guide
with color tabs that can be used to help in
shade selection.
 Remember to use a natural light source when
viewing shades.
 Always check the shade before work begins,
so the teeth are fully hydrated.
Other Factors
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Shelf life
Dispensing and cross-contamination
Contamination
Finishing and polishing
Dental prophylaxis/scaling
Glass Ionomers
 Self-cured or light-cured, tooth-colored,
fluoride-releasing cements that bond to tooth
structures
 Used to cement crowns, bridges, veneers,
and orthodontic appliances
 Also may be used as a liner, base, or core
 For restorations at the cervical portion of the
tooth
Physical Properties of Glass Ionomers
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Biocompatible
Bond to tooth structure
Release fluoride ion
High water solubility in the first 24 hours
Thermal expansion similar to that of natural
teeth
Good insulators
Moderate compressive and tensile strength
Wear faster
Radiopaque
Hybrid Ionomers
 To improve the physical properties of glass
ionomers, resins have been added to the
material.
 These resins have some properties of
composites and some properties of glass
ionomers.
 They are stronger than regular glass
ionomers, are easier to polish, and are more
wear resistant.
Compomers
 Composite resins that have been modified
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with polyacid
Release fluoride but are not the same as glass
ionomers
Good color-matching ability
Polish well
Medium wear rate
Indirect Restorations
 Indirect restorations are fabricated outside of
the mouth.
 They include
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Inlays
Onlays
Veneers
Crowns with porcelain or ceramic facings
Summary
 Composite resins are direct-placement
restorative materials that have a wide variety
of uses.
 Glass ionomer cements also have a wide
variety of uses but are not as strong as
composite resins.