Download DH 104 Chapter 13

Dental Cements
Chapter 13
Dental Cements
 Few materials in dentistry are used as
frequently as dental cements.
 Dental cements typically have multiple uses.
 The doctor will choose the type of cement to
use according to the procedure and/or the
purpose of placement.
 It is the responsibility of the dental auxiliary
to know the particulars and the proper
manipulation of each cement.
Uses of Dental Cements
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Pulpal protection
Luting-cementation
Restorations
Surgical dressings
Pulpal Protection
 The bacterial effects of caries, the biological
response to chemicals contained in restorative
materials, and even the cutting of tooth structure
may cause pulpal irritation.
 Pulpal irritation can also occur as the result of
thermal conductivity of metal restorations placed
over or near the pulp.
 It may also occur when the dentin remaining over
the pulp is too thin to withstand compressive,
tensile, and shearing stresses.
Cavity Varnish
 Acts as a protective barrier between
preparation and restoration
 Natural copal or synthetic resins dissolved in
a solvent such as alcohol or chloroform
 Applied in two or three layers to allow
evaporation voids to be sealed
 Not used as often today because they tend to
wash out at the margins
Liner/Low-Strength Base
 Calcium hydroxide is used as a liner/low-
strength base in a cavity preparation.
 It is used when dentin no longer covers the
pulp, also known as exposure or direct pulp
cap.
 It stimulates reparative dentin formation.
 Calcium hydroxide has an alkaline pH
between 9 and 11.
High-Strength Base
 Provides thermal insulation
 Provides support for restorations
 Cements used as a base are mixed to a
secondary consistency, a thick putty-like
consistency.
 In preparations with an estimated 2 mm or
less dentin remaining, a base is often
recommended.
Buildup
 A buildup, much like a high-strength base,
provides mechanical support for a restorative
material when an excessive amount of tooth
structure is removed or missing.
 Placing a cement buildup reinforces the
remaining tooth structure.
Luting Cementation
 Cements used for permanent or temporary
luting of fixed prostheses, orthodontic bands,
and pins and posts must have good
wetability and flow to provide a thin film
thickness.
 When the tooth structure and fixed
prostheses are in intimate contact, a
microscopic space exists.
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This is the tooth-restoration interface.
Luting
 The primary purpose of luting cement is to
fill the interface.
 Cements mixed to primary consistency must
have thin enough viscosity to be able to flow
into a film thickness of 0.25 µm or less.
 If the viscosity of the cement is such that the
prosthesis fails to regain intimate contact
with the tooth, a thick layer of cement will be
exposed at the margin.
Orthodontic Bands and Brackets
 Ortho bands are retained for months, even years.
 The cement must adhere tenaciously to the enamel
and the orthodontic appliance to provide leverage
for tooth movement.
 Demineralization of the tooth surface caused by
the solubility of cement, with resultant leakage of
bacteria between the band and the tooth surface,
has been problematic.
 Cements that contain fluoride have helped to
minimize the problem.
Restorations
 Because of their lower strength and wear
resistance and higher solubility, cements are
not frequently chosen as permanent
restorations.
 The exception is a glass ionomer cement that
is used at the cervical portion of a tooth.
 Provisional and intermediate restorations
use dental cements in a secondary
consistency, for their sedative effects.
Surgical Dressings
 As surgical dressings, cements are used to
provide protection and support for the
surgical site.
 They provide patient comfort and help
control bleeding.
 They are mixed to a soft, putty-like
consistency that hardens when placed over
the tissue, forming a rigid covering.
 They may be chemical- or light-cured.
Properties of Dental Cements
 Properties differ from one cement to
another.
 No cement is ideal for every situation.
 The clinician must consider both physical
and biological properties when selecting
cement for each individual procedure.
 The most important properties include
strength, solubility, viscosity,
biocompatibility, retention, esthetics, and
manipulation.
Strength
 Cements are brittle materials with good
compressive strength but limited tensile
strength.
 The strongest cements are resin cements.
 The weakest are zinc oxide eugenols (ZOEs).
 Most cements combine a powder and liquid
dispensed in a specific ratio.
Solubility
 Cements have a tendency toward dissolving
in oral fluids, leading to microleakage.
 Most cements disintegrate in the oral
environment over time.
 Resin cements are as close as possible to
insoluble.
Viscosity
 The consistency of mixed cement is the
measure of its ability to flow under pressure.
 This is particularly important in the case of
cement used for luting because it determines
the dentist’s ability to seat the indirect
restoration properly.
 Primary consistency is mixed thin, about the
thickness of honey.
 Secondary consistency is mixed to a puttylike state.
Biocompatibility
 Many cements are a combination of a
powder of zinc oxide or powdered glass and
an acid.
 The pH of the acid both at placement and
after complete setting is a matter of concern.
 Careful attention to powder-to-liquid ratios,
dispensing technique, and mixing
recommendations can minimize this
concern.
Retention
 Retention of indirect restorations is
accomplished by adhesion.
 Adhesion is the bonding of dissimilar
materials by the attractive forces of atoms or
molecules.
 Mechanical adhesion is based on the
interlocking of one material with another.
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Makes the restoration highly retentive and resistant
to microleakage
Esthetics
 Cements are available in a variety of shades
and opacities for luting porcelain veneers,
ceramic or composite inlays, and porcelain
full crowns.
 A shade is chosen that approximates the
color of the restoration.
 Sometimes a masking shade is used to cover
discolorations or densities.
Manipulation
 It is important that cements be mixed to their
appropriate consistency in accordance with
manufacturers’ recommendations by measuring
ratios with meticulous attention to detail.
 Cements that are mishandled may lead to
difficulties in seating or retaining the restoration
or may promote pulp sensitivity.
 The setting of cements may be initiated by three
means: chemical, light-activated, or a combination
of chemical and light-activated (dual).
Mixing
 Cements may be hand-mixed or may come in
pre-dosed capsules and syringes.
 Some cements have been packaged in
automixing cartridges.
 Working time and setting time are
considerations in the selection of cement and
mixing mechanism.
 The dental assistant is responsible for
delivering the cement at the proper
consistency within the appropriate working
time.
Loading the Restoration
 The dental assistant may be responsible for
filling the crown with a luting cement before
passing it to the dentist.
 Once mixed, the cement should be gathered
in one location with the spatula.
 Wipe the blade of the spatula against the
margin of the restoration.
 Cover the walls with a thin, even coating of
cement.
Removal of Excess Cement
 Excess cement must be removed from the
surface of the restoration or the tooth
surface.
 Some cements may be wiped clean with a 2 ×
2 gauze immediately after placement.
 Others must be fully set before removal.
 Read ALL instructions completely to use the
recommended technique.
Cleanup
 The removal of cement from instruments
before it sets allows easier cleanup.
 Clean instruments and equipment that come
in contact with cement as soon as possible
with gauze squares that are saturated in
water or alcohol, in keeping with
manufacturers’ instructions.
 Disinfect or sterilize as recommended.
Zinc Oxide Eugenol (ZOE)
 ZOE cements have been used widely for
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many years.
They are available in powder/liquid and
paste/paste systems.
ZOE has a neutral pH of 7, so it is friendly to
the tissue.
ZOE has low strength and high solubility.
It acts as a sedative to the pulp.
Zinc Phosphate
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The oldest dental cement
Not widely used today
Available in a powder/liquid system
Can be mixed only on a cool glass slab
pH is an acidic 4.2
Causes pulp irritation
Exhibits high solubility
Zinc Polycarboxylate
 First cements developed with an adhesive
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bond
Used primarily for the final cementation of
an indirect restoration
Powder/liquid system
High viscosity
High solubility
Low strength
Short working time
Glass Ionomer
 Introduced in 1969
 Originally developed for esthetic restoration
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of anterior teeth (light-cure)
Used for permanent luting agents (self-cure)
Uses chemical adhesion
Has low to moderate strength
Includes a fluoride ion
Produces postoperative sensitivity
Hybrid Ionomer Cements
 Similar to glass ionomer
 Modified with additional resin (light-cure)
 Improved bond strength, compressive
strength, and tensile strength
 Insoluble
 Includes a fluoride ion
 Not recommended for ceramic restoration
Resin-Based Cements
 Resin cements are basically modified
composites used to bond ceramic indirect
restorations, conventional crowns, and
bridges, and to indirectly bond orthodontic
brackets.
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Light-cured
Dual-cured
Self-cured
Summary
 No single cement satisfies all dental
purposes.
 Cements are chosen for their properties in
each situation.
 Proper manipulation of each material can
enhance the success of the restoration.