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Indirect Veneer Techniques
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Many dentists find that the preparation, placement, and finishing of several direct
veneers at one time is too difficult, fatiguing,
and time-consuming.
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Some patients become uncomfortable and
restless during long appointments.
In addition, veneer shades and contours can
be better controlled when made outside ofthe mouth on a cast.
For these reasons,
indirect veneer techniques are usually preferable.
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Indirect veneers include those made
of:
(1) processed composite,
(2) feldspathic porcelain,
and
(3) cast or pressed ceramic.
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Processed Composite Veneers
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Composite veneers can be processed in
a laboratory to achieve superior
properties.
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After shade selection, the teeth areisolated with bilaterally placed
cotton rolls and gingival retractioncord.
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All existing defective Class III
restorations or small carious lesions
should be restored before preparation.
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Multiple large existing restorationscompromise the potential to bond
the veneer to the tooth and mayrepresent a contraindication.
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Usually no anesthetic is required forintraenamel tooth preparations for
veneers.
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In fact, the patient's response isimportant in judging preparation depth,
especially in the gingival third of thetooth.
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If possible, the preparations should
be restricted entirely to enamel.
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The window preparation is made with a
tapered, rounded end diamond instrumentto a depth of approximately 0.5 to 0.75 mm
midfacially, diminishing to a depth of 0.3to 0.5 mm along the gingival margin,
depending on enamel thickness.
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The gingival margin should be positioned
just at or slightly above the level of the
gingival crest unless defects, caries, or dark
discoloration warrant subgingivalextension.
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Also, the interproximal margins shouldextend into the facial and gingival
embrasures, without engaging an undercut,
yet should be located just facial to the
proximal contacts.
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Generally no temporary restorations
are placed because the preparations are
restricted to enamel.
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An elastomeric impression is made
of the preparations.
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At the second appointment the teeth tobe veneered are cleaned with a pumice
slurry, the shade confirmed, and theoperating site isolated.
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The fit of each veneer is evaluated on
the individual tooth and adjusted ifnecessary.
All of the veneers should fit closely to
the tooth at the gingival area.
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The veneers should be tried in place
(both individually and collectively) to
ensure the fit of adjacent seated veneers.
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Veneers should be tried in place only on
clean, dry teeth to eliminate any potential
for contamination.
If accidental contamination occurs, theveneer should be thoroughly cleaned with
alcohol or acid etchant, rinsed, and dried
before bonding.
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On removal, each veneer is placed tooth
side up (i.e., concave side facing upward)
on an adhesive pad or palette.
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Some processed composites requirethat a priming agent be applied to the
tooth side of the veneer according tothe manufacturer's instructions.
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A light-cured, resin cement is recommended
for bonding the veneer to the tooth.
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Shade selection of the bonding medium is determined when the fit of the
individual veneers has been evaluatedand confirmed.
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Shade selection is made by first placing auniform layer of a selected shade of resin
cement, approximately 0.5 mm in thickness,on the tooth side of a single veneer.
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The veneer is seated on a clean, dry, unetchedtooth, the excess resin cement is removed
with a brush, and the overall shade of theveneer evaluated.
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After try-in, the veneer is removedquickly and placed in a container
to prevent curing of the cement.
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If the shade of the cement is determined to
be appropriate, more of the same shade is
added to the veneer just before bonding.
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If a different shade is deemed necessary,the existing shade is wiped from the inner
aspect of the veneer with a disposable
microbrush and a new shade of resincement is placed in the veneer.
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The veneer loaded with the new shadeof cement is reseated and evaluated as
previously described.
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After the try-in process, a light-curedresin cement of the same shade is used
for final cementation.
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Polyester strips are placed in the proximal
areas of the first tooth to be restored.
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Wooden wedges can be used to secure the position of the strips, but care must be
taken not to irritate the gingival papilla forrisk of inducing hemorrhage.
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The acid etchant is artfully appliedwith a small microbrush, sponge, or
syringe etchant applicator .
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The prepared tooth is ready for veneer
bonding after acid-etching, rinsing, and
drying.
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A thin layer of adhesive is applied to the
etched enamel, lightly blown with air, butnot cured until placement of the veneer.
Premature curing of the bonding agent may
preclude full seating of the veneer.
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The selected shade of light-cured resincement is added to the tooth side of the
veneer with enough material to cover the
entire treated surface.
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The veneer is carefully placed on the
appropriate tooth and lightly vibrated into
position with a blunt instrument or light
finger pressure.
A microbrush is used to remove excess
cement.
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With the veneer properly positioned and
excess cement removed, a visible lightcuring unit is used to polymerize the
material with a minimum exposure time of
40 to 60 seconds each from the facial and
lingual directions for a total exposure of 80
to 120 seconds.
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When the veneers are all bonded, only
a minor amount of finishing is required
at the marginal areas.
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Patients also should be cautioned to avoidbiting hard foods or objects to prevent
fracturing the incisal edge, especially if an
incisal-lapping design was used.
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Etched Porcelain Veneers
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The preferred type of indirect veneer isthe etched porcelain (i.e., feldspathic)
veneer .
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Porcelain veneers etched with hydrofluoricacid are capable of achieving high-bond
strengths to the etched enamel via a resin-
bonding mediums.
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The procedures for preparation, impression,try-in, and cementation are the same as for
indirect processed composite veneers, with
a few exceptions.
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The only difference in this procedure for
porcelain veneers from the composite
veneers is the need to condition the internal
surface of each veneer with a silane primer just before applying
the resin-bonding
agent.
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The silane acts as a coupling agent, forming a
chemical bond between the porcelain and the
resin.
It also improves wettability of the porcelain.
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Pressed Ceramic Veneers
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Another esthetic alternative for veneeringteeth is the use of pressed ceramics, such
as IPS Empress.
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Excellent esthetics are possible using pressed ceramic materials for most cases
involving mild to moderate discoloration.
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Because of the more translucent natureof pressed ceramic veneers, however,
dark discolorations are best treated with
etched porcelain veneers.
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The clinical technique for placing pressedceramic veneers, such as those made by IPS
Empress, is not markedly different from thatfor feldspathic porcelain veneers.
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The procedures for tooth preparation, try-in,and bonding of pressed veneers are the same
as for etched porcelain veneers except that
the marginal fit is often superior.
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For that reason, little marginal finishing is
often necessary.
Only the excess bonding medium needs to beremoved.
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Repairs of Veneers
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Failures of esthetic veneers occur because of
breakage, discoloration, or wear.
Consideration should be given to conservative
repairs of veneers if examination reveals that
the remaining tooth and restoration are sound.
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It is not always necessary to remove all of the
old restoration.
The material most commonly used for makingrepairs is light-cured composite.
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Veneers on Tooth Structure
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Small chipped areas on veneers can often be
corrected by recontouring and polishing.
When a sizable area is broken, it usually canbe repaired if the remaining portion is sound.
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For direct composite veneers, repairs ideallyshould be made with the same material that
was used originally.
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After cleaning the area and selecting the
shade, the operator should roughen thedamaged surface of the veneer or tooth or
both with a coarse, tapered, rounded end
diamond instrument to form a chamfered
cavosurface margin.
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Roughening with microetching (i.e.,
sandblasting) is also effective.
For more positive retention, mechanical locks
may be placed in the remaining composite
material with a small, round bur.
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Acid etchant is applied to clean the prepared area and etch any exposed
enamel, which is then rinsed and dried.
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Next, an adhesive is applied to the preparation
(i.e., existing composite and enamel) and polymerized.
Composite is added, cured, and finished in the
usual manner.
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Indirect processed composite veneers arerepaired in a similar manner.
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To repair porcelain veneers, a mildhydrofluoric acid preparation, suitable for
intraoral use, must be used to etch the fractured
porcelain.
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Hydrofluoric acid gels are available in
approximately 10% buffered
concentrations that are intended for
intraoral porcelain repairs.
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Isolation of the porcelain veneer to be repairedshould be accomplished with a rubber dam to
protect the gingival tissues from the irritating
effects of the hydrofluoric acid.
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The manufacturer's instructions must befollowed regarding application time of the
hydrofluoric acid gel to ensure optimal
porcelain etching.
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A lightly frosted appearance, similar to that
of etched enamel, should be seen if the
porcelain has been properly etched.
A silane coupling agent may be applied tothe etched porcelain surface before the
adhesive is applied.
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Composite materials is added, cured, and
finished in the usual manner.
Large fractures are best treated by replacingthe entire porcelain veneer.