Class I and II Indirect Tooth-Colored Restorations (4,5)

7/29/2019 Class I and II Indirect Tooth-Colored Restorations (4,5)

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Class I and II

Indirect Tooth-Colored Restorations


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Most indirect restorations are made on a replica of

the prepared tooth in a dental laboratory by a

trained technician. Tooth-colored indirect systems

include laboratory-processed composites andceramics, such as porcelain fired on refractory dies

or hot pressed glasses.


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In addition, chairside computer-aideddesign/computer-assisted manufacturing

(CAD/CAM) systems are currently available and

are used to fabricate ceramic restorations.


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Indications


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*Esthetics.* Large defects or previous restorations.

* Economic factors: Some patients desire the best

dental treatment available, regardless of cost.


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Contraindications


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* Heavy occlusal forces


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* Inability to maintain a dry field.

* Deep subgingival preparations.


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Advantages


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*Improved physical properties: A wide varietyof high-strength tooth-colored restorative

materials, includinglaboratory-processed andcomputer-milled composites and ceramics, can

be used with indirect techniques.


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* Variety of materials and techniques: Indirect

tooth-colored restorations can be fabricated with

either composites or ceramics using variouslaboratory processes or CAD/CAM methods.


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* Wear resistance: Ceramic restorations are more

wear-resistant than direct composite restorations,an especially critical factor when restoring large

occlusal areas of posterior teeth. Laboratory-

processed composite restorations wear more thanceramics, but less than direct composites in

laboratory studies .


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* Reduced polymerization shrinkage:Polymerization shrinkage and its resulting

stresses are a major shortcoming of direct

composite restorations.


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* Ability to strengthen remaining tooth structure:

Tooth structure weakened by caries, trauma, or

preparation can be strengthened by adhesivelybonding indirect tooth-colored restorations.


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* More precise control of contours and contacts:Indirect techniques usually provide better contours

(especially proximal contours) and occlusal contacts

than direct restorations because of the improved access

and visibility outside the mouth.


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* Biocompatibility and good tissue response:

Ceramic materials are considered the most

chemically inert of all materials.


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* Increased auxiliary support: Most indirecttechniques allow the fabrication of the

restoration to be totally or partially delegated todental laboratory technicians.


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Disadvantages


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* Increased cost andtime: Most indirect techniques

require two patient appointments, plus fabrication of

a temporary restoration.

These factors, along with laboratory fees, contribute

to the higher cost of indirect restorations relative to

direct restorations.


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* Technique sensitivity: Restorations made

using indirect techniques require a high

level of operator skill.


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* Brittleness of ceramics: A ceramic restorationcan fracture if the preparation does not provide

adequate thickness to resist occlusal forces or if

the restoration is not appropriately supported by

the cement medium and the preparation.


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* Wear of opposing dentition and restorations:

Ceramic materials can cause excessive wear of

opposing enamel or restorations.


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* Resin-to-resin bondingdifficulties: Laboratory-

processed composites are highly cross-linked, so

few double bonds remain available for chemicaladhesion of the composite cement.


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* Short clinical track record: Indirect bonded

tooth-colored restorations have become

relatively popular only in recent years and arestill not placed by many practitioners.


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* Low potential for repair: Indirect restorations,

particularly ceramic inlays/onlays, are difficult to

repair in the event of a partial fracture.


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* Difficult try-in and delivery: Ceramics are

more difficult to polish because of potential

resin-filled marginal gaps and the hardness of theceramic surfaces.


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Laboratory-Processed Composite

Inlays and Onlays


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Processed composite restorations are

indicated when:


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(1) maximum wear resistance is desired

from a composite restoration,


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(2) achievement of proper contours and

contacts would otherwise be difficult, and


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(3) a ceramic restoration is not indicated because

of cost or concerns about wear of the opposingdentition. Regarding the last-mentioned, the

indirect composite would likely cause less wear

of the opposing dentition than a similar ceramic

restoration.


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The fabrication steps for onerepresentative system can be

summarized as follows:


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1. The indirect composite restoration isinitially formed on a replica of the

prepared tooth.


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2. The composite is built up in layers,polymerizing each layer with a brief

exposure to a visible light-curing unit.


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3. After it is built to full contour, therestoration is coated with a special gel to

block out air and thus prevent formation of

an oxygen-inhibited surface layer.


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4. Final curing is accomplished by insertingthe inlay into an oven-like device that

exposes the composite to additional light

and heat, in some cases, pressure.


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5. The cured composite inlay istrimmed, finished, and polished in the

laboratory.


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Ceramic Inlays and Onlays


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Among the ceramic materials used are

feldspathic porcelain, hot pressed ceramics, andmachinable ceramics designed for use with

CAD/CAM systems.


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The physical and mechanical properties of

ceramics come closer to matching those of

enamel than do composites.

They have excellent wear resistance and acoefficient of thermal expansion very close to

that of tooth structure.


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Feldspathic Porcelain Inlays and Onlays


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The fabrication steps for fired ceramic

inlays and onlays can be summarized as follows:


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Master cast for MOD ceramic inlay. Die

spacer is usually applied to axial walls

and pulpal floor before duplicationMaster die is impressed, then a

duplicate die is poured with refractory

investment


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Dental porcelains are added and fired in

increments until inlay is the correct shape.

Inlay is cleaned of all investment, then seated

on master die for final adjustments and

finishing. Ceramic inlay is now ready for

delivery


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Hot Pressed Glass-Ceramics


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The fabrication steps for one type of leucite-

reinforced hot pressed ceramic restoration

are summarized as follows:


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Wax pattern for ceramic inlayWax pattern on sprue base, ready to be

invested


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Device for pressing heated ceramicCeramic inlay as pressed and before

surface characterization


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Inlay following surface characterization


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Computed-Aided Design/Computed-

Assisted Manufacturing: CAD/CAM


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Rapid improvements in technology havespawned several computerized devices that can

fabricate ceramic inlays and onlays from high-

quality ceramics in a matter of minutes.


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Some CAD/CAM systems are veryexpensive laboratory-based units requiring

the submission of an impression or working

cast of the prepared tooth.


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The CEREC system


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The CEREC system was the first commercially

available CAD/CAM system developed for therapid chairside design and fabrication of ceramic

restorations.

The 2005 version of this device is the CEREC 3.


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CEREC 2 (A) and CEREC 3 (B) CAD/CAM devices.

These chairside units are compact

and mobile.

A B


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Generation of a CEREC restoration begins

after the dentist prepares the tooth and uses ascanning device to collect information about

the shape of the preparation and itsrelationship with the surrounding structures.


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An optical impression is made by

placing a small video camera or

scanner over the prepared tooth.


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The restoration is designed onthe computer screen by drawing

position of gingival margins and

proximal contacts.


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A, Computer-driven softwarecontrols two small, diamond-

coated milling devices that cut

the restoration out of a block of

high-quality ceramic. B, Theceramic block rotates as the

diamond cutting instruments

move as needed to generate the

restoration.B


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A major advantage is the quality of the restorative

material. Manufacturers make blocks of

"machinable ceramics" or "machinable composites"specifically for computer-assisted milling devices.

Because these materials are fabricated under idealindustrial conditions, their physical properties have

been optimized.


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The major disadvantages of CAD/CAM

systems are high cost and the need for extra

training.

However, CAD/CAM technology is changing

rapidly, with each new generation of deviceshaving more capability, accuracy, and ease of

use.


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CLINICAL PROCEDURES


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Tooth Preparation


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By definition, an onlay caps all cusps; aninlay may cap none, or may cap all but

one cusp.


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As a first clinical step:

1- The patient is anesthetized and the area

isolated, preferably using rubber dam.


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2- The compromised restoration (if present)is completely removed, and all the caries is

excavated.


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3- If necessary, the walls are restored to amore nearly ideal form with a light-cured

glass-ionomer liner/base or a composite

restorative material.


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Preparations for indirect tooth-colored inlays and

onlays are designed toprovide adequate thicknessfor the restorative material and simultaneously a

passive insertion pattern with rounded internal

angles and well-defined margins.


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1- All margins should have a 90- degreecavosurface angle to ensure marginal strength of

the restoration.


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2- All line and point angles, internal and external,should be rounded to avoid stress concentrations

in the restoration and tooth, reducing the potential

for fractures.


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The carbide bur or diamond used for tooth

preparation should be a tapering instrument thatcreates occlusally divergent facial and lingual

walls.


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The occlusal step should be prepared 1.5 to

2 mm in depth. Most composite and ceramicsystems require that any isthmus be at least 2

mm wide to decrease the possibility of fracture

of the restoration.


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Thepulpal floor should be smooth and

relatively flat.


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The facial, lingual, and gingival margins of the

proximal boxes should be extended to clear theadjacent tooth by at least 0.5 mm.

These clearances will provide adequateaccess to the margins for impression material

and for finishing and polishing instruments.


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For all walls, a 90-degree cavosurface

margin is desired because composite and

ceramic inlays are fragile in thin cross-

section.


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The gingival margin should be extended as

minimally as possible because margins in enamelare greatly preferred for bonding, and because

deep gingival margins are difficult to impress

and to isolate properly during cementation.


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A cusp usually should be capped if the

extension is two thirds or greater than the

distance from any primary groove to the

cusp tip.


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Impression


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Most tooth-colored indirect inlay/onlay systems

require an impression of the prepared tooth and

the adjacent teeth as well as interocclusal

records, which allow the restoration to be

fabricated on a working cast in the laboratory


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Temporary Restoration

A provisional restoration is necessary when


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A provisional restoration is necessary when

using indirect systems that require two

appointments.

The temporary restoration protects the pulp-

dentin complex in vital teeth, maintains theposition of the prepared tooth in the arch, and

protects the soft tissues adjacent to prepared

areas.


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Temporary restorations for porcelain-fused-to-metal and cast gold restorations typically are

cemented with eugenol-based temporary

cements.

l i b li d i f i h i


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Eeugenol is believed to interfere with resin

polymerization, however, and potentially could

reduce the adhesion of the permanent compositecement to tooth structure.

Use of a noneugenol temporary cement isrecommended.


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When the temporary phase is expected to lastlonger than 2 to 3 weeks, zinc phosphate

or polycarboxylate cement can be used to

increase retention of the temporary restoration.


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Computer-Aided Design/Computer-Assisted Manufacturing (CAD/CAM)

Techniques


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Using the CEREC system, an experienced

dentist can prepare the tooth, fabricate an inlay,and deliver it in approximately 1 hour. This

systemeliminates the need for a conventional

impression, temporary restoration, and multiplepatient appointments.


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A, CEREC inlay being milled. B, Completed inlay

B


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Try-in and Cementation


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The inlay or onlay is placed into the

preparation using very light pressure toevaluate its fit. If the restoration does not

seat completely, the most likely cause is an

overcontoured proximal surface.


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A, Initial try-in of CEREC inlay. Proximal contacts are too

tight and must be adjusted.

B, Inlay seated after contact adjustment. Proximal surfaces

of the inlay must be polished before cementation.


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Cementation


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For most laboratory-processed composite inlays/

onlays, the resin matrix has been polymerized tosuch an extent that few bonding sites are

available for the composite cement to chemically

bond to the internal surfaces of the restoration.


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For ceramic inlays and onlays, hydrofluoric acidusually is used to etch the internal surfaces of the

restoration.


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Chairside ceramic etching is done with a 2-minute application of10% hydrofluoric acid on

the internal surfaces of the inlay/onlay.


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After etching, the ceramic is treated with a

silane coupling agent to facilitate chemical

bonding of the composite cement.

Cl l ti t i t i b li d i


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Clear plastic matrix strips may be applied in

each affected proximal area and wedged.

The inlay/onlay can be tried in again and

checked for fit.


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The preparation surfaces are etched and treated with the

components of an appropriate enamel/dentin bonding

system.

Typically, the final step of the bonding system (e.g., an

unfilled resin) also is applied to the internal surfaces of

the restoration previously etched and silanated.

A dual-cure composite cement is mixed and


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inserted into the preparation.

The internal surfaces of the restoration are also

coated with the composite cement and the

inlay is immediately inserted into the prepared

tooth, using light pressure.

A ball burnisher applied with a slight vibrating


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motion is usually sufficient to seat the

restoration.

Excess composite cement is removed with

thin-bladed composite instruments, brushes, or

an explorer

The operator must be careful not to remove


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composite from the marginal interface between

the tooth and the inlay.

The cement is now light-cured from occlusal,

facial, and lingual directions for a minimum

exposure of60 seconds from each direction.


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A, Enamel and dentin are etched with phosphoric acid. B,

Dual-cured composite cement is applied to inlay. C, Afterapplication of the adhesive system, cement is appliedto the

preparation. D, CEREC ceramic inlay is seated into

preparation.


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Cont'd E and F, Before curing, excess

composite cement is removed withexplorer, brushes, and IPC carver. G,

The composite cement is light-cured

from occlusal, facial, and lingual

directions.


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Finishing and Polishing Procedures


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A, Slender, fine-grit, flame-shaped, diamondinstruments are used to remove flash along facial and

lingual margins of CEREC ceramic inlay. B, 30-fluted

finishing burs are used to smooth areas that were

adjusted with diamonds.


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A, Removing excess composite cement using a surgical blade. B,

Smoothing the interproximal area with abrasive finishing strip.


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Polishing sequence for ceramic inlays. A, After using fine-grit diamonds

and 30-fluted carbide finishing burs to adjust contours and margins,rubber abrasive points and cups of successively finer grits are used at

slow speed. B, Final polish imparted by porcelain polishing paste applied

with bristle brush. C, Occlusal view of polished ceramic inlay.


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Common Problems and Solutions

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The most common cause of failure of tooth-colored

inlays and onlays is bulk fracture.

If bulk fracture occurs, replacement of the

restoration is almost always indicated.


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Repair of Tooth-ColoredInlays and Onlays


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For composite and ceramic inlays, the

repair procedure is initiated by mechanical

roughening of involved surface.

For ceramic restorations, the initial mechanical


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For ceramic restorations, the initial mechanical

roughening is followed by brief (typically 2 minutes)

application of10% hydrofluoric acid gel.

Hydrofluoric acid etches the surface, creating further

microdefects to facilitate mechanical bonding.

Although many indirect composites containetchable glass filler particles, hydrofluoric


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etchable glass filler particles, hydrofluoric

acid treatment of composites is neither necessary

nor recommended.

However, a brief application ofphosphoricacid may be used to clean the composite surface

after roughening.

The next step in the repair procedure is application

f il li


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of a silane coupling agent.

Silanes mediate chemical bonding between

ceramics and resins and also may improve the

predictability of resin-resin repairs.

After the silane has been applied a resin


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After the silane has been applied, a resin

adhesive agent is applied and light cured.

A composite of the appropriate shade is placed,

cured, contoured, and polished.

Documents

Class I and II Indirect Tooth-Colored Restorations (4,5)