Intracoronal Restorations in Fpd

7/31/2019 Intracoronal Restorations in Fpd

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The part of a fixed partial denture which unites theabutment(s) to the remainder of restoration.

It is a crown or any restoration that is cemented tothe abutment.

Retainers can be1. Extra coronal retainers-they cover the entire

occluding surface of the tooth e.g. full veneercrowns, partial veneer crowns.

2. Intra coronal retainers


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small metallic extensions that arecemented onto the tooth. E g: inlay, onlay.

INLAY ONLAY


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An inlay is an indirect restoration(filling) consistingof a solid substance (as goldor porcelain) fitted toa cavity in a tooth and cemented into place.

Sometimes the decay or fracture is so extensivethat a direct restoration,such

as amalgamor composite, would compromise thestructural integrity of the restored tooth or fail tobear occlusal (i.e., biting) forces. In such situations,an indirect gold or porcelain inlay restoration may

be used. They are usually used when tooth destruction is less

than half the distance between cusp tips.
http://en.wikipedia.org/wiki/Goldhttp://en.wikipedia.org/wiki/Porcelainhttp://en.wikipedia.org/wiki/Dental_restorationhttp://en.wikipedia.org/wiki/Amalgam_(dentistry)http://en.wikipedia.org/wiki/Dental_compositehttp://en.wikipedia.org/wiki/Dental_compositehttp://en.wikipedia.org/wiki/Amalgam_(dentistry)http://en.wikipedia.org/wiki/Dental_restorationhttp://en.wikipedia.org/wiki/Dental_restorationhttp://en.wikipedia.org/wiki/Porcelainhttp://en.wikipedia.org/wiki/Gold


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An onlay is an indirect restoration whichincorporates a cusp or cusps by coveringor onlayingthe missing cusps.

When decay or fracture incorporate

areas of a tooth that make amalgamorcomposite restorations inadequate, suchas cuspalfracture or remaining toothstructure that undermines walls of a

tooth, an onlay might be used. Onlays are fabricated outside of the

mouth and are typically made out ofgold or porcelain.
http://en.wikipedia.org/wiki/Amalgam_(dentistry)http://en.wikipedia.org/w/index.php?title=Cusp_and_ridgs_(dentistry)&action=edit&redlink=1http://en.wikipedia.org/w/index.php?title=Cusp_and_ridgs_(dentistry)&action=edit&redlink=1http://en.wikipedia.org/wiki/Amalgam_(dentistry)


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A inlay can be used instead of amalgamfor patients with a low caries rate who

require a small class II restoration in a tooth

with ample supporting dentin.

Least complicated cast restoration to

make.

Durable if done carefully.


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An onlay allows the damaged occlusalsurface to be restored with a casting in the

most conservative manner.

Restoration of a severely worn dentition with

minimally damaged teeth or forreplacement of an MOD amalgam

restoration when sufficient tooth structure

remains for retention and resistance form.


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As these rely on intra coronal(wedging)retention, contraindicated unless there is

sufficient bulk to provide resistance and

retention form.

MOD inlays may increase the risk of cusp

fracture and are avoided.

Extensive onlays, where caries extend

beyond the facial or lingual line angles, arecontraindicated unless pins are used to

supplement retention and resistance.


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Long lived because of excellent mechanicalproperties of gold alloys.

Low creep and corrosion. Esthetics. Absence of tooth discoloration as with amalgam. Resistance to occlusal forces.

Protection against recurrent decay. Marginal integrity. Precision of fabrication. Proper contouring for gingival health.

Ease of cleansing. An onlay can support the cusps, reducing the risk

of tooth fracture. If the onlay or inlay is made in a dental laboratory,

a temporary is fabricated while the restoration is

custom-made for the patient.


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For small carious lesion, an inlay is not veryconservative.

To achieve cavity preparation without undercutsand to permit access for impression makingadditional tooth removal is necessary.

This extension may lead to additional display ofmetal and gingival encroachment which affectsperiodontal health.

Inlays rely on buccal and lingual cusps forresistance and retention form.

Due to wedging from inlay high occlusal force mayfracture the cusp.

Very costly.


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Carbide burs are usually used for inlay or onlay

preparations, but diamonds can be substituted ifpreferred:

1. Tapered carbide burs2. Round carbide burs3. Cylindrical carbide burs

4. Finishing stones5. Mirror6. Explorer and periodontal probe7. Chisels8.

Hatchet9. Gingival margin trimmers10. Excavators11. High- and low-speed hand pieces

12. Articulating film


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Occlusal Analysis1. Carefully assess the occlusal contact

relationship and mark it with articulatingfilm. The margins of the restoration shouldnot be too close (


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Outline Form

3. Penetrate the central groove just to the

depth of the dentin (typically about 1.8mm) with a small, round or taperedcarbide bur held in the path of

withdrawal of the inlay. Generally this will be perpendicular to

an imaginary line connecting thebuccal and lingual cusps, notnecessarily perpendicular to theocclusal plane. For example, onmandibular premolars it will be angled

toward the lingual.


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4. Extend the occlusal outline through thecentral groove with the tapered

carbide. The bur should be held in the same path

of withdrawal and kept at the samedepth just into dentin.

The buccolingual extension should beconservative to preserve the bulk of thebuccal and lingual cusps. Resistance toproximal displacement is achieved witha small occlusal dovetail or pinhole.

The outline should avoid the occlusalcontacts.


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5. Extend the outline proximally,Underminingthe marginal ridge, and stop it at theheight of contour of the ridge.

6. Advance the bur cervically to the cariouslesion and then lingually and buccally.

There should be a thin layer of enamelremaining between the side of the burand the adjacent tooth to preventaccidental damage.

The bur should move parallel to theoriginal unprepared proximal surface,

creating a convex axial wall in the box asthe opposing buccal and lingual wallsprovide retention.


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It should be held in the path ofwithdrawal throughout.

The width of the gingival floor of the boxshould be about 1.0 mm (mesiodistally).

Correct cervical,lingual, and buccal

extension is just beyond the proximalcontact area.

A minimum of 0.6 mm of proximal

clearance required to allow an impressionto be made.

Sharp line angles are rounded at this time


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Caries Excavation

7. Identify and remove any caries left,using an excavator or a round bur inthe low-speed handpiece.

8. Place a cement base to restore theexcavated tissue in the axial walland/or pulpal floor.

If necessary, the preparation can be

extended buccally or lingually.


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Axiogingival Groove and Bevel Placement

9. Prepare a small, well-defined groove atthe junction of axial and gingival walls atthe base of the proximal box to enhanceresistance form and prevent distortion ofthe wax pattern during manipulation.

It is easily placed with a gingival margintrimmer held in contact with the axialwall to prevent creating an undercut.


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10. Place a 45-degree gingival marginbevel with a thin, tapered carbide or

fine-grit diamond. Correct orientation is achieved by

holding the instrument parallel to the

gingival one third of the proximalsurface of the adjacent tooth.

The bur should not be tilted buccally

or lingually to the path of withdrawal;otherwise, an undercut will becreated at the corners of the box.


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11. Prepare proximal bevels on the

buccal and lingual walls with thetapered bur oriented in the path ofwithdrawal.

There should be a smooth transitionbetween the proximal and gingivalbevels.

12. Place an occlusal bevel to improvemarginal fit and allow finishing of therestoration.


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When the cuspal anatomy is steep, aconventional straight bevel will create

too little gold near the margin forstrength and durability.

A hollow-ground bevel or chamfer is

normally preferred and can beconveniently placed with a round buror stone.

13. As a final step, smooth thepreparation where necessary,specially the margins.


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The MO inlay preparation. A, Depth hole extending just

into the dentin.B, An occlusal outline is prepared following the central

groove.C, The outline is extended proximally and then gingivally,

undermining the marginal ridge and removing caries.


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D, Unsupported enamel is removed, andthe walls of the proximal box are defined.

This is easily done with hand instruments.

E, Proximogingival bevels can be placed

with tapered or flame-shaped carbides

and hand instruments.

F, An occlusal bevel or chamfer

complete the preparation.

G, Occlusal view of the completed

preparation.

G


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Preparation of a mandibular molar tooth for

an MO inlay.A, Occlusal outline.B, Proximal box initiated.C, Proximal box extended to remove contact.D, Completed preparation.

A B

C D


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The occlusal outline and proximal boxes of an onlay

preparation are similar to those of an inlay. Theadditional steps are the Occlusal reduction and afunctional(centric)cusp ledge.

Outline Form

1. Prepare the occlusal outline with a taperedcarbide bur just beyond the enamel-dentin

junction (approximately 1.8 mm deep) andextend it through the central groove,

incorporating any deep buccal or lingualgrooves.

Existing amalgam restorations are removed.


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2. Extend the outline both mesially anddistally to the height of contour of the

marginal ridge. As with an inlay, the boxes are prepared

by advancing the bur gingivally and

then buccally and lingually, alwaysholding it in the precise path ofwithdrawal of the preparation.

There should be a thin section ofproximal enamel remaining as the buradvances, to prevent damage to theadjacent tooth.


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A minimum clearance of 0.6 mm isneeded for impression making.

Sometimes existing restorations or cariesrequire a box to be extended beyond

optimal so the preparation will have littleresistance form, and an alternativerestoration such as a complete crown

should be considered.


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Preparing the boxes is a key stepwhen fabricating an onlay. Thetapered bur should be held preciselyin the planned path of withdrawalthroughout.

Tilting should be avoided.

3. Round sharp line angles between theocclusal outline and proximal boxes.


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Caries Excavation

4. Remove any remaining caries using an

excavator or a round bur in the low-speed

hand piece.

5. Place a cement base to restore the

excavated tissue. Ensure that adequate

sound dentin is present on the axial walls toprovide retention and resistance.


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Occlusal Reduction

6. Place depth grooves on the centric

(functional) cusps. To give additional clearance at the

cusp tip, the bur must be orientedmore horizontally.

The grooves should be 1.3 mm deep,allowing 0.2 mm for smoothing.

7. Place 0.8 mm grooves on the non

centric cusps. On non centric cusps, the bur is

oriented parallel to the cuspal inclines.


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8. Connect the grooves to form theocclusal reduction maintaining thegeneral contour of the originalanatomy.

9. Prepare a 1.0-mm centric cusp ledgewith the cylindrical carbide bur.

This will give the restoration bulk in ahigh-stress area, preventingdeformation during function.

The ledge should be placed about 1mm apical to the opposing centriccontacts.


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10. Round any sharp line angles,

particularly at the junction of theledge and occlusal surface.

11. Check for adequate occlusal

reduction by having the patient closeinto soft wax and measuring with athickness gauge.


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Margin Placement

12. Establish a smooth, continuous bevel

on all margins. The gingival bevel is placed, as for an

inlay, with the thin carbide or

diamond held at 45 degrees to thepath of withdrawal, or approximatelyparallel to the adjacent toothcontour.

This will blend smoothly with thebuccal and lingual bevels.


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13. Bevel the noncentric and centric cusps.Where additional bulk at the margin is

needed, a chamfer should besubstituted for the straight bevel.

This can be placed with a round-tippeddiamond.

14. Complete the preparation byrechecking the occlusal clearance in allexcursions and assessing for smoothness.


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The MOD onlay preparation.A, An occlusal outline is prepared to follow the central fossa, and themarginal ridges are undermined.B, The proximal boxes are refined.They should extend just beyond the

proximal contact area.C, Depth grooves are placed for occlusal reduction-0.8 mm on thenoncentric cusp and 1.3 mm on the centric cusp.D, Notethe lingual functional cusp bevel as part of the completedocclusal reduction. A lingual shoulderis prepared, approximately atthe level ofthe occlusal isthmus.


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E, Continuous bevel completes the preparation. The

bevel on the Lingual shoulder makes a smooth transitioninto the proximal bevel of the box. A small contrabevel isplaced on the buccal cavosurface margin.F, Occlusal view of the completed preparation

A B C D


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Preparation of a mandibular molar tooth for an MOD onlay.A, Preparation outline.

B, Proximal boxes extended to remove contacts.C, Occlusal reduction grooves.D, Centric cusp ledge

placed for distal half.E and F, Completed preparation.

E F


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For patients demanding estheticrestorations, ceramic inlays and onlays

provide a durable alternative toposterior composite resins.

The ceramic restoration can be bonded

to the prepared tooth with hydrofluoricacid and the use of a silane couplingagent.


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Used for patients with a low caries raterequiring a Class II restoration and

wishing to restore the tooth to its originalappearance.

It is the most conservative ceramicrestoration and enables most of the

remaining enamel to be preserved.


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Because these restorations are timeconsuming and expensive,contraindicated in patients with poororal hygiene or active caries.

Because of their brittle nature,contraindicated in patients with

excessive occlusal loading, such asbruxers.


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Esthetic restorations.

The restoration wear is not a problem.

Marginal leakage associated withpolymerization shrinkage and highthermal coefficient of expansion of theresin is reduced, because the luting layeris very thin.


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Accurate occlusion difficult to achieve.

Rough porcelain is extremely abrasive of theopposing enamel.

Wear of the composite resin-luting agent can

be a problem, leading to marginal

Finishing of the margins can be difficult in

interproximal areas.

Resin flash or overhangs can initiate periodontal

disease. Bonded ceramic inlays are a relatively new

concept, and long-term clinical performance is

hard to judge.


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As for metal inlays, carbide burs are used in thepreparation, but diamonds may be substituted:

Tapered carbide burs

Round carbide burs

Cylindrical carbide burs

Finishing stones Mirror

Explorer and periodontal probe

Chisels

Gingival margin trimmers

Excavators

High- and low-speed handpieces

Articulating film


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Rubber dam isolation.

Before applying the dam, mark and

assess the occlusal contact relationshipwith articulating film.

To avoid chipping or wear of the lutingresin, the margins of the restorationshould not be at a centric contact.


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Outline Form

1. Prepare the outline form- broadly similar

to that for conventional metal inlays andonlays

Axial wall undercuts can be blocked out

with resin-modified glass ionomercement, preserving additional enamel

for adhesion.

However, undermined or weakened

enamel should always be removed.


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The central groove reduction (typically

about 1.8 mm) follows the anatomy of the

unprepared tooth.

The outline should avoid occlusal contacts.

Areas to be onlayed need 1.5 mm of

clearance in all excursions to prevent

ceramic fracture.


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2. Extend the box to allow a minimum of0.6 mm of proximal clearance for

impression making. The margin shouldbe kept supra gingival, which willmake isolation easier and will improve

access for finishing.


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If necessary, electrosurgery or crown

lengthening can be done. The width of thegingival floor of the box should be

approximately 1.0 mm.

3. Round all internal line angles. Sharpangles lead to stress concentrations andincrease the likelihood of voids duringthe luting procedure.


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Caries Excavation

4. Remove any caries not included in the

outline form preparation with anexcavator or a round bur in the low-speed handpiece.

5. Place a resin-modified glass ionomercement base to restore the excavatedtissue in the gingival wall.


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Margin Design

6. Use a 90-degree butt joint for ceramicinlay margins. Bevels arecontraindicated because bulk is neededto prevent fracture.

A distinct heavy chamfer isrecommended for ceramic onlaymargins.


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Finishing

7. Refine the margins with finishing burs

andhand instruments, trimming back anyglass ionomer base. Smooth, distinctmargins are essential to an accuratelyfitting ceramic restoration.


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Occlusal Clearance (for Onlays)

8. Check this after the rubber dam isremoved.

A 1.5-mm clearance is needed toprevent fracture in all excursions. This canbe easily evaluated by measuring thethickness of the resin provisional

restoration with a dial caliper.

A B


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Maxillary first molar preparation for an MOD ceramic inlay.A, Defective restoration.B, The restoration and caries removed.C, Unsupported enamel removed and glass ionomer base placed.D, The completed ceramic restoration.

C D


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Intracoronal Restorations in Fpd