the cast restorations

The Cast Restorations

Cast restoration has been defined as a

precise duplicate for the prepared cavity

which is fabricated outside the oral

cavity and cemented in place in one

piece in order to restore the lost tooth

structure permanently.

It is a precise duplicate fabricated

outside the mouth and cemented into

the corresponding prepared cavity to

restore the missing part of the tooth

structure.

Advantages:

Indestructibility in the oral fluids of the mouth.

High strength properties. Dimensional stability. Convenience of manipulation. Production of tooth anatomy and

contour High abrasion resistance.

1. Superior strength properties enabling the restoration to protect the weakened tooth structure.

2. High surface hardness which makes the material very resistant to mechanical wear and can take and retain a highly polished surface.

3. Indestructibility in oral fluids and high resistance to tarnish and corrosion

.

4. Dimensional stability. The restoration

is casted with a shrinkage compensation

and once cemented in the prepared

cavity it does not undergo further

dimensional change.

5. Perfect restoration of anatomical landmarks and relations with neighboring and opposing teeth.

This is due to the ability of reproduction of details during carving of the wax pattern and the ability to retain the anatomy due to indestructibility and high wear resistance.

6. Bio-compatibility due to inertness of

the gold alloy plus the highly polished

surface which decreases plaque

accumulation and retention, in addition

to high gingival tolerance.

7. Decrease of the actual chair time

work . The insertion of the prefabricated

inlay omits the manipulation procedures

of direct restorations since most of the

work is performed in the lab work.

Disadvantages:

Lack of adaptability to cavity walls and margins.

High thermal conductivity. Less retention. Metallic color. Number of appointments, time and cost.

Indications: Large cavity that is difficult to restore by

other types of restoration. To restore badly broken down tooth. Teeth with excessive attrition and abrasion. For restoration of teeth with wide

interproximal spacing. To restore and cap the endodontically

treated molar and bicuspid which become weak and brittle.

INDICATIONS

a) As an individual restoration: For the restoration of posterior teeth in Class I,II and occasionally in Class IV in anterior teeth in cases of incresed stresses and abnormal occlusion and in some rare cases in Class III in anterior teeth and Class V in posterior teeth.

1. Teeth which are badly broken down or having missing cusp or more in which a gold inlay restoration will serve for their protection.

2. Extensive complex cavities in highly stressed areas.

3. Teeth with extensive attrition where a bulk preparation for direct restoration as amalgam may endanger the pulp.

4. Bicuspids with severe cuspal sloping where the destructive tensile component is maximum and there is a possibility of shearing off a cusp, an onlay with cusp protection is then indicated.

5. When perfect restoration of occlusal anatomy is required for the adjustment of inter-arch relationship.

6. Cases of open interproximal contact to prevent inclination and drifting of teeth.

7. Subgingival cavities, inaccessible areas and sites of impossible moisture control where the manipulation of direct restorations may be critical.

8. Endodontically treated teeth which require protection because of brittlness and loss of its moisture content.

9. In patients who can not tolerate long sessions of clinical work due to less chair time in case of cast gold restoration.

10. In patients with increased stresses because of deep bite, unfavorable occlusion, clinching or nail biting where the occluding surface has to be protected with hard and strong material.

11. Inlay restorations may be constructed to splint periodontally affected teeth together.

12. An inlay restoration may be constructed to serve for resting supports of fixed or removable prosthodontics.

As a bridge retainer.

To restore cavities extended deep

subgingivally where proper contouring of

the restoration would be difficult.

Contraindications:

In patients with high caries susceptibility,

where the chances for solubility of the

luting cements increase and caries

recurrence becomes more likely.

In mouth with multiple amalgam

restorations why???????

In cases where other permanent

restorative materials are preferred for

reason of tooth conservations.

STEPS OF CONSTRUCTION OF GOLD INLAY RESTORATION

I. Cavity preparation. II. Construction of the wax pattern. III. Spruing the pattern, investing, wax

elimination and mould expansion. IV. Heating alloy, melting and casting. V. Inspection of casting, finishing and

polishing.

I. CAVITY PREPARATION FOR CAST GOLD RESTORATION

a) General features:

1. The external diameter of the preparation is greater than the internal for withdrawal of the wax pattern.

2. Parallelism of axial walls for frictional retention against axial displacement. The walls are prepared with a slight

divergence occlusally 5-8o to assure the absence of undercuts which will prevent withdrawal of the wax pattern.

3. Cavosurface bevels (short, long, full and counter) are provided to protect: enamel margins, protect cement line and facilitate burnishing of the gold margin.

4. More extended bucco-lingual outline because of divergence of walls and the cavosurface beveling.

Moreover, the buccal and lingual walls of

proximal cavities should be more flared

and extended into the corresponding

embrassures in self cleansing areas as

well as to facilitate the convenient

burnishing of the margins.

5. Definite and sharp internal line angles to

guide a single pathway of insertion and resist

displacement of the restoration.

6. Extension for retention is an alternative to

augment the retentive features of the preparation

since the gold inlay is a one piece strong

restoration.

7. Slice preparations are possible for the

proximal portions though they are quick,

easy way of preparation and does not

leave a chance of undermined enamel,

yet they have the following disadvantages: a) It decreases retention because there are

no walls at the proximal portion. b) Thin margin of restoration gingivally with

a great chance of marginal bending due to poor resistance form.

c) The cement margin is unprotected and bare for dissolution effect of oral fluids.

d) It does not give chance to remove

proximal caries when deep axially.

e) A large amount of gold display will be

present bringing poor esthetics due to

absence of the buccal wall tooth

structure.

f) Sometimes, in more rounded proximal

surfaces of bulbous teeth , a great amount of

tooth has to be ground to remove the

undercut and locate the gingival border. This

may cause severe reduction of the tooth and

a consequent pulp exposure may occur.

g) There is no chance for making

reverse bevel or proximal axial grooves

with a slice preparation.

Outline form

Internal cavity walls: must be uniformly tapered occlusally

(slight occlusal divergence with a degree of taper 3-5o for each wall)

this will result in a cavity that has wider external outline form than the internal outline form which is needed for the seating of any restoration fabricated outside patient mouth.

Cavo-surface margin: Should be beveled, such bevel must be

proportional to the cavity depth. This means that it should not exceed ¼ of the cavity wall.

This allows for burnishing of the metal alloy to bring the margins of the alloy in contact with enamel and prevent exposure of cement line.

Gingival seat cavo-surface margin:

Should be trimmed with GMT creating

short bevel . This enhances the seating

ability of the final restoration at this area.

All internal line angles: must be well

defined but not sharp.

In case of occluso proximal cavity preparation (class II)

Primary flares that are regularly made with direct restoration to free the contact, are accompanied with secondary flare:Secondary flare are thus created on

proximal walls. This means that in cast gold preparation the facial and lingual walls extended from the facio or linguo-axial line angle into the facial or lingual emabrasure in two planes. The first is termed primary flare and the second is named the secondary flare

Secondary flare is necessary for:

Secondary flaring of the proximal walls

extends the margins into the

embrasures, making the margins more

self cleansing and more accessible to

finishing procedures during inlay

insertion appointment.

The direction of the flare results in 40-

degree marginal metal. Metal with this

angular design is burnishable.

A more blunted and stronger enamel

margin is produced because of the

secondary flare

Resistance and Retention form

Tooth resistance: including that the walls should be

parallel or perpendicular to occlusal force direction.

should follow the direction of enamel rods

Having rounded but definite line angles.

Restoration resistance

is not critical issue as compared to direct

brittle restorative material due to the

inherent strength property of cast gold.

Axial retention:

Mainly by friction of opposing walls and

governed by degree of wall tapering,

length and cement type

Increasing the degree of tapering of occlusal

divergence will decrease the frictional

retention.

For proximal part:

Performing dovetail lock whenever indicated.

Proximal grooves Reverse gingival bevel Secondary flaring are also means of

retention.

Beveling of the cavo-surface angle:Long beveling to the full length of enamel thickness

for the cavo-surface angle of the occlusal walls of the prepared cavity is essential.

1- to eliminate short and unsupported enamel rods at the cavo-surface angle.

2- to provide a strong enamel that is fully supported by dentine.

3- to provide a better burnishing fro the edge of the cast restoration to the cavity mragins.

4- to protect the underlying cement from the effect of oral fluids.

Types and Design Features of Bevels

Short bevel:

○ It includes only a part of the enamel walls

○ Not used with cast restorations.

Long bevel:This includes the entire enamel wall it is the most frequently used bevel for cast

restorations.Its major advantage is that it preserves the

internal resistance and retention form of the preparation.

Full bevel:○ This includes all of the enamel and dentinal

wall of the cavity.○ It deprives the preparation of its internal

resistance and retention form.○ It should be avoided

Counter bevel:○ When capping of the cusp to support them○ This type of bevel is used opposite to an axial

cavity walls on the buccal and lingual surface of the tooth

○ It has gingival inclination both buccally and lingually.

Cavity Preparations:

The same principles of cavity of amalgam have to be followed with some modifications:

The cavity wall must be prepared in a way that allow the wax pattern and the casting to be inserted and removed only in one direction without distortion.

Modifications of cavity prepartion.

In order to give the cavity the maximum retention and resistance form.

The surrounding walls of the cavity should be either parallel to each other or slightly divergent (5°- 8°)

The path of insertion and removal must be opposite to the direction of the masticatory forces.

In other words, the outer portion of the prepared cavity must be slightly greater in the cross-sectional area than the deepest part.

The nearer the cavity walls to parallism, the better is the gripping action and retention.

b) Cavity preparation for occluso-proximal inlay: Occlusal outline is made by initial

penetration into dentin in one of the pits, and then the isthmus is cut to its final extension.

The extension at this time is conservative, because an occlusal bevel will broaden it later

The initial cut is then extended far enough to

undermine the marginal ridge, which will be

removed shortly. Complete the undermining

of the marginal ridge and then penetrate in

an apical direction with the bur, so that the

tip is cervical to the contact.

Cut buccally and lingually to approximate

width of the proposed box without cutting

all the way through the enamel to the

outer surface. Break through the

undermined enamel to rough out the

proximal box using an enamel chisel

Occlusal outline.Undermining marginal ridge. Proximal box.

Using No., 170 bur to finish smoothing the proximal box. Extend it buccally and lingually just far enough to barely break contact with the adjacent tooth. The isthmus is widened where it joins the box. No reverse curve is required where the buccal portion of the isthmus blends into the proximal box “Primary flare” (Fig. 5-5).