Presentation on theme: "The Cast Restorations Cast restoration has been defined as a precise duplicate for the prepared cavity which is fabricated outside the oral cavity and."— Presentation transcript:
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.
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 5-8 o 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 3-5 o 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
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).