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By:- Abhijeet Khade P G StudentDept. of Conservative Dentistry NHDC
CONTENTS:- Introduction. Materials for cast restorations Indications & Contraindications Advantages and disadvantages Principles of Cavity design for Cast inlay restorations. Tooth preparation for Inlay Class II cast metal inlays Bevels- Various types and significance. Variations in proximal margin design. Tooth Preparations For Cast Restorations With Surface Extension. Conclusion References
INTRODUCTION Dr. Phil brook in 1897,was the first to introduce Inlay in dentistry who gave the concept of forming an investment around a wax pattern, eliminating the wax, and filling the resultant mold with a gold alloy. In 1907 Taggart changed the practice of restorative dentistry by introducing his technique for cast gold dental restorations. It was most certainly Taggart who recognized the significance of cast gold restorations.
METERIALS FOR CAST RESTORATIONS Until recently gold-based alloys have been the only ones used for cast dental restorations. The ADA sp#5 still requires 75% of gold-plus- platinum group metals to be present in alloys for cast restorationsAccording to Sturdevant there are 4 distinct groups of alloys. The traditional high gold alloys. Low gold alloys. Palladium-silver alloys Base metal alloys.
ACCORDING TO MARZOUK:1. Class-I: Gold and platinum group based alloys.2. Class-II: Low gold alloys (gold content < 50%).3. Class-III: Non-gold palladium based alloys.4. Class-IV: Nickel-chromium based alloys.5. Castable moldable ceramics
CHARACTERISTICS OF CAST GOLDALLOYSAccording to ADA sp#5 the alloys are characterized as follows-Type I-soft gold alloysType II-medium hard alloysType III-hard alloysType IV-extra hard alloys
According to ADA specification No.5:1. Type-I (Soft): For restorations subject to very slight stress such as inlays.2. Type-II (Medium): For restorations subject to moderate stress such as onlays.3. Type-III (Hard): For high-stress situations, including onlays, crowns, thick veneer crowns and short-span fixed partial dentures.4. Type-IV (Extra hard): For extremely high stress states, such as endodontic posts and cores, thin veneer crowns, long span fixed partial dentures and removable partial dentures.
Alloy Type Total noble metal contentHigh Noble (HN) Contains 40 wt.% Au + 60 wt.% of noble metal elements (Au + Ir + Os + Pd + Rh + Ru).Noble metal (N) Contains 25 wt.% of the noble metal elements.Predominantly base metal Contains < 25 wt.% of the(PB) noble metal elements.
In,Fe,Zn,Type Au Cu Ag Pd Ga I 83% 6 10 0.5 Balance II 77% 7 14 1 Balance III 75% 9 11 3.5 Balance IV 69% 10 12.5 3.5 Balance
INGREDIENTS OF NOBLE METAL ALLOYS:The most important element in dental gold alloys is gold, copper, silver, platinum metals and zinc.1. Gold: Gold is primarily responsible for deformability (ductility). Ranks lowest in strength. Characteristic yellow color with a strong metallic luster. Density (Sp gravity) 19.3 g/cm3. Tarnish resistance. Fusion temperature – 1063o C.
2. Platinum: May be added to1. Strengthen the alloy.2. Raise the fusion point (1755).3. Import rigidity, nobility and hardness.4. Whiten the alloy.5. Specific gravity-- 21.37.6. Also malleable and ductile.3. Palladium: Serves the same functions but is much less expensive than platinum.
4. Iridium, Ruthenium and Rhodium: Trace amounts of these metals are added as “Grain Refiners” melting point . As little as 0.005% is sufficient to refine the grain size. Grain refiners produce smaller grains. Fine-grained alloys are generally stronger and more ductile than coarse-grained alloys. Indium can also act as a scavenger for the alloy during casting procedure. Also serve to increase the tarnish and corrosion resistance.
5. Silver: It contributes to the strength and hardness of the alloy. Although it mimics gold in its deformability effect, it adversely affects the malleability and it lowers tarnish resistance. Food containing sulfur compounds, cause severe tarnish on silver. Silver serves to balance the red color given by copper. Adding small amounts of palladium to silver containing alloys prevents the rapid corrosion of such alloys in the oral environment
6. Copper: Contributes strength and hardness, but decreases the malleability of the alloy, i.e., it decreases the tarnish and corrosion resistance . The content should not exceed 16%. Gives the alloy reddish appearance. Lowers the fusion temperature.7. Zinc: (Present only in low percentages, around 0.5%) Acts as a deoxidizer and reduces the oxygen content (because O2 released during solidification results in porosity).
Modu Dens Yield -lus Rate Type of Melting Hardne -ity stren of of cast Elongation range ss (gm/ gth elasti tarnimaterials (o F) (VHN) cm3) (MPa) city( sh PSI)Class I 20-25% 943-960 16.6 103 80 10-12 0%Class II 20% 924-960 15.9 186 101 12 2-3%Class III 15-18% 924-960 15.5 207 121 5- 15 10% ClassIV 3-11% 834-916 12.8 241 138 30 0% 1021- ClassV 0% 10.6 262 143 60 0% 1099
INDICATIONS Large restorations Endodontically treated teeth Teeth at risk for fracture Dental rehabilitation with cast metal alloys Diastema closure and occlusal plane correction Prosthodontic abutment Correction of occlusion Wide open contacts and occlusal plane correction Adjunct to periodontal therapy to correct tooth anamolies predisposing to plaque accumulation Sub gingival lesions
CONTRAINDICATIONS Physiologically young dentition with large pulp chambers are poor candidates for cast restoration Developing and deciduous teeth High plaque / caries indices. Dissimilar metals. Esthetics Small restorations
ADVANTAGES Strength Biocompatibility Low wear Control of contours & contacts
DISADVANTAGES Extensive tooth preparation Cemented restoration, discrepancy and micro leakage Abrasive and splitting force on natural teeth Galvanic currents Number of appointments and higher chair time Cost and Temporary restoration requirement Technique sensitive
PRINCIPLES OF CAVITY DESIGN FOR CASTINLAY RESTORATIONS.Basic differences between Amalgam and Castrestoration preparation are Intercuspal distance Undercuts Bevels- occlusal and gingival
APICO-OCCLUSAL TAPERPREPARATION For maximum retention in a cast restoration opposing walls and opposing axial surfaces of a tooth preparation should be perfectly parallel to each other. Taper should be an average of 2-5 degree from path of preparation. It can be decreased or increased according to the length of the preparation wall and/or axial surface, surface involvement and internal anatomy in the preparations.
CONVERGENT ANGLEExtension of opposing walls, which diverge toward the occlusal form a convergent angle. A bisection of this angle positions the “line of draw” which is perpendicular to the pulpal floor.
PREPARATION PATH: The preparation should have a single insertion (draw) path, opposite to the direction of the occlusal loading. This path is usually parallel to the long axis of the tooth. So that the completed cavity will have draft (no under cut).
PREPARATION FEATURES OF THECIRCUMFERENTIAL TIE The peripheral margin anatomy of the preparation is called circumferential tie. Enamel must be supported by sound dentin. Enamel rods forming the cavosurface margin should be continuous with sound dentin. Enamel rods forming the cavosurface margin should be covered with the restorative material Angular cavosurface angles should be trimmed
BEVELS Bevels are the flexible extensions of a cavity preparation, allowing the inclusion of surface defects, supplementary grooves, or other areas on the tooth surface. Require minimum tooth involvement Bevels create obtuse-angled tooth structure i.e. the strongest configuration and acute-angled marginal alloy i.e. burnish able. Thus makes it possible to decrease the cement line. A lap, sliding fit is produced at gingival margin. It results in 30-degree metal that is burnish able. Weak enamel is removed.
SIX TYPES OF BEVELS Partial Bevel: involves part of enamel wall, not exceeding 2/3rds its dimension. It is not used in cast restorations, except to trim weak enamel rods. Short Bevel: includes entire enamel wall, but not dentin, it is used with class-I alloys specially for type 1 & 2 (Gold platinum based alloys). Long Bevel: includes all enamel & up to ½ of the dentinal wall, its major advantage is that it preserves the internal boxed-up resistance. , most frequently used for the 1st 3 classes of cast material.
Full Bevel: Includes all of the dentinal and enamel walls of the cavity wall or floor. Its use should be avoided except in cases where it is impossible to use any other form of bevel Counter Bevel: when capping cusps to protect and support these, this type of bevel is used, opposite to an axial cavity wall, on the facial or lingual surface of the tooth. Hollow ground bevel (concave)- All the types of bevels are in the form of a flat plane, but any of them especially that last three can be prepared in a concave form.
PRINCIPLES OF CAVITY DESIGN FORCAST INLAY RESTORATIONS An Inlay is defined as a restoration which has been constructed out of the mouth from gold, porcelain or other metal and then cemented into the prepared cavity of the tooth. The class-II inlay involves the occlusal and proximal surfaces of a posterior tooth and may cap one or more cusps but not all of the cusps. The class-II onlay involves the proximal surfaces of a posterior tooth and caps all of the cusps.
TOOTH PREPARATIONS FOR CLASS IICAST METAL INLAYS Initial preparation Occlusal step Proximal box Resistance and Retention form Final preparation Removal of infected caries and pulpal protection. Preparation of bevels and flares Modifications
Outline form for a DO preparationCarbide burs for preparation
OCCLUSAL STEP Initial entry is made in the central fossa/pit with a tapered fissure bur no.271 to establish the pulpal floor (punch cut) to a depth of 1.5mm. The depth is determined by the extent of existing carious lesions or restorations or the need for additional retention
Long axis of the bur should be parallel with long axis of tooth.
The occlusal outline is extended mesiodistally along the central groove and stopped just short of the marginal ridge. The bur is kept in the vertical position in the long axis of the tooth through-out the preparation so that its taper provides the 3 to 5-degree divergence to the facial and lingual walls (total divergence of 6 to 10 degrees).
PRIMARY RESISTANCE FORM Use of box shape Preservation of cusps and marginal ridges Slight rounding of internal line angles Capping weakened cusps Adequate thickness of restorative material
Removing the remaining infected dentin with no. 2 or 4 round bur
M Insertion of suitable base and completed base.
PREPARATION OF BEVELS AND FLARES The slender flame shaped fine-grit diamond is used to bevel the occlusal and gingival margins and to apply the secondary flare on the proximal-facial and lingual walls. It will result in 30-400 marginal metal & 140-1500 cavosurface margin
Placement of retraction cordfacilitates bevelling gingival margin
For the facial and lingual proximal walls in an inlaycavity preparation for castings flares are used, whichare the flat or concave peripheral portions of the facialand lingual wallsThere are 2 types of flares The primary flare The secondary flareThe primary flare: Is the conventional and basic part of the cavity facially and lingually for an intra coronal preparation. It is very similar to a long bevel formed of enamel and part of dentin on the facial or lingual wall. Primary flares also have a special angulation i.e., 450 to the inner dentinal wall proper.
Functions and indications – These design features perform the same function as bevels. They can bring the facial and lingual margins of the cavity preparation to cleansable finishable areas. They are indicated for any facial or lingual proximal wall of an intracoronal cavity preparation.
SECONDARY FLARE It is almost always a flat plane super imposed peripherally to a primary flare. It is usually prepared solely in enamel. Unlike primary flares, secondary flares may have different angulations, involvement and extent depending on their functionFunctions and indications of secondary flare- Lesions with wide bucco-lingual extensions Contact areas too broad
Extension gingivally to extend root surface lesion
CAPPING CUSPS When the occlusal outline is extended up the cusp slopes more than half the distance from primary groove, capping the cusp should be considered. If it is extended two thirds or more, capping is necessary.
BOXIntroduced by Dr.G.V Black in which the proximalcavities are prepared box shaped with buccal andlingual walls and a definite gingival floor.Advantages- It has its own resistance and retention form. Direct wax pattern can be made. The outline form of the proximal surface can be made on all types of teeth. Minimum display of metal.
Disadvantages- It involves removal of lots of tooth structure. Clinically it is time consuming. Narrow bevels leave a sharp edge and an undercut gingivally , which cannot be satisfactorily reproduced. While taking impression distortions and breaking of wax pattern occurs.
SLICE PREPARATION This form of cavity is modified so that the proximal surface is flat without definite side walls. This is slice preparation which depends for its retention mainly on the occlusal key, channels or locks cut in the axial wall. Historically ,a slice referred to the placement of extra coronal taper using a disk of adequate diameter to contact nearly the entire proximal surface
INDICATIONS As abutment in bridge work Small carious lesion only on the middle of the proximal surface. To improve retention form. Teeth with proximal undercuts can be eliminated which facilitates taking impression. Advocated for quadrant work where proximal outline form can be rapidly developed. For indirect wax pattern technique.
Advantages- Less tooth structure is sacrificed. Quicker and easier. Well protected enamel margins. Increases resistance and retention form by exposing a larger amount of tissue surface to the frictional grasp of the restoration.
Disadvantages- Thoma(1951)pointed out that it displays unnecessary amount of gold. Reduced retention form. Direct wax pattern cannot be made as distinguishing between the margins is difficult. The margins of metal which we’ll get are very thin which can get distorted.
Slice preparation- involves conservative disking of the proximal surface to establish the buccal and lingual extent of finish lines and provide a lap joint for finishing.
Auxiliary slice preparation-wraps partially around the proximal line angles, thus providing additional tooth support. Resistance form is enhanced. Provide external retention form.
MODIFIED FLARE In view of the shortcomings of box type and slice type preparations ,Barishman advocates a modified preparation which may be called the box cum gingival slice. Modified flare is nothing but a combination of box and slice preparation taking advantage of the box preparation and slice preparation. Minimum disking of the proximal walls is done for better finishing and polishing
TOOTH PREPARATION WITH SURFACEEXTENSIONSINDICATIONS- Surface extensions are required to include facial or lingual defects beyond the axial angle of the tooth. Surface extensions are required to eradicate severe peripheral Marginal undercuts, which have not been removed by the maximum angulations and extent of a secondary flare. A surface extension is necessary to encompass an axial angle for reinforcing and supporting reasons.
A surface extensions is needed to add to the retentive capability of the restoration proximally especially with shortened facial and lingual walls or as a reciprocal means of retention More surface extension is required to fulfil the objectives of secondary flares in extremely wide cavities or contact areas
REVERSE SECONDARY FLARES Can be added to a cavity (tooth) preparation in lieu of a secondary flare The reverse secondary flare is in the form a partial bevel. It involves only enamel with its maximum depth at its junction with the main cavity preparation. In ends on the facial or lingual surface with a knife edge finishing line, and its extent should not exceed the height of contour of the facial or lingual surface in the mesio-distal direction nor should it include the tip of the cusp.
SKIRT This is a more extensive surface extension than the reverse secondary flare also superimposed on the basic intracoronal inlay or onlay cavity preparation facially and or linguallyINDICATIONS- Skirting is required to involve defects with more dimensions (especially depth) than those that can be involve in a reverse secondary flare A skirt is required to import resistance and retention on a cast restoration in lieu of a missing or shortened opposing facial or lingual walls.
Skirting is necessary when the contact areas and contour of the proximal surface are to be changed Skirts are essential facially and lingually for tilted teeth in order to restore the occlusal plane.
COLLAR This type of surface extension is the most involving surface wise and depth wise. They are two typesa) Cuspal collarsb) Tooth collars Cuspal collars which involve the facial or lingual surface of one cusp only in a multi-cusped tooth. Tooth collars involve the entire facial or lingual surfaces of the tooth.
INDICATIONS They help in retention and resistance when an entire cusp is lost prior to the tooth preparation or when it is necessary to remove if due to excessive undermining. They help retention in shortened teeth. They help resistance and to enhance support for tooth that is endodontically treated.
CONCLUSIONCast restorations form an integral link in the dentalrestorative chain. They are an excellent choice inmany demanding situations. Understanding theprinciples of tooth preparations and the intricacies ofcast restorations will enable the dentist to optimallyutilize this excellent option when the clinical situationdemands.
REFERENCES Art and science of operative dentistry-Sturdevant Principles and practice Operative Dentistry- Charbeneau Fundamentals of operative dentistry-Marzouk Operative Dentistry-Summit Atlas of inlays, onlays, crown and bridges- Shillinberg Inlays Crowns & Bridges-Cowell and Curson Textbook of Operative Dentistry-Vimal Sikri