BASIC CONCEPTS OF CLASS 2CAST RESTORATIONS (IN AN EASY MANNER)

THIS SLIDE IS BASCIALLY ABOUT THE BASIC CONCEPTS OF CAST RETSORATION REFERREF FROM STANDRED TEXTBOOK ALONG WITH REFERENCE GIVEN IN EACH SLIDE FOR YOUR EASE.HOPE THIS HELPS YOU.ANY CORRECTIONS ARE ALWAYS WELCOME

1. BASIC CONCEPTS OF CAST RESTORATIONS Presented BY , THARA ELIZABETH JES,1 st year Pg DEPARTMENT OF CONSERVATIVE DENTISTRY AND ENDODONTICS GUIDED BY, DR.DEEPAK KURUP DR.SHAZIA MAHREEN DR.RITU RAJ DR.HRISHITA MAJUMDAR DR.HETAL

2. CONTENT Classifications Variations in proximal marginal design Principles Intracoronal and extracoronal circumferential ties Steps for fabricating cast restoration Casting defects Introduction History Indications Contraindications Advantages Disadvantages

3. Cast restorations are those restorations that are fabricated extra orally and then cemented into the prepared tooth Eg:Inlay,Onlay,Crown,etc

4. HISTORY 4500-4000 BC :Ancient Egyptians had the idea of maxing wax replica of an item to be casted by lost wax casting for making jewelry, death masks and statues 1890 D r Swasey – (solid gold inlay ): gold foil adapted into the shape of tooth and invested and filled with 20karat gold 1891 Martin used wax for making gold inlays 1896 Dr Philbrook introduced pressure casting method 1907 Taggart introduced lost wax technique 1920 Coleman and Weinsten introduced cristobalite investment 1962 Dr Abraham Weinstein introduced dental gold alloys and porcelain composites K Asgar casting materials in dentistry Adv Dent Res2(1):33-43,August,1988

5. INDICATIONS Large Restorations The cast metal inlay is an alternative to amalgam or composite when the higher strength of a casting alloy is needed or when the superior control of contours and contacts. Endodontically Treated Teeth T o distribute occlusal loads in such a manner as to reduce the chance of tooth fracture. Teeth at Risk for Fracture Restoring the teeth having fracture lines in enamel and dentin with a restoration that braces the tooth against fracture injury may be warranted sometimes. Sturdevants art and science of operative dentistry 5 th edition

6. Dental Rehabilitation with Cast Metal Alloys Diastema Closure and Occlusal Plane Correction Removable Prosthodontic Abutment Retainers for fixed prosthesis Low incidence of plaque accumulation or decay Sturdevants art and science of operative dentistry 5 th edition

7. CONTRAINDICATIONS High Caries Rate Facial and lingual (especially lingual) smooth-surface caries indicates a high caries activity that should be brought under control before expensive cast metal restorations are used . Young Patients L onger and more numerous appointments A ccess is more difficult The clinical crowns are shorter Y ounger patients may neglect oral hygiene resulting in additional caries. Sturdevants art and science of operative dentistry 5 th edition

8. Aesthetics The dentist must consider the esthetic impact (display of metal) of the cast metal restoration Small Restorations Because of the success of amalgam and composite, few cast metal inlays are done in small Class I and II restorations. ADVANTAGES Sturdevants art and science of operative dentistry 5 th edition

9. ADVANTAGES Strength Biocompatibility Casting alloys are unreactive in the oral environment. This biocompatibility can be helpful for many patients who have allergies or sensitivities to other restorative materials. Low Wear Castings are able to withstand occlusal loads with minimal changes. Control of Contours and Contacts Sturdevants art and science of operative dentistry 5 th edition

10. DISADVANTAGES Number of Appointments and Higher Chair Time Temporary Cost Technique Sensitive Splitting Forces Sturdevants art and science of operative dentistry 5 th edition

11. CLASSIFICATION OF CAST RESTORATIONS I) Based on Noble Metal Content (ADA & Identalloy Classification) High-Noble Alloys: ≥ 60% noble metal (gold ≥ 40%). Titanium and Titanium Alloys: ≥ 85% titanium. Noble Alloys: ≥ 25% noble metal. Predominantly Base Alloys: < 25% noble metal. Shillinburg :Fundamentals of fixed prosthodontics 4 th edition

12. 1)Noble Metal Alloys These alloys contain gold, platinum, palladium, and sometimes silver, copper, or zinc. Key Properties : Gold (Au): Improves corrosion resistance and ductility. Platinum (Pt) & Palladium (Pd): Increase strength and hardness. Silver (Ag): Lightens color , adds ductility. Copper (Cu): Increases hardness and strength. Zinc (Zn): Reduces oxidation. Shillinburg :Fundamentals of fixed prosthodontics 4 th edition

13. 2)Base Metal Alloys (Non-Noble, Nonprecious) Used as alternatives to noble alloys due to lower cost. Common compositions: Nickel-Chromium (Ni-Cr), Cobalt-Chromium (Co-Cr). Properties: High strength, hardness, and tarnish resistance. Oxide Layer: Chromium oxide protects against corrosion . Shillinburg :Fundamentals of fixed prosthodontics 4 th edition

14. Disadvantages: Difficult to polish and finish as they are harder than noble metals. Excessive oxide formation.(Interfere bonding with ceramic ) Potential allergic reactions (nickel sensitivity in 4.5% of the population, 10x more common in women). Beryllium toxicity (added to improve castability but can be hazardous). Shillinburg :Fundamentals of fixed prosthodontics 4 th edition

15. 3)Titanium and Titanium Alloys Highly biocompatible, often used for implants and restorations. Forms a protective oxide layer (despite being chemically reactive). Challenges: High melting temperature (1,668°C). Requires oxygen-free casting to prevent contamination. Shillinburg :Fundamentals of fixed prosthodontics 4 th edition

16. II)Based on Cost: Precious (High Cost): High noble metal content (gold, platinum, palladium). Semiprecious (Medium Cost): Lower gold content (10–75%), silver-palladium alloys Nonprecious (Low Cost): Base metal alloys (nickel, chromium, cobalt). Shillinburg :Fundamentals of fixed prosthodontics 4 th edition

17. ACCORDING TO MARZOUK CLASS 1: According to ADA specification No.5 for inlay casting gold it requires a minimum of total gold plus platinum metals content of 75% wt They are classified into Type I ,Type II , Type III, Type IV CLASS II: Gold content 5-50% CLASS III: Non gold palladium based CLASS IV: Nickel Chromium based alloys CLASS V: Castable moldable ceramics Operative dentistry modern theory and practice: M .A Marzouk

18. 1)CLASS 1: 70-75% gold ,1-5% Pt or Pd,25-30% Silver and traces of Cu,Zn,etc Gold (Au): Increased strength, burnishability and have high density and yellow color Platinum (Pt) & Palladium (Pd): Increase strength , hardeness and whitness Silver (Ag): Adversely affect nobility i.e undergo tarnish and corrosion, cheapest whiting agent Copper (Cu): Increases hardness and strength. Zinc (Zn): Reduces oxidation. Class 1 is divided into 4 types Operative dentistry modern theory and practice: M .A Marzouk

19. Type I (Soft) – small inlays easily burnished and subjected to very light stress with lower hardness and proportional limit and greater elongation Small class 1,class 3 and class 5 restorations(low stress bearing) Direct method of inlay fabrication Type II (Moderate): Inlays subjected to moderate stress. Majority of cast gold restorations , including crowns that are supported by single tooth. Support occlusal stress without deformation better than type 1 Principles and practice of operative dentistry : Charbeneau

20. Type III (hard) : Greater tensile strength required by abutment crowns for fixed prosthodontic restorations and complete crowns High strength and hardness with less elongation Type IV: (Extra hard) Prosthodontic appliances with clasps or precision attachments Principles and practice of operative dentistry : Charbeneau

21. 2)CLASS 2 : Economy gold alloy Palladium substitute gold(60%) Cu,Zn,Ag comprises 25-30% Palladium retains the physical properties of gold but have low density in compared to gold Operative dentistry modern theory and practice: M .A Marzouk

22. 3)CLASS 3 Non gold palladium based alloys Palladium and silver 90% Indium ,Copper , Tin 10% Silver increase strength,whitness but undergo tarnish and corrosion Palladium being a noble metal prevent excessive tarnishing of silver and increase hardness and strength. Copper reduces the fusion temperature and increases its resistance to tarnish and corrosion Zinc acts as a deoxidizer Operative dentistry modern theory and practice: M .A Marzouk

23. 4)CLASS IV Nickel chromium based alloys Nickel chromium with chromium content<30%(to prevent excessive oxide layer , to decrease melting point of alloy ,lower the cost) Low percentage of Mo , Tungsten and Al Be in low percentage(Ga can replace Be) Silicon and Iron<2% Operative dentistry modern theory and practice: M .A Marzouk

24. 5)CLASS V Castable moldable cermaics Aluminium trioxide 50% Magnesium oxide 15% Glass frit 5-25% Silicone polymer 0.5% wax and sterate Operative dentistry modern theory and practice: M .A Marzouk

25. Variations In proximal margin design: The design of the proximal cavity vary with Extent of the tooth tissue loss Location of that loss Tooth form The positional relationship with adjacent tooth The need for retention form Convenience Principles and practice of operative dentistry : Charbeneau

26. The design variations are Box preparation Slice preparation Auxiliary slice preparation (modified slice) Modified flare preparation (hybrid) Principles and practice of operative dentistry : Charbeneau

27. BOX PREPARATION Proximal Margin Design: Allows easy wax manipulation in the mouth. Purpose of Margins: Ensures adequate wax bulk for finishing and adaptation. Buccal and lingual proximal walls are finished. Cavo surface angle (proximal flare at tooth surface) is slightly right or obtuse Cervical Bevel: Required for proper adaptation. Typically placed using hand instruments. Forms a lap joint with bulk wax for direct waxing. Principles and practice of operative dentistry : Charbeneau

28. Box Design: Primarily used in proximal occlusal preparations. Supports direct wax pattern formation. Principles and practice of operative dentistry : Charbeneau

29. SLICE PREPARATION: Initially used for extracoronal tapering with a large disc. Established a cervical finish line and removed proximal undercuts. Allowed easier impressions with non-elastic dental compounds. Conservative disking of the proximal surface. Defines buccal and lingual finish lines. Slices placed independently on buccal and lingual proximal surfaces. Principles and practice of operative dentistry : Charbeneau

30. Extent of Slice Preparation: May reach the cervical floor or stop occlusally, depending on tissue preservation. Tooth Form Considerations: Square-shaped teeth: Slice can extend to the cervical floor with minimal tissue loss. Tapering/ovoid-shaped teeth: Slice should stop before the cervical floor to avoid excessive tissue removal. Principles and practice of operative dentistry : Charbeneau

31. AUXILIARY SLICE Provides external support to weakened tooth tissue. Strengthens areas under high functional stress. Design & Function: Wraps partially around proximal line angles for added support. Enhances resistance form, reducing the risk of tooth fracture. Aids in external retention form. Principles and practice of operative dentistry : Charbeneau

32. Lingual proximal line angle slice: Prevents buccal displacement of casting. Buccal proximal line angle slice: Prevents lingual displacement of casting. Useful when a buccal proximal wall cannot be established due to caries or fracture. Principles and practice of operative dentistry : Charbeneau

33. MODIFIED FLARE PREPARATION Hybrid between box and slice preparations. Technique: Buccal and lingual proximal walls are initially formed with minimal extension. Discing is performed in a way that slightly reduces the proximal wall dimension. Excessive disking can reduce wall retention. Principles and practice of operative dentistry : Charbeneau

34. Key Features: Enhances the obtuseness of the cavosurface angle Aesthetic Considerations: Box-slice preparation is often chosen for mechanical, biological, and aesthetic benefits. Mesial-buccal proximal margins of maxillary bicuspids and first molars often appear better without a slice. Principles and practice of operative dentistry : Charbeneau

35. PRINCIPLES OF CAST RESTORATIONS 1)PREPARATION PATH: Oriented opposite to the direction of occlusal loading. Ensures proper fit and stability of the restoration. All tooth structure reductions (intra-coronal or extra-coronal) should follow one path. This path is usually parallel to the long axis of the tooth crown. Operative dentistry modern theory and practice: M .A Marzouk

36. 2)APICO-OCCLUSAL TAPER Average taper: 2 to 5 degrees from the path of preparation. Can be adjusted based on: Preparation length: Longer walls require more taper (should not exceed 10°). Shorter walls need less taper (close to 0°, but not negative ). Operative dentistry modern theory and practice: M .A Marzouk

37. Surface involvement & internal anatomy: More surface details = more friction between preparation and material. To reduce friction, increase taper (but not beyond 10°). Need for Retention More the need for retention the more will be the need to approach exact parallelism and less taper Operative dentistry modern theory and practice: M .A Marzouk

38. 3)PREPARATION FEATURES OF CIRCUMFERENTIAL TIE The peripheral marginal anatomy of a preparation is known as the circumferential type. If margins are in enamel, they must meet Noy’s ideal cavity wall requirements : Enamel must be supported by dentin. Enamel rods should be continuous with sound dentin Cavosurface margin covered with restorative material. Angular cavosurface angles should be trimmed for better adaptation. Operative dentistry modern theory and practice: M .A Marzouk

39. CIRCUMFERENTIAL TIE FOR INTRACORONAL PREPARATION Circumferential tie for intracoronal preparation consists of bevels and flares BEVELS: Bevels are flexible extensions of a cavity preparation allowing the inclusion of surface defects, supplementary grooves and other areas on the tooth surface. Operative dentistry modern theory and practice: M .A Marzouk

40. TYPES AND DESIGN FEATURES OF OCCLUSAL AND GINGIVAL BEVELS According to their shape and tissue involvement they are classified into 6 types a. Partial Bevel Involves part of the enamel wall, not exceeding two-thirds of its dimension. Rarely used in cast restorations. Operative dentistry modern theory and practice: M .A Marzouk

41. b. Short Bevel Includes the entire enamel wall but not dentin. Mainly used with Type 1 and 2 gold alloys. c. Long Bevel Extends to one-half of the dentinal wall. Maintains boxed-up resistance and retention of the restoration. Used for first three classes of cast materials Operative dentistry modern theory and practice: M .A Marzouk

42. d. Full Bevel Covers both enamel and dentin of the cavity wall or floor. Deprives the cavity of internal resistance and retention. Should be avoided expect in cases where other bevels are impossible to use e. Counter Bevel Placed opposite an axial cavity wall (e.g., buccal or lingual surface) when capping cusps to protect and support them and will have a gingival inclination facially and lingually. Operative dentistry modern theory and practice: M .A Marzouk

43. f. Hollow Ground (Concave) Bevel Can be prepared in concave form Allows more space for cast material bulk Helps in retaining and stabilizing the restoration. Ideal for class IV and V restorations Operative dentistry modern theory and practice: M .A Marzouk

44. FUNCTIONS OF OCCLUSAL AND GINGIVAL BEVELS Enhance marginal tooth strength by creating an obtuse-angled margin. Help in burnishing cast alloys to reduce gaps and eliminate cement lines. Prevent microleakage Major retention and resistance form Operative dentistry modern theory and practice: M .A Marzouk

45. FLARES Flares are flat and concave peripheral portions of facial and lingual walls There are two types of flares Primary flare Secondary flare Operative dentistry modern theory and practice: M .A Marzouk

46. PRIMARY FLARE Basic and conventional part of the circumferential tie. Extends facially and lingually in an intracoronal preparation. Set at a 45° angle to the inner dentinal wall. Functions: Perform the same function of bevels Bring the margins to cleansable finishable areas Operative dentistry modern theory and practice: M .A Marzouk

47. SECONDARY FLARE: Flat plane superimposed peripherally to a primary flare. Functions and Indications: Create obtuse angulation of marginal tooth structure. In wide extended lesions buccolingually a secondary flare superimposed at correct angulation creates an obtuse angulation of marginal tooth structure In broad contact areas where primary flare will not bring margins to cleansable finishable areas To eliminate undercuts with minimal sacrifice of tooth structure in ovoid teeth so as to eliminate the problem of marginal failure Operative dentistry modern theory and practice: M .A Marzouk

48. CIRCUMFERENTIAL TIE FOR EXTRACORONAL PREPARATION CHAMFER FINISHING LINE Tylmann (1965): A concave extra coronal finish line that provides greater angulation than a knife edge and less than that of a shoulder Most universally used for class1,class2 and class 3 cast materials Assures bulk and definite termination for the preparation marginally with little tooth involvement Bur used:round end tapered diamond bur Disadvantages: Limited burnishability of marginal cast alloy Shillinburg :Fundamentals of fixed prosthodontics 4 th edition

49. Can be placed on any finishable , cleansable, or protected axial surface. Most practical for sub-gingival extracoronal preparation. Contraindicated for Class IV and V cast materials due to poor castability when anatomic considerations prevent gingival floor preparation. Shillinburg :Fundamentals of fixed prosthodontics 4 th edition

50. Knife-Edge / Feather-Edge Finishing Line: Circumferential tie constituent with minimal tooth structure involvement. Suitable for highly castable, burnishable alloys Can be placed on inaccessible tooth surfaces .(needle diamond bur/thin flame) Indicated: on lingual surface of mandibular posterior surface Very convex axial surface Blends easily with the beveled constituents of the circumferential tie. Shillinburg :Fundamentals of fixed prosthodontics 4 th edition

51. Disadvantages: Indefinite termination of the casting. Risk of incomplete margin coverage with certain alloys due to lack of bulk space. Chance of fracturing the alloy part of the tie during burnishing, finishing, and polishing. Contraindications : Not suitable for Class III, IV, and V cast materials. Operative dentistry modern theory and practice: M .A Marzouk

52. Shoulder Finishing Line Has a gingival wall perpendicular to axial surface of tooth Flat end tapered diamond bur is used Preferred for ceramic restorations where sufficient thickness is needed at margins All anterior restorations are fabricated so DISADVANTAGE:sharp line angle may cause stress accumulation Shillinburg :Fundamentals of fixed prosthodontics 4 th edition

53. Beveled Shoulder Finishing Line Circumferential type constituent with maximum tooth structure involvement. Indications :used on the facial finish line of metal ceramic crown where esthetics is not a concern. Ideal when maximum marginal bulk is required for low-castability or non- burnishable materials. Blends easily with beveled constituents of the circumferential type. Operative dentistry modern theory and practice: M .A Marzouk

54. Proper marginal adaptation, making it the most reliable extracoronal finishing line. More bulk of material Ideal for sub-gingival margins, ensuring predictable casting termination. Suitable for all classes of cast materials. Diasadvantage : More tooth structure is involved and is less conservative Operative dentistry modern theory and practice: M .A Marzouk

55. Hollow Ground( Concave) Bevel Finishing Line Exaggerated chamfer or a concave bevelled shoulder. Tooth involvement: More than a chamfer, less than a bevelled shoulder. Termination is less predictable than a beveled shoulder but mechanically superior to a chamfer. Operative dentistry modern theory and practice: M .A Marzouk

56. Key Features & Functions: Ensures no residual frail enamel or thin tooth structure at the periphery. Provides good transitional continuation with the beveled portion of the circumferential tie. Stabilizes the casting and allows it to seat preferentially. Ideal finishing line for Class IV and V cast materials.Suitable for materials with limited castability. Operative dentistry modern theory and practice: M .A Marzouk

57. STEPS IN METAL CASTING PROCEDURES STEP 1: Cavity preparation in the tooth STEP 2: Direct wax pattern OR impression of the prepared tooth STEP 3: Preparation of the die from impression & indirect wax pattern on the die Phillips science of dental materials 11 th edition

58. STEP 4: PREPARING WAX PATTERN FOR INVESTING Main objective of sprue is to create an inlet for the wetting melt into the investment mold created by the wax pattern SPRUE Type of sprue formers: waxes,metals,plastics SPRUE DIAMETER : :Diameter range: 8- 18gauge( 3- 0.8mm) SPRUE LENGTH: the end of the wax pattern must me at least 6mm away from the end of the ring SPRUE ATTACHMENT:Flared attachment at the largest cross-section of the pattern. Bulkiest portion of the pattern (Largest non-centric cusps.) SPRUE DIRECTION:45˚ angulation Reservoir:Additional wax build up around sprue 1-2 mm away from the pattern Operative dentistry modern theory and practice: M .A Marzouk

59. CASTING RING: It is a metal or silicone tube in which a refractory mold is made for casting dental restorations(GPT-9) Can be rubber ring or metal ring CASTING RING LINERS:the walls of the casting ring to provide investment expansion. Asbestos was used,but its carcinogenic potential makes it a biohazard Nonasbestos ring liner material are Aluminosilicate ceramic liner Cellulose (paper) liner. Shillinburg :Fundamentals of fixed prosthodontics 4 th edition

60. FUNCTIONS: allow mold expansion Permits easy removal of investment from casting Thermal insulator so prevents heat loss when ring is transferred from furnace to casting machine Shillinburg :Fundamentals of fixed prosthodontics 4 th edition

61. CASTING CRUCIBLE:Part of the investment is in a funnel shape and connected to the sprue Made of rubber,metal or plastic Funnel shaped opening at the bottom ensuring smooth transition for molten metal to flow into the mold . Operative dentistry modern theory and practice: M .A Marzouk

62. STEP 5:INVESTING Objective : capture all the wax pattern details in a solid investment material which is capable of maintaining these details after washing away of the wax pattern Can be gypsum bonded,silica bonded or phosphate bonded Methods of investing: Hand investing Vacuum investing In hygroscopic expansion ring is placed in 37degree Celsius water bath for one hour For thermal expansion the invested ring is allowed to bench set undisturbed for the time recommended by the manufacturer Phillips science of dental materials 11 th edition

63. STEP-6:BURNOUT OF WAX PATTERN Done after 1 hr after investing Ring should never be dried Mold is set in the furnace with the sprue hole placed downwards Phillips science of dental materials 11 th edition

64. Gypsum Investments : Slowly heated to 600°C to 700°C in 60 mins. and held for 15 to 30 min. at the upper temperature. 37 °C for hygroscopic technique for 60-90 min. Phosphate Investments : Phosphate investments much harder and stronger than gypsum investments. Burnout temperature range from 750°C to 1030°C. 315°C for 30 min  heating  held at the upper temperatures for 30 min Phillips science of dental materials 11 th edition

65. STEP 7:MELTING OF THE ALLOY Types of gases : 1) Gas fuels(blow torch) 2) natural gas & oxygen 3) oxygen & acetylene(hottest of all) USING ELECTRICAL ENERGY Types: -electrical resistance -induction melting -direct-current arc melting Phillips science of dental materials 11 th edition

66. CASTING MACHINES GAS PRESSURE CASTING MACHINE: Principle: -CO2 or nitrogen. - pressure of 10-15 psi - gas has no affinity for cast material Used for cast metal VACCUM CASTING MACHINE Vacuum is applied to the external surface of the investment to draw out the mold gases allowing the metal to ingress Phillips science of dental materials 11 th edition

67. CENTRIFUGAL CASTING MACHINE Most commomly used Types: motor driven or spring driven Investment mass is in the center of the revolving arm Adjace nt to the investment mass is the crucible containing melt Centrifugal force produced by revolving arm drive the melt into the mold Phillips science of dental materials 11 th edition

68. STEP 8: RECOVERY & CLEANING OF THE CASTING Quenching :Casting is removed from casting machine and rapidly cooling at water bath or ice water bath Making it soft and ductile i.e. in annealed condition for burnishing and polishing Easy removal For castable ceramics removal can be done with a suitable knife and ceramic cracks on quenching ,so better avoided Sand blasting: Casting is held in a sand blasting machine to clean the investment from the surface. Phillips science of dental materials 11 th edition

69. Pickling :Process in which discolored casting is heated in acid in test tube or beaker(<2 min) 50%HCL 50%Sulphuric acid Phillips science of dental materials 11 th edition

70. STEP 9: FINISHING OF THE CASTING Blebs are corrected by round bur whereas voids are corrected by soldering Hand burnish the marginal metal Grooves ,pits and most inaccessible areas are smoothened by rubber disks and points Rubber polishing wheel to smooth accessible surfaces Apply tripioli to occlusal surface using bristle disk Imparting luster using chamois wheel and rouge Sturdevants art and science of operative dentistry 5 th edition

71. CASTING DEFECTS Any impressions or irregularities that result in unsuccessful casting which interfere with the fit of the final restoration-basically classified into 4 categories DISTORTION SURFACE ROUGHNESS AND IRREGULARITIES POROSITY INCOMPLETE OR MISSING DETAIL Phillips science of dental materials 11 th edition

72. DISTORTION: Wax pattern distortion: can be prevented by proper handling and manipulation Investment material : d uring the expansion of investment material the thin portion of wax pattern cannot resist this expansion. But this is minimal Phillips science of dental materials 11 th edition

73. SURFACE ROUGHNESS AND IRREGULARITIES: Air bubble :when pouring investment material beside wax pattern Prevented by invest wax patter n under vaccum,use wetting agent to prevent collection of bubble on surface Water film :Wax is hydrophobic so some water film is in between wax pattern and investment material Prevented by applying wetting agent on wax pattern before investing Rapid and prolonged heating of investment material: Flaking of the investment due to steam of water Sulphur release from investment material causing discoloration Phillips science of dental materials 11 th edition

74. Underheating :leave wax residues remain in mold space Liquid/powder ratio of investment material :Higher L/P ratio higher the irregularity. Lower the ratio then thicker will be the mix that it won't be able to properly adapt to pattern Pattern position: if investing multiple patterns at the same level these areas will resist the expansion of molds which may cause roughness Carbon inclusions : Carbon from crucible formers,carbon from investment materials are absorbed by alloy during casting forming carbides Phillips science of dental materials 11 th edition

75. POROSITY Solidification defects: Localised shrinkage porosity Suck back porosity Microporosity Absorbed gases: Gas inclusions Subsurface porosity Pinhole porosity Air entrapment-Back pressure porosity Phillips science of dental materials 11 th edition

76. Solidification defects : Localised shrinkage porosity :Premature termination of flow of metal Occurs near sprue – casting junction Prevention: increase sprue diameter and decrease length Use reservoir Suck back porosity: sprue attached to wax pattern at 90 degree causing the formation of a hot spot opposite to that junction Occurs- occlusoaxial,incisoaxial line angle Prevention: Flare the sprue junction Sprue is attached to the wax pattern at 45 degree Phillips science of dental materials 11 th edition

77. Microporosity Occurs – rapid solidification too low casting temperature Cannot be seen externally Prevention :increase the casting temperature Increase the melting temperature of alloy Phillips science of dental materials 11 th edition

78. Absorbed gases: Pin hole :Smaller than gas inclusions and are spherical Gases absorbed by molten metal rather than the gases thar are present in mold space Molten metal have copper and silver in it and have higher affinity for oxygen whereas Pt and Pd have affinity for hydrogen and oxygen During the cooling down the gases will be expelled making pinhole porosity Casting contaminated with gases even appear discolored and cannot be removed by pickling Phillips science of dental materials 11 th edition

79. Gas inclusions : Larger than pinhole and are spherical May be due to dissolve gases and more likely due to gases that are present in the mold space Prevention :carbon crucible to absorb gases Use reducing part of the flame Phillips science of dental materials 11 th edition

80. Subsurface porosity: Not established Occurs- simultaneous nucleation of solid grains and gas bubbles along the mold walls Controlled by the rate at which molten metal enters the mold Phillips science of dental materials 11 th edition

81. Back pressure porosity : Large concave depressions Inability of air in mold to escape through the pores in the investment The entrapped air voids are frequently found in pocket at Cavity surface of a crown/ Mesio occluso distal casting Also occurs due to low mold/casting temperature causing solidification occurs before entrapped air has escaped Prevention :Proper burnout,adequate mold and casting temperature,high casting pressure,distance between wax pattern and end of the ring should be 6 mm Phillips science of dental materials 11 th edition

82. INCOMPLETE CASTING Occurs due to wax residue and molten metal Molten metal prevented from completely filling gold Insufficient pressure and high viscosity Incomplete elimination of wax residues Shiny margins(reducing property) caused by CO left by residual wax Phillips science of dental materials 11 th edition

83. REFERENCES Operative dentistry modern theory and practice: M .A Marzouk Shillinburg :Fundamentals of fixed prosthodontics 4 th edition Phillips science of dental materials 11 th edition Principles and practice of operative dentistry : Charbeneau Sturdevants art and science of operative dentistry 5 th edition K Asgar casting materials in dentistry Adv Dent Res2(1):33-43,August,1988