Casting defects in dentistry

Detailed description of casting defects

1. 1 Good morning

2. PRESENTOR- ZADENO KITHAN PERCEPTOR – DR. SANA FATIMA 26.5.22 CASTING DEFECTS

3. 3 CONTENTS INTRODUCTION HISTORY DEFINITIONS STEPS OF CASTING PROCEDURE CLASSIFICATION OF CASTING DEFECTS -DISTORTION -SURFACE ROUGHNESS AND IRREGULARITIES -POROSITY -INCOMPLETE OR MISSING DETAIL VARIABLES AND PRINCIPLES OF OPTIMAL SPRUE DESIGN CLINICAL RELEVANCE CONCLUSION REFERENCES

4. INTRODUCTION Casting defects may occur when there is any discrepancy in any of the steps followed right through impression making, pouring of master cast, fabrication of wax pattern to investing and casting procedures Tuesday, February 2, 20XX Sample Footer Text 4

5. 5 HISTORY 2500 B.C-Egypt; Dental prosthesis made from gold wire found 1897-Philbrook described a method of casting metal into a mold from a wax pattern for restoration of posterior tooth. 1907- William Taggart introduced “lost wax technique ’’ 1908- Lane introduced mold expansion as a compensation technique 1910- Van horn discovered the value of wax expansion 1930- Carl Scheu, discovered the phenomena known as “Hygroscopic setting expansion”.

6. 6 STEPS OF CASTING PROCEDURE 1.TOOTH PREPARATION 6.RING LINER PLACEMENT 2.IMPRESSION 5. ATTACHMENT OF SPRUE FORMER 3.DIE PREPARATION 7.ASSEMBLY OF CASTING RING 9. BURN OUT OR WAX ELIMINATION 4.WAX PATTERN FABRICATION 10. CASTING 8.INVESTING 11. SAND BLASTING AND RECOVERY 12. FINISHING AND POLISHING

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10. Tuesday, February 2, 20XX Sample Footer Text 10 DEFINITIONS CASTING Casting is defined as something that has been cast in a mold, an object formed by the solidification of a fluid that has been poured or injected into a mold - GPT (7 th edition): Casting is the process by which a wax pattern of a prepared tooth is fabricated and converted to its metallic replica - Rosenteil CASTING DEFECTS   It is an unwanted irregularities that appear in the casting during metal casting process. 

11. Tuesday, February 2, 20XX Sample Footer Text 11 DEFECTS IN CASTING CLASSIFIED AS DISTORTION INCOMPLETE OR MISSING DETAIL SURFACE ROUGHNESS AND IRREGULARITIES POROSITY

12. Tuesday, February 2, 20XX Sample Footer Text 12 DISTORTION

13. 13 DISTORTION Most common cause of marked distortion is related to a distortion of the wax pattern. Distortion of the wax pattern occurs as the investment hardens around it Removal from the oral cavity during direct technique owing to thermal changes, improper handling during removal, contraction on cooling, relaxation of stresses, distortion during storage, etc The setting and hygroscopic expansions of the investment may produce a nonuniform expansion of the walls of the pattern.

14. 14 Clinical relevance : Inaccuracy in the fit of the margin may be due to distortion during removal of the wax pattern from the die . DISTORTION INCREASE As the thickness of the pattern decrease DISTORTION DECREASE Less setting expansion

15. Tuesday, February 2, 20XX Sample Footer Text 15 PREVENTION 1.Use of hard wax for wax pattern fabrication 2.Careful handling of the pattern during removal along the path of insertion taking care not to disturb the margins 3. Softening the wax at uniform temperature of 50°C. -Adding wax in smaller increments at a time 4. Immediate investment of the wax pattern. -The pattern must be stored in a refrigerator for no more than 30 minutes

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17. Tuesday, February 2, 20XX Sample Footer Text 17 SURFACE ROUGHNESS, IRREGULARITIES AND DISCOLORATION

18. Tuesday, February 2, 20XX Sample Footer Text 18 SURFACE ROUGHNESS, IRREGULARITIES AND DISCOLORATION Surface roughness Relatively finely spaced surface imperfections whose height, width, and direction establish the predominant surface pattern Surface irregularities Isolated imperfections, such as nodules, that are not characteristic of the entire surface area. SURFACE DISCOLORATION Any deficiency in the temperature or heating time results in incomplete reaction and formation of carbon residue, which contaminates the alloy and results in discoloration. Can also arise from breakdown products such as sulfur compounds contaminating the alloy

19. Tuesday, February 2, 20XX Sample Footer Text 19 CLINICAL RELEVANCE Excessive roughness or irregularities on the outer surface of the casting necessitate additional finishing and polishing Irregularities on the cavity surface prevent a proper seating of an otherwise accurate casting

20. 20 Material and methods:  A master abutment of a premolar mandibular tooth preparation with 4-mm height and a 0.6-mm deep 120-degree chamfer finish line with a 12-degree angle of convergence was replicated in die stone and scanned. Thirty-six cobalt-chromium alloy copings were produced using 3 different production techniques- laser-sintering, milling, milled wax/lost wax.  Conclusions:  Laser-sintered Co-Cr crown copings showed increased surface roughness and better internal and marginal fit than copings produced by milling or milled wax/lost wax technique .

21. Tuesday, February 2, 20XX Sample Footer Text 21 CAUSES / RELATED FACTORS AIR BUBBLES Small nodules on a casting are caused by air bubbles that become attached to the pattern during or subsequent to the investing procedure . PREVENTED BY Use the vacuum investing technique 2. A wetting agent

22. Tuesday, February 2, 20XX 22 WATER FILMS This type of surface irregularity appears as minute ridges or veins on the surface. If the pattern is slightly moved, jarred, or vibrated after investing, or if the painting procedure does not result in an intimate contact of the investment with the pattern, Appearance Cause Prevention Use of a wetting agent Too high an L/P ratio

23. 23 FOREIGN BODIES A rough crucible former with investment clinging to it may roughen the investment on its removal so that bits of investment are carried into the mold with the molten alloy Cause Sharp, well-defined deficiencies of castings Appearance Pieces of investment and bits of carbon from a flux. Bright-appearing concavities Flux being carried into the mold with the metal. Contamination results not only in surface roughness but also in incomplete areas or surface void

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25. 25 RAPID HEATING RATES Appears as - Fins or spines on the casting Cause Flaking of the investment when the water or steam pours into the mold. such a surge of steam or water may carry some of the salts used as modifiers into the mold, and these salts are left as deposits on the walls after the water evaporates

26. 26 Prevention The mold should be heated gradually; at least 60 min should elapse during the heating of the investment-filled ring from room temperature to 700˚ C The greater the bulk of the investment, the more slowly it should be heated

27. 27 PROLONGED HEATING Causes disintegration of the gypsum-bonded investment The products of decomposition are sulfur compounds that may contaminate the alloy to the extent that the surface texture is affected. When the thermal expansion technique is employed, the mold should be heated to the casting temperature—never higher—and the casting should be made immediately Prevention

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29. 29 UNDER HEATING Incomplete elimination of wax residues may occur if the heating time is too short or if insufficient air is available in the furnace Voids or porosity may occur in the casting from the gases formed when the hot alloy comes in contact with the carbon residues

30. 30 LIQUID/POWDER RATIO The higher the L/P ratio, the rougher the casting. If too little water is used, the investment may be unmanageably thick and cannot be properly applied to the pattern

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32. 32 TEMPERATURE OF THE ALLOY The surface of the investment is likely to be attacked. Prevention Use of gas-air torch Special care should be observed that the color emitted by the molten gold alloy is no lighter than a light orange

33. 33 CASTING PRESSURE A gauge pressure of 0.10 to 0.14 MPa in an air pressure casting machine or three to four turns of the spring in an average type of centrifugal casting machine is sufficient for small castings . Prevention Too high a pressure during casting can produce a rough surface.

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35. 35 COMPOSITION OF THE INVESTMENT The ratio of the binder to the quartz influences the surface texture of the casting. A coarse silica causes a surface roughness.

36. 36 IMPACT OF MOLTEN ALLOY Proper spruing so as to prevent the direct impact of the molten metal at an angle of 90 degrees to the investment surface. Appearance Raised area on the casting, often too slight to be noticed yet sufficiently large to prevent complete seating of the casting. Prevention

37. 37 The expansion of wax is much greater than that of the investment, causing breakdown or cracking of the investment if the spacing between patterns is less than 3 mm. If several patterns are invested in the same ring, they should not be placed too close together Positioning too many patterns in the same plane in the mold should be avoided. PATTERN POSITION Prevention

38. 38 Carbon, as from a crucible, an improperly adjusted torch, or a carbon-containing investment, can be absorbed by the alloy during casting CARBON INCLUSIONS Visible carbon inclusions

39. 39 ENDOGENOUS Degassing and desulfurization products Supersaturated precipitated components The Influence Of Inclusion In Casting POSITIVE oxides and sulfides increase the hardness of the material and increase the wear resistance.  EXOGENOUS mostly oxides N on-metallic inclusions generated by the interaction with the furnace lining NEGATIVE The larger the inclusions, the lower the fatigue limit of the material. source of cracks in part fracture. Sharp-angled inclusions cause stress concentration INFLUENCE

40. Tuesday, February 2, 20XX`1a Sample Footer Text 40 The aim of this study was to assess the surface roughness of 2 base metal alloys, submitted to different casting techniques, to determine the influence of surface roughness on loss of mass after polishing compared to commercially pure titanium castings. Base metal alloys submitted to vacuum casting showed decreased surface roughness, similar to that of titanium, compared to base metal alloys submitted to acetylene-oxygen flame casting. There were no significant differences in loss of mass after polishing for all tested specimens.

41. Tuesday, February 2, 20XX Sample Footer Text 41 Purpose:  This study evaluated the marginal fit and surface roughness of complete crowns made with a conventional and an accelerated casting technique . Materials and methods: A conventional technique (as recommended by the manufacturer) was compared with an accelerated technique that used 13- to 17-minute bench set and 15-minute wax elimination cycle in a 815 degrees C (1500 degrees F) preheated furnace.  Results:  For the marginal discrepancy and surface roughness, crowns fabricated with the accelerated casting technique were not significantly (P > 0.05) different from those fabricated with the conventional technique.

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43. Tuesday, February 2, 20XX Sample Footer Text 43 POROSITY

44. 44 POROSITY within the interior region of a casting and on the external surface External porosity Also a factor in surface roughness Generally a manifestation of internal porosity. Internal porosity weaken the casting location

45. Tuesday, February 2, 20XX Sample Footer Text 45 CLINICAL RELEVANCE Internal porosity weaken the casting, and if it extends to the surface, it may be a cause for discoloration If severe, it can cause plaque accumulation at the tooth-restoration interface, and secondary caries may result.

46. 46 CLASSIFICATION Solidification defects Residual air Trapped gases Localized shrinkage porosity Pinhole porosity Microporosity Gas inclusions Subsurface porosity Back pressure porosity

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48. 48 Premature termination of the flow of molten metal during solidification LOCALIZED SHRINKAGE POROSITY Cause Freezing of sprue before feeding is completed to the casting proper Most common location Near the sprue-casting junction

49. Tuesday, February 2, 20XX Sample Footer Text 49 Prevention Continual feeding of molten metal through the sprue Adequate diameter of the sprue Appearance

50. 50 Attaching one or more small-gauge sprues (e.g., 18-gauge) at the surface most distant from the main sprue attachment and extending the sprue(s) laterally within 5 mm of the edge of the ring Ability of the pontic to retain heat because of its bulk and because it was located in the heat center of the ring Cause Prevention Localized shrinkage porosity in pontic of three-unit bridge

51. 51 SUCK-BACK POROSITY Cause When a hot spot has been created by the hot metal impinging from the sprue channel on a point of the mold wall, it causes the local region to freeze last and results in suck-back porosity Most common location Occlusoaxial line angle or incisoaxial line angle that is not well rounded.

52. 52 Prevention It can be eliminated by flaring the point of sprue attachment and reducing the mold-melt temperature differential, that is, lowering the casting temperature by about 30˚ C.

53. 53 MICROPOROSITY Cause Rapid solidification if the mold or casting temperature is too low Appearance small, irregular voids Generally present in fine-grain alloy castings when the solidification is too rapid for the microvoids to segregate to the liquid pool.

54. Tuesday, February 2, 20XX Sample Footer Text 54 The present study was designed to analyse the average depth of the microporosity of a nickel-chromium (Ni-Cr) system alloy (Verabond II). The metal surface was subject to one of the following surface treatment: (i ) Electrolytic etching in nitric acid 0.5 N at a current density of 250 mA cm(-2); (ii) chemical etching with CG-Etch etchant; and (iii) Sandblasting with alumina particles 50 microm The depth of porosity was measured through photomicrographs (500x) with a profilometer The greatest and identical depth of microporosity was observed following electrolytic etching and chemical etching The least and identical depth of microporosity was observed with chemical etching and sandblasting with alumina particles 50 micron

55. 55 Cause Inability of the air in the mold to escape through the pores in the investment or by the pressure gradient that displaces the air pocket toward the end of the investment via the molten sprue and button. The entrapment is frequently found in a “pocket” at the cavity surface of a crown or mesio-occlusaldistal casting BACK PRESSURE / ENTRAPPED AIR POROSITY location

56. Tuesday, February 2, 20XX Sample Footer Text 56 Appearance Large concave depressions prevention Proper burnout, an adequate mold and casting temperature, a sufficiently high casting pressure, and proper L/P ratio

57. 57 Appearance Spherical in contour Gas inclusion porosities are usually much larger than pinhole porosity PIN HOLE POROSITY GAS INCLUSION POROSITY Entrapment of gas during solidification

58. Tuesday, February 2, 20XX Sample Footer Text 58 Cause Many metals dissolve or occlude gases while they are molten. On solidification, the absorbed gases are expelled and pinhole porosity results. Larger spherical porosities- Gas occluded from a poorly adjusted torch flame, or by use of the mixing or oxidizing zones of the flame rather than the reducing zone Prevention Can be minimized by premelting the gold alloy on a graphite crucible or a graphite block, and by correctly adjusting and positioning the torch flame during melting

59. 59 Appearance Can be diminished by controlling the rate at which the molten metal enters the mold. SUB SURFACE POROSITY Simultaneous nucleation of solid grains and gas bubbles at the first moment that the alloy freezes at the mold walls. Cause Prevention

60. Tuesday, February 2, 20XX Sample Footer Text 60 INCOMPLETE CASTING

61. 61 INCOMPLETE CASTING Incomplete elimination of wax residues from the mold. The molten alloy has been prevented, from completely filling the mold. FACTORS CAUSE Insufficient venting of the mold Discrepancy in temperatures between the casting ring/mold and the molten alloy small diameter of sprue

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64. 64 If insufficient casting pressure is used, the back pressure cannot be overcome. Furthermore, the pressure should be applied for at least 4 sec Directly related to the back pressure exerted by the air in the mold. PREVENTION Insufficient venting of the mold If the air cannot be vented quickly, the molten alloy does not fill the mold before it solidifies.

65. 65 If too many products of combustion remain in the mold, the pores in the investment may become filled so that the air cannot be vented completely Incomplete elimination of wax residues from the mold. If moisture or particles of wax remain, the contact of the molten alloy with these foreign substances produces an explosion that may produce sufficient back pressure to prevent the mold from being filled.

66. 66 Results in molten metal solidifying in the sprue area before completely filling the mold cavity SMALL DIAMETER OF SPRUE Should always be at the bulkiest portion of the wax pattern directed at 45° angulation to the surface. ATTACHMENT OF SPRUE

67. 67 Improper L/P ratio, mixing time, and improper burnout temperature OTHER CASTING DEFECTS UNDERSIZED AND OVERSIZED CASTING Cause Prevention Adherence to the proper protocol of selection of materials and techniques will ensure a proper fit of the casting without any defect

68. Tuesday, February 2, 20XX Sample Footer Text 68 VARIABLES AND PRINCIPLES OF OPTIMAL SPRUE DESIGN The purpose of a sprue former, or sprue pin, is to provide a channel through which molten alloy can reach the mold in an invested ring after the wax has been eliminated

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70. Tuesday, February 2, 20XX Sample Footer Text 70 Sprue Diameter same size as the thickest area of the wax pattern If it is too small, this area will solidify before the casting itself and localized shrinkage porosity (“suck-back” porosity) may develop Sprue Position At the greatest bulk in the pattern to avoid distorting thin areas of wax during attachment to the pattern and to permit the complete flow of the alloy into the mold cavity

71. Tuesday, February 2, 20XX Sample Footer Text 71 Sprue Attachment Flaring of the sprue for mer facilitating the entry of the fluid alloy into the pattern area with the largest cross-sectional areas Sprue Direction Directed away from any thin or delicate parts of the pattern because the molten metal may abrade or fracture investment Not be attached at a right angle to a broad flat surface as it may leads to turbulence within the mold cavity and causes severe porosity Sprue Length 1)Gypsum-bonded investments -Top of the wax pattern is within 6 mm of the open end of the ring 2)phosphate-bonded investments within 3 to 4 mm of the top of the investment

72. CONCLUSION Nuances in casting procedures that results in defective castings may lead to adverse clinical effects and while some casting defects may be unavoidable ; In almost all instances, they can be prevented by strict observance of procedures governed by certain fundamental rules and principles. 72

73. Tuesday, February 2, 20XX Sample Footer Text 73 REFERENCES Phillips science of dental materials 11 th edition Contemporary fixed prosthodontics – Rosenstiel Craig,s Textbook of Restorative Dental Materials -11 th edition Textbook of Operative Dentistry Vimal Sikri 4 th Edition

74. Tuesday, February 2, 20XX Sample Footer Text 74 Gemalmaz D, Alkumru HN. Marginal distortion of metal-ceramic restorations during the porcelain firing procedure. J Marmara Univ Dent Fac. 1993 Sep;1(4):285-9. Bombonatti PE, de Barros LE, Scaranelo RM, Pellizzer AJ. Rugosidade superficial de ligas com alto conteúdo de cobre, em função do aquecimento acima da temperatura de fusão [Surface roughness of high copper alloys as a function of heating above casting temperature]. Rev Odontol UNESP. 1990;19(1):203-9. Bezzon OL, Pedrazzi H, Zaniquelli O, da Silva TB. Effect of casting technique on surface roughness and consequent mass loss after polishing of NiCr and CoCr base metal alloys: a comparative study with titanium. J Prosthet Dent. 2004 Sep;92(3):274-7. Konstantoulakis E, Nakajima H, Woody RD, Miller AW. Marginal fit and surface roughness of crowns made with an accelerated casting technique. J Prosthet Dent. 1998 Sep;80(3):337-45.

75. Tuesday, February 2, 20XX Sample Footer Text 75 Chan D, Guillory V, Blackman R, Chung KH. The effects of sprue design on the roughness and porosity of titanium castings. J Prosthet Dent. 1997 Oct;78(4):400-4. Verrett RG, Duke ES. The effect of sprue attachment design on castability and porosity. J Prosthet Dent. 1989 Apr;61(4):418-24.

76. Thank you . 76