Investment material

An investment is a refractory material that is used to form a mould around a wax pattern.
Following the production of a wax pattern either by direct or indirect method; the next stage in many dental procedures involves the investment of the pattern to form a mould. 
A sprue is attached to the pattern and the assembly is located in a casting ring. Investment material is poured around the wax pattern while still in a fluid state.
When the investment sets hard, the wax and sprue former are removed by burning out to leave a mould which can be filled with an alloy or ceramic using a casting technique.

1. Investment Materials Dr. Neeraja M M enon Dept of Prosthodontics Coorg Institute Of Dental Sciences

2. CONTENTS Introduction History Definition Properties of an ideal investment material Composition Gypsum bonded investments Phosphate bonded investments Ethyl silicate bonded investments

3. Die stone investment combination . Hygroscopic thermal gold casting investments. Soldering investments. Investments for all- ceramic restorations. Investment of titanium & titanium based alloys . Review of literature . Summary & Conclusion. References.

4. Introduction An investment is a refractory material that is used to form a mould around a wax pattern . Following the production of a wax pattern either by direct or indirect method; the next stage in many dental procedures involves the investment of the pattern to form a mould.  A sprue is attached to the pattern and the assembly is located in a casting ring. Investment material is poured around the wax pattern while still in a fluid state. When the investment sets hard, the wax and sprue former are removed by burning out to leave a mould which can be filled with an alloy or ceramic using a casting technique.

5. History Lost wax casting art was widely known in ancient times. The Aztec gold smiths of Pre-Columbian Mexico used it to create their elaborate jewellery.  11th century – Theophilus first described the lost wax technique . 1558 – Benvenuto Cellini, used wax and clay for preparation of castings . 1884 – Aguilhon de saran – used 24K gold to form inlays. 1897 – Philibrook described a method of casting metal fillings. 1907 – Taggart devised a casting machine  Aztec Gold work

6. Definition An investment can be described as a ceramic material that is suitable for forming a mold into which a metal or alloy is cast. - Craig Refractory material used to form a mould casting for cast metals or hot pressed ceramics . - Anusavice .

7. D ental casting investment \ dĕn ΄ tl kas ΄ tĭng ĭn-vĕst ΄ ment \: a material consisting principally of an allotrope of silica and a bonding agent ; the bonding substance may be gypsum (for use in lower casting temperatures) or phosphates and silica (for use in higher casting temperatures ) - GPT9

8. Requirements of an investment materials Easy manipulation Should provide smooth surface to the casting Must not decompose at higher temperatures Sufficient strength Should break away readily from metal surface Porous to permit air and other gases in mould to escape Sufficient expansion Casting temperatures should not be critical Economical

9. Composition of investment material

10. Refractory material: This material is usually a form of silicon dioxide such as :-

11. Binder Material: Since the refractory materials alone do not form a coherent solid mass, some kind of binder is needed. The common binders used for dental casting gold alloy is α -CaSO4 hemihydrate, Phosphate, ethyl silicate.

12. Other Chemicals: These are added in small quantities to modify various physical properties. Sodium chloride. Boric acid. Potassium sulfate . Graphite . Copper powder. Magnesium Oxide .  

13. Classification according to Binders used

14. Gypsum bonded investments American Dental Association/American National Institute For Standards specification no: 2 for casting investments used for gold alloys . Type 1: For casting inlays and crowns. Type 2: For casting complete and partial removable denture bases . Type 3: For partial dentures with gold alloys

15. Composition:  Binder : 25% to 45% - α -calcium sulfate hemihydrate. Refractory material: 65 % to 75% - quartz or cristobalite . MODIFIERS : 2% to 3% - chemical modifiers.

16. Gypsum: 25 % to 45% of α -hemihydrate is present. α -hemihydrate acts as a binder to hold the ingredients together & to provide rigidity. Used in casting gold alloys with melting ranges below 1000ºC . Above 1000ºC greater shrinkage & frequent fractures takes place.

17. All forms of gypsum shrink after dehydration between 200ºC to 400ºC . A slight expansion takes place between 400 ℃ and 700 ℃. And a large contraction then occurs. The shrinkage on heating is due to the dehydration of the set gypsum. 2CaSO4 · 2H2O → ( CaSO4)2 H2O + 3H2O ( CaSO4)2 · H2O → 2CaSO4 + H2O

18. Shrinkage is due to the transformation of calcium sulphate from the hexagonal to the orthorhombic configuration.

19. Silica: 55% to 75%. It acts as a refractory material during the heating of the investment & regulates the thermal expansion. If the proper form of silica is used in the investment, the contraction of gypsum during heating can be eliminated & changed to an expansion.

20. Silica exists in 4 allotropic forms :- 1 ) Quartz . 2) Cristobalite . 3 ) Tridymite . 4 ) Fused quartz.

21. When quartz, cristobalite or tridymite is heated, a change in crystalline form occurs at a transition temperature characteristic of the particular form of silica. Ex : When quartz is heated at 575 ℃ α -Quartz → β- quartz Cristobalite undergoes an anologous transition between 200ºC & 270ºC from α to β form. 2 inversions of Tridymite occurs at 117ºC & 163ºC respectively.

22. Density decreases as α form changes to β form, with a resulting increase in volume exhibited by a rapid increase in linear expansion. On the basis of the type of silica employed, dental investments are classified as:-  Quartz investment .  Cristobalite investment.

23. Effect of varying composition Increasing the proportion of silica in the investment powder Increases : manipulation time, initial setting time, setting expansion both in air & water thermal expansion Decreases : compressive strength. The rate of setting reaction is unchanged.

24. The increase in manipulation & setting time occurs because the particles of the refractory filler, interfere with the interlocking of the growing gypsum crystals & making this less effective in developing a solid structure. The compressive strength of the investment is reduced for the same reason.

25. Modifiers a) Modifying Agents :- Regulates the setting expansion & setting time. They prevents most of the shrinkage of gypsum, when it is heated above 300ºC. E g . NaCl , Boric acid .

26. b) Reducing agents:- They are used in some investments to provide a non- oxidizing atmosphere in the mold when the gold alloy is cast. Eg . Carbon, powdered graphite or powdered copper.

27. Setting time It can be measured by, 1. Loss of Gloss test for initial set. 2 . Initial Gilmore test for initial set. 3. Gilmore Test For Final Setting Time. 4. Vicat test for setting time.

28. According to ADA/ANSI specification no. 2 for dental inlay casting investment, the setting time should not be less than 5 min. or more than 25 min. Usually , the modern inlay investments set initially in 9 to 18 min. Sufficient time should be allowed for mixing & investing the pattern before the investment sets.

29. Normal setting expansion Definition :- The volumetric or linear increase in physical dimensions of an investment caused by chemical reactions that occur during hardening to form a rigid structure. Regardless of the type of gypsum product used, an expansion of the mass can be detected during the change from hemihydrate to dihydrate .

30. A mixture of silica & gypsum hemihydrate results in setting expansion greater than that of the gypsum product when it is used alone. The ADA Specification no. 2 for Type 1 investment permits a maximum setting expansion“in air”of only 0.6%. The setting expansion of modern investments is 0.4%. The setting expansion of an investment with a comparatively high gypsum content is more effective in enlarging the mold than with a low gypsum content.

31. Factors affecting normal setting expansion If the pattern has thin walls , the effective setting expansion is somewhat greater, than for a pattern with thicker walls. The softer the wax , the greater is the effective setting expansion. If a wax other than the Type 2 inlay wax is used, the setting expansion may cause a serious distortion of the pattern. The lower the W:P ratio for the investment, the greater is the effective setting expansion.

32. Hygroscopic setting expansion If the setting process is allowed to occur under water(slurry), the setting expansion may be more than double in magnitude because of the additional crystal growth permitted. ADA Specification no. 2 for Type 1 investments requires a minimum setting expansion in water of 1.2% & maximum expansion permitted is 2.2%.

33. Purpose:- To expand the casting mold to compensate for the casting shrinkage of the gold alloy The HSE differs from the NSE in that, it occurs when gypsum is allowed to set under or in contact with water & that it is greater in magnitude than NSE.

34. Factors controlling the hygroscopic expansion Effect of Composition - Finer silica particle size, greater expansion - α hemihydrate, in presence of silica, produces greater expansion when expansion is unrestricted. Effect of Water/Powder Ratio - Higher ratio, less expansion. Effect of Spatulation - Reduced mixing time, decreased expansion.

35. Effect of Time of Immersion - More expansion observed if immersion takes place before the initial set. Shelf Life - Older investment, lower expansion.

36. Effect of Added Water - Magnitude of the hygroscopic expansion is in direct proportion to the amount of water added during the setting period until a maximum expansion occurs. - The term ‘hygroscopic’ is a misnomer as although the added water may be drawn into the setting material by capillary action, the effect is not related to hygroscopy

37. Thermal expansion Definition :- It is the increase in dimension of a set investment due to temperature increase during burnout. The expansion of a gypsum bonded investment is directly related to the amount of silica present & to the type of silica employed .

38. A considerable amount of quartz is necessary to counterbalance the contraction of the gypsum during heating. Even when the quartz content of the investment is increased to 60% with the balance being hemihydrate binder, the initial contraction of the gypsum is not eliminated. The contraction of the gypsum is entirely balanced when the quartz content of the investment is increased to 75%.

39. The thermal expansion of quartz investment are influenced by:- - The particle size of the quartz. - Type of gypsum binder - W:P ratio Since greater expansion occurs during the inversion of the crystobalite , the normal contraction of the gypsum during heating is easily eliminated.

40. According to ADA/ANSI Specification no. 2 for Type 1 investment which rely on the thermal expansion for compensation, the thermal expansion must not be <1% nor >1.6%. Type 2 investment which rely on hygroscopic expansion for compensation of the contraction of the gold alloy, the thermal expansion be between 0% & 0.6% at 500ºC

41. Thermal Contraction When an investment is allowed to cool from 700°C , its contraction curve follows the expansion curve. Due to inversion of the beta quartz to its stable form at room temperature , it shrinks to less than its original dimension because of the shrinkage of the gypsum when first heated. In practice, the investment should not be heated a second time, since internal cracks may develop which affect the quality of the casting. Curve 1 is first heating Curve 2 is cooling Curve 3 is re heating

42. Factors affecting thermal expansion W:P ratio:- The magnitude of thermal expansion is related to the amount of solids present. ↑W:P ratio → ↓ thermal expansion .

43. 2) Effect of Chemical Modifiers – A disadvantage of an investment is the weakening effect of silica. The addition of small amount of Na, K or Lithium chloride to the investment eliminates the contraction caused by the gypsum & increases the expansion. Boric acid hardens the set investment but, it disintegrates during the heating of the investment & a roughened surface of the casting may result.

44. 3) Strength Increases rapidly as the material hardens after initial setting time. The free water content of the set product affects its strength. The strength of an investment must be adequate to prevent fracture or chipping of the mold during heating & casting of the gold alloy and is measured in terms of its compressive strength.

45. The compressive strength is increased according to Type & amount of gypsum binder present Use of chemical modifiers. According to ADA Specification no. 2, the compressive strength for the inlay investment should not be less than 2.4 MPa when tested 2hrs after setting.

46. Other gypsum investment considerations Fineness :- Finer the investment, the smaller are the surface irregularities on the casting. Porosity :- More gypsum crystals present in the set investment, less porosity. More uniform the particle size, greater is its porosity. Storage :- The investment should be stored in airtight & moisture proof containers.

47. Technical specifications Mixing ratio (powder: distilled water): 100 g :32-40 ml Total expansion (in % linear) : 1.3% - 1.6%

48. Expansion control The expansion of the compound can be controlled by varying the amount of liquid added to compensate the contraction of the casting alloy. The less water used, the greater the total expansion of the investment compound. Distilled water Setting expansion (average) Thermal expansion (average) Total expansion 32 ml 0.4% 1.2% 1.6% 40 ml 0.1% 1.2% 1.3%

49. Manipulation Mix the investment compound by hand for approximately 30 seconds with a spatula, allow to stand under a vacuum for approx. 30 seconds. Then mix under vacuum for 60 seconds with a mixing and evacuation unit. After mixing, place the mixing bowl on a vibrator (approx. 30 seconds) and allow the investment compound to flow together. Then let the compound to flow into the mould, shaking gently and ensuring that no bubbles form. After the mould has been filled, switch off the vibrator. Allow the mould to set for 45-60 minutes, depending on the size. If the mould is preheated too soon the investment compound can crack.

50. During wax elimination, place the mould in the oven in such a way that the wax can run out of the mould easily, otherwise wax residue will be absorbed by the investment compound capillaries and will carbonize damaging the cast object. The mould which have dried overnight should be wetted slightly before casting rings are placed in furnace. Devesting - Allow the casting ring to dry slowly in the air at room temperature after casting and removing the investment compound under running water with a plier.

51. PHOSPHATE BONDED INVESTMENTS The rapid growth of the use of metal ceramic restorations, cast removable partial dentures and higher melting alloys resulted in an increased use of phosphate bonded investment materials. 1) Type I - For crowns, inlays & other fixed restorations 2 ) Type II - For partial denture & other cast removable restorations - Make soldering fixtures.

52. Composition Consists of :- Filler - Silica, in the form of Cristobalite , Quartz, or a mixture of the two and in a concentration of 80%. - Provides high temperature and a high thermal expansion . Binder - The binder consists of magnesium oxide and a phosphate .

53. 3) Colloidal Silica Liquid Suspensions:- - The colloidal silica suspensions are used with the phosphate investments in place of water to compensate for the greater contraction of the high fusing alloys during solidification, as it increases the setting expansion of the investment. - For base metal alloys, a 33% dilution of the colloidal silica is required.

54. 4) Carbon:- - Often added to the powder to produce clean castings to facilitate the divesting of the casting from the mold . - Appropriate if the casting alloy is gold. - Evidence indicates that palladium react with carbon at temperature above 1504°C. Thus, if the temperature exceeds this temperature during casting, a carbon free investment should be used.* * Dental Materials and Their Selection - 3rd Ed. (2002) by William J. O'Brien

55. Setting reaction Magnesium ammonium phosphate formed is polymeric. An excess of magnesia is usually present, and some of it is never fully reacted. - So, colloidal multimolecular aggregate around excess MgO and fillers is formed. On heating, the binder of the set investment undergoes thermal reactions. NH4H2PO4 + MgO + 5H2O → NH4MgPO4 6H2O

56. NH4. H2PO4 + MgO + 5H2O → Mg.NH4.PO4.6H2O ↓ Room Temperature Mg.NH4 . PO4. 6H20 ↓ Dehydration on heating at 160 ℃ NH4 . MGPO4. H2O ↓ At 300 ℃ - 650 ℃ , NH3 is released Mg2 . P2O7 + 2NH3 + 13H20 ↓ 1040 ℃ Mg3(P2O4)2 Crystalline form

57. Setting & thermal expansions Instead of shrinkage , the reaction entails slight expansion which increases by using colloidal silica solution instead of water. The early thermal shrinkage of phosphate investments is associated with the decomposition of the binder magnesium ammonium phosphate, and is accompanied by evolution of ammonia. Some of the shrinkage is masked because of the expansion of the refractory filler especially in cristobalite .

58. Phosphate investments when mixed with H2O have shrinkage in essentially the same temperature range, as gypsum bonded investments at 200-400  C (400-750  F). This contraction is practically eliminated when a colloidal silica solution replaces the water, expansion of a phosphate bonded investment is decreased by increasing the liquid to powder ratio. The early thermal shrinkage in phosphate investments is due to the decomposition of the binder magnesium ammonium phosphate and is accompanied by evolution of ammonia’s which is readily apparent by its odour.

59. Working & setting time Phosphate investments are affected by temperature as warmer the mix, faster it sets. The setting reaction itself gives off heat, and this further accelerates the rate of setting. Increase in mixing time and mixing efficiency results in faster set & a greater rise in temperature. Increase in w:p ratio, increases the working time

60. Miscellaneous properties Increasing the special liquid to water ratio used for the mix markedly enhances casting surfaces smoothness but can lead to oversized extra coronal castings.

61. Technical Data Mixing ratio ( Water:powder ) 100g :22 ml-23 ml Total linear expansion 1.2% - 2.4% Mixingtime (under vacuum) 60sec Compressive strength (depending on concentration of the mixing liquid) 4MPA- 8MPa

62. Advantages They have high strength which makes them easy to handle without breaking before burnout & strong enough afterwards to withstand the impact & pressure of centrifugally cast molten alloy. Provide setting & thermal expansion high enough to compensate for the thermal contraction of cast metal prosthesis or porcelain veneers during cooling. Have the ability to withstand the burnout process with temperature that reach 900ºC.

63. Disadvantages When used with higher melting alloys i.e. those with casting temp. ≥ 1375ºC, these investments results in mold breakdown & rougher surface on castings . The high strength of these investments can make removal of the casting from the investment difficult.

64. REVIEW OF LITERATURE The Effect of Investment Materials on the Color of Feldspathic Ceramics Cubas et al, European Journal of Dentistry, October 2015, Vol.5 The aim of this study was to evaluate the influence of investment type on the color of feldspathic ceramics. Ceramic specimens were constructed using four investments (i.e., Vitadurvest , Duravest , Duceralay Superfit , and Fortune) to observe their effect on the color of five commercially available ceramics (i.e., Super Porcelain EX-3, Vision Esthetic , Vintage Halo, IPS Classic, and Vitadur Alpha). The color analysis of the ceramics was performed with a colorimeter.

65. RESULT : Two investments ( Duravest and Fortune) produced alterations in color parameters with three of the five ceramics tested. Hence the investment materials produced alterations on the ceramic color parameters.

66. MARGINAL GAP OF CROWNS MADE WITH A PHOSPHATE-BONDED INVESTMENT AND ACCELERATED CASTING METHOD Shilling RE et al, J Prosthet Dent 2011;81:129-34 . This study measured the marginal gap and determined the clinical acceptability of single castings invested in a phosphate-bonded investment with the use of conventional and accelerated methods. 44 individual stone casts were poured from impressions made from a master die. Conventional and accelerated methods of investing and casting were followed. 22 casts were used in each of the 2 groups. Each casting and its respective stone die were examined with a microscope at 4 predetermined sites. M arginal gap were documented for each.

67. RESULT: A phosphate-bonded investment ( Ceramigold ) selected for an accelerated casting technique produced single castings within 30 minutes with marginal gaps comparable to those found that used conventional methods.

68. Devesting :- After casting, let the casting ring cool down to room temperature and devest . For this purpose the investment material mold must be soaked for approx. 15 min and carefully split open at several points using plaster pliers. When this method is employed, the dental casting can be easily removed from the investing compound, and formation of dust is prevented. Final residues of investing compound in the crowns can be picked out or carefully blasted out with aluminum oxide , granularity 100 µm to 150 µm.

69. ETHYL SILICATE-BONDED INVESTMENT These are used for high fusing base metal alloys. Losing popularity - complicated and time consuming procedures involved . Consists of powder & liquid. - Powder contains refractory particles of silica & glass along with calcined MgO & some other oxides in minor amount. - 2 Liquids are ethyl silicate & acidified solution of denatured ethyl alcohol. - Binder is a silica gel that reverts to silica ( crystobalite ) on heating.

70. COMPOSITION: 1) REFRACTORY MATERIAL : Silica 2 ) BINDER: BINDER BASED ON SODIUM SILICATE: An aqueous solution of sodium silicate is acidified by the addition of HCl acid to form a bonding silicic acid gel. However such investments are not generally used.

71. An aqueous suspension of colloidal silica can also be converted to a gel by the addition of an accelerator, such as AMMONIUM CHLORIDE. BINDER BASED ON ETHYL SILICATE: A colloidal silicic acid is first formed by hydrolyzing ethyl silicate in the presence of hydrochloric acid, ethyl alcohol and water. The solution is then mixed with quartz or cristoballite , to which is added small amount of MgO . Thus polysilicic acid gel is formed within one hour after mixing.

72. Advantages The investments have the ability to cast high temp. cobalt- chromium & nickel- chromium alloys with good surface finish, low distortion & high thermal expansion. They are less dense than Phosphate bonded investments & thin sections with fine details can be reproduced. The low strength makes removal of casting from investment easier than with Phosphate bonded investments.

73. Disadvantages Added processing attention & extra precaution needed in handling the low strength fired molds . The low strength & high thermal expansion requires a more precise burnout process & firing schedule to avoid cracking.

74. Die stone investment combination In this the die material & the investing medium have a comparable composition. A commercial Gypsum Bonded material called “Divestment” is mixed with colloidal silica liquid. The setting expansion of the material is 0.9% & thermal expansion is 0.6%, when heated to 677ºC. Not recommended for high fusing alloys, as used for metal ceramic restorations.

75. Hygroscopic thermal gold casting investment Designed for use with either hygroscopic or thermal type of casting technique. Thermal expansion of this investment takes place in the range 482ºC & 649ºC . This expansion is high enough to use the investment with the thermal casting technique without water immersion. But when it is immersed in a water bath, then the investment expands hygroscopically . With the hygroscopic technique the investment only needs to be heated to 482ºC to provide appropriate expansion.

76. Soldering/brazing investments When soldering the clasps on a RPD, the parts must be surrounded with a suitable investment material before the heating operation. The assembled parts are temporarily held together with sticky wax until they are surrounded with the investment material, after which the wax is softened & removed. The portion to be soldered is left exposed & free from investment to permit wax removal & effective heating before it is joined with solder.

77. Types of brazing investments are:- - Type 1 - Gypsum bonded. - Type 2 - Phosphate bonded. The investment for soldering is similar to casting investment. They are designed to have lower setting & thermal expansions than casting investments, a feature that is desirable so that the assembled parts do not shift in position during the setting & heating of the investment.

78. Investments for all-ceramic restorations Type I – Used for the cast glass technique composed of phosphate bonded refractories. Type II – Refractory die type of material, used for all- ceramic veneers , inlays & crowns. Refractory dies are made by pouring the investment into impressions. When investment is set, the die is removed & is heated to remove gases that may be detrimental to the ceramic (degassing). A refractory die spacer may be added to the surface.

79. Then, the porcelain or other ceramic powders are added to the die surface & fired. Materials must accurately reproduce the impression, remain undamaged during the porcelain firing & have a thermal expansion compatible with that of ceramic, otherwise the ceramic could crack during cooling. These materials are phosphate bonded & they generally contain fine grained refractory fillers to allow accurate reproduction of detail.

80. Investment of titanium & titanium based alloys Ti is highly reactive with oxygen & is capable of reducing some of the oxides commonly found in phosphate and silica bonded investments. Ti can also dissolve residual oxygen, nitrogen & carbon from the investment. These elements can harden & embrittle Ti in the solid state. Hence , modification in the existing refractory formulation & binder are required.

81. COMPOSITION :- These investments can be classified as:- 1 ) Phosphate bonded 2 ) Ethyl silicate bonded 3 ) Cemented REFRACTORIES :- - Silica(SiO2) - Alumina(Al2O3) - MgO - Zirconia(ZrO2)

82. PHOSPHATE BONDED TITANIUM INVESTMENT :- - To achieve expansion without the use of reactive powders , a PBI that contains both magnesia & alumina as refractories was developed. - This investment can achieve large expansion by the reaction of alumina & magnesia, when it is burned out at 1150ºC - 1200ºC . ETHYL- SILICATE BONDED INVESTMENT :- - Reactions with the liquid Ti has been reported to be somewhat less than that of Phosphate bonded investments due to the use of highly refractory oxides in the powder.

83. CEMENTED TITANIUM INVESTMENT :- - This investment use magnesia bonded by an aluminous cement & contains 5% zirconium powder by weight. - The aluminous cement serves as binder for the magnesia refractory & it sets by mixing with water. - Oxidation of the zirconium powder to zirconia during the burnout process provides irreversible expansion to compensate for the shrinkage of the casting during cooling from the solidification temperature. - The zirconia formed is highly stable & it does not contaminate Ti. Ti castings from this investment have smooth surface which are free of contamination.

84. Recently a new investment material for titanium casting has been developed, which contains calcia (CaO2) as refractory and cold-cure acrylic resin (PMMA) as binder, known as “RESIN-BONDED CALCIA INVESTMENT”.

85. CALCIA BONDED INVESTMENT This is a the recently developed investment for casting titanium inlays, crowns and bridges. REFRACTORY - Zirconia BINDER - Calcia PROPERTIES: 1 . Total thermal and setting expansion found was 1.5 to 2.5% 2. The maximum thermal expansion was found at 900 to 1200°C

86. CERAMIC OR SILICA FREE INVESTMENT Casting of ceramic crowns using castable glasses is done in refractory moulds. Castable moldable ceramic are hot pressed into ceramic mould by pressure where no compensation expansion is needed Special GBI of low thermal expansion are used, made from pure gypsum and Calcium sulphate hemihydrate Same investment additives as GBI to prevent their contraction or deterioration on heating.

87. Effect of Investment Type and Mold Temperature on Casting Accuracy and Titanium-Ceramic Bond Leal MB et al, Brazilian Dental Journal (2013) 24(1): 40-46 This study evaluated the casting accuracy of crown margins and metal-ceramic shear bondstrength (SBS) of pure titanium injected into casting molds made using phosphate-bonded investment(P) and magnesium oxide-bonded(U) investment types at 400,550 and 700°C mold temperatures. 60 crown (30-degree beveled finish line) and 60 cylinder (5mm diameter x 8 mm high) patterns were divided into 6 groups (n=10) and casted. Crown margins were recorded in impression material, the degree of marginal rounding was measured and margin length deficiencies ( μm ) were calculated. Titanium-ceramic specimens were prepared using Triceram ceramic (2 mm high) and SBS was tested.

88. Result The results of the study suggest that there were no significant differences for titanium-ceramic SBS for any of the combinations of investments and mold temperatures. Nevertheless, marginal accuracy of crowns cast with CPTitanium was significantly affected by investment type and mold temperature.

89. Conclusion As Prosthodontists , our aim is to make a restoration as accurate as possible. Hence knowledge about various materials and techniques used in casting dental restoration is important. Investment materials are to be selected based on the type of restoration, the type of metal or alloy to be casted etc and also the technique used for casting and investing a wax pattern is a very important procedure as it will determine the seating accuracy of the final casting.

90. References Phillips science of dental materials - Kenneth J.Anusavice , 11th edition Introduction to dental materials - Richard van noort,1st edition Applied dental materials - John F, Mc.Cabe , 8th edition Dental materials and their selection - Willian J .O’Brien, 2nd edition Restorative dental materials - Robert . G.Craig , 11 th edition

91. 6. Contemporary fixed prosthodontics – Rosenstiel , 3 rd edition 7. Fundamentals of fixed prosthodontics – Shillingburg , 4th edition Dental laboratory procedures - Rudd & Morrow, 2nd edition 9 . Operative dentistry-modern theory & practice, M.A.Marzouk 10. Internet sources