BASE METAL ALLOYS presentation in dental materials
- 1. BASE METAL ALLOYS presented by: Dr Siddharth desai
- 2. CONTENTS: Introduction Introduction History History Classification of alloys Classification of alloys Basemetal alloys Basemetal alloys composition composition properties properties heat treatment heat treatment Cobalt Chromium alloys Cobalt Chromium alloys Nickel Chromium alloys Nickel Chromium alloys Titanium alloys Titanium alloys Review of literature Review of literature Conclusion Conclusion References References
- 3. Introduction The pressure of economics, as well as a research for improved mechanical properties, have led to the development of base metal alloys for the construction of dental prosthesis devices.
- 4. History Main factors that are driving new developments are Economy Performance Aesthetics
- 5. Taggart – 1907 1932-classification of gold –based casting alloys 1933-replacement of Co-Cr for gold in removable partial dentures 1959-Successful veneering of a metal substructure with dental porcelain Intensive research into base metal alloys started in 1970’s
- 6. Classification-ADA(1984): Classification-ADA(1984): Classification of alloys Classification of alloys Alloy type Total nobel metal content High nobel (HN) Must contain > 40wt% Au and > 60wt% of nobel metal elements (Au,Pt,Pd,Rh,Ru,) Nobel (N) Must contain > 25wt% of nobel elements (Au,Pt,Pd,Rh,Ru) Predominantly base metal (PB) Contain <25wt% of nobel metal elements,
- 7. ADA Classification • Type-1 –low strength Type-1 –low strength • Type-2–Medium strength Type-2–Medium strength • Type-3-High strength Type-3-High strength • Type-4-Extra high strength Type-4-Extra high strength
- 8. According to elements present: Alloy Type All metal Metal ceramics Partial Denture High noble Au-Ag-Cu-Pd Metal – ceramic alloys Au-Pt-Pd Au-Pd-Ag< 12wt % Au-Pd-Ag>12wt % Au-Pd (no Ag) Au-Ag-Cu-Pd Noble Ag-Pd-Au-Cu Ag-Pd Metal Ceramic alloys Pd-Au (noAg) Pd-Au-Ag Pd-Ag,Pd-Cu Pd-Co,Pd-Ga-Ag Ag-Pd-Au-Cu Ag-Pd Base Metal Pure Ti Ti-Al-V Ni-Cr-Mo-Be Co-Cr-Mo Pure Ti Ti-Al-V Ni-Cr-Mo-Be Ni-Cr-Mo Co-Cr-Mo Pure Ti Ti-Al-V Ni-Cr-Mo-Be Ni-Cr-Mo Co-Cr-Mo
- 9. Predominantly base metal alloys Predominantly base metal alloys • 75% or more of base metal 75% or more of base metal elements elements • Less than 25% noble Less than 25% noble metals metals • Low cost Low cost
- 10. ALLOYING ELEMENTS: •Chromium Chromium •Cobalt and nickel Cobalt and nickel •Carbon Carbon •Molybdenum Molybdenum •Aluminium Aluminium •Berylium Berylium •Silicon and manganesne Silicon and manganesne
- 11. PHYSICAL PROPERTIES 1.Melting Temperature 14000 -15000 C. •Though one commonly used nickel chromium alloy ticonium melts at 12750 C. •Addition of 1-2% Beryllium lowers melting temperature of ticonium by about 100 0 c. 2. The Average Density : 7-8gms /Cm3 .
- 12. •Hardness Difference in composition of cast base metal alloys have some effect on hardness. Hardness is an indication- Finishing the structure & its resistance to scratching when in service. Higher the hardness, requires the use of special polishing equipment.
- 13. •Fatigue Fatigue resistance of alloys is important when it is considered that these alloys are removed and placed daily. At these times the clasps are strained as they slide along the retaining tooth, and the alloy undergoes fatigue. Comparisons of Cobalt ,Chromium, Titanium and Gold alloys show that, Cobalt Chromium alloys possess superior fatigue
- 14. Passivation Elements In some Base Metal Alloys have high affinity for Oxygen, but the Oxide film formed can serve a protective layer against oxidation and corrosion. This formation Of protective film by a reactive substance is called Passsivation Three metals are known for their Passivation potential. aluminium. chromium, titanium The most corrosion resistant of these is Titanium
- 15. HEAT TREATMENT OF BASE METAL ALLOYS Soldering Or Welding must be performed at the lowest possible temperature, with the shortest possible time of heating to the elevated temperature. Heat treatment of these alloys at 10000 C upto 1 hour did not change their mechanical properties.
- 16. COBALT- CHROMIUM ALLOYS: •‘Stellites’ by Eldwood haynes in 1900. Types Type I – High fusing Type II – low fusing
- 17. Cobalt- 35-65% Chromium- 23-30% Nickel- 0-20% COMPOSITION Molybdenum or tungsten-0-7% Iron, copper, beryllium- 0-5% Carbon- up to 0.2 % Manganese and silicon- in traces
- 18. Properties Co-Cr Type IVGold Comments Tensile Strength (Mpa) 850 750 Both acceptable Density (gms / cu.cm) 8 15 More difficult to produce defect free castings for CO-Cr but dentures are lighter. Hardness (Vickers) 420 (Hard than enamel) 250 (Softer than enamel) More difficult to polish but retains polish during services. Stiffness Stiff More flexible Ductility 2 15 (as cast) 8 (hardened) Co-Cr clasps may fracture if adjustments are made. Modulus of elasticity (GPa) 220 100 Co-Cr more rigid for the same thickness Proportional limit (MPa) 700 500 Both resist stresses without deformation. Melting temperature (oC) As high as 1500 Lower than 1000 Co-Cr require electrical induction or oxyacetylene Casting shrinkage 2.3 1.25 – 1.65 Tarnish resistance price adequate Reasonable adequate high COMPARISON OF THE PROPERTIES OF TYPE IV AND Co- Cr ALLOY :
- 19. APPLICATIONS • Denture Base • Cast Removable Partial Denture Framework • Crowns And Bridges • Bar Connectors
- 20. • Cobalt chromium alloys are ideal materials for major connectors, they are rigid and strong in thin sections. • They can be finished to high polish. • They have excellent life span. • They are rather difficult to adjust at chair side
- 21. NICKEL - CHROMIUM ALLOYS Composition: Nickel 61-81% Chromium 11-27% Molybdenum 2-9% Minor additions Beryllium, Aluminum, Iron, Silicon, Copper, Manganese, Cobalt and Tin.
- 22. PROPERTIES Density- 7.8-8.4gm/cm3 . Castability - extremely technique sensitive. Hardness and workability- 175-360 VKN. Modulus of elasticity- Ranges from 150-210 Mpa. Percent elongation- Ranges From 10- 28%. Tarnish and Corrosion Resistance-They are highly resistant to tarnish and corrosion .
- 23. SOLDERING- Long span bridges are often cast in 2 parts to improve fit and accuracy Base metal alloys are much more difficult to solder than gold alloys Casting shrinkage – These alloys have a higher casting shrinkage than the gold alloys. Greater mould expansion is needed to compensate for this. Inadequate compensation for casting shrinkage can lead to a poorly fitting casting
- 24. BIOLOGICAL CONSIDERATIONS Those alloys that contain beryllium, contain 1.6% -2% of the element. Precaution should be taken to avoid exposure to metallic vapor ,dust or grindings containing beryllium and nickel. The nickel chromium alloys can be divided into those containing and those not containing beryllium.
- 25. Nickel may produce allergic reactions in some individuals. Incidence of nickel sensitivity reported to be 5-10 times more in females than males, with 5-8% of females showing sensitivity. It is also a potential carcinogen. Inhalation of beryllium containing dust, or fumes is the main route. It causes a condition called Beryllosis, Characterized by flu like symptoms, and granulomas of lungs.
- 26. Physiological response may range from Contact Dermatitis to severe Chemical Pneumonitis. Safety standard for Beryllium dust is 2 Ug/m3 of air in a time waited 8 hour/ day. Safety standard for nickel is 15 Ug/m3 of air for a 40 hour/ week. To minimize exposure to metallic dust containing nickel or beryllium intraoral finishing should be done with a high speed evacuation system.
- 27. COBALT CHROMIUM NICKEL ALLOYS They were known as elgiloy. COMPOSITION: 40% cobalt, 20% chromium, 15% nickel, 15.8% iron, 7% molybdenum, 2% manganese, 0.16% carbon 0.04% beryllium. TYPES: It is available in four tempers which are color coded. The soft variety is color blue and the most widely used.
- 28. HEAT TREATMENT The softening heat treatment is at 1100°C to 1200°C followed by a rapid quench. The age hardening temperature is 260°C to 650°C for elgiloy it should be kept at 482°C for 5 hours. PROPERTIES Ductility is greater than the stainless steels in the softened state whereas less in the hardened state. APPLICATIONS orthodontic appliances removable partial denture framework
- 29. TITANIUM Titanium was first discovered in 1791 by Wilheim Gregor. was named as Titanium by Klaproth in 1794. Exist in two crystal form Alpha phase Hexagonal close pack structure. Stable at all temperatures upto 8820 C Beta phase Beta transis temperature . At this temperature ,the alpha phase gets transformed to beta phase Is stable from 882º C to melting point of titanium at 1668ºC
- 30. COMMERCIALLY PURE TITANIUM • Available in four grades according to purity. • According to american society of testing and material standard specification, as the grades increase from 1 to 4 ,the amount of contaminating oxygen, iron and nitrogen increases.
- 31. •Density is 4.5 g/cm3. Light weight metal •Modulus of elasticity is 100 Gpa. Half the value of other base metal alloys PROPERTIES •Melting point is quite high 16680 C. Therefore special equipment is required for casting titanium.
- 32. • Biocompatibility – it is nontoxic and has excellent biocompatibility with hard and soft tissues • Tarnish and Corrosion – Titanium has the ability to self passivate. It forms a thin protective oxide layer which protects the metal from further oxidation.
- 33. • Pure titanium has alpha crystalline structure, hence it is mostly used in chemical industry, where the excellent corrosion resistance is more vital than good mechanical qualities. • The need for mechanical qualities are more in orthopaedic implants, dental prosthesis and implants.
- 34. NICKEL-TITANIUM ALLOYS •It was introduced commercially during the 1970s following research by Andreason and his colleagues. •They were called as NITINOL and this name came from the two elements nickel and titanium and the Naval Ordinance Laboratory where these alloys were developed first by Duehler and associates. •These contain 54% nickel, 44%Titanium and generally 2% or less of cobalt.
- 35. •The alloying elements stabilizing the beta phase includes: hydrogen, manganese, chromium, molybdenum, iron and vanadium •The presence of even small amounts of interstitial elements alter the mechanical properties, e.g. A very low hydrogen conc. (0.15%) can produce great brittleness •Small quantities of carbon, nitrogen and oxygen can raise the strength of titanium and decrease its ductility.
- 36. BETA -TITANIUM ALLOY COMPOSITION: : Ti-78% Mo-11.55% Zr-6% Sn-4.5% PROPERTIES: : •Lower Elastic Modulus •Lower Yield Strength •Good Ductility •Good Weldability
- 37. TITANIUM PROCESSING • Titanium casting is highly technique sensitive due to its tendency to interact with atmospheric components • A heat source powerful enough to melt titanium is required • The molten metal should be isolated from air and the crucible should not react with molten titanium.
- 38. The melting occurs inside inert gas atmosphere such as argon gas The electric arc or high frequency induction is used to reach the high melting point of titanium.
- 39. OTHER APPLICATIONS OF CAST BASE METAL ALLOYS •In surgical repair of bone fracture . •Metallic obturators and implants. •Cobalt chromium alloys have been implanted directly into bone structure for long periods with favourable response of the tissue, probably due to low solubility and electrogalvanic action of the alloy. The product known as surgical vitallium is used extensively for this purpose .
- 40. METALLIC DENTURE BASE MATERIALS • Used in clinical situations where a single maxillary CD opposes a partial component of natural mandibular teeth. • Heavy masticatory load directed to a thin palatal resin plate which may result in denture fracture.
- 41. TECHNIQUE • Relatively thin metal base is cast to contact denture bearing surface. • Acrylic resin is used to retain the denture teeth and provide buccal and labial flanges that enhances esthetic quality • The processed resin is attached to cast metal base by a retentive meshwork.
- 42. ADVANTAGES • High thermal conductivity • Decreased bulk across palate • Dimensional stability, increased fit • Superior bio-compatibility • Stronger denture bases • Does not break easily, strength is many times more, hence can be made thinner.
- 43. DISADVANTAGES • Greater technical costs, expensive • Difficulty in relining and rebasing • Repair is difficult • Color is unaesthetic
- 44. ETCHING OF BASE METAL ALLOYS •When first introduced ,micromechanical retention of etched metal resin retainers was obtained by electrolytically etching the base metal alloys •More recently chemical etchants have been marketed •Technique- the surfaces of the restoration that are to be bonded to etched enamel are treated with acid gels or liquids for short periods of time
- 45. Property Property High noble High noble alloy alloy Co-Cr Co-Cr Ni-Cr-Be Ni-Cr-Be CPTi CPTi Biocompatib Biocompatib ility ility Excellent Excellent Excellent Excellent Fair Fair Excellent Excellent Density Density (g/cm (g/cm3 3 ) ) 14 14 7.5 7.5 8.7 8.7 4.5 4.5 Elastic Elastic Modulus Modulus (GPa) (GPa) 90 90 145-220 145-220 207 207 103 103 Sag Sag resistance resistance Poor- Poor- excellent excellent Excellent Excellent Excellent Excellent Good Good Technique Technique sensitivity sensitivity Minimal Minimal Moderately Moderately High High Moderately Moderately Extremely Extremely Bond to Bond to porcelain porcelain Excellent Excellent Fair Fair High High High High COMPARISON OF PROPERTIES OF THE VARIOUS TYPES OF BASE METAL ALLOYS
- 46. Review of literature 1.Mechanical properties and microstructures of cast Ti- Cu alloys:-Masafumi kikuchi,Yukyo Takada, Seigo Kiyosue, Masanobu yoda, Margaret Woldu, Zhuo Cai Osamu Okuno,Toru Okabe Dental Materials – 2003 , vol-19, 174-181 This study evaluated the mechanical properties of cast Ti-Cu alloys This study evaluated the mechanical properties of cast Ti-Cu alloys with the hope of developing an alloy for dental casting with better with the hope of developing an alloy for dental casting with better mechanical properties than unalloyed titanium mechanical properties than unalloyed titanium Result – By alloying with copper , the cast titanium became stronger. Result – By alloying with copper , the cast titanium became stronger. Increase in the tensile strength(30%) and yield strength (40%) over Increase in the tensile strength(30%) and yield strength (40%) over CP Ti were obtained for the cu alloy. CP Ti and the o.5 and 1 % Cu CP Ti were obtained for the cu alloy. CP Ti and the o.5 and 1 % Cu alloys showed higher ductility. alloys showed higher ductility.
- 47. 2.Bond Strength and Surface characterisation of a Ni-Cr- Be alloy:- Ana M .Diaz, Arnold ,John C.Kellar ,James P.Wightman and Vincent D.Williams. Dental Materials- 1996 ,vol-12,issue 1, 58-63 The purpose of the study was to determine the tensile bond strength, The purpose of the study was to determine the tensile bond strength, and assess predominant surface oxides and oxide layer depth after and assess predominant surface oxides and oxide layer depth after subjecting the alloy to various surface treatments subjecting the alloy to various surface treatments Results of this study suggests differences in oxide composition and Results of this study suggests differences in oxide composition and thickness due to various surface treatments. Furnace oxidation may thickness due to various surface treatments. Furnace oxidation may not be required as a separate step for metal preparation ,if a resin not be required as a separate step for metal preparation ,if a resin adhesive is used. adhesive is used.
- 48. CONCLUSION There have been major advances in There have been major advances in development of dental casting alloys during past 20 development of dental casting alloys during past 20 years. Because of large number and types of years. Because of large number and types of casting metals available for use , one of the major casting metals available for use , one of the major complex challenges of dentists is the proper complex challenges of dentists is the proper selection of casting alloys for restorations. selection of casting alloys for restorations.
- 49. References • Craig R.G., Restorative Dental Materials, 11 Craig R.G., Restorative Dental Materials, 11th th Edition, Edition, 2002, India. 2002, India. • John McCabe, Applied Dental Materials, 8 John McCabe, Applied Dental Materials, 8th th Edition Edition • Phillips , Science of dental materials, 11 Phillips , Science of dental materials, 11th th Edition Edition
- 50. Masafumi Kikuchi, Yukyo Takada, Seigo Kiyosue, Masanobu Yoda, Margaret Woldu,Zhuo CAI,osama Okuno, Toru Okabe-Mechanical Properties and microstrutures of cast Ti-Cu alloys Dental Materials-2003 ,Vol-19,174-181 - - Ana M.Diaz.Arnold , John C .kellar, James P.wightman and Vincent D.Wiilliams –Bond strength and surface characterisation of Ni-Cr –Be alloy Dental Materials -1996, Vol-12, Issue,58-63 - - - -