Base metal alloys

BASE METAL ALLOYS IN PROSTHODONTICS

1. BASE METAL ALLOYS BASE METAL ALLOYS

2. 2 CONTENTS INTRODUCTION HISTORY CLASSIFICATION REQUIREMENTS PROPERTIES CAST BASE METAL ALLOYS WROUGHT BASE METAL ALLOYS DENTAL APPLICATIONS REFERENCE

3. INTRODUCTION In dentistry, metals represent one of the three major classes of materials used for the reconstruction of damaged or missing oral tissues. Although metals are readily distinguished from ceramics and polymers.The wide varieties of complex dental alloy compositions consist of the following: Dental amalgams containing the major elements mercury, silver, tin, and copper. Noble metal alloys in which the major elements are some combination of gold, palladium, silver and important secondary elements including copper, platinum, tin, indium and gallium. Base metal alloys with a major element of nickel, cobalt, iron or titanium and many secondary elements that are found in the alloy compositions.

4. HISTORICAL PERSPECTIVE ON DENTAL CASTING ALLOYS Taggart’s presentation: Year Event 1907 Introduction of Lost-Wax Technique 1933 Replacement of Co-Cr for Gold in Removable Partial Dentures 1950 Development of Resin Veneers for Gold Alloys 1959 Introduction of the Porcelain Fused-to-Metal Technique 1968 Palladium-Based Alloys as Alternatives to Gold Alloy 1971 Nickel-Based Alloys as Alternatives to Gold Alloys 1980s Introduction of All-Ceramic Technologies 1999 Gold Alloys as Alternatives to Palladium-Based Alloys The 20th century generated substantially new changes to dental prosthetic materials. The major factors that are driving new developments are : i)Economy→ The new material performs the same function as the old material but at a lower cost. ii)Performance → The new material performs better than the old product in some desirable way, such as ease of processing, improved handlinig characteristics, or increased fracture resistance. iii) Aesthetics → The new material Provides a more aesthetic result, such as increased translucency

5. 5 IDEAL REQUIREMENTS Should Not Produce Toxicological Or Allergic EffectS Provide Resistance To Corrosion And Physical Changes When In Oral Fluids Thermal Conductivity ,Melting Temperatures, Coefficient Of Thermal Expansion Should Be Satisfactory. Use Should Be Feasible. Metals ,Alloys And Companion Materials Should Be Abundant, inexpensive And Readily Available.

6. 6 COMPOSITION Cobalt, Chromium, And Nickel (82%-92%) Minor Alloying Elements- Carbon, Molybdenum ,beryllium ,tungsten And Aluminum . Carbon Upto 0.2 %,-Is Most Critical Small Amounts may Have Pronounced Effect on Strength ,Hardness and Ductility.

7. 7 PHYSICAL PROPERTIES 1.Melting Temperature – most of the base metal alloys have at 1150-1500 c •Though One Commonly Used Nickel Chromium Alloy [ Ticonium ] Melts At 1275C. •Addition Of 1-2% Beryllium Lowers Melting Temperature Of Ticonium By About 100 c. 2.Density- The Average Density Of Cast Base Metal Alloys Is Between 7-8gms /Cm3 which is half the density of most dental gold alloys.

8. 8 MECHANICAL PROPERTIES • Yield Strength: • Gives an indication of when a permanent deformation of a part such as clasp will occur. •Base metal dental alloys have greater than 600Mpa to Withstand Permanent Deformation When Used As Partial Denture . •Tensile Strength: Greater Than 800 Mpa •Elongation: Indication Of Relative Brittleness And Ductility. The combined effect of elongation and tensile strength is an indication of toughness of material. . • Increasing the nickel content with a corresponding reduction in cobalt generally increases the ductility and elongation. • High values of elongation are obtained by casting at the normal melting temperature. High elongation is achieved without sacrificing strength and is the result of the precise and proper combination of carbon, nitrogen, silicon, manganese, and molybdenum content

9. 9 HEAT TREATMENT OF BASE METAL ALLOYS •Reduces The Yield Strength And Elongation . •Soldering Or Welding Must Be Performed At The Lowest Possible Temperature with shortest possible time of heating . • Heat Treatment Of These Alloys At 100 C Upto 1 Hour Did Not Change Their Mechanical Properties. 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 .

10. 10 . BASE METAL ALLOYS -Nickel based -Cobalt based Alloys in both systems contain chromium as the second largest constituent . A classification of base metal casting alloys Base metal Casting alloy Removable Partial denture Co-Cr Co-Cr-Ni Ni-Cr Co-Cr-Mo Co-Cr-Mo Surgical Implant Ni-Cr Co-Cr (Class-III) Fixed Partial denture Be. Cont.(Class-II) No Be. (Class-I) BASE METAL ALLOYS -Nickel based - Cobalt based Alloys in both systems contain chromium as the second largest constituent. A classification of base metal casting alloy

11. 11 Nickel-chromium (Ni-Cr) System These metal-ceramic alloy offer such economy that they are also used for complete crown and all metal fixed partial denture prosthesis ( Bertolotti , 1983). The major constituents are nickel and chromium, with a wide array of minor alloying elements. The system contains two major groups : -Beryllium free (class 1) -Beryllium (class 2) Of the two, Ni-Cr-Beryllium alloy are generally regarded as possessing superior properties and have been more popular ( Tuccillo and Cascone,1984).

12. 12 NICKEL-CHROMIUM-BERYLLIUM ALLOY Composition : Nickel – 62% to 82 % Chromium – 11% to 20% Beryllium – 2.0% Numerous minor alloying elements include aluminum , carbon, gallium, iron, manganese, molybdenum, silicon, titanium and /or vanadium are present . Advantages Disadvantages Low cost 1 . Cannot use with nickel sensitive patients 2.. Low density, permits more 2 . Beryllium exposure may be potentially casting per ounce . harmful to technicians and patients. 3 . High sag resistance 3. Proper melting and casting is a learned skill. 4 . Can produce thin casting 4 . bond failure more common in the oxide layer. 5 . Poor thermal conductor 5 . High hardness (May wear opposing teeth 6. Difficult to solder retention 7 . Ingots do not pool 8 . Difficult to cut through cemented castings

13. 13 NICKEL-CHROMIUM BERYLLIUM FREE ALLOYS Composition: Nickel – 62% to 77 % Chromium – 11% to 22% Boron , iron, molybdenum, Niobium or columbium and tantalum (trace elements). Advantages Disadvantages 1.Do not contain beryllium 1 . Cannot use with Nickel sensitive patients. 2.Low cost 2 . Cannot be etched. (Cr doesn’t dissolve in acid ) 3. Low density means more casting 3 . May not cast as well as Ni-Cr-Be alloys per ounce 4 . Produces more oxide than Ni-Cr-Be alloys.

14. 14 DISADVANTAGES OF NICKEL-CHROMIUM ALLOYS : Nickel may produce allergic reactions in some individuals (contact dermatitis). It is also a potential carcinogen. Beryllium which is present in many base metal alloys is a potentially toxic substance.Inhalation of beryllium containing dust or fumes is the main route of exposure. It causes a condition know as ‘ berylliosis ’. It is characterized by flu-like symptoms and granulomas of the lungs. Adequate precautions must be taken while working with base metal alloys. Fumes from melting and dust from grinding beryllium-containing alloys should be avoided. The work area should be well ventilated.

15. 15 COBALT-CHROMIUM ALLOYS COMPOSITION : Cobalt : 35 to 65% Chromium : 23 to 30% Nickel : 0 to 20 % Molybdenum : 0 to 7% Iron : 0 to 5 % Carbon : up to 0.4% Tungsten , manganese, silicon and platinum in traces PROPERTIES OF COBALT CHROMIUM Cost Lower and good mechanical properties Density : half that of gold alloys, lighter in weight (8 to 9 gm /cm3 ) Fusion temperature : Type-1(high fusing)- liquidus temperature greater than 1300° c Type-2(low fusing)- liquidus temperature not greater than 1300 ° c Yield strength : higher than the gold alloys Elongation : ductility is lower Modulus of elasticity : twice as stiff as gold alloys, casting made thinner , the weight of the RPD Hardness : harder than gold alloys,cutting,grinding,finishing are difficult Tarnish and corrosion resistance : Chromium oxide prevents tarnish and corrosion – passivating effect Caution : hypochlorite denture cleaning cause corrosion ,should not be used to clean chromium based alloys Casting shrinkage : shrinkage is much greater due to high fusion temperature Porosity : is due to shrinkage of alloy and release of dissolved gases

16. TITANIUM AND TITANIUM ALLOYS : The most widely used titanium alloy in dentistry is Ti-6Al-4V (Ti- 10.2Al- 3.6V in atomic percent ), which is an α-alloy. Titanium derives its corrosion protection from a thin passivating oxide film (approximately 10 nm thick), which forms spontaneously with surrounding oxygen . Titanium has a high melting point (1668 °C) and high rate of oxidation above 900 °C . Greater strength than that of CP Ti . 16

17. 17 ADVANTAGES OF TITANIUM  High strength  Light weight  Bioinert  Low tarnish and corrosion because of ability to passivate  Can be laser welded  Limited thermal conductivity DISADVANTAGES  Highly technique sensitive  Require expensive machines for casting and machining

18. 18 WROUGHT BASE METAL ALLOYS •Stainless Steel •Cobalt Chromium Nickel • Nickel –Titanium •Beta- Titanium

19. 19 STAINLESS STEEL • This was first discovered by Brearely of Sheffield, England in 1913 . • Stainless steel is an alloy of steel containing minimum of 13% chromium . • It is chromium which makes the steel resistant to tarnish and corrosion. FERRITIC (Alpha Form) • Solid iron in which carbon is insoluble,because of small space in between atoms . • It has a Body centered cubic structure • This condition remains from room temperature to 912 C . AUSTENITE(Gamma Form ) • Exists at Temperature Between 912- 1394 C As Face Centered Cubic Structure in Which Carbon Is Soluble, Because the Space Between the Atoms Is Larger and So the Carbon Atoms Occupy These Spaces to Form Interstitial Solid Solution. MARTENSITE • a Austenitic Steel at a Temperature Above 912 C Is Suddenly Cooled , It Undergoes Transformation in Its Structure to Form a Body Centered Tetragonal Structure Called Martensite • This Change Makes the Metal Hard,strong but Brittle. . .

20. 20 USES OF 18-8 STAINLESS STEEL • In Prosthetics For Partial Denture Clasps ,Bars For Swaged Plates,implants . • In Orthodontics For Wires, Ribbons, Bands, Bows, Hooks, Springs.  ADVANTAGES OF 18-8 STAINLESS STEEL • Heat and Corrosion Resistance. • More Ductile and Can Be Cold Worked . • Can Be Easily Welded . • Hardened by Cold Working . • Can Be Stabilized Against Corrosion.

21. 21 NICKEL- TITANIUM ALLOYS (NITINOL) COMPOSITION : Ni-54%, Ti-44%, Co-2% • was introduced in 1972 , characterized by high resiliency,limited formability,thermal memory Properties • Shape Memory effect- it is the ability of the alloy to retain and memorize a particular shape given to it • Mechanism of shape memory Structure of nitinol at room temperature is BCC( austentic phase) when this is heated it changes to HCP(martensitic phase).This change is responsible for shape memory effect. Superelasticity

22. 22 WROUGHT Co-Cr- Ni ALLOYS (ELGILOY) COMPOSITION : CO-40% Mn-2 % Cr-20 % C-0.15 % NI-15 % Be-0.04% Mo-7 % Fe-15.8 % Excellent Tarnish And Corrosion Resistance . WROUGHT 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

23. 23   RECENT ALLOYS Palladium- Copper- Gallium Palladium- 75% Copper- 10% Gallium- 5-10% Palladium –Gallium- Silver Palladium- 80-85% Gallium- 5-10% Silver- 0.5-8% Cobalt-Chromium- Neobium -Molybdenum-Zirconia- an increased corrosion resistance and overall biocompatibility Co 60% Cr 26.5% Mo 4.5% Nb 6.0% Zr 0.8% These alloys have superior mechanical properties .

24. 24 DENTAL APPLICATIONS

25. 25 Cast Cobalt Chromium Alloys . ( Vitalium & Nobilium ). Partial Denture Framework ,Porcelain Metal Restorations • Cast Nickel Chromium Alloys ( Ticonium ). Partial Denture Framework Crowns & Bridges Porcelain Metal Restorations • Cast Titanium and Titanium Alloys Implants , Crowns, Bridges • Wrought Stainless Steel Endodontic Instruments , Orthodontic Brackets ,Preformed Crowns • Wrought Cobalt- Chromium -Nickel Alloys Orthodontic wires Endodontic files • Wrought Nickel -Titanium Alloys Orthodontic wires Endodontic files • Wrought Beta- Titanium Alloys Orthodontic wires

26. 26 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 in to a Thin Palatal Resin Plate Which May Result in Denture Fracture. 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. • MATERIALS used : Cobalt chromium alloys, Nickel chromium alloys, Titanium alloys . Cobalt and nickel containing alloys could be potential allergens ,biological risks of metal ions being released suggests use of titanium.

27. 27 OTHER APPLICATIONS OF BASE METALALLOYS •In Surgical Repair Of Bone Fracture . • Metallic Obturators And Implants. • Cobalt Chromium Alloys Have Been Implanted Directly Into Bone Structure For Long Periods With Favorable Response Of The Tissue, Probably Due To Low Solubility And Electro- Galvanic Action Of The Alloy. The Product Known As Surgical Vitalliun Is Used Extensively For This Purpose .

28. 28 CONCLUSION

29. 29 REFERENCES : •Craig R.G., Restorative Dental Materials, 11th Edition, 2002, India . • Anusavice , Science of Dental Materials, 10th Edition, 1998, India • Micheal McCcracken

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