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By- Abhishek SharmaM.D.S(1st year) Deptt. Of Orthodontics and Dentofacial Orthopaedics
Definition History Uses Structure
of matter Basic properties of metal Mechanical properties of metal Clinical implications Toxicity Futuristic views
Metal an opaque lustrous chemical substance that is a good conductor of heat and electricity and, when polished ,is a good reflector of light.(metal handbook 1992) Alloy A crystalline substance with metallic properties that is composed of two or more chemical elements, at least one of which is metal. Wrought alloys Alloys which are hammered or drawn or bent into shape at temp. well below recrystallization temp. of the metal, often a room temp.
Gold Stainless Steel Cobalt-Chromium ( Elgiloy) Titanium AlloysNickel-Titanium. Beta-Titanium. (TMA)
Brief history of orthodontics
As early as 400 BC Hippocrats referred in his writings the correction of tooth irregularities. Meanwhile Etruscans were burying their dead with appliance in their mouth. Then in a Roman tomb in Egypt the dead were found with teeth bound with gold wire by Breccia. Later at the time of Christ, Aurelius Cornlius Celsus first records teeth by finger pressure.
Inherent malocclusion and use of corrective forces are recognized, the virtue of maintaining space is appreciated and the first orthodontic material is documented a gold ligature wire.
In the latter half of the 19th century Henry Clifton Sorby(1863-1887) and Edward Hartley Angle(1886-1930) professionally become the pioneers of modern metallography and modern orthodontics. In 1887 (German silver or Neusilber) were introduced by Angle which was alloy of copper, nickel and zinc alloys.
During this period, Gold, Platinum, brass, Silver, Steel, Gum rubber, Vulcanite were used in the form of loops, hooks, spurs and ligatures.
14-18 karat gold was routinely used for- wires, bands, clasps, ligatures and spurs as well as iridium- platinum bands and archwires and platinized gold for brackets.
From 1930s-1960s, the proliferation of materials did not occur.
During this stagnation period, Gold alloys were found to have deficiencies. Dumas, Guillet and Portevin 1st made Stainless Steel in France and its qualities 1st reported in Germany by Monnartz during 1900 1910. During World War 1, the Germans, British, and Americans developed an austenitic, martensitic and ferritic Stainless Steel. In 1930- Stainless steel was generally available.
In 1940s, Begg partnered with Wilcox and formed Australian Stainless Steel which is the back bone of light arch wire technique. 1n 1950, Stainless Steel was gaining prominence as ligature wire over soft brass wire. In 1960s, Gold was officially abandoned for Stainless Steel ever since most of the practitioners have relied on it. In 1960 Cobalt Chromium was introduced. In 1962, Buehler discovered Nitinol at the Naval Ordinance Lab. 1978 Andreasen introduced Nitinol to orthodontics.
1n 1981 Burstone introduced Beta titanium (TMA) to the orthodontic profession. In 1986, two superelastic alloy are offered- a Japanese by Dr. Tien Hua Cheung and a Chinese NiTi by Miura F. In the early 1990s Neo Sentalloy is introduced. In 1994, three Copper NiTi products are introduced by Rohit Sachdev and Suchio Miya Saki.
Esthetic wires were introduced such as Optiflex wires by Dr Talan and also composite and teflon coated wires.
(Robert P.Kusy Angle Orthodontist vol 72, no 6, 2002 Orthodontics Biomaterials : From the past to the present.)
Space Lattice - Any atom arrangement of atoms in space in which every atom is situated similarly to every other atom.
Unit Cell - It is the smallest box containing one or more atoms in a spatial arrangement of atoms.
14 possible lattice types, but many of the metals used in dentistry belong to the cubic system.
Pure iron at room temperature has body centered cubic (BCC) structure and is referred to as ferrite.
This phase is stable upto 9120C.
The spaces between atoms in BCC structure are small and oblate, hence carbon has very low solubility in ferrite (0.02 wt%).
At temperature between 9120C and 13940C the stable form of iron is face centered cubic structure called austenite.
The interstices in (FCC) are larger than BCC structure.
Maximum carbon solubility is 2.11 wt %.
When austenite form is cooled very rapidly (quenched) it undergoes a spontaneous, diffusion less transformation to body centered tetragonal (BCT) structure called Martensite.
This lattice is highly distorted and strained, resulting in very strong hard and brittle alloy.
Grain- a microscopic single crystal in the microstructure of a metallic material. Nucleus- stable cluster of atoms of a new phase that forms within a parent phase, such as during solidification of a metal. Dendritic microstructure- a cast alloy microstructure consisting of highly elongated crystals a branched morphology.
Stress Strain Youngs modulus Resilience Toughness Hardness Strain hardening Strength
Stress- it is the force per unit area acting on millions of atom or molecule in a given plane of a material. Stress = Force/Area tensile stress. shear stress. compressive stress.
Strain . Whenever a force is applied to a body it undergoes deformation. Strain is described as the change in length ( L = L LO) per unit length of the body when it is subjected to a stress. Change in length Strain ( ) = ___________________ Original length
Youngs modulus It describe the relative stiffness or rigidity of a material, which is measured by the slope of the elastic region of the stress-strain graph. Stress Elastic Modulus =_________ Strain
Resilience Amount of energy absorbed within a unit volume of a structure when it is stressed to its proportional limit. Toughness - It is defined as the amount of elastic and plastic deformation energy required to fracture a material.
Hardness The ability to resist scratching.Cold working( strain or work hardening) When a metal is stressed beyond its proportional limit, the hardness and the strength of the metal but the ductility of the metal decreases Strength- it is the stress necessary to cause either fracture (ultimate strength) or a specified amount of plastic deformation (yield strength).
Orthodontic wires manufactured by series of steps-
Initially, the wire is drawn in form of ingot, which must be subjected to deformation stages, until the crossection becomes small for wire drawing.
Round wires manufactured by drawing through the dies.
Rectangular wires are fabricated by rolling round wires, using Turks head apparatus that consists of pairs of rollers.
The surface roughness of the wire has a clinically effect on archwire-bracket sliding friction.
Generally greater in beta-titanium and nickel-titanium wires.
At stress below proportional limit, atoms in crystal lattice displaced elastically and when stress is relieved they can return to their original position.
Once proportional limit exceeded both plastic and elastic deformation occurred and when stress relieved structure does not return to original position.
Lattice Imperfections Crystallization from nucleus does not occur in a regular fashion.
Instead growth is more random with some lattice positions vacant and other overcrowded with atoms, these are classified as POINT DEFECTS
Dislocations The simplest type of dislocation known as Edge Dislocation The plane along which a dislocation moves Slip planes
Springback- This is also referred to as maximum elastic deflection, maximum flexibility, range of activation, range of deflection, or working range.1.
Springback is related to the ratio of yield strength to the modulus of elasticity of the material (Y S / E).Springback is also a measure of how far a wire can be deflected without causing permanent deformation
Stiffness or load deflection rate -This is the force magnitude delivered by an appliance and is proportional to the modulus of elasticity (E).2.
Low stiffness or load deflection rates provide (1) the ability to apply lower forces. (2) a more constant force over time as the appliance experiences deactivation, and (3) greater ease and accuracy in applying a given force
Formability - High formability provides the ability to bend a wire into desired configurations such as loops, coils, and stops without fracturing the wire.3.
Modulus of resilience or stored energy (MR). This property represents the work available to move teeth. It is reflected by the area under the line describing elastic deformation of the wire4.
Biocompatibility and environmental stability Biocompatibility includes resistance to corrosion and tissue tolerance to elements in the wire. Environmental stability ensures the maintenance of desirable properties of the wire for extended periods of time after manufacture.5.
joinability - The ability to attach auxiliaries to orthodontic wires by welding or soldering provides an additional advantage when incorporating modifications to the appliance.6.
Friction.-Space closure and canine retraction in continuous arch wire techniques involve a relative motion of bracket over wire. Excessive amounts of bracket/wire friction may result in loss of anchorage or binding accompanied by little or no tooth movement.7.
The preferred wire material for moving a tooth relative to the wire would be one that produces the least amount of friction at the bracket/wire interface.
(Mechanical properties and clinical applications of orthodontic wires by Sunil kapila and Rohit sachdeva, Ajo 1989;96:100-109)
2 types of gold wires are recognized in A.D.A specification no. 7 : type 1 and t