structure and properities of orthodontic materials

5/24/2018 ...Structure and Properities of Orthodontic Materials

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STRUCTURE AND PROPERTIES OF

ORTHODONTIC MATERIALS

AKSHAYA PANDIAN

I Yr M.D.S

Department of Orthodontics and

Dentofacial Orthopaedics


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CONTENTS

Structure of orthodontic materials

Properities of orthodontic materials

Dental materials used in orthodontics


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DEMOCRITUS460 BC


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ATOMIC STRUCTURE AND ELEMENTS


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INTERATOMIC BONDS

PRIMARY BONDS


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SECONDARY BONDS


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SPACE LATTICE

any arrangement of atoms in space in which

every atom is situated similarly to every other atom.


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ORTHODONTIC MATERIALS BASEDON STRUCTURE

Metallic materials

Ceramic materials

Polymeric materials


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METALLIC MATERIALS

Wire Alloys

Orthodontic Bands Orthodontic Brackets


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ATOMIC ARRANGEMENTS OF

METALLIC MATERIALS


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CHARACTERISTICS OF METALS

Crystalline structures in the solid state

BCC, FCC, or HCP unit cells Atoms held together by metallic bonding

Properties: high strength and hardness, high

electrical and thermal conductivity FCC metals are generally ductile


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CERAMIC MATERIALS

Alumina and Zirconia in bracket materials

Powder portion of cements Silicafiller in composite restorative

materials.


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ATOMIC ARRANGEMENTS OF

CERAMIC MATERIALS

Structure of Alumina

Structure ofFeldspathic Dental

Porcelain


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CHARACTERISTICS OF CERAMICS

Most ceramics have crystal structure, while

glass (SiO2) is amorphous

Molecules characterized by ionic or

covalent bonding, or both

Properties: high hardness and stiffness,

electrically insulating, refractory, andchemically inert


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POLYMERIC MATERIALS

Elastomeric impression materials

Polyurethane modules for tooth movement

Adhesive cements for bonding brackets to enamel

Polycarbonate brackets


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ATOMIC ARRANGEMENTS OFPOLYMER MATERIALS


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CHARACTERISTICS OF POLYMERS

Many repeating mersin molecule held together by

covalent bonding Polymers usually carbon plus one or more other

elements: H, N, O, and Cl

Amorphous (glassy) structure or mixture of

amorphous and crystalline

Properties: low density, high electrical resistivity, andlow thermal conductivity, strength and stiffness varywidely


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PROPERITIES OF CLINICALIMPORTANCE IN ORTHODONTICS

Mechanical properities Surface properities

Corrosion properities

Thermal properities Optical properities


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MECHANICAL PROPERTIES

Measures of the resistance of a material to

deformation or fracture under an applied

force.

StressForce per unit area within a structure

subjected to a force or pressure

StrainChange in dimension per unit initial

dimension.


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Compressive stressCompressive force perunit area perpendicular to the direction of

applied force.


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Tensile stressRatio of tensile force to the

original cross-sectional area perpendicular

to the direction of applied force.

Shear stressRatioof shear force to the

original cross-sectional area parallel to the

direction of the applied force.


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STRESS STRAIN CURVE


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Elastic strainAmount of deformation that is

recovered instantaneously when an

externally applied force or pressure is

reduced or eliminated.

Plastic strainIrreversibledeformation that

remains when the externally applied force is

reduced or eliminated.


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Elastic modulus (also modulus of elasticityand Youngs modulus)Stiffness of a

material that is calculated as the ratio of

elastic stress to elastic strain.

Proportional limitMagnitudeof elastic

stress above which plastic deformationoccurs.


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ResilienceThe amount of elastic energyper unit volume that is sustained on loading

and released upon unloading of a test

specimen.

Yield strengthThestress at which a test

specimen exhibits a specific amount of

plastic strain.


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FLEXIBILITY: The flexibility is defined as theflexural strain that occurs when the material

is stressed to its proportional limit.

POISSONS RATIO:


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Ductility: Ductility represents the ability of amaterial to sustain a large permanent

deformation under a tensile load up to thepoint of fracture

Malleability: Malleability is the ability of amaterial to sustain considerable permanentdeformation without rupture undercompression, as in hammering or rolling into asheet

Hardness: is a property used to predict thewear resistance of a material and its ability toabrade opposing dental structures.


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SURFACE PROPERTIES


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The amount of energy required to create aunit surface area of the material isSURFACE

ENERGY

The amount of force required to extend

the surface of a material by unit length is the

SURFACE TENSION


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CONTACT ANGLE

To report the wettability of various liquids to

solid materials.


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THERMAL PROPERTIESThermal conductivity

Property that describes the thermal energy transport inwatts per second through a specimen 1 cm thick with a cross-sectional area

of 1 cm2 when the temperature differential between the surfaces of thespecimen perpendicular to the heat flow is 1 K (1 C).


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Thermal diffusivityMeasure of the speed with which atemperature change will proceed through an object whenone surface is heated.

Coefficient of thermal expansion (linear coefficient ofexpansion)Change in length per unit ofthe original lengthof a material when its temperature is raised by 1 K (1 C).


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CORROSION PROPERITIES

Chemical or electrochemical process in

which a solid, usually a metal, is attacked byan environmental agent, resulting in partial

or complete dissolution.


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ORTHODONTIC MATERIALS

WIRE

STAINLESSSTEEL

GOLD ALLOYS

Co-Cr-Ni(ELGILOY)

BETA- TITANIUM

Ni-TITANIUM

OPTIFLEX

BRACKETS

ELASTOMERICLIGATURE AND

CHAINS

ORTHODONTICADHESIVE

COMPOSITE RESIN

CEMENTS

MISCELLANEOUS

STAINLESSSTEEL

TITANIUM

PLASTICS

POLYCARBONATE

CERAMIC

CONVENTIONALLIGATURES

FLOURIDERELEASINGELASTOMERS

CHEMICALLYCURED

LIGHT CURED

THERMOCURED

Zn PHOSPHATE

ZnPOLYCARBOXYLATE

GLASS IONOMER

ALGINATEIMPRESSIONMATERIAL

MINI IMPLANTS


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BRACKETS

Metallic brackets: Metal brackets rely onmechanical retention for bonding, mesh gauzeis the conventional method of providingretention.

Stainless steel brackets:have been usedsuccessfully for decades.

- AISI type 316L austenitic stainless steel alloy iscurrently used for bracket manufacturing.

Alloy contains Cr 16-18% Ni 10-14% Mo 2-3% C Max 0.03%


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Titanium Brackets :

- The increasing concern of nickel allergy insome patients had led to the use of passive

metalcommercially pure titanium forbrackets


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2. Aesthetic brackets Plastic bracket:

- The first plastic brackets were manufacturedfrom unfilled polycarbonate and introducedin early 1970s.

- The reinforced polycarbonate brackets wereintroduced in response to enamel damage.


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Ceramic brackets;

- Ceramic brackets are made of high purityaluminum oxide (alumina) and thebrackets are available in both

polycrystalline and single crystal(sapphire) forms.

- Zirconia brackets are manufactured by

impression molding


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ORTHODONTIC WIRESWire characteristics of clinical relevance;

1. Spring back - Range of action;Spring back is related to ratio of yield

strength to the modulus of elasticity ofmaterial. YS/E.

2. Stiffness or load deflection rate;Low stiffness or low load deflection rate

provide: Ability to apply lower forces


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A more constant force over time as theappliance experiences deactivation.

Greater ease and accuracy in applying agiven force.

3. Formability; Formability is the ease with which a material

can be plastically deformed. High formability provides the ability to bend

wire into desired configurations, such as loops,coils, and stops without fracturing the wire.


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4. Resilience (stored energy) : Resiliency is defined as amount of strain energy

per unit volume, which can be stored withoutpermanent set.

Strain energy = [yield stress]elastic modulus

5. Biocompatibility and environmental stability: Biocompatibility includes resistance to corrosion

and tissue tolerance to elements in the wire


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6. Joinability : This represents the ease of auxiliary attachment

to orthodontic wires by welding or soldering.

7. Friction:

This friction is proportional to the force ofcontact, and nature of the surface at thebracket / wire interface.

8. Zero stress relaxation: This is the ability of a wire to deliver a constant

light elastic force when subjected to anexternal force or forces of occlusion


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WIRES

Gold alloys

Stainless steel Co-Cr-Ni

B-titanium

Ni-Ti


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STAINLESS STEEL

Different classes of steels are based on threepossible lattice arrangements of iron.

1. Pure iron at room temperature has a bodycentered cubic (BCC) structure calledferrite.

2. Stable form of iron, a face centered cubicstructure called austenite is formed attemperature between 9120C and 13940 C.


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3. If the austenite is cooled rapidly, it will

undergo a spontaneous diffusion lesstransformation to a body-centeredtetragonal (BCT) structure calledmartensite.

Composition:When 12% to 30% chromium is added to

steel, the alloy is called stainless steel. 1720 % Cr.

812 % Ni

0.15 % C (max).


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CLASSIFICATION : AISI have classified stainlesssteel into:


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Australian stainless steel

orthodontic wires :

This was produced by A.J. Wilcock Sr.

These wires exhibit zero stress relaxation,

which allows the wire to maintain its force

over a long period of time, yet resist

permanent deformation from elastic load.


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Co-Cr-Ni Wires

A cobaltchromium nickel orthodontic wirealloy (Elgiloy) was developed during the1950s by the Elgiloy corporation.

This alloy, which was originally used forwatch springs is available in four tempers(levels of resilience) that are color coded bythe manufacturer:

Blue Soft Yellow Ductile Green Semi resilient

Red Resilient


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Composition of blue elgiloy :

Co 40%

Cr 20%

Ni 15% Fe 15.8%

Mo 7%

Mn 2% C 0.15%

Be 0.04%


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BETA TITANIUM WIRES

It is commercially available as TMA (Titanium

molybdenum alloy)

Ti 77.8%

Mo 11.3% Zr 6.6%

Sn 4.3%


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Advantages :

1. Have superior spring back property.

2. Excellent formability.

3. True weldability

4. Biocompatibilityabsence of Ni.

5. Excellent corrosion resistance


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NICKEL TITANIUM

Developed by William F. Buhler, using 55% Niand 45% Ti, in the naval ordinancelaboratory.

Properties :

Good spring back and flexibility, whichallows for large elastic deflections.

Changes in crystallographic arrangementcaused by heating produce the shapememory effect.

Lower bracket / wire friction with nitinol thanwith stainless steel wires.

Super-elastic property


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TOOTH COLOURED ORTHODONTICWIRES

Optiflex :is a nonmetallic orthodontic arch wirehaving highly esthetic appearance made of clear

optical fibre. It comprises of three layers :

A silicon dioxide core that provides the force formoving teeth.

A silicon resin middle layer that protects the corefrom moisture and adds strength.

A strain resistant nylon outer layer that preventsdamage to the wire and further increases strength.


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ELASTOMERIC LIGATURES AND CHAINS

Elastomeric products are used in orthodontics

as ligatures and as continuous modules

(chains).

Composition and structure: The elastomeric ligatures and chains are

polyurethanes which are thermosetting

polymers.

(NH)(c = 0)o[structural unit]

Formed by step reaction polymerization.


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ORTHODONTIC ADHESIVE RESINS AND

COMPOSITES

Direct bonding and indirect bonding of

orthodontic brackets utilize- Resin composite adhesive and require that

the enamel be etched.

- Glass ionomer cement can be used withoutetching of tooth structure.


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Based upon the polymerizationinitiation mechanism, orthodonticadhesives may be classified as:

Chemically activated (auto cured or selfcured) two paste or one paste.

Light cured (photo cured)

Dual cured (chemically activated and

light cured) Thermo cured


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ACRYLIC RESINS

1.Chemically activated resins:

Composition:

Powderprepolymerised sphere of poly methyl

methacrylate and a small amount of benzoylperoxide (initiator).

Liquid - unpolymerized methyl methacrylate withsmall amount of hydroquinone.

-Hydroquinone acts as inhibitor.-Glycol dimethacrylate is used as a cross linking agent.-Tertiary amine such as dimethyl para toludiene acts a

activators.


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2.Heat activated acrylic resins :

Thermal energy is required for polymerization

which may be provided by water bath asmicrowave oven. Composition of polymerand monomer are similar but thepolymerization procedure differs.Comparison with self cured resins:

Heat activated acrylic is stronger than selfactivated acrylic.

Degree of polymerization achieved usingchemically activated resins is not as

complete as that using heat activatedsystems.

Color stability is superior using heatactivated resins.


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3.Light activated denture base resins This material is described as composite

having a matrix of urethene dimethacrylate,

micro fine silica, and high-molecular-weight

acrylic resin.

Visible light is activator

Camphoroquinone serves as initiator.


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IMPRESSION MATERIALS

Potassium alginate 15% Form soluble alginate

Calcium sulfate 16% Reactor

Zinc oxide 4% Filler particles

Potassium titanium

fluoride

3% Accelerator

Diatomaceousearth

60% Filler particles (controlconics they before

setting and flexibility)

Sodium phosphate 2% Retarder

ALGINATE HYDROCOLLOID


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Gelation Reaction :

3CaSo4+ 2Na3Po4+ H2OCa3(Po4)2 + 3Na2So4

CaSo4+ k-alginate+ H2OCa-Alginate + K2So4 + H2O

(sol) (gel)

For an ideal mix:

W: P ratio15g for 40 ml.

Optimal temperature 200C

Figure of 8 motion

At least 3 mm thickness of material between

tray and tissues.


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RUBBER BASE nonaqueous elastomeric dental impression

materials. Chemically, there are 4 kinds of dental

elastomers used as impression materials: Polysulfide

Condensation polymerizing silicone Addition polymerizing silicone

Polyether

Based on Viscosity:

Light body Medium or regular body Heavy body


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DENTAL CEMENTS USED IN

ORTHO DONTICS

GIC

Zinc polycarboxylate

Zinc phosphate

GLASS IONOMER


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Powder Liquid

Calcium fluro alumino

silicate glass

Aqueous solution of

polyacrylic acid, malic,

polycarboxylic acid

copolymers containingitaconic acid (5% by wt)

Silica 41.9% D (+) isomer of tartaric acid -

Alumina 28.6%

Aluminium fluoride 1.6%

Calcium fluoride 15.7%

Sodium fluoride 9.3%

Aluminium phosphate 3.8%

GLASS IONOMER

Clinical implication :


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Prior to application of GIC, enamel surface isconditioned with 10-40% concentration of

aqueous solution of polyacrylic acid.

The ability of GIC to bond to base metal

alloys is important feature of this material. Salivary fluoride levels increases on the day

of placement of cement but eliminates after

a period of four weeks. It is used in orthodontic band and bracket

placement


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ZINC POLYCARBOXYLATE

Composition : Powder :- Zinc oxidebasic ingredient- Magnesium oxide or tin oxide10%

- Bismuth salts- Stannous fluoride4.5% - increases strength, controls

setting time.- Pigmentsfor shades

Liquid :

- Homo polymer of acrylic acid or copolymer ofacrylic with unsaturated carboxylic acids such asitaconic and maleic acid.

- Molecular weight of acids22,000-50,000.- Polyacid may be as freeze dried powder.


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Outstanding feature of this cement is itsability to bond to enamel and dentin.

Glossy appearances indicates the free

carboxylic groups which bond to tooth forcement and tooth tissues.

They are capable of bonding with surfaces

of metallic restorations, prosthesis and

appliances.


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ZINC PHOSPHATES

Composition :

Powder :1. Zinc oxide 90% principal ingredient

2. Magnesium oxide 10% aids in sintering

3. Bismuth trioxide smoothens the mix4. Silica filler

Liquid :

1. Phosphoric acid 45-64% - reacts with zinc oxide.2. Aluminum phosphate2.3% buffering action

3. Zinc phosphate 1-9%

4. Water controls rate of reaction



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Large differences in tensile and compressivestrength reflects the brittle nature of the

cement.

Solubility in water about 0.04% to 3.3% by

weight. Because of the low initial pH, it may irritate

the pulpal tissue.

Used for placing the orthodontic bands.


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CONCLUSION

Thus it is essential that the scientific

basis for the selection and proper useof materials for clinical practice bethoroughly understood in order to

bring about effective treatmentoutcome.


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REFERENCES

Textbooks :

Anusavice K.J. Phillips Science of dentalmaterials11th edn

Brantley and Eliades. Orthodontic materials Graber vanersdawl

Proffitt W. Contemporary orthodontics.


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THANK YOU

structure and properities of orthodontic materials

Documents

atomic structure

crystal structure

ceramic materials alumina

amorphous glassy structure

metallic bonding properties

crystalline properties

bonding brackets

high strength