physical properties of dental materials m&a

8/10/2019 Physical Properties of Dental Materials M&A

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Physical

Properties of

Dental Materials


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These are properties which are not related to forceapplication .These are:

1- Mass-related properties: Density2- Thermal properties:- Thermal conductivity

- Coefficient of thermal expansion and contraction- Heat of fusion & latent heat of fusion- Melting and freezing temperature- Specific heat

3- Less specific properties: - Water sorption.- Fluidity, viscosity and plasticity.

4- Optical properties


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Mass- Related Properties:DensityIt is the mass per unit volume of the material.Units are gm/cm 3 or pound/in 2

Clinical importance in Dentistry:1- Retention of the upper denture.2- Weight of complete or partial denture.

3- During casting.


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Thermal Properties:1- Thermal Conductivity:It is the amount of heat in calories or joules passing persecond through a body 1cm thick, 1cm 2 cross sectionalarea when the temperature difference is 1 C

Clinical importance in Dentistry:1- Metallic filling materials.


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2- Metallic denture base materials.


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2- Thermal Coefficient of expansion( )

The change in length per unit length of the materialfor a 1 C change in temperature is called thelinear coefficient of thermal expansion( )

L original-L final= L original x ( C final- C original)


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Clinical importance in Dentistry:of the coefficient of thermalClose matching

expansion ( ) is important between:1-The tooth and the restorative mater ials to prevent

.marginal leakage Opening and closing of gap results in breakage of marginal seal between the filling and the cavity wall,this breakage of seal

leads to:(marginal percolation)

i. Marginal leakage ii. Discoloration iii. Recurrent caries iv. Hypersensitivity.


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2-Porcelain and metal in ceramometallicrestorations (crowns and bridges) to provide

bonding.metal ceramic

.crazingto avoiddenture base andtooth Artificial -3
http://www.cr.nps.gov/hps/tps/briefs/images/10_crazing.jpg


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3- Heat of fusion Heat of fusion (L) is the amount of heat in calories or

joules required to convert l gm of a material from thesolid to the liquid state at the melting temperature. It is calculated as follows:

is the heat of fusion.L:WhereQis the total heat absorbed.Q: ----------------L =

mass of the substance meltedm:m

As long as the mass is molten, the heat of fusion is retained by the, this heat isWhen the liquid is frozen or solidifiedliquid.

liberated. It is called "Latent heat of fusion".


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Latent heat of fusion

It is the amount of heat in calories or joulesliberated when 1 gm of a material is convertedfrom liquid to solid state.

Importance in dentistry:During casting, the metal must be heated 100 Cmore than its melting temperature for propermelting


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Latent heat of fusion

Heat of fusion


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Dental significance

During casting metal must be heated 100 Cabove its melting temperature

Tm

Time

L

L + S

S


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4-Melting and freezing temperature

Tm

Time

Dental Importance:

For the fabrication of indirect metallic restorations (casting), the melting temperature of metals and alloysis important in determining the melting machine usedfor casting


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5-Specific heatIt is the quantity of heat needed to raise the temperature

of one gram of the substance 1 CTherefore Metals have low specific heat ,

while non metals have high specific heat

Importance in dentistry:- Because of the low specific heat of dental gold alloys, prolonged heating is

unnecessary, during casting


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Less specific properties

1- Water Sorption:It represents the amount of water adsorbed on the

surface and absorbed into the body of the

material.Importance : 1- Acrylic resin denture base materials have the

tendency for water sorption.2- Hydrocolloid impression materials will imbibe

water if immersed in it leading to dimensional

changes.


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2-Fluidity, viscosity andplasticity:

Fluidity is the tendency of liquids to flow.

Viscosity is the resistance to flow.

Plasticity is a property related to solids orsemisolids and indicates that the material iseasily and permanently deformed underforce.


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Optical Properties

The perception of the Color of an object isthe result of a physiological response to aphysical stimulus (light).

Light is an electromagnetic radiation that canbe detected by the human eye. It can be seenthat the visible electromagnetic radiation is in the range from 400-700 nanometers.

P i f i l i l i li h


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Properties of materials in relation to lighttransmission and absorption

Transparencyis a property of a material, that allows the passage of light in such a manner that little distortion takes

place so that objects can be clearly seen through them e.g. glass, pure acrylic resin.

Translucency is a property of the material, which allows the passage of some light and scatters or reflectsthe rest . In such manner, the object cannot be clearly seen through them Translucency decreases with increasing the scattering centers.e.g. tooth enamel, porcelain, composite and pigmented acrylic resin.
http://images.google.com/imgres?imgurl=http://www.neilblevins.com/cg_education/translucency/tut28_fig04.jpg&imgrefurl=http://www.neilblevins.com/cg_education/translucency/translucency.htm&h=332&w=500&sz=49&tbnid=P33JK-2XaW5xrM:&tbnh=84&tbnw=127&hl=en&start=3&prev=/images%3Fq%3Dtranslucency%26svnum%3D10%26hl%3D


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Opacity is a property of the material that

prevents the passage of light. Opaquematerial absorbs all of the light. Objectscannot be seen through them.

-Black color materials absorb all light colors .-White color materials reflect all light colors .

-Blue color materials absorb all light colorsbut reflect its color .


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Interaction of light and matterWhen a beam of light encounters or falls on a

surface of a medium, the following mayoccur :


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1- Reflection:Reflections on a smooth surface give aSmooth surface:-A

Specular Reflectionto the surfaceglossy appearanceangle of incidence = angle of reflectionSmooth surface:

The restoration should have a highly smooth and polished surface to simulate the tooth structure and match it.

B- Rough surface: Reflections of light on a rough surface arediffused (i.e: in all directions). Diffuse Reflection

The surface appears to have little gloss (i.e dull)


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2- Refraction:It is the change of the direction of a beam of light on entering

second medium.Refraction results from the difference in refractive indices of the

two media.

F or per fect matching the refractive index of the restorationshould be **equal to the refractive index of the tooth.

transparent solid while ** large differences result in opaque materials .

Example: Control of refractive index of the filler andmatrix phases in composite resins and porcelain.


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Scattering:-3 If light rays passing through a medium are obstructed by any different

inclusions it will be redirected in another direction and is attenuated.

i.e The original beam is weakened by scattering in adirection away from the observer eye OPACITY TRANSLUCENCY .

Importance in dentistry:1- Opacifiers & pigments added to composite resins act as scattering centers thatgive rise to opaque shades of the material.

2- Incorporated air bubblesin a restoration act asscattering centers.


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Complete Transmission Transparent

Incomplete Transmission TranslucentNo Transmission (absorption) Opaque

. Transmission:4Light passing through an optical medium

without attenuation

completely transmitted. Total transmission occurs in perfectly transparent materials.If part of the light is transmitted and part is reflected

( i.e. diffuse transmission ), the material appears translucent .


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C O LO R

Color parameters:A- Hue: It is the dominant wave length. It representsthe color of the material,i.e yellow , green , red and blue .

B- Chroma: It represents the strength of the color ordegree of saturation of the color (color intensity).

A beaker of water containing one drop of colorant is lower in

chroma than a beaker of water containing ten drops of thesame colorant.

C V l


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C- Value:It represents the lightness or darkness of color

(the amount of grayness).

A black standard is assigned a value of O,whereas a white standard is assigned 10.

* * * A tooth of low value appearsgray and non vital = DEAD ,

therefore, it is the most important parameter.Because it is intimately related to theaspect of vitality in human teeth.


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Factors affecting colorappearance and selection

Shade guide is used for color matching. So, itis important to match colors underappropriate conditions.

1- Source:Different sources have different color

content. i.e Incandesnt light has a colorcontent different from that offluorescent light.


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M etamer ism: It is the change of colormatching of two objects under differentlight sources .

M etamer ic pairs: Two objects that are

matched in color under one light sourcebut are not matched under other lightsources form metameric pair.

I somer ic pair : They are color matchedunder all light sources .

Thus, if possible, color matching should be done

under two or more dif ferent l ight sources .


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2- Surrounding:

Colors of wall, lips or clothes of the patientmodify the type of light reaching the object.

3- Object:A- Translucency:

It controls lightness or darkness of color.

High translucency gives a lighter colorappearance (higher value) i.e more vital toothappearance


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B- Surface texture (surface finish):

This determines the relative amount of lightreflected from the surface, smooth surfaceappears brighter than rough surface.

C- Presence of scattering centers asinclusions or voids:This increase opacity and lower the value(more dark)


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D- Fluorescene:It makes the teeth bright and vital, as it

increases the brightness.

E- Thickness:

The thickness of a restoration can affect itsappearance.Increase in thickness, increase opacity, and

lower the value.

F- Metamerism


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4- Observer:

A- Color response:Eye responds differently among individuals.

B- Color Vision:Some individuals may have color blindness

and inability to distinguish certain colors.

C- Color Fatigue:Constant stimulus of one color decreases theresponse to that color.

L


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L aser L ight A mplification by Stimulated E mission of R adiation .

The principle of laser production is simply that an elementor compound (medium) can be excited by high energy toproduce a special type of light called laser

Characteristics of laser beam: a- Monochromatic: all photons have the same wave length.

b- Coherent : all waves are bin phase (have the same speed ).

c- Collimated: all waves are parallel ( minimum divergence )


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Clinical applications oflaser

a- Surgery for removal of softtissues.

b- Removal of initial cariouslesions.

c- Curing of composite resin .


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Decontamination and sterilization Aphtous Ulcer treatment , Draining Abscess

Enamel exposureRoot canal treatmentBleaching


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s RO LOC

Primary colors

:

Blue , green and red are primary colors.Combining suitable proportions of wave lengths of the three

primary colors results in white.

Secondary colors : Each secondary color(cyan ,magenta & yellow ) results from the combination of

two primary colors, e.g . green and red gives yellow,blue and red gives magenta, blue and green gives cyan.

Complementary colors : Two colors are complementary toeach other when their combination results in white e.g . yellow isthe complementary color of blue .

physical properties of dental materials m&a

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