material properties student 1

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Dental Materials

Dr Hanan AlZraikat

BDS, PhD in Dental materialscience

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Course information

Course Title Dental Materials

Course Number Dent 203

Credit hours Two

Prerequisites None

Instructor/Coordinator Dr Hanan AlZraikat

Lecture venue and time Tuesday 2:15-4:15 pm, Science hall 2

Laboratory sessions venue and time Prosthodontic lab :

Sunday:8.00-10.00 am

Monday: 8.00-10.00 am

Tuesday: 8.00-10.00 am

Wednesday: 8:00-10:00 am

Office Location Postgraduate dental hospital. Level 1

Office Phone 23975

Office Hours Upon appointments. Available times are:

1.00-2.00 pm Tuesday

E-mail [email protected]


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Text Book and Resources

Dental materials. Clinical

applications for dental

assistants and dental

hygienists.

C. D.

Hatrick

Saunders

publications

1st

ed2003

Introduction to dental

materialsVan noort Mosby

2nd

ed2002

Applied Dental Materials.J.F.

McCabe

Blackwell

Scientific

Publications

8th

ed

Phillips Science of Dental

Materials

Kenneth

J.Anusavic

e

Sunders

publications

11th

ed2003

Dental materials,

properties and

manipulation

Robert G.

CraigJohn M.

Powers

John C.

Wataha

Mosby 8th 2004

Assessment policy Weight

Theory exams; 80 % of the total mark divided as follows:

Midterm = 35%

Final = 45%

Laboratory sessions assessment 15% of the total mark

Quizzes 5% of the total mark.

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Week Lecture title Areas of interest Reference/chapter

1. Introduction into the

course

2. Oral-cavity (1)

considerations;

Properties of Materials

To identify factors inside the oral cavity that

affect selection and performance of dentalmaterial

To become familiar with material properties

Reference booksand lecture notes

3. Impression materialsHydrocolloid systemsRubber systems

Compound systems

Others

Reference books

4. Midterm Exam: Tuesday 10/7/2012- 2.15-3.15 pm Location:10H1,2,3

5. Gypsum and investmentmaterials

Impression plaster

Dental plaster

Dental stone

Special die stone

Investment materials

Reference books

6. Waxes Different sources of dental waxes and

propertiesWaxes used in clinical and laboratory

applications

Handling of waxes

Reference books

7. Polymers Denture base materials

Denture relining materials

Alternatives to conventional materials

Reference books

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Laboratory sessions

Week Lab. subject Areas of interest

2. Introduction to dental materials

And laboratory sessions

regulations

Laboratory session regulations

Students groups identification

Quiz

3. Impression Materials To identify different types of impression material, their properties, uses and

the correct method of mixing them:

oHydrocolloid systems

oRubber systems

oCompound systems

oQuiz

4. Gypsum and waxes To identify different gypsum materials, their properties and how to mixthem:

oPlaster

oStone

oDie stone

oInvestment material

To identify waxes used in dental laboratories and clinics and their

properties

Quiz

5. PolymersTo identify dental acrylic materials compositions and their properties usedas:

oDenture base material

oDenture relining materials

oDenture teeth

Quiz


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Oral environment and patient

consideration

The oral environment represents a challenge to the

success of dental materials. Understanding these challenges and limitations, is

essential for a successful treatment.

Materials must be biocompatible, aesthetic and

durable.

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Intraoral factors

Force and stress:

a. Compressive: crushing biting forces

b. Tensile: biting force stretches a materialc. Shear: e.g. an incisor used for cutting

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a cb


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Resisting these forces creates stress within

the material, which may lead to deformation,

strain.

Dental materials can withstand one type of

stress while fail under another. But failure

usually occurs after repetitive force

application i.e. fatigue failure.

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Moisture and acid levels:

Intraoral pH depends on diet and acidproducing bacteria.

Moisture. Interaction with moisture: Some materials take up

water, color, odor, tastes of foods and beverages(e.g. resins, acrylic).

Metals (except noble metals) are affected byacid and moisture, i.e. corrosion, tarnish

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Galvanism: an electric current transmitted

between two dissimilar metals.

Temperature:

Dimensional changes (expansion/contraction)

Coefficient of thermal expansion (CTE). Percolation: definition and consequences.

Thermal conductivity and insulators (pulp

sensitivity).

Exothermic rxn of restorative material.

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Retention: the ability of the materialto maintain its position and resist

displacement

Mechanical

Chemical Bonding

(micromechanical/chemical).

Affected by:

Wetting

Viscosity

Film thickness

Surface characteristics:

cleanliness, moisture

contamination, texture, energy.

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Rough enamel

surface

Micromechanical

retention with dentine

Resin

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Adhesion: Chemical bond to enamel &dentine by ion

exchange

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Microleakage: the

seepage of harmful

materials through the

gap between toothand restoration. Can

cause:

Staining

Recurrent caries

Sensitivity

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Shrinkage outcomes

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Biocompatibility: dental material must not

have an adverse effect on living tissue Materials used on hard tissue vs. soft tissue

Short term vs. long term exposure

Small doses vs. high doses (fluoride treatment)

Adverse effects maybe due to materials itself or the

breakdown of its components.

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Amalgam tattoo

Fluoroses

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Esthetics

Color components:

Hue: dominant color of wavelength detected

(tooth color is seen in yellow and brown range) Chroma: color intensity or strength

Value: how bright or dark a color is.

Transparent vs. opaque

Shade guide

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Shade guide

Conditions for assessing restorations:

Dry field

Good lighting

Sharp explorer Radiographs

Magnification

Good knowledge of material

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End of part one

Reference:

Dental materials

Clinical applications for dental

assistants and dental hygienists (ch. 2)

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Material properties

Physical properties: properties based on the laws of

mechanics, optics, thermodynamics, electricity etc.(Phillips science of dental materials)

A. Rheological properties (ref. Introduction to dentalmaterials ch.1.8)

Definition: The study of flow or deformation of materials.

Solids: elasticity and viscoelsticity

Liquids: viscosity = shear stress/shear rate

Consider extrusion of a fluid from syringe.

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Viscosity: resistance of a liquid to flow. The ways in which

materials flow or deform under stress are important to their

use in dentistry.

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Thixotropy: for some liquids, the viscosity may change at aparticular shear rate, so, the viscosity for an increasing shearrate is different from the viscosity for a decreasing shear rate(the gel become liquefied under repeated pressure such as

when shaken, stirred or vibrated). A thixotropic fluiddisplays a decrease in viscosity over time at a constantshear rate. A shear thinning fluid displays decreasingviscosity with increasing shear rate.

Viscoelasticity: intermediate behaviour between elastic solidand viscous liquid. Depends on the amount of load, andduration of the load applied. (elastomeric impression

materials), so, to prevent permanent deformation, thesematerials should not be loaded for a long time

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B. Mechanical properties (ref. Dental Materials,properties and manipulation)

Properties defined by the laws of mechanics; the

physical science that deals with energy and

forces and their effects on bodies.

Maximum biting force decreases from molars toincisors. Average biting force

1st and 2nd molars = 580 N

Bicuspids (premolars) = 310 N

Cuspids (canines) = 220 N

Incisors = 180 N

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To compare the performance of materials irrespective oftheir shape or size, an objective standard is needed.This standard is stress and strain. Description ofmechanical properties depends on these two.

Stress = force/unit area (compressive, tensile, shear)

Strain: the deformation per unit of length as a result offorce = deformation/length(e.g. rubber vs. gold alloy)

Force (N) Area (mm) Stress (MPa)

111 645 0.1724

111 64.5 1.724111 6.45 17.24

111 0.645 172.4

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Stress-strain curves are a convenient way to comparematerials mechanical properties whether in compression,tension or shear, especially when strain is independentof the length of time the load is applied

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Strain-time curves are sometimes used when strain

depends on the time the load is maintained (e.g.

alginate, rubber impression material)

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Values resulting from stress-strain curves:

Elastic modulus = stress/ strain (MPa), a measure

of stiffness

Proportional limit: measure of stress allowed

before permanent deformation occurs.

Ultimate strength: maximum amount of strength a

material can withstand without breaking.

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Other mechanical properties

Elasticity: the ability to stretch and not break

(impression material and undercuts)

Elastic (recovery immediate) vs. viscoelastic

(recovery slow or with some degree of permanent

deformation

Toughness

Resilience

Creep

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Hardness: resistance to wear or abrasion (enamel

and porcelain are among the hardest). Hardness is

measured using several tests such as Knoop, or

Vickers hardness tests

Fatigue properties (refer to slides only):

Materials are subjected to intermittent stress overlong period of time, stress is small, but over time,

failure may occur by a fatigue process. This

involves the formation of microcracks, resulting

from stress concentration at a surface fault, so

crack propagates until fracture occurs. Final

fracture occurs at a low stress level.

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Fatigue is studied in 2 ways:1. Fatigue life: application of stress cycles at a certain

amount and frequency and observe number of

cycles needed to cause failure.

2. Fatigue limit: select a number of cycles (e.g. 10

000) and determine the value of the cyclic stress

which is required to cause fracture within this

number of cycles.

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Ultimate strength values of selected dental

materials

Material Tensile strength Compressive strength

Dentine 98 297Enamel 10 400

Amalgam 48-69 310-483

Gold alloys 414-828 -----

Composite 34-62 200-345

Porcelain 40 150

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C. Thermal properties: (ref. Dental Materials, propertiesand manipulation)

Materials have different rates of conducting

heat. (Metals vs. plastics and ceramics). Thermal conductivity: its a measure of heattransferred through a material or rate of heat

flow. Compare Enamel and dentine to dental

amalgam.

Coefficient of thermal expansion (explained

previously)

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Insulation

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D. Electrical properties: (ref. Dental Materials, properties andmanipulation)

Galvanism: generated electrical current a

patient can feel resulting from dissimilar metals

present in a solution that contains ions (e.g.oral cavity)

Corrosion: can result from

adjacent dissimilar metals. Galvanic action can cause the

metal to dissolve resulting in pitting and roughness.

Chemical corrosion

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E. Solubility and sorption: (ref. Dental Materials,properties and manipulation)

important criteria for dental materials selection.

Laboratory studies are used to evaluate and

rank materials. Sorption includes:

Absorption vs. Adsorption

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F. Wettability: (ref. Dental Materials, properties and manipulation)

measure of the affinity of a liquid for a solid indicated

by spreading of a drop of the liquid on a solid.

wettability is observed by shape of a drop of liquid onsolid surface identified by contact angle:

Low contact angle = high wettability (hydrophilic

if liquid is water)

High contact angle = low wettability (hydrophobic

if liquid is water)

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Good wetting of a solid by a liquid with low

contact angle (left), poor wetting forming a high

contact angle (right).

liquid

solid solid

liquid

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G. Optical properties: (ref. Introduction to dental materials) Every object we see is as a result of reflectance of light from

that object reaching an extremely sensitive photodetector,namely the eye. This is characterized by:

Color:

(Hue, value, chroma).

Perception of color is subjective. Cone cells in retina aresensitive to light, rod cells are sensitive to brightness, bothsend signals to the brain.

Visible light wavelength is 380-780 nm

The light we see is a combination of wavelengths

Translucency: Translucent materials allows some light to pass, absorbs

some, and scatters the rest

Opaque material does not transmit light, but absorbs andscatters it.

Surface texture: the polishability of a material is an importantcriteria for selection

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Important terms to know:

*Metamerism: change of color of an object due

to a change in light source

*Fluorescence: the ability of an object to absorblight near ultraviolet and then release light in a

longer wavelength range wavelength

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Shade guide and selection

A (reddish brown)

B (reddish-yellow)

C (grey)

D (reddish grey) 49

H. Biological properties: (ref. applied dental materialsch.2)

Primary requirements of any dental material:

Non-toxic

Non-irritant

Should not have carcinogenic or allergic potential

If used as filling material should be harmless to pulp

Biological evaluation of dental materials:

Level 1

Level 2

Level 3

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material properties student 1

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