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7/31/2019 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 hjsa@just.edu.jo
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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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6
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
tags
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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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