June 13, 2013
[DENTAL MATERIALS: PROPERTIES OF DENTAL MATERIALS]
Lecturer: Dr Angelina Atienza
SCIENCE OF DENTAL MATERIALS
Involves the study of the composition and properties of materials and the way in which they interact
with the environment in which they are placed.
Ideal properties of a restorative material
Main Goal: Should be as close as the part of the teeth being replaced
 Biocompatible - (non-toxic, non-carcinogenic, non-allergic, non-mutagenic)
 Bonds permanently to tooth structure or bone
 Good aesthetics- same appearance with natural teeth
 Properties are similar to structures of the teeth and other tissues
 Can initiate repair or regeneration of missing or damaged hard or soft tissues
Terminologies on classifications of dental materials
 Preventive Dental Materials – prevents or inhibits progression of dental disease (e.g. caries)
- Toothpaste, pit and fissure sealants, glass ionomer cement, therapeutic materials
 Restorative Dental Materials – used to repair or replace tooth structure
- Glass ionomer cement (bonds chemically to tooth structure and release fluoride for
relatively long period), ceramics, metals, polymers
 Auxillary Dental Materials – used in the process but not part of the final restoration
- Waxes, Impression materials, gypsum
 Indirect Restorative – extraorally fabricated e.g. crowns
done outside the mouth and placed inside the mouth
 Direct Restorative - intraorally fabricated e.g. fillings
 Temporary / Short term - days to weeks e.g. temporary pasta
 Intermediate / Moderate – months
 Long term – years e.g. fillings
Standards / Specifications
 ADA Council on Scientific Affairs
 FDA – Food & Drug Administration
 FDI – Federation Dentaire International
 ISO – International Standards Organization
 Others: Japan, Australia, Europe, etc.
*PDA does NOT perform lab tests
PROPERTIES OF DENTAL MATERIALS
 PHYSICAL
 CHEMICAL
 MECHANICAL
 THERMAL
 ELECTRICAL
 BIOLOGIC
UPCD 2017 | Paolo Romeo Dorado, Gladys Ann Ponce
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June 13, 2013
[DENTAL MATERIALS: PROPERTIES OF DENTAL MATERIALS]
BIOLOGIC
CHEMICAL
THERMAL
• Biocompatible
• Solubility
• Expansion
• Irritancy
• Erosion – chemical wear
• Conductivity
• Toxicity
• Corrosion resistance - rusting
of metal *(due to acid)
• Diffusivity (  diffusivity,  insulating
prop)
• Tarnish resistance - lacking
luster (can be precursor of
corrosion)* (tarnishdiscoloration)
• Exothermic reactions- release of heat
• Safety of use
*Attrition- physiologic; normal wear and tear (grinding of teeth)
*Abrasion-mechanical; wrong brushing of teeth
Thermal Properties
Linear coefficient of thermal expansion –change in length per unit of the original length of a material
when its temperature is raised by 1®C.
Coefficient of Thermal Expansion:
α = L/ Lo ®C -1
T
Linear Thermal Coefficient of Expansion of Dental Materials in
the Temperature Range of 20°C to 50°C
Material
Coefficient (x10-6/°C)
Human teeth
10 – 15 ~ 11.4
Dental amalgam
22 – 28 ~ 25
Composite plastics
25 – 68 ~14-50
Inlay wax
Gold alloys
“those coefficients with “~” are those
from the presentation”. –JCU*
300 – 100
12 – 15
CLINICAL APPLICATION: HOT stimulus causes filling to expand-can stress the tooth and fracture it; COLD
stimulus: shrink, fall off/plaque/bacteria could get in
*percolation - the slow passage of liquid coming out from the tooth
UPCD 2017 | Paolo Romeo Dorado, Gladys Ann Ponce
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June 13, 2013
[DENTAL MATERIALS: PROPERTIES OF DENTAL MATERIALS]
Thermal Conductivity - thermophysical measure of how well heat is transferred through a material by
the conductive flow. The rate of heat flow through a structure is proportional both to the area through
which the heat is conducted and to the temperature gradient across the structure.
THERMAL CONDUCTIVITY of Dental Materials
Material
Thermal conductivity
(cal/sec/cm2[°C/cm])
Human enamel
0.0022
Human dentin
0.0015
Dental amalgam
0.055
Gold alloys
0.710
Zinc phosphate cement
0.0028
Zinc oxide eugenol cement
0.0011
CLINICAL APPLICATION: Insulation of pulp when one drinks hot or cold beverages; irritation of pulp leads
to it becoming non-vital


Materials that have a higher Thermal Conductivity are called conductors.
Materials that have a lower Thermal Conductivity are called insulators.
THERMAL DIFFUSIVITY: Controls the time rate of temperature change as heat passes through a
material. Important in predicting the transfer of thermal energy.
- An insulator with a high thermal diffusivity is more desirable.*
THERMAL ENERGY
- Kinetic energy of atoms or molecules at a given temperature
-dependent on temperature
-Higher temp, greater amplitude, greater kinetic/internal energy, greater interatomic spacing
-Brings about: thermal expansion and change of state occurs
-Linear coefficient of thermal expansion is inversely proportional to melting temperature
-High melting point is accompanied by greater stiffness
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June 13, 2013
[DENTAL MATERIALS: PROPERTIES OF DENTAL MATERIALS]
ELECTRICAL
PHYSICAL
• Galvanism
(electrogalvanism)accelerated attack
occurring on a less
noble metal when
electrochemically
dissimilar metals
are in electrical
contact within a
liquid corrosive
environment e.g.
braces
• Aesthetics
• Optical Properties- deals with
phenomena of light, vision and sight.
Ex. Hue-color, chroma-intensity,
value-lightness/darkness and
translucency
• Density / Specific gravity - weight of
the material
• Rheological properties (how
materials flow)
 Viscosity – resistance to flow
 creep & flow
creep- deformation/behaviour
after the material has set
flow- deformation/behaviour
during processing (unset)
• Wetting – hydrophilic and
hydrophobic nature
• Bonding
• Setting time & Dimensional
changes
• Shelf life & stability on storage
MECHANICAL
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Abrasion resistance
Hardness
Stress
 tensile
 compressive
 shear
 complex
Strain
 elastic
 plastic
Strength
 tensile
 compressive
 shear
 impact
 yield
Elastic limit
Proportional limit
Rigidity, Elasticity
Flexibility
Fatigue, Deformation
Ductility, Malleability
Resilience
Toughness, Brittleness
Clinical significance: Materials with low rates of diffusion help protect the pulp.
Attrition- normal stress or wear*
WETTABILITY
• Can be observed by the shape of a drop of liquid on the solid surface
• Is a measure of the affinity of a liquid for a solid as indicated by spreading of a drop
HARDNESS - Gives an indication or resistance of a material to indentation and abrasion resistance
Common methods for hardness evaluation:
- Vickers (VHN) brittle
- Knoop (KHN)
hard & soft
UPCD 2017 | Paolo Romeo Dorado, Gladys Ann Ponce
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June 13, 2013
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[DENTAL MATERIALS: PROPERTIES OF DENTAL MATERIALS]
Brinell (BHN) metals
Rockwell - metals
Shove – rubber/plastic
Barcol – rubber/plastic
 


Increasing hardness
STRESS: force per unit area in a body which resist an external force (load)
Force
Area
= Stress (MPa or psi) pounds per square inch*
Types of Stress

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•
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Tensile - Internal resistance to deformation caused by a load that tends to stretch or elongate a
body.
Compressive - Force that resists a deformation caused by a load that tends to compress or shorten
a body.
Shear - Force that tends to resist a twisting motion of a sliding of one portion of a body over
another.
Complex – Combination of any or all of the above stresses
STRAIN - the resulting deformation or change in dimensions as a result of the load.
Change in length (ΔL) = Strain
Original length (Lo)
Types of Strain:

Elastic Strain - reversible (elastic recovery)

Plastic Strain - permanent displacement of the atoms inside the material (viscoelastic)
STRESS – STRAIN CURVE
UPCD 2017 | Paolo Romeo Dorado, Gladys Ann Ponce
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June 13, 2013
[DENTAL MATERIALS: PROPERTIES OF DENTAL MATERIALS]
Young’s/Elastic Modulus: gives an indication of the rigidity or stiffness of a material (not its elasticity)
Modulus of elasticity = Stress
Strain
 strain for a given stress =  ME
a. Greater Stress, Lesser Strain = Higher Modulus of Elasticity

Elastic Limit - Is the greatest stress to which a material can be subjected, such that it will return to its
original dimensions when the forces are release *spring back

Proportional Limit:
o When a material is reported as having a high value of PL it indicates that a sample of the
material is more likely to withstand applied stress without permanent deformation
o Often used to give an approximation to the values of the elastic limit
•
Yield Strength - it is the measure of the stress / load allowed before permanent deformation
•
Ultimate Strength - value is determined at the point where a material subjected to stress will
fracture or rupture
o Tensile strength
o Compressive strength
o Shear strength
o Impact strength
Stress – strain curve illustrating the areas that give a measure of the resilience (A) and toughness (B).
UPCD 2017 | Paolo Romeo Dorado, Gladys Ann Ponce
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June 13, 2013
[DENTAL MATERIALS: PROPERTIES OF DENTAL MATERIALS]
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Resilience - Indicates the energy required to deform a material permanently
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Toughness - Total amount of energy necessary to fracture a material, opposite is Brittleness
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Flexibility - property of the material to be flexible
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Ductility - ability of a material to withstand permanent deformation under a tensile load without
rupture.
•
Malleability - ability of a material to withstand permanent deformation without rupture under
compression.
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Fatigue - subsequent failure of a material when subjected to intermittent stresses (even if the stress
value is below the ultimate strength), over a period of time. There are formations of micro-cracks.
Final fracture often occurs at quite a low level of stress.
•
Abrasion Resistance - a measure of wear of a material considered to be of mechanical origin.
*Hardness- resistance of material for plastic deformation
UPCD 2017 | Paolo Romeo Dorado, Gladys Ann Ponce
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