Assessment of mechanical,physical,chemical and biological properties of dental alloys . This presentation discusses the assessment of the properties of different alloys used in dentistry such as gold,NiTi and base metal alloys .

1. Assessment of dental alloys by
different methods
Mohamed Mahmoud Abdul-Monem
09708
Spring 2019

2. Assessment
Mechanical
properties
1.Elongation%
2.Modulus of elasticity
3.Yield strength
4.Fracture toughness
5.Hardness
6.Creep
Physical
properties
1.Thermal
conductivity
2.Thermal
diffusivity
3.COTE
4.Microstructure
5.Wettability
6.Surface
roughness
7.Adhesion
Chemical
properties
1.Elemental
analysis
2.Tarnish
3.Corrosion
Biological
properties
1.Biocompatibility
2.Ion release
3.Antibacterial
activity
4.Cell attachment

3. Assessment of Mechanical
properties of dental
alloys

4. Assessment of Mechanical properties
of dental alloys
1. Elongation percentage
2. Modulus of elasticity
3. Yield strength
4. Fracture toughness
5. Hardness
6. Creep

5. Elongation percentage
• The percentage of elongation is an indicator of
the relative brittlement or material’s flexibility.
• This property is particularly significant for a
clasp in the partial dentures.
• Elongation and ultimate tensile strength affect
the ductility of each material.

6. Specimen preparation
Aluminum Mold

7. Specimen

8. Specimens

9. Universal
testing
machine

11. Elongation %

12. Modulus of elasticity
• Higher value of the
elastic modulus indicates
a higher stiffness and
lower flexibility of the
cast construction of
partial denture or other
prostheses.
• Alloys with a high elastic
modulus allow the
production of smaller
restorations.
• The implant becomes
lighter by reducing the
thickness.

13. Yield stress
• Is the material
property defined as
the stress at which a
material begins
to deform
plastically

14. 2.Fracture toughness
• Fracture toughness is an
indication of the amount of
stress required to propagate
a preexisting flaw.
• Flaws may appear as cracks,
voids, metallurgical
inclusions, weld defects,
design discontinuities.

15. 3.Hardness
• It represents the
resistance of a material to
penetration of another
much harder indenter.
• There are different
procedures for testing the
hardness, and in
dentistry the most
common are Knoop and
Vickers methods.

16. 4.Creep
• Is the tendency of a solid
material to move slowly
or deform
permanently under the
influence of
mechanical stresses.
• It can occur as a result of
long-term exposure to
high levels of stress that
are still below the yield
strength of the material

17. 4.Creep

18. Mechanical properties of shape
memory alloys

19. Austenitic(480˚C )
twinned martensitic
(room temp)
detwinned martensitic
(reshaping)
austenitic
(body temp)
tooth movement

20. Assessment of
physical properties
of dental alloys

21. Assessment of physical properties of
dental alloys
1. Thermal conductivity
2. Thermal diffusivity
3. Coefficient of thermal expansion
4. Microstructure
5. Wettability
6. Surface roughness
7. Adhesion

22. 1.Thermal
concductivity
• Thermal conductivity λ is
defined as ability of material to
transmit heat and it is
measured in watts per square
metre of surface area for a
temperature gradient of 1 K
per unit thickness of 1 m.

23. 2.Thermal diffusivity
• Thermal diffusivity is
the thermal
conductivity divided
by density and specific
heat capacity at constant
pressure.
• It measures the rate of
transfer of heat of a
material from the hot end
to the cold end.

24. 3.Coefficient of thermal expansion
• The coefficient of
thermal
expansion describes
how the size of an
object changes with a
change in
temperature.

25. 4.Microstructure SEM

26. Crystalline structure by XRD
Is a measuring instrument for
analyzing the structure of a
material from
the scattering pattern produced
when a beam of radiation or
particles (such as X-
rays or neutrons) interacts with it.

27. Internal structure by XRD

30. 5.Wettability
Optical tensiometers
are used in research
to calculate :
• Wettability ·
• Adsorption ·
• Surface tension ·
• Contact angles ·
• Surface heterogeneity ·
• Interfacial rheology ·
• Surface free energy

32. 6.Surace roughness
Atomic Force
Microscope

33. Portable surface roughness
measurement device

34. 7.Adhesion
Shear bond strength Microtensile bond strength

35. Assessment of
Chemical properties
of dental alloys

36. Assessment of chemical properties of
dental alloys
1. Elemental composition
2. Tarnish
3. Corrosion

37. 1.Elemental composition by EDX

38. 3.Corrosion
• Is an electrochemical
process and is dependant on
the ability of metals to conduct
electrical current.
• It causes metal deterioration
and subsequent mechanical
failure.
• It causes pulpal pain(galvanic
shock).
• Toxic and allergic responses to
metal ions.
• Metallic taste
• It may be desirable as in dental
amalgam ?? As corrosion
products seal the marginal gap.
(limitied corrosion)
2.Tarnish
• Surface discoloration on a
metal or slight loss or
alteration of the surface finish
or luster.
• Occurs due to formation of
deposits ,oxides, sulfides and
chlorides on the restoration
surface.
• It is an early indication and
precursor of corrosion.

39. Corrosion Tarnish

40. Types of corrosion
Chemical corrosion
• (Dry corrosion) It occurs in
absence of water or any fluid
electrolyte
• Direct combination of a metallic
and nonmetallic element to yield a
chemical compound through
oxidation reactions.
• E.g (1) Oxidation of Ag-Cu
eutectic alloy particles of dental
amalgam. Oxidation limits their
reactivity with mercury.
• (2) Sulfurization of silver in
amalgam (Ag2S)
Electrochemical corrosion
Galvanic corrosion/wet
corrosion : requires the
presence of water or
any fluid electrolyte
and an electric current .

43. Assessment of
Biological properties
of dental alloys

44. Assessment of Biological properties of
dental alloys
1. Biocompatibility
2. Anti-bacterial activity
3. Ion release
4. Cell adhesion

45. 1.Biocompatibility
Biocompatibility
In Vitro
tests
Animal
tests
Usage
tests

46. In vitro tests
Direct contact
with cells without
barriers
Indirect contact
There is a barrier

47. In vitro tests
measure
Cytotoxicity
Or cell growth
Cell death caused by a
material by measuring
cell number or
growth before and
after exposure to the
material
Cell
Membarane
permiability
Metabolic
or cell
function
Measure
DNA or
protein
synthesis
MTT
assay
Effect on the
genetic
material in a
cell
(Mutagenesi
s
assay)

48. Cytotoxicity
Noncytotoxic interaction Cytotoxic interaction

49. Animal tests
Mucous membrane irritation test Skin sensitization test

50. Animal tests :
Implantation tests
Subcutaneous implantation Bone implantation

51. 2.Anti-bacterial activity

52. 3.Ion release
Atomic absorption
spectrophotometer
Atomic absorption
spectroscopy is
based on
absorption of
light by free
metallic ions

53. 3.Ion release

54. 4.Cell attachment Confocal
Microscope

59. References
• Niinomi M. Mechanical properties of biomedical titanium alloys.
Materials Science and Engineering A243 (1998) 231–236
• Prabhu et al .DentalProsthesis: An Evaluation on Mechanical
Properties of Recast Base Metal Alloys. Journal of Clinical and
Diagnostic Research. 2011 December, Vol-5(8): 1682-1685
• Slokar et al. Metallic materials for use in dentistry . The Holistic
Approach to Environment 7(2017)1, 39-58 .
• Thompson S .An overview of nickel–titanium alloys used in
dentistry. International Endodontic Journal.2000;33: 297–310
• Craig’s restorative dental materials 13th edition
• Phillip’s science of dental materials.12th edition