1. INTRODUCTION TO DENTAL MATERIAL
Dr. Inas A. M. Jawad

2. Science Of Dental Materials
Science Of Dental Materials is defined as, “The Study of composition and properties of dental materials and the manner in which they interact with the environment in which they are placed”.

3. Science of dental materials is a basic science which deals with physical, mechanical and biological properties of dental materials. The study of Science of dental materials gives the operator a basic knowledge about the materials. This help to choose a material and allow him/her to effectively manipulate it.

4. “Why are we studying this field?”
1. for the knowledge to make optimal selection of materials 2. To understand the behavior of the materials, use, handling and manipulation 3. Safety considerations of the materials 4. Patient education regarding dental restoratives 5. Recognition of materials proper care of prostho/restorations 6. Understand the professional literature

5. Oral Environment The Oral Environment is very demanding. There can be
1. Temperature variations.
2. pH Variations.
3. Variatios in Masticatory forces.

6. Temperature Variations
Normal temperature of oral cavity (32℃ to 37℃).
On intake of cold/hot food or drink, the oral temperature range increases (0℃ to 70℃).

7. PH Variations pH of saliva is neutral (7.0)
On intake of acidic fruit juices or
alkaline medicaments, pH may
vary from 2.0 to

8. Variations in Masticatory Forces
Muscles of Mastication apply forces to the dentition.
Masticatory forces vary from tooth to tooth.
Average force applied by the tooth increases from anterior to posteriors.
Tooth
Average force (N)
Incisors
155
Cuspid
208
Bicuspid
288
1st Molar
390
2 nd Molar
800

9. Importance of dental materials science;
The science of dental materials has two main benefits; 1. Selection of the materials 2. Evaluation of the materials

10. Importance of dental materials science; (cont.)
Selection of the materials:
This process should follow a logical sequence involving;
1. analysis of the problem
2. consideration of requirements
3. consideration of available materials and their properties
4. comparison of requirements and properties of available materials.
5. choice of material.

11. Importance of dental materials science; (cont.)
B. Evaluation of the materials: Most manufacturers of dental materials operate an extensive quality assurance program and the materials are thoroughly tested before being released to the general practitioner. 1. standard specifications; 2. laboratory evaluations; 3. clinical trials;

12. Importance of dental materials science; (cont.)
B. Evaluation of the materials: (cont.)
Standard specifications;
These tests, of both national and international standards organizations, effectively maintain quality levels for some dental materials, e.g. American Dental Association (ADA), Federation Dental Association (FDA), International Standard Organization(ISO). Such specifications are essentially standards by which a value of certain dental materials can be gauged. They present the requirements as to the physical and chemical properties of a material which will insure that the material will be satisfactory if properly employed by the dentist.

13. Importance of dental materials science; (cont.)
B. Evaluation of the materials: (cont.) 2. Laboratory evaluations; Example, a simple solubility test can indicate the solubility of a material in aqueous media ( a very important property for filling materials).

14. Importance of dental materials science; (cont.)
B. Evaluation of the materials: (cont.) 3. Clinical trials; Many manufacturers carryout extensive clinical trials of new materials, normally in cooperation with a university or hospital department, prior to releasing a product for use by general practitioners.

15. PROPERTIES OF DENTAL MATERIALS
Dental materials are available in different forms like liquid, powder, paste, sheets, rolls, metal wire, and others. Many materials used in dentistry are supplied as two or more components which are mixed together and undergo a chemical reaction during which the mechanical and physical properties may be changed.

16. PROPERTIES OF DENTAL MATERIALS (cont.)
1. properties of unmixed materials (during strage);
i. shelf life (limited or extended shelf life).

17. PROPERTIES OF DENTAL MATERIALS (cont.)
2. properties of materials during mixing,
liquid-powder ratio,
viscosity both of the components and the mixed material,
method of dispensing,
method of mixing
Mixing time

18. PROPERTIES OF DENTAL MATERIALS (cont.)
3. properties during setting;
Rate of set
working time ( the time available for mixing and manipulating a material),
setting time ( the time taken for the material to reach its final set state or to develop properties which are considered adequate for that application).
Dimensional stability
Temperature rise on setting

19. PROPERTIES OF DENTAL MATERIALS (cont.)
3. properties of the set materials;
These are the important properties that must be available in a dental material to be used in the oral cavity. they include:
Physical properties
Chemical properties.
Biological properties.

20. Classification of the properties of set materials;
Physical: 1) mechanical properties.
i. stress strain relation
ii. modulus of elasticity.
iii. resiliency.
iv. toughness.
v. fatigue property.
vi. flexibility
vii. abrasion resistance.
viii. hardness
ix. ductility
x. malleabilty.

21. Classification of the properties of set materials; (cont.)
2) rheological properties. i. viscosity ii. viscoelasicity iii. creep 3) thermal properties. i. thermal conductivity ii. thermal diffusivity. iii. exothermic reactions. iv. coefficient of thermal expansion.

22. Classification of the properties of set materials; (cont.)
4) electrical properties. i. galvanism. 5) optical properties. i. color ii. translucency iii. surface texture. 6) Radiation 7) Atomic structure

23. Classification of the properties of set materials; (cont.)
2. Chemical: i. tarnish ii. corrosion. 3. Biological:

24. Concepts of Stress and Strain
When a force (external) acts on the body, tending to produce deformation, a resistance is developed within the body to this external force. STRESS: it is the internal resistance of the body to the external force. Stress is equal in magnitude but opposite in direction to the load (the external force applied). Stress= Force per unit area

25. Concepts of Stress and Strain (cont.);

26. Concepts of Stress and Strain (cont.);

27. Concepts of Stress and Strain (cont
Concepts of Stress and Strain (cont.); Relationship between stress and strain :
The stress and strain may be elastic or plastic or combination of two;
Elastic stress: does not cause permanent damage (produce elastic strain).
Elastic strain: reversible (not permanent). It disappears after the stress is removed. i.e proportional limit, resilience, modulus of elasticity.
Plastic stress: causes permanent damage (produces plastic strain).
Plastic strain: irreversible. It permanently remains once the external load that caused it is removed i.e percentage elongation.
Combination of elastic and plastic strain i.e toughness or yield strength.

28. Concepts of Stress and Strain (cont
Concepts of Stress and Strain (cont.); Relationship between stress and strain (cont.):

29. Concepts of Stress and Strain (cont.); types of stress and strain :
1. Tensile stress: a stress resisting a tensile force (stretching force) and produce tensile strain.
Compressive stress: a stress resisting a compressive force (shorting force) and produce compressive strain.
Shear stress: a stress resisting a shear force (twisting or rotational force). It is a combination of tensile and compressive stresses. It produces shear strain.
Flexural (bending) stress: a stress resisting a flexural force. It is a complex combination of all the three former types of stresses. It is produces a flexural strain.

30. Hardness
Hardness: is the resistance to permanent surface indentation or penetration. Hardness is measured as a force per unit area of indentation. The value of hardness, often referred to as the hardness number, depends on the method used for its evaluation. Generally, low values of hardness number indicate a soft material and vice versa.

31. Hardness (cont.)
The surface hardness tests commonly used in dentistry are: Brinell test: A steel ball is used, and the diameter of the indentation is measured after removal of the indenter. Rockwell test: A conical indenter is impressed into the surface. Under a minor load anti a major load, and M is the difference between the two penetration depths. Vickers test: A pyramidal point is used, and the diagonal length of the indentation is measured. Barcol test: is a spring loaded needle with a diameter of 1 mm that is pressed against the surface to be tested. The reading on the scale decreases as the indenter penetrates the surface.

32. Hardness (cont.)
Knoop test: A rhombohedra pyramid diamond tip is used, and the long axis of the indentation is measured. Shore test: Hardness A and hardness D. The depth of indentation or penetration is measured on a scale of 0 to 100. The steal rod is either configured as a frustum cone (Shore A) or a needle pin (Shore D).
Shore hardness tester

33. Hardness (cont.)

34. Thermal expansion: the linear coefficient of thermal expansion of a material is the fractional increase in length of a body for each degree centigrade increase in temperature. Thermal conductivity: is a measure of how well heat is transferred through a material by the conductive flow. Dimensional stability: it is measured by the degree to which the dimensions of a material alter after setting.

35. Viscosity: is defined as a resistance of a liquid to flow
Viscosity: is defined as a resistance of a liquid to flow. It is controlled by internal frictional
forces and is measured in poise (Mpa/sec) or
centipoise.
Creep: a time dependent plastic strain of a material under a static load or constant stress.
Because of its low melting range, dental amalgam can slowly creep from a restored tooth site under periodic sustained stress, such as would be imposed by patients who clench their teeth.

36. Title
Flow: is a measure of its potential to deform under a small static load even that associated with its own mass.
The term flow, rather than creep, has generally been used in dentistry to describe the rheology of liquids (e.g. saliva) and amorphous materials (e.g. waxes).
The term creep implies a relatively small deformation produced by a relatively large stress over a long period of time whereas flow implies a greater deformation produced more rapidly with a smaller applied stress.

37. Color: is a visual response to light
Color: is a visual response to light. it consists three dimensions; hue, value, and chroma (saturation).
Hue: refers to the dominant wavelengths present in the spectral and the names distribution associated.
Chroma: refers to the strength or degree of saturation for a particular hue.
Value: is a photometric parametric associated with total reflectance or luminance. i.e. the brightness or darkness.

39. Opacity: is a property of materials that prevents the passage of light.
When all of the colors of the spectrum from a white light source such as sunlight are reflected from an object with the same intensity as received, the object appears white. When all the spectrum colors are absorbed equally, the object appears black. An opaque material may absorb some of the light and reflect the remainder. If, for example, red, orange, yellow, blue, and violet are absorbed, the material appears green in reflected white light.

40. Translucency: is a property of substances that permits the passage of light, but disperses the light, so objects cannot be seen through the material.
Some translucent materials used in dentistry are ceramics, resin composites, and denture plastics.
Transparency:is a property of material allows the passage of light in such a manner that little distortion takes place and objects may be clearly seen through them.

41. Transparent substances such as glass may be colored if they absorb certain wavelengths and transmit others. For example, if a piece of glass absorbed all wavelengths except red, it would appear red by transmitted light. If a light beam containing no red wavelengths were shone on the glass, it would appear opaque, because the remaining wavelengths would be absorbed.