Physical properties of dental materials.pptx

Physical properties of Dental Materials

1. Physical properties and chemical properties of materials Dr.Mandeep kaur Senior Lecturer Date- 16 th oct 2023

2. Physical properties are based on the laws of mechanics, acoustics , optics, thermodynamics, electricity, magnetism, radiation , atomic structure, and nuclear phenomena . Hue, value , and chroma relate to color and perception and are physical properties based on the laws of optics, which is the science that deals with the phenomena of light, vision, and sight .

3. Physical properties are based on the laws of Mechanics Acoustics Optics Thermodynamics Electricity Rheology Magnetism Radiation Atomic Structure

4. THERMAL PROPERTIES Thermal conductivity Coefficient of thermal expansion and contraction Heat of fusion & latent heat of fusion Melting and freezing temperature Specific heat

5. THERMAL CONDUCTIVITY It is the c h ar a cteri s tic t h at de t ermi n es the ra t e at which heat flows through a material. It is a function of the composition which determines the heat capacity magnitude of the temperature change thickness of the object.

6. Clinical importance in Dentistry: 1- Metallic filling materials. 2- Metallic denture base materials.

7. THERMAL DIFFUSIVITY It is a measure of the rate at which a body with a non uniform temperature reaches a state of thermal equilibrium. Clinical importance in Dentistry: Thermal insulation  Thickness of liner or base  1 / thermal diffusivity

8. COEFFICIENT OF THERMAL EXPANSION When materials undergo a temperature increase, the vibrational motion of atoms and mean interatomic (bond) distances ncrease . This results is an increase in volume—an expansion . The increase is described by the coefficient of thermal expansion, α, which is defined as the change in length per unit of the original length of a material when its temperature is raised 1 °C (1 K ). where L is the original length, ΔL is the change in length ΔT is the temperature change .

9. Clinical importance in Dentistry: Close matching of the coefficient of thermal expansion (α) is important between: The tooth and the restorative materials to prevent marginal leakage. Opening and closing of gap results in breakage of seal (marginal percolation): Marginal leakage Discoloration Recurrent caries Hypersensitivity.

10. Thermal stresses produced from a thermal expansion or contraction difference are also important in the production of metal-ceramic restorations. Consider a porcelain veneer that is fired to a metal substrate (coping). It may contract to a greater extent than the metal during cooling and induce tangential tensile stresses or tensile hoop ( circumferential) tensile stresses in the porcelain, which may cause immediate or delayed crack formation .

11. HEAT OF FUSION (L) The amount of heat in calories or joules required to convert 1 gm of a material from the solid to the liquid state at the melting temperature. As long as the mass is molten, the heat of fusion is retained by the liquid.

12. LATENT HEAT OF FUSION It is the amount of heat in calories or joules liberated when 1 gm of a material is converted from liquid to solid state. Importance in dentistry : During casting, the metal must be heated 100 °C more than its melting temperature for proper melting

13. Heat of fusion Latent heat of fusion

14. SPECIFIC HEAT I t i s the qu a ntity o f hea t nee d ed to raise the tem perature of one gram of the substance 1°C Met a l s have low specific he a t, wh i le non met a l s have h i g h specific heat Importance in dentistry: - Because of the low specific heat of dental gold alloys prolonged heating is unnecessary, during casting

15. Gold has about one tenth the heat capacity of dentin , about 500 times the thermal conductivity, and about 600 times the thermal diffusivity. Thus a pure gold filling would provide the tooth pulp with very little protection against thermal shock as compared with natural dentin .

16. The science of study of flow and deformation of matter. Importance in dentistry: Many dental materials are mixed as fluid pastes which subsequently solidify. The mixed pastes are adapted to the required shape The setting of such materials initially involves a change in viscosity with time and then the development of an elastic modulus on solidification RHEOLOGICAL PROPERTIES

17. VISCOSITY Viscosity of a fluid is its resistance to flow. Viscosity of fluids depends on many factors i.e . T he nature of the substance, temperature, pressure, etc.

18. Newtonian fluid : Ideal fluid demonstrates a shear stress that is proportional to the strain rate and thus plot a straight line

19. Non – Newtonian fluids . 1. Plastic Some classes of materials behave like a rigid body until minimum value of shear stress is reached known as PLASTIC. E.g. Ketchup – a sharp blow to the bottle is usually required to produce an initial flow.

20. 2. Psuedoplastic behavior-- Viscosity decreases with increasing shear until it reaches a nearly c o n s ta n t val u e ( Sh e ar t h i n n i ng ) e. g . po l ym e r , natural resins , impression materials.

21. 3. Dilatants – Materials whose viscosity increases with increasing shear rate until constant value (shear hardening) i.e. becomes more rigid as rate of deformation increases.

22. Thixotropic behavior When some fluids are sheared at a steady rate viscosity decreases with time . On standing , the fluid regains its original viscosity, this is called THIXOTROPY , and is caused by structural break down and reformation. e.g . fluoride gels, prophylaxis paste, resin cements, plaster of paris, impression materials

23. CREEP Time dependent plastic strain of a material under a static load or constant stress. The slow change in the dimensions of an object due to prolonged (i.e. time dependent) exposure to stress and high temperature. FLOW . Rheology of amorphous material e.g. waxes has potential to deform under small static

24. Metals used in dentistry , for cast restorations or substances for porcelain veneers have melting points that are much higher than mouth temperature, and thus are not susceptible to creep deformation. An exception is dental amalgam having components with melting point slightly above room temperature, can slowly creep from restored tooth Importance in dentistry:

25. Galvanism is defined as accelerated corrosion of a metal due to electrical contact with a more noble metal in a corrosive electrolyte. Also called as Wet corrosion . The resulting current flow can produce nerve stimulation , unpleasant taste and other physiological reaction . ELECTROCHEMICAL PROPERTIES

26. The electrochemical properties of dental materials causes important phenomenons known as TARNISH and CORROSION . TARNISH is defined as a process by which a metal surface is dulled in brightness or discolored through the formation of chemical film , such as sulfide and an oxide . CORROSION is defined as the action , process, or effect of corroding ie, the loss of elemental constituents to the adjacent environment.

27. CHEMICAL CORROSION Direct combination of metal and non metal components to yield chemical compound . This is also called as Dry corrosion. e.g. oxidation of silver-copper alloy particles med with mercury to prepare dental amalgam

28. Importance in dentistry: Stress corrosion Due to fatigue or cyclic loading in oral cavity. Concentration cell corrosion e.g . pitting corrosion or crevice corrosion The oxygen concentration is lower around amalgam margins within the crevicular area as compared to outside, so acidity is greater and plaque accumulation further increases the acidity which causes corrosion .

29. Corrosion can be considered somewhat beneficial in case of amalgam because corrosion products seal the bacterial leakage from saliva thus improving the longevity of restoration by decreasing the recurrent caries. Metallic ions may also serve as bacteriostatic and bactericidal agents. However, this type of deterioration can also be harmful when it occurs in thin sections at solder joints of appliances .

30. According to GPT-8, color is defined as A phen omenon of ligh t or visual p e r c e pti o n t h a t e n ab l es on to differentiate otherwise identical objects . T h e qu a l i t y of a n objec t o r substance w it h r espe c t to light reflected or transmitted by it . A visual r espons e t o ligh t c o nsisting o f th e th r ee di m e n s i on s of hue, value, and saturation.

31. The perception of the Color of an object is the result of a physiological response to a physical stimulus (light). Light is an electromagnetic radiation that can be detected by the human eye. It can be seen that the visible electromagnetic radiation is in the range from 400-700 nanometers.

32. Properties of materials in relation to light transmission and absorption- Transparency - that allows the passage of light in such a manner that little distortion takes place. e.g . glass, pure acrylic resin. Translucency- which allows the passage of some light and scatters or reflects the rest . In such manner, the object cannot be clearly seen through them . e.g. tooth enamel, porcelain, composite and pigmented acrylic resin. Opacity- that prevents the passage of light. Opaque material absorbs all of the light. Objects cannot be seen through them.

33. When a beam of light encounters or falls on a surface of a medium, the following may occur :

34. 1- Reflection: Specular Reflection- Smooth surface: angle of incidence = angle of reflection The restoration should have a highly smooth and polished surface to simulate the tooth structure. Diffuse Reflection- Rough surface- the surface appears to have little gloss.

35. 2- Refraction: I t i s the c hange o f t h e d i rect i o n o f a bea m o f l i ght o n entering second medium. Refraction results from the difference in refractive indices of the two media. For perfect matching the refractive index of the restoration should be equal to the refractive index of the tooth. Ex a m p l e : C ont rol o f r e f r active i n de x o f the fill e r an d mat rix ph a s es in composite resins and porcelain.

36. 3- Scattering I f l i ght rays passing thr ou g h a medium are obst r ucted b y an y di f ferent inclusions it will be redirected in another direction and is attenuated. ↑ O P A C ITY ↓ TR A N S LU C ENC Y . Importance in dentistry: Opacifiers & pigments ad d e d to composite resins act a s scatt e r ing centers that give rise to opaque shades of the material .

37. 4. Transmission: Light passing through an optical medium without attenuation → completely transmitted. Total transmission occurs in perfectly transparent materials. If part of the light is transmitted and part is reflected ( i.e. diffuse transmission), the material appears translucent .

38. THE THREE DIMENSIONS OF COLOR Color parameters: A- Hue: It is the dominant wave length. It represents the color of the material, i.e yellow, green, red and blue. B- Chroma: It represents the strength of the color or degree of saturation of the color (color intensity).

39. C- Value: It represents the lightness or darkness of color. A black st a ndard i s assigned a value of 0, wher e as a white stan d ard is assigned 10. A tooth of low value appears gray and non–vital = DEAD, Ther e fore, i t i s the most im p orta n t p a ramet e r . Bec a u s e i t i s intim a tely related to the aspect of vitality in human teeth.

40. CIE L*a*b* COLOR SPACE

41. Factors affecting color appearance and selection: According to GPT-8 : Sh a de i s a term u s ed t o d e s c r ibe a p a rtic u lar hue, or v a riation of a primary hue such as a greenish shade of yellow. Tooth color selection is the determination of the color and other attributes of appearance of an artificial tooth or set of teeth for a given individual. Shade guide is used for color matching. So, it is important to match colors under appropriate conditions.

42. 1- Source- Different sources have different color content. i.e Incandescent light OR fluorescent light. Metamerism: It is the change of color matching of two objects under different light sources. Metameric pairs: Two objects that are matched in color under one light source but are not matched under other light sources form metameric pair. Isomeric pair: They are color matched under all light sources. Color matching should be done under two or more different light sources.

43. 2- Surroundings: Colors of wall, lips or clothes of the patient modify the type of light reaching the object.

44. 3- Object: Translucency: High translucency gives a lighter color appearance (higher value) i.e more vital tooth appearance. Surface texture (surface finish): smooth surface appears brighter than rough. Presence of scattering centers as inclusions or voids: This increase opacity and lower the value (more dark). Fluorescence: It makes the teeth bright and vital. Thickness: The thickness of a restoration can affect its appearance. Increase in thickness, increase opacity, and lower the value. Metamerism

45. 4- Observer: Eye and color perception Under low lighting conditions, only the rods are used (scotopic vision). These receptors allow interpretation of the brightness (but not the color) of objects to be made. They are most sensitive to blue-green objects. Color vision is dependent on the cones, which are active under higher lighting conditions (photopic vision). The change from photopic to scotopic vision is called Dark Adaptation.

46. A- Color response: Eye responds differently among individuals. B - Color V isio n : Some individuals may ha v e color b lindness and inability to distinguish certain colors. C - Color Fatigu e : Consta n t stimulus o f on e color d ecrea s e s the response to that color.

47. It is measure of the affinity of the liquid for a solid as indicated by spreading of a drop. e.g. Wetting of denture base by saliva, wetting of enamel by pit and fissure sealants . Wettability of solid by a liquid can be observed by the shape of a drop of liquid on the solid surface. Shape of the drop can be identified by contact angle. .

48. The degree of wetting depends on the relative surface energies of the solids and liquids and on their intermolecular attraction. High energy solids and low energy liquids encourage good wetting thus liquids generally wet higher energy solids well. e.g. water on metals and oxides. On the other hand, liquids bead up on the lower energy solids- e.g. wax, Teflon, and polymers.

49. The contact angle is the angle formed by the adhesive with the adherent at their interface. Hydrophobic surface Hydrophilic surface

50. The contact angle of water and saliva on denture : it relates to the retention of the denture. Contact angle for water on wax is about 110 and for water on acrylic is around 75 The spreading of molten solder on the surface of the parts to be assembled : If the wetting is not adequate, soldering may fail, and if contact angle of solder is too great, it will not penetrate into the fine details of metals to be soldered.

51. ADHESION is defined as the property of remaining in close proximity, as that resulting from the physical attraction of molecules to a substance or molecular attraction existing between the surfaces in contact. BONDING is defined as the procedure of using an adhesive, cementing material of fusible ingredient to combine, unite, or strengthen . Attachment of plaque or calculus to the tooth surface can be partially explained by adhesion attachment.

52. Leakage adjacent to dental restorative material is severely affected by poor adhesion and bonding. Retention of artificial dentures depends on adhesion between the denture and saliva, and between saliva and soft tissue. Strong adhesion increases the likelihood that a given restoration or appliance will be retained on the teeth. Strong chemical adhesion eliminates the need for excessive removal of tooth structure to ensure retention, through mechanical undercuts thus chemical adhesion conserves tooth structures.