Chemical properties of dental materials

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Chemical properties of dental materials

  1. 1. Dr Mumtaz ul Islam 11/14/2013 1
  2. 2.     Chemical stability Chemical composition of material remains unchanged Solubility how much a material is soluble Erosion dissolution of material with a mild mechanical action 11/14/2013 2
  3. 3.    When assessing the solubility or erosion rate of materials it is important to consider the vast range of conditions which may exist in the mouth The pH of oral fluids may vary from pH 4 to pH 8.5 representing a range from mildly acidic to mildly alkaline Highly acidic soft drinks and the use of chalkcontaining toothpastes extend this range from a lower end of pH 2 up to pH 12 11/14/2013 3
  4. 4.   It is possible for a material to be stable at near neutral pH values but to erode rapidly at extremes of either acidity or alkalinity This partially explains why certain materials perform adequately with some patients but not with others 11/14/2013 4
  5. 5.  Often involve the storage of disc specimens of materials in water for a period of time the result being quoted as the percentage weight loss of the disc 11/14/2013 5
  6. 6.    Many materials, when placed in an aqueous environment absorb water by a diffusion process. Constituents of the material may be lost into the oral fluids by a diffusion process commonly referred to as leaching This may have serious consequences if it results in a change of material properties or if the leached material is toxic or irritant 11/14/2013 6
  7. 7.   Occasionally leaching is used to the benefit of the patient. For example, in some cements containing calcium hydroxide slow leaching causes an alkaline environment in the base of deep cavities. This has the dual benefit of being antibacterial and of encouraging secondary dentine formation 11/14/2013 7
  8. 8.   Soft acrylic polymers used for cushioning the fitting surfaces of dentures due to large quantities of plasticizer Slow leaching of these plasticizer causes the resin to become hard and ineffective as a cushion 11/14/2013 8
  9. 9.     Glass ionomer cements release fluorides which produce strength as well as antibacterial environment If this release is confined only to ion exchange there will be no harm at all If all the material leached out this should be considered as washout Disintegration of material is obvious 11/14/2013 9
  10. 10.      Property of metals and alloys These are good conductors First stage of corrosion involves formation of an electrolytic cell A device which converts electrical energy in to chemical energy and vice versa Electrode potential affinity of a material to be reactive against charges 11/14/2013 10
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  14. 14.    measure of the extent to which the reaction M → M+ (ion) + electron will occur In an electrolytic cell involving two metals material is lost from the metal with the most negative electrode potential 11/14/2013 14
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  16. 16.      when zinc and copper come into contact in the presence of a suitable electrolyte material loss occurs from the zinc by the reaction: Zn → Zn2+(ion) + 2 electrons In this simple cell zinc gives a pair of electrons hence called as anode Corrosion occurs here While copper receives electrons so it is cathode 11/14/2013 16
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  18. 18.  chromium is electrochemically active it reacts readily forming a layer of chromic oxide which protects the metal or alloy from further decomposition 11/14/2013 18
  19. 19.  Excessive or continued bending can accelerate the rate of corrosion and may lead to failure by stress corrosion cracking 11/14/2013 19
  20. 20.     Pits in rough surfaces can lead to the setting up of small corrosion cells in which the material at the bottom of the pit acts as the anode and that at the surface acts as the cathode It accomplished with oxygen concentration Deeper area becomes anodic Corrosion occours 11/14/2013 20
  21. 21.     pain due to the flow of galvanic current Metallic taste due to the release of ions Deterioration in appearance and mechanical properties Increased body burden of metallic ions 11/14/2013 21
  22. 22.   Surface discolouration due to interaction between a metal and its environment Usually a sulfide layer is present on the material 11/14/2013 22
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  25. 25.       A material should be harmless to the manufacturers and users Placed into a patient’s mouth Non-toxic Non-irritant Non-carcinogenic or non-allergic potential filling material should be harmless to the pulp 11/14/2013 25
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