Lecture 2 Dental Biomaterials PDF

Dental biomaterials I course # DEN-DBM201-1 Lecture 2: Structure of Matter DR. Fahiem M. El-shamy Lecturer in Dental Biomaterials Faculty of Dentistry, Menoufia National University OBJECTIVES After reading this chapter, the student should be abl...

Dental biomaterials I course # DEN-DBM201-1 Lecture 2: Structure of Matter DR. Fahiem M. El-shamy Lecturer in Dental Biomaterials Faculty of Dentistry, Menoufia National University OBJECTIVES After reading this chapter, the student should be able to: 1. Describe the close relation between the atomic basis of a material and its properties.. 2. Compare and contrast ionic, covalent, metallic bonds and Secondary bonds their role in restorative dental materials. 3. Describe the differences between molecules and lattices and cite which restorative materials occur in which. 10/6/2024 DR/ FAHIEM M. EL-SHAMY  Matter MATTER is any substance which has mass and occupies space. Atom Is the unit structure of matter, the smallest unit of an element, having all the characteristics of that element and consisting of 1. Protons Nucleus 2. Neutrons 3. Electrons There is a close relation between the atomic basis of a material and its properties. 10/6/2024 DR/ FAHIEM M. EL-SHAMY  Interatomic attraction 10/6/2024 DR/ FAHIEM M. EL-SHAMY Atoms achieve a stable state by having 8 electrons in their outer shell (valence shell). This obtained by: A) Receiving extra electrons atoms and become negative ion. B) Releasing electrons and become positive ion.. C) Sharing of electrons. 10/6/2024 DR/ FAHIEM M. EL-SHAMY  In solids, atoms are held together by either 1. Primary bonds (Chemical). 2. Secondary bonds (Physical). 10/6/2024 DR/ FAHIEM M. EL-SHAMY  Interatomic Bonding Primary Secondary (Chemical) bond (Physical) bond Ionic Covalent Metallic Van der Hydrogen Bonds Bonds Bonds Waals Bonds Forces  Primary (Chemical) bond 10/6/2024 DR/ FAHIEM M. EL-SHAMY  1- Ionic bonds: It is the attraction of positive and negative ions. Occurs between metal and nonmetal  The classic example is sodium chloride (Na+Cl-).  In dentistry, ionic bonding exists in some dental materials, such as gypsum and phosphate-based cements.  Zinc phosphate cement Gypsum products Chemically “CaSO4.l/2H2O", 11 10/6/2024 DR\ FAHIEM M. EL-SHAMY Characteristics of ionic bonds:  Strong bond.  Heat resistant.  Insoluble in organic solvents.  Easily dissolved in ionized solvents such as water, acids, and alkalis.  Can conduct electricity in solution.  2- Covalent bonds:  It is sharing of electrons.  Two valence electrons are shared by adjacent atoms.  Occurs between Non-metal + non-metal  Example , H2 and many organic compounds (C & H), such as dental resin 10/6/2024 DR/ FAHIEM M. EL-SHAMY  Dental resin (Type of Dental polymer) Composite resin Acrylic resin Uses: Denture base& special tray & removable ortho. Appliance. Composite resin (organic resin matrix & inorganic filler) 10/6/2024 DR\ FAHIEM M. EL-SHAMY 14   Characteristics of covalent bonds:  Strong bond.  Water insoluble  soluble in organic solvent  Insulator (electrical & thermal).  Basic bond of polymer. 10/6/2024 DR/ FAHIEM M. EL-SHAMY  3- Metallic bonds:  Atoms give up their valence electrons which form an electron cloud.  Metallic bond is the attraction between +ve core and –ve free electrons or electron cloud.  It occurs in metals (dental amalgam, casting alloys, dental wrought wires). 10/6/2024 DR/ FAHIEM M. EL-SHAMY 10/6/2024 DR/ FAHIEM M. EL-SHAMY  Characteristics of the metallic bonds: Free mobility of electrons contributes to: 1. High thermal and electrical conductivity. 2. Opacity (due to absorption of light by free electrons). 3. Metallic luster (free electrons re-emit light). 4. High ductility and malleability. 10/6/2024 DR/ FAHIEM M. EL-SHAMY  Ionic bonding Covalent bond Metallic bond Metal + non-metal Non-metal + non-metal Metal + metal Atoms release & atoms Atoms share electrons with Atoms release free electrons receive electrons other atoms Attraction between +ve core and electron cloud Can conduct an electric Insulator Can conduct electricity and current (in solution). heat. Heat resistant Heat insulator High thermal conductivity Low melting and boiling High melting point point BRITTLE (Easily break ) Depend on the state High ductility and malleability Water soluble Water insoluble Water insoluble Insoluble in organic solvent soluble in organic solvent Insoluble in organic solvent Examples Dental resin Metals NaCL (dental amalgam, casting Gypsum alloys, dental wrought Phosphate cements wires) DR/ FAHIEM M. EL-SHAMY  Secondary (Physical) bond 10/6/2024 DR/ FAHIEM M. EL-SHAMY  Secondary bonds don’t share electron.  Arise from the polarization (charge variations) among molecules or atomic groups i.e. formation of electrical dipoles. Characteristics of secondary bonds:  physical and weak  Low melting point.  High thermal expansion. Mainly two types: 1- Hydrogen Bonding: 2- Van der Waals Forces 10/6/2024 DR/ FAHIEM M. EL-SHAMY  1. Hydrogen Bonding: (Permanent dipole or polar forces): ✓ Occurs in asymmetric molecules->one atom attracts the electrons→ becomes –ve pole. ✓ Other atom becomes +ve pole. ✓ Resulting in permanent dipole. ❑ H2O is an example: 10/6/2024 DR/ FAHIEM M. EL-SHAMY ❑ H2O is an example: The hydrogen bond is formed between Oxygen (O) as electronegative atoms (electrons are more) and Hydrogen (H) portion is positive.  Stronger than van der Waals but weaker than covalent and ionic bonds. 10/6/2024 DR/ FAHIEM M. EL-SHAMY  2. Van der Waals Forces:  Normally, the electrons of the atoms in inert gas are distributed equally around the nucleus and produce an electrostatic field around the atom.  However, this field may fluctuate so that its charge becomes momentarily positive and negative.  A fluctuating dipole is thus created that will attract other similar dipoles. Such interatomic forces are quite weak.  Hydrogen Bonding Van der Waals Forces Occurs in asymmetric molecules Occurs in symmetric molecules, H2O is an example as inert gas One atom attracts the electrons→ The electrostatic field around inert becomes –ve gas atom →fluctuate → charge Other atom becomes +ve. becomes momentarily positive and negative. Polarization : Permanent dipole or Polarization : fluctuating dipole polar forces weaker than covalent and ionic Quite weak bonds. Stronger than Vander Waal forces  The structure of solids 10/6/2024 DR/ FAHIEM M. EL-SHAMY  The structure of solids  In general, materials can be subdivided into two categories according to their atomic arrangement. crystalline & noncrystalline (amorphous). Quartz Salt Diamond Rubber Glass 10/6/2024 DR/ FAHIEM M. EL-SHAMY  Crystalline  Their atoms are regularly arranged in a three-dimensional periodic pattern known as space lattice.  Have definite melting temperature. Examples:  Metals, Quartz, Diamond.  Noncrystalline (Amorphous)  Amorphous means without any form and no regular arrangement of atoms.  No definite melting temperature, gradually softens on heating and gradually hardens on cooling.(remember waxes are amorphous)  Glass transition temperature Tg: Is the temperature at which the amorphous structure begins to change from solid to liquid state. Examples : ✓ Gases , liquids and some solids like glass and some polymer (waxes, rubber dental resins) Crystalline Noncrystalline (Amorphous)  Amorphous means without any form and  Their atoms are regularly arranged in a three-dimensional periodic no regular arrangement of atoms. pattern known as space lattice.  No definite melting temperature,  Have definite melting temperature. gradually softens on heating and gradually hardens on cooling.(remember waxes are amorphous)  Glass transition temperature Tg: Examples: Is the temperature at which the amorphous  Metals : are crystalline. structure begins to change from solid to liquid state. Examples : ✓ Gases , liquids and some solids like glass and some polymer (waxes, rubber dental resins) ✓ Ceramics, such as porcelains, consists of Noncrystalline glass matrix and crystalline inclusions. ✓ Composites have organic (a Noncrystalline) matrix and inorganic (crystalline) filler particles. Space lattice : An arrangement of atoms in space in which every atom is situated similarly to every other atom. Space lattice  It may the result of primary or secondary bonds.  Unit cell which is the smallest repeating unit in the space lattice. Unit cell 10/6/2024 DR/ FAHIEM M. EL-SHAMY  There are 14 possible lattice types or forms. Type of space lattice defined by 1. Length of the axes. 2. Angles between the edges. Many of the metals used in dentistry belong to the cubic system. Types of cubic system: A, Simple cubic. B, Body centered cubic. C, Face centered cubic. THANK YOU 33  EVALUATION SHEET #2 1. Compare between the three types of primary bonds? 2. Compare between types of secondary bond? 3. Compare between crystalline and noncrystalline solids? 4. Draw and label the following: ionic bond, covalent bond, and another ionic bond. Provide dental examples for each.?