lec_1_P_P_Introduction_and_physical_properties_of_dental_material.pdf

Lec:1 Dental Materials Professor Dr. Ghassan Abdul-Hamid Naji B.D.S, M.Sc, Ph.D in Prosthodontics 1 2  Dental material science Definition: a science dealing with the development, properties (physical and chemi...

Lec:1 Dental Materials Professor Dr. Ghassan Abdul-Hamid Naji B.D.S, M.Sc, Ph.D in Prosthodontics 1 2  Dental material science Definition: a science dealing with the development, properties (physical and chemical and mechanical), manipulation, evaluation of dental materials. These aspects affect how different materials are selected for particular clinical/laboratory application. Thorough knowledge ensure success of dental service provided to patients. 3  Definition of Dental Material It is the science that deal with the materials used in dentistry Physical properties Mechanical properties Their manipulation Evaluation of dental materials The study of dental materials takes into consideration certain standards set to evaluate a material or a technique before it is used in the patients mouth. 5  Standards for dental materials American Dental Association (ADA) Food and Drug Administration (FDA) International Standards Organization (ISO). International Dental Federation (FDI). *FDI and ISO establish standards for DM on an international level. 6 Evaluation of dental materials Standard specifications Laboratory evaluations can be used to indicate the suitability of dental materials. These tests need to be clinically relevant Clinical trials: are the ultimate tests. 7  Information provided by a DM package Name of the material Manufacturer Ingredients Uses Contents of the package Storage conditions Dispensing method 8 9 10 11 12 Classification of Dental Materials 1. Clinical materials a) Filling materials: dental cement, amalgam, composite resin, gold b) Finishing and polishing agents c) Prevention materials d) Prosthesis materials: impression materials, dental implants. 2.Laboratory materials a) Model and die: gypsum product, die material b) Materials used in fabricated prosthesis: denture base resin, dental ceramic, dental waxs.  Biological requirement of dental materials Dental materials should be: 1. Non-toxic 2. Not irritant 3. Non-allergenic, not mutagenic or carcinogenic  Properties of dental material  Physical properties Color, Solubility, Density, Dimentional stability  Mechanical properties Hardness, Strength. There is no material have an ideal properties  The elements of study Physical properties include: 1- Density 2- Thermal properties 3- Electrical properties 4- Optical properties  Mass- Related Properties Density: Mass/Volume It is the mass per unit volume of the material. Units are gm/cm3 or pound/in2 Clinical importance in Dentistry: 1- Lightness is nearly always advantageous in retention of the upper denture. 2- Weights of tin and leads were added to control the mobility of lower complete and partial dentures.  Examples of density of some dental materials a) Acrylic resin = 1.2 gm/cm³ b) Water = 1 gm/cm³ c) Gold alloys = 14 gm/cm³ d) Cobalt – chromium alloys = 8.3 gm/cm³  Importance in dentistry 1) Upper denture must be made up of the materials that are of low density to help its retention. 2) Molten alloys of low density require higher pressure to fill the mold cavity during casting procedures.  Thermal Conductivity It is the amount of heat in calories or joules passing per second through a body 1cm thick, 1cm2 cross sectional area when the temperature difference is 1°C Unit cal/sec/cm/(°C/cm2). Is the physical property that deals with heat transfer through a material by conductive flow. Heat flows from points of higher temperature to points of lower temperature.  Thermal conductivity: Material have different rate on conducting heat, thermal conductivities increase in the following order: polymers (such as acrylic resin) < ceramics < metals (such as amalgam). Materials that have a high thermal conductivity are called Conductors & materials of low thermal conductivity are called Insulators.  Clinical Importance in Dentistry: 1- Metallic filling material: e.g. The high thermal conductivity of amalgam is a disadvantage because if it is near the pulp it may cause patient discomfort as a result of temperature changes produced by hot or cold foods and beverages unless adequate tooth tissue remains or non- metallic substances are placed between the tooth and filling as a base for insulation. While, composite and ceramic restorations are non- conductive and do not need insulators.  Examples of (K): a) Enamel = 0.0022 cal/sec/cm²/(°C/cm). b) Amalgam = 0.055 cal/sec/cm²/(°C/cm). c) Gold alloys = 0.710 cal/sec/cm²/(°C/cm). Amalgam filling Insulation (calcium hydroxide) 2- Metallic denture base materials is an advantages as it gives feeling closer to the normal condition and the patient will feel normal also it will protect him from drinking very hot drinks which may burn his mouth. Metallic denture base material is an advantage because heat transmission causes tissue stimulation through vasodilatation and vasoconstriction of blood vessels of underlying tissues keeping it in a healthy state. Thermal diffusivity: The speed with which a temperature change will spread through an object when one surface is heated. 3- Coefficient Thermal of expansion( α) The change in length per unit length of the material for a 1°C change in temperature is called the linear coefficient of thermal expansion (α) α = L final- L original L original x (°C final- °C original) Unit is: / °C or Cm/Cm. ° C 4) Thermal expansion (α) : When a material is heated, the energy absorbed causes the atoms or molecules to vibrate and the material expands. the most common way of measuring this expansion is by taking a length of material, heating it to a certain temperature and then measuring the resultant change in length. This change in length, per unit length for a 1°C change in temperature, is called the linear coefficient of expansion, α.  L final – L original α =--------------------------------------- L original x (C final – C original) Examples: Enamel = 11 x 10-6/°C Gold = 14 x 10-6/°C Composite = 22 x 10-6/°C Impression compound = 250 x 10-6/°C  Importance in dentistry: In a composite restoration, the seal between the composite and tooth may be affected by the repeated temperature changes in the mouth which cause different amounts of expansion and contraction of the composite and the tooth. This difference may create gaps between the two (marginal percolation) which leads to leakage of salivary components into the tooth leading to tooth discoloration, recurrent caries, and pain. Clinical importance in Dentistry: Close matching or the same of the coefficient of thermal expansion (α) is important between: 1-The tooth and the restorative materials to prevent marginal leakage. Opening and closing of gap results in → breakage of marginal seal between the filling and the cavity wall, this breakage of seal Marginal percolation leads to: i. Marginal leakage ii. Discoloration iii. Recurrent caries iv. Hypersensitivity. 2-Porcelain and metal in ceramometallic restorations (crowns and bridges) to provide metal ceramic bonding. 3-Artificial tooth and denture base to avoid crazing. 4- Investment used for casting gold alloy which is used for casting crown and bridges should have high coefficient of thermal expansion. To compensate the solidification shrinkage of wax and alloy. 5- Investment used for soldering should have low α to fix the joined parts.  Dimensional stability The degree to which the dimensions of material alter after setting Dental material should not change their dimension after setting  Dimensional changes may continue to occur in materials long after the apparent setting there are many possible causes. 1- The changes may be due to continued slow setting or release of stresses set up during setting. 2- Or due to water absorption or loss constitutes from the materials.  Tissue reaction Some restorative materials are damaging to the living tissue when in contact with like silicate filling and zinc phosphate cement which is acidic and may kill the dental pulp unless a protective lining is used. Dental materials should not show any allergic reaction to the tissue and also should not provide good culture to the growth of bacteria and Candida albicans to grow and cause infection like soft lining materials.  Less specific properties Water Sorption It represents the amount of water adsorbed on the surface and absorbed into the body of the material. Importance: 1- Acrylic resin denture base materials have the tendency for water sorption for one day and then stop so its acceptable. 2- Hydrocolloid impression materials will imbibe water if immersed in it leading to dimensional changes and unhygienic results.  Solubility Solubility : Is the amount of a material that dissolved in the liquid such as water. Restorative materials should not dissolve in the mouth and if its dissolves, it should no release toxic substances. Some material have capacity to absorb water and other fluid , if this is occur it will be unhygienic. And cause dimensional change, on other hand there is other material as acrylic which absorb water for one day and stops and this consider acceptable.  Electrical activity (galvanism and corrosion) Galvanism: Result from presence of dissimilar metal in the mouth. Metal are placed in an electrolyte (liquid that contain ions) oral fluid act as electrolyte and system similar to electrical cell, when two metal restoration became in contact current flow and patient fell discomfort able(pain and metallic test). Corrosion: Is electromechanically process and is depend on the ability to conduct electrical current either by means of free electrons in metal or via ions in solution.  Adhesion The bonding of dissimilar materials when they are brought into contact with each other by either: ^ Chemical bonding (True) OR ^ Mechanical bonding (retention).  Cohesion The bonding of similar materials when they are brought into contact with each other. When the molecule of the same substance holds together, the forces are said to be cohesion.  Optical Properties 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. Color: One of the most demanding requirements of dental restorative materials is that they should match the natural hard and soft tissues in appearance.  Esthetic is an important demand in dentistry and this depend on the reflection or absorption of the material to the light. The restorative material should be translucent in order to look like the natural teeth. Also not stained or changed the color by time. Translucency Is a property of the material, which allows the passage of some light and scatters or reflects the rest. In such manner, the object cannot be clearly seen through them Translucency decreases with increasing the scattering centers.  Translucent It is optical properties Allows the light to go short way in the material before reflecting again The color of an object or material results from a number of factors including: 1-The composition of the material and its thickness. 2- Surface roughness 3- The nature of illuminating light. Shade guide is used for color matching. So, it is important to match colors under appropriate conditions. THANK YOU Prof. Dr. Ghassan Al-Taie