Dental Materials PDF

Lec.1 Dental material Dr.Makarem Almomen Dental materials: it is the science which deal with the materials used in dentistry, their physical, chemical and mechanical properties and with their manipulation as such properties are related to the proper sel...

Lec.1 Dental material Dr.Makarem Almomen Dental materials: it is the science which deal with the materials used in dentistry, their physical, chemical and mechanical properties and with their manipulation as such properties are related to the proper selection and use by the dentist. History  Dentistry started since the Christian era, gold bands and wires were used by the Phoenicians for the construction of partial dentures. It is evident that many of the restorative and accessory materials of today have been in use for quite some time ago.  In the middle of the nineteenth century, research studies on amalgam were done by G. V. black. Later on, the American Dental Association determined the physical and chemical properties of dental materials and the development of new dental materials, instruments and test methods. The primary objective of it is to formulate standards or specification for dental materials and to certify the products which meet those requirements.  The study of dental materials enables the dentist to understand the behavior of these materials and how to use them to their best advantage. The service that a restoration or appliance gives to the patient is largely determined by the proper selection and use by the dentist General properties of dental materials:  All materials have physical properties like color, weight, solubility, thermal conductivity and others, also mechanical properties like hardness or softness, strength or weakness.  There is no material till now that has ideal physical and mechanical properties. Most materials have some good and bad properties and sometime a property that is bad in one material may be good or acceptable in other materials. Physical properties 1-linear coefficient of thermal expansion and contraction: 1 As the temperature rises a solid material will expand and on cooling it will contract, this is measured by the liner coefficient of thermal expansion and contraction which is the change in length per unit length for 1°C temp. change. final length- original length α= original length × temp. change. Clinical importance in Dentistry: Close matching of the coefficient of thermal expansion (α) is important between: 1-The tooth and the restorative materials to prevent marginal leakage: Filling materials should have the same coefficient as the tooth, if it dose not, it will press too hard against the cavity wall on expansion & may cause pressure on the pulp, or pull away from the wall when chilled by cold water. The later effect will cause the filling to leak temporarily, which may in turn, lead to further caries. Opening and closing of gap results in → breakage of marginal seal between the filling and the cavity wall, this breakage of seal leads to: a. Marginal leakage b. Discoloration c. Recurrent caries d. Hypersensitivity. 2-Porcelain and metal in ceramic - metal restorations (crowns and bridges) to provide metal ceramic bonding. 3-Artificial tooth and denture base to avoid crazing. Hard tooth structure has the smallest coefficient, metals are intermediate, and polymers have the largest. Tooth = 11*10-6 cm/cm C0 Gold = 14* 10-6 cm/cm C0 2 Impression compound = 250* 10-6 cm/cm C0 2-Dimentional stability: Many material change shapes when they set or harden. Impression material should not change dimensions when set. Also dental material should have no dimensional changes after setting. Amalgam filling material for posterior teeth it may sometimes change shape permanently as a result of heavy biting force. This is bad property; on the other hand, the investment material that forms the mold for dental casting should expand for certain amount to compensate for the contraction of the molten metal after it is cooled from the molten stage. Dimensional change occurs due to: A- Water absorption: Dental material should not have high water absorption; because it will lead to dimensional changes and if water absorbed too great, it will lead to unhygienic condition. Some materials have absorption which extends to certain period of time, like acrylic which has absorption of 1.4%. But it continues for 24 hours only so water absorption should not continue for long time. B- Solubility: is a measurement of the extent to which the material will dissolve in a given fluid, for e.g. water or saliva. Restorative materials should not dissolve in the mouth, and if it dissolves it should not release toxic substances. It's measured in µg/mm².  Solubility of composite :0.01mg/mm² 3   Solubility of resin cement maximum: 7.5 mg/mm². 3- Density: Is the mass per unit volume. lightness is nearly always an advantage in restorative materials, but sometimes tin or lead is used inside full lower denture to make it heavy to control its mobility. Density of gold: 14gm/cm³ Acrylic: 1.2gm/cm³ Cobalt chromium: 8.3gm/cm³ Water: 1gm/cm³ 4-Thermal conductivity: is the quantity of heat in calories, or joules, per second passing through a body 1 cm thick with a cross section of 1 cm² when the temperature difference is l° C. The units are cal/sec/cm² Clinical importance in Dentistry: 1- Metallic filling materials. 2- Metallic denture base materials. Generally, metals are better conductors than non-metals. Metal filling material like amalgam filling in proximity to the pulp may cause the patient considerable discomfort when hot or cold foods produce temperature changes; thus they require heat insulating layer are placed between the tooth and filling for insulation. Such filling materials as cements are relatively poor conductors and insulate the pulp area. Here it is undesirable property. On the other hand, the thermal conductivity of metallic denture base material is an advantage as it gives feeling closer to the normal condition and the patient will protect him from drinking very hot drinks which may burn his mouth. Silver:1 Cal/Sec/Cm2 Amalgam:0.055 Cal/Sec/Cm2 Zinc oxide eugenol:0.011 Cal/Sec/Cm2 Enamel:0022 Cal/Sec/Cm2 5- Electrical activity: it is the ability of metals to ionize by losing electrons. If there is a high difference in the electrode potentials of two metals in contact with the same solution like gold and aluminum an 4 electrolytic cell may develop and patient may feel discomfort. When two dissimilar metals are placed adjacent to or opposing each other (e.g. amalgam/gold) it is possible to set up a galvanic cell which not only accelerates corrosion but can cause pain. The use of an electrically insulating lining material helps to prevent such activity. GALVANISM IN DENTISTRY: Phenomenon of electric cell and flow of electrons in oral cavity which is perceived by patient as pain or discomfort and metallic taste. Requires presence of two metals of different electric potential and an electrolyte (saliva). 6-Adhesion and cohesion  Adhesion is the force which causes two or more different substances to attach when they are brought in contact with one another. The property of adhesion is recognized as being of major importance for filling materials, luting materials and fissure sealants. In each case the aim is to produce a tight seal between tooth substance and material with minimal destruction of tooth tissue.  Cohesion: When the molecule of the same substances hold together the forces are said to be cohesion  candida albicans to grow and cause infection, like soft lining materials. Optical Properties Dental materials have to look like natural teeth and gum and should not stain or change color by time. Translucency Is a property of the material that allows the passage of light but disperses the light, so object cannot be seen through the material. Some translucent materials used in dentistry are ceramics, resin composite, and acrylics. Transparency Is a property of the material that allows the passage of light in such a manner that little distortion takes place so that objects can be clearly seen through them. Opacity Is a property of the material that prevents the passage of light. Opaque material absorbs all of the light. Objects cannot be seen through them. 5 Complete Transmission Transparent Incomplete Transmission Translucent No Transmission (absorption) Opaque COLOR It is the visible aspect of an object other than form and size. 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). A beaker of water containing one drop of colorant is lower in chroma than a beaker of water containing ten drops of the same colorant. C- Value. describes how light or dark the color is. The color of teeth is also determined by the way they reflect light. If light passes through an object it is transparent, if light completely absorbed by the object, it is opaque. Color sensitivity: Eye responds differently among individuals. Color Vision: Normal is trichromatic vision. Some individuals may have color blindness and inability to distinguish certain colors. Color Fatigue( hue adaptation): Constant stimulus of one color decreases the response to that color. Shade guide: Is used for color matching. So, it is important to match colors under appropriate conditions. Metamerism: Two objects that are matched in color under one light source but are not matched under other light sources form metameric pair. 6  Surrounding: Colors of wall, lips or clothes of the patient modify the type of light reaching the object. Avoid colored and inclined walls, Cover patient’s clothes if so bright. Remove lip sticks and heavy make up. Biological Properties  Tissue reaction: some restorative materials are damaging to the living tissue which is in contact with, like zinc phosphate cement which is acid 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 Dental materials should be biocompatible, –nontoxic for patient, dentist and staff. –non irritating to oral cavity and tooth tissues. –non allergenic. –non mutagenic or carcinogenic. 7 8