Dental Materials Properties PDF

DENTAL MATERIALS  Chapter 43 MDA Restorative & Esthetic Materials Selection of the most appropriate dental material depends on: The extent of decay Type of defect on tooth Condition of entire mouth Whether restoration will be visible Cost factors Most common dental materials: Silver Ama...

DENTAL MATERIALS  Chapter 43 MDA Restorative & Esthetic Materials Selection of the most appropriate dental material depends on: The extent of decay Type of defect on tooth Condition of entire mouth Whether restoration will be visible Cost factors Most common dental materials: Silver Amalgam (Am/Ag) Composite Resin (CR) Glass Ionomer (GI) Temporary materials Tooth Whitening products Gold Alloys Ceramic castings Restorative: The ability to replace or bring something back to its natural appearance and function Esthetic Restoring to an artistically pleasing appearance Dental Assistant needs to know….. General characteristics of materials Selection criteria for each Preparation of material for each procedure Setup for each material Infection control: not to cross contaminate use over gloves, tissues, paper towel, cotton pliers or 2x2 gauze when handling containers of materials Standardization of Dental Materials All new materials must undergo strict evaluation and assessment before marketed to the profession Criteria For New Dental Materials Must not be poisonous or harmful to the body or tissues of the oral cavity Must help protect the tooth and tissues of the oral cavity Must resemble the natural dentition as much as possible for esthetics Criteria For New Dental Materials Must conform and function despite limited access, wet conditions, and poor visibility Must be easily formed and placed in the mouth to restore the mouth’s natural contour Properties of Dental Materials Mechanical Properties Thermal Properties Electrical Properties Corrosive Properties Application Properties Mechanical Properties Biting Forces Average biting/chewing force with natural dentition = 130 - 170 lbs molars , 40 lbs incisors Approximately 28,000 lbs of pressure per square inch on a single cusp of a molar  Types of Stress and Strain Tensile Stress Pulls and stretches the material Compressive Stress Pushes the material together. Shear Stress The breakdown of the material as a result of something sliding over the two areas. Types of Stress and Strain A) Tensile B) Compressive C) Shear  Ductility & Malleability Ductility = measure of the capacity of a metal to be stretched or drawn by a tensile force without fracture Malleability = measure of the capacity of a metal to be extended in all directions by a compressive force Thermal Properties Thermal Change Causes contraction and expansion Need to protect the pulp from thermal shock Thermal Change Significantly different rates of contraction and expansion can cause the dental materials to pull away from the tooth, which can result in microleakage, or a faulty restoration. Microleakage = microscopic space between tooth structure and the restoration in which fluid debris and microorganisms could enter Electrical Properties Electrical Properties An electrical current, or galvanic action, is created when two different metals are present in the oral cavity. Electrical Properties Conditions For This To Occur Saliva (contains salt) Two metallic components of different composition Galvanic action, or shock, which is the coming together of all these conditions Corrosive Properties  Corrosive Properties Type of reaction within a metal when it comes into contact with corrosive factors (temperature, humidity & saline) Certain foods cause corrosion of dental materials Most corrosion is only surface discoloration (e.g. tarnish)  Solubility A substance dissolving in another substance. Sugar has a high solubility because it dissolves easily A material that dissolves easily in the oral cavity is of limited use as it will wash away and leave the tooth structure exposed. Application Properties  Application Properties Flow: The dental material must be pliable enough to be placed in the preparation. Adhesion: The force that causes unlike materials to adhere to each other  Application Properties Adhesion: The force that causes unlike materials to adhere to each other Can be affected by wetting, viscosity, surface characteristics and film thickness Adhesion cont’d Wetting is the ability of a liquid to flow over the surface & into small irregularities e.g. water has a high wetting ability Viscosity is the property of a liquid that causes it not to flow easily. Syrup is a liquid with high viscosity and does not flow easily, this is not effective in wetting a surface Adhesion cont’d Surface characteristics - a liquid flows more easily on a rough surface than on a very smooth surface & will influence the wetting ability. Film thickness - the thinner the film, the stronger the adhesive junction. e.g. ideal film thickness for cementing a permanent restoration is 25 microns or less  Application Properties Retention - the ability to hold two things firmly together when they will not adhere to each other naturally. Example: an amalgam filling does not adhere directly to tooth structure Application Properties Curing - Setting of material into a hardened, permanent state: Auto-cured Light-cured Dual-cured Auto-cured Material Hardens as a result of a chemical reaction of the materials being mixed together Material must be mixed and placed within the working and setting times Light-cured Material Does not harden until it has been exposed to a curing light Allows more flexibility with the working time Dual-cured Material Some curing takes place as the material is mixed. Final cure does not occur until the material has been exposed to a curing light More to come……