By Dr.Reham Mohammed Abdallah

Science of dental materials  Is defined as; compositionproperties manner in which they interact with the environment “The Study of composition and properties of dental materials and the manner in which they interact with the environment in which they are placed”.  It represents a marriage between the basic and clinical sciences.

Goals of Studying Dental Materials  The main goal of studying course of dental materials is to let the student: 1. Familiar with all materials used in dentistry. 2. Know all the properties of dental materials. 3. Know how to manipulate dental materials. 4. Know and understand causes of failure of restorations. 5. Improve dental materials.

Oral environment  An understanding of the physical, electrical and mechanical properties of materials used in dentistry is of tremendous importance. This is because these materials are exposed to the oral environment and subjected to biting forces.

Oral environment is characterized by  Wet (saliva, food and drinks). This may have an effect on solubility, water sorption and staining of the restorations.  Temperature Fluctuation (Ice cream, 5 o C to coffee or tea, 55 o C).  The pH variation (pH of saliva is neutral (7.0) and on intake of acidic fruit juices or alkaline medicaments, pH may vary from 2.0 to 11.0 ).  Masticatory forces variation.

Characteristics of ideal dental materials 1. Biocompatibility (nontoxic, non-irritating, non allergic). 2. Mechanically stable and durable (strong and fracture resistant). 3. Dimensionally stable (minimally affected by temperature or solvents). 4. Esthetics (oral tissue-like appearance)

5. Easy manipulation (easy use with no specific equipment). 6. Tasteless and odorless (non-irritating or unpleasant). 7. Cost effective (within the patient's budget). 8. Cleanable (can be maintained). 9. Resistance to corrosion or chemicals (does not deteriorate over time. 10. Low thermal conductivity (insulators) as in filling and cement materials. However, thermal conductivity is needed as for denture bases.

Quality Assurance Programs  Many programs or agencies were developed to establish guidelines for some minimal level of evaluation that has been deemed sufficient to ensure the safe use of the particular device or material and maintaining quality of dental materials.

These agencies include 1. American Dental Association (ADA) Specifications. 2. Federal Drug Administration (FDA). 3. Federation Dentaire Internationale (FDI). 4. International Standard Organization (ISO). 5. Occupational Safety and Health Agency (OSHA). 6. National Institute for standard and Technology (NIST).

Classification of Materials Used in Dentistry  Based on the chemical composition; There are four classes of materials used in dentistry: a. Polymers b. Metals c. Ceramics d.Composites (mixture of two or more of the first three classes).

Polymers  Chemical compound consisting of large organic molecules formed by the union of many smaller monomer units is called a “POLYMER”  Chemical reaction in which low molecular weight monomers are converted into high molecular weight polymer chains “POLYMERIZATION”

Metals  “An opaque lustrous chemical substance that is a good conductor of heat and electricity, and when polished is a good reflector of light”. Ceramics  “An inorganic compound with non metallic properties, typically composed of metallic (or semi-metallic) and non metallic elements.”

Composites  “A material formed from two distinct phases is called a composite material”  Two distinct phases can be easily separated on microscopic scale.  Final properties are either superior or intermediate to the individual constituents.

Based on the use of materials 1.Preventive dental materials 2.Restorative dental materials 3.Auxiliary dental materials

 Pit and Fissure Sealants  Sealing agents that prevent leakage  Materials used primarily for their antibacterial effects.  Liners, bases, cements and restorative materials that are used primarily because they release fluoride.

 Synthetic components that can be used to repair or replace tooth structure, including amalgams, resin-based composites, cast metals, metal-ceramics, ceramics, and denture polymers.

Direct restorative materials Used intraorally to fabricate restoration or prosthetic devices directly on the teeth. Indirect restorative materials Made extraorally in which the materials are formed indirectly on the teeth or tissues. Temporary restorative materials Intended to be used to restore the tooth temporarily. 1. Orthodontic wires. 2. Cements used as temporary liners. 3. Cements used as temporary filling materials.

 Substances used in the process of fabricating dental prostheses and appliances but do not become part of these devices.  Acid – etch solutions, impression materials, casting investments, gypsum cast, and model materials and dental waxes.

Properties of Matter  Properties of materials include microscopic and macroscopic properties.  Microscopic properties are responsible about the behavior or macroscopic properties of a material;

Microscopic properties  Atomic structure  Crystal structure Macroscopic properties  Physical properties  Mechanical properties  Surface properties  Time-dependent properties

Failure of Materials in the Oral Cavity  There are four modes of failure of restorations/ materials in the oral cavity:  Corrosion (occurs only in metals)  Wear  Fracture  Craze (occurs only in polymers)