The goal of repair of damaged tooth is for two primary purposes:
- Restoration of function.
Mainly four categories of materials are used in dentistry:
An ideal restorative material would:
- Be biocompatible
- Bond permanently to tooth structure or bone
- Match natural appearance of tooth and surrounding tissues
- Exhibit properties similar to tooth structures
- Be capable of initiating tissue repair or regeneration of missing/damaged tissues.
Metals (Fig. 1.1)
- A metal is based on an element that diffusely shares electron among all of the atoms in the solid instead of forming local bonds.
- A metal alloy is an intentional mixture of metallic elements that occurs in a chemically intimate manner.
- As a result of mixing the elements may be completely soluble (e.g. Au-Cu) or may be only partially soluble (e.g. Ag-Sn) producing more than one phase.
- Metallic elements are almost exclusively crystalline and exists as polycrystalline solids.
- Individual crystals or grains are microscopic. In metal alloys no phase (crystals/grains) ever represent pure metallic element.
- Metals and metal alloys generally are prone to chemical and electrochemical corrosion.
- Metal handbook defines metal as ‘an opaque lustrous chemical substance that's good conductor of heat and electricity and when polished is a good reflector of light.’
- Metal alloys used in dentistry are dental amalgam alloy, cast noble and base metal alloys.
- Ceramics are chemically intimate mixtures of metallic and non-metallic elements which allow ionic (K2O) bonding or covalent bonding (SiO2) to occur.
- Carbon, oxygen, nitrogen, hydrogen and chlorine are non-metallic.
- Most common ceramics in dentistry are semi-crystalline and are chemical mixtures of three main metallic oxides (SiO2, Al2O3, K2O).
- Ceramics may be classified on the basis of:
- Being crystalline or non-crystalline or both.
- Being predominantly based on SiO2 called silicates.
- Being predominantly formed by metal reactions with oxygen and called oxides.
- Involving relatively simple parent structures (main structures) or highly substituted ones (derivative structures).
- Most ceramics are semicrystalline, silicates, oxides and derivative structures.
Polymers (Fig. 1.2)
- Polymers are long molecules composed principally of non-metallic elements (e.g. C, O, N, H) that are chemically bonded by covalent bonds.
- Their principal distinction is their large size and molecular weight.
- The process of forming a polymer from identifiably subunits—Monomers is called polymerization.
- Monomer—One unit, polymer—Many units.
- Most polymers are named by adding ‘poly’ as a prefix to the word for the major monomer in the polymer chain.
- Almost all polymers are non-crystalline.
- Polymers are formed by either chain reaction polymerization or step-wise reaction polymerization.
- Composites are physical mixtures (or blends) of metals, ceramics or polymers.
- The goal is to blend the properties of the parts to obtain intermediate properties and to take advantage of best properties of each phase.
- Composites can be described as dispersed (filler) phase mixed into a continuous (matrix) phase.
Dental materials may be classified as (depending on their use):
- Preventive materials
- Restorative materials
- Auxiliary materials.
Include pit and fissure sealant, sealing agents, liners, bases and restorative materials that release anti-cariogenic substance (fluoride), e.g. hybrid ionomer, glass ionomer, zinc silicophosphate, and chlorhexidine or other agents.
They have no therapeutic effect.
They may be used as temporary restorative materials.
They consist of all synthetic components that can be used to replace or repair tooth (structure, including bonding agents, cements, amalgams, resin based composites, cast metals).
Restorative materials can be further classified as direct restorative materials and indirect restorative materials.
AUXILIARY DENTAL MATERIALS
Auxiliary dental materials are substances that are used in the process of fabricating dental prosthesis and appliances but do not become part of prosthesis, e.g. acid etchant, impression materials, polishing abrasives:
- In 1928, the Dental Research Fellowship at the National Bureau of Standards was assumed by the American Dental Association (ADA).
- The work at the ADA is divided into number of categories, including the measurement of physical and chemical properties of dental materials and development of new materials and test methods (Table 1.1).
- On May 1976 U.S. Food and Drug Administration (FDA) the regulatory authority to protect the public from hazardous or ineffective medical and dental devices.
- There are 3 classes of instruments identified here:
- Class-I low risk instruments
- Class-II general controls are not themselves adequate to ensure safety.
- Class-III most stringent category requires that devices be approved for safety before marketing.
- Two organizations, the Federation Dentaire Internationale (FDI) and the International Organization for Standardization (ISO) are concerned with establishments of specifications for dental material on an international level.