Basic Dental Materials John J Manappallil
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DENTISTRY AND DENTAL MATERIALS1

Dental materials play an integral role in dentistry. Besides use in the oral cavity many materials are also used in the laboratory to aid in the fabrication of appliances or prostheses. Dentistry over the years has evolved into a highly complex field and materials play a crucial role in every aspect of treatment.
Most dental treatment may be divided into three phases:
  • Prevention
  • Restoration
  • Rehabilitation
 
PREVENTION
The preventive phase is probably the most important. This includes educating the patient on how to maintain his oral hygiene through regular brushing, flossing and periodic checkup at the dental office. Regular brushing with a suitable brush and paste has been shown to be very effective at controlling caries as well as gum (periodontal) problems. The role of fluorides and fluoride therapy in the control of dental caries has been known to us for a long time. Fluoridation of drinking water and fluoride therapy at the dental office has played a significant role in reducing dental caries especially in children. Caries often begins in deep fissures in teeth. Fissure sealants is another preventive measure especially in children to prevent caries.
 
RESTORATION
The next stage is the actual development of dental caries and periodontal disease. Caries involves the actual demineralization and destruction of tooth structure. The next focus is to arrest the caries process. This involves removing the carious tooth structure and restoring the cavity with a suitable filling material. The famous silver filling has been in use for more than a century and is currently the most widely used filling material. The silver amalgam restoration would certainly look unpleasant if used for the front (anterior) teeth. Therefore anterior teeth are restored with an esthetic (tooth colored) material. Other ways to restore teeth involve the use of gold inlays and ceramic inlays.
As caries progresses, it gets closer to the pulp, which can lead to pain (pulpitis) and infection of the pulp. If the pulp is only mildly affected, pulp therapy is started using materials which have a therapeutic effect on the pulp. These materials can be soothing and promote healing by forming a new layer of dentin (secondary dentin).
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If the pulp is infected, it is removed (pulpectomy) and root canal treatment popularly known as RCT is initiated. After removing the pulp, the canal is made sterile and sealed using root canal filling materials. The root canal treated tooth is weak and is prone to fracture if not protected with a crown or onlay.
Before the discovery of tooth colored crown materials, metallic crowns were given (the famous gold tooth). Modern dentists are able to provide crowns that are natural looking and pleasing. Many of these structures are processed outside the mouth, in the laboratory. The dental technician uses an accurate model of the teeth to fabricate these restorations. Models are made from a negative record of the mouth called an impression. This is sent to the laboratory where the technician pours a mix of plaster or stone into the impression. When the mix hardens we obtain a model.
If the coronal tooth structure is entirely gone or destructed, even a crown would not stay. In this case the dentist has to place a post and core. The part placed into the root canal is known as post and the rest of it is known as the core. The crown is then constructed and cemented on to the core.
 
REHABILITATION
Unfortunately the reality is that often patients come too late for any kind of conservative treatment. Hopeless teeth have to be extracted. After extraction the patient often desires that it be replaced with an artificial tooth. There are many ways of replacing the tooth. Today implants have become very popular. A titanium screw can be implanted into the jaw surgically followed by an artificial crown. The implant is quite an expensive proposition and involves surgery.
The next choice is the fixed partial denture (bridge). Usually the teeth by the side of the missing tooth is reduced in size (prepared) in order to receive the bridge. The bridge is then cemented on to these teeth.
If too many teeth are missing, we might have to consider the removable partial denture which replaces the missing teeth but is not fixed in the mouth. It can be removed by the patient for cleaning and hygiene. The ideal removable partial denture is usually made of a combination of metal and plastic (cast partial denture). Interim or temporary partial dentures are made entirely of plastic also and are often referred to as treatment partial dentures.
The final stage is when all the teeth have to be replaced. One is of course familiar with the complete denture which is often seen in elderly individuals. These artificial teeth replace the entire dentition and are usually of the removable type (fixed complete dentures are also available which are supported and retained by implants). The complete denture is usually made of a type of plastic called acrylic. The teeth used in the denture can be made of acrylic or porcelain.
Besides all the materials mentioned above, different specialties in dentistry have their special materials. Some of these are not covered in this book. For example, endodontists use various medicaments to clean and debride the root canal. A variety of root canal sealing pastes and medicaments are also available. The periodontist uses different types of graft material to restore lost periodontal bone and tissue. Unfortunately not all the materials used in dentistry are within the scope of this book.
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THE DENTAL LABORATORY
Many materials are used in the dental laboratory to aid in the fabrication of stents, prostheses, appliances and other structures used in and around the mouth. These include cutting, abrading and polishing materials. Investment materials are used in the creation of moulds in the casting of metal structures. Waxes are used in various stages of construction of different structures. Gypsum products are used to make casts, models, molds and to secure articulators.
 
CLASSIFICATION OF DENTAL MATERIALS
Dental materials may be classified into: (1) Preventive materials (2) Restorative materials and (3) Auxiliary materials.
Preventive materials include pit and fissure sealants and other materials used to prevent the onset of dental diseases.
Restorative materials include materials used to repair or replace tooth structure. This includes materials like amalgam, composites, ceramics, cast metal structures and denture materials.
Auxiliary materials are substances that aid in the fabrication process but do not actually become part of the restoration, appliance or prosthesis. This includes materials like gypsum products, impression materials, casting investments, waxes, etching gels, custom tray materials, etc.
 
INTERNATIONAL STANDARDS
The Federation Dentaire Internationale (FDI) and the International Organizations for Standardization (ISO) are two organizations working for the development of specifications and terminology on an international level. The FDI is restricted to dental products whereas the ISO covers all products. The ISO is a nongovernmental body composed of the national organizations of more than 80 countries including India (Bureau of Indian Standards). The ISO standards (Fig. 1.1 A) (see also appendix) are formulated by a ‘technical committee’ (TC). Dental products are covered by TC 106. Various subgroups known as ‘subcommittees’ (SC) cater to specific areas. The subcommittees are further divided into ‘working groups’ (WG) to cover individual products or items. For example, TC 106/SC 1: WG 7 covers dental amalgam and mercury.
Considering the worldwide supply and demand for dental products the benefits from the ISO are invaluable. Suppliers and consumers can be assured of impartial reliable data to assess the quality of products and equipment regardless of its country of origin and use.
 
US STANDARDS FOR DENTAL MATERIALS
Standards are specifications by which the quality of a product can be gauged. Standards identify the requirements of physical and chemical properties of a material which ensures satisfactory performance for the function for which it is intended.
The earliest standards in the US were developed by The National Bureau of Standards in 1919 on the request of the US Army for the purchase and use of dental amalgam. The task was assigned to a team led by Wilmer Souder. Souder's report and testing methods were well received by the dental profession and test data were requested for other dental materials. By 1928 the responsibility for continued research into standards were assumed by the ADA.
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Figures 1.1A and B: Examples of standards: (A) International standards organization's specification for zinc oxide eugenol cement(ISO); (B) ANSI/ ADA Specification No. 122 for dental waxes.
 
ADA CERTIFICATION
Currently the ADA under direction of the ANSI (American National Standards Institute) sponsors two committees. The ADA Standards Committee for Dental Products develops specifications for all dental products, instruments and equipment (excluding drugs and X-ray films). The ADA's Council on Scientific Affairs is responsible for the evaluation of drugs, teeth cleaning agents, teeth whitening agents, therapeutic agents used in dentistry and dental X-ray films. After formulation of the specifications by the ADA, it is submitted to the ANSI. On approval it becomes a national standard (Fig. 1.1 B).
Manufacturers can submit their product for the ADA seal of approval. This falls into 3 categories—Accepted, Provisionally accepted, and Unaccepted. ADA certification is an important symbol of a dental products safety and effectiveness. ADA acceptance is effective for a period of 5 years.
 
SUMMARY
Materials used for dentistry are highly specialized. Each one is designed with a specific set of properties depending on what it is used for. For example, materials used as tooth restorations should be able to withstand occlusal forces as well as bond to tooth structure. Impression materials should be highly accurate and stable in order to duplicate the original structure. Modern science, research and technology has provided dentistry with an ever expanding selection of unique combinations of materials and techniques to serve dental treatment needs.