Overview of Dentistry and Dental MaterialsCHAPTER 1

Dentistry over the years has evolved into a highly complex field and materials play a crucial role in every aspect of treatment. Dental treatment not only includes the practice of medicine and surgery but also restoration of missing or lost structures. Besides restorations, appliances for various functions are also constructed for use in the mouth. The oral cavity is a challenging environment and materials placed in the mouth have to withstand high masticatory forces as well as corrosion. Besides direct use in the oral cavity, many materials are also used in the laboratory to aid in the fabrication of appliances or prostheses. Thus dentistry incorporates the knowledge of various materials as well as principles of engineering.

For convenience of description, dental care may be divided into various phases. These include preventive, disease control and elimination, restorative, rehabilitative and maintenance phases.

The preventive phase is very important. It 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.

The next stage in the progress of dental disease is the actual development of dental caries and periodontal disease. This phase of treatment focuses on eliminating or controlling diseases of the mouth to halt their destruction. Commonly, patients will come to a dental office because 4of pain caused by cavities or infection. This phase focuses on treating cavities (by placing fillings), eliminating infection (by root canal or tooth removal), and managing gum health (oral prophylaxis and other periodontal procedures).

Caries involves the demineralization and destruction of tooth structure. The focus is to arrest the caries process. This involves removing the carious tooth structure and restoring the cavity with a suitable temporary or permanent 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).

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.

This phase of treatment focuses on restoring the function and/or form of the teeth and mouth following the destruction caused by the original disease process. Common treatments during this phase include prosthesis (implants, bridges, partials, and dentures) to replace missing teeth and crowns to protect teeth.

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 onto the core.

Following extraction of teeth, 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.

Another 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 onto 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 5entire 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 root canal files along with various irrigants to clean and debride the root canal. A variety of root canal sealing pastes and medicaments are also available. The periodontists use 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.

Once the treatment is completed, a maintenance phase focuses on keeping the dental work in functioning order through periodic recalls, maintaining health (oral prophylaxis), and screening for oral cancer at each six-month exam.

Currently nine specialties are recognized by the Dental Council of India.

Conservative dentistry That phase of dentistry concerned with restoration of parts of the teeth that are defective through disease, trauma, or abnormal development to a state of normal function, health, and esthetics, including preventive, diagnostic, biologic, mechanical, and therapeutic techniques, as well as material and instrument science and application.^*1

Endodontics Endodontics is the branch of dentistry which is concerned with the morphology, physiology and pathology of the human dental pulp and periradicular tissues. Its study and practice encompass the basic and clinical sciences including biology of the normal pulp, the etiology, diagnosis, prevention and treatment of diseases and injuries of the pulp and associated periradicular conditions.^*1

Periodontics Periodontics is that specialty of dentistry which encompasses the prevention, diagnosis and treatment of diseases of the supporting and surrounding tissues of the teeth or their substitutes and the maintenance of the health, function and esthetics of these structures and tissues.

Prosthodontics Prosthodontics is the dental specialty pertaining to the diagnosis, treatment planning, rehabilitation and maintenance of the oral function, comfort, appearance and health of patients with clinical conditions associated with missing or deficient teeth and/or oral and maxillofacial tissues using biocompatible substitutes.^*2

6Public health dentistry Dental Public Health is the science and art of preventing and controlling dental diseases and promoting dental health through organized community efforts. It is that form of dental practice which serves the community as a patient rather than the individual. It is concerned with the dental health education of the public, with applied dental research, and with the administration of group dental care programs as well as the prevention and control of dental diseases on a community basis.^*2

Oral and maxillofacial surgery Oral and Maxillofacial Surgery is the specialty of dentistry which includes the diagnosis, surgical and adjunctive treatment of diseases, injuries and defects involving both the functional and esthetic aspects of the hard and soft tissues of the oral and maxillofacial region.^*2

Orthodontics and dentofacial orthopedics Orthodontics and dentofacial orthopedics is the dental specialty that includes the diagnosis, prevention, interception, and correction of malocclusion, as well as neuromuscular and skeletal abnormalities of the developing or mature orofacial structures.^*2

Oral and maxillofacial pathology Oral Pathology is the specialty of dentistry and discipline of pathology that deals with the nature, identification, and management of diseases affecting the oral and maxillofacial regions. It is a science that investigates the causes, processes, and effects of these diseases. The practice of oral pathology includes research and diagnosis of diseases using clinical, radiographic, microscopic, biochemical, or other examinations.^*2

Pedodontics and preventive dentistry Pediatric Dentistry is an age-defined specialty that provides both primary and comprehensive preventive and therapeutic oral health care for infants and children through adolescence, including those with special health care needs.^*2

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.

Traditionally the subject of dental materials primarily included materials used in Restorative Dentistry including related auxiliary material. Currently, there is a trend to be more inclusive and include materials from specialties, which have traditionally been excluded like the Endodontic and Surgical specialties.

There is no classification that satisfactorily categorizes all materials used in dentistry. This is because many of the materials have multiple utilities and overlapping functions.

All materials can be classified into four classes

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.

Prosthetic materials are materials used to replace missing teeth and oral and maxillofacial structures. These include the alloys, ceramics and polymers used in fixed and removable partial denture construction and maxillofacial prostheses.

A biomaterial is a biological or synthetic substance which can be introduced into body tissue as part of an implanted medical device or used to replace an organ, bodily function. Although many traditional materials qualify as biomaterials, this term has been introduced to include bone and tissue grafts.

Therapeutic agents include various chemicals, medicaments, antimicrobials and other locally applied agents that are capable of producing a specific effect in the area to which it is applied.

In reality, many materials have dual or multiple uses and so the above categorization is difficult to strictly apply.

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. 1.1A) (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. Standards are constantly revised; therefore, it is imperative for manufacturers and researchers alike to refer to the latest edition of the ISO specifications to stay abreast of changes in requirements and classifications.8

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 was assumed by the ADA.

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. 1.1B).

Manufacturers can submit their product for the ADA seal of approval. This falls into three categories — Accepted, Provisionally Accepted, and Unaccepted. ADA certification is an important symbol of a dental product safety and effectiveness. ADA acceptance is effective for a period of 5 years.

Currently, the ADA have adopted the ISO specifications. The ADA specification for a particular product is identical to its ISO counterpart.

Materials used for dentistry are highly specialized. Each one is designed with a specific set of properties depending on what it is intended 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.