Teeth comprise around 20% of the surface area of the oral cavity, maxillary more so than mandibular teeth. Tooth types of both arches within the primary dentition include 8 incisors, 4 canines, and 8 molars, for a total of 20 teeth (see Figures 15-1 and 2-4). The anatomy of the primary dentition is discussed further in Chapter 18.

Tooth types of both arches within the permanent dentition include 8 incisors, 4 canines, 8 premolars, and 12 molars, for a total of 32 teeth (see Figure 15-2). Note that only the permanent dentition has premolars; in contrast, the primary dentition does not have premolars. The anatomy of the permanent dentition is discussed further in Chapter 16 (anterior teeth) and Chapter 17 (posterior teeth).

Each tooth type has a specific form, no matter which dentition it is in. This tooth form is related to the function during mastication for the tooth, as well as to its role in speech and esthetics. The form and function of each tooth type are similar for both the primary and permanent dentitions.

The incisors function as instruments for biting and cutting food during mastication, because of their triangular proximal form. The canines, because of their tapered shape and their prominent cusp, function to pierce or tear food during mastication.

The premolars, which are found only in the permanent dentition, function to assist the molars in grinding food during mastication because of their broad occlusal surface and their prominent cusps. The premolars also assist the canines in piercing and tearing food with their cusps. Finally, as the teeth with the largest and strongest crowns, the molars function in grinding food during mastication, assisted by the premolars. It is the wide occlusal surfaces of the molars, with their prominent cusps, that help with mastication.

The primary teeth and the permanent teeth are both designated by the Universal Tooth Designation System (Figure 15-3). This system is the most widely used in United States for the designation of both dentitions because it is adaptable to electronic data transfer; this textbook uses the Universal System. With the Universal Tooth Designation System, the primary teeth are designated in a consecutive arrangement by using capital letters, A through T, starting with the maxillary right second molar, moving clockwise, and ending with the mandibular right second molar (see Figure 15-1).

The permanent teeth are designated by the Universal Tooth Designation System in consecutive arrangement as the patient is observed from in front by using the digits 1 through 32, starting with the maxillary right third molar, moving clockwise, and ending with the mandibular right third molar (see Figure 15-2). The clockwise convention also is also used when charting restorations or periodontal conditions in the oral cavity for a patient.

However, the need for a system that can be used internationally, as well as by electronic data transfer, is recognized; thus the acceptance of the International Standards Organization Designation System (ISO System) by the World Health Organization (see Figure 15-3). With this system, the teeth are designated by using a two-digit code. The first digit of the code indicates the quadrant (see later discussion under general dental terms), and the second indicates the tooth in this quadrant. This is based on the system of the Fédération Dentaire Internationale (FDI).

With the ISO System, the digits 1 through 4 are used for quadrants in a clockwise manner in the permanent dentition, and digits 5 through 8 are used in a clockwise manner for those quadrants of the primary dentition. For the second digit, which indicates the tooth, the digits 1 through 8 are used for the permanent teeth, with this designation using the median line in a distal direction for numbering. The digits 1 through 5 are then used for the primary dentition, with this designation also using the median line in a distal direction for numbering.

Another system that is commonly used in orthodontics is the Palmer Notation Method also known as the Military Tooth Numbering System (see Figure 15-3). It is helpful with this dental specialty because it allows immediate discussion of the teeth that require prompt treatment, and it can produce a very graphical image, akin to a map of the dentition. In this system, the teeth are designated with a right-angle symbol indicating the quadrants with the tooth number inside, similar in numbering to the ISO System that superseded it.