| SECTION I | GENERAL DESCRIPTION OF INCISORS |
OBJECTIVES FOR SECTIONS I, II, AND III
These sections are designed to prepare the learner to perform the following:
- Describe the location of incisors in the mouth.
- Describe the functions of incisors.
- List class traits common to all incisors.
- List arch traits that can be used to distinguish maxillary from mandibular incisors.
- From a selection of all teeth, select and separate out the incisors (using class traits).
- Divide a selection of all incisors into maxillary and mandibular (using arch traits).
A. LOCATION OF INCISORS IN THE MOUTH
Refer to Figure 2-1 or, better yet, to a model of the complete set of permanent teeth while becoming familiar with the location and Universal number of each incisor. There are four maxillary incisors: two central incisors (Universal numbers 8 and 9) and two lateral incisors (7 and 10). There are four mandibular incisors: two central incisors (teeth 24 and 25) and two lateral incisors (23 and 26).
FIGURE 2-1. Adult dentition with Universal numbers on the incisors highlighted in red.
Central incisors are located on either side of their respective arch (maxillary or mandibular) with their mesial surfaces next to one another at the midline, normally in contact. Their distal surfaces contact the mesial surfaces of the adjacent lateral incisors. Lateral incisors are therefore just distal to central incisors, with their mesial surfaces in contact with the distal surfaces of the adjacent central incisors. Their distal surfaces contact the mesial surfaces of the adjacent canines. Incisors in the mouth are identified with Universal numbers in Figure 2-2.
FIGURE 2-2. Relative size and shape of incisors in the mouth show that maxillary central incisors are the widest, followed by maxillary laterals, then mandibular laterals, and, finally, the narrowest teeth in the mouth, the mandibular central incisors.
Mandibular incisors function with the maxillary incisors to (a) cut food (mandibular incisors are moving blades against the maxillary incisors), (b) enable articulate speech (consider the enunciation of a toothless person), and (c) help to support the lip and maintain an esthetic appearance. By current standards, a person lacking one or more incisors has an undesirable appearance (Fig. 2-3). (Did you ever hear the song “All I want for Christmas are my two front teeth”?) Their fourth function, by fitting the incisal edges of the mandibular incisors against the lingual surfaces of the maxillary incisors, is to (d) help guide the mandible posteriorly during the final phase of closing just before the posterior teeth contact.
FIGURE 2-3. Missing anterior teeth greatly affect an esthetic smile.
LEARNING EXERCISE
Begin with your front teeth touching together edge to edge, and then begin to close your back teeth together. If you have ideal occlusion, when you move posteriorly, you should feel your upper incisors touching (and guiding) your mandibular incisors as your mandible moves posteriorly and your teeth close together.
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