5: Clinical Oral Structures, Dental Anatomy, and Root Morphology

Clinical Oral Structures, Dental Anatomy, and Root Morphology

Heidi A. Schlei and the publisher acknowledge the past contributions of Marilyn Beck to this chapter.

The practice of dental hygiene is based on oral anatomy, a fundamental dental science. A thorough knowledge of oral anatomy provides the basis for assessing, diagnosing, planning, implementing, and evaluating clients during the dental hygiene process of care. Oral structures reflect local and systemic health. Oral anatomy also provides the basis for client education, fluoride and pit-and-fissure sealant therapy, periodontal and tooth assessment, instrumentation, and nonsurgical and periodontal maintenance care, all of which require imagery and tactile perception. The dental hygienist also uses oral anatomy to assess the relationship of teeth, both within and between the arches. These factors influence care plans, evidence-based decision making, professional recommendations, and referral to other health care practitioners.

Clinical Oral Structures

Oral tissues are indicators of a client’s oral and general health. Abnormal conditions can be recognized if the appearance of normal oral structures is known (Figures 5-1 to 5-8 and Table 5-1). Oral structures are identified according to their specific locations and functions. Generally, oral structures appear in shades of pink and may be pigmented in dark-complexioned individuals. In the oral cavity, the presence of melanin pigmentation is random, scattered, and unpredictable.


Oral Structures







FIGURE 5-2 Buccal mucosa.


FIGURE 5-7 Hard palate.

Dental Terminology

Parts of a tooth (see the section on “Tissues of the Tooth” in Chapter 2)

1. Crown

2. Root—part of the tooth covered by cementum

a. Apex—rounded end of the root

b. Periapex (periapical)—area around the apex of a tooth

c. Foramen—opening at the apex through which blood vessels and nerves enter

d. Furcation—area of a two-rooted or three-rooted tooth, where the root divides

e. Root trunk—area from the cemento-enamel junction (CEJ) to the furcation

f. Root concavity—broad, shallow, vertical depression on the root; named by location: mesial, distal, and lingual; a concavity located on the furcation side of a root is called a furcal concavity

3. Enamel—hardest calcified tissue covering the dentin in the crown of the tooth; 96% mineralized

4. Cementum—bone-like calcified tissue covering the dentin in the root of the tooth; 50% mineralized

5. Dentin—hard calcified tissue surrounding the pulp and underlying enamel and cementum; makes up the bulk of the tooth; 70% mineralized

6. Pulp—innermost noncalcified tissue containing blood vessels, lymphatics, and nerves

7. Pulp cavity—space containing the pulp

Junction of parts

Tooth surfaces

1. Facial—surface toward the face

2. Lingual—surface toward the tongue; may also be called palatal for maxillary teeth

3. Proximal—surface toward the adjacent tooth

4. Contact area—area that touches the adjacent tooth in the same arch

5. Incisal—surface of an incisor that is toward the opposite arch; the biting surface; newly erupted permanent incisors have mamelons (projections of enamel) on this surface

6. Occlusal—surface of a posterior tooth that is toward the opposite arch; the chewing surface; this surface has elevations and depressions; the expression of these anatomic landmarks varies with the population from which they are derived (Figure 5-9)


FIGURE 5-9 Occlusal anatomy.

a. Cusp—large, rounded, elevated area of enamel

b. Ridge—rounded, linear elevation of enamel

c. Cuspal inclines—two surfaces of a cusp that slant or slope down and away from the crests of the triangular ridge toward developmental grooves

d. Groove—narrow linear depression

e. Fossa—a shallow, broad depression

f. Pit—a sharp, pointed depression generally located at the junction of developmental grooves (fissures) or at their termination; the opening of a pit may be narrow or wide but is smaller than a toothbrush bristle; pits may be shallow or deep, and their apical descent may be steep or gradual; pits in primary teeth are not as deep as those in permanent teeth

Junction of surfaces—a tooth has curved surfaces; therefore, no “corner,” where one surface begins and another ends, is present; the transition area is called the line angle area and is named for the surfaces that are involved (e.g., MB, mesiobuccal, DL, distolingual, MO, mesio-occlusal)

Embrasure—the interproximal space between teeth that begins at the contact area and widens in facial, lingual, occlusal–incisal, and cervical directions; functions as a spillway and escapement area by deflecting food and reducing the forces placed on the periodontium during chewing; also provides a self-cleaning area; the interproximal gingiva fills the cervical embrasure

Dental Anatomy

Permanent dentition (Table 5-2)

1. Humans are diphyodonts, that is, they have two sets of teeth in a lifetime—a primary dentition and a permanent dentition—that span three dentition periods: primary, mixed, and permanent

2. The permanent dentition consists of:

a. Eight incisors, two in each quadrant, named central and lateral incisors, respectively. The four quadrants in a dentition are: maxillary right, maxillary left, mandibular right, and mandibular left

b. Four canines—one in each quadrant

c. Eight premolars, two in each quadrant, named first and second premolars

d. Twelve molars, three in each quadrant; named first, second, and third molars

3. The Universal Numbering System (UNS) uses Arabic numerals 1 to 32 to specify permanent teeth, beginning with the maxillary right third molar and ending with the mandibular right third molar; the International Standards Organization (ISO) TC 106 designation system (also referred to as the International Numbering System) uses a two-digit code; the first digit—1 to 4—designates the quadrant in the dentition, clockwise from the upper-right quadrant. The second digit—1 to 8—designates the tooth, from the central incisor to the third molar. For example, tooth 11 is the permanent maxillary right central incisor

4. General characteristics of tooth form

a. All proximal surfaces converge toward the apex from the crests of curvature (height of contour) (Figure 5-10)

b. All facial and lingual surfaces converge toward the apex and toward the incisal–occlusal surface from the crests of curvature; this convergence facilitates mastication (Figure 5-12)

c. All facial surfaces of the crown are convex, and the crest of the curvature is located in the cervical third; the lingual surfaces of posterior teeth are convex, and the crest of curvature is located in the middle third; the lingual surfaces of anterior teeth are concave in the middle third; these contours deflect food away from the gingiva and facilitate the function of teeth (Figure 5-13)

d. The CEJ on the proximal surface curves toward the incisal–occlusal surface and is more prominent on anterior teeth than on posterior teeth; the CEJ curves more on the mesial surface than on the distal surface (see Figure 5-13)

e. From a proximal view, the long axes of the crown and the root are in line except for the posterior mandibular teeth, which have the long axis of the crown tilting lingually to the long axis of the root; this lingual inclination enables the intercusping relationship of posterior teeth and the distribution of forces along their long axes (Figure 5-14)

f. Proximal surfaces converge toward the lingual; this is most prominent on maxillary incisors and canines (the two exceptions are the mandibular second premolar and the maxillary first molar) (see Table 5-2 and Figure 5-15)

5. General characteristics of roots

a. Root anatomy is not as complex as crown anatomy, but variations in size, shape, and number frequently occur

b. Teeth have one, two, or three roots

c. Teeth with two or three roots have a root trunk with depressions that deepen until the trunk divides at the furcation

d. Some roots have longitudinal depressions called root concavities

e. Individual roots are basically cone shaped, being widest at the CEJ and converging (tapering) to the apex; more root surface area is present in the cervical than apical third

f. A cervical cross-section of a tooth with one root shows three basic shapes (Figure 5-16; see Table 5-2), which may be slightly altered by the presence of root concavities

g. Roots that appear triangular or ovoid in cross-section have narrower lingual surfaces

h. A cervical cross-section of molars follows the form of the crown

i. From a facial or lingual view, roots have a distal inclination

j. Second-molar and third-molar roots are more likely to be closer together, fused, and distally inclined

k. The CEJs on posterior teeth have a much less pronounced curvature on all surfaces

l. Cementum is not as hard as enamel

m. Variations in root form

6. Clinical considerations of permanent tooth form

a. Clinical considerations of incisor form

b. Clinical considerations of canine form

c. Clinical considerations of premolars

d. Clinical considerations of molars

Jan 1, 2015 | Posted by in Dental Hygiene | Comments Off on 5: Clinical Oral Structures, Dental Anatomy, and Root Morphology
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