TOOTH MORPHOLOGY

Descriptive anatomy

• Median sagittal plane: the imaginary plane in the center that divides right from left.
• Median line: an imaginary line on that plane that bisects the dental arch at the center.
• Mesial: toward the center (median) line of the dental arch.
• Distal: away from the center (median) line of the dental arch.
• Occlusal plane: A plane formed by the cusps of the teeth. It is often curved, as in a cylinder. We will speak often of the occlusal surface of a tooth.
• Proximal: the surface of a tooth that is toward another tooth in the arch.
• Mesial surface: toward the midline.
• Distal surface: away from the midline.
• Facial: toward the cheeks or lips.
• Labial: facial surface of anterior teeth (toward the lips).
• Buccal: facial surfaceof anterior teeth (toward the cheeks).
• Lingual: toward the tongue.
• Occlusal: the biting surface; that surface that articulates with an antagonist tooth in an opposing arch.
• Incisal: cutting edge of anterior teeth.
• Apical: toward the apex, the tip of the root.

Crown stage

Hard tissues, including enamel and dentin, develop during the next stage of tooth development. This stage is called the crown, or maturation, stage by some researchers. Important cellular changes occur at this time. In prior stages, all of the inner enamel epithelium cells were dividing to increase the overall size of the tooth bud, but rapid dividing, called mitosis, stops during the crown stage at the location where the cusps of the teeth form. The first mineralized hard tissues form at this location. At the same time, the inner enamel epithelial cells change in shape from cuboidal to columnar. The nuclei of these cells move closer to the stratum intermedium and away from the dental papilla.

The adjacent layer of cells in the dental papilla suddenly increases in size and differentiates into odontoblasts, which are the cells that form dentin. Researchers believe that the odontoblasts would not form if it were not for the changes occurring in the inner enamel epithelium. As the changes to the inner enamel epithelium and the formation of odontoblasts continue from the tips of the cusps, the odontoblasts secrete a substance, an organic matrix, into their immediate surrounding. The organic matrix contains the material needed for dentin formation. As odontoblasts deposit organic matrix, they migrate toward the center of the dental papilla. Thus, unlike enamel, dentin starts forming in the surface closest to the outside of the tooth and proceeds inward. Cytoplasmic extensions are left behind as the odontoblasts move inward. The unique, tubular microscopic appearance of dentin is a result of the formation of dentin around these extensions.

After dentin formation begins, the cells of the inner enamel epithelium secrete an organic matrix against the dentin. This matrix immediately mineralizes and becomes the tooth's enamel. Outside the dentin are ameloblasts, which are cells that continue the process of enamel formation; therefore, enamel formation moves outwards, adding new material to the outer surface of the developing tooth.

FUNCTIONS OF PERIODONTIUM

Tooth support
Shock absorber
Sensory (vibrations appreciated in the middle ear/reflex jaw opening)

Maxillary First Deciduous Molar.

-The notation is B or I.

-It looks a bit like an upper 1st premolar.

-There are three roots.

-It has a strong bulbous enamel bulge that protrudes buccally at the mesial.

-It is the smallest of the deciduous molars in crown height and in the mesiodistal dimension.

Alveolar bone (process)

1. The bone in the jaws that contains the teeth alveoli (sockets).

2. Three types of bone :

a. Cribriform plate (alveolar bone proper)

(1) Directly lines and forms the tooth socket. It is compact bone that contains many holes, allowing for the passage of blood vessels. It has no periosteum.

(2) Serves as the attachment site for PDL (Sharpey’s) fibers.

(3) The tooth socket is constantly being remodeled in response to occlusal forces. The bone laid down on the cribriform plate, which also provides attachment for PDL fibers, is known as bundle bone.

(4) It is radiographically known as the lamina dura.

b. Cortical (compact) bone

(1) Lines the buccal and lingual surfaces of the mandible and maxilla.

(2) Is typical compact bone with a periosteum and contains Haversian systems.

(3) Is generally thinner in the maxilla and thicker in the mandible, especially around the buccal area of  the mandibular premolar and molar.

c. Trabecular (cancellous, spongy) bone

(1) Is typical cancellous bone containing Haversian systems.

(2) Is absent in the maxillary anterior teeth region.

3. Alveolar crest (septa)

a. The height of the alveolar crest is usually 1.5 to 2 mm below the CEJ junction.

b. The width is determined by the shape of adjacent teeth.

(1) Narrow crests—found between teeth with relatively flat surfaces.

(2) Widened crests—found between teeth with convex surfaces or teeth spaced apart.

LOCATION OF THE TEETH

Normally, a human receives two sets of teeth during a lifetime.

The first (deciduous or primary) set consists of 20 teeth ("baby" teeth).

The second (permanent) set usually consists of 32 teeth. In each quadrant, there are eight permanent teeth: two incisors, one cuspid, two bicuspids, and three molars 

The tooth positioned immediately to the side of the midline is the central incisor, so called because it occupies a central location in the arch.

To the side of the central incisor is the lateral incisor. Next is the cuspid, then the two bicuspids (the first bicuspid, followed by the second bicuspid). The last teeth are three molars. After the second bicuspid comes the first molar, followed by the second molar, followed by the third molar or more commonly called the "wisdom tooth."

Another method of describing the location of teeth is to refer to them as anterior or posterior teeth .

Anterior teeth are those located in the front of the mouth, the incisors, and the cuspids. Normally, these are the teeth that are visible when a person smiles.

The posterior teeth are those located in the back of the mouth-the bicuspids and molars.