Learning objective: to evaluate the knowledge acquired at practical classes, to study the structure of dentition, forms of dental arches, dental formulas.
Teeth located in the jaws form dental arches (dentition).
A dental arch is a line drawn through the incisal edges and occlusal surfaces of the teeth near the vestibular contour (fig. 9.1).
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Fig. 9.1
The upper dental arch has the shape of a half-ellipse, the lower one is a parabola. The upper dental arch is somewhat wider than the lower one, so the chewing surfaces of the upper teeth are located anteriorly and externally from the lower ones.
In addition to dental arches, alveolar and apical arches are distinguished in dentistry.
The alveolar arc is a line passing along the edge of the alveolar process near the neck of the teeth from the vestibular side.
The apical arc is a line drawn along the apices of dental roots.
On the upper jaw, the crowns are inclined to the vestibular side, therefore the widest arc on the upper jaw is the dental one, and the narrowest is the apical one. Teeth of the lower jaw are inclined to the tongue, therefore the widest arc is apical, and the narrowest is occlusal.
OCCLUSION CURVES
The occlusal surfaces of the chewing teeth are not located in the same plane, but form so-called sagittal occlusal curves.
The sagittal occlusal curve (the curve of Spee) is a line passing through the buccal tubercle of the first premolar and the distal buccal tuber of the last molar.
On the upper jaw, the sagittal occlusal curve has a convex shape, and on the lower one -a concave one. Due to the presence of the curve, when the lower jaw is lowered and pulled forward, contact is kept between the chewing teeth (the so-called three-point contact of Bonville). Therefore, this curve is also called compensatory. A plane passing through the incisal point on the lower jaw and touching the occlusal curves on the right and left is called occlusal.