| Abstract: | As a rule, the occlusal plane in man is not flat but curved in the three dimensions. This curved organization is related to a specific phenomena: the continuity of the dental arch without diastema. The Page's proposal of the tangent law explains the sagittal organization of the mandibular teeth by geometrical analyses. A cephalometric analysis of 485 subjects, in natural dentition, is the basis for the present statistical study of the mandibular teeth sagittal inclination, related to the direction of the tangent. Mandibular incisors follow the tangent law, but the long axis of the posterior mandibular teeth exhibits a postero-anterior and progressive differential angle with the direction of the tangent: 15 degrees, 20 degrees, 25 degrees, 28 degrees. The differential angle with the direction of vertical strength during closure movement generates an horizontal strength component, with a tendency to create a forward tooth movement. This horizontal component of force is tightening the proximal contacts, maintaining the continuity of the dental arch: it also originates the mesial "drift" and mandibular incisor crowding. |
