MANDIBULAR INCISORS

* L1 to NB (Mand. Incisor to NB): Angular 25 +/- 7, Linear 3 +/- 2mm
Reference Line: Nasion – B point
The relationship of the mandibular central incisor to the N-B reference line is used to establish the position of the mandibular incisors relative to the mandibular apical base.
Both the inclination of the long axis of the incisor to the line and the distance of the labial surface of the incisor in front of the line are measured. The millimeter distance establishes the prominence of the incisors relative to the supporting bone, while the inclination indicates whether the tooth has been tipped to its position or moved bodily.
• Labially inclined (proclined) incisors will have a greater than average angular and linear measurement (Class II division 1 cases).
• Upright or retroclined incisors will have a smaller than average angular and linear measurement (Class II division 2 cases).
• Positive values are recorded if the labial surface of the incisor is anterior to the NB line, negative values if posterior.
* L1 – MP (Mand. Incisor to MP) : 90 +/- 5
Reference Plane: Mandibular Plane
Also known as IMPA (Incisor Mandibular Plane Angle). It defines the axial inclination between the mandibular incisor and the inferior border of the mandible. The more the incisor is labially inclined, the greater the angle.