Table 2.

Description of mandibular shape differences between subsequent age groups. For visualization see Fig. 6i,ii

Birth	The symphysis is vertical and the anterior teeth have an upward-forward orientation (Fig. 6ai). The floor of the tooth chambers is located below the tongue (T). On the labial side of the symphysis, the mental region has a pointed configuration anteriorly and, on the lingual side, the triangle formed by GH, RAD and LAD is roughly equilateral (Fig. 6aii).
From birth to mid-DS1	The floor of the tooth chambers, the landmarks T, GH, RAD, LAD and the basal symphysis simultaneously move downward and forward (Fig. 6bi) in the Procrustes coordinate system. The deciduous incisors reorient to an approximately vertical position. The distance between the tongue and the genio-hyoid decreases, and the floor of the tooth chambers is now at the same level as T (Fig. 6bi). The triangle GH-RAD-LAD and the mental region retain the same configuration as at birth (Fig. 6bii). The ramus heightens supero-posteriorly; it also broadens antero-posteriorly more than the corpus does.
From mid-DS1 to end-DS1	While RAD and LAD maintain their position, T and GH continue to displace both inferiorly and ventrally (Fig. 6ci,ii). The triangle GH-RAD-LAD is no longer equilateral (Fig. 6cii). Simultaneously, at the labial side of the symphysis, the mental region flattens and widens medio-laterally (Fig. 6cii). The teeth continue to move mesially, and the floor of the incisor, canine and dm1 chambers move upward, away from the inferior border of the mandible, during tooth emergence (Fig. 6ci). The ramus continues to increase supero-posteriorly but becomes relatively narrower antero-posteriorly. The height of the symphysis also increases (Fig. 6ci) and becomes relatively narrower antero-posteriorly when the deciduous incisors emerge (Fig. 6ci).
From end-DS1 to mid-DS2	T and GH continue to displace downward and forward (Fig. 6di), while RAD and LAD remain fixed (Fig. 6dii). The triangle GH-RAD-LAD becomes much more obtuse. Simultaneously, the mental region widens medio-laterally (Fig. 6dii). The deciduous incisors, canines and first molars have now fully erupted.
From DS2 to DS3	When dm2 reaches its full occlusal position, the landmarks GH, RAD and LAD simultaneously project anteriorly as the mental region projects forward (Fig. 6d,ei). The distance between T and GH increases (Fig. 6d,ei.ii). The ramus rotates toward the corpus leading to a more closed gonial angle. Simultaneously, the gonial region becomes less ventrally pointed. The ‘incurvatio mandibularis’ (Hublin & Tillier, 1981), the inward curvature of bone below the labial alveolar margin, becomes well distinguished as the symphyseal alveolar region displaces backward (Fig. 6ei).