Early Modern Human from Tianyuan Cave, China

Chapter 5 The Tianyuan 1 Dentition

41 C h a p t e r 5 The Tianyuan 1 Dentition THE DENTITION of Tianyuan 1 was markedly reduced, antemortem and postmortem. Prior to death, the individual sustained substantial tooth loss, which is reflected in the altered alveolar process of the mandible and the supereruption of the right M3 (Chapter 12). There is also advanced occlusal and interproximal wear on the remaining teeth. After death and through fossilization and recovery, any left mandibular teeth that might have been there and all but one of the remaining maxillary teeth were lost. However, the remaining eight teeth (right I2 to M3 and left M2? ) and their alveolar processes provide considerable data on the dentition of this individual. Occlusal and Interproximal Attrition Maxillary Molar The single maxillary molar, a left M1 or M2 , has an incomplete crown (Figure 5-1). It is still possible to determine that its lingual occlusal enamel was largely lost antemortem through attrition, leaving only an enamel ring around the dentin basin. Buccally, the crown edge was lost postmortem, but there are the remains of the enamel from the sulcus between the paracone and the metacone. The wear most closely approximates Molnar’s (1971) wear stage 5. This buccolingual wear differential is in agreement with a normal maxillary overbite, despite antemortem tooth loss. Its degree of wear, with some remaining occlusal enamel, is less than the wear on the M1 and more closely approximates that of the M2 (Table 5-1). This attrition suggests that the tooth is most likely an M2 . It is not possible to determine the extent of the interproximal wear facets given the buccal wear damage. However , they planed off the mesial and distal crown surfaces, leaving only thin borders of enamel between the exposed occlusal dentin and the interproximal surfaces . CHAPTER 5 42 Incisor, Canine, and Premolars The I2 , the C1 and both lower right premolars had their occlusal surfaces planed off to horizontal dentin surfaces with thin rings of enamel (Figure 5-2). Their buccal crown heights are slightly greater than their lingual ones (Table 5-1), but their largely flat occlusal surfaces remain buccolingually essentially horizontal relative to the alveolar plane of the mandible. The C1 and the P3 occlusal surfaces slope downward slightly to their interproximal contact area, and the P4 surface slopes slightly distally toward the M1 . All four teeth match Molnar’s wear stage 6. In combination with their marked occlusal attrition, these four teeth have high cervix to alveolar crest (C/AC) heights; only the buccal P4 value is noticeably below 3 mm. In healthy adults, a C/AC measurement of 1–2 mm is considered normal (Wood and Goaz, 1997). The values are not likely to have been influenced by the minor damage to the anterior buccal alveoli. Since there is no evidence of alveolar degeneration, especially mesially, these elevated cervix to alveolar crest measurements reflect normal dental supereruption in response to the pronounced reductions in crown heights of these teeth. Supereruption of the teeth is sometimes confused with alveolar recession due to periodontal disease (Whittaker et al., 1982; Costa, 1982; Newman, 1998). Given the absence of diagnostic periodontal indicators , such as interdental bony pockets, on the Tianyuan 1 mesial alveoli, it is likely that the increased C/AC heights are due to normal supereruption. Figure 5-1. Views of the maxillary molar (M1 or M2 ). M: mesial; D: distal; L: lingual. Scale in millimeters. Table 5-1. Crown height and C/AC measurements for the Tianyuan 1 mandibular dentition, in millimeters Crown height C/AC (cervix to alveolar crest) Buccal Lingual Buccal Lingual Wear stage1 I2 3.1 2.5 2.8 3.0 6 C1 2.5 2.3 2.7 3.8 6 P3 2.0 1.1 3.4 3.3 6 P4 2.5 1.9 2.3 3.7 6 M1 mesial 1.1 2.1 4.2 3.0 6/7 M1 distal 0.2 2.3 — 3.6 M2 mesial 3.6 2.2 4.8 4.0 5 M2 distal 2.4 2.3 4.9 5.1 M3 mesial 4.8 2.4 — — 6 M3 distal 4.3 2.2 — — M1-2 — 3.3 — — 5 1 Molnar (1971) occlusal wear stages for the teeth. Figure 5-2. Views of the mandibular I2 to M2 dentition. Right: occlusal; upper left: buccal; lower left: lingual. Scale in centimeters. CHAPTER 5 44 Molars The right M1...