[A study of the internal structure of the Japanese edentulous mandible]

With the aim of improving understanding of the transition the mandible internal structure undergoes between the dentulous and edentulous states, the thickness of the substantia compacta, the ratio of trabecular bone to the total substantia spongiosa, and the thickness of the trabecular bone were measured in 9 edentulous mandibles aged 45 to 65 years. The measurements were made with an image-treatment device outfitted with a personal computer. Results 1. Thickness of the substantia compacta The thickest zones (3.00-3.81 mm) were located on the lingual side of the anterior teeth; the second thickest zones (2.20-2.48 mm) were located on the superior lingual and buccal side of the molars. The thinnest zones (1.66-1.67 mm) were located on the labial side of the anterior teeth; the second thinnest zones (1.71-1.75 mm) were located on the buccal side of the premolars. Little difference (1.90-2.18 mm) was observed in the bases of the mandibular areas. In the region of the lingual side, the thickest zones occurred in the premolars. Little difference in thickness was observed between the premolar and molar zones. On the labial-buccal side, thicknesses increased from the premolar to the molar zones (which were the thickest) and decreased gradually from the mental to the premolar zones. Comparisons showed that the anterior teeth zoon in the edentulous mandible the substantia compacta is thinner on the labial side and thicker on the lingual side than it is in the dentulous mandible. Little difference between the dentulous and edentulous mandibles was observed in the lingual side of the molar zone, although the buccal side was thinner in the edentulous than in the dentulous mandible. 2. Ratio of trabecular bone to the total substantia spongiosa The highest ratios (74.03-89.62%) occurred in the mental zone; the second highest (69.07-82.92%) occurred in the incisor zone. The lowest ratios (30.61-39.61%) occurred in the superior and middle regions of the premolar zone. The inferior area of the premolar zone, however, was relatively wider (42.83-55.66%) than the superior and middle areas. The following ratios of trabecular bone to total substantia spongiosa were observed: The highest ratio occurred in the zone of the anterior teeth, the next highest ratio in the molar zone, and the lowest ratio in the premolar zone. Although, differences in ratios between dentulous and edentulous mandibles were only slight, a lower ratio occurred in the inferior area of the premolar zone. 3. Thickness of trabecular bone within the substantia spongiosa.(ABSTRACT TRUNCATED AT 400 WORDS)