The inner enamel of human permanent teeth has been reported to be divided into three zones : I, II, and III. In this study, we observed the inner enamel in the lingual side of deciduous incisor teeth with a scanning electron microscope. All transverse ground sections were treated with chromium sulfate. The about 10-μm-thick innermost enamel consisting of prism-like structures was deeply and almost entirely etched. This zone, which was similar to Zone I in permanent teeth, was suggested to contain a smaller amount of organic material and to show a lower calcification. The inner enamel except for the innermost zone may be divided into Zone II and III, because the prisms in the inner enamel adjacent to the innermost zone, about 30 to 40 μm in thickness, contained a larger amount of organic material than the outer-side inner enamel. However, the inner enamel can not be divided into two zones, when the outer-side inner enamel showing an arrangement of Pattern 3 prisms is contained in the middle enamel. Abnormal-shaped prisms were observed in the middle enamel as well as in the inner enamel. The lamella-like stalks of enamel tufts, insoluble with chromium sulfate, ran through the prism bodies surrounded by chromium sulfate-insoluble sheaths for a short or a longer distance towards the enamel surface and then ran together with the prism sheath regions. Many of the tuft stalks appeared discontinuously in the prisms, and some of them had fine branches within prisms. Discontinuous structures of the tuft stalks suggest that the lamella shows a fenestrated membrane.
To examine the three-dimensional arrangement of bone matrix fibrils at their attachment with Sharpey's fibers or muscle tendons, we observed the surface of the body of the mandible, the angle of the mandible, and the coronoid process with a scanning electron microscope. Materials were three male crab-eating macaques (three years old). The fibrous layers of the ectoperiosteum were dissected free. Specimens were incubated in 1% trypsin solution for 72 hours at 37°C to digest both osteoblasts and amorphous organic matrix. At the external and internal surfaces of the body of the mandible, collagen fibril bundles ran horizontally. Spindle-shaped openings were observed between collagen fibril bundles, and we believe that the Sharpey's fibers entered the spindle-shaped openings. At the uneven area of the body of the mandible, collagen fibril bundles crossed each other. Many openings into which tendons of the masseter muscle entered were observed at the external surface of the angle of the mandible. The collagen fibril bundles organizing the surface matrix surrounded the places where the tendons entered. At the external surface of the coronoid process, collagen fibril bundles ran up and down in parallel. Tendons of the temporal muscle entered between collagen fibril bundles.