Sheath configurations in human cuspal enamel

To determine the prism sheath configurations in human cuspal enamel 80 teeth were initially ground to produce flat surfaces through the following planes: a horizontal series at successively greater distances from the dentinoenamel junction and longitudinally through the center of the cusps. Individual teeth were suspended in an acid‐alcohol solution (1 cm 3 conc. HCl in 100 cm 3 95% ethanol) at 37°C for seven to ten days. The treatment “softened” the enamel to a depth of approximately 1 mm. The teeth were embedded in Epon and sectioned at 0.5 to 10 μm with a diamond knife. Thick and thin ground sections for phase contrast microscopy and acid‐etched ground sections for Nomarski differential interference microscopy were prepared through the same regions. In thicker longitudinal sections, the prisms in gnarled enamel formed a zig‐zag pattern which was unlike the twisting pattern generally observed in ground sections. The thinnest transverse sections showed the sheath outlines to be dramatically different from those seen elsewhere in the enamel. Some prism sheaths were circular, others were in the form of spirals. What could be described as sheaths within sheaths were also seen. In the thinnest longitudinal sections the prisms were seen to be elongated and discontinuous. Sheath outlines in enamel adjacent to the central core of gnarled enamel were similar to those described elsewhere in the body of the enamel. Keyhole, modified keyhole patterns and arcade forms were the dominant sheath patterns. Other atypical sheath configurations were seen scattered throughout this region.