Alternating lamellar structure in human cellular cementum and rat compact bone: Its structure and formation

Human cellular cementum and compact bone exhibit an alternating lamellar structure, in which intensely and faintly stainable lamellae are stratified in an alternating manner. Many investigators, including our group, have accumulated considerable data regarding lamellar structure. In this review, we summarize the alternating lamellar structure, based on available data, and introduce our hypothesis regarding its formation.

We implemented 10% and 24% NaOH maceration methods for scanning electron microscopy. The 10% NaOH maceration method was used for detailed examination of the collagen fibril arrangement, whereas the 24% NaOH maceration method was used for examination of cell morphology in the absence of collagen fibrils. The following findings were obtained: (1) sections of cementum and bone showed two types of alternating lamellae-those comprising longitudinally and nearly longitudinally arranged fibril arrays, and those comprising transversely and nearly transversely arranged fibril arrays; (2) the fibril arrays appeared to shift arrangement in a regular and periodic manner, such that the alternating lamellar structure appeared in sections; (3) where the alternating lamellar structure was being formed, osteoblasts and cementoblasts extended slender processes alongside newly deposited fibrils.

Our data showed that the alternating lamellar structure was consistent with the twisted plywood model previously proposed for osteonal lamellae. For the formation of this structure, there have been two major hypotheses: a self-assembly hypothesis and a cellular control hypothesis. Our data support the latter; osteoblasts and cementoblasts move their processes synchronously and periodically to control fibril arrangement, thereby forming the alternating lamellar structure.