Interpretation of the concepts of dentinal tubule and dentinal canaliculus

The biology of dentin occupies a central place in the theory of tooth integrity as an organ, and knowledge about the microstructure of dentin changes with the development of new research methods, such as scanning electron microscopy. The structures that form dentin, and the odontoblast processes, are an extremely complex biological structure due to cellular polarization. The structure of the dentin of crowns from 30 intact teeth extracted for orthodontic reasons has been studied. Dentin was examined on longitudinal chips using scanning electron microscopy, determining the average number of dentinal tubules per unit area of dentin, the length and diameter of the dentinal canaliculi along the dentinal tubule. Scanning electron microscopy of demineralized teeth showed that numerous fine fibrillar structures were found in the predentin, connecting the odontoblast processes (dentinal canaliculi) and the walls of the dentinal tubules. The odontoblast processes were always in close contact with the microfibrillar network and were located within the dentinal tubule. It was found that the dentinal canaliculi have their own anchoring microfibrillar system, which allows each dentinal canaliculus to be held in a central position. The microfibrils are attached to the wall of the dentinal tubule and form a continuous mesh structure among the dentin tissue and are directly fixed on one side to the wall of the dentinal tubule, and on the other side to the wall of the dentinal canaliculus, which is a derivative of the odontoblast process. In different areas of the dentin, the length, number, and diameter of the microfibrils have a wide variative range. Microstructures were numerous in different regions of the dentinal tubule. Their number decreased with distance from the level of the outer dentin. In the inner third of the dentinal tubule, microfibrillar structures are observed that form a dense network of different types, thicknesses and diameters. The most common direction of the microfibrils was from the surface of the odontoblast process to the wall of the dentinal tubule, and in other cases these microfibrils were attached to both opposite inner surfaces of the dentinal tubule. The base of the microfibril is attached to the wall of the dentinal tubule, as if forming a continuous structure among the dentin tissue and the surface of the odontoblast process. It is shown that the microfibrillar structures may be a previously unknown framework system that ensures the stabilization of odontoblast processes inside the dentinal tubule. In the scientific classification of dentin ultrastructure, it is advisable to use the term "dentinal tubule" and "dentinal canaliculus", since this structure is a derivative of the odontoblast process.