Cementum‐like tissue deposition on the resorbed enamel surface of human deciduous teeth prior to shedding

Abstract

Prior to the shedding of human deciduous teeth, odontoclastic resorption takes place at the pulpal surface of the coronal dentin, and this resorption occasionally extends coronally from the dentinoenamel junction into the enamel. After the end of resorption, however, the resorbed enamel surface is repaired by the deposition of a cementum-like tissue. Using this phenomenon as an observation model, in this study we examined the sequence of cellular and extracellular/matrix events involved in the enamel resorption repair by light and electron microscopy. As the odontoclast terminated its resorption activity, it detached from the resorbed enamel surface; thereafter, numerous mononuclear cells were observed along the resorbed enamel surface. Most of these mononuclear cells made close contact with the resorbed enamel surface, and coated pits or patches were observed on their plasma membrane facing this surface. Furthermore, they frequently contained thin needle-or plate-like enamel crystals in their cytoplasmic vacuoles as well as secondary lysozomes. Following the disappearance of these monononuclear cells, the resorbed enamel surface now displayed a thin coat of organic matrix. Ultrastructurally, this organic layer was composed of a reticular and/or granular organic matrix, but contained no collagen fibrils. Energy-dispersive X-ray microanalysis of this thin organic layer in undecalcified sections revealed small spectral peaks of Ca and P. Cementum-like tissue initially formed along this thin organic layer, increased in width, and appeared to undergo mineralization as time progressed. The results of our observations demonstrate that regardless of type of matrix of dental hard tissues, tooth repair may be coupled to tooth resorption, and suggest that mononuclear cells and an organic thin layer found on the previously resorbed enamel surface may play an important role in the repair process initiated after resorption of the enamel. © 2004 Wiley-Liss, Inc.Key words: enamel; resorption; cementum; repair; deciduous teeth; human Tooth, unlike bone, is not resorbed under physiological conditions except for the resorption of decidious teeth that occurs during the process of shedding. However, tooth resorption occasionally takes place under pathological conditions such as infection, trauma, or tumor development (Andreasen, 1988;Tronstad, 1988). It is well known that after cessation of tooth resorption, the area resorbed is rapidly repaired by the deposition of cementum or cementum-like tissue (Orban, 1928;Mueller, 1931; Kronfeld, 1932;Henry and Weinmann, 1951;Furseth, 1968;Schroeder, 1986;Sasaki et al., 1990;Sahara et al., 1992Sahara et al., , 1993Bosshardt and Schroeder, 1994;Kimura et al., 2003). This site-specific localization of repair seems to resemble that found in bone formation during bone remodeling. In bone remodeling, osteoclastic bone resorption is always followed by osteoblastic bone formation. A basophilic and electron-dense cement line/reversal line can be detected at the interface between the residual ...

The Isolation of Stem Cells from Human Deciduous Teeth Pulp Is Related to the Physiological Process of Resorption

“…The increase of cellular influx could be accelerating the phenomenon, causing anoikia and apoptosis of pulp cells (eg, odontoblasts), and, moreover, it could be promoting the release of cytokines acting in the activating stem cells (29,30). The latter are the cells responsible for the intermittency of resorption by differentiating and producing a mineralized tissue similar to the cement in the root and coronal dentin (14,17). In deciduous teeth, the cement-like tissue is responsible for the fixed/mobile variation of the tooth during physiological resorption (15).…”

“…Morphological changes occurring in the pulp tissue during the phenomenon of physiological resorption of deciduous teeth have been previously described in the literature (14)(15)(16)(17)(18)(19)(20)(21)(22). This phenomenon, genetically programmed, starts from an environment that leads to the apoptosis of cementoblasts and, in sequence, promotes osteoclastogenesis (23).…”

“…The course of the process changes the characteristics of the pulp tissue; when the root is completely resorbed, the pulp no longer has the same components and structure. It shows vascular and cellular changes, such as the absence of odontoblasts and the increase in inflammatory and clastic cells, as well as mononuclear precursors (14)(15)(16)(17)(18)(19)(20)(21)(22). The metabolic activity of the pulp tissue increases along with proteins and cytokines from the extracellular matrix change, showing the active role of the pulp in the process of resorption (20)(21)(22)(23).…”

Operative Dentistry and the Abuse of Dental Hard Tissues: Confocal Microscopical Imaging of Cutting

“…[2][3] The same phenomenon or resorption-formation coupling of (a bone-like tissue) cementum to enamel also occurs piecemeal during the later stages of resorption of human deciduous teeth. 4 However, with the ravages of caries, tooth wear and trauma, the need for some form of mechanical preparation often arises. Again, one would consider that this a relatively modern phenomenon, but recent work has shown that the first interventional dental procedures date back to between 7500-9000 years ago.…”

How Odontoblasts React Ultra-Structurally to Orthodontic Intrusive Forces.

“…Furthermore, mononuclear cells were found adjacent to degenerating odontoclasts and resorbed enamel surface from which the odontoclasts had moved or detached in the transitional stage of shedding (Sahara et al, 2004). This might indicate completion of resorptive process in the radicular part under heavy forces.…”