High-resolution electron-microscopic study of the relationship between human enamel and dentin crystals at the dentinoenamel junction

Abstract

The development of dentin and of enamel share a common starting locus: the dentinoenamel junction (DEJ). In this study the relationship between enamel and dentin crystals has been investigated in order to highlight the guiding or modulating role of the previously mineralized dentin layer during enamel formation. Observations were made with a high-resolution electron microscope and, after digitalization, image-analysis software was used to obtain digital diffractograms of individual crystals. In general no direct epitaxial growth of enamel crystals onto dentin crystals could be demonstrated. The absence of direct contact between the two kinds of crystals and the presence of amorphous areas within enamel particles at the junction with dentin crystals were always noted. Only in a few cases was the relationship between enamel and dentin crystals observed, which suggested a preorganization of the enamel matrix influenced by the dentin surface structure. This could be explained either by the existence of a proteinaceous continuum between enamel and dentin or by the orientation of enamel proteins by dentin crystals.

Calcium orthophosphates (CaPO 4 ): Occurrence and properties

“…Some authors claim that enamel crystals grow epitaxially on the preexisting dentine crystals because of a high continuity between enamel and dentine crystals (Arsenault and Robinson 1989;Hayashi 1992Hayashi , 1993. Others have shown that enamel crystals are formed at a given distance from the dentine surface (Simmer and Fincham 1995;Diekwisch et al 1995;Aoba 1996;Bodier-Houllé et al 2000) and could either reach dentine crystals by a subsequent growth (Takano et al 1996) or remain distant (Bodier-Houllé et al 2000;Dong and Warshawsky 1996). In addition, there are both a cementum-enamel junction (CEJ) (Wang et al 2006b), which is quite similar to DEJ, and a cementumdentine junction (CDJ) (Ho et al 2004(Ho et al , 2005Jang et al 2014).…”

Apatite Biominerals

“…A small deviation of crystal orientation across each prism can be observed in densely packed enamel apatite prisms. Small disorientation angles have also been identified between enamel and dentin crystals excluding epitactic relationships [113]. Several studies report that the ribbon-like shaped structures formed at the earliest stage of enamel formation include a non-crystalline mineral (ACP) and/or octacalcium phosphate (OCP) crystals, both potent precursors of enamel apatite [114,115].…”

“…Beniash et al [116] hypothesize that this transformation can be triggered by proteolytic degradation of the enamel matrix proteins and suggest that the shape and organization of the mineral particles is determined very early, implying direct control of mineral shape and organization by the matrix proteins. Bodier-Houllé et al [113] have also identified the presence of amorphous calcium phosphate at the interface of enamel and dentin (dentino-enamel junction).…”

“…The crystals grow bigger and their composition can be strongly altered [147]. Although the ions released by dissolution can certainly be locally reused at the precipitation loci, similar to the in vivo remodeling of bone, the system around the fossil is largely open and several foreign elements stabilizing the apatite structure such as fluorine, silicon, heavy metals (Pb, Ba) and rare earth elements play a determining role in this recrystallization, modify the apatite composition and characteristics [113]. The kinetics of these processes depend on the presence of groundwater, dissolved mineral ions, pH and temperature and also on the fossil apatite characteristics (composition, crystal size) and fossil porosity [141,144,147].…”

“…Several studies report that the ribbon-like shaped structures formed at the earliest stage of enamel formation include a non-crystalline mineral (ACP) and/or octacalcium phosphate (OCP) crystals, both potent precursors of enamel apatite [114,115]. Several authors have identified an amorphous calcium phosphate phase which transforms with time into the final apatitic crystalline mineral during enamel formation in murine incisor teeth [113,115,116]. Beniash et al [116] hypothesize that this transformation can be triggered by proteolytic degradation of the enamel matrix proteins and suggest that the shape and organization of the mineral particles is determined very early, implying direct control of mineral shape and organization by the matrix proteins.…”