Maturogenesis of an Immature Dens Evaginatus Nonvital Premolar with an Apically Placed Bioceramic Material (EndoSequence Root Repair Material®): An Unexpected Finding

Dens evaginatus is a dental developmental anomaly that arises due to the folding of the inner dental epithelium that leads to the formation of an additional cusp or tubercle on the occlusal surface of the affected tooth. This accessory tissue projection may carry with it a narrow and constricted pulp horn extension. Occasionally, the tubercle easily fractures, thus leading to microexposure of the pulp horn and eventual pulp necrosis. Often, the pulp necrosis occurs at a time the root development of the affected tooth is incomplete. Apexification with calcium hydroxide and mineral trioxide aggregates has been the mainstay of treatment options before root canal obturation in immature nonvital permanent teeth. Lately, regenerative endodontics (maturogenesis) is becoming one of the preferred treatment modalities to manage such teeth. The current case highlights the possibility of a bioceramic material (EndoSequence Root Repair Material, BC RRM-Fast Set Putty™, Brasseler, USA) which supposed to provide apical root closure (apexification) and could also induce continuation of root growth (maturogenesis).

An Explanation for How FGFs Predict Species-Specific Tooth Cusp Patterns

Species-specific cusp patterns result from the iterative formation of enamel knots, the epithelial signaling centers, at the future cusp positions. The expressions of fibroblast growth factors (FGFs), especially Fgf4, in the secondary enamel knots in the areas of the future cusp tips are generally used to manifest the appearance of species-specific tooth shapes. However, the mechanism underlying the predictive role of FGFs in species-specific cusp patterns remains obscure. Here, we demonstrated that gerbils, which have a lophodont pattern, exhibit a striped expression pattern of Fgf4, whereas mice, which have a bunodont pattern, have a spotted expression pattern, and these observations verify the predictive role of Fgf4 in species-specific cusp patterns. By manipulating FGFs’ signaling in the inner dental epithelium of gerbils, we provide evidence for the intracellular participation of FGF signaling, specifically FGF4 and FGF20, in Rac1- and RhoA-regulated cellular geometry remolding during the determination of different cusp patterns. Our study presents a novel explanation of how different FGF expression patterns produce different cusp patterns and implies that a conserved intracellular FGF-GTPase signaling module might represent an underlying developmental basis for evolutionary changes in cusp patterns.

Autoradiographic study of the formation of enameloid and dentine matrices in teleost fishes using tritiated amino acids

The patterns of synthesis and secretion of the matrix proteins of dentine and enameloid were studied in developing teleost teeth by light microscope autoradiography after injection of 3 H-proline in the ballan wrasse and after injection of 3 H-proline or 3 H-tyrosine in the common eel. In both species, the collagenous matrix of dentine was laid down incrementally, as in the teeth of tetrapods. In the wrasse, it was observed that both the odontoblasts and the inner dental epithelium secreted protein into the matrix of the enameloid forming the tooth tip (cap enameloid). It is concluded that the protein secreted by the odontoblasts is collagen and that the matrix of cap enameloid increases in bulk by deposition of collagen at the surface of the papilla. The protein secreted by the inner dental epithelium diffused into the preformed enameloid matrix. In the eel, the epithelial and odontoblastic components of enameloid matrix were not clearly distinguishable in the experiment with 3 H-proline but, when 3 H-tyrosine was employed, the labelling of collagen was reduced to a low level and the protein secreted by the inner dental epithelium was demonstrable. In both the wrasse and the eel, the inner dental epithelium continued to secrete protein into the enameloid for some time after mineralization of the tissue had commenced. Because the epithelial com­ponent of enameloid diffused into the matrix, unlike the collagenous odontoblastic component, and because the former protein was labelled more intensely with 3 H-tyrosine than the latter, it is concluded that the enameloid protein originating from the inner dental epithelium resembles the matrix proteins (amelogenins) of mammalian enamel in organization and composition. Enameloid matrix is, therefore, a composite tissue containing collagen and an amelogenin-like protein. It is suggested that the epithelial protein plays an important part in enameloid mineralization and may be responsible for initiating the removal of collagen from the matrix by a non-enzymatic mechanism. Enameloid as found in fishes could have evolved into true enamel either by a prolongation of the secretory activity of the inner dental epithelium (Poole 1971) or by a delay in the onset of this activity. It was found that collar enameloid is homologous with cap enameloid, not with enamel, and that the cuticle overlying the cap enameloid in teleosts is produced entirely by the inner dental epithelium.