New cellular models for tracking the odontoblast phenotype.

Odontoblasts and osteoblasts differ functionally and histologically. Because of their close relationship, mesenchymal cells derived from teeth and bone are difficult to distinguish ex vivo. Indeed, the main non-collagenous components of the odontoblastic extracellular matrix, dentin sialoprotein (DSP) or dentin matrix protein 1 (DMP1), have also been detected in osteoblasts. The need to develop cellular models of odontoblast differentiation and to identify markers specific for the odontoblast lineage, has led us to establish clonal cell lines from tooth germs of day 18 mouse embryos transgenic for an adenovirus-SV40 recombinant plasmid. In this study, we analyzed the phenotypes of three independent clones by RT-PCR and Western blot. These clones synthesised DSP, DMP1 and other extracellular matrix proteins typical of the odontoblast and are therefore likely to be derived from the pulp. Transcripts encoding a set of homeobox proteins involved in craniofacial development, such as Pax9, Msx1, Cbfa1, Dlx2 and 5 were also expressed albeit at a different level. These features of the pulpal clones are shared by the C1 mesodermal cells that are capable of differentiating along osteogenic, chondrogenic or adipogenic lineages In contrast, transcripts for two LIM-domain homeobox family genes (Lhx6 and Lhx7) were only detected in the dental clones. Since these genes are preferentially expressed in the mesenchyme of the developing tooth, this suggests that our transgenic-derived cell lines retain intrinsic properties of odontoblastic cells. They may help to characterise genes specifying the odontoblast phenotype and the signalling pathways underlying odontoblast differentiation.

TEGDMA modulates glutathione transferase P1 activity in gingival fibroblasts.

Dental resinous materials can contain large amounts (from 30 to 50%) of triethylene-glycol-dimethacrylate (TEGDMA). This compound leaches into aqueous media and is toxic to dental pulp, as well as to gingival fibroblasts in vitro. To elucidate the mechanism of TEGDMA toxicity, we investigated the effects on glutathione (GSH) level and glutathione transferase P1 (GSTP1) activity in cultured human gingival fibroblasts. TEGDMA cytotoxic concentrations (from 0.5 to 2 mM) induced a depletion of GSH without formation of oxidized GSH (GSSG). In fibroblasts expressing the wild-type GSTP1, TEGDMA both inhibited and potentiated GSTP1 activity at high (IC50 = 1.1 mM) and low concentrations, respectively. In contrast, cells expressing the GSTP1 *A/*B variant showed a weak inhibition of GST activity only, associated with greater sensitivity to drug toxicity. Biochemical analysis of GSTP1 inhibition revealed that TEGDMA is a non-competitive antagonist with respect to GSH and substrate. Thus, TEGDMA interference with GSH and GSTP1 activity may contribute to dental-resin-induced adverse effects.

The dentino-enamel junction revisited.

The dentino-enamel junction is not an simple inert interface between two mineralized structures. A less simplistic view suggests that the dentino-enamel junctional complex should also include the inner aprismatic enamel and the mantle dentin. At early stages of enamel formation, fibroblast growth factor (FGF)-2 is stored in and released from the inner aprismatic enamel, possibly under the control of matrix metalloproteinase (MMP)-3. The concentration peak for MMP-2 and -9 observed in the mantle dentin coincided with a very low labeling for TIMP-1 and -2, favoring the cross-talk between mineralizing epithelial and connective structures, and as a consequence the translocation of enamel proteins toward odontoblasts and pulp cells, and vice versa, the translocation of dentin proteins toward secretory ameloblasts and cells of the enamel organ. Finally, in X-linked hypophosphatemic rickets, large interglobular spaces in the circumpulpal dentin were the major defect induced by the gene alteration, whereas the mantle dentin was constantly unaffected. Altogether, these data plead for the recognition of the dentino-enamel junctional complex as a specific entity bearing its own biological characteristics.

[Mineralization of the dental pulp: contributions of tissue engineering to tomorrow's therapeutics in odontology]. / Minéralisation de la pulpe dentaire: apports de l'ingénierie tissulaire aux thérapeutiques de demain en odontologie.

When bioactive molecules such as bone sialoprotein (BSP), bone morphogenetic protein-7 (BMP-7, also termed OP-1) and chondrogenic Inducing Agents (CIA, A+4 and A-4) were implanted in the pulp of the first upper molars, mineralizations were induced. They were either limited to the formation of a reparative dentinal bridge closing the pulpal wound (CIA A+4), or filled the mesial part of the coronal pulp (BSP), or filled totally the pulp located in the root canal (BMP-7 and CIA A-4). Consequently, these molecules may change in the next future the every day practice in dentistry.