BMPs and FGFs target Notch signalling via jagged 2 to regulate tooth morphogenesis and cytodifferentiation.

The Notch signalling pathway is an evolutionarily conserved intercellular signalling mechanism that is essential for cell fate specification and proper embryonic development. We have analysed the expression, regulation and function of the jagged 2 (Jag2) gene, which encodes a ligand for the Notch family of receptors, in developing mouse teeth. Jag2 is expressed in epithelial cells that give rise to the enamel-producing ameloblasts from the earliest stages of tooth development. Tissue recombination experiments showed that its expression in epithelium is regulated by mesenchyme-derived signals. In dental explants cultured in vitro, the local application of fibroblast growth factors upregulated Jag2 expression, whereas bone morphogenetic proteins provoked the opposite effect. Mice homozygous for a deletion in the Notch-interaction domain of Jag2 presented a variety of severe dental abnormalities. In molars, the crown morphology was misshapen, with additional cusps being formed. This was due to alterations in the enamel knot, an epithelial signalling structure involved in molar crown morphogenesis, in which Bmp4 expression and apoptosis were altered. In incisors, cytodifferentiation and enamel matrix deposition were inhibited. The expression of Tbx1 in ameloblast progenitors, which is a hallmark for ameloblast differentiation and enamel formation, was dramatically reduced in Jag2(-/-) teeth. Together, these results demonstrate that Notch signalling mediated by Jag2 is indispensable for normal tooth development.

Tissue-dissolving capacity and antibacterial effect of buffered and unbuffered hypochlorite solutions.

OBJECTIVE: The goal of this study was to compare the dissolving potential of Dakin's solution with that of equivalent buffered and unbuffered sodium hypochlorite solutions on fresh and decayed tissues. In addition, the antimicrobial effect of Dakin's solution and equivalent unbuffered hypochlorite was tested. STUDY DESIGN: Tissue specimens were obtained from freshly dissected pig palates. Unbuffered 2.5% and 0.5% sodium hypochlorite solutions and 0.5% solutions buffered at a pH of 12 and a pH of 9 (Dakin's solution) were tested on fresh and decayed tissue. Tissue decay was assessed histologically. Antimicrobial testing was performed with Enterococcus faecalis in dentin blocks and on filter papers. RESULTS: The 2.5% NaOCl solution was substantially more effective than the three 0.5% solutions in dissolving the test tissues. Buffering had little effect on tissue dissolution, and Dakin's solution was equally effective on decayed and fresh tissues. No differences were recorded for the antibacterial properties of Dakin's solution and an equivalent unbuffered hypochlorite solution. CONCLUSIONS: In contrast to earlier statements, the results of this study do not demonstrate any benefit from buffering sodium hypochlorite with sodium bicarbonate according to Dakin's method. An irrigation solution with less dissolving potential may be obtained by simply diluting stock solutions of NaOCl with water.