Adrian K. Jowett

Identification of BMP-4 as a signal mediating secondary induction between epithelial and mesenchymal tissues during early tooth development

Growth factor-mediated signaling has been implicated in the regulation of epithelial-mesenchymal interactions during organogenesis. Bone morphogenetic protein 4 (BMP-4), a member of the transforming growth factor beta superfamily, is expressed in the presumptive dental epithelium at the initiation of tooth development. Subsequently, epithelial signaling leads to mesenchymal induction of BMP-4 expression. To address the role of this factor, BMP-4-releasing agarose beads were added to dental mesenchyme in culture. These beads induced a translucent mesenchymal zone similar to that induced by dental epithelium. Moreover, three transcription factors (Msx-1, Msx-2, and Egr-1) whose expression is governed by epithelial signaling were induced in response to BMP-4. In addition, BMP-4 induced its own mesenchymal expression. These findings support the hypothesis that BMP-4 mediates epithelial-mesenchymal interactions during early tooth development.

Biologic Interaction of Three-Dimensional Periodontal Fibroblast Spheroids With Collagen-Based and Synthetic Membranes

BACKGROUND Cell-based therapy using autologous cells has been suggested as a potential approach for periodontal tissue regeneration. Spheroid systems are a form of three-dimensional cell culture that promotes cell matrix interaction, which could recapitulate the aspect of cell homeostasis in vivo. The aim of this study is to assess the interaction of periodontal fibroblast spheroids with synthetic and collagen-based membranes that have been used in guided tissue regeneration. METHODS Commercially available normal human periodontal ligament fibroblasts were grown in spheroid forms using a liquid overlay technique and then transplanted onto a collagen-based and a polyglycolic acid-based membrane. The biologic interaction of the spheroids with the membranes was assessed using basic histology, Alamar blue tissue viability assay, scanning electron microscopy, and immunohistochemical analysis. RESULTS Periodontal fibroblast spheroids adhered to both membranes, and the cells were able to proliferate and migrate from the spheroids both horizontally and vertically into the membrane scaffolds. Immunohistochemical analysis showed expression of collagen type I, periostin, and Runx2 by the periodontal fibroblasts. CONCLUSION Periodontal fibroblast spheroids were able to grow three-dimensionally on the biologic membranes and may have the potential to be used together with guided tissue regeneration approaches as an adjunct for periodontal regeneration.

Immunofluorescent lectin binding patterns and glycoprotein co-localization in the developing murine molar tooth.

Fluorescein-conjugated lectins were used in conjunction with antibodies to laminin, tenascin and amelogenin to investigate saccharide expression in the developing tooth germ. At the bud stage, peanut agglutinin (PNA) binding demonstrated residues that may be D-galactose-(beta 1----3)DGalNAc, and this staining occurred after the expression of tenascin. Only the cap-stage enamel organ suprabasal cells and the enamel knot stained intensely with Ulex europeus agglutinin-I, but not Lotus tetragonolobus agglutinin, implying the transient presence of blood group H type I oligosaccharides. At the late stages of amelogenesis, enamel synthesis is preceded by en bloc loss of inner enamel basement membrane components. Before this, Bandeiraea (Griffonia) simplicifolia--I (BSL-I) staining was lost from postmitotic ameloblasts, suggesting that a glycosylated species is initially removed. Additionally, PNA was co-localized with amelogenin protein, suggesting that it may express beta-D-galactosyl sequences. These results indicate that the glycosylation patterns of matrix components during odontogenesis may be important as they vary in a manner similar to that of the well-known glycoproteins.

Mucosa and taste buds of the human epiglottis

The position of taste buds around the human mouth, pharynx and larynx is outlined in many texts. While their distribution, histological differences and taste sensitivity on the dorsum of the tongue are well described, extralingual taste buds are described in far less detail both in adults (Bannister, 1995) and neonates (Lalonde & Eglitis, 1961). Studies on a variety of grazing mammals (e.g. Bradley et al. 1980 in sheep; Shrestha et al. 1993 in buffalo), omnivores (Andrew & Oliver, 1951 in rat) and carnivores (Palmieri et al. 1983 in cat and dog) have shown abundant taste buds on the laryngeal surface of the epiglottis. Some authors have suggested that these taste buds may be important in initiating reflexes protecting the airway (Bradley et al. 1980) and in this context it is surprising that literature on their distribution on the human epiglottis is not available.

Biocompatibility testing of a posterior composite and dental cements using a new organ culture model

Mandibular first molars from day 14 and 17 mouse embryos were cultured in vitro for 7 days in chemically defined Pratts medium in a submerged culture system. Ameloblast and odontoblast polarization and morphogenesis occurred in the control tooth germs. Discs of Occlusin, Silicate, ChemFil, IRM and Dycal were exposed to the culture system as either fresh material, leached discs (by pre-incubation in media) or the leachate from the incubated discs. Their effects on dental differentiation were assessed histologically. Day 17 tooth germs were slightly more sensitive to the effects of the exogenous agents than day 14 tooth germs. In general, silicate and ChemFil were toxic, IRM was slightly less toxic and the major effect was from the leachate. Dycal was toxic but most of this effect resulted from pH changes in the leachate. Occlusin was the most biocompatible material tested. Only a very mild adverse effect was detected, and this appeared to be caused by an agent (not a pH change) released into the leachate.

In vitro biocompatibility testing: A new organ culture model

Abstract Mandibular first molars from Theiler stage 25 mouse embryos were cultured in vitro for 7 days in Eagles minimum-essential medium supplemented with glutamine, glycine, ascorbic acid, penicillin, streptomycin and fungizone. Cadmium, zinc, copper and tin nitrate were added to give metallic levels up to 30 parts/10 6 . When the aliquoted solutions were analysed by inductively coupled plasma analysis, the measured level for each metal was markedly less than that calculated to have been aliquoted. At all measurable levels, cadmium caused overt cytotoxicity whereas zinc, copper and tin caused little cell death at levels below 20 parts/10 6 . Dentine matrix secretion was inhibited by 10 parts/10 6 of copper and 8 parts/10 6 of zinc. Additionally, the internal enamel epithelium failed to differentiate into polarized ameloblasts with copper above 1·5 parts/10 6 and zinc above 5 parts/10 6 . Tin caused loss of papillary Alcian blue staining, but cellular differentiation did not appear to be affected below 18 parts/ 10 6 . Preliminary investigations of amalgam biocompatibility using this system indicate that although gross corrosion of the samples occurred, all corrosion products were particulate and so removed by filter-sterilization. Amalgam was corroded as single pellets placed in 9 g/1 saline at a volume of 40 mm 2 pellet area per millilitre and incubated for between 2 and 10 weeks at 60°C. Caution must therefore be exercised in interpreting data from biocompatibility studies in vitro as the proportion of particulate and soluble material is unknown, as is the significance of their action. Defined organ culture of tooth germs appears to be a useful model for in vitro biocompatibility testing despite the complexity of the effects observed.

A double blind randomised controlled clinical trial comparing a novel anti-stain and calculus reducing dentifrice with a standard fluoride dentifrice.

OBJECTIVES This clinical trial tested the anti-stain efficacy at 3 and 6 months of a novel, sodium polyaspartate-containing, anti-stain dentifrice. In addition, the efficacy of the new dentifrice in controlling gingival inflammation and inhibition of calculus deposition was tested. METHODS Participants were recruited to this double blind randomised control clinical trial, and allocated to either test or control groups. The presence of stain and calculus were entry criteria. Measurements of stain, calculus and gingival inflammation were recorded using the Shaw and Murray Stain score, Volpe-Manhold Calculus score and the Modified Gingival Index respectively. Measurements were made at baseline, prior to the removal of stain and calculus, and after 3 and 6 months. Missing data were imputed by and the outcomes were analysed using univariate analysis. RESULTS At three months, toothpaste containing sodium polyaspartate was better (difference of mean 1.13 with SEM 0.57) than control for the control of dental stain (p<0.05). Stain scores also showed a trend in favour of the test product (difference of mean 1.03 with SEM 0.78) at six months (p>0.05). There was no difference between toothpastes with respect to calculus deposition or gingival inflammation. CONCLUSIONS Toothpaste containing sodium polyaspartate was more effective than a control toothpaste at preventing deposition of dental stain for 3 months after professional tooth cleaning but showed no significant effect at 6 months. CLINICAL RELEVANCE Sodium polyaspartate toothpaste was more effective than a control toothpaste at preventing dental stain formation and maybe helpful in controlling staining between episodes of scaling and polishing.

Evaluation of Osteogenic and Cementogenic Potential of Periodontal Ligament Fibroblast Spheroids Using a Three-Dimensional In Vitro Model of Periodontium.

The aim of this study was to develop a three-dimensional in vitro model of periodontium to investigate the osteogenic and cementogenic differentiation potential of the periodontal ligament fibroblast (PDLF) spheroids within a dentin-membrane complex. PDLFs were cultured in both spheroid forms and monolayers and were seeded onto two biological collagen-based and synthetic membranes. Cell-membrane composites were then transferred onto dentin slices with fibroblasts facing the dentin surface and further cultured for 20 days. The composites were then processed for histology and immunohistochemical analyses for osteocalcin, Runx2, periostin, and cementum attachment protein (CAP). Both membranes seeded with PDLF-derived cells adhered to dentin and fibroblasts were present at the dentin interface and spread within both membranes. All membrane-cell-dentine composites showed positive staining for osteocalcin, Runx2, and periostin. However, CAP was not expressed by any of the tissue composites. It can be concluded that PDLFs exhibited some osteogenic potential when cultured in a 3D matrix in the presence of dentin as shown by the expression of osteocalcin. However the interaction of cells and dentin in this study was unable to stimulate cementum formation. The type of membrane did not have a significant effect upon differentiation, but fibroblast seeded-PGA membrane demonstrated better attachment to dentin than the collagen membrane.

Did the Market Force Subject Review? A Case Study.

This study sought to discover if staff in a university department believed the 1998 Subject Review to be a valid Quality Assurance process and if its findings could benefit the department. Fifteen academic staff members took part in semi-structured interviews and the content of their responses was analysed qualitatively. Respondents described how Subject Review arose from an emerging ethos of accountability in public services and the demand for performance indicators from stakeholders. By considering their own viewpoints, as non-academics, they identified with these pressures and accepted the need for Subject Review. The methodology of Subject Review was well understood by staff and they explained how it was unnecessarily bureaucratic for its aims. Respondents suspected that the outcome of Subject Review would have an effect on the Department’s place in the education marketplace and described why its impact would be minor. In explaining their views of Subject Review staff largely predicted the basis of the future quality assurance process.