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Biomedical subjects

A J Sloan

Publications and source records attributed to A J Sloan.

16 recordsLinked to original sources
PubMed2003

The influence of fluoride on the cellular morphology and synthetic activity of the rat dentine-pulp complex in vitro.

Exposure to high fluoride concentrations in the immediate environment of the tissue is recognized to result in the post-translational modification of non-collagenous dentine extracellular matrix (ECM) components, potentially altering dentine mineralization. However, less is known about the effects of fluoride exposure on the morphology or metabolism of the cells associated with the dentine-pulp complex. This study examined the effects of fluoride exposure at defined concentrations on the cellular morphology and ECM synthetic activities of odontoblasts and pulpal fibroblasts by the culture of tooth sections from male Wistar rat incisors in Trowel-type cultures for up to 14 days, in the presence and absence of 6mM sodium fluoride. Histomorphometric analysis of the dentine-pulp complex of sodium fluoride-exposed tooth sections demonstrated no obvious gross morphological differences with respect to the odontoblasts and pulpal fibroblasts throughout the 14-day culture period, in comparison with unexposed tooth sections. No significant differences in odontoblast and pulpal fibroblast cell numbers were determined in the absence and presence of fluoride. Image analysis examination of odontoblast cytoplasmic:nuclear (C/N) ratios also showed no significant differences in fluoride-exposed and unexposed tooth sections, although reductions in the C/N ratios of pulpal fibroblasts were evident in fluoride-exposed sections at days 10 and 14. No significant differences in predentine width were observed in fluoride-exposed and unexposed tooth sections over the 14-day culture period. Autoradiography following [3H]proline incorporation into the dentine-pulp complex demonstrated inhibition of collagen synthesis, particularly by the odontoblasts in tooth sections exposed to 6mM sodium fluoride. These findings, in association with those from previous studies, imply that dentine ECM alterations may contribute to the altered mineralization of dentine during fluorosis, rather than secretory-related changes in odontoblast morphology.

Animals↗
PubMed2002

Analysis of incisor pulp cell populations in Wistar rats of different ages.

Pulp cell function and viability is important for maintaining tooth vitality throughout life. However, the effects of ageing on pulpal cell populations and pulp tissue remodelling are still unclear. The aim here was to quantify age-related cell-density changes in the pulp of rat incisor teeth, using histomorphometric analysis and ANOVA. Mandibular (n=35) and maxillary (n=34) incisors were carefully extracted from 20 Wistar rats aged between 1 and 18 months, fixed and processed for light microscopy. Cell counts were performed in mature and immature regions at both labial and lingual aspects of all teeth. Odontoblast and subodontoblast cell densities were reported per mm of pulp-dentine border and core fibroblast density per mm2 pulp tissue. Irrespective of age, odontoblast and subodontoblast densities were lower in the immature than the mature regions of both maxillary and mandibular incisors (P<0.001). However, in both regions odontoblast and subodontoblast densities decreased significantly with increasing age (P<0.0001). The age-related reduction in odontoblasts was significantly greater in mature than immature regions (P<0.02) but not influenced by other variables. In contrast, the age-related reduction in subodontoblasts was significantly different between mandibular and maxillary teeth (P=0.012) but not influenced by site. Unlike odontoblasts and subodontoblasts, core fibroblasts showed small but significant increases with increasing age (P<0.0001). These age-related reductions in the density of odontoblasts and subodontoblasts may partly explain the slower rate of secondary dentine secretion and decreased pulp repair activity associated with ageing.

Aging↗
PubMed2002

Effects of alginate hydrogels and TGF-beta 1 on human dental pulp repair in vitro.

The objective of this study was to investigate the use of alginate hydrogels to present either exogenous or endogenous transforming growth factor (TGF)-beta 1 to the dentin-pulp complex to signal reparative processes. Hydrogels were prepared, applied to cultured human tooth slices and the effects on tertiary dentinogenesis examined histologically. Both TGF-beta 1-containing and acid-treated alginate hydrogels, but not untreated hydrogels, upregulated dentin matrix secretion and induced odontoblast-like cell differentiation with subsequent secretion of regular tubular dentin matrix on cut pulpal surfaces. It is concluded that TGF-beta 1 can signal both induction of odontoblast-like cell differentiation and upregulation of their matrix secretion in the human dentin-pulp complex. Alginate hydrogels provide an appropriate matrix in which dental regeneration can take place and may also be useful for delivery of growth factors, including TGF-beta s, to enhance the natural regenerative capacity of the dental pulp.

Acids↗
PubMed2002

TGF-beta latency-associated peptides (LAPs) in human dentin matrix and pulp.

Transforming growth factor (TGF)-beta s in dentin matrix provide a pool of bioactive molecules, but association with latency-associated peptides (LAPs) may influence their activity. We investigated TGF-beta 1, -beta 2, and -beta 3 LAP expression in sound and carious human teeth. Teeth were fixed and processed immediately following extraction prior to staining with rabbit polyclonal antibodies to the TGF-beta LAPs. A soluble dentin matrix fraction was prepared from dissected human dentin and sequential extraction of pulpal ECM was performed prior to purification. Fractions were Western blotted and probed with the LAP antibodies. All three LAPs were present in odontoblasts, cells of the pulp, and predentin; however, no staining of mineralized dentin matrix was seen. Similar patterns of expression were seen in carious tissue. Expression of TGF-beta LAPs in cells and pulpal matrix of healthy and carious teeth will be important in regulation of TGF-beta activity and may modulate the tissue response to injury.

Dental Caries↗
PubMed2001

Trans-dentinal stimulation of tertiary dentinogenesis.

Trans-dentinal stimulation of tertiary dentinogenesis has long been recognized, and has traditionally been ascribed to diffusion of irritant substances arising during injury and restorative treatment. Identification of bio-active components, especially growth factors including TGF-beta s, sequestered within dentin matrix provides a new explanation for cellular signaling during tertiary dentinogenesis. Both isolated dentin matrix components and pure growth factors (TGF-beta s) have been shown to signal cellular events leading to reactionary and reparative tertiary dentinogenesis. Release of these bio-active components from dentin matrix may arise during carious attack and other injury to the tissue, and also during subsequent surgical intervention and restoration of the tooth. Both cavity-conditioning agents and leaching from restorative materials may contribute to release of these components. Distance of diffusion, as determined by cavity residual dentin thickness, and other restorative parameters may influence the signaling process after release of these components. Careful consideration of the interplay between tissue injury and surgical and restorative material factors is required for optimum exploitation of the exquisite regenerative capacity of dentin-pulp for more biological approaches to clinical treatment of dental disease.

Animals↗
PubMed2001

Expression of TGF-beta receptors I and II in the human dental pulp by in situ hybridization.

Members of the TGF-beta family of growth factors are important in modulation of odontoblast secretory activity during dental tissue repair. Odontoblast expression of TGF-beta isoforms during development leads to their sequestration within the dentin matrix, from where they may be released during carious injury and participate in reparative processes. Two receptors, implicated in TGF-beta-mediated cell signaling, have been identified immunohistochemically in both odontoblasts and pulpal cells of healthy and carious human molar teeth. This study aimed to characterize the expression of the TGF-beta receptors I and II in sound and carious teeth by means of in situ hybridization, to help our understanding of the response of these cells to TGF-beta stimulation. Sound and carious human third molar teeth were routinely processed immediately following extraction, and 10-microns paraffin-embedded sections prepared. These sections were hybridized with 32P-labeled probes to TGF-beta receptors I and II, and the subsequent signal was detected by autoradiography. mRNA for both receptors I and II was mainly detected within the odontoblasts and nerve-associated cells of healthy tissues, with expression at lower levels seen within the subodontoblast and pulp core cells. The expression in odontoblasts was higher for TGF-beta receptor I than for receptor II. Expression of both receptors was more homogenous in all pulp cells within carious teeth, because of an increase of signal within the underlying pulp cell population, including blood-vessel-associated cells. We conclude that the TGF-beta receptors I and II were expressed in odontoblasts and pulp cells, and that subtle variations in the levels of their expression could be involved in the tissue response to injury.

Activin Receptors, Type I↗
PubMed2000

Stimulation of the rat dentine-pulp complex by bone morphogenetic protein-7 in vitro.

Human recombinant bone morphogenetic protein-7 (BMP-7), when applied to freshly cut dentine in monkey teeth, stimulated tertiary dentine formation, but it is unclear whether this response involved upregulation of the synthetic and secretory activity of existing odontoblasts or the induction of differentiation of new odontoblast-like cells. Using a recently developed organ-culture system for whole tooth slices, the aim here was to examine the effects of BMP-7 on the stimulation and modulation of existing odontoblasts in the absence of tissue injury. Agarose beads were soaked in a 500 ng/ml or 100 ng/ml solution of BMP-7 in culture medium and placed on the odontoblast area of the dentine pulp complex of rat tooth slices. The slices were embedded in a semisolid agar-based medium and cultured at the liquid gas interface for 7 days. Results showed that beads soaked in 500 ng/ml BMP-7 stimulated a localized increase in extracellular matrix secretion by odontoblasts at the site of application, with greater stimulatory effects than from the lower concentration. These effects may be important in the reparative processes after tissue injury within the dentine-pulp complex and may be useful in the therapeutic induction of tertiary dentinogenesis.

Animals↗
PubMed2000

Transforming growth factor-beta isoform expression in mature human healthy and carious molar teeth.

Transforming growth factor (TGF)-beta isoforms have been implicated in cellular signalling during tooth development and repair, but little is known of their cellular localisation or distribution within the dental tissues in the mature tooth. This study investigated the presence of TGF-beta1, beta2 and beta3 isoforms in tissues of sound and carious human molar teeth, to understand better the expression of TGF-betas during health and disease. In healthy tissues, odontoblasts, cells of the cell rich layer, pulpal fibroblasts and endothelial cells were stained to varying degrees for all isoforms, with TGF-beta3 showing the greatest intensity and TGF-beta1 the weakest intensity. Similar patterns of staining were observed in carious teeth; however, TGF-beta1 showed significantly increased staining intensity within odontoblasts and pulpal cells of carious teeth (p < 0.001). Biochemical analysis showed greater amounts of TGF-beta1 in tertiary dentine than in primary dentine samples. The expression of TGF-betas in odontoblasts and the increased presence of TGF-beta1 in tertiary dentine suggest that these isoforms may be important in odontoblast behaviour and the modulation of the tissue response to injury.

Edetic Acid↗
PubMed2000

Ultrastructural localisation of TGF-beta exposure in dentine by chemical treatment.

Transforming growth factor-beta (TGF-beta) sequestered in dentine matrix has an important role in dental tissue repair after injury and its exposure at sites of injury may stimulate tertiary dentinogenesis. This study aimed to investigate the expression of TGF-beta isoforms in mature human dentine matrix and the ability of chemical treatments to expose TGF-beta on the cut surface of dentine using gold immunolabelling and subsequent scanning electron microscopy examination. TGF-beta1 was the only isoform that could be detected in human dentine and the nature of the chemical treatment of the tissue influenced its detection. EDTA treatment provided good exposure of TGF-beta1 on the dentine surface, whilst citric acid and sodium hypochlorite treatments revealed lesser amounts of this isoform. Only minimal staining for TGF-beta1 was observed in samples treated with phosphate-buffered saline. TGF-beta2 and -beta3 could not be detected in the specimens with any of the treatments. This study suggests that TGF-beta1 is the only TGF-beta isoform expressed by human odontoblasts to be sequestered in dentine implying that differences in isoform-extracellular matrix interactions may exist. Information on chemical treatment of tissue specimens for immunostaining may provide a useful basis for selection of tissue preparation techniques for clinical restorative treatment procedures to facilitate TGF-beta mediated reparative processes at sites of dental injury.

Citric Acid↗
PubMed1999

Stimulation of the dentine-pulp complex of rat incisor teeth by transforming growth factor-beta isoforms 1-3 in vitro.

Expression of transforming growth factor-beta (TGF-beta) isoforms by odontoblasts leads to their sequestration within dentine matrix. TGF-beta1 and -beta3 stimulate matrix secretion and also initiate odontoblast cytodifferentiation in vitro and in vivo. Using a recently established organ-culture model, the aim here was to examine the effects of TGF-beta isoforms on the response of the dentine-pulp complex during culture. Agarose beads were soaked in isoforms 1-3, and placed on the odontoblast area of slices of 28-day-old rat incisor tooth. The slices were maintained in Trowel-type cultures for 7 days. Both TGF-beta1 and -beta3 stimulated a local increase in predentine secretion at the site of the bead application when compared to control cultures. Mitogenic effects on the cells of the subodontoblast layer were also seen and occasionally small foci of newly differentiated odontoblast-like cells could be observed a little distant from the application site of TGF-beta3. TGF-beta2 had a minimal effect on the cultured tissues. These results demonstrate that TGF-beta1 and -beta3 can stimulate secretion of extracellular matrix by odontoblasts, are mitogenic to pulp cells, and that TGF-beta3 may have inductive effects on pulpal cells. Such activities might be important during reparative processes in the dentine-pulp complex after tissue injury.

Animals↗
PubMed1999

TGF-beta receptor expression in human odontoblasts and pulpal cells.

Transforming growth factor-beta (TGF-beta) isoform expression by odontoblasts leads to their sequestration within the dentine matrix, from where they may be released during caries and participate in the reparative processes. Two receptor types for TGF-beta have been implicated in TGF-beta induced signalling. The aim of this study was to characterise immunohistochemically the expression of these receptors in sound and carious human teeth to facilitate our understanding of the ability of these cells to respond to TGF-beta stimulation. Sound and carious human teeth were routinely processed and paraffin sections stained for TGF-beta receptors I and II, using the StrAviGen immunoperoxidase method. Strong specific staining for both receptor types was observed in the odontoblasts of healthy teeth with the greatest intensity seen with receptor I. Staining of weaker intensity was also observed for both receptors in the underlying cell rich area and pulp core. Similar patterns of staining were observed within carious tissues. We conclude that odontoblasts and other cells of the pulp of mature human molar teeth show the presence of both TGF-beta receptors I and II in health and disease with odontoblasts showing the strongest expression. Such findings may be important in the response of these cells to tissue injury.

Activin Receptors, Type I↗
PubMed1998

An in vitro approach for the study of dentinogenesis by organ culture of the dentine-pulp complex from rat incisor teeth.

Culture of the developing dental tissues has contributed to understanding of developmental processes during early odontogenesis. However, to understand fully the mechanisms involved during dentinogenesis and tissue repair there is a need to develop culture models for the dentine-pulp complex from more mature dental tissues. This study describes the development of a system for the organ culture of mature rodent teeth. Slices of incisors from 28-day-old rats were embedded in a semisolid, agar-based medium and cultured on floating Millipore filters at the liquid-gas interface for up to 14 days. Preservation of cell and tissue morphology was observed throughout the entire dentine-pulp complex after each culture period and autoradiographic studies showed that the odontoblasts were actively synthesizing and secreting extracellular matrix during culture. Transmission electron microscopy confirmed that the phenotypic morphology of the odontoblasts had been maintained during culture. These results demonstrate that the dentine-pulp complex from mature rodent tissues can be cultured successfully for substantial periods of time and will provide a useful model for the study of dentinogenesis and tissue repair.

Animals↗