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Biomedical subjects

J Kirkham

Publications and source records attributed to J Kirkham.

At least 55 records · Page 3Linked to original sources
PubMed1996

The chemical composition of tooth enamel in recessive dystrophic epidermolysis bullosa: significance with respect to dental caries.

Previous reports have linked the prevalence of tooth abnormalities with high caries experience in the different types of epidermolysis bullosa (EB). However, it is not known to what extent the apparent susceptibility to enamel caries is due to disease-related altered enamel chemistry in these cases. The aim of this study was to characterize the enamel of teeth from patients suffering from recessive epidermolysis bullosa dystrophica (rEBD) in terms of its mineral content, carbonate content, protein content, and amino acid composition. The results showed that dental enamel from these patients was essentially normal in terms of its chemistry. It is therefore concluded that the high caries experience in recessive dystrophic epidermolysis bullosa patients is probably related to other factors, such as compromised oral hygiene and prolonged oral clearance due to extensive oral soft tissue damage and a cariogenic diet.

Amino Acids↗
PubMed1996

Crystal growth in dental enamel: the role of amelogenins and albumin.

Amelogenin-mineral interactions were investigated using an in vitro binding approach. Rat incisor enamel matrix proteins (mainly amelogenins) were dissolved in synthetic enamel fluid and allowed to equilibrate with deproteinised developing enamel crystals. The results showed that amlogenin proteins of 21, 23, 24, 26 and 27-kDa (corresponding to nascent and partially degraded amelogenins) were associated with the crystals whilst the lower Mr amelogenins (< 21 KDa) remained free in the synthetic enamel fluid. These data suggest the nascent and partially degraded amelogenins may interact with developing enamel crystals and could influence their growth. Albumin-mineral interactions were investigated by extracting developing rat incisor enamel with synthetic enamel fluid. Insoluble material (including the enamel crystals) was then further extracted with 0.1 M phosphate buffer (pH 7.4) to desorb any mineral bound proteins. Western blotting using anti-albumin antibodies showed that almost all of the albumin from the secretory stage enamel and a significant proportion of the albumin present in early transition stage was extractable in the synthetic enamel fluid. However, synthetic enamel fluid did not extract albumin from late transition or maturation stage tissue, which could only be removed following further extraction with phosphate buffer. Albumin degradation was apparent during the transition and maturation stages, where it is degraded and ultimately removed. This binding pattern may be related to amelogenin degradation and removal during the transition stage, permitting albumin access to the previously obscured crystal surfaces. That the secretory stage matrix appears to "protect" secretory stage crystals from albumin may be an important consideration in the aetiology of enamel hypoplasias (i.e. incomplete crystal growth) and when using dissociative extraction procedures for the identification of mineral bound proteins.

Albumins↗
PubMed1996

The rat amelogenin gene--some aspects of evolution and expression.

This study presents data to support the hypothesis that a major portion of the coding sequence of the amelogenin gene may have arisen by tandem duplication of internal sequences which as a consequence has introduced several additional potential RNA splice acceptor sites into the sequence. This duplication of splice sites has led to an increase in the heterogeneity of amelogenin forms found in developing enamel. By screening a rat enamel organ cDNA library for alternatively spliced products, it appears that as much as 20% of the amelogenin mRNA molecules may be alternatively spliced forms.

Alternative Splicing↗
PubMed1995

The effect of glycosylaminoglycans on the mineralization of sheep periodontal ligament in vitro.

The effect of removal of glycosylaminoglycans on the mineralization of sheep periodontal ligament was determined using enzyme digests followed by incubation in solutions supersaturated with respect to hydroxyapatite at pH 7.4. TEM revealed that control periodontal ligament remained unmineralized. However, tissue from which glycosylaminoglycans had been removed contained plate-like crystals arranged parallel to and within the collagen fibrils. Electron probe and electron diffraction studies suggested that the crystals were apatitic with a similar order of crystallinity to dentine, and a Ca:P ratio of 1.61. In addition, the glycosylaminoglycan content of periodontal ligament, cementum and alveolar bone was compared using cellulose acetate electrophoresis. Periodontal ligament contained predominantly dermatan sulfate while cementum and alveolar bone contained mostly chondroitin sulfate. A role for glycosylaminoglycans in maintaining the unmineralized state of the periodontal ligament is suggested. Control of expression of specific proteoglycan species on a spatially restricted basis is presumably central to this role.

Alveolar Process↗
PubMed1995

The control of ingress of albumin into developing enamel from adjacent dentine of the rat incisor.

The present study used an immunohistochemical approach to map the distribution of albumin within the dentine adjacent to the developing enamel of both impeded and unimpeded rat incisors to determine if the dentine could be a possible route of entry for this protein into the developing enamel matrix. In dentine adjacent to the secretory and transition stages of the developing enamel, the dentinal tubules were labelled only over approximately the pulpal quarter of their length. The bulk of the dentine showed no labelling. However, labelling within the dentine appeared at the ADJ at a position approximately 2.5 mm occlusal to the distal root of the first molar, adjacent to enamel with no visible residual matrix. The results of this study suggest that adventitious ingress of albumin into enamel from the dentine is restricted during enamel secretion and can only potentially occur once enamel maturation has been initiated.

Albumins↗
PubMed1995

The chemistry of enamel development.

The central problems of enamel biochemistry are the mechanisms concerned with initiation and development of the mineral crystals, together with their architectural arrangement within the tissue. These processes are mediated by the extracellular matrix as well as the composition of the mineral itself. Initial mineral deposition occurs at the dentine surface, nucleated either by dentinal components or early enamel matrix, possibly non-amelogenin molecules. The early crystals are small in size and rich in magnesium and carbonate resulting in relatively poor crystallinity. This is in spite of the fact that fluoride is high at this stage. Crystal development includes a reduction in magnesium, carbonate and fluoride as crystals increase in length following the retreating ameloblasts from the dentine. The matrix acquires increasing concentrations of amelogenin and albumin. Prismatic structure begins to develop together with some growth of crystals in width and thickness. Degradation of amelogenin and non-amelogenin molecules generates a series of specific molecular fragments possibly concerned with modulating crystal growth and morphology and the creation of prismatic and interprismatic structures. Towards the end of secretion, matrix, now almost completely degraded, is replaced by fluid followed by massive crystal growth during maturation. Degradation of albumin also occurs at this stage, probably as a result of comprehensive destruction of molecules which might impair crystal growth. Selective acquisition of magnesium and fluoride at this stage may reflect the hydrated state of the tissue as well as cell changes. Fluid is displaced as crystals grow and the enamel acquires concentrations of mineral characteristic of mature tissue.

Ameloblasts↗
PubMed1994

Isolation and characterisation of an alternatively-spliced rat amelogenin cDNA: LRAP--a highly conserved, functional alternatively-spliced amelogenin?

A cDNA coding for a 59 amino acid polypeptide containing both the carboxy- and amino-termini, but lacking the central domain, of the rat tooth enamel matrix protein, amelogenin, was cloned and sequenced. The deduced polypeptide sequence indicates that this cDNA was derived from an amelogenin RNA molecule by using an alternative intra-exonic 3' splice acceptor site. This alternatively spliced product is almost identical to products previously identified in both cow and mouse enamel organs: the leucine-rich amelogenin peptide (LRAP). The conservation of this truncated polypeptide across the species suggests that it may have an important role in the formation of tooth enamel.

Alternative Splicing↗
PubMed1994

Molecular cloning and DNA sequence of rat amelogenin and a comparative analysis of mammalian amelogenin protein sequence divergence.

The developing rat incisor is a common model used in the study of enamel development. It has been impossible to study correlation between rat enamel structure and the sequence of the major developing enamel protein in this species as to date a DNA sequence for rat amelogenin has not been reported. This study presents the first cloning of a full-length cDNA copy of rat amelogenin and its deduced primary sequence. Detailed analysis of this sequence provides evidence that the gene has evolved by internal sequence duplication. Comparison of the rat amelogenin primary sequence with those published for other species provides evidence that this protein, while exhibiting extreme levels of sequence conservation, has been subject to significant structural changes that may be related to alterations in enamel structure in different mammalian groups.

Amelogenin↗
PubMed1994

Uptake and metabolism of albumin by rodent incisor enamel in vivo and postmortem: implications for control of mineralization by albumin.

The distribution of albumin throughout enamel development in the rat mandibular incisor was investigated using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS PAGE) and Western blotting employing an anti-rat albumin antibody. Intact albumin was detectable at all stages of enamel development but was most evident during late secretion/transition. Its concentration was subsequently reduced during the maturation stage. Albumin degradation products appeared during the transition/early maturation stage indicating that albumin breakdown preceded its removal. As albumin inhibits apatite crystal growth, its degradation and removal may be a necessary prerequisite for normal enamel crystal growth, perhaps reflecting a general mechanism for removal of residual endogenous matrix or adventitious crystal growth inhibitors. Additional studies revealed that the maturation stage was particularly susceptible to albumin influx postmortem. Albumin could therefore form part of the natural crystal growth control process, which, if not removed, could hamper maturation and lead to white spot hypoplasias.

Albumins↗
PubMed1994

Effects of frequency and duration of acid exposure on demineralization/remineralization behaviour of human enamel in vitro.

An in vitro oscillating system, employing human enamel and realistic time intervals and temperature (approximately 35 degrees C) and measuring mineral loss/gain on a volume basis, was used to investigate the effects of both frequency and duration of exposure to low pH (< 5) on the demineralization and remineralization behaviour of human enamel. Sections of human teeth were cycled through one of three different regimens: (1) 3 x 20-min acid challenges; (2) 6 x 10-min acid challenges and (3) 6 x 20 min acid challenges, over single 24-hour periods. The acid challenge periods of 3 x 20, 6 x 10 and 6 x 20 min produced no significant differences in net mineral lost, i.e., the volume of mineral lost per volume of enamel exposed was similar irrespective of frequency or duration of acid exposure (approximately 0.5% vol/vol). Increased frequency of acid exposure did, however, tend to alter the total demineralization/total remineralization amounts, resulting in significantly greater amounts of mineral loss and gain. The data suggest that the remineralization capacity of enamel is considerable and that factors such as inhibition of remineralization may be important in determination of net mineral loss from the tooth.

Acetates↗
PubMed1993

The effect of rate of eruption on periodontal ligament glycosylaminoglycan content and enamel formation in the rat incisor.

The rate of eruption of rat mandibular incisors was either increased by cutting one tooth out of occlusion or eliminated by means of pinning. The effects of such changes in eruption rate on the sulphated glycosylaminoglycan content of the periodontal ligaments was analysed. The length of the enamel secretory zone and the composition of the developing enamel matrix protein was also compared. Sulphated glycosylaminoglycan content of the periodontal ligament increased fourfold (P < 0.001) during accelerated eruption but decreased to a corresponding extent (P < 0.001) in the absence of eruption, when compared with controls. The length of the enamel secretory zone was also significantly reduced in the immobilised teeth, although the protein content was similar compared with controls. The results demonstrate the differential response to varied eruption rates of the periodontal ligament and enamel, particularly in respect of the extracellular matrix. The data are consistent with the view that the ground substance of the periodontal ligament plays a role in the generation of the eruptive force.

Amelogenin↗
PubMed1993

An immunohistochemical study of the effects of fluoride on enamel development in the rat incisor.

A monoclonal antiamelogenin antibody was used to investigate the effects of fluoride on enamel development in the rat incisor. The results suggested that during secretion the enamel matrix molecules are arranged in such a way as to mask the epitope recognized by the monoclonal antibody. However, during the transition stage of development as the matrix begins to be degraded the epitope becomes exposed and labelling intensity increases to reach a maximum at the end of transition/start of maturation. The effect of fluoride is to delay the appearance of labelling within the enamel matrix until the end of transition. This suggests that the fluoride may inhibit enzymatic degradation or disaggregation of the matrix, the resulting residual matrix then inhibiting crystal growth.

Ameloblasts↗
PubMed1993

Enamel ultrastructure and protein content in X-linked amelogenesis imperfecta.

X-linked amelogenesis imperfecta has been proven in a number of families to be linked to or involve a variety of mutations in the X chromosome amelogenin gene. The purpose of this study was to characterize the enamel ultrastructure and enamel protein in a kindred affected by X-linked amelogenesis imperfecta. Exfoliated primary teeth were obtained from two related persons (one male, one female) who had X-linked amelogenesis imperfecta with marked hypoplasia. Normal enamel (age and sex matched) was used as the control for all analyses. The teeth were evaluated using light microscopy, scanning electron microscopy, and microradiography. The enamel of the heterozygous female was hypoplastic and rough with marked surface depressions. Enamel beneath these depressions was poorly organized and lacked a prismatic structure. The affected male had very thin enamel (approximately 40 microns) that also lacked an organized structure. Enamel protein from the teeth of the heterozygous female and the control was characterized using amino acid analysis. The protein content of the enamel of the female with amelogenesis imperfecta was 0.40% (N = 1) whereas the control enamel ranged from 0.17% to 0.45% (N = 4; mean = 0.34%). This study indicates that although the enamel in both the male and female with X-linked amelogenesis imperfecta displayed marked structural abnormalities the enamel protein was similar in quantity and amino acid composition for normal and X-linked amelogenesis imperfecta (female) enamel.(ABSTRACT TRUNCATED AT 250 WORDS)

Amelogenesis Imperfecta↗
PubMed1992

Immunohistochemical investigation of epidermal growth factor receptor expression during periods of accelerated rat incisor eruption.

The effect of accelerated odontogenesis of the rat mandibular incisor on the expression of receptors for epidermal growth factor (EGF) was examined using specific monoclonal antibodies to the receptor molecule. Acceleration of odontogenesis was achieved by regular trimming of the tooth crown. At normal eruption rates the major area of cross-reactivity was over the secretory ameloblasts. Some labelling of the papilla and preameloblasts was evident. When proliferation was increased the major area of effect was at the preodontoblast/odontoblast boundary where there was a marked increase in labelling, initially at the proximal end of the cell adjacent to the basal lamina. The ameloblasts did not show such a dramatic increase in receptor numbers. Increase in labelling was also evident in the remainder of the papilla. The results suggest that an increase in proliferation with normal morphogenesis is associated with an overall increase in the numbers of EGF receptors, particularly in a population of cells immediately before and after elongation and differentiation of odontoblasts.

Ameloblasts↗
PubMed1992

The effect of periodontal disease on sulphated glycosylaminoglycan distribution in the sheep periodontium.

The glycosylaminoglycan (GAG) distribution in the soft periodontal tissues of the sheep was investigated topographically in healthy tissue and the changes associated with periodontal disease determined and correlated with increasing disease severity. Total sulphated GAG content was determined spectrophotometrically and the proportions of individual GAGS measured after separation by cellulose acetate electrophoresis. In healthy tissue, total sulphated GAG distribution was found to mirror that described previously for collagen, being highest in the gum-pad region and adjacent to alveolar bone. This changed markedly in relation to periodontal disease. Early disease-related changes in GAGs were first detected adjacent to alveolar bone. In severely diseases tissue, an overall increase in sulphated GAG, particularly in the gum-pad region, was present. Increasing disease severity was accompanied by a decrease in dermatan sulphate and a concomitant increase in the proportion of chondroitin-4-sulphate. These changes may be due to the combined effects of chronic inflammation and alterations to the mechanical loading of the tissue owing to loss of attachment.

Animals↗
PubMed1992

A flexible and rapid pH cycling procedure for investigations into the remineralisation and demineralisation behaviour of human enamel.

A rapid and flexible model system has been developed to study human enamel behaviour under conditions of oscillating pH similar to those experienced in the mouth. The model uses realistic time intervals and operates at in vivo temperatures (35-37 degrees C). Mineral loss or gain is measured quantitatively on a volume basis. Results indicate that for single 1-day periods with three 20-min exposures to acid, 1% v/v of enamel mineral was lost. These results, together with the histological appearance of the tissue, are in close agreement with previous studies of enamel caries.

Calcium↗