Biomedical subjects

J Kirkham

Publications and source records attributed to J Kirkham.

At least 19 recordsLinked to original sources

PubMed2001

Fluoride concentrations at and near the neonatal line in human deciduous tooth enamel obtained from a naturally fluoridated and a non-fluoridated area.

This study sought to obtain a precise profile of fluoride concentrations at and near the neonatal line in deciduous incisors and canines from the naturally fluoridated area (1.0--1.3 parts/10(6) F in drinking water) of West Hartlepool and the non-fluoridated area (less than 0.1 parts/10(6) F in drinking water) of Leeds in England. An abrasive microsampling method was used to determine the distribution of fluoride and phosphorus concentrations. The profile of fluoride concentrations in 100-microm layers before and after the neonatal line, that is, in the prenatal and postnatal enamel, were significantly higher in teeth from the fluoridated than non-fluoridated areas. It was concluded that the fact that the fluoride concentrations were about the same prenatally and postnatally in deciduous enamel obtained from the fluoridated and non-fluoridated areas indicates that fluoride enters the prenatal deciduous enamel and that it is transferred through the placenta.

Calcium↗

PubMed2001

Amelin extracellular processing and aggregation during rat incisor amelogenesis.

Amelin (also known as ameloblastin and sheathlin) is a recently described protein that is secreted by ameloblasts during enamel formation. Here, the extracellular distribution and processing of amelin during rat incisor amelogenesis were investigated by Western blot probing using anti-recombinant rat amelin antibodies. In addition, the solubility behaviour and aggregative properties of rat amelin were investigated using a sequential extraction procedure involving (1) extraction with simulated enamel fluid to extract proteins most likely to be soluble in vivo; (2) extraction with phosphate buffer to desorb proteins bound to enamel crystal surfaces; (3) extraction with sodium dodecyl sulphate (SDS) to extract proteins present as insoluble aggregates; followed by (4) a final acid demineralization step to release any remaining proteins. Proteins immunoreactive to the anti-amelin antibodies were detectable in secretory- and transition-stage enamel. Maturation-stage enamel appeared devoid of amelin. The largest immunoreactive protein detected migrated at 68 kDa on SDS gels, corresponding to the M(r) of nascent amelin. Other immunoreactive bands at 52, 40, 37, 19, 17, 16, 15, 14 and 13 kDa were presumably amelin processing products. The sequential extraction procedure revealed that the 68-, 52-, 40-, 37- and 13-kDa amelins were completely extracted under solution conditions similar to those reported to exist in vivo. In contrast, the 19-, 17- and 16-kDa amelins were only partially extracted, whilst the 15- and 14-kDa amelins could not be extracted with simulated enamel fluid. A proportion of the remaining 17- and 16-kDa amelins was desorbed from the enamel crystals with phosphate buffer and appeared to have been mineral-bound. The 15- and 14-kDa amelins and the remainder of the 17- and 16-kDa amelins were extracted with SDS only, suggesting that these species were present in vivo as an insoluble aggregate. The results provide additional information on amelin processing and degradation, and on how such processing influences the solubility and aggregative properties of amelin-derived proteins.

Ameloblasts↗

PubMed2000

Determination of the ionization state of 11-thioundecyl-1-phosphonic acid in self-assembled monolayers by chemical force microscopy

The present article describes the preparation and preliminary characterization of a novel phosphate-functionalized self-assembled monolayer (SAM) and the determination of the surface ionization states of the phosphate headgroup in aqueous solutions by chemical force microscopy (CFM). The phosphate headgroup used was PO(OH)2, a diprotic acid. The adhesion force between an AFM probe and a flat substrate, both of which were chemically modified with the same phosphate SAM, was also measured as a function of pH and ionic strength. At low ionic strength (10(-4) M), two peaks were observed in the force titration curve (adhesion force versus pH) at pH 4.5 and 8.4. The two peaks are positioned 2.4 and 1.2 pH units higher, respectively, than the acid dissociation constants obtained for the phosphate group free in aqueous solution. At high ionic strength (10(-1) M), the adhesion forces were reduced by 1 order of magnitude and the peaks were replaced by shoulders similar to those previously reported for acid force titrations. On the basis of JKR theory, the surface pKa values of the phosphate group in high ionic strength solutions were found to be 4.5 and 7.7, respectively. However, in light of the effects of ionic strength on the force titration curves, we discuss the applicability of JKR theory to nanoscopic measurements of adhesion force and surface pKa.

Journal Article↗

PubMed2000

Magnesium and fluoride distribution in human cementum with age.

Sixty-two human teeth, obtained from subjects aged 11 to 80 years, were used to determine the magnesium and fluoride concentration and distribution with age in human cementum. Transverse sections were prepared from the root region of teeth. Samples, each 30 microm thick, were abraded in sequence from the cementum surface and the cemento-dentine junction by an abrasive micro-sampling technique. Magnesium concentrations were lower in the cementum surface, and increased towards the cemento-dentine junction (CDJ), while fluoride concentrations were higher in cementum surfaces and tended to decrease towards CDJ. Fluoride distribution patterns were similar to that reported earlier while average fluoride concentration increased with age, however, either no change or decreasing tendencies were observed with magnesium.

Adolescent↗

PubMed2000

The chemical composition of tooth enamel in junctional epidermolysis bullosa.

The junctionalis form of epidermolysis bullosa (EBJ) is associated with a number of clinical problems involving tooth enamel, including increased susceptibility to caries. The aim here was to carry out a chemical characterization of the enamel of teeth from EBJ patients compared with that of unaffected controls. The results showed that while protein concentration, amino acid composition and carbonate content were similar in both groups, EBJ enamel contained a significantly reduced mineral per volume content, resulting in enamel hypoplasia. In addition, Western blotting revealed the presence of serum albumin (a known inhibitor of enamel crystal growth) in EBJ enamel. This was not detected in control enamel or in enamel of teeth from patients with the dystrophic form of the disease. It is concluded that EBJ enamel is developmentally compromised and that the enamel defects are commensurate with the reported genetic lesions.

Amelogenesis↗

PubMed2000

Fluoride and magnesium concentrations in human dental calculus obtained from Japanese and Chinese patients.

Calculus deposited on a total of 68 permanent teeth from patients 30-60 years old from Nagoya in Japan and Beijing in China was investigated. An abrasive microsampling method was used to examine the fluoride (F) and magnesium (Mg) distribution, using a fluoride ion-specific electrode and atomic absorption spectrophotometry, respectively. F concentrations decreased from the surface towards the interior of the calculus. Mg concentrations, however, gradually rose towards the innermost surface adjacent to the tooth. In all parts of the depth profiles, the average concentrations of both magnesium and fluoride were higher in the Japanese than in the Chinese calculus. Towards the inner surface of the calculus, F and Mg concentrations were also much higher in the Japanese than in the Chinese group. A greater intake of sea foods and greater use of fluoride dentifrices are possible reasons for the higher F and Mg concentrations in the Japanese individuals.

Adult↗

PubMed2000

Spatially related amelogenin interactions in developing rat enamel as revealed by molecular cross-linking studies.

A cleavable cross-linker (dithiobis[succinimidyl propionate], DTSP) was used to investigate the subunit structure of the developing enamel matrix. Intact matrix was cross-linked under conditions chosen to simulate those found in vivo. The cross-linked complexes were isolated by preparative sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and their subunit composition determined by analytical SDS-PAGE following reductive cleavage of the cross-links. Western blotting using antiamelogenin antibodies was used to confirm the identity of the proteins involved. The results showed that nascent amelogenins tended to be cross-linked to other nascent amelogenins while amelogenin-processing products tended to be cross-linked to other processed molecules at the same stage of processing. The results suggest that nascent amelogenins are in close association after secretion and during extracellular processing, and that processed products are not free to associate with nascent molecules, presumably due to diffusion constraints in the tissue. This conclusion implies that individual amelogenin molecules within supramolecular aggregates (nanospheres) are processed in situ and remain in the same nanosphere while all the individual component amelogenins undergo processing. The biological function of amelogenin processing remains unclear but the fact that amelogenin-amelogenin associations are maintained during processing indicates that matrix stability is an important factor while the enamel layer is being deposited.

Amelogenesis↗

PubMed2000

Architecture of intact natural human plaque biofilms studied by confocal laser scanning microscopy.

Determination of the structure of human plaque will be of great benefit in the prediction of its formation and also the effects of treatment. However, a problem lies in the harvesting of undisturbed intact plaque samples from human volunteers and the viewing of the biofilms in their natural state. In this study, we used an in situ device for the in vivo generation of intact dental plaque biofilms on natural tooth surfaces in human subjects. Two devices were placed in the mouths of each of eight healthy volunteers and left to generate biofilm for 4 days. Immediately upon removal from the mouth, the intact, undisturbed biofilms were imaged by the non-invasive technique of confocal microscopy in both reflected light and fluorescence mode. Depth measurements indicated that the plaque formed in the devices was thicker round the edges at the enamel/nylon junction (range = 75-220 microm) than in the center of the devices (range = 35-215 microm). The reflected-light confocal images showed a heterogeneous structure in all of the plaque biofilms examined; channels and voids were clearly visible. This is in contrast to images generated previously by electron microscopy, suggesting a more compact structure. Staining of the biofilms with fluorescein in conjunction with fluorescence imaging suggested that the voids were fluid-filled. This more open architecture is consistent with recent models of biofilm structure from other habitats and has important implications for the delivery of therapeutics to desired targets within the plaque.

Biofilms↗

PubMed2000

Evidence for charge domains on developing enamel crystal surfaces.

The control of hydroxyapatite crystal initiation and growth during enamel development is thought to be mediated via the proteins of the extracellular matrix. However, the precise nature of these matrix-mineral interactions remains obscure. The aim of the present study was to use a combination of atomic and chemical force microscopy to characterize developing enamel crystal surfaces and to determine their relationship with endogenous enamel matrix protein (amelogenin). The results show regular and discrete domains of various charges or charge densities on the surfaces of hydroxyapatite crystals derived from the maturation stage of enamel development. Binding of amelogenin to individual crystals at physiological pH was seen to be coincident with positively charged surface domains. These domains may therefore provide an instructional template for matrix-mineral interactions. Alternatively, the alternating array of charge on the crystal surfaces may reflect the original relationship with, and influence of, matrix interaction with the crystal surfaces during crystal growth.

Amelogenesis↗

PubMed2000

The chemistry of enamel caries.

The chemical changes which occur during the process of carious destruction of enamel are complex due to a number of factors. First, substituted hydroxyapatite, the main component of dental enamel, can behave in a very complex manner during dissolution. This is due not only to its ability to accept substituent ions but also to the wide range of calcium phosphate species which can form following dissolution. In addition, the composition, i.e., the extent of substitution, changes throughout enamel in the direction of carious attack, i.e., from surface to interior. Both surface and positively birefringent zones of the lesion clearly illustrate that carious destruction is not simple dissolution. Selective dissolution of soluble minerals occurs, and there is the probability of reprecipitation. The role of fluoride here is crucial in that not only does it protect enamel per se but also its presence in solution means that rather insoluble fluoridated species can form very easily, encouraging redeposition. The role of organic material clearly needs further investigation, but there is the real possibility of both inhibition of repair and facilitation of redeposition. For the future, delivering fluoride deep into the lesion would appear to offer the prospect of improved repair. This would entail a delivery vehicle which solved the problem of fluoride uptake by apatite at the tooth surface. Elucidation of the role of organic material may also reveal putative mechanisms for encouraging repair and/or protecting the enamel mineral.

Animals↗

PubMed2000

Morphology and elemental composition of subgingival calculus in two ethnic groups.

BACKGROUND: The aim of the present study was to compare the morphology and elemental composition of subgingival calculus between Indo-Pakistani and Caucasian patient groups. METHODS: Extracted teeth from 14 Indo-Pakistani and 19 Caucasian subjects were collected. Of these, 12 Indo-Pakistani and 10 Caucasian teeth had sufficient subgingival calculus for analysis. Subgingival calculus present on the 22 teeth was classified into six morphological types: 1) crusty/spiny/nodular; 2) ledge/ ring; 3) thin, smooth veneers; 4) finger/fern-like; 5) individual islands/spots; or 6) supramarginal on submarginal. Subgingival calculus was zoned: coronal, mid, and apical. A sample obtained from each zone was subdivided to allow 3 separate analyses: transmission electron microscopic (TEM) x-ray microanalysis for elemental composition, fluoride analysis, and carbonate analysis. RESULTS: Crusty/spiny/nodular, ledge/ring, and thin, smooth veneers were more commonly found in the Indo-Pakistani group; individual islands were more prevalent in the Caucasian subjects. Supramarginal on submarginal calculus was found only in the Indo-Pakistani group. No finger/fern-like deposits were found. No differences within or between the two ethnic groups were found with regard to calcium:phosphate ratios, fluoride, or carbonate content. However, the Indo-Pakistani group showed significantly lower levels of sodium in apical samples than in coronal samples (ANOVA, F1,16 = 5.98, P= 0.03), and significantly lower levels of sodium (ANOVA, F1,12 = 4.75, P= 0.05) and magnesium (ANOVA, F1,12 = 5.16, P= 0.04) in apical samples than in those from Caucasians. After adjusting for smoking, the magnesium results remained significant (ANOVA, F2,11 = 4.64, P= 0.05). CONCLUSIONS: Subgingival calculus demonstrated differences in morphology between these two ethnic groups and differences in elemental composition, which may influence its overall solubility and contribute to its greater accretion in the Indo-Pakistani subjects.

Adult↗

PubMed1999

Photo-modulation of horseradish peroxidase activity via covalent attachment of carboxylated-spiropyran dyes.

The photo-modulation of the enzyme horseradish peroxidase modified with photochromic spiropyran dyes is reported. The degree of photo-modulation, greater than 90% reduction in enzyme activity under visible compared to UV illumination, matches the greatest degree of photo-modulation previously reported in the literature. The observation that only a small fraction of the conjugated photochromic molecules are photo-switched suggests that the dyes influence the enzyme activity via local interaction with the enzyme active site.

Benzopyrans↗

PubMed1999

An in vitro study of the use of photodynamic therapy for the treatment of natural oral plaque biofilms formed in vivo.

Seven-day oral plaque biofilms have been formed on natural enamel surfaces in vivo using a previously reported in situ device. The devices are then incubated with a cationic Zn(II) phthalocyanine photosensitizer and irradiated with white light. Confocal scanning laser microscopy (CSLM) of the biofilms shows that the photosensitizer is taken up into the biomass of the biofilm and that significant cell death is caused by photodynamic therapy (PDT). In addition, the treated biofilms are much thinner than the control samples and demonstrate a different structure from the control samples, with little evidence of channels and a less dense biomass. Transmission electron microscopy (TEM) of the in vivo-formed plaque biofilms reveals considerable damage to bacteria in the biofilm, vacuolation of the cytoplasm and membrane damage being clearly visible after PDT. These results clearly demonstrate the potential value of PDT in the management of oral biofilms.

Biofilms↗

PubMed1998

An audit of anti-D sensitisation in Yorkshire.

OBJECTIVE: To determine the likely factors that contribute to RhD sensitisation. DESIGN: Retrospective study of all new cases of RhD sensitisation occurring between 1988 and 1991. SETTING: Leeds Blood Centre, National Blood Service, Yorkshire. POPULATION: One hundred and forty-seven cases of RhD sensitisation from 15 obstetric units within the Yorkshire region, of which 129 (312 pregnancies) could be assessed. MAIN OUTCOME MEASURE: S Identification of potential immunising events and adherence with recommendations on anti-D immunoglobulin administration. RESULTS: Twenty-eight women (22%) had immune anti-D antibodies during their first pregnancy or at delivery and 50 (39%) in their second pregnancy. Overall, 98 potential immunising events were identified in 62 women, excluding delivery; 67 women (52%) had no events, other than delivery. Miscarriages and medical terminations of pregnancy accounted for 81% of all identified events. Iatrogenic failure to adhere to recommendations for the administration of anti-D immunoglobulin occurred in a significant proportion of women who subsequently developed immune anti-D antibodies. Anti-D immunoglobulin failed to protect against immunisation despite adherence to the protocol in 20 events (20%), 13 of which involved miscarriages or termination of pregnancy < 20 weeks of gestation. Potentially, antenatal prophylaxis might have prevented 86% of immunisations that were identified during the first pregnancy. CONCLUSIONS: The introduction of antenatal administration of anti-D immunoglobulin could significantly reduce the level of sensitisation in primigravidae, and adherence to recommendations for administration of anti-D immunoglobulin could be improved. Consideration should be given to reviewing the current recommendation that a dose of 250 IU of anti-D immunoglobulin is adequate following termination of pregnancy before a gestational age of 20 weeks.

Abortion, Induced↗

PubMed1998

The developing enamel matrix: nature and function.

The hydroxyapatite crystals of mature enamel are unusually large, uniform and regularly disposed within the tissue, implying that their development is a highly controlled process. The organic matrix of developing enamel is presumed to play an important role in the modulation of mineral deposition and growth during tooth morphogenesis but the precise functions of individual matrix proteins remain unclear. The aim of this review was to survey the current knowledge of enamel matrix proteins with a view to suggesting possible functions. The organic matrix is highly heterogeneous, comprising proteins derived from a number of different genes, including amelogenin, enamelin, ameloblastin (amelin/sheathlin), tuftelin, dentine sialophosphoprotein, enzymes and serum proteins such as albumin. Each of these classes appears to undergo post-secretory sequential degradation which contributes further towards matrix heterogeneity. Possible functions of these proteins include de novo mineral nucleation/initiation (dentine sialophosphoprotein, tuftelin), mineral ion binding as crystal precursors (amelogenin, enamelin), control of crystal growth (amelogenin, enamelin, ameloblastin), support of growing crystals (amelogenin, enamelin), determination of prismatic structure (ameloblastin), cell signalling (tuftelin, ameloblastin), control of secretion (breakdown products) and protection of the mineral phase (amelogenin, enamelin). Failure of these mechanisms could lead to incomplete maturation of the enamel and the eruption of dysplastic tissue.

Ameloblasts↗

PubMed1998

Identification of human serum albumin in human caries lesions of enamel: the role of putative inhibitors of remineralisation.

Carious attack on enamel is not a unidirectional process but involves both demineralisation and remineralisation. The chemistry of carious attack on enamel has, to a large extent, now been clarified as far as mineral components are concerned but little attention, however, has been paid to the identity of organic material in carious lesions and its possible role in the caries process. The only clear information available is that organic material accumulates with time within enamel lesions. The present study was aimed at identifying a specific protein component known to bind to hydroxyapatite (albumin) in carious lesions with a view to investigating its role in the disease process. The distribution of albumin within both white spot and fissure lesions and adjacent sound enamel of extracted human teeth was investigated using SEM immunohistochemistry on undermineralised sections of human enamel and employing a polyclonal antibody to human serum albumin. The nature of the protein, i.e. whether it was in the form of intact molecules or degraded fragments, was investigated by Western blotting, employing the same antibody. The immunohistochemistry revealed the presence of albumin within both interproximal white spot and fissure lesions with little if any present in sound enamel. The Western blotting indicated that the albumin was in the intact form with no evidence of degradation products. The ability of albumin to bind and to inhibit growth of calcium phosphate crystals raises the question as to the possible role of such a molecule in the development of carious lesions.

Antibodies↗

PubMed1998

Atomic force microscopy studies of crystal surface topology during enamel development.

During the secretory stage of enamel development, the hydroxyapatite crystals appear as thin ribbons which grow substantially in width and thickness during the later maturation stage. In this study, the atomic force microscope (AFM) was used to investigate developmentally-related changes in deproteinized enamel crystal surface topography in normal animals and in those receiving daily doses of fluoride. The AFM revealed previously undescribed surfaces features, some of which may represent growth sites or different crystalline phases. Secretory stage crystals had greater surface rugosity and were more irregular, with spherical sub-structures of 20-30 nm diameter arranged along the "c"-axis. Maturation stage crystals were smoother and larger but revealed both subnanometer steps and lateral grooves running parallel to the "c"-axis. Crystals from fluorotic tissue showed similar features but were more irregular with a higher degree of surface roughness, suggesting abnormal growth. The AFM may prove an important adjunct in determination of the mechanisms controlling crystal size and morphology in skeletal tissues.

Animals↗

PubMed1998

Identification of rat enamel organ RNA transcripts using differential-display.

Enamel formation is a complex process which involves the expression of a number of genes, the most obvious being those related to the mineralized extracellular matrix. In this study the differential-display technique, first described by Liang and Pardee, has been used to identify genes specifically expressed in enamel organ cells. By comparing results obtained from RNA derived from rat enamel organ with RNA derived from other cellular sources, a number of differentially expressed transcripts have been identified. The nucleotide sequences of two of these have been analyzed and shown to have no homology with any previously published sequences. Further analysis will provide information on the type of protein that they may encode, their tissue distribution and their potential role in enamel formation.

Amino Acid Sequence↗