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B H Clarkson

Publications and source records attributed to B H Clarkson.

At least 19 recordsLinked to original sources
PubMed2002

Binding of dentin noncollagenous matrix proteins to biological mineral crystals: an atomic force microscopy study.

Noncollagenous matrix proteins (NCPs) of dental hard tissues (dentin, cementum) are involved, both temporally and spatially, in the mineralization of their collagen matrices. Two of the NCPs thought to initiate mineral nucleation and control crystal growth in dentin, are dentin phosphoproteins (DPP) and dentin sialoprotein (DSP). Control of crystal growth would depend on the binding capacity of these two molecules, which may be related to the charge domains on the crystals and/or the phosphorylation of the protein. Phosphophoryn (a highly phosphorylated DPP) and DSP were isolated, purified, and characterized from the immature root apicies of human teeth. Dephosphorylation of phosphophoryn was carried out using bovine intestinal alkaline phosphatase. Enamel crystals were prepared from the maturation stage of developing rat incisor enamel. Protein-coated crystals were prepared for viewing in an atomic force microscope fluid cell using tapping mode. Desorption of the proteins was achieved using a phosphate buffer and surface roughness measurements were obtained from all specimens. Time-lapsed images of the crystals showed "nanospheres" of protein distributed along the crystals but only the phosphophoryn-coated crystals showed a distinctive banding pattern, which was still visible after the phosphate desorption experiments. The surface roughness measurements were statistically greater (P <0.01) when compared to the control for only the phosphophoryn-coated specimens. It is hypothesized that the phosphophoryn binding may be associated with charge arrays on the crystal surface and its phosphorylation. Also, based on its affinity for the crystalsurfaces, phosphophoryn seems the most likely candidate for controlling dentin crystal growth and morphology.

Crystallization↗
PubMed2001

Emerging methods used in the prevention and repair of carious tissues.

A systematic review was undertaken to investigate four emerging methodologies that might be used in the prevention of caries and/or repair of carious tissues. These included a partitioned dentifrice, laser technology, fluoride-releasing dental materials, and for deep carious lesions, bone morphogenic protein (BMP) therapy. The search strategy was to review articles written in English, indexed in MEDLINE and EMBASE databases and published since 1976. Over two hundred articles were read but because of the inclusion and exclusion criteria, only thirty-three were included in the evidence tables. The review of partitioned toothpaste showed either a greater remineralizing effect or a greater increase in the resistance to demineralization of both enamel and dentin, with the exception of its lack of effectiveness on coronal caries in the only clinical trial. Five of the six in vitro studies on enamel and the one study on dentin reported that lased tissue was less soluble than nonlased. Six clinical and four in situ studies were reviewed in answering the question as to whether fluoride-releasing restorative materials increase the remineralization or resistance to demineralization of human enamel and dentin. Eight of these reported positive findings. Six animal studies investigating BMP were reviewed, and all showed the ability of BMP to induce tubular dentin formation. Although the laboratory, animal, and limited clinical trials report encouraging results, independent, randomized, controlled clinical trials need to be carried out before these emerging technologies can be recommended for use in general practice.

Animals↗
PubMed2000

Molecular cloning of a human dentin sialophosphoprotein gene.

Dentin sialoprotein (DSP) and dentin phosphoprotein (DPP; phosphophoryn) are two principal dentin-specific non-collagenous proteins. DPP is extremely acidic and is rich in aspartic acid and serine. By virtue of this structure, DPP may bind large amounts of calcium and may facilitate initial mineralization of dentin matrix collagen as well as regulate the size and shape of the crystals. The function of DSP is not known. DSP and DPP are encoded by a single gene in both rat and mouse, and are uniquely expressed in odontoblasts and transiently in pre-ameloblasts. Because DSP and DPP are isolated from dentin as distinct proteins and appear to be present in different amounts, the nascent dentin sialophosphoprotein (DSPP) is likely cleaved to yield DSP and DPP. However, when, where and how the DSPP is cleaved into DSP and DPP is not clear. To further elucidate the structure and function of human DSP and DPP, we have cloned DPP and DSP cDNA by reverse transcriptase-polymerase chain reaction (RT-PCR) strategies, and then cloned and initiated characterization of a human dentin sialophosphoprotein gene. The genomic organization of human DSPP is very similar to that of mouse, containing five exons and four introns, suggesting it is a homologue of mouse dentin sialophosphoprotein (DSPP). Exons 1-4 encode for DSP, while exon 5 encodes for the C-terminus of DSP and the whole DPP. A 4.6-kb RNA transcript was detected on Northern blot analyses of total RNA extracted from immature (open root apices) human teeth using either a human DPP or DSP probe.

Amino Acid Sequence↗
PubMed1999

Introduction to cariology.

This article examines the discipline of cariology. A brief history is presented, and an overview of the origin and management of caries is discussed. This article frames the picture that the other authors in this issue paint.

Bacteria↗
PubMed1998

Fluoride release and re-uptake in direct tooth colored restorative materials.

OBJECTIVES: Glass ionomers may be "recharged" through topical fluoride (F-) treatments; however, this reported "recharging," may be attributed to surface changes after F- treatment. This study examined differences in F- release and re-uptake among dual-cured and chemically-cured glass ionomers, and a photo-cured F- releasing composite. A secondary goal was to determine if tensile strength or surface roughness changed due to F- release, or F- re-uptake and re-release. METHODS: In Phase 1, initial surface roughness and diametral tensile strength were measured. F- release was measured for 30 days. Strength and roughness were then remeasured. In Phase 2, surface roughness was measured, then materials were treated with a 5000 ppm neutral F- gel, the same gel without F-, or phosphoric acid. F- release was measured for 30 days, then final surface roughness and strength were determined. RESULTS: Significant differences were found in amount and rate of F- release, and F- re-uptake and re-release among study materials and enamel controls (p < 0.001). The amount and rate of F- re-release after NaF treatment differed significantly from F- release after acid treatment in glass ionomers, although both groups showed increased F- release after surface treatment (p < 0.001). There were no significant changes in tensile strength or surface roughness after F- release or F- re-uptake and re-release as determined by ANOVA. SIGNIFICANCE: The results of this in vitro study indicate that applications of neutral 5000 ppm F- gel to aged glass ionomer restorations results in a significant fluoride uptake and subsequent release. The data suggest that the application of neutral fluoride gel to glass ionomer restorations in situ may result in increases in oral fluoride concentrations, without affecting the restoration's surface roughness or tensile strength.

Analysis of Variance↗
PubMed1998

Human dentin phosphophoryn nucleotide and amino acid sequence.

Dentin sialoprotein (DSP) and phosphophoryns (DPP) are major dentin-specific non-collagenous proteins and are synthesized by odontoblasts. DPP are extremely acidic, rich in aspartic acid and serine, possess a high affinity for calcium and collagen, and are believed to function in dentin mineralization. Whereas DSP and DPP are the products of a single gene in mouse and rat, an analogous human gene has not been described. Using RT-PCR based cloning strategies, we have cloned human DPP cDNA from immature molar root total RNA. The open reading frame of this human DPP cDNA comprises 2364 bp encoding 788 amino acids rich in serine (58%), aspartic acid (26%) and asparagine (9%). These are mostly arranged as (DSS)n (n = 1-16), DS and NSS motifs. The N-terminal sequence (DDP) matches that obtained from human DPP extracted from the roots of immature teeth. The core protein of this human DPP was calculated to have a molecular weight of 76,906 Da and a net charge of -206 with an isoelectric point of 2.65. Of the serine residues, 53% can potentially be phosphorylated by casein kinases I and II. Thus, this newly cloned human cDNA, which encodes a protein with characteristics similar to rat and mouse DPP, is identified as a human DPP.

Amino Acid Sequence↗
PubMed1998

Phosphoprotein analysis of sequential extracts of human dentin and the determination of the subsequent remineralization potential of these dentin matrices.

Phosphoprotein appears to play an important role in the mineralization of dentin during tooth development and remineralization after demineralization by dental caries. To better understand this role, we describe the extraction and characterization of phosphoprotein from immature, human root apex dentin during and after EDTA demineralization. The extraction procedure included dissociation of the demineralized dentin matrix by guanidine hydrochloride (Gdn.HCl) followed by subsequent digestion with cyanogen bromide (CNBr) and collagenase. Characterization of these extracts included 'Stains-All' staining of SDS polyacrylamide gels (SDS-PAGE) and amino acid, protein and phosphorus analyses. The ability of these matrices to remineralize was determined by TEM and measuring calcium levels in the remineralized tissue by atomic absorption spectroscopy. The staining of SDS-PAGE gels and amino acid analysis showed that an intact phosphophoryn was extracted from the dentin of the immature apices during EDTA demineralization and that it had an apparent Mr approximately 140,000. In the subsequent extracts and digests, the phosphoprotein has a range of molecular weights, some of which may have been degraded products of the intact phosphoprotein. A greater quantity of phosphoprotein was found in the EDTA-demineralized dentin matrices than in dentin after Gdn.HCl, CNBr and collagenase digests. These EDTA-demineralized matrices also remineralized to a greater extent than those dissociated with Gdn.HCl. The differences in both the quantity and the quality, as defined by the amino acid residue profile, of the phosphoprotein in the sequential extracts of the root apex dentin may be important in affecting the ability of this tissue to remineralize.

Adolescent↗
PubMed1996

Characterization and identification of a human dentin phosphophoryn.

The present study further characterizes an extract from immature, human tooth apicies from which an intact dentin phosphoprotein has been identified. Third molar apicies from developing roots were decalcified in 10% EDTA until Ca2+ was undetectable in the decalcifying solution. The crude extract was run on 7.5% SDS-PAGE and stained with "Stains-All." Four distinct bands were found and the molecular weights were 140, 60, 50, and 34 k. When run on a SDS-PAGE under nonreducing conditions the 60, 50, and 34 k bands were absent. These results suggest that the lower molecular weight bands may be subunits of the larger protein. The extract was then further purified by adding CaCl2 and MgCl2 to precipitate the phosphoprotein. The precipitate was subjected to a DEAE-Sepharose CL6B column and eluted by 0-0.7 M NaCl gradient solution. The amino acid composition of the purified phosphoprotein was determined and the extract was found to be rich in serine and aspartic acid residues. The N-terminal peptide Asp-Asp-Pro was identified. The sequence of the three amino acids is identical to rat incisor phosphoprotein.

Amino Acid Sequence↗
PubMed1994

Fluoride profile in mature unerupted enamel following removal of surface organic material.

The aim of the present study was to determine fluoride profiles in mature unerupted enamel following removal of the surface organic material. Thirty teeth were randomly allocated into three groups. The surface organic material (Nasmyth's membrane) was left intact in group I; it was removed by tooth-brushing in group II, and in group III the surface organic layer was removed along with subsurface organic material by deproteinizing. Each tooth was then sectioned into halves and a standardized biopsy area was created. Initially alkali-soluble fluoride was extracted with 1M KOH followed by acid etch analysis to measure the remaining fluoride. No difference was seen in the alkali-soluble fluoride levels but residual fluoride concentrations were significantly reduced (p < 0.05) after deproteinizing but not after toothbrushing. It would appear that a substantial amount of fluoride (approximately 25%) in mature enamel from unerupted teeth can be removed by a deproteinizing agent, which may suggest an association of this fluoride with subsurface organic material.

Acid Etching, Dental↗
PubMed1993

Effects of phosphoprotein on collagen fibril formation in vitro.

Transmission electron microscopy showed that when either dentinal phosphoprotein or calcium-treated phosphoprotein or phosvitin were introduced during type I collagen fibrillogenesis the fibrils formed were significantly wider and the cross-banding was more distinct than in the absence of phosphoprotein. The collagen fibril width also increased with increasing concentrations of these molecules. When either bovine serum albumin (BSA) or dephosphorylated dentine phosphoprotein were used, no differences in the fibril characteristics were seen when compared to the controls that contained no phosphoprotein or BSA. When these dialysed matrices were placed into mineralizing solutions, no mineral was observed in any of the samples.

Animals↗
PubMed1992

Comparison of phosphoprotein isolated from mature and immature human tooth roots.

Mature (average patient age = 29.5 yr, closed apical foramen) and immature (average patient age = 17.5 yr, open apical foramen) root shards were placed in dialysis tubing and demineralized to completion using either 10% disodium EDTA plus protease inhibitors or 0.6 N HCl. The demineralized shards were re-extracted (five times) with 0.05 M tris-HCl, 1.0 M NaCl and then collagenase digested. No major differences were observed in chromatograms of extracts, re-extracts or collagenase digests from root shards demineralized in either way. In contrast, chromatograms of immature and mature roots showed qualitative differences. Chromatograms of mature roots demineralized in either way showed broader protein peaks and less organic phosphorus than those from immature tooth roots. A distinct band amid degraded phosphoprotein (150 K) was found in SDS-PAGE gels (7.5%) from EDTA-extracted immature tooth roots but not from mature tooth roots. Electroelution of this band revealed a typical phosphoprotein amino-acid profile containing increased aspartic acid and serine residues. Comparison of the total phosphoprotein and amino acid composition of extracts, re-extracts and collagenase digests revealed that phosphoprotein, serine and to a lesser extent aspartic acid were recovered in greater quantities from immature roots than mature tooth roots. These data suggest that the degree of maturation is crucial to the isolation of an intact phosphoprotein and provides additional evidence that human dentine phosphoprotein undergoes amino acid compositional changes during maturation.

Adolescent↗
PubMed1991

Effects of phosphoprotein moieties on the remineralization of human root caries.

The noncollagenous proteins, especially phosphoprotein, have been shown to modulate biomineralization. The objective of this study was to investigate the remineralization potential of human tooth root organic matrices which did or did not contain soluble non-collagenous proteins including phosphoprotein. Human tooth roots were completely demineralized using conditions that either removed or did not remove soluble phosphoprotein and were then subjected to remineralization conditions. Removal of soluble phosphoprotein resulted in remineralization while no remineralization occurred in tooth roots that still contained soluble phosphoprotein. Transmission electron microscopy and microradiography demonstrated that demineralized cementum did not remineralize under any of the conditions used in this study. Collagenase digestion of demineralized and salt-reextracted tooth root organic matrices revealed that a nonsoluble phosphoprotein was present in the matrices. Amino acid analysis and SDS-PAGE showed that this nonsoluble phosphoprotein was similar in composition to the soluble phosphoprotein. This work suggests that the removal of soluble, noncollagenous proteins, especially phosphoprotein from root caries lesions, may enhance their remineralization potential.

Amino Acids↗
PubMed1991

Caries prevention--fluoride.

A clear understanding of the mechanism of action of fluoride and its pharmacokinetics would ensure appropriate clinical use of fluoride and fluoride-containing modalities. Convincing evidence exists that fluoride has a major effect on the demineralization and remineralization of dental hard tissues, and that it interferes with the acid production from "cariogenic" bacteria. However, it has also been shown to be physiologically harmful if fluoride concentrations and/or exposure periods are inappropriate. In order to establish appropriate clinical concentrations and exposure periods for fluoride administration, this review is concentrated on the theme that fluoride controls but does not prevent caries. The review is organized along classical lines, with a discussion of the role of systemic vs. topical fluoride. Discussion of the systemic effects of fluoride includes ingestion through water fluoridation, fluoride supplements, topical fluoride applications, and dentifrices. The benefits and problems associated with the systemic route of fluoride administration are discussed with special reference to caries control and fluoride's mechanism of action and its toxic effect. The same discussions are focused on the role of the topical effects of fluoride, with particular emphasis placed upon: low vs. high fluoride concentrations; calcium fluoride vs. fluorhydroxyapatite; and fluoride distribution, in both the mouth and in the teeth.

Dental Caries↗
PubMed1990

Phosphoprotein extraction from the dentine/cementum complex of human tooth roots.

Root shards were placed in dialysis tubing and demineralized to completion in either 10% disodium EDTA, pH 7.4, 0.6 M HCl, 0.1 M HCl, 0.5 M acetic or 75 mM-25 mM lactic-acetic acids. The demineralized shards were then re-extracted with 0.05 M tris-HCl, 1.0 M NaCl. DEAE chromatography revealed that the major peak of the 0.6 M CHl and EDTA extracts contained organic phosphorus, whereas much less organic phosphorus was found in the major peak of the 0.1 M HCl extract. Analysis of the re-extracts gave a pattern opposite to that obtained from the initial extractions. Measurements of protein and organic phosphorus released during extraction and re-extraction confirmed these results. Staining of SDS-PAGE gels for phosphoprotein with Stains-All resulted in a blue smear in fractions containing organic phosphorus. Thus the extraction of phosphoproteins from human tooth roots differed depending upon the demineralizing conditions. This ability to remove phosphoprotein differentially will allow further investigation of the role of phosphoprotein in mineralization and remineralization.

Acetates↗
PubMed1988

Effect of topical fluoride treatments on fluoride distribution during in vitro caries-like lesion formation.

Tooth sections were treated in vitro for 4 min with APF, SnF2, or received no treatment. Each treatment group then received washes of KOH, (24 h), an inorganic solution (24 h), or DDH2O (2 min) and were placed into dialyzed 15% w/v gel (pH 4.3) containing 0.15 mM hydroxyapatite, but no fluoride (less than 0.02 ppm F). Adjacent nontreated sound enamel acted as the control. Lesion microdissection, after 2 weeks exposure to the acidified gel, revealed an inverse relationship between lesion body fluoride concentration and lesion depth. The lesion depth was smallest, and the lesion body fluoride concentration was greatest in both fluoride-treated groups after a 2-min DDH2O wash, a 24-hour inorganic wash, and a 24-hour KOH wash, respectively. These data support the theory that the progress of carious lesions is related to the fluoride concentration in the lesion and that the fluoride concentration in the lesion is related to the acquired fluoride concentration in sound enamel.

Acidulated Phosphate Fluoride↗
PubMed1987

In vitro caries-like lesion production by Streptococcus mutans and Actinomyces viscosus using sucrose and starch.

We investigated the formation of caries-like lesions on root and enamel sections by S. mutans and A. viscosus when grown in four different carbohydrate substrates. The substrates were: sucrose, starch + alpha-amylase, and a combination of starch and sucrose with and without alpha-amylase. Twenty-four sections with exposed windows on both the root and enamel surfaces were exposed to the individual bacterial species in each of the four substrates for three weeks. At three weeks, the sections were removed and lesion depths measured. When grown in sucrose alone, S. mutans produced significantly deeper lesions in both root and enamel surfaces when compared with A. viscosus. However, S. mutans failed to produce lesions when grown in "limited" sucrose with starch added, whereas A. viscosus in this same substrate produced lesions in the enamel and root surfaces. A viscosus also produced either similar or significantly deeper lesions in both root and enamel surfaces, when compared with S. mutans grown in the two substrates with amylase. Thus, under these in vitro conditions, it was demonstrated that A. viscosus could utilize starch, whereas utilization of starch by S. mutans was alpha-amylase-dependent.

Actinomyces↗