'The comparative strengths of commercial glass ionomer cements with and without metal additions'.
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Cermet Cements↗
Biomedical subjects
J W McLean
Publications and source records attributed to J W McLean.
Molecular cloning of a cDNA encoding the glycoprotein of hen oviduct microsomal signal peptidase.
Detergent-solubilized hen oviduct signal peptidase has been characterized previously as an apparent complex of a 19 kDa protein and a 23 kDa glycoprotein (GP23) [Baker & Lively (1987) Biochemistry 26, 8561-8567]. A cDNA clone encoding GP23 from a chicken oviduct lambda gt11 cDNA library has now been characterized. The cDNA encodes a protein of 180 amino acid residues with a single site for asparagine-linked glycosylation that has been directly identified by amino acid sequence analysis of a tryptic-digest peptide containing the glycosylated site. Immunoblot analysis reveals cross-reactivity with a dog pancreas protein. Comparison of the deduced amino acid sequence of GP23 with the 22/23 kDa glycoprotein of dog microsomal signal peptidase [Shelness, Kanwar & Blobel (1988) J. Biol. Chem. 263, 17063-17070], one of five proteins associated with this enzyme, reveals that the amino acid sequences are 90% identical. Thus the signal peptidase glycoprotein is as highly conserved as the sequences of cytochromes c and b from these same species and is likely to be found in a similar form in many, if not all, vertebrate species. The data also show conclusively that the dog and avian signal peptidases have at least one protein subunit in common.
Amino Acid Sequence↗
The clinical use of glass-ionomer cements.
The use of glass-ionomer cements in clinical dentistry has expanded greatly over the last decade. Their use in treating early carious or erosion lesions has been investigated widely and established techniques include fissure filling, restoration of erosion lesions without cavity preparation, and the internal or tunnel restoration. Because of their adhesion to moist tooth structure, biologic compatibility, and fluoride release, increasing use also has been made of their anticariogenic properties in treating geriatric patients. Glass-ionomers have proved very successful as dentin substitutes for attaching composites to enamel without involving risk of pulpal damage in the deeper cavity. The deficiencies of glass-ionomer cements are well known, including lack of toughness, early water sensitivity, low abrasion resistance, and porosity, leading to poor surface polish. Solving these problems is formidable because inherently the strength of these cements is related to their water content. The clinician should be aware of these deficiencies and stay within the parameters of the techniques outlined in this article. In particular, clinical success depends on early protection of the cement from hydration or dehydration and the current use of light-cured bonding agents largely has solved this problem. The future probably lies in using laminate techniques in which materials that attach to dentin and form a biologic seal can be covered by tougher and harder enamel veneers, thus mimicking the structure of the tooth. It is possible that future materials will be developed on the lines of these polyelectrolyte cements in which higher molecular weight polymers are used in conjunction with polymers that contain photoinitiators to effect light curing and toughen the matrix. In addition, the possibility of developing laboratory-cured glass-ionomer inlays in which porosity can be reduced and tougher polymers used should be considered.
Dental Restoration, Permanent↗
Clinical applications of glass-ionomer cements.
The use of glass-ionomer cements in clinical dentistry is now well established. They have a number of unique properties, including adhesion to moist tooth structure, biological compatibility, and anticariogenic properties due to their fluoride release. Their use in treating early carious or erosion lesions has been widely investigated. Established techniques include fissure filling and sealing, restoration of class 5 erosion lesions without cavity preparation, and the internal occlusal fossa or tunnel restoration. The "sandwich" technique using glass-ionomer cements as "dentin substitutes" has enabled composite restorations to be used with greater safety where pulpal damage may occur. The future probably lies in using a laminate technique where materials that attach to dentin and form a biological seal can be covered by tougher and harder enamel veneers, thus mimicking the structure of the tooth. The deficiencies of glass-ionomer cements are well known, including lack of toughness, early water sensitivity, low abrasion resistance, and porosity leading to poor surface polish. Solving these problems is formidable, since inherently the strength of these cements is related to their water content. The clinician should be aware of these deficiencies and stay within the parameters of the techniques outlined in this paper. In particular, clinical success depends upon early protection of the cement from hydration or dehydration, and the current use of light-cured bonding agents has largely solved this problem.
Cermet Cements↗
Cloning and expression of a divergent integrin subunit beta 8.
Rabbit and human cDNA clones have been identified that encode a novel integrin beta subunit. The sequences that encode this subunit, which has been designated as beta 8, were isolated initially from rabbit placental cDNA libraries using an oligonucleotide probe derived from a highly conserved region of integrin beta subunit sequences. The rabbit clone was used to isolate human beta 8 cDNA clones from human placental and MG-63 osteosarcoma cell libraries. The putative beta 8 polypeptides, which comprise 769 and 768 residues in human and rabbit, respectively, show a high degree of inter-species conservation (approximately 90% identity). In contrast, beta 8 is distinct from the other integrin beta subunits. At the amino acid level human beta 8 ranges from 31 to 37% identity with human beta 1-7. The domain structure of beta 8 is typical of the integrin beta subunits. Human beta 8 has a 42-residue N-terminal signal peptide, a large extracellular domain (approximately 639 residues) that contains four cysteine-rich repeats, a transmembrane domain (approximately 30 residues), and a C-terminal cytoplasmic domain (approximately 58 residues). There are several structural features that are unique to the beta 8 polypeptide, as compared with the other integrin beta subunits. Six of the 56 cysteine residues that are conserved within the extracellular domains of beta 1, beta 2, beta 3, beta 5, beta 6, and the beta subunit from Drosophila are absent in the beta 8 polypeptide. Also, the cytoplasmic domain of the beta 8 subunit shares no homology with the cytoplasmic regions of any of the other integrin beta subunits. Northern analysis demonstrated an approximately 8-kilobase beta 8 mRNA in rabbit placenta, kidney, brain, ovary, and uterus. PCR analysis revealed that beta 8 mRNA is also present in several transformed human cell lines. The beta 8 polypeptide has been transiently expressed in 293 human embryonic kidney cells. A polyclonal antipeptide antibody specific for beta 8 and a polyclonal antibody that recognizes alpha v epitopes were used to show that beta 8 can complex with the endogenous alpha v subunit in 293 cells and that the resulting integrin is expressed as a cell surface complex.
Amino Acid Sequence↗
Lipoproteins in pinnipeds: analysis of a high molecular weight form of apolipoprotein E.
We have examined the apolipoprotein content of the lipoproteins of several marine mammals by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Their apolipoprotein (apo) B-100, apoB-48, and apoA-I migrated to virtually the same position as the comparable human apolipoproteins. In cetaceans (bottlenose dolphins and killer whales), the molecular mass of the apoE was identical to that of human apoE (35 kDa). In contrast, in the lipoproteins of pinnipeds (harbor seals, sea lions, and walrus) there was no protein comparable in size to human apoE; however, there were two proteins in the 40- to 44-kDa range. The protein with the higher apparent molecular weight (44 kDa) was apoA-IV, as determined by NH2-terminal amino acid sequencing. Sequencing of the NH2-terminal 15 amino acids of the lower molecular weight protein (40-42 kDa) revealed no obvious homology with human apoE. However, a human apoE-specific monoclonal antibody, 1D7, bound to the 40- to 42-kDa protein, allowing us to identify that protein as apoE. Sequencing of sea lion apoE cDNA clones demonstrated that sea lion apoE is 311 amino acids in length, 12 residues longer than human apoE. All 12 additional residues are located in the NH2-terminal 31 amino acids, a region that has extremely low homology with the NH2-terminal portion of human apoE. The remainder of the sea lion apoE sequence is 74% homologous to human apoE. The sea lion apoE cDNA was expressed in Chinese hamster ovary (CHO) cells as well as CHO ldlD cells, a cell line that is deficient in O-glycosylation of proteins. The size of the sea lion apoE secreted by these two cell lines, compared with the apoE in sea lion plasma, indicated that the predominant form of apoE in sea lion plasma must be posttranslationally modified. Thus, our studies have demonstrated that the higher apparent molecular weight of pinniped (sea lion) apoE is due to a longer polypeptide chain as well as posttranslational modification of the protein.
Amino Acid Sequence↗
cDNA sequence of the human integrin beta 5 subunit.
A novel integrin receptor involved in cell adhesion to the matrix protein vitronectin has recently been described from a human lung epithelial-derived cell line (Cheresh, D. A., Smith, J. W., Cooper, H. M., and Quaranta, V. (1989) Cell 57, 59-69). This receptor has an alpha subunit that appears identical to the alpha v of the vitronectin receptor alpha v beta 3 expressed in melanoma and endothelial cells, but is complexed with a distinct beta subunit, beta 5. cDNA clones coding for beta 5 have been isolated and used to determine the mRNA and amino acid sequence of this new subunit. A 3.3-kilobase mRNA was found to code for a mature protein of 775 amino acid residues with a hydrophobic leader sequence of 24 amino acids. A 56% identity was found between the beta 5 and beta 3 protein sequences, making them the most closely related of the integrin beta subunits. Polymerase chain reaction abundance analysis revealed that alpha v and beta 5 mRNAs were found in seven very different cell lines, compared with beta 3 mRNA which was found in only three of the them, indicating that this new integrin receptor may be widely distributed.
Amino Acid Sequence↗
The integrin beta 1 subunit associates with the vitronectin receptor alpha v subunit to form a novel vitronectin receptor in a human embryonic kidney cell line.
We describe a novel integrin heterodimer on the surface of the human embryonic kidney cell line 293. This receptor is comprised of alpha v and beta 1 subunits, each of which has been previously found in association with other integrin subunits. This alpha v.beta 1 complex was identified as the predominant vitronectin receptor (VnR) on the surface of 293 cells by immunoprecipitation with antibodies raised against the alpha v subunit. Polymerase chain reaction analysis detected mRNAs for alpha v and beta 1 subunits while no evidence was obtained for beta 2, beta 3, or alpha IIb integrin subunit mRNA. Immunoprecipitation of surface-iodinated proteins with antibodies to alpha v gave bands of 150 and 120 kDa. The 120-kDa band reacted with antibodies to beta 1 in immunoblotting experiments. 293 cells adhere to vitronectin, fibronectin, laminin, and collagen IV, while von Willebrand factor and fibrinogen, known ligands of the VnR (alpha v.beta 3), did not support adhesion. A polyclonal antibody directed against both subunits of the VnR (alpha v, beta 3) inhibits attachment of 293 cells to vitronectin but not to other adhesive proteins. A beta 1-specific monoclonal inhibited attachment to fibronectin, laminin, and collagen IV, known ligands of beta 1 integrins, as well as vitronectin. This novel (alpha v. beta 1) VnR thus appears to mediate cell adhesion exclusively to vitronectin, in contrast to previously described VnRs which have multiple ligands.
Antibodies↗
Cermet cements.
Cermet ionomer cements are sintered metal/glass powders, which can be made to react with poly(acids). These new cements are significantly more resistant to abrasion than regular glass ionomer cements and are widely accepted as core build-up materials and lining cements. They can strengthen teeth and provide the clinician with an opportunity to treat early dental caries.
Cermet Cements↗
The failed restoration: causes of failure and how to prevent them.
Ceramic restorations lack tensile strength and suffer from static fatigue. The margins of safety required to prevent fracture are much greater than for metal. Composite restorations, even laboratory cured, have yet to be fully tested over long periods. The hydrolytic stability of these materials still requires improvement. Glass-ionomer cements lack fracture toughness and will not accept a high polish due to their porous surfaces. Failure in restorations can only be avoided by recognizing the deficiencies in physical properties of all our restorative materials and using them in areas where the hostile oral environment causes minimal damage. The cast-gold restoration will probably remain supreme for crown and inlay work. The unique properties of the metallic bond are ideally suited to withstand maximum occlusal stress under most clinical conditions.
Crowns↗
Tissue-specific expression, developmental regulation, and chromosomal mapping of the lecithin: cholesterol acyltransferase gene. Evidence for expression in brain and testes as well as liver.
Lecithin:cholesterol acyltransferase (LCAT) catalyzes the esterification of cholesterol in high density lipoproteins, thereby facilitating transport of excess cholesterol from peripheral tissues to liver. We report here studies of the developmental, dietary, and genetic control of LCAT gene expression. In adult male Sprague-Dawley rats fed a standard chow diet LCAT mRNA was most abundant in liver, a major source of the plasma enzyme, but appreciable levels were also present in brain and testes. Since both brain and testes are isolated from blood by tight cellular barriers, undoubtedly greatly reducing the level of plasma-derived LCAT in cerebrospinal fluid and testes, the production of LCAT in these tissues may be important for removal of excess cholesterol. Noteworthy changes in the expression of LCAT mRNA were observed during development of both rodents and humans. On the other hand, LCAT mRNA levels were relatively resistant to dietary challenge or to drugs affecting cholesterol metabolism. Since human epidemiological studies have suggested an association between LCAT levels and variations of high density lipoprotein cholesterol, we examined LCAT gene polymorphisms in a mouse animal model. Mapping of the LCAT gene (Lcat) to mouse Chromosome 8 within 2 centimorgans of the Es-2 locus indicates that it does not correspond to any previously mapped loci affecting high density lipoprotein phenotypes in the mouse.
Aging↗
Expression of recombinant platelet glycoprotein IIbIIIa results in a functional fibrinogen-binding complex.
The ability of cDNAs encoding the human platelet glycoprotein IIbIIIa to be expressed and assembled into a functional integrin receptor was assessed by transient transfection into a human cell line. Transfection of full length cDNAs resulted in synthesis of high levels of integrin subunits which appear to be stable within the cell for several days. Coexpression of both subunits resulted in a proteolytically processed form of GPIIb that associated with GPIIIa as a heterodimeric complex as the cell surface. Transport to the cell surface required association of these subunits with each other or with endogenous integrin subunits. When expressed alone, the GPIIb subunit remained intracellular, while the GPIIIa subunit was found to complex with endogenous proteins and was mobilized to the cell surface. The GPIIbIIIa receptor complex facilitated attachment of cells to known ligands for GPIIbIIIa: fibrinogen, vitronectin, and von Willebrand factor. This adhesion was sensitive to inhibition by the peptide GRGDV and the monoclonal antibody AP2, known inhibitors of platelet aggregation
Base Sequence↗
Rhesus monkey apolipoprotein(a). Sequence, evolution, and sites of synthesis.
Human lipoprotein(a) is a low density lipoprotein-like lipoprotein whose concentration in plasma is correlated with atherosclerosis. The characteristic protein component of lipoprotein(a) is apolipoprotein(a) (apo(a)) which is disulfide-linked to apolipoprotein B-100. Sequencing of rhesus monkey apo(a) cDNA suggests that this protein, like human apo(a), is highly similar to plasminogen. Sequence data suggests that a plasminogen-like protease activity and kringle 1-, 2-, 3-, and 5-like domains are unnecessary for apo(a) function, but a highly repeated kringle four-like domain is important. Liver is the major site of apo(a) RNA synthesis; reduced amounts of message were also found in testes and brain. Co-expression with apoB-100 and plasminogen in rhesus tissues is not mandatory.
Amino Acid Sequence↗
Expression of human plasminogen cDNA in a baculovirus vector-infected insect cell system.
A cDNA that encodes the human plasminogen (HPg) amino acid sequence has been inserted adjacent to the polyhedrin promoter in the genome of the baculovirus, Autographa californica nuclear polyhedrosis virus, which was then used to infect cultured cells of the farm armyworm, Spodoptera frugiperda. Under the conditions of cell growth employed, recombinant (rec)-HPg was secreted into the medium after 24 h postinfection (p.i.), at which point virtually no rec-HPg antigen remained inside the cells. At 48 h p.i., a maximal level of intact rec-HPg was present in the medium, which underwent substantial proteolytic digestion after that time. The rec-HPg produced by this expression system possessed a molecular weight equivalent to that of plasma [Glu1]-plasminogen. In addition, the rec-HPg adsorbed to Sepharose-lysine, and was eluted with epsilon-aminocaproic acid (EACA). The recombinant protein also interacted with polyclonal antibodies generated to plasma HPg, as well as with a monoclonal antibody directed against a distinct region (kringle 1-3) of the plasma HPg molecule. Finally, the insect-expressed rec-HPg was activatable to plasmin (HPm) by urokinase. The results demonstrate that this expression system produces a full-length functional single-chain rec-HPg, which can be isolated intact from the culture medium, with some consideration for the temporal events that occur in secretion and longer-term degradation of the protein. The fact that this rec-HPg was converted to HPm with a plasminogen activator, and that it interacted with anti-plasma HPg polyclonal and monoclonal antibodies, as well as with the ligand, EACA, indicates that the molecule retains many of its important functional properties and is folded in an integral manner.
Animals↗
A perspective on dentistry today.
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Australia↗
[Glass-ionomer cement].
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Dental Cavity Preparation↗
'Ceramics in clinical dentistry'.
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Ceramics↗