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Biomedical subjects

C H Turner

Publications and source records attributed to C H Turner.

At least 163 records · Page 9Linked to original sources
PubMed1983

Conformation and domain structure of the non-histone chromosomal proteins, HMG 1 and 2. Isolation of two folded fragments from HMG 1 and 2.

Proteins HMG 1 and 2 have been digested with trypsin and two major products, stable to further digestion between 8 min and 2 h, have been purified (peptides A and B). Peptide B from HMG 1 has been identified as residues 12-75 and peptide A as residues 94/96-169 by amino acid analyses and Edman degradations. Peptide B spontaneously folds with the formation of 51% helix and exhibits the majority of the perturbed NMR resonances characteristic of folded intact HMG 1. Peptide B is stably folded in the presence of 150 mM NaCl between pH 3 and 10, like intact HMG 1. Peptide A forms 30% alpha-helix and also exhibits tertiary folding but is denatured by pH 10. The 11 N-terminal residues removed by trypsin contain both sites of post-synthetic acetylation (residues 2 and 11), a situation very similar to that found with core histones. It is proposed that HMG 1 and 2 consist of four structural domains, viz: (a) residues 1-11, (b) residues 12 to approximately 75, (c) residues 94-169 and (d) the very acidic region beyond residue 169. The instability of peptide A may mean that it is not a truly independent domain. No structural similarities to histone H1 are therefore observed in HMG 1 and 2.

Animals↗
PubMed1983

An investigation of the process of casting cores on to preformed wrought dental posts.

The casting of gold on to wrought "Wiptam" and "G.T." posts has been investigated. Notching of "Wiptam" posts gave rise to grain structure rearrangement; carbon deposits from the wax burn were retained in the notches and prevented complete filling by the gold. Serious cracks developed from these notches when the core was cast on centrifugally but only slightly when Solbrig's method was used. These cracks explain why "Wiptam" posts occasionally fracture. The above problems were not encountered with the "G.T." post, which has inbuilt retention channels, and allows a more complete burn out of the wax pattern.

Crowns↗
PubMed1983

Intra-radicular hydrostatic pressure changes during the cementation of post-retained crowns.

The intra-radicular hydrostatic pressures generated during the cementation of parallel-sided dental posts have been measured. Pressures are generated only when cement is inserted into the prepared post hole. Using zinc phosphate cement, with posts placed 2 min from the commencement of mixing, pressure has been shown to depend on post diameter, the closeness of fit, and the powder-liquid ratio. The maximum pressure recorded was 1.7 x 10(4) kN/m2 using a 1.3 mm diameter post, a mean cement film thickness of 37 microns, and an ideal powder-liquid ratio of 3.0. Pressures similar to that generated using zinc phosphate cement were recorded when black copper phosphate was used as the lute, but zinc polycarboxylate generated less pressure, and an ortho-ethoxy benzoic acid cement markedly less pressure. Before it is possible to confirm the ideal luting cement for posts, further studies of the effectiveness of cement release channels, and post retention, are necessary.

Cementation↗
PubMed1983

Investigation of hydrostatic pressure changes during cementation of screw-retained posts, and posts with integral cement release channels.

Intra-radicular pressures during the cementation of screw-retained posts have been found to reach 1.5 x 10(4) KN/m2 when cement is inserted into the prepared post hole or no pressure, indicating that an incomplete cement lute had developed, when the post was coated with cement. The effectiveness of cement channels was investigated and for the traditional single channel, using the cement 'insertion' method, there was an intra-radicular pressure of 8.5 x 10(4) KN/m2, compared with 1.1 x 10(4) KN/m2 for the corresponding round post. Multiple cement release channels gave an enhanced pressure reduction to 2.0 x 10(3) KN/m2.

Cementation↗
PubMed1982

The utilization of roots to carry post-retained crowns.

A retrospective study of 5-year-old post-retained crowns made using a matched reamer/sprue technique, was carried out. Standardized radiographs enabled the length of post within the root to be compared with the maximum available length, and this was related to the success of the restoration. Six posts (11.5% of the sample) had become dislodged, of which four were successfully re-cemented. The range of root utilization varied from 46 to 137% of the calculated ideal maximum length, indicating that radiographs or measurements were not used routinely as an aid to root preparation, and in some cases the integrity of the apical seal had been severely prejudiced. Despite some very short posts, no roots had fractured. The minimum length of post which ideally should be used has been calculated as 9 mm.

Crowns↗
PubMed1982

A retrospective study of the fit of jacket crowns placed around gold posts and cores, and the associated gingival health.

A retrospective study has been carried out of the marginal fit and associated gingival health of jacket crowns placed around gold posts 5 years previously. Crown fit was classified as either visibly or palpably satisfactory, overhanging or deficient. 67.2% of crowns showed one or more discrepancies of marginal fit, and this varied with the position around the tooth. Palatal margins of maxillary porcelain jacket crowns fitted poorly and there was frequent caries at this site. Periodontal pocketing developed mesially and distally, and little gingival recession. In contrast gingival recession, exposing the crown margins, occurred frequently labially and palatally, but the mean periodontal pocket depth remained within normal limits.

Adolescent↗
PubMed1980

Metabolic activation of benz[a]anthracene in hamster embryo cells: the structure of a guanosine-anti-BA-8,9-diol 10,11-oxide adduct.

The structures of two guanosine-hydrocarbon adducts prepared from polyG that had been incubated with anti-BA-8,9-diol 10,11-oxide (r-8,t-9-dihydroxy-t-10,11-oxy-8,9,10,11-tetrahydrobenz[a]anthracene) were investigated by examining their H-n.m.r. spectra, their pK values before and after treatment with nitrous acid and their stabilities in 1M KOH. The data show that both of the adducts were formed by reaction between the exocyclic amino group of guanine and the 11-position of the diolepoxide. One of these adducts is indistinguishable from an adduct isolated from hamster embryo cells that had been treated with benz[a]anthracene and that may contribute to the biological activity of this weak carcinogen.

Animals↗