Oxidised micrometeorites as evidence for low atmospheric pressure on the early Earth.

Reconstructing a record of the partial pressure of molecular oxygen in Earth's atmosphere is key for understanding macroevolutionary and environmental change over geological history. Recently, the oxidation state of iron in micrometeorites has been taken to imply the presence of modern Earth concentrations of oxygen in the upper atmosphere at 2.7 Ga, and therefore a highly chemically stratified atmosphere (Tomkins et al., 2016). We here explore the possibility that the mixing ratio of oxygen in Earth's upper atmosphere, that probed by micrometeorites, may instead be sensitive to the surface atmospheric pressure. We find that the concentrations of oxygen in the upper atmosphere required for micrometeorite oxidation are achieved for a 0.3 bar atmosphere. In this case, significant water vapour reaches high up in the atmosphere and is photodissociated, leading to the formation of molecular oxygen. The presence of oxidised iron in micrometeorites at 2.7 Ga may therefore be further evidence that the atmospheric pressure at the surface of the early Earth was substantially lower than it is today.

A randomised clinical study to evaluate the efficacy of alcohol-free or alcohol-containing mouthrinses with chlorhexidine on gingival bleeding.

OBJECTIVES: Gingival bleeding following twice-daily use of 0.2% w/v chlorhexidine digluconate mouthrinse with and without alcohol (0.2% CHX-alcohol; 0.2% CHX-alcohol-free, respectively) and brushing with a standard fluoride toothpaste was compared to brushing alone. METHODS: Three hundred and nineteen subjects with mild-to-moderate gingivitis (with ≥16 gradable permanent teeth including four molars, bleeding after brushing and ≥20 bleeding sites) completed this randomised, examiner-blinded, parallel-group study. A prophylaxis was performed at baseline. Gingival Severity Index (GSI; primary objective), Gingival Index (GI) and Plaque Index (PI) were assessed at baseline and after 6 weeks of treatment. Adverse events (AEs) were recorded throughout the study. RESULTS: Between treatment differences at week 6 demonstrated significantly lower GSI for the 0.2% CHX-alcohol and 0.2% CHX-alcohol-free groups compared to brushing alone (primary endpoint; treatment difference -0.061 [95% CI -0.081, -0.041] and -0.070 [95% CI -0.090, -0.050], respectively; both p <0.0001). There were also significant reductions in GI and PI for the 0.2% CHX-alcohol and 0.2% CHX-alcohol-free groups compared to brushing alone (all p <0.0001). The proportion of subjects reporting ≥1 treatment-related adverse events (TRAEs) was 27.8% (0.2% CHX-alcohol), 24.8% (0.2% CHX-alcohol-free) and 3.7% (brushing alone). CONCLUSIONS: Chlorhexidine mouthrinse with or without alcohol as an adjunct to brushing with regular fluoride toothpaste significantly reduces bleeding scores, plaque and gingival inflammation compared to brushing alone. TRAEs are characteristic of those associated with the use of chlorhexidine and are similar for both mouthrinses.

An in vivo comparison of radiographic and directly assessed clinical caries status of posterior approximal surfaces in primary and permanent teeth.

At general dental practices in Scotland 211 children between the ages of 5 and 15 years were examined by 1 observer. A comparison of the status of 1,468 permanent and 756 primary posterior approximal surfaces was made on the basis of their appearance on posterior bite-wing radiographs and the findings of a direct in vivo visual examination, made after temporary tooth separation had been achieved over 1 week using elastomeric separation. For permanent tooth surfaces, 0% of radiolucencies in the outer half of enamel, 10.5% in the inner half of enamel, 40.9% extending to the outer half of dentine, and 100% extending to the inner half of the dentine were found clinically to be cavitated. The analogous results for primary teeth were that 2.0, 2.9, 28.3, and 95.5%, respectively, of radiolucencies appeared to be cavitated. Although further research with larger numbers of permanent teeth is indicated, these results may contribute to a re-evaluation of the optimal threshold for restorative intervention at approximal sites. Greater numbers of approximal radiolucencies and carious lesions (p less than 0.001) were found in those surfaces which initially had a normal anatomical contact when compared to those which did not.

Effects of diagnostic threshold and overlapped approximal surfaces on reported caries status.

The aims of this study were to examine the influence upon reported caries status of: 1) employing different diagnostic thresholds and 2) using differing conventions for treating approximal surfaces which appeared overlapped on posterior bitewing radiographs. Caries prevalence data from a group of 211 Scottish schoolchildren aged 5-15 yr studied during a trial of elective temporary tooth separation in general dental practice in Scotland were used. In this "moderate" caries group, values for dmft/DMFT rose significantly (P less than 0.001) when the D1 diagnostic threshold (all grades of lesion accepted) was applied in comparison with the D3 threshold (only caries into dentine recognised); dmft increasing from 3.9 to 5.4 and DMFT increasing from 1.7 to 4.7. This demonstrated that an over-optimistic impression of overall caries levels may be given when only the D3 threshold is used uncritically. In this study the status of approximal surfaces which were overlapped on bitewing radiographs was assessed by direct clinical examination using the temporary elective tooth separation technique. The investigation showed that, for this juvenile population, most (81.8% mesial, 93.1% distal) overlapped approximal surfaces were sound. Significantly more mesial than distal surfaces were found to be overlapped.

The use of bitewing positioning devices in children's dentistry.

The use of film-holding, beam-aiming devices have been shown to have a number of potential advantages in achieving high quality bitweing radiographs, however, little information is available about their acceptability to children. The aims of this study were: (1) to determine the level of acceptance of a conventional type of film positioner to child patients in a general practice setting in Scotland and (2) to compare the acceptability to children of bitewing procedures using: the freehand technique, a 'Rinn' positioner and a new positioner, the 'HPL' device. In the general practice group, following modifications made during a pilot study, 211 children aged 3-15 years were offered a bitewing examination with a modified Rinn positioner at recall. The overall acceptance rate of the bitewing procedure was 82.5%. All 10 children aged 3-4 years offered bitewings refused, while 77 (69%) of subjects aged 5-9 years accepted, as did all the 89 children aged 10-15 years. In the comparison of acceptability investigation, three groups of 30 children aged 6-15 years requiring bitewing radiographs were selected at random. Each group had a different bitewing technique carried out by the same operator. The children's acceptance of all three techniques was high (87-97%) and no statistically significant difference was found between the acceptability of the freehand method and those involving film positioning devices. Although the unmodified Rinn design suffered from a number of problems, the modified version was found to be acceptable by many children.(ABSTRACT TRUNCATED AT 250 WORDS)

Temporary elective tooth separation as a diagnostic aid in general dental practice.

This study examined the feasibility, acceptability and potential diagnostic value of using a 'blanket' technique for placing elastomeric separators as a diagnostic aid in a general practice situation. Five practices were visited and 211 children between 5 and 15 years were examined. All 211 children accepted the 'clinical without separators' examination, 37 children were unwilling to have the radiographic examination and 12 of the 146 children who required separators refused or removed them. The use of the technique as a routine aid was acceptable to the host practitioners, the parents, most of the patients and to the clinician conducting the study. The method was shown to be valuable in revealing additional approximal lesions. A total of 703 lesions were disclosed by the 'clinical with separators' method, compared with 479 diagnosed by routine clinical examination alone. As many of the additional lesions were at the precavitation stage, this information could be used to target those patients with special needs for preventive care. While the larger dentinal lesions revealed by temporary elective tooth separation were confirmed by bitewing radiographs, many of the small precavitation lesions were not. The results showed, however, that bitewing radiographs were still an important diagnostic aid, especially in the deciduous dentition. Elastomeric separators may have a role as a diagnostic aid in conjunction with bitewings, rather than as a replacement for them.

Urbanization of the Malays since independence: evidence from West Malaysia, 1957 and 1970.

PIP: The authors attempt to evaluate the Malaysian policy for promoting urbanization of Malays by comparing their geographical location in 1957 and 1970. Data are taken primarily from the 1970 census.^ieng