The expansion field: The value of H_0

Any calibration of the present value of the Hubble constant requires recession velocities and distances of galaxies. While the conversion of observed velocities into true recession velocities has only a small effect on the result, the derivation of unbiased distances which rest on a solid zero point and cover a useful range of about 4-30 Mpc is crucial. A list of 279 such galaxy distances within v<2000 km/s is given which are derived from the tip of the red-giant branch (TRGB), from Cepheids, and from supernovae of type Ia (SNe Ia). Their random errors are not more than 0.15 mag as shown by intercomparison. They trace a linear expansion field within narrow margins from v=250 to at least 2000 km/s. Additional 62 distant SNe Ia confirm the linearity to at least 20,000 km/s. The dispersion about the Hubble line is dominated by random peculiar velocities, amounting locally to <100 km/s but increasing outwards. Due to the linearity of the expansion field the Hubble constant H_0 can be found at any distance >4.5 Mpc. RR Lyr star-calibrated TRGB distances of 78 galaxies above this limit give H_0=63.0+/-1.6 at an effective distance of 6 Mpc. They compensate the effect of peculiar motions by their large number. Support for this result comes from 28 independently calibrated Cepheids that give H_0=63.4+/-1.7 at 15 Mpc. This agrees also with the large-scale value of H_0=61.2+/-0.5 from the distant, Cepheid-calibrated SNe Ia. A mean value of H_0=62.3+/-1.3 is adopted. Because the value depends on two independent zero points of the distance scale its systematic error is estimated to be 6%. Typical errors of H_0 come from the use of a universal, yet unjustified P-L relation of Cepheids, the neglect of selection bias in magnitude-limited samples, or they are inherent to the adopted models.Comment: 44 pages, 4 figures, 6 tables, accepted for publication in the Astronony and Astrophysics Review 15

Challenges in the transition to clinical training in dentistry: An ADEE special interest group initial report

Introduction: Curricular integration in higher education has been widely supported in the educational literature. As a result, several health care and specifically dental curricula have evolved from compartmentalised disciplinary training to integrated modalities; however, in many courses, a pre-clinical-clinical watershed remains a barrier to integration in dental education. This article introduces a general description of the pre-clinical-clinical transition in dentistry according to the outcomes of the discussion held during the first working group session of the “Transition to Clinical Training” Special Interest Group during the 2016 annual meeting of the Association for Dental Education in Europe. Materials and Methods: An online questionnaire was made available before the meeting to survey the curricular characteristics of the participants’ schools. During the meeting, a working session related to the pre-clinical-clinical transition occurred. Conclusions from the discussion are summarised in this article. Results: Fourteen dental schools from 12 countries participated in the online survey. The included programmes had an average duration of 5.3 years (SD = 0.48), with high school or the local equivalent as the required entrance level for dentistry. The hybrid curriculum was the leading curriculum design (n = 9) followed by competence-based curricula (n = 3), with patient treatment as the core of clinical training in every included programme. Conclusion: The pre-clinical-clinical transition in dentistry is a recognisable matter in dental education that requires assessment and research to ease the management of a stage with relevant influence on educational outcomes. This article presents an initial framework for further research and educational intervention

Effects of instrumentation, irrigation and dressing with calcium hydroxide on infection in pulpless teeth with periapical bone lesions

Aim The aim of this study was to evaluate the fate of microorganisms in root canals of teeth with infected pulps and periapical bone lesions with and without the use of calcium hydroxide medication. Methodology Endodontic samples were cultured and microorganisms were counted and identified in 4 3 teeth before (sample 1) and after (sample 2) treatment during the first visit and before (sample 3) and after (sample 4) treatment during the second visit. In the first visit teeth were instrumented and half of the teeth were filled with a thick slurry of calcium hydroxide in sterile saline, The other teeth were obturated with gutta-percha and AH-26 seater. After 4 weeks the teeth with calcium-hydroxide were accessed again and after microbiological sampling they were obturated with gutta-percha and AH-26 sealer. Results The mean total colony forming unit (CFU) counts of positive samples dropped significantly as a result or canal preparation during the first visit from 1.0 X 10(6) to 1.8 x 10(3) (between samples 1 and 2) but increased to 9.3 x 10(3) in the period between the two visits (sample 2 and 3). There was no difference in mean total CFU counts of positive samples between the end of the first (sample 21) and the end of the second visit (sample 4). The most frequently isolated species were Prevotella intermedia, Capnocytophaga spp.. Actinomyces odontolyticus, Propionibacterium acnes and Peptostreptococcus micros. Conclusions Although a calcium hydroxide paste was placed in the prepared canals. the number of positive canals had increased in the period between visits. However, the number of microorganisms had only increased to 0.93% of the original number of CFU (sample 1). It is concluded that a calcium hydroxide and sterile saline slurry limits but does not totally prevent regrowth of endodontic bacteria

Influence of scan setting selections on root canal visibility with cone beam CT

OBJECTIVES: The aim of this study was to assess the influence of scan setting selection, including field of view (FOV) ranging from small to large, number of projections and scan modes on the visibility of the root canal with cone beam CT (CBCT). METHODS: One human mandible cadaver was scanned with CBCT (Accuitomo 170; J Morita MPG Corp., Kyoto, Japan) using six different FOVs (4×4 cm, 6×6 cm, 8×8 cm, 10×10 cm, 14×10 cm and 17×12 cm) with either 360 or 180 projections in standard and high resolution. The right canine was selected for evaluation. Ten observers independently assessed the visibility of the canal space and overall image quality on a five-point scale. RESULTS: The results indicate that both selections of FOV and number of projections have significant influence on root canal visibility (p = 0.0001), whereas scan mode, whether standard or high resolution, was less relevant (p = 0.34). CONCLUSIONS: The smallest FOV available should always be used for endodontic applications, and it is not recommended to reduce the number of projections to 180. Using the standard scan mode instead of high resolution does not negatively influence the visibility of the root canal space and is therefore recommended