11,731 research outputs found
Outcome of secondary root canal treatment: a systematic review of the literature.
UNLABELLED: AIMS (I): To investigate the effects of study characteristics on the reported success rates of secondary root canal treatment (2 degrees RCT or root canal retreatment); and (ii) to investigate the effects of clinical factors on the success of 2 degrees RCT. METHODOLOGY: Longitudinal human clinical studies investigating outcome of 2 degrees RCT which were published upto the end of 2006 were identified electronically (MEDLINE and Cochrane database 1966-2006 Dec, week 4). Four journals (Dental Traumatology, International Endodontic Journal, Journal of Endodontics, Oral Surgery Oral Medicine Oral Pathology Endodontics Radiology), bibliographies of all relevant papers and review articles were hand-searched. Two reviewers (Y-LN, KG) independently assessed and selected the studies based on specified inclusion criteria and extracted the data onto a pre-designed proforma, independently. The criteria were: (i) Clinical studies on 2 degrees RCT; (ii) Stratified analyses available for 2 degrees RCT where 1 degrees RCT data included; (iii) Sample size given and larger than 10; (iv) At least 6-month post-operative review; (v) Success based on clinical and/or radiographic criteria (strict = absence of apical radiolucency; loose = reduction in size of radiolucency); and (vi) Overall success rate given or could be calculated from the raw data. Three strands of evidence or analyses were used to triangulate a consensus view. The reported findings from individual studies, including those excluded for quantitative analysis, were utilized for the intuitive synthesis which constituted the first strand of evidence. Secondly, the pooled weighted success rates by each study characteristic and potential prognostic factor were estimated using the random effect model. Thirdly, the effects of study characteristics and prognostic factors (expressed as odds ratios) on success rates were estimated using fixed and random effects meta-analysis with DerSimonean and Laird's methods. Meta-regression models were used to explore potential sources of statistical heterogeneity. Study characteristics considered in the meta-regression analyses were: decade of publication, study-specific criteria for success (radiographic, combined radiographic & clinical), unit of outcome measure (tooth, root), duration after treatment when assessing success ('at least 4 years' or '<4 years'), geographic location of the study (North American, Scandinavian, other countries), and qualification of the operator (undergraduate students, postgraduate students, general dental practitioners, specialist or mixed group). RESULTS: Of the 40 papers identified, 17 studies published between 1961 and 2005 were included; none were published in 2006. The majority of studies were retrospective (n = 12) and only five prospective. The pooled weighted success rate of 2 degrees RCT judged by complete healing was 76.7% (95% CI 73.6%, 89.6%) and by incomplete healing, 77.2% (95% CI 61.1%, 88.1%). The success rates by 'decade of publication' and 'geographic location of study' were not significantly different at the 5% level. Eighteen clinical factors had been investigated in various combinations in previous studies. The most frequently and thoroughly investigated were 'periapical status' (n = 13), 'size of lesion' (n = 7), and 'apical extent of RF' (n = 5) which were found to be significant prognostic factors. The effect of different aspects of primary treatment history and re-treatment procedures has been poorly tested. CONCLUSIONS: The pooled estimated success rate of secondary root canal treatment was 77%. The presence of pre-operative periapical lesion, apical extent of root filling and quality of coronal restoration proved significant prognostic factors with concurrence between all three strands of evidence whilst the effects of 1 degrees RCT history and 2 degrees RCT protocol have been poorly investigated
A prospective study of the factors affecting outcomes of nonsurgical root canal treatment: part 1: periapical health.
AIM: To investigate the probability of and factors influencing periapical status of teeth following primary (1°RCTx) or secondary (2°RCTx) root canal treatment. METHODOLOGY: This prospective study involved annual clinical and radiographic follow-up of 1°RCTx (1170 roots, 702 teeth and 534 patients) or 2°RCTx (1314 roots, 750 teeth and 559 patients) carried out by Endodontic postgraduate students for 2-4 (50%) years. Pre-, intra- and postoperative data were collected prospectively on customized forms. The proportion of roots with complete periapical healing was estimated, and prognostic factors were investigated using multiple logistic regression models. Clustering effects within patients were adjusted in all models using robust standard error. RESULTS: proportion of roots with complete periapical healing after 1°RCTx (83%; 95% CI: 81%, 85%) or 2°RCTx (80%; 95% CI: 78%, 82%) were similar. Eleven prognostic factors were identified. The conditions that were found to improve periapical healing significantly were: the preoperative absence of a periapical lesion (P = 0.003); in presence of a periapical lesion, the smaller its size (P ≤ 0.001), the better the treatment prognosis; the absence of a preoperative sinus tract (P = 0.001); achievement of patency at the canal terminus (P = 0.001); extension of canal cleaning as close as possible to its apical terminus (P = 0.001); the use of ethylene-diamine-tetra-acetic acid (EDTA) solution as a penultimate wash followed by final rinse with NaOCl solution in 2°RCTx cases (P = 0.002); abstaining from using 2% chlorexidine as an adjunct irrigant to NaOCl solution (P = 0.01); absence of tooth/root perforation (P = 0.06); absence of interappointment flare-up (pain or swelling) (P =0.002); absence of root-filling extrusion (P ≤ 0.001); and presence of a satisfactory coronal restoration (P ≤ 0.001). CONCLUSIONS: Success based on periapical health associated with roots following 1°RCTx (83%) or 2°RCTx (80%) was similar, with 10 factors having a common effect on both, whilst the 11th factor 'EDTA as an additional irrigant' had different effects on the two treatments
Composition of Jupiter irregular satellites sheds light on their origin
Irregular satellites of Jupiter with their highly eccentric, inclined and
distant orbits suggest that their capture took place just before the giant
planet migration. We aim to improve our understanding of the surface
composition of irregular satellites of Jupiter to gain insight into a narrow
time window when our Solar System was forming. We observed three Jovian
irregular satellites, Himalia, Elara, and Carme, using a medium-resolution
0.8-5.5 micro m spectrograph on the National Aeronautics and Space
Administration (NASA) Infrared Telescope Facility (IRTF). Using a linear
spectral unmixing model we have constrained the major mineral phases on the
surface of these three bodies. Our results confirm that the surface of Himalia,
Elara, and Carme are dominated by opaque materials such as those seen in
carbonaceous chondrite meteorites. Our spectral modeling of NIR spectra of
Himalia and Elara confirm that their surface composition is the same and
magnetite is the dominant mineral. A comparison of the spectral shape of
Himalia with the two large main C-type asteroids, Themis (D 176 km) and Europa
(D 352 km), suggests surface composition similar to Europa. The NIR spectrum of
Carme exhibits blue slope up to 1.5 microm and is spectrally distinct from
those of Himalia and Elara. Our model suggests that it is compositionally
similar to amorphous carbon. Himalia and Elara are compositionally similar but
differ significantly from Carme. These results support the hypotheses that the
Jupiter irregular satellites are captured bodies that were subject to further
breakup events and clustered as families based on their similar physical and
surface compositions
Neutrino masses along with fermion mass hierarchy
Recently a new mechanism has been proposed to cure the problem of fermion
mass hierarchy in the Standard Model (SM) model. In this scenario, all SM
charged fermions other than top quark arise from higher dimensional operators
involving the SM Higgs field. This model also predicted some interesting
phenomenology of the Higgs boson. We generalize this model to accommodate
neutrino masses (Dirac & Majorana) and also obtain the mixing pattern in the
leptonic sector. To generate neutrino masses, we add extra three right handed
neutrinos in this model.Comment: 20 pages, the content on results and phenomenology have been
expanded, a new section on UV completion of the model has been added and also
some new references, this version has been accepted by Physical Review
Free fields via canonical transformations of matter-coupled 2D dilaton gravity models
It is shown that the 1+1-dimensional matter-coupled Jackiw-Teitelboim model
and the model with an exponential potential can be converted by means of
appropriate canonical transformations into a bosonic string theory propagating
on a flat target space with an indefinite signature. This makes it possible to
consistently quantize these models in the functional Schroedinger
representation thus generalizing recent results on CGHS theory.Comment: 15 pages, Late
Covariance and Time Regained in Canonical General Relativity
Canonical vacuum gravity is expressed in generally-covariant form in order
that spacetime diffeomorphisms be represented within its equal-time phase
space. In accordance with the principle of general covariance, the time mapping
{\T}: {\yman} \to {\rman} and the space mapping {\X}: {\yman} \to {\xman}
that define the Dirac-ADM foliation are incorporated into the framework of the
Hilbert variational principle. The resulting canonical action encompasses all
individual Dirac-ADM actions, corresponding to different choices of foliating
vacuum spacetimes by spacelike hypersurfaces. In this framework, spacetime
observables, namely, dynamical variables that are invariant under spacetime
diffeomorphisms, are not necessarily invariant under the deformations of the
mappings \T and \X, nor are they constants of the motion. Dirac observables
form only a subset of spacetime observables that are invariant under the
transformations of \T and \X and do not evolve in time. The conventional
interpretation of the canonical theory, due to Bergmann and Dirac, can be
recovered only by postulating that the transformations of the reference system
({\T},{\X}) have no measurable consequences. If this postulate is not deemed
necessary, covariant canonical gravity admits no classical problem of time.Comment: 41 pages, no figure
Topological dilaton black holes
In four-dimensional spacetime, when the two-sphere of black hole event
horizons is replaced by a two-dimensional hypersurface with zero or negative
constant curvature, the black hole is referred to as a topological black hole.
In this paper we present some exact topological black hole solutions in the
Einstein-Maxwell-dilaton theory with a Liouville-type dilaton potential.Comment: 8 pages, Revtex, no figure
The contribution of boundary layer nucleation events to total particle concentrations on regional and global scales
International audienceThe contribution of boundary layer (BL) nucleation events to total particle concentrations on the global scale has been studied by including a new particle formation mechanism in a global aerosol microphysics model. The mechanism is based on an analysis of extensive observations of particle formation in the BL at a continental surface site. It assumes that molecular clusters form at a rate proportional to the gaseous sulfuric acid concentration to the power of 1. The formation rate of 3 nm diameter observable particles is controlled by the cluster formation rate and the existing particle surface area, which acts to scavenge condensable gases and clusters during growth. Modelled sulfuric acid vapour concentrations, particle formation rates, growth rates, coagulation loss rates, peak particle concentrations, and the daily timing of events in the global model agree well with observations made during a 22-day period of March 2003 at the SMEAR II station in Hyytiälä, Finland. The nucleation bursts produce total particle concentrations (>3 nm diameter) often exceeding 104 cm?3, which are sustained for a period of several hours around local midday. The predicted global distribution of particle formation events broadly agrees with what is expected from available observations. Over relatively clean remote continental locations formation events can sustain mean total particle concentrations up to a factor of 8 greater than those resulting from anthropogenic sources of primary organic and black carbon particles. However, in polluted continental regions anthropogenic primary particles dominate particle number and formation events lead to smaller enhancements of up to a factor of 2. Our results therefore suggest that particle concentrations in remote continental regions are dominated by nucleated particles while concentrations in polluted continental regions are dominated by primary particles. The effect of BL particle formation over tropical regions and the Amazon is negligible. These first global particle formation simulations reveal some interesting sensitivities. We show, for example, that significant reductions in primary particle emissions may lead to an increase in total particle concentration because of the coupling between particle surface area and the rate of new particle formation. This result suggests that changes in emissions may have a complicated effect on global and regional aerosol properties. Overall, our results show that new particle formation is a significant component of the aerosol particle number budget
Effective action for the Regge processes in gravity
It is shown, that the effective action for the reggeized graviton
interactions can be formulated in terms of the reggeon fields and
and the metric tensor in such a way, that it is local in
the rapidity space and has the property of general covariance. The
corresponding effective currents and satisfy the
Hamilton-Jacobi equation for a massless particle moving in the gravitational
field. These currents are calculated explicitly for the shock wave-like fields
and a variation principle for them is formulated. As an application, we
reproduce the effective lagrangian for the multi-regge processes in gravity
together with the graviton Regge trajectory in the leading logarithmic
approximation with taking into account supersymmetric contributions.Comment: 39 page
- …