Upscaling Mixing-Controlled Reactions in Unsaturated Porous Media.

We study mixing-controlled chemical reactions in unsaturated porous media from a pore-scale perspective. The spatial heterogeneity induced by the presence of two immiscible phases, here water and air, in the pore space generates complex flow patterns that dominate reactive mixing across scales. To assess the impact of different macroscopic saturation states (the fraction of pore volume occupied by water) on mixing-controlled chemical reactions, we consider a fast irreversible reaction between two initially segregated dissolved species that mix as one solution displaces the other in the heterogeneous flow field of the water phase. We use the pore-scale geometry and water distributions from the laboratory experiments reported by Jiménez-Martínez et al. (Geophys. Res. Lett. 42: 5316-5324, 2015). We analyze reactive mixing in three complementary ways. Firstly, we post-process experimentally observed spatially distributed concentration data; secondly, we perform numerical simulations of flow and reactive transport in the heterogeneous water phase, and thirdly, we use an upscaled mixing model. The first approach relies on an exact algebraic map between conservative and reactive species for an instantaneous irreversible bimolecular reaction that allows to estimate reactive mixing based on experimental conservative transport data. The second approach is based on reactive random walk particle tracking simulations in the numerically determined flow field in the water phase. The third approach uses a dispersive lamella approach that accounts for the impact of flow heterogeneity on mixing in terms of effective dispersion coefficients, which are estimated from both experimental data and numerical random walk particle tracking simulations. We observe a significant increase in reactive mixing for decreasing saturation, which is caused by the stronger heterogeneity of the water phase and thus of the flow field. This is consistently observed in the experimental data and the direct numerical simulations. The dispersive lamella model, parameterized by the effective interface width, provides robust estimates of the evolution of the product mass obtained from the experimental and numerical data.

Prospective case controlled clinical study of post-endodontic pain after rotary root canal preparation performed by a single operator.

OBJECTIVES: The aim of this study was to assess the influence of the shaping technique on incidence, intensity, duration and type of postoperative pain (PP). METHODS: Root canal treatments were carried out with rotary instrumentation (n=80) during a single-visit, and data about pre-treatment conditions were collected. Patients were given a questionnaire to record the presence or absence of post-endodontic pain, its duration and level of discomfort. A matching patient (same pre-treatment conditions but manual instrumentation) was randomly selected from a pool (n = 374) and assigned to the control group. A total of 44 pairs of patients matched completely and were included in the study. Incidence (yes/no) of PP was assessed using Chi-square tests, intensity (mild, moderate, severe) with trend tests and duration (days) with Mann-Whitney U tests. RESULTS: A significantly greater proportion of the patients in the control group reported pain than did patients in the rotary shaping group (p < 0.05). However, pain duration was shorter (p = 0.008) in the control group. Differences in level of discomfort were not statistically significant. CONCLUSIONS: The results of this prospective in vivo study suggest that a higher incidence of PP should be expected after manual root canal preparation. However a second major finding of the study is that when present, PP after a rotary canal preparation is expected to last longer. CLINICAL SIGNIFICANCE: There has been an increase in the use of rotary techniques among dentists in recent years. The present study analyses the differences in the incidence and characteristics of postoperative pain that should be expected after rotary canal preparation compared to traditional manual methods that had not been reported yet.

Scaling of convective mixing in porous media.

Convective mixing in porous media is triggered by a Rayleigh-Bénard-type hydrodynamic instability as a result of an unstable density stratification of fluids. While convective mixing has been studied extensively, the fundamental behavior of the dissolution flux and its dependence on the system parameters are not yet well understood. Here, we show that the dissolution flux and the rate of fluid mixing are determined by the mean scalar dissipation rate. We use this theoretical result to provide computational evidence that the classical model of convective mixing in porous media exhibits, in the regime of high Rayleigh number, a dissolution flux that is constant and independent of the Rayleigh number. Our findings support the universal character of convective mixing and point to the need for alternative explanations for nonlinear scalings of the dissolution flux with the Rayleigh number, recently observed experimentally.

Relationship between postendodontic pain, tooth diagnostic factors, and apical patency.

This study compares the incidence, degree, and length of postoperative pain in 300 endodontically treated teeth, with and without apical patency, in relation to some diagnostic factors (vitality, presence of preoperative pain, group, and mandible of treated tooth). Of the questionnaires received back, apical patency was maintained during shaping procedures with a #10 K-file in one group (n = 115) and not in the other (n = 121). There was significantly less postendodontic pain when apical patency was maintained in nonvital teeth. If pain appeared, its duration was longer when apical patency was maintained in teeth with previous pain or located in the mandible. Maintenance of apical patency does not increase the incidence, degree, or duration of postoperative pain when considering all variables together.

Appraisal of psychomotor skills of dental students at University Complutense of Madrid.

The aim of this study was to evaluate the psychomotor skills of the dental students at University Complutense of Madrid (UCM), using a battery of psychometric tests. The sample comprised 306 students of the 1st, 2nd, 3rd and 4th years of Odontology, who, during the last month of the academic term, took the test on rotation of solid shapes, the Embedded Figures test in its group form (GEFT), the O'Connor Tweezer test, the MacQuarrie test for mechanical ability and the indirect vision test. Before these tests began, some personal data of all students were collected. The results showed some statistically significant correlation between several personal variables (sex, manual dominance and previous skills) and performance in the psychometric tests, although no significant relation was found between these variables and the students' academic qualifications. When comparisons were made between the psychomotor tests and the academic results of the students, significant differences appeared in the tracing and dotting subtests of the MacQuarrie test, whereby those students with higher practical qualifications reached the best punctuation. In the O'Connor Tweezer test, the students who obtained the worst results were those with lower qualifications. These data could serve to detect at an early stage those students who need greater educational support. No relation was found between the GEFT and the indirect vision test.