Cavity Extent Research Articles

Sealing of cavitated occlusal carious lesions in the dentine of deciduous molars: a two-year randomised controlled clinical trial.

This two-arm, parallel-group, tooth-randomised, controlled noninferiority clinical trial aimed to compare survival rates between the sealing and restoring of cavitated occlusal carious lesions in dentine [International Caries Detection and Assessment System (ICDAS) 5] of deciduous molars using resin-modified glass-ionomer cement (RMGIC) and to assess caries progression radiographically. A total of 68 molars with ICDAS 5 occlusal lesions were randomly allocated into two groups, a sealing group (n = 31), in which RMGIC was placed directly over the carious lesion, and a restoration group (n = 37), in which a restoration with the same material was placed after selective caries removal. During the baseline and follow-up visits, dental caries was registered and caries activity was assessed according to a visuotactile criterion. At baseline, patient caries status (dmf-t) and cavity depth and extent (mesiodistal and buccolingual) were measured before RMGIC placement. An independent and blinded examiner evaluated the treated teeth using the USPHS criteria after one and two years. Standardised interproximal radiographs were taken for caries progression assessments. During the follow-up period, no lesion progression was observed radiographically. After one year (n = 60; 27 sealed and 33 restored) and two years (n = 48; 23 sealed and 25 restored) of follow-up, the treatment success rates were 78.8% and 76.0% in the restoration group and 59.3% and 47.8% in the sealing group, respectively. Multivariate Cox regression showed that lesions smaller than 2mm in the mesiodistal extent were less prone to fail after one year (p = 0.03). However, survival curves (log-rank test) were statistically significantly different only after two years (p < 0.001). Sealing ICDAS 5 occlusal lesions of deciduous molars using RMGIC achieved lower survival rates than restorations. Both sealing and restoration effectively arrested caries progression for two years. Clinical relevance Sealing dentine carious lesions can be effective for treating lesions involving the inner and outer half of the dentine. Ultraconservative treatments can arrest carious lesions presenting obvious cavitation in primary molars. ReBEC Register no. RBR-225n35.

A Review of Silorane and Methacrylate Based Composites and Effective Factors on Microleakage of them

Introduction: An important disadvantage of current dental resin composites is their polymerization shrinkage and production of microleakage. This shrinkage can cause tooth sensitivity, marginal discoloration, and secondary caries. The objective of this study was to review the effective factors on microleakage of methacrylate and silorane composites and compare them with each other. This reviewed article was compiled and searched on library sources and Google scholar, Pubmed, ISI of science database, using the key words “Microleakage, Siloran-Based Composite, Methacrylate-Based Composite, Retentive Groove, Light Curing Technique,” from 1984 -2019. Although it is not yet definitely clear, which methods of layering techniques (oblique, vertical, split) are more suitable, it seems that the layering technique has advantage over the bulkythat can effective in decreasing the shrinkage caused by polymerization and the resulting microlaekage. It can also be concluded that silorane base composites have less shrinkage, but some factors such as cavity type, cavity extent, cavity margin distance to CEJ, type of silorane base bonding system are also involves in their microleakage. It seems the presence of retention grooves in the cavities seems useful, because it increases the bonding area and mechanical retention as well as decreases the marginal shrinkage due to polymerization and the resulting microleakage. Conclusion: Finally, it can be said that microleakage cannot be stopped completely, and more studies, especially clinical studies, should be conducted to show the effects of these cases clinically.

Correlation between Vista Cam, ICDAS-II, X-ray bitewings and cavity extent after lesion excavation: an in-vivo pilot study.

To correlate fluorescence-based camera (FC), visual inspection (ICDAS-II) and radiographic examination X-rays bitewings (BW) to the extent of caries after excavation. The occlusal sites of 20 permanent first and second molars in 14 young adolescents (12±2 years old) were examined at 1st Observation Unit of Department of Oral and Maxillofacial Sciences, "Sapienza" University of Rome. All the enrolled patients were asked to provide with X-rays bitewing of the studied teeth. The assessment of ICDAS-II and FC was performed by a trained operator. Then a second blind operator removed the carious lesion and evaluated the cavity extent (depth, width, length) after caries removal with a calibrated probe. To correlate FC measurements with bitewing sensitivity, 10 dentists evaluated the presence/absence of caries on the X-rays. All the occlusal sites assessed by fluorescence camera, ranged from 1.7 to 2, indicating in all cases deep enamel lesions with possible extent to dentine with a mean of 1.7±0. In accordance, visual inspection by ICDAS-II showed scores of 3 and 4. By contrast, the radiographic documentation, i.e. bitewing X-rays, was evaluated in only 6 cases as presence of caries. The extent of the cavities was determined by three consecutive measurements: depth, width and length, with a mean of 3.5+1.73, 2.8+1.07 and 3.2+1.64 mm respectively. These results confirmed the agreement between FC and ICDAS-II for diagnosis of cavities with extent to enamel and dentine, while showed the low sensitivity of bitewings X-rays, in accordance with the existing evidence in Literature. Moreover, the results of this study for the first time provide information about the cavity extent after caries removal for the occlusal sites with ICDAS-II 3 and 4 scores and FC≥1.7. X-rays evaluation showed diagnostic accuracy in 6% of the sample. VistaCam measurement of 1.7 was correlated to a cavity with 3.5, 2.8 and 3.2 mm of depth, width and length.

Повышение эффективности комплексного лечения пришеечного кариеса

Clinical evaluation of the quality of restorative materials carried out taking into account indicators hygiene index, some criteria: absence of side effects on the tissue surrounding the tooth. While taking into account the almost constant contact with the seal gums determined the importance of assessing the extent of its impact on their functional status. Have been revealed the direct dependence of the state of oral hygiene, pathological changes in the soft tissues and the seal quality. One of the objectives of the study was to determine the quality of the restoration carried out in the cervical area, depending on the depth of gingival sulcus in the presence of inflammation in periodontal tissues. The maximum depth of the gingival pocket, which is permissible under the direct defect filling, was 3 mm clinical studies found a direct relationship between the restoration qualities and cavity extent below the gingival margin. Maximum positive results on the quality of sealing recorded in the first group, an intact periodontal pocket depth. Analysis of the results of clinical studies of the oral cavity examined patients before and after treatment and preventive measures are revealed a number of features. Carrying out preventive and curative action using both traditional means and biologically neutral drugs has reduced the value of the index OHI-S GI and achieve significant improvements in oral hygiene status in patients in all stages of clinical trials.

A reduced-order hydroelastic analysis of 2D hydrofoil considering supercavitation effects

ABSTRACTAn efficient two-dimensional reduced-order hydroelastic model for studying supercavitation phenomenonwith zero cavitation number is proposed. In order to compute fluid eigenmodes, unsteady hydrodynamic model is derived using the finite-element method along with the potential flow assumption. This model takes advantage of a new real time, direct algorithm to compute the pressure distribution around the hydrofoil, which avoids any iterative scheme to find cavity extent as like as conventional method. The present approach starts by specifying the steady cavitation domain for the zero cavitation number, then, it is assumed that unsteady cavitation flow around the steady-state leads to small fluctuation of the flow velocity around the steady boundaries. According to the present non-iterative scheme, the unsteady hydrodynamic lift and moment are attained and utilised with the structural model, obtained by Lagrange equations of motion, to construct governing reduced-order hydroelastic model. Using such an approach, the hydroelastic behaviour of a model with two degrees of freedom in pitch and plunge direction is investigated and the instability margin of the foil is assessed.

Glass hybrid restorations as an alternative for restoring hypomineralized molars in the ART model

BackgroundThis study aimed to evaluate the survival rate of glass hybrid restorations placed under the atraumatic restorative treatment (ART) technique in first permanent molars affected by molar incisor hypomineralization (MIH).MethodsSixty teeth with severe MIH associated to carious dentin lesions without pulp involvement were included. Treatments were performed by one trained dentist using the ART approach and restored with a glass hybrid restorative system (Equia Forte, GC®) on school premises. Treatments were evaluated after 6 and 12 months by an independent examiner using the modified ART criterion. Data analysis involved descriptive statistics and actuarial success analysis.ResultsThe sample comprised 24 (54.54%) girls and 20 (45.45%) boys with a mean age of 10.55 (±1.25) years. In regard to the number of surfaces involved in the restorations, 29 (48.3%) comprised one surface and 31 (51.7%) two or more surfaces. Considering cavity extent, 25 (41%) presented dentin cavitation without cusp weakness, 23 (37.7%) with large dentin cavitation with cusp weakness and 13 (21.3%) with large dentin cavitation with the breakdown of one or more cusps. Only 4 teeth required local anesthesia. A success rate of 98.3% after 6 and 12 months was observed, as only one restoration failed. The only failure occurred in a restoration involving three or more sur-faces presenting the breakdown of all cusps.ConclusionRestorations using a glass hybrid restorative system and performed in the field with the ART technique proved, after 12 months of evaluation, to be an effective approach to preserving first permanent molars affected by MIH.Trial registrationREBEC-RBR-8drccq (17/06/15).

Glacier velocity variability due to rain-induced sliding and cavity formation

The largest accelerations of glaciers and ice sheets are caused by changes in basal slip. Here we examine glacier speed and rain-induced accelerations using a near-continuous 26-month-long GNSS time series from a large maritime glacier (Tasman Glacier, New Zealand). During periods of high rain-rate we observe short-term increases in 24-hour speeds to up to 15-times background speed. Speeds calculated over 3-hour intervals increase to up to 36-times background speed. Acceleration events correspond with times when bed separation also increases rapidly indicating that the acceleration is associated with the growth of water-filled cavities at the bed. Glacier speeds then decrease prior to the reduction in bed separation, indicating cavity growth, not cavity extent, controls the acceleration. The short-term accelerations are superimposed on longer-term periods of enhanced velocity that persist for days to weeks and decay at similar rates to bed separation estimates and proglacial lake levels. A power-law relationship between observed rain-rate and speed exists at the glacier front and exhibits no apparent upper bound. Overall, we estimate that rain-induced accelerations account for 11–14% of Tasman Glacier's displacement during the observation period. The rain-rate–velocity relationship and the rainfall record since 2001 indicate that rain-induced speed-up events result in interannual variability in glacier displacement of 2%–13%.

On the impact of a concave nosed axisymmetric body on a free surface

We report on an experimental study of the vertical impact of a concave nosed axisymmetric body on a free surface. Previous studies have shown that bodies with a convex nose, like a sphere, produce a well defined splash with a relatively large cavity behind the model. In contrast, we find that with a concave nose, there is hardly a splash and the cavity extent is greatly reduced. This may be explained by the fact that in the concave nosed case, the initial impact is between a confined air pocket and the free surface unlike in the convex nosed case. From measurements of the unsteady pressure in the concave nose portion, we show that in this case, the maximum pressures are significantly lower than the classically expected “water hammer” pressures and also lower than those generally measured on other geometries. Thus, the presence of an air pocket in the case of a concave nosed body adds an interesting dimension to the classical problem of impact of solid bodies on to a free surface.

Eigenanalysis and reduced-order modelling of unsteady partial cavity flows using the boundary element method

This paper presents an efficient reduced-order modelling approach to predict unsteady behaviour of partial cavity flows (PCROM). The boundary element method (BEM) along with the potential flow is used to analyze unsteady partial cavity flows. Partial cavity flow is modelled based on a new non-iterative approach and the PCROM is based on fluid eigenmodes. To construct fluid eigenmodes the spatial iterative scheme to find cavity extent is removed. The eigenvalue problem of the unsteady flows is defined based on the unknown wake singularities. Eigenanalysis and reduced-order modelling of unsteady flows over a NACA 16-006 section are performed using the PCROM. Numerical examples are presented to demonstrate the accuracy of the proposed method. Comparison between the obtained results of the proposed method and those of other and conventional method indicates that the present algorithm works well with sufficient accuracy. Moreover, it is shown that the PCROM is computationally more efficient than the conventional one for unsteady sheet cavitations analysis on hydrofoils.

Numerical modelling of subglacial erosion and sediment transport and its application to the North American ice sheets over the Last Glacial cycle

Present-day sediment distribution offers a potentially strong constraint on past ice sheet evolution. Glacial system models (GSMs), however, cannot address this constraint while lacking appropriate representations of subglacial sediment production and transport. Incorporating these elements in GSMs is also required in order to quantify the impact of a changing sediment cover on glacial cycle dynamics.Towards these goals, we present a subglacial process model (hereafter referred to as the sediment model) that incorporates mechanisms for sediment production, entrainment, transport, and deposition. Bedrock erosion is calculated by both Hallet's and Boulton's abrasion laws separately, and by a novel quarrying law parametrized as a function of subglacial cavity extent. These process-oriented erosion laws are compared against a simple empirical relationship between erosion rate and the work done by basal stress. Sediment entrainment is represented by Philip's law for regelation intrusion and soft-bed deformation is included as a subglacial sediment transport mechanism. The model is driven by the data-calibrated MUN (3D) GSM and a newly developed subglacial hydrology module.The sediment model is applied to the last North American glacial cycle and predicts sediment thickness and cumulative erosion patterns. Results are obtained in the context of a sensitivity analysis and are compared against the present-day distribution of glacigenic sediment and geological estimates of Laurentide Ice Sheet erosion. Given plausible ranges for the sensitivity parameters, chosen a priori based on available literature or on heuristic arguments, the calculated erosion depths overlap with the geological estimates of Laurentide erosion. Most of the runs in the sensitivity set produce unrealistically thick and continuous moraines along the eastern, southern and western margins of the North American ice complex, which suggests that the model overestimates sediment entrainment and thus englacial transport. A realistic sediment distribution is only obtained when the entrainment rate is capped at the average basal melting rate, which suggests that modelled entrainment and basal melting rates should be of the same order of magnitude.

Numerical Model for Cavitational Flow in Hydraulic Poppet Valves

The paper presents a numerical simulation and analysis of the flow inside a poppet valve. First, the single-phase (liquid) flow is investigated, and an original model is introduced for quantitatively describing the vortex flow. Since an atmospheric outlet pressure produces large negative absolute pressure regions, a two-phase (cavitating) flow analysis is also performed. Both pressure and density distributions inside the cavity are presented, and a comparison with the liquid flow results is performed. It is found that if one defines the cavity radius such that up to this radius the pressure is no larger than the vaporization pressure, then both liquid and cavitating flow models predict the cavity extent. The current effort is based on the application of the recently developed full cavitation model that utilizes the modified Rayleigh-Plesset equations for bubble dynamics.

LES of unsteady cavitation on the delft twisted foil

In this paper, the cavitating flow around the Delft twisted hydrofoil with unsteady inflow condition is numerically simulated using Large Eddy Simulation in combination with a volume of fluid implementation to capture the liquid-vapor interface and Kunz's model for the mass transfer between the phases. Main cavitation mechanisms, including periodic shedding of main and secondary cavities, side- and re-entrant jets, as well as the cavity extent and the lock-in effect between the inflow variation and the cavity are compared with experimental observations.

Implicit LES Predictions of the Cavitating Flow on a Propeller

We describe an approach to simulate dynamic cavitation behavior based on large eddy simulation of the governing flow, using an implicit approach for the subgrid terms together with a wall model and a single fluid, two-phase mixture description of the cavitation combined with a finite rate mass transfer model. The pressure-velocity coupling is handled using a PISO algorithm with a modified pressure equation for improved stability when the mass transfer terms are active. The computational model is first applied to a propeller flow in homogeneous inflow in both wetted and cavitating conditions and then tested in an artificial wake condition yielding a dynamic cavitation behavior. Although the predicted cavity extent shows discrepancy with the experimental data, the most important cavitation mechanisms are present in the simulation, including internal jets and leading edge desinence. Based on the ability of the model to predict these mechanisms, we believe that numerical assessment of the risk of cavitation nuisance, such as erosion or noise, is tangible in the near future.

Performance Characteristics of Controllable Pitch Side Thrusters with Different Skew Distributions

In the previous paper, authors presented experimental and theoretical data on open water characteristics of two side thrusters which impellers have the forward skew (type (A)) and the backward skew (type (B)).In this report, cavitation characteristics and blade stress of these two side thrusters are investigated theoretically and experimentally. Cavity extent on the impeller blades was estimated by the propeller lifting surface theory. Then, cavitation tests were performed by using the impeller models with the duct in the cavitation tunnel. These results show that the cavity extent on the impeller blades is similar comparing these two impellers. But, the tip vortex cavitation of impeller (B) is much stronger than that of impeller (A), which causes more severe noise and vibration. The finite element method was applied for the stress analysis of the impeller blades. The stress level of impeller (B) was normal, but slightly high stress, which was acceptable, was found on the blade of impeller (A) near the leading edge of 0.7 R-0.8 R.

Numerical Model of Cavitating Propeller Inside of a Tunnel

The unsteady cavitating flow of a propeller subject to a nonaxisymmetric inflow inside of a tunnel is addressed. A numerical method is developed which solves for the fully unsteady propeller problem and the tunnel problem separately, with the unsteady effects of one on the other being accounted for in an iterative manner. The propeller influence on the propeller is considered via velocity. The iterative process is found to converge very fast, usually within three iterations, even for a heavily loaded propeller. The effect of the tunnel extent and the number of panels on the predicted mean propeller forces is investigated. In the case of uniform inflow the equivalent open water velocity is calculated and then compared to that predicted from Glauert’s formula. The two velocities are found to be very close to each other in the case of light propeller loading, and to deviate from each other as the propeller loading increases. In the case of nonuniform flow the predicted unsteady propeller forces are found not to be affected appreciably by the tunnel effects in the case of noncavitating flow. In the case of cavitating flows the tunnel effects have been found to be appreciable, especially in terms of the predicted cavity extent and volume. The predicted cavity patterns are shown to be very close to those observed in CAPREX, a CAvitating PRopeller Experiment performed at MIT’s cavitation tunnel.

Moon‐solar wind interactions: First results from the WIND/3DP Experiment

Launched on November 1, 1994, the WIND spacecraft passed behind the moon on December 27, 1994 and remained in its optical shadow for ∼41 minutes. At the time the moon was immersed in the interplanetary medium and a large amount of new data has been collected by the WIND/3DP experiment. The nature of the flow near the moon is described by presenting detailed electron and ion plasma parameters in various regions; a structured lunar plasma umbra is clearly observed downstream of the moon at XSSE ∼ −6 RM, characterized by a gradual decrease of electron and ion densities to values of &lt;0.5 cm−3 near the center of the optical umbra. The plasma umbra is surrounded by a penumbra region in which plasma densities and magnetic field magnitude decrease and plasma flow undergoes small but noticeable variations. Analysis of magnetic shielding effects show that medium energy electrons follow the interplanetary magnetic field lines and are partially occulted by the moon. These first WIND results on the detailed properties of the downstream flow and the cavity extent are compared with fluid descriptions of the global moon‐solar wind interaction.

A Boundary Element Method for the Analysis of the Flow Around 3-D Cavitating Hydrofoils

The three-dimensional steady cavitating hydrofoil problem is treated in nonlinear theory by employing a low-order potential-based boundary element method. The cavity extent and shape are determined for given cavitation number by satisfying the three-dimensional kinematic and dynamic boundary conditions on the hydrofoil surface beneath the cavity and on the portion of the wake sheet overlapped by the cavity. A unified discretization and algorithm is developed to predict the occurrence of general cavity planforms, including partial cavitation, supercavitation, and mixed partial/supercavitation. The cavity planform is determined iteratively by searching for the planform which corresponds to a closed cavity at all spanwise locations. Cavity shapes predicted by the present method, applied in two dimensions, are compared to the converged nonlinear cavity shapes and are found to differ only slightly for a range of foil thicknesses and angles of attack. The accuracy of the 3-D method is gaged by satisfying Green's formula, subject to a kinematic boundary condition, on a modified foil consisting of the union of the original foil and the cavity predicted by the present method. Comparing the resulting pressure distribution to the pressure distribution from the present method shows that the dynamic boundary condition is satisfied to within acceptable accuracy.

Prediction of Propeller Cavitation by the Three-Dimensional Theory based on the Vortex Lattice Method

This paper describes the numerical study on the cavitation problem of marine propellers by three-dimensional theory, based on the mathematical model of the trailing vortex geometry including the phenomena of the flow separation from the tips by using the vortex lattice method.The numerical procedure is developed to solve the partial-and super-cavitating propeller problem and to predict the cavity extent and the cavity thickness distribution.The results of the present numerical study are compared with the experimental results both in uniform and non-uniform flows. Although the comparison shows that the present method is advantageous to predict the cavity extent and the cavity thickness distribution, further problems still exist in the numerical studies to predict the propeller cavitation more accurately.

Whirl Instabilities in Pressure Step Bearings

The effect on the stability of a dynamically loaded journal bearing of introducing a pressure step is examined by calculating numerically the whirl orbits described by the journal for a range of values of physical effects. In all full film cases the configuration is unstable in that the orbits spiral outwards to the bearing case; the tightness of the spiral is, however, much influenced by parameter values. The presence of appropriate cavitation permits a degree of stability, with the existence of stable whirl orbits. Cavity position and extent are vitally important to the stability characteristics, a result one would expect to be true of more realistic cavitation models than the single one used here.

Phenomenology of the Pokaranpne experiment

The phenomenology of the Pokaranpne experiment (yield - 12 kiloton oftnt) conducted in a shale-sandstone rock, 107 meters underground, is described with the aid of computations using a one-dimensional spherical symmetric rock mechanics computer code developed by the authors. The calculated values of cavity radius, spall velocity and extent of rock fracturing are in good agreement with the observed values. The principal mechanism for crater formation at Pokaran was spall and the relatively smaller crater dimensions and non-venting of radioactivity gases were due to lower kinetic energy transferred to the shale-sandstone rock.