Necessary and Sufficient Elastic Stability Conditions in Various Crystal Systems

While the Born elastic stability criteria are well-known for cubic crystals, there is some confusion in the literature about the form it should take for lower symmetry crystal classes. We present here closed form necessary and sufficient conditions for elastic stability in all crystal classes, as a concise and pedagogical reference to stability criteria in non-cubic materials

How does indirect air-cooling influence pulp chamber temperature in different volume teeth and absence/presence of resin-based composite during light curing?

Background Light-curing of materials during restorative dental procedures poses a risk for pulp tissue overheating. Therefore, the aim of this study was to investigate the effect of indirect air-cooling on pulp chamber temperatures during light-curing of varying volume teeth and absence/presence of resin-based composite (RBC) at different exposure time. Methods The volume of 11 human teeth was measured by micro computed tomograph. An experimental rig controlled the thermal environment of the teeth and a thermocouple inserted retrograde into the root canal measured temperature changes. Pulp chamber temperature was measured with and without air-cooling on teeth without and with RBC at 15 s, 30 s and 60 s intervals. Generalized estimating equations were used for statistical analysis. Results The temperature increase with air-cooling (versus no air-cooling) was lower in teeth despite absence/presence of RBC (β = − 4.26, 95%CI − 5.33 and β = − 4.47, 95%CI − 5.60, respectively). With air-cooling, the temperature increase in teeth with RBC was lower compared to teeth without RBC (β = − 0.42, 95%CI -0.79; − 0.05). Higher teeth volume resulted in lower temperature increase with air-cooling than without air-cooling (β = − 0.04, 95%CI -0.07; − 0.01 and β = − 0.17, 95%CI -0.30; − 0.05, respectively). Conclusions Air-cooling resulted in lower pulp chamber temperature increase. Using air-cooling, the temperature increase was lower in teeth with RBC compared to teeth without RBC. Lower volume teeth resulted in higher temperature increase, thus they seemed to benefit more from air-cooling compared to higher volume teeth. Air-cooling could be an effective tool in controlling pulp temperature increase during light-curing, especially when the tooth volume is small

Effet de la durée d'impulsion et la forme sur flambage dynamique des panneaux raidis sous compression axiale

Ce papier présent le flambage dynamique des panneaux raidis est analysé numériquement grâce à une formulation incrémentale non linéaire utilisant la procédure d'intégration explicite en temps sous la logiciel Abaqus. Fixation la durée d'impulsion et l'ampleur de la déviation initiale ainsi que le rapport de la dégradation des matériaux dans la zone affectée par la chaleur, la charge de flambage dynamique a été identifié pour chaque configuration donnée. Ce processus a permis la dérivation d'un modèle de surface de réponse qui a été utilisé avec la méthode de Monte Carlo pour déterminer la fiabilité du panneau raidi en ce qui concerne l'état de flambage dynamique. Le critère de flambement Budiansky et Roth a été utilisé pour prédire l'instabilité sous une donnée modèle de charge dynamique. Différents profils y compris rectangulaire, triangulaire, double-triangulaire et demi-sinus ont été examinées. Les résultats obtenus ont montré que tant la durée d'impulsion et la forme d'impulsion ont un effet drastique sur la force de flambage. Pour la limite considérée conditions, des impulsions ayant des périodes qui sont comparables à deux fois la période de la première mode propre de vibrations ont été trouvés pour réduire la résistance à la déformation à 67% du statique flambage valeur dans le régime en plastique élastique et 44% dans le régime élastique

Light-curing units used in dentistry: factors associated with heat development – potential risk for patients

Source: doi: 10.1007/s00784-016-1962-5Objectives:To investigate how heat development in the pulp chamber and coronal surface of natural teeth with and without cusps subjected to irradiance using light-emitting diode (LED)–light-curing units (LCUs) is associated with (i) irradiance, (ii) time, (iii) distance, and (iv) radiant exposure. Materials and methods:Three different LED-LCUs were used. Their irradiance was measured with a calibrated spectrometer (BlueLight Analytics Inc., Halifax, Canada). An experimental rig was constructed to control the thermal environment of the teeth. The LED-LCU tip position was accurately controlled by a gantry system. Tooth surface temperature was measured by thermography (ThermaCAM S65 HS, FLIR Systems, Wilsonville, USA) and pulp chamber temperature with a thermocouple. LED-LCU tip distance and irradiation times tested were 0, 2, and 4 mm and 10, 20, and 30 s, respectively. Ethical permission was not required for the use of extracted teeth. Results:Maximum surface and pulp chamber temperatures were recorded in tooth without cusps (58.1 °C ± 0.9 °C and 43.1 °C ± 0.9 °C, respectively). Radiant exposure explained the largest amount of variance in temperature, being more affected by time than irradiance. Conclusions:At all combinations of variables tested, repeated measurements produced consistent results indicating the reliability of the method used. Increased exposure time seems to be the factor most likely to cause tissue damage. Clinical relevance:Risk of superficial tissue damage at irradiances >1200 mW/cm2 is evident. There is a risk of pulp damage when only thin dentin is left at higher irradiances (>1200 mW/cm2). Clinicians should be aware of LED-LCU settings and possible high temperature generated

The educational gradient in dental caries experience in Northern- Norway: a cross-sectional study from the seventh survey of the Tromsø study

Background Although, studies from Norway indicate a reduction in dental caries experience, in Northern-Norway this non-communicable oral condition is still prevalent. There is conflicting evidence of presence of social inequalities in dental caries in an adult population. Therefore, the aim of this study was to assess an association between educational level and dental caries experience in adults in urban Tromsø municipality, Northern-Norway, using The World Health Organization (WHO) Commission on Social Determinants of Health (CSDH) framework of health determinants. Methods Data from 3752 participants having recorded dental caries status and educational level in the seventh survey of the Tromsø Study: Tromsø7 were included. Dental status was examined clinically as decayed-, missing-, filled-teeth (DMFT score). For statistical analyses DMFT score was grouped into lower (DMFT<19) and higher (DMFT≥20). Educational level was obtained from a questionnaire and categorized as primary/partly secondary education, upper secondary education, tertiary education, short and tertiary education, long. Data on social and intermediary determinants was also self-reported. Univariable and multivariable binary logistic regression analyses were applied. Result This study included 1939 (52%) women and the mean age of the participants was 57.11. The mean DMFT score was 18.03. The odds of having higher DMFT score followed a gradient based on educational level. Participants who reported lower than secondary education had 2.06 -fold increased odds of having higher DMFT score than those with tertiary education, long (OR: 2.06, 95% CI: 1.50–2.83). Those with upper secondary education had 60% higher odds of having higher DMFT score (OR: 1.60, 95% CI: 1.21–2.11), and those with tertiary education, short had 66% higher odds of having higher DMFT score (OR: 1.66, 95% CI: 1.24–2.22). Conclusion The current cross-sectional study suggested an educational gradient in dental caries experience in an adult population of Northern- Norway. Further studies validating our results and investigating mechanisms of educational inequalities in oral health are warranted

Changes in management preference of deep carious lesions and exposed pulps: questionnaire studies with a 10-year interval among dentists in Lithuania

We aimed to investigate changes in management preferences for deep carious lesions and pulps exposed during carious tissue removal that occurred during the last 10 years and identify associated dentists’ background factors. The data were collected among dentists registered with the Lithuanian Dental Chamber at two time points using a similar questionnaire. In 2011, 400 randomly selected dentists received a questionnaire by mail, and 153 (38.3%) responded. In 2021, an electronic invitation to an online questionnaire was sent to all members of the Lithuanian Dental Chamber, and 213 (8.9%) dentists responded. The questionnaire included the definitions of management options, a radiograph, and a clinical picture of a deep carious lesion reaching to the inner fourth of dentine in a mature permanent tooth, asked management preferences in four different scenarios, as well as participants’ background characteristics, reasons for management, and procedural preferences. Data were analyzed using bivariate and multivariable analyses. Compared to 2011, participants in 2021 had 60% lower odds of preferring nonselective versus selective caries removal (OR 0.4, 95% CI 0.2–0.7) and endodontic treatment versus nonselective and selective caries removal (OR 0.4, 95% CI 0.2–0.6) in the scenario of asymptomatic and symptomatic (indicating reversible pulpitis at most) deep lesions, respectively. For exposed pulp, participants in 2021 had lower odds than in 2011 of preferring endodontic treatment versus vital pulp therapy (direct pulp capping and pulpotomies) for both scenarios without symptoms (OR 0.4, 95% CI 0.2–0.7) and with symptoms (OR 0.2, 95% CI 0.1–0.4). A higher proportion of respondents in 2021 reported using rubber dam (44% vs. 17% in 2011, p < 0.001) and hydraulic calcium silicate cements as a capping material (68% vs. 40% in 2011, p < 0.001). The management preferences were associated with the university of graduation and the number of years in dental practice, indicating “recommended in textbooks” and “recommended in scientific publications” as reasons for management preferences. To conclude, a change toward less invasive management options was observed. To a certain extent, dentists have implemented evidence-based recommendations in dental practice. To ensure further adoption of scientific evidence, dentists should be encouraged to update themselves on the newest evidence-based practices

Effect of pulse duration and shape on dynamic buckling of stiffened panels

Dynamic buckling of stiffened panels under axial compression loading having the form of finite duration pulse was analyzed by finite element modeling. Welding induced defects modifying the skin plate curvature were incorporated. Material degradation in the heat-affected zone was also taken into account. The Budiansky and Roth criterion was employed to predict the collapse load. Various pulse shapes were investigated. The obtained results have shown that the pulse period and profile have severe effects on the buckling strength. For the considered boundary conditions and load pulses up to 56% reduction of the strength was observed in comparison with static buckling

Buckling analysis of rectangular plates with centered cut-out subjected to in-plane two directions under different boundary conditions

Abstract In this research, buckling behavior of rectangular plates of symmetric and antisymmetric laminated composite having centered circular hole under in-plane static loadings is analyzed with the aid of first shear deformation theory and the finite element method is used to find critical loads. The presence of hole may cause redistribution of stresses in plates with reduction of stability. The aim of the current paper is to find critical buckling load. The loads depend on many parameters like geometric aspect ratios (a/b) and (d/b), plate thickness (t), diameter of the circular hole (d), orientation of ply and boundary conditions. Numerical simulations for various boundary conditions obtained are shown in tables and graphical forms and compared with each other

Stability analysis of embankment dam and forecast of failure scope based on point safety factor

Abstract In the context of verification of civil engineering structures stability and determination of sliding surface and safety factor, a careful analysis of several parameters was carried out to guarantee their safety against failure. To quantitatively forecast failure scope, the embankment dam located on Oued Rhiss in the province of Hocemia is chosen as the model of this study. A static stability analysis is performed by using the Slope/W software. A parametric study performed to evaluate the influence of dam's height, the height of water in the reservoir and the length of drains on the safety coefficient and pore pressures. Reliability analysis elaborated by using the Comrel application, and it allows to statistically quantifying the probability of failure by employing the Monte Carlo distribution. Results show that the dam structure has some weak zones and not strong enough as the safety factor is less than one, it is related to structure's parameters and the drainage system