Validity assessment of a single tooth model in clenching and chewing simulations

Experimental investigation of the mechanical behaviour and structure of the bovine periodontal ligament

Gear strength analysis is important to gear drive design, and its calculating accuracy is mainly decided by gear model. Several factors influencing the spur gear model building accuracy by finite element method (FEM) are presented, including geometric model and boundary, loading position and load types. The research includes: (1)A geometric model of spur gear is built. (2)Based on the gear model, geometric boundary of analytic model is determined. (3) The loading point of bending strength calculation is studied. (4)Static effective load and dynamic contact load effects on root stresses and tooth deformation are researched. The results show that tooth profile, geometric boundary, loading position and effective load, are the key factors of calculating accuracy and gear strength analysis. The reasonable FEM modeling methods can improve the calculating precision.

AIM: The purpose of this study is to compare the stress effects developed on the periodontal ligaments and teeth by three different types of mandibular advancement devices (MADs) using a finite element method (FEM) analysis. Introduction: Obstructive sleep apnea (OSA) is a disease with a high prevalence and, in recent years, the use of MADs as an alternative or support treatment to the continuous positive airway pressure (CPAP) has spread. Their use finds relative contraindications in the case of partial edentulism and severe periodontal disease. Given the widespread of periodontal problems, it is essential to know the effects that these devices cause on the periodontal ligament of the teeth. Materials and methods: Starting from the computed tomography (CT) scan of a patient’s skull, 3D reconstructions of the maxilla and mandible were implemented. Three different MADs were prepared for the patient, then 3D scanned, and lastly, coupled with the 3D models of the jaws. The devices have two different mechanics: One has a front reverse connecting rod (OrthoapneaTM), and two have lateral propulsion (SomnodentTM and HerbstTM). A FEM analysis was performed to calculate the stress applied on periodontal ligaments, on every single tooth and the displacement vectors that are generated by applying an advancement force on the mandible. Results: HerbstTM and SomnodentTM devices present very similar stress values, mainly concentrated on lateral teeth, but in general, the forces are very mild and distributed. The maximum stresses values are 3.27 kPa on periodontal ligaments and 287 kPa on teeth for SomnodentTM and 3.56 kPa on periodontal ligaments and 302 kPa on teeth for HerbstTM. OrthoapneaTM has, instead, higher and concentrated stress values, especially in the anterior maxillary and mandibular area with 4.26 kPa and 600 kPa as maximum stress values, respectively, on periodontal ligaments and teeth. Conclusions: From the results, it is concluded that devices with a bilateral mechanism generate less and more distributed stress than an anterior connecting rod mechanism. Therefore, they may be advisable to patients with compromised periodontal conditions in the anterior area.

Water is a major limiting factor of human survival and social economic development. Water security is also important for the ecological system. In this paper, the water security assessment index system of the Yellow River basin was developed based on three subsystems: the water resources subsystem, the water environment subsystem and the social economic subsystem. The integrated assessment of water security was developed based on the combination of set pair analysis (SPA) and fuzzy analytical hierarchy process (FAHP) as well as technique for order preference by similarity to ideal solution (TOPSIS), gray relational analysis (GRA), vague sets (VS) and matter element (ME) models. First, fuzzy cluster analysis method was used to check the consistency of all the models before and after implementing the integrated assessment. Secondly, the ranking values of four single assessment models (i.e., TOPSIS, GRA, VS and ME models) were analyzed by SPA method to get the consistency connection degree. Then FAHP was constructed to describe the relative importance of the four different single models when determining the weight coefficient in the integrated assessment model. And lastly, the integrated assessment model of water security was developed based on the ranking values and weight coefficients of the selected single assessment models. The conclusion of the developed integrated assessment model which was applied in the Yellow River basin showed that Sichuan province was at security level; Henan, Shandong, Qinghai and Shaanxi provinces were at the threshold security level; Shanxi, Gansu and Inner Mongolia provinces were at the relative insecurity level; Ningxia province was water no secure. The integrated assessment results showed that the improved integrated model presented in this paper had relatively better performance than single assessment models. The intention of this paper was to provide an integrated assessment model, propose potential countermeasures, and achieve sustainable water utilization in the Yellow River basin.

Hybrid ensemble-based machine learning model for predicting phosphorus concentrations in hydroponic solution

During orthodontic tooth movement, the mechanical behaviour of the extracellular matrix of the periodontal ligament (PDL) determines the cellular processes involved in turnover of the PDL and alveolar bone. This mechanical behaviour is the basis for finite element (FE) models and FE analyses. Five young adult male beagle dogs were used to test the null hypothesis that the mechanical behaviour of the PDL is identical in normal and hyalinized PDL. Therefore, tooth transposition was measured after standardized force application by super-elastic nickel titanium (NiTi) coil springs, exerting a constant force of 100 cN for 5 hours in both conditions. A rapid transposition during the first few seconds was found. However, it was significantly less for hyalinized than for non-hyalinized PDL. Subsequently, a short-lived creep movement was found for hyalinized PDL, while creep persisted at the non-hyalinized sides (analysis of variance and Tukey's multiple comparisons post hoc tests). The results showed substantial biomechanical differences between hyalinized and non-hyalinized PDL at different time points (Mann-Whitney). This indicates that FE models in the study of long-term orthodontic tooth movement, which are based solely on the characteristics of normal PDL should be reconsidered.

The aim of this work is to analyze the function of natural teeth’s periodontal ligament and the effects of periodontal ligament on implants by the finite element method (FEM), when static functional loads occur. The finite element analysis models are established, which consist of fragment of mandible, natural teeth, periodontal ligament, and implant. Finite element software Abaqus is used to analyze the stress transfer in models with or without periodontal ligament, and mandibular first molar is implant. The implant obtained the maximum stress value of 87.71MPa when periodontal ligament of natural tooth is absent, but the maximum value reduces to 38.43 MPa with the action of periodontal ligament. It illustrates that periodontal ligament has significant effects on stress transfer. When the finite element model of single natural tooth or dentition with implant is generated, periodontal ligament should be taken into account.

The air gap flux density of the superconducting synchronous condenser is high. If the stator core uses a magnetic teeth structure, the teeth are easily overheating. For a 10Mvar superconducting synchronous condenser, Firstly, based on electromagnetic design and ventilation cooling calculation, the stator windings are determined to be water-cooled, and the radial ventilation channels are 10 grades. Then the stator core structure design without magnetic teeth is proposed, and the core slot and core end, and fastening structure are obtained. Two sets of clamping rings are used to realize the radial tightening of the core. Finally, a single tooth and single slot finite element model of the non-magnetic tooth was established, and the structural strength of the non-magnetic teeth was analyzed. The results show that the non-magnetic teeth meet the strength requirements of the rated condition and the strong excitation condition.

In silico study of cuspid' periodontal ligament damage under parafunctional and traumatic conditions of whole-mouth occlusions. A patient-specific evaluation

Enhanced finite elements are elements with an embedded analytical solution which can capture detailed local fields, enabling more efficient, mesh-independent finite element analysis. In the present study, an enhanced finite element is applied to generate a general framework capable of modeling an array of joint types. The joint field equations are derived using the principle of minimum potential energy, and the resulting solutions for the displacement fields are used to generate shape functions and a stiffness matrix for a single joint finite element. This single finite element thus captures the detailed stress and strain fields within the bonded joint, but it can function within a broader structural finite element model. The costs associated with a fine mesh of the joint can thus be avoided while still obtaining a detailed solution for the joint. Additionally, the capability to model non-linear adhesive constitutive behavior has been included within the method, and progressive failure of the adhesive can be modeled by using a strain-based failure criteria and re-sizing the joint as the adhesive fails. Results of the model compare favorably with experimental and finite element results.

Enhanced finite elements are elements with an embedded analytical solution that can capture detailed local fields, enabling more efficient, mesh-independent finite element analysis. In the present study, an enhanced finite element, referred to as a bonded joint element, that is capable of modeling an array of joint types is developed. The joint field equations are derived using the principle of minimum potential energy, and the resulting solutions for the displacement fields are used to generate shape functions and a stiffness matrix for a single joint finite element. This single finite element thus captures the detailed stress and strain fields within the bonded joint, but it can function within a broader structural finite element model. The costs associated with a fine mesh of the joint can thus be avoided,whilestillobtainingadetailedsolutionforthejoint.Additionally,thecapabilitytomodelnonlinearadhesive constitutivebehaviorhasbeenincludedwithinthemethod,andprogressivefailureoftheadhesivecanbemodeledby using a strain-based failure criteria and resizing the joint as the adhesive fails. Results of the model compare favorably with available experimental and finite element results.

Whilst the periodontal ligament (PDL) acts as an attachment tissue between bone and tooth, hypotheses regarding the role of the PDL as a hydrodynamic damping mechanism during intraoral food processing have highlighted its potential importance in finite element (FE) analysis. Although experimental and constitutive models have correlated the mechanical function of the PDL tissue with its anisotropic, heterogeneous, viscoelastic and non-linear elastic nature, in many FE simulations the PDL is either present or absent, and when present is variably modelled. In addition, the small space the PDL occupies and the inability to visualize the PDL tissue using μCT scans poses issues during FE model construction and so protocols for the PDL thickness also vary. In this paper we initially test and validate the sensitivity of an FE model of a macaque mandible to variations in the Young's modulus and the thickness of the PDL tissue. We then tested the validity of the FE models by carrying out experimental strain measurements on the same mandible in the laboratory using laser speckle interferometry. These strain measurements matched the FE predictions very closely, providing confidence that material properties and PDL thickness were suitably defined. The FE strain results across the mandible are generally insensitive to the absence and variably modelled PDL tissue. Differences are only found in the alveolar region adjacent to the socket of the loaded tooth. The results indicate that the effect of the PDL on strain distribution and/or absorption is restricted locally to the alveolar bone surrounding the teeth and does not affect other regions of the mandible.

The Johan Sverdrup oil field was discovered in 2010 and is one of the largest in the North Sea having exceptional reservoir quality with matrix permeabilities of more than 50 Darcy. However, even with more than 30 appraisal wells, 8 drillstem tests (DST) and extensive core sampling, some uncertainties remain large. Conventional pressure transient analysis (PTA) indicates ambiguity in for example kh and barriers, so in order to support the selection of development concepts and optimize the drainage strategy, there was an opportunity to reduce this subsurface uncertainty by combining several DSTs into one single reservoir simulation model. This would take advantage of overlapping radii of investigation (ROI) from the large drainage areas of each well. A fully integrated computer assisted history matching (CAHM) approach was used to consolidate DSTs into one single simulation model by varying both static and dynamic parameters simultaneously. Static parameters such as structure and sand thickness were varied together with permeability, fault transmissibility and relative permeability. Simulation grids were optimized before implementation in the full field model to better understand and minimize numerical artifacts. Characteristics of the derivative were transformed to numerical values through an objective function and calculation of derivatives was automated for inclusion in the integrated workflow. For each well test, pressure build-up derivatives were divided into early, mid and late time periods and used as partial objective elements in the global objective function (J). Absolute values, shape and time until an event/feature were matched and/or monitored for derivative diagnostics. Finally, several alternatives were investigated to how the DSTs could condition the final integrated static and dynamic uncertainty assessment for probabilistic forecasting. The identification of uncertainties was a multidisciplinary approach, as was the definition of ranges for adjusting the uncertainties. This team approach ensured consistent parameter changes and realistic models. Several thousand models were run to better understand and calibrate the reservoir models to DST data. Large amounts of output from reservoir simulations were analyzed and acceptance ranges for each well was defined. Considerable insight was achieved in how each uncertainty impacts different periods of the pressure derivatives, and how the match in one well correlated with another well. As an example, ranges of uncertainties and range of alternative models suggested by analytical PTA were discarded when tested in the full field model using DST data combined into a single model. Results were integrated into an uncertainty assessment workflow to condition all reservoir models to DST data. Acceptable models were used to calculate probabilistic production profiles (e.g. Mean, P10-P50-P90), and a few discrete models were selected for further analysis and studies (e.g. Low-Mid-High). Based on this study, the uncertainty in initial oil in place volume (STOIIP) was reduced, the placement and number of development wells was improved and thus the drainage strategy was optimized. The resulting Mean production profiles were used together with discrete models and sensitivities for field development planning, resource management and investment decisions. The workflow was robust and repeatability is high as the work can be redone when new data is available, and also deployed in other projects, with little effort. It may be implemented on simple desktop computers, but works best on larger computer clusters with sufficient calculation power. This paper describes the fully integrated uncertainty assessment workflow for probabilistic forecasting, and focuses on automating pressure transient derivative diagnostics and presenting some alternatives of using, and integrating, numerical well testing with uncertainty assessment, history matching and probabilistic forecasting.

To fit a model which describes the complex interaction between various work-related factors and both musculoskeletal and psychosomatic complaints of nurses simultaneously and to compare the results with those of two LISREL models, in which the health outcome variables are analyzed separately in terms of their correlation with the same set of work-related factors. Nurses (n=718) working in four Dutch nursing homes completed a questionnaire about work-related factors and musculoskeletal and psychosomatic complaints (response 81%). LISREL was used to describe and analyse the models. The full model had a reasonable overall fit. The strongest (and statistically significant) correlations were found between work postures and musculoskeletal complaints and between psychosocial work demands and psychosomatic complaints. In the two single models, health outcomes showed statistically significant correlations with the same work-related factors as they did in the full model. The full model could be slightly improved when the variable somatized complaints (e.g., dizzyness, headache) was related both to musculoskeletal complaints and to psychosomatic complaints. Although a model that simultaneously describes more dependent variables appears to provide a better approximation of the complexity of the actual relationship between work-related factors and health effects, the models in which only one health outcome is studied seem to give a proper description of the data at hand. This is an important finding because these single health outcome models resemble the usual analysis strategy by means of standard regression analysis. The adapted version of the full model suggests that musculoskeletal complaints of nurses can partly be understood as non-specific health complaints.

Stress analysis in single molar tooth