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2.
J Oral Rehabil ; 44(10): 791-799, 2017 Oct.
Article in English | MEDLINE | ID: mdl-28681442

ABSTRACT

Studies have explored occlusal marking interpretation, repeatability and accuracy. But, when an occlusion detection product is interposed between teeth, direct tooth-tooth occlusal contact relationships are replaced by tooth-material-tooth structures. Thus, the marks cannot reflect the original contacts. This has been shown for single tooth pair contacts. The purpose of this laboratory study was to similarly examine full dentitions. A dentiform was set into Class I centric occlusion with the mandible supported by a load cell. The maxillary arch was guided by precision slides. As the weighted (~52 N) upper assembly was lowered onto and raised off the mandibular arch, the loads on the mandible were measured. With and without (control) occlusal marking material, the steps were as follows: (cleaning - control 1 - material 1) … (cleaning - control 6 - material 6). The six materials were as follows: Accufilm I and II, Rudischhauser Thick and Thin, Hanel Articulating Silk and T-Scan. Then, the six sets of (cleaning - control - material) measurements were repeated with the mandibular assembly shifted, in turn, by 0·1 mm in the Anterior, Posterior, Right and Left directions. The five (Centric and four 0·1 mm shifted) occlusal relationships produced grossly different tooth-tooth (control) load profiles. And, in general, these controls were affected, in different ways, by the marking products. Among the five conventional products, the Rudischhausers fared the worst and the electronic T-Scan was an extreme outlier. Thus, in general, popular occlusal detection products alter the occlusal contact forces, and therefore, their markings cannot characterise the actual occlusion.


Subject(s)
Dental Occlusion , Dental Stress Analysis/instrumentation , Models, Dental , Bite Force , Dental Articulators , Dentition , Humans , Jaw Relation Record/methods , Reproducibility of Results
3.
J Oral Rehabil ; 42(5): 348-54, 2015 May.
Article in English | MEDLINE | ID: mdl-25484034

ABSTRACT

Contacting surfaces of opposing teeth produce friction that, when altered, changes the contact force direction and/or magnitude. As friction can be influenced by several factors, including lubrication and the contacting materials, the aim of this study was to measure the occlusal load alterations experienced by teeth with the introduction of different salivas and dental restorative materials. Pairs of molar teeth were set into occlusion with a weighted maxillary tooth mounted onto a vertical sliding assembly and the mandibular tooth supported by a load cell. The load components on the mandibular tooth were measured with three opposing pairs of dental restorative materials (plastic denture, all-ceramic and stainless steel), four (human and three artificial) salivas and 16 occlusal configurations. All lateral force component measurements were significantly different (P < 0·0001) from the dry (control) surface regardless of the crown material or occlusal configuration, while the effects of the artificial salivas compared to each other and to human saliva depended on the crown material.


Subject(s)
Bite Force , Saliva/chemistry , Dental Materials , Dental Stress Analysis , Humans , In Vitro Techniques
4.
J Oral Rehabil ; 39(5): 357-63, 2012 May.
Article in English | MEDLINE | ID: mdl-22211464

ABSTRACT

Clinicians rely on occlusal contact detection products to identify high contacts and to equilibrate occlusions. Concerns about these products have stimulated numerous investigations into marking reproducibility, accuracy and interpretation, but none have looked at their effects on the occlusion itself. The aim of this study was to assess whether these products alter the occlusion that they purport to measure by determining whether there are differences in the forces and moments experienced by occluding teeth with and without their presence. A matched pair of IPN Portrait 33° molar denture teeth was placed into occlusion with the mandibular tooth supported by a load sensor and the maxillary tooth mounted onto a vertically sliding assembly with a total weight of 15·1N. The three-dimensional force and moment components on the mandibular tooth were measured when the teeth were in direct crown-crown contact (control) and with the products in place. All six products, (Accufilm I, Accufilm II, Hanel Articulating Silk, Rudischhauser Thick and Thin, and T-scan) showed significant (P<0·05) differences in forces and moments from control.


Subject(s)
Bite Force , Dental Articulators/adverse effects , Dental Occlusion , Models, Dental , Humans , Jaw Relation Record/methods , Molar , Reproducibility of Results
5.
Article in English | MEDLINE | ID: mdl-19625175

ABSTRACT

We have previously demonstrated that the EP1 subtype of PGE2 receptor is expressed in the differentiated compartment of normal human epidermis and is coupled to intracellular calcium mobilization. We therefore hypothesized that the EP1 receptor is coupled to keratinocyte differentiation. In in vitro studies, radioligand binding, RT-PCR, immunoblot and receptor agonist-induced second messenger studies demonstrate that the EP1 receptor is up-regulated by high cell density in human keratinocytes and this up-regulation precedes corneocyte formation. Moreover, two different EP1 receptor antagonists, SC51322 and AH6809, both inhibited corneocyte formation. SC51322 also inhibited the induction of differentiation-specific proteins, cytokeratin K10 and epidermal transglutaminase. We next examined the immunolocalization of the EP1 receptor in non-melanoma skin cancer in humans. Well-differentiated SCCs exhibited significantly greater membrane staining, while spindle cell carcinomas and BCCs had significantly decreased membrane staining compared with normal epidermis. This data supports a role for the EP1 receptor in regulating keratinocyte differentiation.


Subject(s)
Cell Differentiation , Keratinocytes/cytology , Keratinocytes/metabolism , Receptors, Prostaglandin E/classification , Receptors, Prostaglandin E/metabolism , Skin Neoplasms/metabolism , Skin Neoplasms/pathology , Animals , Calcium/metabolism , Humans , Immunohistochemistry , Mice , Mice, Inbred C57BL , Mice, Knockout , Phenotype , Receptors, Prostaglandin E/antagonists & inhibitors , Receptors, Prostaglandin E/biosynthesis , Receptors, Prostaglandin E, EP1 Subtype , Reverse Transcriptase Polymerase Chain Reaction , Signal Transduction , Tumor Cells, Cultured , Xanthones/pharmacology
6.
J Phys Condens Matter ; 20(20): 204123, 2008 May 21.
Article in English | MEDLINE | ID: mdl-21694252

ABSTRACT

In this work we describe the observations of structural transitions in ferronematics based on the thermotropic nematics 6CHBT (4-trans-4'-n-hexyl-cyclohexyl-isothiocyanato-benzene). The ferronematic droplets were observed in solutions of nematogenic 6CHBT dissolved in phenyl isocyanate and doped with fine magnetic particles. The phase diagram of the transitions from the isotropic phase to the nematic phase via a droplet state was found. Magneto-dielectric measurements of various structural transitions in this new system enabled us to estimate the type of anchoring of the nematic molecules on the magnetic particle surfaces in the droplets.

7.
Dentomaxillofac Radiol ; 36(6): 311-6, 2007 Sep.
Article in English | MEDLINE | ID: mdl-17699700

ABSTRACT

OBJECTIVES: The purpose of this project was to analyse the effects of X-ray source location on mathematical compensations used in the clinical assessment of external apical root resorption (EARR). METHODS: Using geometric constructions, governing equations were derived to express the relationships between actual tooth, root and crown lengths, and their image sizes on "before" and "after" radiographs. RESULTS: Good agreement was found between calculated and published experimental results. More importantly, errors associated with the assessment methods are demonstrated. CONCLUSION: It is established that root resorption assessment algorithms cannot reliably compensate for the inherent distortions in radiographic evaluations of EARR, even in the best-case scenario of an idealized, precisely characterized, linear tooth.


Subject(s)
Algorithms , Odontometry/statistics & numerical data , Root Resorption/diagnostic imaging , Tooth Apex/diagnostic imaging , Humans , Models, Biological , Radiography , Reproducibility of Results , Tooth Cervix/diagnostic imaging , Tooth Crown/diagnostic imaging , Tooth Root/diagnostic imaging
8.
Comput Methods Biomech Biomed Engin ; 10(4): 257-63, 2007 Aug.
Article in English | MEDLINE | ID: mdl-17671859

ABSTRACT

Dental studies evaluating microCT output often examine resolution as a parameter that affects the data, but many other factors can influence image quality. The objective of this paper is to present the issues involved with the optimization of microCT data acquisition and processing for two biomechanical animal models. The first model evaluates surface and volumetric changes in root structure after in vitro fatigue loading of dog incisors. The second evaluates the in vivo morphometric bone and tooth responses to application of orthodontic force in inbred and transgenic mice. This type of data required specific magnification and noise control microCT settings to segment and render objects with acceptable definition. The proposed procedures enabled high definition rendering of changes in tooth and bone morphology in orthodontic studies. They also allowed for the construction of solid models for finite element analyses.


Subject(s)
Dental Stress Analysis , Orthodontic Wires , Tooth/diagnostic imaging , Animals , Biomechanical Phenomena , Dogs , Mandible/diagnostic imaging , Mice , Mice, Inbred C57BL , Tomography, X-Ray Computed
9.
J Radiol Prot ; 25(4): 375-91, 2005 Dec.
Article in English | MEDLINE | ID: mdl-16340067

ABSTRACT

In the framework of the BioMoSA project for the development of biosphere assessment models for radioactive waste disposal the Reference Biosphere Methodology developed in the IAEA programme BIOMASS was applied to five locations, situated in different European countries. Specific biosphere models were applied to assess the hypothetical contamination of a range of agricultural and environmental pathways and the dose to individuals, following contamination of well water. The results of these site-specific models developed by the different BioMoSA partners, and the individual normalised dose to the exposure groups were compared against each other. Ingestion of drinking water, fruit and vegetables were found to be among the most important pathways for almost all radionuclides. Stochastic calculations revealed that consumption habits, transfer factors, irrigation rates and distribution coefficients (Kd(s)) were the most important parameters that influence the end results. Variations in the confidence intervals were found to be higher for sorbing elements (e.g. (36)Cl, (237)Np, (99)Tc, (238)U, (129)I) than for mobile elements (e.g. (226)Ra, (79)Se, (135)Cs, (231)Pa, (239)Pu). The influence of daughter products, for which the distribution into the biosphere was calculated individually, was also shown to be important. This paper gives a brief overview of the deterministic and stochastic modelling results and the parameter sensitivity. A screening methodology was introduced to identify the most important pathways, simplify a generic biosphere tool and refine the existing models.


Subject(s)
Models, Theoretical , Radioactive Waste , Radiometry/methods , Refuse Disposal/methods , Water Pollutants, Radioactive/analysis , Water Supply , Adult , Environmental Exposure , Europe , Humans , Infant , Monte Carlo Method , Refuse Disposal/standards , Risk Assessment
10.
J Radiol Prot ; 25(4): 343-73, 2005 Dec.
Article in English | MEDLINE | ID: mdl-16352869

ABSTRACT

This paper describes the development and application of site-specific biosphere models that might be used for assessment of potential exposures in the framework of performance assessment studies of nuclear waste disposals. Model development follows the Reference Biosphere Methodology that has been set up in the framework of the BIOMASS study. In this paper, the application is to real sites at five European locations for which environmental and agricultural conditions have been described and characterised. For each of the sites a biosphere model has been developed specifically assuming a release of radionuclides to waters that are used by humans, for example as drinking water for humans and cattle and as irrigation water. Among the ingestion pathways, the intakes of drinking water, cereals, leafy vegetables, potatoes, milk, beef and freshwater fish are included in all models. Annual individual doses were calculated, and uncertainties in the results were estimated by means of stochastic calculations. To enable a comparison, all results were normalised to an activity concentration in groundwater of 1 Bq m(-3) for each of the radionuclides considered ((36)Cl, (79)Se, (99)Tc, (129)I, (135)Cs, (226)Ra, (231)Pa, (230)Th, (237)Np, (239)Pu, and (238)U), i.e. those that are usually most relevant in performance assessment studies of nuclear waste disposals. Although the results do not give answers in absolute terms on potential future exposures, they indicate the spectrum of exposures that might occur in different environments and specify the interaction of environmental conditions, human habits and potential exposure.


Subject(s)
Environmental Exposure/standards , Radioactive Waste , Radiometry/methods , Refuse Disposal/methods , Animals , Europe , Food Contamination/prevention & control , Humans , Risk Assessment , Soil Pollutants, Radioactive/standards , Water Pollution, Radioactive
11.
Phys Rev E Stat Nonlin Soft Matter Phys ; 72(4 Pt 1): 041712, 2005 Oct.
Article in English | MEDLINE | ID: mdl-16383407

ABSTRACT

We characterize three nonstandard electrohydrodynamic instabilities in nematic liquid crystals composed of bent-core molecules. In addition to their shape, another important attribute of this material is that the anisotropy in the electrical conductivity changes sign as the frequency of the applied electric field changes. These instabilities do not appear to fit within the standard model for electroconvection. The first instability creates a pattern with stripes parallel to the initial director orientation, with a wavelength about equal to the separation of the cell plates. The next is the previously reported prewavy instability. The third instability is optically and dynamically identical to the prewavy instability, but is distinguished by different threshold behavior.

12.
J Environ Radioact ; 79(2): 223-30, 2005.
Article in English | MEDLINE | ID: mdl-15603909

ABSTRACT

The inhalation dose due to radon and its progenies could be averted by ventilation in dwellings; however, on the other hand the increased ventilation augments the heating cost. Therefore a cost-benefit analysis could contribute to optimise the ventilation rate. In our current work we applied our former defined parameters of the optimising procedure to assess the optimised ventilation and radon concentration in dwellings with average parameters. To assess the inhalation dose rates the time-dependent concentrations of all the progenies were calculated in case of periodic and continuous ventilation as well, at three different radon entry rates (5, 10, 20kBqh(-1)). The optimal ventilation rates in case of continuous ventilation are 0.22, 0.40 and 0.66h(-1), respectively. By these conditions the optimal radon concentration takes 160-210Bqm(-3). According to the more detailed analysis the periodic ventilation gives, in general, a better solution than the continuous one. The Monte Carlo simulations provided a large uncertainty; therefore, before the practical application of the results the uncertainty should be decreased taken into account the local conditions.


Subject(s)
Air Pollutants, Radioactive/analysis , Air Pollution, Indoor , Housing , Radon/analysis , Ventilation , Air Pollutants, Radioactive/adverse effects , Costs and Cost Analysis , Health Physics , Humans , Kinetics , Monte Carlo Method , Radiation Dosage , Radon/adverse effects
13.
Phys Rev E Stat Nonlin Soft Matter Phys ; 66(1 Pt 1): 011701, 2002 Jul.
Article in English | MEDLINE | ID: mdl-12241369

ABSTRACT

Pressure-electric (hydrostatic piezoelectric) measurements are reported on bookshelf textures of a ferroelectric smectic-C (Sm C*) liquid crystal with a glass transition. The continuous variation of a partially fluid state to the solid glass enables one to trace how the piezoelectric effect depends on the consistency of the material. It was observed that in the Sm C* samples with poled glass the piezoelectric constants are comparable to conventional piezoelectric crystals and poled piezoelectric polymers. This implies their application possibilities. The magnitude of the piezoelectric constant in the glassy state depends very much on the poling conditions. The studies indicate that there are two counteracting effects, which cancel each other out in the Sm C* phase near the glass transition. Our analysis indicates that the pressure-induced director tilt change has a dominating effect both in the fluid and the glassy Sm C* states.

14.
Phys Rev E Stat Nonlin Soft Matter Phys ; 66(5 Pt 1): 051713, 2002 Nov.
Article in English | MEDLINE | ID: mdl-12513509

ABSTRACT

Electroconvection in an unusual nematic compound with strongly positive dielectric anisotropy and negative anisotropy of the conductivity is investigated. For homeotropic alignment, where one has a direct transition to rolls or squares depending on the frequency of the applied voltage, we present a quantitative theory. From the comparison we infer values for some viscosities, which are rather unusual, but not unreasonable in view of the vicinity of the nematic-smectic transition. For planar alignment, electroconvection sets in above a splay Freedericksz transition with "parallel rolls," which is also captured by the theory.

15.
J Prosthet Dent ; 86(6): 636-43, 2001 Dec.
Article in English | MEDLINE | ID: mdl-11753317

ABSTRACT

STATEMENT OF PROBLEM: It is recognized that high or misdirected forces can cause occlusal trauma. It is also known that the coefficient of friction between contacting teeth depends on (salivary) lubrication and on the material surfaces in contact. Friction changes the directions and magnitudes of contact forces, but the exact influence of friction on occlusal trauma is unknown. PURPOSE: The purpose of this mathematical study was to ascertain the influence of changed friction (as a result of xerostomia or a restoration) on the forces experienced by contacting teeth and the temporomandibular joint (TMJ). MATERIAL AND METHODS: Equations were derived for the forces on teeth and the TMJ. To assess the effects of friction on these forces, a parametric analysis was performed in which the coefficient of friction between teeth was set to 0.0 (idealized frictionless contact), 0.2 (salivary lubrication), 0.4 (xerostomia), or 1.0 (some artificial saliva lubrication). RESULTS: The computations indicated that a change in friction influences the directions and magnitudes of the forces experienced by teeth and the TMJ. The effect can be subtle or profound depending on the cusp angle and the direction of impending motion. CONCLUSION: Within the limitations of this study, the results suggest that change in friction between teeth, for any reason, should be considered a possible cause of occlusal trauma.


Subject(s)
Dental Occlusion, Traumatic/etiology , Dental Amalgam/adverse effects , Dental Porcelain/adverse effects , Dental Restoration, Permanent/adverse effects , Dental Stress Analysis , Friction , Humans , Masticatory Muscles/physiopathology , Models, Biological , Saliva/physiology , Saliva, Artificial/adverse effects , Surface Properties , Temporomandibular Joint/physiopathology , Xerostomia/complications
16.
Phys Rev E Stat Nonlin Soft Matter Phys ; 64(5 Pt 2): 056225, 2001 Nov.
Article in English | MEDLINE | ID: mdl-11736072

ABSTRACT

Viscous fingering of an air-nematic interface in a radial Hele-Shaw cell is studied when periodically switching on and off an electric field, which reorients the nematic and thus changes its viscosity, as well as the surface tension and its anisotropy (mainly enforced by a single groove in the cell). Undulations at the sides of the fingers are observed that correlate with the switching frequency and with tip oscillations that give maximal velocity to smallest curvatures. These lateral undulations appear to be decoupled from spontaneous (noise induced) side branching. It is concluded that the lateral undulations are generated by successive relaxations between two limiting finger widths. The change between these two selected pattern scales is mainly due to the change in the anisotropy. This scenario is confirmed by numerical simulations in the channel geometry, using a phase-field model for anisotropic viscous fingering.

17.
Am J Orthod Dentofacial Orthop ; 120(3): 263-71, 2001 Sep.
Article in English | MEDLINE | ID: mdl-11552125

ABSTRACT

Numerous theories have been propounded to explain the various aspects of tooth eruption, but no general consensus exists about some of the underlying mechanisms that govern these aspects. An important unresolved issue is the source of the motive forces that displace teeth. We proposed that supraosseous eruptive forces are generated by tooth socket distortions caused by functional jaw deformations. Previous studies used basic equations of static equilibrium to demonstrate that the concomitant stretching of the oblique periodontal ligament (PDL) fibers give rise to forces that may cause supraosseous tooth eruption. For a more rigorous and expanded analysis, we applied the finite element method (FEM). Three functional loads were considered, but the FEM calculations strongly suggested that all jaw deformations contribute to tooth extrusion. It was also demonstrated that the PDL fiber disruptions that are likely to occur with increased stretching can provide a mechanism to stabilize the erupted position.


Subject(s)
Dental Stress Analysis , Tooth Eruption/physiology , Computer Simulation , Dental Stress Analysis/methods , Elasticity , Finite Element Analysis , Humans , Mandible , Models, Biological , Models, Dental , Periodontal Ligament/physiology , Stress, Mechanical , Tensile Strength , Tooth Socket/physiology
18.
Am J Orthod Dentofacial Orthop ; 120(3): 272-9, 2001 Sep.
Article in English | MEDLINE | ID: mdl-11552126

ABSTRACT

The effects of mechanical loads on the tooth-alveolus complex are of particular concern in orthodontics. The concepts of center of resistance (CRes) and center of rotation (CRot) are used to characterize tooth responses to orthodontic loads. The mechanical environment (stresses and strains) associated with orthodontic tooth movement is a unique model in bone adaptation physiology. Numerous finite element models of varying complexity have been developed to calculate tooth movements and stress distributions within the alveolar bone and the periodontal ligament (PDL). In general, the PDL has been idealized as a homogeneous isotropic material. For this project, a 3-dimensional tooth/PDL/mandible/finite element model was developed in which, for the first time in such an analysis, the PDL's principal-fiber structure was also incorporated. Parametric analyses showed that the fiber orientation and the mechanical properties do not exert much influence on the locations of the CRes and the CRot and on the stress patterns within the bone and the PDL matrix. However, the absence of principal fibers produces not only different stress magnitudes, but also differences in stress patterns. Furthermore, the no-fiber-associated CRes and CRot are considerably separated from the cluster of fiber-influenced centers. It was concluded that it may be more realistic to incorporate "generic" principal fibers into finite element models than not to include them at all, despite the lack of reliable information about fibers.


Subject(s)
Dental Stress Analysis , Periodontal Ligament/anatomy & histology , Periodontal Ligament/physiology , Tooth Movement Techniques , Alveolar Process/physiology , Animals , Bone Remodeling , Computer Simulation , Dogs , Elasticity , Finite Element Analysis , Mandible , Models, Biological , Models, Dental , Rotation , Stress, Mechanical
19.
J Biomed Mater Res ; 53(5): 554-9, 2000 Sep.
Article in English | MEDLINE | ID: mdl-10984704

ABSTRACT

An important consideration in improving the longevity of dental resin composite restorations is how to minimize the stresses that develop between resin composites and the wall of the preparation as the resin shrinks during polymerization. If the stress is too great, failure of the bonded interface occurs and microleakage results, with possible margin failure, staining, and secondary caries. This present project was performed to validate a previously developed FEM approach for investigating polymerization shrinkage. Light-cured resin composite was condensed into a cylindrical cavity preparation, which contained a centrally located wire. A profilometer stylus was positioned on the end of the wire to detect the initial surface displacement as the wire moved with the superficial layer of composite resin. The plots of the experimentally derived data were compared to the data plot from the FEM. The initial segments of the experimental plots matched the calculated plot very closely in shape, thus validating the FEM approach.


Subject(s)
Dental Materials/chemistry , Resins, Plant/chemistry , Light , Materials Testing/instrumentation , Materials Testing/methods , Polymers , Reproducibility of Results , Stress, Mechanical
20.
Angle Orthod ; 70(1): 48-51, 2000 Feb.
Article in English | MEDLINE | ID: mdl-10730675

ABSTRACT

The moments and forces produced by various orthodontic T-loop spring designs were measured. The effects of dimension changes (within clinically used ranges) and the addition of gable bends with heat treatment were assessed. Increasing the vertical or horizontal dimension reduced the spring's load-deflection rate and its moment-to-force ratio. Gable preactivation with heat treatment had the opposite effects.


Subject(s)
Orthodontic Appliance Design , Orthodontic Wires , Stainless Steel/chemistry , Analysis of Variance , Calibration , Confidence Intervals , Elasticity , Hot Temperature , Humans , Materials Testing , Stress, Mechanical , Surface Properties
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