Does the presence of an occlusal indicator product affect the contact forces between full dentitions?

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.

The effects of salivas on occlusal forces.

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.

Do occlusal contact detection products alter the occlusion?

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.

The structural transitions in 6CHBT-based ferronematic droplets.

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.

Optimization of microCT data processing for modelling of dental structures in orthodontic studies.

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.

Nonstandard electroconvection in a bent-core nematic liquid crystal.

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.

Cost assessment of ventilation and averted dose due to radon in dwellings.

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.

Microdamage adjacent to endosseous implants.

Intense remodeling occurs in lamellar bone adjacent to osseointegrated endosseous implants. The purpose of this study was to compare microdamage accumulation subsequent to ex vivo fatigue loading of bone that surrounds an endosseous implant, (a) immediately after placement (nonadapted bone) and (b) following a 12 week healing period after placement (adapted bone). We hypothesize that there is less microdamage in the more compliant adapted bone than in the older nonadapted bone. Nonthreaded titanium plasma sprayed (TPS)-coated endosseous implants were placed into dog mid-femoral diaphyses and allowed to heal for 12 weeks. Block sections of bone, each containing one implant, were cut anteroposteriorly, resulting in an implant containing lateral cortex, and a medial cortex that was used for testing the nonadapted specimens. Control specimens (n = 14 each for adapted and nonadapted) were loaded at 0 N. Experimental specimens (n = 13, adapted; n = 14, nonadapted) were loaded at 100 N in cantilever bending for 150,000 cycles at 2 Hz, at 37 degrees C on a Bionix 858 testing machine. Specimens were bulk stained with basic fuchsin and 120-140 microm sections were obtained. Crack numerical density (Cr.Dn = Cr.N/ B.Ar, #/mm2), crack surface density (Cr.S.Dn = Tt.Cr.Le/ B.Ar, mm/mm2), and percent damage area (Dm.Ar = Cr.Ar x 100/B.Ar, mm2/mm2) were measured at x 250. Statistically significant differences (p < 0.0001) were seen for Cr.Dn, Cr.S.Dn, and Dm.Ar on the compressed cortices suggesting that adapted bone near the implant accumulated significantly less microdamage than nonadapted bone. Also, the adapted nonloaded control specimens had approximately 20-fold less damage than the respective nonadapted specimens. This study suggests that the compliant adapted bone adjacent to endosseous implants is relatively resistant to fatigue loads. The high success rates of endosseous implants may be due to the presence of a rapidly remodeling region that maintains tissue compliance and limits microdamage initiation.

Microhardness and anisotropy of the vital osseous interface and endosseous implant supporting bone.

Limited information is available on the mechanical properties of the rapidly remodeling bone that surrounds endosseous implants. Fifteen implant-bone blocks were obtained from the mid-femoral diaphyses of three mature male hounds 12 weeks after placement of the implants. To evaluate the microhardness and cortical anisotropy of bone, the implants were sectioned along their long axes. In this process, the femurs were sectioned transversely. Knoop microhardness measurements (HK) were made with a 50 g force on cortical bone and a 25 g force on periosteal callus, endocortical callus, and circumferential lamellar bone. The long diagonal of the indenter was placed parallel to the implant (in the radial bone direction). Measurements were made in cortical bone at 200, 400, 600, 800, 1,000, 1,500, 2,000, and 2,500 microm from both sides of the implant. To detect cortical anisotropy in the radial compared with the tangential direction, a second set of indentations was made perpendicular to the first. Microhardness of periosteal callus and endocortical callus and anisotropy of circumferential lamellar bone near the endocortical surfaces of the femur were also evaluated. Repeated measures analysis of variance showed significantly (p < 0.05) lower microhardness values (30.6 +/- 0.8 HK [mean +/- SEM]) for cortical bone at 200 microm than at any other location (range: 40.3-46.6 HK). Microhardness anisotropy was not detected in cortical bone. Furthermore, within 200 microm of the implant surface, the Knoop microhardness values were significantly lower for periosteal and endocortical calluses than for cortical bone. These data provide information about the mechanical properties of bone adjacent to endosseous implants at a microstructural level. The results are consistent with the high rate of remodeling seen adjacent to endosseous implants at 12 weeks after implantation.

Stress analysis of a bulk-filled Class V light-cured composite restoration.

Clinical failures are often associated with the polymerization shrinkage of resin composite restorative materials. These problems include tooth sensitivity and fracture, marginal leakage, loss of the restoration, and recurrent decay. Our goal was to examine transient composite distortions and interface stresses as a bulk-filled light-cured composite polymerized in a Class V restoration. The analysis was based on a finite element model. The curing of the restoration was divided into 4 steps: approximately 1/30, 1/4, 1/2, and full depth (1/1) of cure. Since the actual curing pattern is not known, calculations were performed for three hypothetical (flat, convex, and concave) polymerization front shapes. The calculations showed that the assumed shape was a critical factor in determining cured surface deformations. For example, the initial cure depth (1/30) resulted in a surface bulge if the polymerization front was presumed convex, while the concave front resulted in a large intrusion. By the time that about 1/2 the depth of the restoration was cured, the differences were essentially gone. The final surface outline was intruded. Interface stresses in the curing restoration were qualitatively similar regardless of the assumed polymerization shape. As with surface distortions, the stresses changed with curing depth. It was concluded that (1) transient events during polymerization are possible contributors to clinical complications, and (2) more must be known about the polymerization pattern.

Finite element stress analysis of three filling techniques for class V light-cured composite restorations.

An important disadvantage of current dental resin composites is polymerization shrinkage. This shrinkage has clinical repercussions such as sensitivity, marginal discoloration, and secondary caries. The objective of this study was to compare three filling techniques in terms of the transient stresses induced at the resin composite/tooth interface during polymerization. The techniques were: bulk filling (B), three horizontal increments (HI), and three wedge increments (WI). A simple Class V cavity preparation was modeled in finite element analysis. Polymerization shrinkage was simulated by a thermal stress analogy, thereby causing 1% shrinkage due to an arbitrary coefficient of thermal expansion. Interface normal and shear stresses were calculated at nine steps during polymerization, proceeding from 0% to 100% volume of cured resin. The importance of the interface transient stresses was revealed by the finding that, in most cases, their peak values exceeded the final or residual stress. Also, the WI and B techniques consistently exhibited the highest and lowest maximum transient stresses, respectively. These results from the simple model of a Class V restoration suggest that bulk filling of light-cured resin composites should be used in restorations which are sufficiently shallow to be cured to their full depth.

Stress analysis of bone modeling response to rat molar orthodontics.

The purpose of this project was to determine if alveolar bone modeling could be associated with altered mechanical environment. Finite element stress analysis of an orthodontically tipped rat molar periodontium was performed. The distributions of mechanical components within the periodontal ligament and cortical bone were compared to the well-documented bone formation and resorption patterns in the alveolus of the tooth. It was concluded that in orthodontically induced bone modeling activity, locations of osteogenesis uniquely coincided with increased tension within the periodontal ligament, while bone resorption areas could be associated with increases in other components (minimum principal and maximum shear stresses, strain energy density, and von Mises) within the bone itself.

Physicochemical properties, pharmacokinetics, and biodistribution of gadoteridol injection in rats and dogs.

RATIONALE AND OBJECTIVES: The physicochemical properties of gadoteridol, a macrocyclic nonionic gadolinium complex, were studied together with its pharmacokinetics and biodistribution in rats and dogs. METHODS: Studies in rats were conducted after single intravenous injections at 0.1 or 0.35 mmol/kg using 153Gd-labeled gadoteridol or with seven daily doses of 0.1 mmol/kg to examine the levels of residual gadolinium in organs. Nonradioactive biodistribution and excretion studies were performed in dogs following injection at 0.1 mmol/kg. RESULTS: After injection, the dose was rapidly cleared from rat blood and excreted such that more than 90% of the dose appeared in the urine within 4 hr of injection. At 7 and 14 days postinjection, only extremely low levels of gadolinium were observed in liver and bone; these levels were two to eight times lower than the levels reported after the injection of gadopentetate dimeglumine. CONCLUSION: The extracellular distribution and rapid urinary excretion of gadoteridol is in agreement with data obtained with other gadolinium-containing chelates used as intravascular magnetic resonance imaging contrast agents. Differences observed in the long-term retention of gadolinium between gadoteridol and gadopentetate dimeglumine were consistent with the reported greater in vivo resistance to transmetallation of gadolinium macrocycles compared with the linear gadolinium chelate molecules.

A computer model of the periodontal ligament space in man.

An engineering model of the periodontal ligament fibres was used to calculate length changes in the fibres with: direct occlusal forces on the tooth, occlusal loads on other teeth in the arch and splinting. The fibre elongations appear to influence tooth eruption, the clinical behaviour of splinted and non-splinted teeth, and the establishment of vertical dimension of occlusion and occlusal plane height. The model also provides insight into the controversy surrounding the intermediate plexus of the ligament.

Angiogenic induction and cell migration in an orthopaedically expanded maxillary suture in the rat.

The purpose was to examine the effect of an angiogenic factor on cell migration patterns and osteoblast histogenesis during the 96 h following orthopaedic expansion of the anterior maxillary suture. Fifty rats were divided into four groups: (1) a control group that received only angiogenic induction via injection of 5 ng/g body wt recombinant human endothelial-cell growth factor; (2) an experimental group that received orthopaedic expansion and angiogenic induction; (3) a sham group that received orthopaedic expansion and normal saline injection; and (4) a baseline group that received no expansion or injection. The experimental and sham groups were subdivided to conduct experiments over 1, 2, 3 or 4 days. The anterior portion of each maxilla was dissected free and demineralized. Sections (4 microns thick) were cut from every block and stained with Mayer's haematoxylin and eosin. Cell migration was analysed using a previously established cell-kinetics model. The osteoprogenitor cells were divided into four categories according to nuclear volume: A cells (40-79 microns3), B cells (80-119 microns3), C cells (120-169 microns3) and D cells (> or = 169 microns3 A' cells are the portion of the A cell population that responds to osteogenic stimulus. As previously defined in periodontal ligament, the reciprocal association of a decreasing number of less differentiated (A + A) cells and an increasing number of C + D cells, as a function of distance from the nearest major blood vessel, was consistently found in all groups. This suggests a vascularly oriented gradient of progressively more differentiated osteoprogenitor cells. Also, A + A' cells were predominately located within 20 microns of the nearest major blood vessel whereas the C + D cells were found at a distance > 30 microns from the nearest major blood vessel. These results suggest that the A'-->C shift occurs 20-30 microns from the nearest major blood vessel. In the angiogenic induction groups, the numbers of committed osteoprogenitors (A + A') were significantly higher than in the sham group at day 1. At day 3, the numbers of preosteoblasts (C + D) in angiogenic sutures were significantly higher than in the sham groups. This enhancement of preosteoblast population strongly suggests the possible role of activated pericytes in expanded sutures as a source of osteoprogenitor cells.

Mechanisms of tooth eruption in a computer-generated analysis of functional jaw deformations in man.

Two mechanisms that contribute to tooth eruption are proposed from analysis of the human jaws as elastic structures which are deformed intermittently under functional occlusal loads. One possible source of eruptive force is the transient pressure gradient established within each jaw as it is deformed. The second source, suggested by the computer model, is a consequence of the tension placed on periodontal-ligament fibres as individual tooth-sockets are distorted within the deformed jaws.

Piezoelectricity of a ferroelectric liquid crystal with a glass transition.

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.

Periodic forcing in viscous fingering of a nematic liquid crystal.

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.

Electroconvection in nematic liquid crystals with positive dielectric and negative conductivity anisotropy.

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.