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At least 865 records · Page 48Linked to original sources
PubMed1996

Establishing the gingival emergence profile of restorations by using a resilient gingival replica.

All references to gingival morphology are destroyed once the die is trimmed during construction of crowns, onlays, or veneers. The need for reconstruction of a gingival replica to assist in the reproduction of a restoration's gingival contour and emergence profile is discussed. A simple, practical approach to duplicate the natural sulcus and free gingival morphology with currently available materials is presented. The advantages and limitations of implementing this technique and its multiple uses in prosthodontic and implant reconstructions and implant cases are presented.

Crowns↗
PubMed1998

Effects of periodontal support and fixed splinting on load transfer by removable partial dentures.

STATEMENT OF PROBLEM: Periodontally compromised abutment teeth complicate the design of bilateral distal extension removable partial dentures. PURPOSE: This study investigated the stress induced in the remaining oral structures by a bilateral distal extension I-bar-retained RPD with periodontally involved abutments in a photoelastic simulation model. MATERIAL AND METHODS: Composite photoelastic models were used as a simulation model in determining the stress generating characteristics of I-bar RPDs with varying degrees of periodontal involvement of the distal abutments. Effects of fixed splinting were considered. RESULTS AND CONCLUSIONS: Under the same load conditions, the highest stresses developed in the model with the largest osseous defect. Increasing the number of splinted teeth did not provide a proportional decrease in maximum stress levels. The more severe the osseous defect, the greater assistance was provided by splinting to periodontally sound teeth. This simulation study suggests that routine cross-arch splinting may not be appropriate.

Acrylic Resins↗
PubMed2000

Cortical-basal ganglionic degeneration: a clinical, functional and cognitive evaluation (1-year follow-up).

We decided to evaluate a patient who was diagnosed with cortical-basal ganglionic degeneration from a clinical, instrumental and neuropsychological perspective. Our aim was to employ a new instrumental tool, functional magnetic resonance, in order to evaluate his cortical damage. We then followed the pathological course for 1 year and tested the patient again: we discuss the results of our evaluation, having an overview of the literature on the topic. In particular, we focused our attention on his apraxia, trying to suggest a dynamic and anatomical model to guarantee a possible explanation of his behavior.

Aged↗
PubMed1983

Renal anatomy for endourologic stone removal.

A transparent kidney model that shows the position of the calices in relation to the surface can be fabricated easily and is invaluable in planning percutaneous nephrostolithotomies and other endourological procedures.

Humans↗
PubMed2003

Wall shear stress differentially affects NO level in arterioles for volume expanders and Hb-based O2 carriers.

The endothelium-derived nitric oxide (NO) is one of the mediators of smooth muscle (SM) relaxation. The release of NO by endothelium depends on the wall shear stress (WSS) to which endothelium is exposed. During hemodilution or isovolemic exchange transfusion with hemoglobin-based oxygen carriers (HBOCs) or volume expanders, the systemic hematocrit, blood viscosity, and blood flow rate are affected that would change WSS at endothelium. The effect of WSS-dependent NO release on SM NO availability has not been determined by direct measurements. We have formulated a mathematical model that is capable of predicting NO concentration in and around arteriolar vessels. The model predicts that the normal physiological SM NO concentration is approximately 100 nM at a physiological WSS of 24 dyn/cm(2) and the NO concentration is linearly dependent on WSS. With volume expanders, the SM NO concentration increases significantly and the levels of SM NO are significantly higher with increase in WSS. The SM NO decreases several-fold even for 5 microM luminal HBOC. For HBOCs, the NO levels are not restored to normal physiological level even with a significant increase in WSS (>48 dyn/cm(2)). These predictions are consistent with the results of animal studies of vascular tone following administration of HBOCs and volume expanders.

Animals↗
PubMedDate not supplied

Airflow mechanics in models of equine obstructive airway disease under conditions simulating exercise.

Effects of respiratory tract obstructions on ventilatory mechanics in horses exercising at high speeds were tested with a fibreglass replica of the airways (nares to mainstem bronchi) of an adult horse. Segmental pressures were recorded at six sites along the model at four different unidirectional flows (1300-4100 litre min-1), and the respective resistances (R) to airflow were calculated. The external nares and the larynx made the greatest contributions to the total resistance (RTOT) when no obstruction was present. Modifying the model to simulate severe pharyngeal lymphoid hyperplasia (PLH) had no effect on R at the larynx or at any point in the trachea under these flow conditions. Two 16 litre anaesthetic rebreathing bags were attached to the bronchial end of the model, and tidal ventilation generated by a piston pump. Upper (nares to pharynx) and lower tract R (RU and RL) and RTOT, and dynamic compliance were determined for pump volumes (Vp) of six and 12 litres, at pumping frequencies (fp) of 20-100 min-1 while the airway was clear, and after modifying it to simulate either PLH or partial bronchial obstruction. Model condition had no effect on RU. However, RL and RTOT were higher in the PLH simulated condition when fp > or = 90 and Vp = 12 litres (P < 0.05). This suggested that severe PLH may significantly interfere with airflow distal to the site of the lesions during high frequency high volume ventilation of the type seen in galloping horses. With partial bronchial obstruction RL and RTOT were increased when fp > 34 with each Vp. The applicability of the model was verified by comparing results from the unobstructed state with those from normal horses exercising on a treadmill.

Animals↗
PubMed2004

[Static anterior glenohumeral subluxation following coracoid bone block in combination with pectoralis major transfer: a case report and biomechanical considerations].

We report the case of a patient who experienced post-traumatic static anterosuperior subluxation of the shoulder. The displacement worsened after surgical treatment associating a preglenoid bone block and pectoralis major transfer. We studied the lines of action of the conjoint tendon on an anatomic model. The biomechanical study demonstrated that alone, the coracoid bone block did not provoke the anterior glenohumeral subluxation. On the contrary, the compression components of the humeral head into the glenoid cavity increased and could not explain the worsening dislocation. Inversely, the tendon of the pectoralis major passed in front of the conjoint tendon because of the absence of the subscapularis and could have been the cause of the aggravated anterior subluxation.

Biomechanical Phenomena↗
PubMed2004

[Limitations of orthognathic model surgery: theoretical and practical implications].

Orthognathic model surgery is a classical technique used to simulate orthognathic surgical cases. However, a detailed analysis of this technique demonstrates that theoretical errors and inaccuracies can occur in routine practice. 2D and 3D cephalometric analysis is the first source of inaccuracies. Then, during the occlusal plane transfer from the patient to the semi-adjustable dental articulator, errors can occur by inaccurate manipulation of the facial bow. Simulating the operation on the plaster cast is difficult due to the lack of a real link between the cephalometric analysis and the model surgery. Rotation and translation movements of the plaster casts are insufficiently controlled during the model surgery stage. Finally, the splint, which transfers the final relative position of maxilla to the mandible, summates all of the errors of the previous stages.

Cephalometry↗
PubMed1978

Three-dimensional architecture of blood vessels of tendons demonstrated by corrosion casts.

Three-dimensional observation of the microcirculation of the tendon was readily and clearly demonstrated by preparing methyl methacrylate casts and observing them under the scanning electron microscope. In the muscles blood vessels made a network like a ladder surrounding every muscle fibre. The fibrous digital sheath had blood vessels made in a fine meshed cylinder. By microdissection of the vessels of the sheath the blood vessels of the vinculae and tendons were observed stereoscopically in relation to the peritendinous tissues. The casting method contributes to better understanding of vascular architecture of tendons.

Animals↗
PubMed2006

Role of peripherin/rds in vertebrate photoreceptor architecture and inherited retinal degenerations.

The vertebrate photoreceptor outer segment (OS) is a highly structured and dynamic organelle specialized to transduce light signals. The elaborate membranous architecture of the OS requires peripherin/rds (P/rds), an integral membrane protein and tetraspanin protein family member. Gene-level defects in P/rds cause a broad variety of late-onset progressive retinal degenerations in humans and dysmorphic photoreceptors in murine and Xenopus models. Although proposed to fulfill numerous roles related to OS structural stability and renewal, P/rds molecular function remains uncertain. An increasingly resolved model of this protein's oligomeric structure can account for disease inheritance patterns and severity in some instances. Nonetheless, the pathogenic mechanisms underlying the uniquely broad spectrum of retinal diseases associated with P/rds defects are not currently well understood. Recent findings point to the possibility that P/rds acts as a multifunctional scaffolding protein for OS architecture and that partial-loss-of-function mutations contribute to the hallmark phenotypic heterogeneity associated with inherited defects in RDS.

Amino Acid Sequence↗
PubMedDate not supplied

Sarcomere length changes in a 3D mathematical model of the pig ventricles.

Measurements of the geometry and fibrous-sheet structure of the left and right ventricles of the pig heart are fitted with a finite element model. Mechanical changes during the heart cycle are computed by solving the equations of motion under specified ventricular boundary conditions and using experimentally defined constitutive laws for the active and passive material properties of myocardial tissue. The resulting patterns of deformation, such as axial torsion and changes in wall thickness and base-apex length, are consistent with experimental observations. The model can therefore be used to predict sarcomere length changes and other strain patterns throughout the myocardium and throughout the cardiac cycle. Here we present sarcomere length changes at a limited number of material points within the wall. Sarcomere length typically varies by 10% above and below the unloaded length; although under the boundary conditions imposed in the current model the midwall circumferentially oriented sarcomere lengths increased by up to 20% at end diastole. We provide web-access details for a downloadable software program designed to provide more extensive information on mechanical deformation, such as the principal strains and muscle fibre cross-sectional area changes during the cardiac cycle.

Animals↗
PubMed1998

Finite element analysis of defibrillation fields in a human torso model for ventricular defibrillation.

In order to optimize defibrillation electrode systems for ventricular defibrillation thresholds (DFTs), a Finite Element Torso model was built from fast CT scans of a patient who had large cardiac dimensions (upper bound of normal) but no heart disease. Clinically used defibrillation electrode configurations, i.e. Superior Vena Cava (SVC) to Right Ventricle (RV) (SVC-RV), left pectoral Can to RV (Can-RV) and Can + SVC-RV, were analyzed. The DFTs were calculated based on 95% ventricular mass having voltage gradient > 5 V/cm and these results were also compared with clinical data. The low voltage gradient regions with voltage gradient < 5 V/cm were identified and the effect of electrode dimension and location on DFTs were also investigated for each system. A good correlation between the model results and the clinical data supports the use of Finite Element Analysis of a human torso model for optimization of defibrillation electrode systems. This correlation also indicates that the critical mass hypothesis is the primary mechanism of defibrillation. Both the FEA results and the clinical data show that Can + SVC-RV system offers the lowest voltage DFTs when compared with SVC-RV and Can-RV systems. Analysis of the effect of RV, SVC and Can electrode dimensions and locations can have an important impact on defibrillation lead designs.

Computational Biology↗