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At least 1,009 records · Page 56Linked to original sources
PubMed2002

Optimizing presurgical orthodontic planning by means of the transverse coordinate simulation system (TCSS).

INTRODUCTION: When planning bilateral sagittal split osteotomies according to Obwegeser and Dal Pont, inaccuracies in the presurgical prediction of the transverse osteotomy gaps may occur. This is due to limitations of plaster models when simulating surgery on an articulator. AIM: This paper demonstrates the transverse coordinate simulation system which allows presurgical prediction of the transverse discrepancy between the tooth bearing and the proximal segment after displacement, thus minimizing uncertainty for the surgeon. METHOD: Diagnostic landmarks (taken from lateral and frontal cephalograms) and clinical data describing mandibular dimensions are transferred to a two-dimensional coordinate diagram. A mandibular model is then constructed using the anterior arch form, the temporomandibular joint distance and the prospective incision pattern. RESULT: Movements in the horizontal plane and displacement of the three segments (two condylar and one mandibular arch segment) can be simulated and measured. CONCLUSION: Transverse coordinate simulation system effectively increases the accuracy of presurgical planning without additional CT data or three-dimensional jaw models. This technique may decrease the number of additional surgical manoeuvres resulting from unexpectedly wide transverse discrepancies at the osteotomy site, which often increase surgery time, necessitate additional bone grafting, and entail the risk of healing disturbances and of malrotation or dislocation of the condyle.

Cephalometry↗
PubMed2005

[Navigated control: a new concept in computer assisted ENT-surgery].

This work conceived and evaluates a mechatronical system for ORL-surgery by example of a Shaver for Functional Endoscopic Sinus Surgery controlled by navigation. The Shaver is automatically on/off-regulated depending on the current position in relation to the planned working space. This working space is defined on the basis of the individual CT data. Within this area the Shaver reacts to the signal of the surgeon (foot pedal). If the Shaver leaves the working space, an interruption of the drive regulation to the Shaver takes place. The evaluation of the planning software based on 32 patient CT-data sets. The registration accuracy in a anatomical model was examined on 451 measurements of endonasal attached titanium screws. The conversions of the working space were evaluated at 5 different technical models. The average time for segmenting the working space was found at 4.23 minutes per case. An average registration accuracy of the Shaver of 1.08 mm resulted. The pre-defined cavity was to be cleared away without restrictions. The preoperative determined work-space was converted by 3.1 mm over all levels. The study proves the feasibility of a mechatronical assistant system by the example of the navigate-controlled Shaver in paranasal sinus surgery. Contrary to conventional CAS solutions redundancy and cognitive discharge of the surgeon are considered in this conception. We see numerous applications according to the explained principle for power-control of instruments in ORL-surgery in the future such as drilling, high frequency surgery or laser.

Feasibility Studies↗
PubMed2006

[Experimental principles of the V.A.C.-therapy -- pressure values in superficial soft tissue and the applied foam].

OBJECT OF THE STUDY: Measurement of the pressure during V.A.C.(R)-therapy in superficial parts of the affected soft tissue as well as at the soft tissue/foam-interface, measurement of pressure values along bigger distances in the foam and the comparison of pressure transfer between polyurethane and polyvinyl-alcohol foams. MATERIAL AND METHODS: A multi-channel electronic transducer-tipped catheter system based on the piezo-resistant principle was used. Measurement was performed on a plain table surface, at a bovine muscle as well as in human tibial anterior muscle of a patient after fasciotomy. Applied pressure values by V.A.C.(R)-therapy-units were 50 to 200 mm Hg (continuous suction modus). RESULTS: 100 % pressure transition through vacuum-therapy-foams to wound surface, almost 100 % pressure transition even along 60 cm in very large polyurethane-foams using only one trac-pad connector. Pressure values > 125 mm Hg using polyvinyl-alcohol-foams showed a reduction of up to 25 % in distances > 15 cm from trac-pad-connector. On the surface of the affected soft tissue there are negative and positive pressure values (25 % quartile: - 25 mm Hg; 75 % quartile: + 15 mm Hg). DISCUSSION: Pore walls of the foam can produce positive pressure conditions resulting in soft tissue compression and consecutively hypoperfusion or ischemia. V.A.C.(R)-therapy seems to produce an heterogeneity of pressure distribution at the wound ground leading to pressure gradients and facilitating drainage of interstitial fluid. This mechanism could explain the anti-edema effects of V.A.C.(R)-therapy resulting indirectly in an increased nutritive perfusion.

Animals↗
PubMed1996

[Calculated organ doses and effective dosage for computerized tomography examination of the thorax and abdomen: are these doses realistic?].

PURPOSE: To analyse how far dose calculations for the CT examination of the thorax and abdomen can lead to faulty estimations of organ doses and effective dose due to differences in the topographic anatomy between mathematical phantom and man. METHODS: For the CT examination of the thorax, upper abdomen, pancreas, pelvis and the entire abdomen, organ doses were calculated with conversion factors, first with regard to the topographic relation within the phantom, then with additional regard to the real anatomy of the man. RESULTS: In the phantom, the abdomen lies outside the scan volume in case of CT-examination of the thorax and the whole intestine outside the scan volume in case of CT-examination of the upper abdomen and the pancreas, whereas the entire intestine is directly exposed in case of CT-examination of the pelvis. Dependent on whether dose calculations take real anatomy into account, doses of special organs can differ by a factor greater than 15. The calculated effective doses differ by a factor less than 1.5. CONCLUSIONS: Calculations of organ doses for the CT examination of the thorax and abdomen can lead to considerable errors due to different topographic relations between phantom and man. In contrast the calculated effective dose is realistic. Hence, dose calculations with the help of mathematical phantom is an efficient method to estimate the total radiogenic risk.

Female↗
PubMedDate not supplied

[Optimization of the dynamic compression in angle-plated osteosynthesis by static interfragmentary compression--experimental results].

Osteosynthesis with an angled plate after intertrochanteric osteotomy is mainly a tension-band-osteosynthesis. Because of the lack of interfragmentary compression at the medial corticalis this technique may lead to pseudarthrosis or delayed bone union. On the basis of theoretical considerations and extensive experiments, we found a distinct improvement in interfragmentary compression when the osteotomy-planes are set at an angle of 6 degrees open to the lateral side before external compression with 1000 N. In this way "functional plate-prebending" is achieved. Thus tension-band-osteosynthesis is completed by compression osteosynthesis.

Bone Plates↗
PubMed1980

[Finite element analysis, its limitations and the relevance of its results to orthopaedic surgery as shown by simultaneous experimental measurements (author's transl)].

For a stress analysis of the femur, intact or with an implant, the Finite Element Method appears to be the only practicable one. In order to evaluate the limitation of this method and the relevance of its results for orthopaedic problems, bones were modelled for 2-dimensional and 3-dimensional analysis. Strain gauges were attached to the actual bones. Strains were calculated and measured exerimentally. The results led to these conclusions: The Finite Element Method alone is an appropriate means for qualitative and comparative studies. Complicated geometry of bones and uncertainties about their mechanical properties make it mandatory that calculated values by corroborated by experimental measurements at least in certain points. This ought to be considered particularly if practical consequences are to be drawn from Finite Element calculations in orthopaedic surgery.

Epoxy Resins↗
PubMed1980

[Early experience with a large format image intensifier for thoracic, abdominal and peripheral angiography (author's transl)].

By the use of a 36 cm image intensifier, its position under the table top and its great focus-image intensifier distance radiation geometric conditions were produced which are identical with the full-size film technique. With this equipment angiographic examinations of the thorax, abdomen as well as extremities were possible with the help of indirect fluorography, In accordance with examinations at anatomical models it turned out that the detail perception of the image intensifier-series fluorography was almost comparable to conventional full size film technique. Aside from the lower radiation dose and the shorter exposure time indirect fluorography offered additional advantages: By means of the fluoroscopic control of the contrast medium and the fluoroscopically controlled exposure a reduction of the methodical procedure was possible with regard to numbers of exposures and series just as saving of time for the complete examination. The evaluation and clinical demonstration of the 100 mm films were critically tested in the daily routine work.

Abdomen↗
PubMed1981

A mathematical approach to the common bile duct.

Changes in the shape of the common bile duct (CBD) can be expressed mathematically by measuring the C.B.D.-diameter at five points and expressing these measurements as a percentage of the mean diameter. Variations in magnification are compensated for by relating the mean diameter to the length of the C.B.D. By comparing the shape of the C.B.D. in patients with various diseases with the shape of the normal common bile duct it was possible to define pathognomonic signs of various diseases of the extrahepatic biliary system. Indirect signs of pathology of the extrahepatic bile ducts are discussed.

Adult↗
PubMed2005

Oscillator clustering in a resource distribution chain.

The paper investigates the special clustering phenomena that one can observe in systems of nonlinear oscillators that are coupled via a shared flow of primary resources (or a common power supply). This type of coupling, which appears to be quite frequent in nature, implies that one can no longer separate the inherent dynamics of the individual oscillator from the properties of the coupling network. Illustrated by examples from microbiological population dynamics, renal physiology, and electronic oscillator theory, we show how competition for primary resources in a resource distribution chain leads to a number of new generic phenomena, including partial synchronization, sliding of the synchronization region with the resource supply, and coupling-induced inhomogeneity.

Arterioles↗
PubMed2002

A simplified conceptual model of the human cervical spine for evaluating force transmission in upright static posture.

OBJECTIVE: To develop a simplified graphical model appropriate for the evaluation of proposed theoretical force transmission mechanisms in the upright static cervical spine. The model is used to demonstrate in a visual format the underlying mechanical principles contributing to an optimal mechanical configuration of the cervical spine in upright posture. The model is also used to explore the relative mechanical efficiency of 2 different force transmission methods. METHOD: A graphical model was developed to illustrate relevant force vectors acting on the head and neck in upright posture. This model was used to calculate theoretical static loading on the structures of the neck under various loading conditions resulting from specific configurations of passive elements and active supportive muscle effort. RESULTS: From the information gained from the model, a theorized optimal mechanical configuration and theorized role of various components of the cervical spine in static upright posture is presented. The model is used to test the mechanical validity of a concurrent force system with intersegmental muscle force rather than the parallel force system presented in the literature. The alternate models are examined in relation to their predictions and theoretical implications with respect to force transmission in the cervical spine. CONCLUSION: A simplified model has been developed that facilitates the graphical representation of forces involved in maintaining static upright posture in the human cervical spine. The model is used to explore the optimal spinal configuration of the major mechanical components of the neck.

Biomechanical Phenomena↗
PubMed2001

A comparison between friction and frictionless mechanics with a new typodont simulation system.

This study was designed to explore the differences between friction and frictionless mechanics for maxillary canine retraction with the use of a new typodont simulation system, the Calorific machine system. The unit was designed to observe the whole process of tooth movement and is composed of 3 parts: a temperature regulating system, electrothermodynamic teeth, and an artificial alveolar bone component. The efficiency of maxillary canine retraction was compared with the sliding mechanics (along a.016 x.022-in stainless steel labial arch and nickel-titanium closed coil spring) and a canine retraction spring. The patterns of tooth movement obtained with both of these mechanics were measured 5 times each. Friction mechanics were superior to frictionless mechanics in terms of rotational control and dimensional maintenance of the arch (P <.0001); frictionless mechanics were shown to be more effective at reducing tipping and extrusion (P <.0001). However, the observed differences between the 2 methods were relatively small in terms of their clinical significance, and no differences were found in anchorage control (P =.2078). In conclusion, this study indicated that friction and frictionless mechanics perform similarly.

Alveolar Process↗
PubMed2002

Reliability of a 3D surface laser scanner for orthodontic applications.

A device for recreating three-dimensional (3D) objects on a computer is the surface laser scanner. By triangulating distances between the reflecting laser beam and the scanned surface, the surface laser scanner can detect not only an object's length and width but also its depth. The scanner's ease of use has opened various possibilities in laboratory research and clinical investigation. We assessed the reliability of generating 3D object reconstructions using the Minolta Vivid700 3D surface laser scanner (Minolta USA, Ramsey, NJ). Accuracy and reproducibility were tested on a geometrical calibrated cylinder, a dental study model, and a plaster facial model. Tests were conducted at varying distances between the object and the scanner. It was found that (1) in the calibrated cylinder tests, spatial distance measurement was accurate to 0.5 mm (+/- 0.1 mm) in the vertical dimension and 0.3 mm (+/- 0.3 mm) in the horizontal dimension; (2) in the study model test, molar width was accurate to 0.2 mm (+/- 0.1 mm, P >.05), and palatal vault depth could be measured to 0.7 mm (+/- 0.2 mm, P > 0.05); and (3) for the facial model, an accuracy of 1.9 +/- 0.8 mm was obtained. The findings suggest that the surface laser scanner has great research potential because of its accuracy and ease of use. Treatment changes, growth, surgical simulations, and many other orthodontic applications can be approached 3-dimensionally with this device.

Cephalometry↗
PubMed2001

Fabrication of imaging and surgical guides for dental implants.

Research and experience have suggested that the success of dental implants depends on a well-developed and careful treatment plan approach. Historically, implant size and angulation were determined with the use of panoramic radiographs and clinical judgment during surgery. This occasionally resulted in mechanical and esthetic compromise. This article describes the step-by-step fabrication process for 4 different imaging and surgical guides. Set-up disks, which enhance the design and fabrication of guides, also are introduced. These guides are used in conjunction with cross-sectional tomography during the preimplant assessment of surgical sites.

Dental Implantation, Endosseous↗
PubMed2002

A surgical guide for accurate mesiodistal paralleling of implants in the posterior edentulous mandible.

Malaligned implants often complicate the clinical and laboratory procedures employed for the fabrication of superstructures. Due to improper load distribution, an overall increase in stress concentrations on supporting implants may occur; in the long run, this may compromise the maintenance of the bone-implant interface. The utilization of surgical stents is imperative for optimum implant installation. This article describes a modified surgical stent that serves as a guide to proper mesiodistal paralleling of dental implants.

Bicuspid↗
PubMed2002

Use of transitional implants to support a surgical guide: enhancing the accuracy of implant placement.

Surgical guides for edentulous patients often lack the stability desired for accurate implant placement. The difficulty is emphasized in the edentulous mandible when implant-supported metal-ceramic restorations, which require precise placement of implants, are planned. A technique is presented for the fabrication of a surgical and radiographic template, supported by transitional implants, that guides the placement of conventional implants. This template can enhance placement accuracy in an efficient way to achieve predictable, esthetic results.

Dental Implantation, Endosseous↗
PubMed2002

The neural basis of intermittent motor control in humans.

The basic question of whether the human brain controls continuous movements intermittently is still under debate. Here we show that 6- to 9-Hz pulsatile velocity changes of slow finger movements are directly correlated to oscillatory activity in the motor cortex, which is sustained by cerebellar drive through thalamus and premotor cortex. Our findings suggest that coupling of 6- to 9-Hz oscillatory activity in the cerebello-thalamo-cortical loop represents the neural mechanism for the intermittent control of continuous movements.

Adult↗