Effect of masticatory function on the internal bone structure in the mandible of the growing rat.

The influence of changes in the masticatory function on bone mass, bone density and cortical thickness was analyzed in different functional units of the mandible of the growing rat. Young male albino rats were fed either a hard diet or a soft diet for 4 wk. Undecalcified coronal sections were selected from five mandibular regions and microradiographic images of the specimens alongside an aluminium stepwedge were obtained. Bone mass and density were measured at selected sites with a computer-aided image analysis system. Cortical thickness was measured on diagrams. The reduced masticatory function in the soft diet group produced different adaptive responses in the tested regions of the mandible. Some regions showed reduced cortical thickness (underneath the incisor and lateral to the first molar and some locations of the ramus), a few showed reduced bone density (medial to the first molar and in the ramus), and only one showed both (in the ramus). Reduced bone mass was associated mostly with thinner cortical bone rather than lower cortical bone density. Changes in cortical thickness and changes in bone density may be two different mechanisms for adjusting local mechanical properties in the mandible of the rat. Masticatory muscle function is a determinant for the amount and density of cortical and trabecular bone and may possibly influence results of orthodontic tooth movement and its possible relapse.

Effects of masticatory muscle function on bone mass in the mandible of the growing rat.

The effect of altered masticatory muscle function on bone mass at different sites in the rat mandible was studied using aluminium as a reference substance in computer-assisted image analysis. Forty-two growing male rats were divided into three groups, of which one group was killed at the beginning of the experiment to provide baseline values. Of the remaining two, one received a hard diet (control group) and the other a soft diet. After 28 days the rats were killed and the mandibles were excised. Lateral radiographs were taken of the mandible halves together with an aluminium stepwedge and then analysed by an image analysis system. Radiographic bone mass was measured in the transverse plane as "aluminium-equivalent thickness' in millimetres. Standardized areas were chosen to investigate regions with different functional demands. Significant differences were found between the groups in the alveolar bone of the molars and the incisor, as well as in the condylar costa and the condylar process. Significant differences were also found in some areas related to muscle insertion, such as the anterior lower border of the ramus, whereas no statistically significant differences could be found in others, such as the posterior lower border of the angular process. In conclusion, altered masticatory function influences the amount of bone mass in certain parts of mandible, where changes in applied bending forces have possibly altered the bone strain.

Migration of human granulocytes in filters: effects of gravity and movable gradients of f-MLP.

The Boyden chamber technique for chemotaxis uses a mesh filter that constitutes a matrix for cell locomotion and, at the same time, creates a local restriction for convective fluid movements that allows the establishment of a diffusive concentration gradient of chemotactic substance in the filter. In the present study, the Boyden chamber was modified by the introduction of a filter sandwich that allowed cell migration both upwards and downwards and by the use of a fluid density gradient controlling cell buoyancy and mechanically supporting a movable chemotactic gradient. This method was used to study chemotaxis and random migration of human granulocytes under the influence of gravitational forces and movable gradients of f-MLP. The results show that gravity affected cell motion significantly during random migration but not during chemotaxis. The rate of chemotactic migration was dependent on the steepness of the spatio-temporal f-MLP gradients. A stationary spatial gradient produced less migration than a gradient that was slowly moved through the filter sandwich in a direction opposite to that of the cell migration. The presence of f-MLP at constant concentration caused a minor, statistically insignificant, increase of the rate of random migration.

Pressure-induced local venous constrictor responses in human fingers.

Particularly in humans, systemic veins are often exposed to extensive changes in transmural pressure at altered body positions, when centrally conveyed constrictor reflexes provide compensation to maintain a proper venous return. The present aim was to explore whether also purely local mechanisms, of e.g. myogenic and/or axon reflex nature and operating at the venular-small vein levels, may contribute to offset venous pooling at local pressure increases. For such purposes the capacitance vascular responses were recorded plethysmographically in human fingertips, as most of the blood content is here contained in venules and small veins. Local increases in transmural pressure, induced by graded venous outflow obstructions, first induced by a corresponding passive-venous distension which within a few seconds was followed by a venoconstrictor response that could return the local blood content to nearly control level within 25-35 s. On sudden release of venous obstruction this 'active' response was unmasked as a prompt volume 'undershoot' that subsided in another 15-30 s. These microvascular responses could be powerful enough almost to offset the venodistension caused by transmural pressures up to 90-100 mmHg, and at brisk pressure increases they could be quite rapid in onset. As general reflex influences seemed to be excluded. these results in humans suggest that also the capacitance microvessels, like the precapillary resistance ones, can display myogenic responses to offset pressure increases. As the venular-small vein compartment contains up to 40% of the total blood volume such local responses, if generalized, may importantly contribute to venous control in humans.

Backscatter radiation at tissue-titanium interfaces. Biological effects from diagnostic 65 kVp x-rays.

The induced secondary electrons from a metal surface by diagnostic x-rays are thought to contribute to cell damage near the tissue-metal boundaries of metal implants. Titanium implants are becoming increasingly more popular for tissue reconstructions and it is rather often desirable to take radiographs of the operated area. In this study we compared the biological effects of radiation on cultured mammalian test cells grown on titanium plates with the radiation effects on cells that were grown on plastic control plates. In order to study the acute radiation effects on cell growth it was necessary to work with rather high radiation doses (0.7-5 Gy). Photon energies, suitable for diagnostic radiography in odontology, 65 kV, were applied. We found that the cells grown on titanium plates were, in terms of the applied dose in the surrounding culture medium, more sensitive to the irradiations than the cells growing on plastic plates. The survival curve for the cells on titanium had a steeper slope, showed no shoulder in the low-dose region and looked like curves normally obtained for high LET radiation. It was not possible to resolve to what degree the titanium-dependent changes were due to an increased dose near the titanium surface or to a change in the radiobiological effectiveness. Although there was a significant decrease in cellular survival near the metal, postoperative intraoral radiography after titanium implantations need not be excluded. The maximal doses given in odontological x-ray examinations are less than 1 mGy and, if the results in this study are applied, the biological effects near the titanium implant will correspond to biological effects in soft tissue of doses less than 20 mGy which is lower than the doses that give acute effects. The risk of acute healing disturbances are significant only at much higher radiation doses.

Heterochromatin variants in 109 ovarian cancer patients and 192 healthy subjects.

Aberrations of the C-band region of chromosome no. 1 (1qh) were studied in 109 patients with ovarian cancer and 192 healthy subjects. The groups were compared for heterochromatin size variations, intrapair size asymmetry, and inversion. No significant correlation was found between the size of 1qh and ovarian cancer. Heterochromatin size asymmetry was estimated visually and determined by objective measurement of 1qh length or area; the methods show strong correlation. The measurements were normalised by comparison with the length or area of 16p or the entire chromosome no. 1. However, since good reliability was found by simply relating the 1qh size difference to the mean 1qh size, this was considered an appropriate and simpler method of normalisation. Asymmetry indices of length and area measurements correlated well, implying that the simpler method of length measurements can be readily used. 1qh asymmetry, measured objectively or estimated visually, was significantly increased in the cancer patient group. The incidence of C-band inversion was significantly increased in the patient group. Moreover, inversion increased significantly with increasing 1qh asymmetry.

Radiographic videodensitometry for quantitative monitoring of experimental bone healing.

A method for non-invasive assessment of experimental bone healing in animals is described. Optimized radiographs were analysed by digital processing using a computer-based image analysis system. Values of the total mass were expressed as the equivalent mass of a simultaneously exposed aluminium roentgen-density reference. In order to assess the potential of the method, measurements were initially performed on phantoms and bone specimens. The systematic error was negligible. An excellent correlation (r = 0.999) was found between the densitometric weight (mu) and the corresponding dry weight (m) of the analysed bone samples and a calibration factor mu/m = 1.38 was established. The total random error was low, the coefficient of variation (CV) amounting to less than 5% or, if duplicate analyses were performed, less than 3%. The accuracy was not impaired when radiography was carried out with addition of water to mimic overlying soft tissue in the model. The method was applied to the assessment of callus mass longitudinally in vivo in the healing of a bone defect in the rabbit radius, yielding reproducible values (CV less than 5%) and a quantitative analysis of the healing sequence.

Bone repair in implant models: a review with emphasis on the harvest chamber for bone regeneration studies.

The vital microscopic chamber is an experimental implant of commercially pure titanium that admits in vivo and in situ observations of bone vascularity and bone remodeling. The bone growth chamber and the bone harvest chamber, in particular, are useful tools for quantifying bone regeneration under the most variable experimental conditions.

Bone mass determination from microradiographs by computer-assisted videodensitometry. II. Aluminium as a reference substance.

Aluminium was evaluated as a reference substance in the assessment of rabbit cortical bone by microradiography followed by videodensitometry. Ten dense, cortical-bone specimens from the same tibia diaphysis were microradiographed using prefiltered 27 kV roentgen radiation together with aluminium step wedges and bone simulating phantoms for calibration. Optimally exposed and processed plates were analysed by previously described computer-assisted videodensitometry. For comparison, the specimens were analysed by physico-chemical methods. A strict proportionality was found between the 'aluminium equivalent mass' and the ash weight of the specimens. The total random error was low with a coefficient of variation within 1.5 per cent. It was concluded that aluminium is an appropriate reference material in the determination of cortical bone, which it resembles in effective atomic number and thus x-ray attenuation characteristics. The 'aluminium equivalent mass' is suitably established as the standard of expressing the results of bone assessment by microradiography.

Bone mass determination from microradiographs by computer-assisted videodensitometry. I. Methodology.

The mass of hard-tissue specimens is assessed by optimised microradiography followed by computer-assisted videodensitometry. Radiographs are produced with 27 kV roentgen radiation, filtered through 0.5 to 1 mm of aluminium, on high-resolution glass plates. Aluminium step wedges are used for density calibration, the result being expressed as 'aluminium equivalent mass'. The plates are subjected to digital image analysis by an operator in interaction with a computer-based image processor, a television camera being used for image input. The program stored in the computer provides calibration of geometry and--via the step wedge images--of densitometry, background adjustment, etc. Measurement takes place by integration over the specimen-image area. No assumptions being needed concerning a specific attenuation model, the errors stemming from the common presumption of exponential attenuation are eliminated. Density profiles or maps of mass distribution are readily obtained from the computer. From measurements of aluminium phantom samples, the total random error (coefficient of variation) was determined at 1.8 per cent, the microradiographic and videodensitometric procedures contributing 1.6 per cent and 0.9 per cent, respectively, whereas the systematic error was negligible. Since specimens need not be sectioned, this method does not interfere with subsequent histologic preparation.

Detectability of artificial marginal bone lesions as a function of lesion depth. A comparison between subtraction radiography and conventional radiographic technique.

Subtraction of serially obtained standardized radiographs of the marginal periodontal bone offers possibilities for an increased detectability of small bony changes compared to conventional radiography. In this study, the depth of artificially induced bone lesions in the alveolar crest was assessed by means of 125I absorptiometry. The results served as reference values when a series of radiographs containing lesions of various depths was interpreted by 10 examiners. Both conventional radiographs and subtraction images made from the conventional radiographs after digitization were interpreted. The ROC-curve technique was used to evaluate the two techniques. A close to perfect accuracy was found at a lesion depth corresponding to 0.49 mm of compact bone using the subtraction technique. A similar degree of accuracy was not reached for the conventional technique until the lesions were approximately 3 times deeper.

Metacarpophalangeal joint replacement with osseointegrated endoprostheses.

A new type of endoprosthesis for reconstruction of the metacarpophalangeal (MCP) joint has been tested. The novel arthroplasty consists of a joint mechanism with two screw-shaped fixtures for bone anchorage. These fixtures, of commercially pure titanium, are gently screwed into the anchoring bone on each side of the diseased joint, the aim being to achieve osseointegration, i.e. a direct contact between implant and bone without interposed soft tissue layers. The hand was immobilized in a dorsal splint for 8-10 days post-operatively after which a carefully controlled mobilization program was initiated. In principle, the titanium fixtures, the surgical technique and the primary immobilization represent an approach similar to that previously used in various reconstruction procedures of the jaw. This paper describes 5 case histories of reconstructions required because of osteoarthrosis in a single MCP joint. Prior to the operation, all patients suffered from severe problems resulting from their arthrotic joints and they had not been able to work for several months. After surgery they were evaluated by a clinical assessment program and X-rays were taken at various times of follow-up. As well as visual inspection all radiograms were subjected to densitometry by means of a computer-based image-analysis system in order to provide information on the development of bone density in the bone-to implant interface region. From a functional point of view the treatment with osseointegrated prostheses must be regarded as being successful. All patients were able to go back to their original work and their hands had a satisfactory range of movement and grip strength with no signs of impaired function on longer follow-up time. Clinical problems were one re-operation, one case of implant fracture and one case requiring exchange of the joint mechanism. The computer-assisted evaluation of the radiograms revealed the presence of calcified tissue in many sections where the naked eye was not capable of differentiating any bone. In conclusion, it seems possible to establish osseointegration of MCP-endoprostheses in the arthrotic human joint in complicated cases which were regarded as contraindicated for any other joint arthroplasty.

On the application of photogrammetry to the fitting of jawbone-anchored bridges.

Misfit between a jawbone-anchored bridge and the abutments in the patient's jaw may result in, for example, fixture fracture. To achieve improved alignment, the bridge base could be prepared in a numerically-controlled tooling machine using measured abutment coordinates as primary data. For each abutment, the measured values must comprise the coordinates of a reference surface as well as the spatial orientation of the fixture/abutment longitudinal axis. Stereophotogrammetry was assumed to be the measuring method of choice. To assess its potentials, a lower-jaw model with accurately positioned signals was stereophotographed and the films were measured in a stereocomparator. Model-space coordinates, computed from the image coordinates, were compared to the known signal coordinates. The root-mean-square error in position was determined to 0.03-0.08 mm, the maximum individual error amounting to 0.12 mm, whereas the r. m. s. error in axis direction was found to be 0.5-1.5 degrees with a maximum individual error of 1.8 degrees. These errors are of the same order as can be achieved by careful impression techniques. The method could be useful, but because of its complexity, stereophotogrammetry is not recommended as a standard procedure.

The initiation of post-capillary margination of leukocytes: studies in vitro on the influence of erythrocyte concentration and flow velocity.

Leukocyte margination is an important rheological phenomenon, being a prerequisite for leukocyte adhesion and invasion of the tissues in inflammation. In the present study the influence on leukocyte radial distribution of erythrocyte concentration and flow velocity was studied with fluorescence microscopy in a glass capillary model. This consisted of a narrow (10 microns) short stenosis expanding into a 50 microns straight tube. The blood cells were brought to the centre of the stream by the stenosis whereas the radial position of the leukocytes was determined in the straight post-stenotic segment of the glass tube. The analyses showed that a 0 hematocrit 86% (flow velocity 0.2 mm/s) to 99% (flow velocity 1.2 mm/s) of the leukocytes stayed in the centre of the tube after leaving the stenosis. No leukocytes were observed at the capillary wall. At 10% hematocrit and low flow velocity, 0.1 and 0.3 mm/s, 36 and 34%, respectively, of the leukocytes were displaced to a marginal position. At 1.0 mm/s only 10% of the leukocytes were displaced from the central stream. At 40% hematocrit, 45, 47 and 40% of the leukocytes were found in a wall near position at 0.1, 0.4 and 0.7 mm/s flow velocity, respectively. Although the results obtained in the present study are valid only for the special geometry of the in vitro model they clearly indicate the importance of leukocyte-erythrocyte interactions for the initiation of leukocyte margination in post-capillary vessels.

Storage and display of information in roentgen films.

Roentgen images of high density, without actually being overexposed, tend to leave small details of low contrast unrecorded. Still, these details may be reproduced by the same film if the density is lower, even if the gamma value is kept constant. The present report is concerned with how information is stored in the film and the information stored is displayed to the inspecting eye. It appears that films of high density contain information which is invisible, so that the disappearance of image details to a certain extent reflects a defect of display.

Significance of quantum fluctuations in roentgen imaging.

Quantum fluctuations in the roentgen radiation relief are analysed mathematically. The intrinsic signal-to-noise ratio of the radiation relief for a given object contrast is proportional to the square root of the number of photons contributing to the image of a characteristic detail in the object. In the presence of secondary radiation the signal-to-noise ratio is impaired, since the fluctuations of secondary radiation increase the noise of the radiation relief. By efficient secondary screening, the quality of the relief can be partially recovered. With a dynamically limited recording device, i.e. a film-screen combination, increased detection speed in conjunction with improved secondary screening will either result in unchanged image quality with the gain of an object-dose reduction or provide improved imaging at an unchanged dose value. As regards the relation between contrast resolution and spatial resolution, the dose required to barely demonstrate an object detail of given geometry and composition is found to vary inversely with the fourth power of the linear size of the detail. It is also concluded that recording and secondary-screening devices should always be considered together as far as recording quality is concerned.

Receptor saturation in roentgen films.

Roentgen-film recording of small object details of low attenuation differences (e.g. pulmonary vessels) is regularly seen to be impaired when the film is exposed to yield high values of optical density (D). The high-density failure is due to receptor saturation, which implies that at high exposure values most silver halide grains of the film are made developable, leaving few grains available to receive additional informative photons. The receptor saturation is analysed by means of a mathematical model of a non-screen film yielding Dmax = 2.0. Optimum recording, defined by maximum signal-to-noise ratio in the image, is found at D = 0.64, corresponding to, on an average, 1.6 photons absorbed per grain. On the other hand, maximum contrast occurs at D approximately 1.4, where, on the average, 3.6 photons are absorbed per grain. The detective quantum efficiency of the film, i.e. the fraction of the photons actually contributing to the information content of the image, drops from 41 per cent at maximum signal-to-noise ratio to a mere 10 per cent at maximum contrast. Receptor saturation does not manifest itself as 'mottle' in the image--it is therefore easily overlooked. The importance of adequate removal of secondary radiation is emphasised by these results.

Relevance of radiographic resolution capacity.

Resolution capacity is traditionally evaluated by radiography of metal objects (lead bar grids or fine slits). These objects yield high image contrast. Resolution, then, is limited by the sideways spread of information as expressed by the MTF. However, biologic objects of fine dimensions give rise to much less image contrast than the test objects of metal. Since the amplitude of the signals thus becomes reduced the signal/noise ratio in fact limits resolution capacity much more effectively than does the sideways spread of information. Thus, the MTF expresses a property of the radiographic system which appears only rarely to affect the information capacity of clinical radiographic images.