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Biomedical subjects

A Viidik

Publications and source records attributed to A Viidik.

At least 55 records · Page 3Linked to original sources
PubMed1986

A biomechanical study of the human periodontal ligament.

The mechanical properties of the normal human periodontal ligament (PDL) were investigated at eight different root levels. One millimetre transverse sections of teeth, PDL and alveolar bone of mandibular premolars were examined in a materials testing machine. During testing bone was supported by metal rings and teeth by metal cylinders of individually adjusted sizes. Having corrected for differences of size and width of the PDL the influence of root level was estimated using a multivariate analysis of variance. The shear strength was almost constant at the upper part of the root, diminishing in apical direction. The shear extensibility and the relative failure energy in shear were higher at the middle of the root, diminishing coronally and apically. Only the elastic stiffness did not vary significantly along the root. These results demonstrate that in order to compare the mechanical properties of PDL care should be taken to compare areas at the same root level.

Adult↗
PubMed1985

Correlation between the compressive strength of iliac and vertebral trabecular bone in normal individuals.

Intrabone and interbone variations and age-related changes in vertical and horizontal trabecular bone compressive strength (CS) were evaluated for loadbearing (vertebral) and nonloadbearing (iliac crest) trabecular bone from 30 normal individuals, 17 females and 13 males, aged 15-87 years. All had died suddenly. The vertebral bodies of Th6, L1, and L3 and the right and left iliac crests were frozen at -20 degrees C immediately after removal. Cylindrical bone samples in the vertical and horizontal direction were taken from the frozen bone, and load-deformation curves were recorded by a materials testing machine. For all vertebral bodies, the vertical CS was much larger than the horizontal CS (P less than 0.01), whereas no significant difference was found for the iliac crests. The anisotropy expressed as an index of vertical to horizontal CS, therefore, was higher in the vertebrae than in the iliac crest. The anisotropy index (Al) increased with age in the vertebrae but not in the iliac crest (r = 0.56, P less than 0.01). Age related, almost identical decreases in CS were observed in the vertebrae (vertical direction) (r = 0.81, P less than 0.01) and in the iliac crest (horizontal direction) (r = -0.69, P less than 0.01). In spite of the pronounced differences in the architecture between the vertebral body and iliac trabecular bone, the vertical vertebral CS could be predicted from the horizontal iliac crest CS (r = 0.88, P less than 0.01, SEE = 0.9 MPa). The vertical iliac crest CS showed a less significant correlation to the average vertical vertebral CS (r = 0.53, P less than 0.05, SEE = 1.25 MPa).

Adolescent↗
PubMed1982

On fundamental and phenomenological models, structure and mechanical properties of collagen, elastin and glycosaminoglycan complexes.

This paper reviews the structure (from molecular to macroscopic level) of collagen, elastin and glycosaminoglycans, with special reference to their functional properties and to how their behavior can be elucidated from in vitro manipulations of the tissues by biochemical means. Modes to analyse the mechanical behavior are briefly discussed and exemplified by data from reconstituted collagenous "tissue". It is concluded that the basic equation for the "non-linear elasticity" component in Fung's law (and for the reconstituted "tissue" a modification of it) is a powerful tool for analysis of the physiological range of the stress-strain curve. Further, enzymatic "dissection" of one tissue element at a time provides a valuable method for the analysis of tissue element interactions. This approach is illustrated with data from aortic tissue. It is shown that the mechanical properties of the aorta depend on the interaction between elasticity and collagenous elements and that the strength of the tissue is not derived from its collagen fibers per se.

Animals↗
PubMed1980

The influence of adrenalectomy on the biomechanical properties of collagenous structures of rats in the post-partum phase.

Pregnancy influences the functional properties of both genital and extragenital connective tissues. The sex hormones induce a major part of these changes but also corticosteroids may play a role, as their concentration is elevated during pregnancy and early post-partum. The biomechanical properties of the pubic symphysis, muscle tendon and skin of intact and adrenalectomized rats during the first ten days of the post-partum phase were investigated. For the pubic symphysis and the muscle tendon of the intact animals there was a decrease of the stiffness in the early post-partum phase followed by a restoration. For the adrenalectomized animals there was no such initial decrease, which indicates that relaxation during pregnancy has been less pronounced. However, the strength of muscle tendons from the adrenalectomized animals was markedly decreased during the post-partum phase. The stiffness of the skin from the intact animals was increased in the early post-partum period. The increase was also found in adrenalectomized animals, but here the strength and stiffness were not only restored to the intact level but became further reduced during the post-partum period. It seems therefore that the adrenal glands not only participate in the development of adaptive changes during pregnancy, but also play a role in the stabilization of extragenital connective tissues in the post-partum phase.

Adrenal Glands↗
PubMed1979

Connective tissues--possible implications of the temporal changes for the aging process.

Two of the "old" mono-cause theories of aging have temporal changes in the connective tissues, especially those in collagen, as main events. The crosslinking of collagen is stable under physiological conditions shortly after the formation of fibrils and the additional physico-chemical stability attained later on probably does not influence the physiological functions of the tissues significantly. The temporal changes in collagen seen as increased thermal stability, decreased solubility and increased mechanical stiffness are discussed in relation to the underlying structural changes. It is concluded that the increased stability of the collagen (mainly type I) in the locomotive system and skin are not "true" aging phenomena. It is possible that the changes in the connective tissues of the lungs and kidneys contribute to the decrease of function with age. The "normal" increase of stiffness of type I collagen may contibute to the increased compliance and residual volume of the aging lung. Our present knowledge of the structure and function of collagens and ground substances in various basement membranes does not permit an evaluation of the role of connective tissues in the age changes in the alveolo--capillary complex, the glomeruli and the exchange between tissues and capillaries in general.

Adrenal Cortex Hormones↗
PubMed1979

The influence of cortisol on wound healing of the skin and distant connective tissue response.

The effect of moderate dosage cortisol treatment on healing wounds and on the response in skin distant to the wounds was investigated. The stress-strain characteristics of a skin wound and intact skin specimens were examined. Also, skin thickness, water content and collagen content were measured. Cortisol treatment resulted in reduced extensibility and increased stiffness for ten day wounds, but unchanged failure energies; for 20 day wounds, failure energies were reduced, indicating reduced ability to withstand rupturing forces. Thus, the mechanical properties of healing wounds under moderate dosage, long term corticosteroid treatment were found to be slightly impaired. A systemic effect of wounding at day 10 resulted in decreased stiffness and increased collagen content of the skin distant to the wound.

Animals↗