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Bone loss may affect the structure of cancellous bone. But its effect on trabeculae with different characteristics, like rods and plates, is not accurately known. This study analyzes the effect of bone loss on individual rod-like and plate-like trabeculae. 94 specimens were obtained from mandibular condyles from both dentate and edentate humans and scanned with a micro-CT scanner. The bone volume fraction (BV/TV) of these specimens ranged from 7% to 30%. Next, the rod-like and plate-like trabeculae were identified with an especially developed algorithm. Plate volume fraction (PV/TV), rod volume fraction (RV/TV), plate thickness, rod thickness, number of plates, and number of rods were determined. In individual specimens, the thickness of the rods ranged from 40 mum to 180 mum, while the thickness of the plates ranged from 40 mum to 300 mum. In every specimen, the thickness of the plates was larger than the thickness of the rods. Statistical analysis revealed that PV/TV was proportional (r = 0.98, P < 0.001) and RV/TV inversely proportional (r = -0.45, P < 0.001) to BV/TV. Also the thickness of the plates correlated with BV/TV (r = 0.62, P < 0.001), while the thickness of the rods (mean = 90 mum, SD = 7 mum) remained constant (r = -0.09, P = 0.378). A four-fold reduction of the bone volume fraction was accompanied by a three-fold reduction of the number of plates and a 40% reduction of their thickness, but also by a three-fold increase in the number of rods and RV/TV. It was concluded that the effect of bone loss on plate-like trabeculae was opposite to its effect on rod-like trabeculae. Remarkably, the thickness of the rods (90 mum) was independent of the bone volume fraction. This suggests that there is a minimal thickness for trabeculae.

Objective: To investigate the influence of decreased mechanical loading on the density and mechanical properties of the cancellous bone of the human mandibular condyle., Design: Destructive compressive mechanical tests were performed on cancellous bone specimens.Background. Reduced masticatory function in edentate people leads to a reduction of forces acting on the mandible. As bone reacts to its mechanical environment a change in its material properties can be expected., Methods: Cylindrical bone specimens were obtained from dentate and edentate embalmed cadavers. Mechanical parameters were determined in the axial and in the transverse directions. Subsequently, density parameters were determined according to a method based on Archimedes' principle., Results: The apparent density and volume fraction of the bone were about 18% lower in the edentate group; no age-related effect on density was found. The decrease of bone in the edentate group was associated with a lower stiffness and strength (about 22% and 28%, respectively). The ultimate strain, however, did not differ between the two groups. Both groups had similar mechanical anisotropy; in axial loading the bone was stiffer and stronger than in transverse loading., Conclusions: Reduced mechanical load had affected the density and herewith the mechanical properties of condylar cancellous bone, but not its anisotropy., Relevance: The change in material properties of the cancellous bone after loss of teeth indicate that the mandibular condyle is sensitive for changes in its mechanical environment. Therefore, changes in mechanical loading of the condyle have to be accounted for in surgical procedures of the mandible.

The objective of the present study was (1) to test the hypothesis that the elastic and failure properties of the cancellous bone of the mandibular condyle depend on the loading direction, and (2) to relate these properties to bone density parameters. Uniaxial compression tests were performed on cylindrical specimens (n=47) obtained from the condyles of 24 embalmed cadavers. Two loading directions were examined, i.e., a direction coinciding with the predominant orientation of the plate-like trabeculae (axial loading) and a direction perpendicular to the plate-like trabeculae (transverse loading). Archimedes' principle was applied to determine bone density parameters. The cancellous bone was in axial loading 3.4 times stiffer and 2.8 times stronger upon failure than in transverse loading. High coefficients of correlation were found among the various mechanical properties and between them and the apparent density and volume fraction. The anisotropic mechanical properties can possibly be considered as a mechanical adaptation to the loading of the condyle in vivo.

The renal vascular effects of aporphines and related compounds were studied on the isolated perfused rat kidney in the presence of 10(-5) M phenoxybenzamine and 10(-5) M sotalol and after contraction of the vascular bed with prostaglandin F2 alpha (10(-7) -3 X 10(-6) M). Under these conditions, (R)-(-)-apomorphine showed renal dopaminomimetic activity, i.e. renal vasodilation competitively inhibited by (+)-butaclamol (10(-8) M) but not by (-)-butaclamol (3 X 10(-8) M). It had an apparent affinity 25 times higher but a markedly lower intrinsic activity than dopamine. N-n-Propyl and trihydroxylated aporphines were less potent and the mono-10-hydroxylated aporphine was completely inactive. (S)-(+)-Bulbocapnine also showed weak dopaminomimetic activity but tetrahydropapaveroline was devoid of such an effect. (-)-N-(2-Chloroethyl)-norapomorphine (10(-5) M) irreversibly antagonised dopamine-induced renal vasodilation. At concentrations above 3 X 10(-6) M, most aporphines and tetrahydropapaveroline induced additional non-dopamine receptor related renal vasodilation.

The renal vascular effects of dopaminomimetics were studied in the isolated perfused rat kidney after pretreatment with 10(-5) M phenoxybenzamine and 10(-5) M sotalol and after contraction of the vascular bed with prostaglandin F2 alpha (10(-7) to 3 x 10(-6) M). Under these conditions, our criterion for vascular dopaminomimetic activity was renal vasodilation, competitively inhibited by d-butaclamol (10(-8) M) but not by 1-butaclamol (3 x 10(-8) M). Dopamine is active at micromolar concentrations (ED50 = 2.53 +/- 0.34 x 10(-6) M). The N-alkylated analogues of dopamine preserve this activity if the alkyl group is a methyl group (epinine) or two n-propyl groups (di-n-propyl-dopamine). The catechol nucleus appears essential for renal vascular dopaminomimetic activity (SK&F 38393, active; p-tyramine, di-n-propyl-m-tyramine and RU 24926, inactive). Bromocriptine reproduces renal dopaminergic vasodilation with an ED50 of 1.3 +/- 0.14 x 10(-6) M. The study of structure-activity relationships of dopaminomimetics relates the vascular dopamine receptor, associated with renal vasodilation, to the dopamine receptor, associated with stimulation of dopamine-sensitive adenylate cyclase.