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Objectives-To investigate articular cartilage collagen network, thickness of birefringent cartilage zones, and glycosaminoglycan concentration in macroscopically normal looking knee joint cartilage of young beagles subjected to experimental slowly progressive osteoarthritis (OA). Methods-OA was induced by a tibial 30°v algus osteotomy in 15 female beagles at the age of 3 months. Fifteen sisters were controls. Cartilage specimens were collected seven (Group 1) and 18 months (Group 2) postoperatively. Collagen induced optical path diVerence and cartilage zone thickness measurements were determined from histological sections of articular cartilage with smooth and intact surface by computer assisted quantitative polarised light microscopy. Volume density of cartilage collagen fibrils was determined by image analysis from transmission electron micrographs and content of glycosaminoglycans by quantitative digital densitometry from histological sections. Results-In the superficial zone of the lateral tibial and femoral cartilage, the collagen induced optical path diVerence (birefringence) decreased by 19 to 71% (p < 0.05) seven months postoperatively. This suggests that severe superficial collagen fibril network deterioration took place, as 18 months postoperatively, macroscopic and microscopic OA was present in many cartilage areas. Thickness of the uncalcified cartilage increased while the superficial zone became thinner in the same sites. In operated dogs, glycosaminoglycan content first increased (Group 1) in the lateral tibial condyle and then decreased (Group 2) (p < 0.05). Conclusion-In this OA model, derangement of the superficial zone collagen network was the probable reason for birefringence reduction. This change occurred well before macroscopic OA.

Results obtained by the indirect zonal isotropic uniform random (IUR) estimation were compared with those obtained by the direct point and interception counting methods on vertical (VS) or IUR sections in a stereological study of bovine articular cartilage collagen fibrils at the ultrastructural level. Besides comparisons between the direct and indirect estimations (direct IUR vs indirect IUR estimations) and between different sampling methods (VS vs IUR sampling), simultaneous comparison of the 2 issues took place (direct VS vs indirect IUR estimation). Using the direct VS method, articular cartilage superficial zone collagen volume fraction (V v 41 %) was 67 % and fibril surface density (S v 0n030 nm#\nm$) 15 % higher (P 0n05) than values obtained by the indirect IUR method (V v 25 % and S v 0n026 nm#\nm$). The same was observed when the direct IUR method was used : collagen volume fraction (V v 40 %) was 63 % and fibril surface density (S v 0n032 nm#\nm$) 21 % higher (P 0n05) than those obtained by the indirect IUR technique. Similarly, in the deep zone of articular cartilage direct VS and direct IUR methods gave 50 and 55 % higher (P 0n05) collagen fibril volume fractions (V v 43 and 44 % vs 29 %) and the direct IUR method 25 % higher (P 0n05) fibril surface density values (S v 0n025 vs 0n020 nm#\nm$) than the indirect IUR estimation. On theoretical grounds, scrutiny calculations, as well as earlier reports, it is concluded that the direct VS and direct IUR methods systematically overestimated the V v and S v of collagen fibrils. This bias was due to the overprojection which derives from the high section thickness in relation to collagen fibril diameter. On the other hand, factors that during estimation tend to underestimate V v and S v , such as profile overlapping and truncation (' fuzzy ' profiles), seemed to cause less bias. As length density (L v ) and collagen fibril diameter are minimally biased by the high relative section thickness, the indirect IUR method, based on utilisation of these estimates, is here regarded as representing a ' gold standard '. The sensitivity of these 3 methods was also tested with cartilage from an in vitro loading experiment which caused tissue compression. In the superficial zone of articular cartilage V v and S v of collagen fibrils increased (P 0n05). This difference in the stereological estimates was only detected by the indirect IUR estimation but not by the direct VS or direct IUR methods. This indicated that the indirect IUR estimation was more sensitive than the direct VS or direct IUR estimations. On the basis of these observations, the indirect zonal IUR estimation can be regarded as the technique of choice in the electron microscopic stereology of cartilage collagen.

Young Osborne-Mendel rats were given different diets for 6 weeks. Effects of soft and rough food as well as acidic sport drink on the lingual surfaces of first mandibular molars were studied. In addition, the effect of fluoride on erosion was examined. A Jeol JSM-35 scanning electron microscope was used to visualize tooth surface ultrastructure. Intact surfaces were found in the rats given soft food and distilled water. Sport drink (pH 3.2) caused severe erosion with total loss of supragingival enamel and exposure of dentin. Attrition effects were seen on the cuspal parts of the surface when rough food was given. Tooth tissue loss was greatest in the rats given rough food and sport drink; signs of both erosion and attrition could be seen. When fluoride was added to the sport drink erosion lesions were less severe and if dentin was exposed, the dentinal tubules were partly occluded. These SEM observations support earlier studies which have suggested that erosion may alter tooth surface so that it is more susceptible to attrition; in those lesions, however, clinical diagnosis of the initial causes may be difficult.

Objectives Articular cartilage proteo-