Abnormal compartmentalization of cartilage matrix components in mice lacking collagen X: implications for function.

There are conflicting views on whether collagen X is a purely structural molecule, or regulates bone mineralization during endochondral ossification. Mutations in the human collagen alpha1 (X) gene (COL10A1) in Schmid metaphyseal chondrodysplasia (SMCD) suggest a supportive role. But mouse collagen alpha1 (X) gene (Col10a1) null mutants were previously reported to show no obvious phenotypic change. We have generated collagen X deficient mice, which shows that deficiency does have phenotypic consequences which partly resemble SMCD, such as abnormal trabecular bone architecture. In particular, the mutant mice develop coxa vara, a phenotypic change common in human SMCD. Other consequences of the mutation are reduction in thickness of growth plate resting zone and articular cartilage, altered bone content, and atypical distribution of matrix components within growth plate cartilage. We propose that collagen X plays a role in the normal distribution of matrix vesicles and proteoglycans within the growth plate matrix. Collagen X deficiency impacts on the supporting properties of the growth plate and the mineralization process, resulting in abnormal trabecular bone. This hypothesis would accommodate the previously conflicting views of the function of collagen X and of the molecular pathogenesis of SMCD.

Acrylic resins reinforced with woven highly drawn linear polyethylene fibres. 3. Mechanical properties and further aspects of denture construction.

Previous work has established the feasibility of producing acrylic denture bases reinforced with layers of highly drawn linear polyethylene fibres in a woven form. This paper reports on the mechanical properties of the system, including the effect of water conditioning. It is confirmed that substantial improvements in impact strength can be obtained by the incorporation of the polyethylene fibres in woven form. The fibre/resin integration within the dentures has also been studied by optical microscopy. It was found that delamination may occur during some processing stages and steps are suggested to avoid this problem.

The effects of etching, micro-abrasion, and bleaching on surface enamel.

Conservative techniques for improving the appearance of discolored teeth have become popular in the past decade. These include: in-office bleaching with 30% hydrogen peroxide, which is applied on etched enamel with a gauze pad and then exposed to a bleaching light; home bleaching with a mild form of peroxide, such as 10% carbamide peroxide, which is applied on the tooth surface with custom-made mouthguards; and enamel micro-abrasion with 18% hydrochloric acid, which is applied in a pumice slurry. In this study, the in-office bleaching and enamel micro-abrasion techniques were performed on extracted teeth for investigation of their microscopic effects on the surface enamel. Specimens treated only with 37% phosphoric acid showed an enamel loss of 5.7 +/- 1.8 microns. The specimens treated with 37% phosphoric acid followed by 30% hydrogen peroxide showed enamel loss of 5.3 +/- 1.6 microns; this loss was probably not caused by the hydrogen peroxide, but rather by the etching with 37% phosphoric acid which preceded the hydrogen peroxide application. A direct application of 18% hydrochloric acid for 100 s resulted in a loss of 100 +/- 47 microns. The extent of enamel loss was much greater when the 18% hydrochloric acid was applied in a pumice slurry for the same period of time (360 +/- 130 microns), and the effect was time-dependent. Thus, the pumice and rotary prophy cup used in conjunction with the 18% hydrochloric acid contributed markedly to the loss of surface enamel, enhancing the non-selective stain-removing action of the hydrochloric acid. Therefore, the hydrochloric acid-pumice technique must be used clinically with caution.

Estimation of Ammonium Ion Distribution between Cytoplasm and Vacuole Using Nuclear Magnetic Resonance Spectroscopy.

Evidence is presented that intracellular ammonium is trapped in vacuoles of maize (Zea mays L.) root tips because of rapid movement of ammonia between cytoplasm and vacuoles. The concentration of cytoplasmic ammonium is estimated to be <15 mum at extracellular ammonium concentrations up to 1 mm. The implications for pathways of ammonium assimilation are discussed.

Scanning electron microscopy of odontogenic cyst epithelium.

The epithelial lining of 8 odontogenic keratocysts (OKC), 9 radicular (RC) and 3 dentigerous cysts (DC) were examined in SEM in order to study the ultrastructural surface topography of the lumenal surface cells. The orthokeratinized OKC showed a reticular network of intercommunicating microridges surrounding micropits giving a honeycombed appearance to the entire surface. The deep surface of these cells was covered by a complementary array of short stubby microvilli. This pattern was identical to that described for oral epithelium in areas of masticatory mucosa. The parakeratinized OKC showed a complex pattern of microplications (MP) on both upper and deep cell surfaces. The non-keratinized linings of RC and DC revealed a similar MP pattern but of a less complex nature. The MP pattern of cells from para- and non-keratinized cysts was identical to that described for oral epithelial cells from lining mucosa. The surface ultrastructure of ciliated, mucus and brush cells occurring in RC was found to be indistinguishable from that described in the mammalian respiratory tract. The MP pattern forms part of the cellular interdigitation mechanisms in stratified squamous epithelium. Differences in the ultrastructural configuration are related to the type of epithelium in terms of keratinization rather than to protective functions.

Prostaglandin synthesis and its inhibition by cyclic AMP and forskolin in postpartum follicles of the guppy (Poecilia reticulata).

Prostaglandin synthesis in vitro and its inhibition by dibutyryl cyclic AMP and forskolin were examined in postpartum follicles of the guppy. The follicles were cultured for up to 72h under chemically-defined conditions, and the synthesis of prostaglandins was determined by radioimmunoassay. The results show unequivocally that the ovarian follicles devoid of embryos can synthesize PGE and PGF from both endogenous precursors as well as added arachidonic acid. That this could be inhibited by indomethacin is indicative of active synthesis rather than release of preformed prostaglandins. Dibutyryl cAMP and forskolin also inhibited prostaglandin synthesis in a dose-dependent manner, as did 3-isobutyl-l-methylxanthine. A similar effect was also evident in vitellogenic oocytes surrounded by follicle layers at the yolk-globule stage of development. While the physiological significance of this action of the cyclic nucleotide remains uncertain at this stage, it is hypothesized that it could explain the non-occurrence of ovulation in this viviparous fish soon after final oocyte maturation.