Effect of resin coating on highly viscous glass ionomer cements: A dynamic analysis.

OBJECTIVES: This study determined the effects of self-adhesive resin coatings on viscoelastic properties of highly viscous glass ionomer cements (HVGICs) using dynamic mechanical analysis. MATERIALS AND METHODS: The HVGICs evaluated were Zirconomer [ZR] (Shofu), Equia Forte [EQ] (GC) and Riva [RV] (SDI). Sixty specimens (12mm x 2mm x 2mm) of each material were fabricated using customized Teflon molds. After initial set, the specimens were removed from their molds, finished, measured and randomly divided into 3 groups of 20. Half the specimens in each group were left uncoated while the remaining half was covered with the respective manufacturers' resin coating. The specimens were subsequently conditioned in distilled water, artificial saliva or citric acid at 37°C for 7 days. The uncoated and coated specimens (n=10) were then subjected to dynamic mechanical testing in flexure mode at 37°C with a frequency of 0.1 to 10Hz. Storage modulus, loss modulus and loss tangent data were subjected to normality testing and statistical analysis using one-way ANOVA/Scheffe's post-hoc test and Ttest at significance level p<0.05. RESULTS: Mean storage modulus ranged from 1.39 ± 0.36 to 10.80 ± 0.86 GPa while mean loss modulus varied from 0.13 ± 0.03 to 0.70 ± 0.14 GPa after conditioning in the different mediums. Values for loss tangent ranged from 39.4 ± 7.75 to 213.2 ± 20.11 (x10 -3 ). Significant differences in visco-elastic properties were observed between mediums and materials. When conditioned in distilled water and artificial saliva,storage modulus was significantly improved when ZR, EQ and RV were uncoated. Significantly higher values were, however, observed with resin coating when the materials were exposed to citric acid. CONCLUSION: The visco-elastic properties of HVGICs were influenced by both resin coating and chemical environment.

The micromorphology of the nauplius eye of the estuarine calanoid copepod, Sulcanus conflictus Nicholls (Crustacea).

The nauplius eye consists of one median and two lateral ocelli, each within a pigment cup. The three pigment cups are made up from two multi-nucleate pigment cells: each cell forming one lateral cup and half of the median cup. The three cups are lined on the insides by tapetal cells which contain layers of reflectile crystals. Each of the ocelli contains six sensory cells which protrude from the rims of the pigment cups and the protruding parts are sheathed by the conjunctiva cells. The whole eye is enveloped by a thin membrane which also sheaths the proximal parts of the five nerve bundles that leave the eye. All the sensory cells of the lateral ocelli are similar and have rhabdomeric microvilli on the terminal end, and contain phaosomes and a multitude of other organelles and cytoplasmic inclusions. The complex median ocellus contains a superior group of three retinular cells, linked by interdigitating processes, and an inferior group consisting of a large central cell enclosed in two cup-shaped peripheral retinular cells. A two-tiered rhabdome arrangement exists, with a rather complex inferior rhabdome set made up of a central rhabdomere and two hemi-annulate rhabdomeres. The cytoplasm of the retinular cells of the median ocellus lack phaosomes but instead contain double-walled tubular elements, possibly formed by the inpushings of microvilli into adjacent cells. The possible functional significance of the unique arrangement seen in the median ocellus is discussed. The retinular cells are of the inverse type. There are no efferent nerve fibres from the brain nor any nervous connection between the lateral and the median ocelli.