A laboratory evaluation of the construction of resin-bonded cast restorations

OBJECTIVE: To compare the effect of two construction techniques and two pattern materials on the fit of resin-bonded cast restorations. DESIGN: In-vitro study carried out by one operator. SETTING: Postgraduate university hospital. SUBJECTS AND METHODS: 65 nickel-chrome castings were constructed using refractory die and lift-off techniques with wax and acrylic resin pattern material. They were cemented onto master silver dies, embedded in self-curing acrylic resin and sectioned along their long axes. Interfacial distance between the master silver die and casting was measured. RESULTS: A significant different between the range of figures in each group (Mann-Whitney Test, P < 0.01) was found. Construction techniques can be ranked in order of fit of castings: 1. Refractory die, wax patterns: 42.6 microns (SD 12.03). 2. Refractory die, acrylic resin patterns: 53.7 microns (SD.16.06).3. Conventional technique, acrylic resin patterns: 85.5 microns (SD 31.62). 4. Lift-off technique, wax patterns: 139 microns (SD 53.15).5. Lift-off technique, acrylic patterns: 172.8 microns (SD 74.04). CONCLUSIONS: Castings constructed using refractory die technique and subsequently cemented resulted in a more accurate and less variable fit than those produced with the lift-off technique. Wax patterns lead to more accurate castings than acrylic resin and locating indentations may interfere with the cementation of castings when lift-off techniques are used.     

Attenuation of the discriminative stimulus effects of ethanol by the benzodiazepine partial inverse agonist Ro 15-4513

The aim of the present study was to investigate whether ethanol training affects the ability of Ro 15-4513 to block the discriminative stimulus effects of ethanol dose differentially. Three different groups of rats were trained to discriminate 1.0 g/kg ethanol (n = 8), 1.5 g/kg ethanol (n = 7) or 2.0 g/kg ethanol (n = 8) from water in a two-lever, food-reinforced procedure. Ethanol and water were administered by gavage 20 min before the onset of the session. When the discrimination performance was stable, rats were pretreated with Ro 15-4513 (1-17 mg/kg; i.p.) 5 min before the administration of ethanol. Ro 15-4513 attenuated the discriminative stimulus effects of 1.0 and 1.5 g/kg ethanol but not 2.0 g/kg ethanol in each of the ethanol training groups. Overall, blockade of the discriminative stimulus effects of 1.0 and 1.5 g/kg ethanol by 5.6 mg/kg Ro 15-4513 occurred without significantly altering response rates or blood ethanol concentrations. A decrease in blood ethanol concentration was, however, found with 17 mg/kg Ro 15-4513 in combination with 2.0 g/kg ethanol. These results suggest that the benzodiazepine partial inverse agonist, Ro 15-4513, can attenuate the discriminative stimulus effects associated with low to moderate doses of ethanol (1.0-1.5 g/kg).     

Characterization of I2 imidazoline and sigma binding sites in the rat and human stomach

This study investigated the effect of chronic hypertonicity on the OKP cell Na/H antiporter, encoded by Na/H exchanger 3 (NHE3). Chronic (48 h) increases in extracellular glucose, mannitol, or raffinose concentration caused a significant increase in Na/H antiporter activity, while increases in urea concentration were without effect. This effect was seen with changes in osmolality of only 20 mOsm/liter, a magnitude that is observed clinically in poorly controlled diabetes mellitus. Increases in mannitol concentration acutely inhibited and chronically stimulated Na/H antiporter activity. The increase in Na/H antiporter activity induced by hypertonic incubation was resistant to 10(-7) and 5 x 10(-6) M but inhibited by 10(-4) M ethylisopropyl amiloride, consistent with regulation of NHE3. In addition, hypertonicity increased total cellular and plasma membrane NHE3 protein abundance twofold, with only a small increase in NHE3 mRNA abundance. We conclude that chronic pathophysiologically relevant increases in tonicity lead to increases in NHE3 protein abundance and activity. This may be responsible for increased proximal tubule apical membrane Na/H antiporter activity in poorly controlled diabetes mellitus, which could then contribute to hypertension, glomerular hyperfiltration and diabetic nephropathy.     

Later orthodontic appliance reactivation stimulates immediate appearance of osteoclasts and linear tooth movement

BACKGROUND: Delays in the appearance of osteoclasts at compression sites occur after orthodontic appliance reactivation, when this is done during both the period of osteoclast recruitment and the peak expansion in the osteoclast population. This experiment examines osteoclasts and tooth movement in alveolar bone after appliance reactivation coinciding with alveolar bone formation and the time when reactivation osteoclasts first appear (ie, 10 days after initial appliance activation). METHODS: Bilateral orthodontic appliances were activated to mesially tip maxillary molars with 40 cN in 144 rats. After 10 days, all rats were randomized into two groups of 72. Group I had appliances reactivated in precisely the same manner as the first activation. Group II had appliances sham-reactivated. Nine to 12 rats were then sacrificed at 1, 3, 5, 7, 10, and 14 days in both groups (eg, day 1 represents an interval of 11 days after the first appliance activation and 1 day after either sham or real reactivation). Orthodontic movement was measured cephalometrically; changes in osteoclasts and root resorption were assessed at both compression and tension sites histomorphometrically. RESULTS: Teeth in the reactivated group (Group I) displayed linear tooth movement (62.6 micrometers/day), and 0.9 mm tooth movement by day 10. Significant increases in osteoclast numbers, osteoclast surface percentage, and surface per individual osteoclast were evident in these animals by 1 day postreactivation (P <.01). Significant treatment-related increases in root resorption were not evident at compression sites at any time. CONCLUSIONS: These findings indicate that, after appliance reactivation during the time when reactivation osteoclasts appear, a second cohort of osteoclasts can be recruited immediately, along with immediate and substantial tooth movement and no greater risk of root resorption.     

Spontaneous neoplastic transformation of WB-F344 rat liver epithelial cells

Several studies have shown that cultured rat liver epithelial cells transform spontaneously after chronic maintenance in a confluent state in vitro. In the present study, multiple independent lineages of low-passage WB-F344 rat liver epithelial stem-like cells were initiated and subjected in parallel to selection for spontaneous transformation to determine whether spontaneous acquisition of tumorigenicity was the result of events (genetic or epigenetic) that occurred independently and stochastically, or reflected the expression of a pre-existing alteration within the parental WB-F344 cell line. Temporal analysis of the spontaneous acquisition of tumorigenicity by WB-F344 cells demonstrated lineage-specific differences in the time of first expression of the tumorigenic phenotype, frequencies and latencies of tumor formation, and tumor differentiations. Although spontaneously transformed WB-F344 cells produced diverse tumor types (including hepatocellular carcinomas, cholangiocarcinomas, hepatoblastomas, and osteogenic sarcomas), individual lineages yielded tumors with consistent and specific patterns of differentiation. These results provide substantial evidence that the stochastic accumulation of independent transforming events during the selection regimen in vitro were responsible for spontaneous neoplastic transformation of WB-F344 cells. Furthermore, cell lineage commitment to a specific differentiation program was stable with time in culture and with site of transplantation. This is the first report of a cohort of related, but independent, rat liver epithelial cell lines that collectively produce a spectrum of tumor types but individually reproduce a specific tumor type. These cell lines will provide valuable reagents for investigation of the molecular mechanisms involved in the differentiation of hepatic stem-like cells and for examination of potential causal relationships in spontaneously transformed rat liver epithelial cell lines between molecular/cellular alterations and the ability to produce tumors in syngeneic animals.     

Effect of transforming growth factor-beta on proteoglycan synthesis by chondrocytes in relation to differentiation stage and the presence of pericellular matrix

The effects of transforming growth factor-beta (TGF-beta) on proteoglycan synthesis of chondrocytes are controversial. The hypothesis that the differential effect of TGF-beta is related to the differentiation stage of the chondrocytes is investigated in this study. Rabbit auricular chondrocytes were cultured in alginate. When seeded in alginate immediately after isolation, cells keep their cartilaginous phenotype. When cells are first cultured in monolayer, they lose their cartilaginous phenotype and become dedifferentiated. We used three different cell populations: (1) Differentiated cells (P0: immediately after isolation); (2) partially (de)differentiated cells (P1: after one passage in monolayer); (3) dedifferentiated cells (P4: after four passages in monolayer). Cells were characterized by morphology using electron microscopy, amount of proteoglycans using the Farndale assay and type of collagen produced using immunohistochemistry. The effects of addition of 10 ng/ml TGF-beta2 for 7 days to P0, P1 and P4 cells were compared. TGF-beta was added either directly from the start of the alginate culture, or after a preculture period of three weeks in alginate. The amount of proteoglycans was increased in all chondrocyte populations when TGF-beta was added immediately after seeding in alginate, indicating that the effect of TGF-beta on proteoglycan synthesis does not depend on the differentiation stage of cells. After preculture in alginate, stimulation of proteoglycan synthesis (as measured by amount of proteoglycans and 35S-sulfate incorporation) had vanished. This effect was independent of differentiation stage . A dose-response experiment with TGF-beta (1, 10, 50 ng/ml) confirmed this differentiation-stage-independent effect of TGF-beta on proteoglycan synthesis. Stimulation by TGF-beta can be retained after enzymatic digestion of the pericellular matrix and reseeding of the cells in alginate, indicating the importance of pericellular matrix for the effect of TGF-beta on matrix synthesis. Alkaline phosphatase (ALP) activity was largely inhibited by TGF-beta in P0 chondrocytes, either with or without preculture in alginate. After culturing in monolayer, ALP activity was not substantially changed by TGF-beta. This indicates that the effect of TGF-beta on ALP activity, in contrast to the effect on proteoglycan synthesis, does depend on the differentiation stage of the cells. Furthermore, the fact that ALP synthesis in P0 cells is still inhibited by TGF-beta after preculture indicates that these cells remain responsive to TGF-beta. This provides additional evidence for the importance of the pericellular matrix for regulation of the effect of TGF-beta on proteoglycan synthesis. The results indicate that, in pathological cartilage, matrix depletion might be the trigger for increased matrix synthesis in reaction to TGF-beta, suggesting an important role for TGF-beta in cartilage repair.     

Quantitative mechanical assessment of the extraocular muscles.

The active and passive behaviour of the extraocular muscles can be investigated by measuring the force that must be applied to rotate the eyeball when the muscles are relaxed (the forced duction test) or the force required to maintain the eyeball stationary while the contralateral eye follows a moving target (the force generation test). Apparatus and test procedures for carrying out both tests are described. Normal values and confidence intervals for the tests have been obtained and the results of muscle entrapment and palsy illustrated.