Tribological behaviour of unveneered and veneered lithium disilicate dental material.

The friction and wear behaviour of a lithium disilicate dental ceramic against natural dental enamel is studied, including the effect of the presence of a fluorapatite veneering upon the tribological properties of the material. The tribological behaviour was assessed using reciprocating pin-on-plate test configuration, at pH 3 and pH 7. The surface energy of the plates was determined, as well as the zeta potential of fluorapatite, lithium disilicate and enamel particles in artificial saliva. It was found that the friction and wear behaviour of the tested enamel/plate material tribocouples is less severe in unveneered plates. Initial surface roughness of the plate does not affect wear results. However the topography of the resulting wear track affects the corresponding wear loss: a smoother final wear track is associated with lower wear. The surface topography of the wear track, and thus the tribological performance of the tested materials, is very sensitive to the pH of the sliding solution. This is because the dissolution trend, wettability and surface charge of the used materials are pH dependent. Overall friction and wear are higher under basic pH conditions, especially when plates are veneered. A wear model is proposed that correlates the effect of the described parameters with the observed tribological behaviour at pH 7. Attained results show that fluorapatite coating of lithium disilicate dental crowns affects tooth/crown wear behaviour, resulting in increased wear of both the artificial crown and the opposing natural teeth. Coating should therefore be avoided in occlusal crown surfaces.

Lavandula luisieri essential oil as a source of antifungal drugs.

This work reports the antifungal activity of Lavandula luisieri essential oils against yeast, dermatophyte and Aspergillus strains responsible for human infections and food contamination. The oil's cytotoxicity and its effect on the yeast-mycelium transition in Candida albicans, an important virulence factor, were also evaluated. Analyses by GC and GC/MS showed a peculiar composition of irregular monoterpenes. Significant differences between the samples occurred in the amounts of 1,8-cineole, fenchone and trans-α-necrodyl acetate. The oil with higher amounts of irregular monoterpenes was the most effective. The influence of the oils on the dimorphic transition in C. albicans was also studied through the germ tube inhibition assay. Filamentation was completely inhibited at concentrations sixteen times lower than the minimal inhibitory concentration. The results support the use of L. luiseiri essential oils in the development of new phytopharmaceuticals and food preservatives and emphasise its antifungal properties at concentrations not cytotoxic or with very low detrimental effects on mammalian cells.

Antifungal activity of phenolic-rich Lavandula multifida L. essential oil.

This study evaluates the antifungal activity and mechanism of action of a new chemotype of Lavandula multifida from Portugal. The essential oil was analyzed by gas chromatography (GC) and gas chromatography/mass spectrometry (GC/MS), and the minimal inhibitory concentration (MIC) and minimal lethal concentration (MLC) of the oil and its major compounds were determined against several pathogenic fungi responsible for candidosis, meningitis, dermatophytosis, and aspergillosis. The influence of the oil on the dimorphic transition in Candida albicans was also studied, as well as propidium iodide (PI) and FUN-1 staining of C. albicans cells by flow cytometry. The essential oil was characterized by high contents of monoterpenes, with carvacrol and cis-ß-ocimene being the main constituents. The oil was more effective against dermatophytes and Cryptococcus neoformans, with MIC and MLC values of 0.16 µL/mL and 0.32 µL/mL, respectively. The oil was further shown to completely inhibit filamentation in C. albicans at concentrations below the respective MIC (0.08 µL/mL), with cis-ß-ocimene being the main compound responsible for this inhibition (0.02 µL/mL). The flow cytometry results suggest a mechanism of action ultimately leading to cytoplasmic membrane disruption and cell death. L. multifida essential oil may be useful in complementary therapy to treat disseminated candidosis, since the inhibition of filamentation alone appears to be sufficient to treat this type of infection.

Effect and analysis of phenolic compounds during somatic embryogenesis induction in Feijoa sellowiana Berg.

The effect of phenolic compounds on somatic embryogenesis in Feijoa sellowiana was analysed. The results showed that caffeic acid (140-560 microM) significantly increased somatic embryogenesis induction compared with the control. The presence of phloridzin, even at lower concentrations (11.5 microM), or caffeic acid or phloroglucinol at concentrations greater than 140.0 and 197.5 microM, respectively, inhibited somatic embryo development beyond the globular stage. When somatic embryos were transferred to the germination medium, the highest rates of germination (81.9%) were obtained with embryos induced in the presence of phloroglucinol (79.0 microM). At all concentrations tested, somatic embryos induced in medium containing phloroglucinol germinated at higher rates than those induced in the presence of caffeic acid. Histological and ultrastructural studies showed that somatic embryos were formed in close association with phenolic-rich cells which, in more advanced stages of development, formed a zone isolating the embryo from the maternal tissue. A comparative analysis of total phenolic content indicated that phenolics reached a peak by the third week of culture, independently of the medium used. However, after that period, the amount of phenolic compounds was significantly higher in explants cultured in the presence of phloroglucinol than in those cultured in the control or in caffeic acid-containing medium. Attempts to identify the type of phenolic compounds showed that flavan-3-ols and gallic acid derivatives were mainly produced in phloroglucinol-containing medium, whereas flavanones and dihydroflavonols were also present in medium containing caffeic acid. Flavones were the main phenols detected in the control. The ways in which phenolic compounds may affect somatic embryogenesis are discussed.

Induction of pollen callus in anther cultures of Feijoa sellowiana Berg. (Myrtaceae).

Anthers of Feijoa sellowiana Berg. (feijoa) produced pollen callus when cultured in Murashige and Skoog medium containing 2,4-dichlorophenoxyacetic acid and benzyladenine or in nurse cultures. Somatic callus was also formed in large amounts from the connective and from the cut end of the filament. Anthers containing microspores at the stage immediately prior to the first pollen mitosis cultured in the presence of 3% sucrose, presented the highest frequencies of induction. Androgenetic divisions were initiated by the formation of two morphologically equal cells, the so-called B-pathway. Attempts to regenerate pollen plants were unsuccessful but leaf-like structures could be obtained in regeneration media containing combinations of gibberellic acid and benzyladenine.