PubMed · 290960
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G Oilo. 1979. [Microleakage].. https://pubmed.ncbi.nlm.nih.gov/290960/
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We studied conidiogenesis and adhesive knob formation (maturation) by newly developed conidia of the nematophagous fungus Drechmeria coniospora. Upon conidiogenesis on infected nematodes or during saprophytic growth of the fungus in axenic cultures compact clusters of conidia developed. Less than 10% of such clustered conidia matured; mature conidia were invariably located on the periphery of the clusters. The kinetics and rate of maturation of conidia were studied in in vitro systems and in soil. In both cases adhesive knobs were formed; the rate at which knobs were formed appeared to be determined by the age of the conidia, the temperature and the soil moisture. In addition, knob formation was suppressed at increasing conidial densities. Under favorable conditions, however, over 90% of the conidia matured within a period of 3 days. The rate of knob formation was neither influenced by the presence of nematodes nor by that of exogenous nutrients, which suggests that maturation is an autonomous process. Electron-microscopical analysis indicated that budding of the conidia at the initial stage of maturation occurred simultaneously with the deposition of the sticky, adhesive layer around the wall of the developing knob. The ecological significance of the time- and spatially separated maturation of conidia after conidiogenesis is discussed with respect to survival of the conidia.
For attaching orthodontic brackets glass ionomer cements are being discussed as an alternative material to synthetic glues since they are less aggressive toward the tooth enamel. A serious disadvantage consists in a lower degree of adhesion to enamel. The adhesion can, however, be increased to some extent by enamel preparation. In order to investigate further improvement in this area, 250 freshly extracted bovine teeth were treated with 22 chemicals and their enamel-conditioning properties were tested. For the attachment of the brackets the glass ionomer cements AqaCem and Ketac-cem are used. Tensile shear tests were carried out with a Wolpert universal testing machine. Best results were obtained with the aromatic carbonacids benzoic acid and salicylic acid in acetonic solution. The mean adhesive power was 9.8 MPa. This means an increase of 38% as compared to other pre-conditioning materials such as polyacrylic acid. It can be assumed, that aromatic carbonacids as small, very reactive molecules can establish a closer contact to the phosphate groups of enamel than can the macromolecular polyacrylic acid. Thus, a further step on the way to using glass ionomer cements as a bracket bonding material seems to have been taken.
The tensile bond strength of bracket bases coated with metal plasma were examined. The aim was to investigate, whether the conditioning of bracket bases by metal plasma is a possible means to increase the tensile bond strength. Two typical orthodontic adhesives were used. Three test groups were differentiated: 1. Metal mesh bracket bases (coated and uncoated with metal plasma), 2. metal bracket bases without mesh (coated with metal plasma), 3. ceramic bracket bases coated with metal plasma. Metal bracket bases with mesh, coated with metal plasma showed superior bond strength in comparison to usual uncoated mesh bracket bases. The former were nearly four times stronger than the uncoated bases with reference to the first adhesive and two times stronger referring to the second adhesive. The primary source of the enhancement of adhesion is due to the enormous increase of the retentive active surface created by the metal plasma. This structure guarantees an excellent micromechanical interlocking for the adhesive. The mean tensile bond strength of titanium coated mesh bases was 20.03 N/mm2 (= 286 N/bracket). Plasma coated bases without mesh reached average interlocking forces comparable to conventional uncoated mesh bases. Ceramic bracket bases were found not to be suitable for plasma coating. As a result of these experimental findings metal plasma coating of metal bracket bases can be regarded as an excellent means to increase the tensile bond strength.