Effect of interfacial variables on metal-porcelain bonding.

While ceramic-to-metal bonding has been used in many applications, the actual chemical and physical factors leading to optimum bond strength are not well understood. In this work, several variables affecting the bonding between dental porcelain and a palladium alloy (85% Pd, 10% Cu, and 5% Ga) were investigated: 1) precoating the metal by sputtering various oxides before porcelaining; 2) peroxidation of the metal base before porcelaining; 3) porcelaining under reducing atmosphere; and 4) surface roughening at controlled levels before porcelaining. Using a modification of the push doughnut shear bond strength test to measure bond strength the following results were obtained. 1) Compared with standard "control" samples, the aluminum oxide precoated specimens showed a bond strength improvement of 46%, while the copper, manganese, and tin oxide precoatings exhibited smaller effects. 2) Preoxidation of the metal base led to pronounced bond strengthening (152%) by surface roughening as well as oxide formation. 3) Porcelaining under a reducing atmosphere severely reduced bond strength (88% lower than the controls) indicating the role of oxidation during the standard firing cycle. 4) Mechanical roughening of the surface by controlled amounts gave pronounced improvements with greater notch depth. Coarse roughening produced the highest bond strength improvements (486%).

Eagle's syndrome: a comparison of intraoral versus extraoral surgical approaches.

Eagle first described vague orofacial pain associated with styloid elongation in 1937. Since that time, many authors have described the various clinical symptoms, radiographic features, and treatment regiments seen with Eagle's syndrome. Two cases of Eagle's syndrome treated surgically are presented in this article. Both extraoral and intraoral approaches were separately used. These two surgical approaches are critically discussed in depth. The extraoral approach is advocated. In addition, diagnostic procedures and nonsurgical treatment alternatives are discussed.

Effect of gibberellic Acid on silica content and distribution in sugarcane.

The effect of gibberellic acid on the content and distribution of silicon in the stem, leaf sheath, and leaf lamina of sugarcane was analyzed in relation to the effect of gibberellic acid on stem growth. Silicon content was measured by neutron activation analysis, and its distribution was followed by scanning electron microscopy and X-ray analysis.Foliarly applied gibberellic acid increased stem length and fresh weight and decreased silicon content. Gibberellic acid treatments had little or no effect on growth or silicon content of leaf laminae or sheaths. The close correlation between increase in growth of an internode in response to gibberellic acid and the decrease in silicon content of that internode indicated a dilution effect of growth on the amount of silicon rather than a direct effect of gibberellic acid on silicon deposition. This conclusion was supported by scanning electrom microscopy, X-ray map photos, and counts of silica cells per unit of epidermis area.

Biological strandard for electron microprobe analysis of intracellular sodium concentration.

A method is described for the determination of the intracellular concentration of sodium in individual cells using the electron microprobe analyzer. This method gives an accuracy equal to that obtained by using flame photometry on tissues with large cell populations. Intracellular sodium was precipitated in the cell by a fixative containing pyroantimonate. Cartilaginous needles from shark fins which were equilibrated in saline solutions of differing concentrations were used as biological standards.

Electron-probe microanalysis of silicon in the epidermis of rice (Oryza sativa L.) internodes.

Electron-probe X-ray microanalysis showed that significant amounts of silicon are accumulated in the entire epidermal system of the rice internode except in the stomatal apparatuses. Thus, there is a lack of specific sites for Si deposition from levels just above the base to the tip of the rice internode. In the intercalary meristem region, 1 cm above the base of the internode, point-count data indicate more Si accumulation in the dumb-bell shaped silica cells than in the long epidermal cells. Above this region, Si is accumulated essentially in a uniform pattern in all epidermal cells. Such a pattern for Si accumulation in rice internodes markedly contrasts with that for Avena internodes and may explain, in part, why rice plants have a higher percentage Si (dry weight basis) in their shoots. The adaptive significance of this silicification pattern in rice is discussed.

Silica in developing epidermal cells of Avena internodes: electron microprobe analysis.

Silica is present in significant amount in mature guard and subsidiary cells of stomata, in trichomes and silica cells, and in the walls of long eidermal cells of Avena. No silica was detectable in cork cells of cork-silica cell pairs. Silica must be accumulated in these specialized epidermal cells quite rapidly.