Crystal Structures and Mechanism of Thermal Expansion of High Cordierite and Its Solid Solutions

The crystal structure of high cordierite and that of high cordierite solid solutions containing either Mn or Ga or Ge were refined. The structural changes caused by substitutions and the characteristic features of deformations of each T1O₄, T2O₄ tetrahedron and MO₆ octahedron were clarified. Thorough crystal chemical considerations led to a conclusion that the structure of Mn-bearing solid solution at room temperature may be regarded as a model structure of high cordierite at an elevated temperature. On the basis of the thermal expansion mechanism derived from this consideration, the thermal expansion behavior of the solid solutions is presented.     

Adherent bacteria cells in five dental materials: sonication effect

Adherent bacterial cells on the surfaces of two dental porcelain ceramics, three composite resins and human enamel were examined using four types of bacteria strains. Their adherent cells were counted on saliva-coated and uncoated material surfaces after sonication, and contact angle and potential were measured for each adherent cell tested. A correlation between contact angle and bacterial cells on an uncoated surface was found to be higher in two Streptococcus sanguis cells than in S. mutans Ingbritt and S. sobrinus OMZ 176, whereas there appeared to be a higher correlation between S. mutans Ingbritt or S. sobrinus OMZ 176 and potential on the uncoated surface. On the saliva-coated surface, a significantly high correlation was found between the adherent cells, with the exception of S. sanguis ATCC 10 557, and the potential. Contact angle and potential values were small when the surfaces of the materials were coated with saliva, as compared with those on the uncoated surface. The sonication condition (120 s) of adherent cells on the surface of the material significantly depended on the types of bacteria cells, showing that S. mutans Ingbritt (>50–60%) had a greater removal percentage than the others (<50%). © 1998 Chapman & Hall