Powder formulation advantage

Systematic attempts to formulate improved materials have met with no success (Manly et al., 1951 Rockett, 1968). The last and, in some ways, most promising attempt at improving the dental silicate cement was made by Pendry (Pendry Cook, 1972 Pendry, 1973) who improved its resistance to acid by adding indium to both powder (5-8 %) and liquid (5-65 %). The cement, however, lacked suflScient translucency, and by this time the glass-ionomer cement had arrived with its advantages of translucency and resistance to staining and acid attack. 

The ZOE cement is easy to mix and a greater amount of powder can be incorporated into this cement (5 1 by mass) than any other, where even 4 1 by mass is unusual. Because the ZOE cement is sensitive to moisture it can be formulated to have a long working time under normal room conditions (23 °C, relative humidity 50 %) and a rapid set once placed in the warm and moist conditions of the mouth. This is a considerable clinical advantage, making it convenient to use. The cement can be used in a war pack for use on the battlefield. Nevertheless, sensitiveness to humidity can give rise to problems in use under tropical conditions. 

A mixture of ammonium nitrate/TNT/aluminum powder/charcoal (65/15/17/3) called Ammonal had been used in World War I for mining, demolition and in bombs and grenades. However, in World War II, shortage of aluminum powder restricted its use for such HE formulations. The effect of addition of aluminum powder to high explosive fillings of bombs and shells had been found to be of advantage which is evident from the data given in Table 3.3. 

All three grades of mannitol showed similar, relatively low BFI values. This low tendency for brittle fracture represents a very significant advantage of mannitol, particularly with direct compression formulations where material properties, and not powder processing, must be used alone to overcome deficiencies of the API and other ingredients. It should be remembered that low BFI is but one consideration of many when selecting excipients for direct compression formulations. 

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