An investigation of the adequacy of interproximal matrices commonly used with posterior composite restoratives.
Abstract The adequacy of six interproximal matrix systems commonly used during the placement of Class II composites has been assessed in vitro . The results indicate that none of the matrix systems investigated can be considered to be ideal.
A comparison of methods for contouring the occlusal surfaces of posterior composite restorations.
Abstract Four different techniques considered appropriate for contouring the occlusal portions of Class II composites have been evaluated and compared in terms of ability to restore occlusal morphologies and to leave the occlusal portions of Class II restorations of three different types of composite restoratives with acceptable marginal adaptation. The results indicate that none of the contouring techniques tested can be considered ideal. The type of composite restorative used was not found to significantly influence the adequacy of the techniques investigated It is suggested that for most posterior composites a free-hand anatomical contouring/counter-die contouring technique may be shown to be simpler and more effective than any of the techniques tested in the present study.
HYPERGOLIC REACTION MECHANISMS OF CATALYTICALLY PROMOTED FUELS WITH ROCKET GRADE HYDROGEN PEROXIDE
Abstract The coupling of the physical and chemical processes controlling the ignition delays (τ ign ) of hypergolic propellants complicates the direct analysis of the transient ignition processes. The transport properties of both the propellants and the ambient gas, and the heat of vaporization and reaction affect τ ign and must be considered experimentally. Furthermore, since hypergolic ignition occurs, by definition, on contact, the mechanics of initial contact and subsequent mixing can affect τ ign and must also be considered. Experimental results from a study of the hypergolic ignition of a catalytically promoted fuel with rocket grade hydrogen peroxide (RGHP) are presented. Statistical analysis of the experimental data was conducted to evaluate the relative effects of RGHP concentration, initial ambient pressure, and the ambient gas on τ ign . At RGHP concentrations of less than 92% in water, stable ignition was difficult to achieve. At sufficiently high Lewis number, an oscillatory ignition process is observed. A phenomenological model comprising mixing, RGHP decomposition, fuel heating and vaporization, and auto-ignition is presented and compared to the experimental results.