The effect of powder-liquid ratio and the mixing method on the surface hardness of phosphate-bonded investment materials.

In this experimental study the surface-hardness changes of three phosphate-bonded investments were observed in relation to: a) the ratio of liquid-powder, b) the way of the mixing, in 3 hours and 24 hours after mixing. The Vickers hardness test was used for testing the surface hardness of the specimens (ISOMA SA, Bienne, Swiss, hardness testing apparatus). This study indicated that the surface hardness of the specimens increased after mechanical mixing, and also that it was higher in 24 hours than in 3 hours. Also, as more water was included in the mixing liquid, as lower became the surface hardness of the materials. Finally, it was observed that one material appeared to have the greatest fluctuations of surface hardness: Maruvest MI.

Fabrication of a custom-made impression tray for making preliminary impressions of edentulous mandibles.

Severe mandibular alveolar ridge resorption is usually observed in patients with long-term edentulism and/or ill-fitting dentures. In some of these patients, the genial tubercles project into the floor of the mouth as a high point in the anterior area of the mandibular residual ridge. The lingual flanges of mandibular stock impression trays usually impinge on the most prominent areas of the resorbed mandibular edentulous ridge (i.e., internal oblique lines and genial tubercles). It is suggested that a preliminary custom tray be made in such cases to pour an initial impression so that individual custom trays can be fabricated. An efficient method for constructing such a custom impression tray from readily available materials is described.

Using cephalometry to evaluate maxillomandibular relationships in complete denture construction.

Long-term denture wearers undergo facial changes as a result of occlusal wear of the dentures and residual ridge resorption. This study examined 12 such patients, presenting with a clinical appearance of Angle's Class III occlusal relationships, to evaluate a clinical method of determining the correct mandibular position. Complete dentures were fabricated for each patient using standard clinical procedures, but acrylic resin blocks were left on the mandibular posterior bases instead of denture teeth. Ensuing changes in maxillomandibular relationships were recorded. After the stabilization of the mandibular relationship, the dentures were completed using mandibular posterior teeth. Patients were evaluated using cephalometric analysis before and after treatment. Results show that a careful procedure of denture fabrication allows the determination of the correct mandibular relationship, even in patients who have experienced extreme facial collapse.