Nonuniform vertical and horizontal setting expansion of a phosphate-bondedinvestment

Purpose. This study developed a new device for measuring the internal setti ng expansion of phosphate-bonded investment and assessed the effect that di fferent pattern materials may have on the internal setting expansion. Material and methods. The measuring device consisted of 2 horizontal plunge rs, a vertical needle, 2 digital dial gauges, and a protection tube with a disk. Outward displacement of the 2 horizontal plungers by investment setti ng expansion was transmitted to a digital dial gauge through the vertical n eedle. Upward displacement of a protection tube was measured by another dig ital dial gauge. Three pattern materials, including soft and hard inlay wax es and an autopolymerizing resin, were used. Data were analyzed with ANOVA and Scheffe's F test for all post hoc pairwise comparisons (95% confidence level). Results. For all pattern materials, vertical setting expansion (range of me ans, 2.26% to 2.73%) was significantly higher than the horizontal setting e xpansion (range of means, 0.09% to 1.50%) (P<.05). In addition, for the har d inlay wax pattern, the horizontal setting expansion for the cervical aspe ct (means, 1.39%) was significantly higher than that of the occlusal aspect (means, 0.54%) (P<.05). Conclusion. In this study, the new measuring device was a convenient and re liable method for quantitative assessment of internal setting expansion. Re gardless of the type of pattern material, a phosphate-bonded investment cau sed nonuniform setting expansion, especially in a horizontal direction, whi ch lead to the distortion of the pattern.