Nonuniform vertical and horizontal setting expansion of a phosphate-bonded investment.
OBJECTIVE
This study developed a new device for measuring the internal setting expansion of phosphate-bonded investment and assessed the effect that different pattern materials may have on the internal setting expansion.


METHODS
The measuring device consisted of 2 horizontal plungers, a vertical needle, 2 digital dial gauges, and a protection tube with a disk. Outward displacement of the 2 horizontal plungers by investment setting expansion was transmitted to a digital dial gauge through the vertical needle. Upward displacement of a protection tube was measured by another digital dial gauge. Three pattern materials, including soft and hard inlay waxes 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 means, 2.26% to 2.73%) was significantly higher than the horizontal setting expansion (range of means, 0.09% to 1.50%) (P <.05). In addition, for the hard inlay wax pattern, the horizontal setting expansion for the cervical aspect (means, 1.39%) was significantly higher than that of the occlusal aspect (means, 0.54%) (P <.05).


CONCLUSIONS
In this study, the new measuring device was a convenient and reliable method for quantitative assessment of internal setting expansion. Regardless of the type of pattern material, a phosphate-bonded investment caused nonuniform setting expansion, especially in a horizontal direction, which lead to the distortion of the pattern.
Takahashi
J
J
Faculty of Dentistry, Osaka University, Suita, Osaka, Japan.
Okazaki
M
M
Taira
M
M
Kubo
F
F
D000704:Analysis of Variance; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003442:Crowns / Q000706:statistics & numerical data; D003734:Dental Casting Investment / Q000737:chemistry*; D003735:Dental Casting Technique / Q000295:instrumentation / Q000706:statistics & numerical data; D006801:Humans; D007284:Inlays / Q000706:statistics & numerical data; D010710:Phosphates / Q000737:chemistry*; D013997:Time Factors
D003734:Dental Casting Investment; D010710:Phosphates