Objectives: To identify deformation in phosphate-bonded investment materials during dental casting procedures and to consider the influence of air bubble pores on the degree of deformation. Methods: Survived high strain rate disc rupture strength test specimens for four investment materials were assessed for deformation (Croform W/B. Davis Schotlander Davis, Letchworth, UK: Rema Exakt. Dentaurum, Pforzheim, Germany: Levotherm. Bayer Dental, Leverkusen, Germany: Rematitan. Dentaurum, Pforzheim, Germany). An electronic dental centrifugal casting (Fusus Super D. Galloni, Milan, Italy) was used to apply the loads. An indirect technique for measuring deformation using a computerised image analysis system (Global Lab Image Version 3. Data Translation Ltd, Basingstoke, UK.) was devised for investment diaphragms with both a wide pore size distribution and with virtually no pores. A total of 128 high strain rate specimens were investigated. A one-way analysis of variance was carried out to determine statistical significance. Results: All but one of the test specimens showed a measurable degree of deformation. However, there was no statistically significant difference in deformation between specimens with no pores and those with a large pore size distribution (P>0.05). Conclusions: PBI must survive all casting procedures without deformation if the resultant prosthesis is to fit. 100µm is generally recognised as the acceptable tolerance of fit for removable metal-based restorations. The amount of deformation measured during this investigation was considerably greater than 100µm. Although there was no statistically significant difference between specimens with and without air bubble pores, the degree of deformation measured for both variables could be of considerable clinical significance.

Back to the Dental Materials: VIII - Others-Non-metallic Program
Back to the IADR/AADR/CADR 83rd General Session (March 9-12, 2005)

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