A Study on the Retention Force of Crowns. Influence to the Changes in the Powder Particle Size Distribution of Glass Ionomer Luting Cement on the Retention Force of Crowns

When cementing a crown, the amount of final seating is affected by the film thickness of the dental cement. To decrease the film thickness of glass ionomer cement (GIC), a GIC powder (Shofu Hybond Glass ionomer CX) was milled and three experimental fine particle powders were produced. The purpose of this study was to investigate the physical properties of fine particle GICs (ISO-9917, compressive strength, setting time, film thickness) and retention force of the crown cemented. The powder was milled with Centrifugal Fluidized Milling Machine (CF-160 Ube Kousan Co.) to produce the particle size (CX-01: maximum particle size:∅6μm, CX-02: 8μm, CX-03: 12μm). The results were as follows: In specimen containing a large amount of fine particles (CX-01), the best seating of a crown was accomplished (total film thickness: 8.0μm), though both compressive strength and film thickness was reduced to some extent. On the other hand, there was no significant difference between the retention force of normal GIC and fine particle cement (CX-01, 02, 03). The setting time of CX-01, 02, 03 was slightly longer than that of normal GIC.