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INTRODUCTIONDisinfection of impressions is required in order to prevent the transmission of infectious diseases in dentistry 1-3） . The disinfection method and the brand of alginate impression material have been reported to have varying effects on the resultant stone model in terms of surface roughness, reproduction of detail, dimensional stability, and deformation 4-9） . Stone models are expected to be sufficiently hard in order to resist marginal fracture and abrasion during curving. However, disinfection of impressions may reduce the surface hardness of stone models due to effects arising from water absorption, impression dissolution, or disinfectant solution remaining on the impression surface. Therefore, a hardness evaluation study is required to establish a suitable disinfection method whereby the reproducibility of stone models will not be adversely affected by disinfected impressions. The measurement conditions for a scratch hardness test for stone models were investigated in a previous study 10） . Based on the results of the previous study, we conducted the hardness test for stone models and investigated the effects of disinfecting alginate impressions on the scratch depth of resultant stone models. MATERIALS AND METHODSThe materials listed in Table 1 were used according to the instructions of the respective manufacturers.Eleven brands of alginate impression material （de-tails in Table 1） were mixed for 15 seconds using an automatic alginate impression material mixer （Rakuneru, GC, Tokyo, Japan） . A type V dental stone （New Plastone, GC, Tokyo, Japan） was first mixed by hand for 45 seconds and then vibrated for 30 seconds.Disinfectants were 1％ sodium hypochlorite solution （SH） and 2％ glutaraldehyde solution （GA） . The disinfectant products, Purelox （Oyalox, Tokyo, Japan） and Sterihyde （Maruishi Pharmaceutical, Osaka, Japan） , were diluted with distilled water to concentrations of 1％ and 2％ respectively.Stone specimens were produced using the equipment shown in Fig. 1 This study investigated the effects of disinfecting alginate impressions on the scratch depth of resultant stone models. Eleven brands of alginate impression material and two disinfectants, 1％ sodium hypochlorite and 2％ glutaraldehyde, were used. Impressions were immersed in disinfectant solutions or stored in sealed bags after spraying with disinfectants, and then poured with a type V dental stone. The scratch depth of the stone model obtained from disinfected impression was measured. The storage of alginate impressions after spraying with disinfectants did not increase the scratch depth of resultant stone models. However, the effect of immersion in disinfectants on scratch depth varied with the brand of the alginate impression material.

In this study, wedge-shaped CP titanium castings and Ti-6Al-7Nb alloy castings were produced by three types of investment.