| 2662 Additions to Portland Cement to Improve Setting Time and Hardness | ||
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W.C. WAGNER, and J. VITALE, University of Detroit Mercy, MI, USA Portland and calcium aluminate cements have recently been used for dental restorative materials. Objectives: To determine what effect: 1) water, 2) calcium aluminate cement (CAC), 3) lithium fluoride (LiF), and 4) bismuth oxide (Bi2O3) additions have on setting time and hardness of Portland cement. Methods: Three samples (N=3) were prepared for combinations of distilled water (20, 25, 29% of total weight), CAC (Secar 71, LaFarge) (0-100% powder weight), LiF (0 and 1% of powder weight), and Bi2O3 (0 and 25% of powder weight) added to white Portland cement. The dry components were combined and mixed, then the water was mixed in. The samples were stored at 100% relative humidity for one week before testing. Setting time was determined using a Gillmore needle. Knoop microhardness was measured at three locations on each sample. The three hardness values were then averaged and then subjected to statistical testing. ANOVA and Tukey tests were used to determine if differences in setting time and hardness were statistically significant (α=0.05). Results: Setting time was significantly influenced by the amount of water, CAC, and LiF (p≤0.05). Setting times ranged from 23 minutes to over 1 day. The lowest setting times were associated with low water amounts with higher levels of CAC and LiF. Hardness was significantly influenced by amount of CAC and Bi2O3 (p≤0.05). Increasing CAC to 100% resulted in the highest hardness observed (74 Hk) while Bi2O3 generally lowered hardness. Lowest hardness values (17 Hk) were observed with 25% Bi2O3 and approximately equal mixtures of Portland Cement and CAC. Conclusion: Statistically significant differences in setting time and hardness resulted from additions to Portland cement (p≤0.05). CAC and LiF both decreased setting time. Increased water increased setting time. Adding CAC increased hardness while adding Bi2O3 lowered hardness. | ||
| Seq #277 - Cements: Citotoxicity and Endodontics 10:45 AM-12:00 PM, Saturday, March 24, 2007 Ernest N. Morial Convention Center Exhibit Hall I2-J | ||
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