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At least 487 records · Page 27Linked to original sources
PubMed1990

Calcium phosphate cements: study of the beta-tricalcium phosphate--dicalcium phosphate--calcite cements.

The setting and strengthening properties of beta-tricalcium phosphate (beta-TCP)--dicalcium phosphate dihydrate (DCPD)--calcite blends upon admixture with water were investigated at 25 and 37 degrees C. Setting was accelerated by seeding the system with hydroxyapatite (HAp), and strengthening improved when the solids were mixed with a solution saturated with DCPD and HAp. The relationship strength versus ageing time in wet conditions was correlated with mineralogical changes of the material. X-Ray diffraction, thermal analysis and scanning electron microscopy observations showed that DCPD and calcite react together to form small HAp crystals acting as bridges between the beta-TCP aggregates present in the paste. Both gaseous CO2 released by the reaction of calcite and the conversion of lower (DCPD, calcite) to higher-density phases (HAp) contributed to increase the porosity of the material. Nevertheless, quite acceptable diametral strengths (around 1.5 MPa) could be achieved, despite the high porosity of the hardened product (up to 54 vol%). After exhaustion of DCPD, calcite can react with beta-TCP to form further HAp, but this process is detrimental to the strength of the material. Both the mineralogical transformations, and the strengthening of the material were accelerated considerably upon increasing the ageing temperature.

Adhesives↗
PubMed1988

[Comparison of 4 technics for collecting bacteria on cement, asbestos-cement and steel in hen-breeding buildings].

A comparative study between 4 sampling techniques (swabbing, pistol-washing, printing on agar medium either with or without neutralizer) was performed on three materials (concrete, asbestos-concrete, steel) following numeration of three bacterial flora (the total aerobic flora, faecal streptococci, pseudomonas). The highest levels of contamination were detected with pistol-washing irrespective of the substrate and flora recovered. A correlative study carried out from the contamination levels reveals that a significant correlation exists in all cases, with a low probability of error.

Alloys↗
PubMed1998

Effect of cement space and delayed placement on the seating of crowns luted with Vitremer, Fuji Duet and Dyract Cem.

PURPOSE: To determine the effects of cement space and delayed placement on the post-cementation elevation of crowns luted with two resin-modified glass ionomer luting cements (Vitremer, Fuji Duet) and a self-curing polyacid-modified composite resin luting cement (Dyract Cem). MATERIALS AND METHODS: The investigation was conducted in two parts: (1) A loading apparatus was employed to simulate the seating of a crown on a die. Six dies, differing in the amount of cement space allowed from 6-52 microns, were used. The loading apparatus allowed for a test cement to be placed in the crown, and subsequent activation of the apparatus lead to seating of the die into the crown. After seating, post-cementation crown elevation was measured. The cements Phosphacap, Vitremer, Dyract Cem and Fuji Duet were used. Each cement was tested 10 times at each of the six cement spaces. The post-cementation crown elevation data was analyzed by one- and two-way ANOVA tests, and Tukey's HSD test. (2) The cements Vitremer, Fuji Duet and Dyract Cem, were tested in a similar fashion to Part 1, except activation of the loading apparatus was delayed. Three cement spaces (6, 29 and 52 microns) and three delay periods (60, 120 and 180 seconds) were investigated. Each cement was tested five times. The post-cementation crown elevation data was analyzed by one- and two-way ANOVA tests, and Tukey's HSD test. RESULTS: The amount of cement space provided and the cement used significantly affected post-cementation crown elevation (P = 0.001). Where cementation was delayed, post-cementation crown elevation was significantly affected by both the cement used and the amount of cement space provided (P = 0.001). Delayed placement of Dyract Cem had no significant effect on post-cementation crown elevation (P = 0.01). Post-cementation crown elevation when Vitremer was used was significantly affected by both the amount of cement space and delayed placement (P = 0.01). A 180-second delay in placement of Vitremer resulted in significantly worse post-cementation crown elevation (P = 0.01). Seating was not possible 120 seconds after Fuji Duet had been mixed.

Analysis of Variance↗