Beneficial reuse of precast concrete industry sludge to produce alkaline stabilized biosolids.

The precast concrete industry generates waste called concrete sludge during routine mixer tank washing. It is highly alkaline and hazardous, and typically disposed of by landfilling. This study examined the stabilization of municipal sewage sludge using concrete sludge as an alkaline agent. Sewage sludge was amended with 10 to 40% of concrete sludge by wet weight, and 10 and 20% of lime by dry weight of the sludge mix. Mixes containing 30 and 40% of concrete sludge with 20% lime fulfilled the primary requirements of Category 1 and 2 (Canada) biosolids of maintaining a pH of 12 for at least 72 hours. The heavy metals were below Category 1 regulatory limits. The 40% concrete sludge mix was incubated at 52 degrees C for 12 of the 72 hours to achieve the Category 1 and 2 regulations of less than 1000 fecal coliform/g solids. The nutrient content of the biosolids was 8.2, 10 and 0.6 g/kg of nitrogen, phosphorus and potassium respectively. It can be used as a top soil or augmented with potassium for use as fertilizer. The study demonstrates that concrete sludge waste can be beneficially reused to produce biosolids, providing a long-term sustainable waste management solution for the concrete industry.

Innovative silicate-based cements for endodontics: a study of osteoblast-like cell response.

Silicate-based filling materials were designed to obtain new endodontic sealers and root-end filling materials with adequate workability and consistency. Four different formulations (TC, TC 1%, TCf 1%, and TCf) were prepared incorporating calcium chloride as accelerant agent. A plasticizing compound (phyllosilicate) was added to TC 1% and TCf 1%. TC and TC 1% were prepared with water, whereas TCf and TCf 1% were mixed with a latex polymer as fluidizing agent. The aim of this study was to assess the in vitro biological compatibility of designed materials. White-MTA and AH Plus were tested as reference materials. Human osteoblast-like Saos-2 cells were challenged in short-term cultures (72 h) with solid materials and with material extracts in culture medium, and cell viability and number, cellular adhesion, and morphology were assessed. The new cements exerted no acute toxicity in the assay systems. Saos-2 like cells adhered and proliferated on solid samples of the experimental cements and MTA whilst AH Plus did not allowed cell growth. The extracts from the latex-containing cements showed some toxicity. By SEM analysis, osteoblast-like cells appeared adherent and spread on the new materials, and showed the maintenance of polygonal osteoblastic phenotype. Similar morphology was observed for cells on MTA, whereas only few cells were noted on the AH Plus surface. In conclusion, the new materials proved non toxic and supported the growth of bone-like cells, and resulted suitable to be used as endodontic sealers and root-end filling materials.

Penetration of ions from silicate cement restorations into Copalite--covered cavity walls.

This study aimed to asses the effect of silicate cement on Copalite -covered cavity walls in extracted human teeth. Class V cavities were prepared in 24 premolars and filled with silicate cement (Bio-Trey). Four cavities were unlined, the rest of the cavities were lined with 1 or 2 layers of Copalite before insertion of the restorations. After 6 months, 70-100 microns thick longitudinal sections of the teeth were studied by polarized light microscopy, microradiography and electron probe microanalysis. When imbibed in water or quinoline, a subsurface zone of altered birefringence was noticed in nearly all cavity walls. Nearly half of the cavity walls in the experimental groups showed a surface zone of increased radiopacity. In a few instances a subsurface radiolucent zone was present. By electron probe microanalysis F (0,4-3% by weight), Zn (1-4%) and Al (0,2-6%) were measured in the outer 10-60 microns of the cavity walls. The study shows that even with a double layer of Copalite, known to prevent microleakage, a desirable uptake of F and Al from silicate restorations into cavity walls can take place. Copalite does not prevent a phosphoric acid effect on the cavity walls.

Evaluation of biologic effects of dental materials using four different cell culture techniques.

The cytotoxicity of fresh and 1-day-old silicate cement, composite restorative material and zinc oxide-eugenol cement (ZOE) was tested using human epithelial cells (NCTC 2544) in four different cell culture systems: (1) 51Cr-release from prelabeled cells after incubation for 4 and 24 h in the presence of the materials. (2) Implanting the materials on an agar everlay and visualizing any cytotoxic effects after 24 h by neutral red vital stain. (3) Cell growth during 5 d in the presence of the materials. (4) Colony-forming ability after exposure of the cells for 30 min to medium previously incubated with the materials for 24 h. Freshly prepared and 1-day-old ZOE exhibited a prominent cytotoxic effect in all four systems. A less marked effect was found for the composite material in systems 2, 3, and 4, while silicate cement appeared to be the least toxic material in these three systems. Neither silicate cement nor composite showed any cytotoxic effect in system 1 based on 51Cr-release. It is concluded that the effects obtained by the cell culture techniques did not mimic the reactions obtained when the materials are tested under conditions which reflect their clinical use.

Fluoride uptake from restorative dental materials by human enamel.

The purpose of the study was to determine the uptake in vitro of fluoride from restorative materials by tooth enamel and whether prior etching of the enamel causes a change of uptake. The outermost layer of the labial surface of extracted canines was removed by grinding and the enamel was covered with five different fluoride-containing materials; a silicate, a composite resin, an amalgam, a silicophosphate, and a polycarboxylate luting cement. The material was either removed immediately or after storing the tooth in distilled water. The fluoride content was determined using a sensitive physical method based on the 19F (p,alpha gamma) 16 O reaction. In addition, the fluoride content of enamel after etching for different periods of time and of etched enamel which had been in contact with silicate cement was determined. The mean fluoride content of uncovered interior enamel was 226 parts/10(6). All materials, except the composite, increased clearly the fluoride content of the underlyaing enamal. Etching of interior enamel also increased the fluoride values. No difference could be shown in fluoride uptake from silicate and composite resin between etched and unetched enamel.