Galvanic effect of pyrite on arsenic release from arsenopyrite dissolution in oxygen-depleted and oxygen-saturated circumneutral solutions.

Arsenopyrite (FeAsS), the most common arsenic-bearing mineral, is usually found associated with pyrite (FeS2) in gold mining tailings. This work examined the galvanic effect of FeS2 on As release from FeAsS oxidation in circumneutral media under oxygen-depleted and oxygen-saturated conditions. The oxidation experiments were conducted with a flow-through reactor in the absence of FeS2 particles and in the presence of different contents of this sulfide. The results indicated that the permanent, physical contact between FeAsS and FeS2 particles causes an increase in the accumulated As release, mainly under O2-saturated conditions. At 30% wt. FeS2, the increases relatively to FeS2-free conditions were 82% and 117% in O2-depleted and O2-saturated solutions, respectively. At steady-state, the As release rates increased from (4.9 ± 0.5)× 10-4 µmol m-2 s-1 (0% wt. FeS2) to (1.1-1.9)× 10-3 µmol m-2 s-1 (5-30% wt. FeS2) under O2-saturated conditions. Analysis of FeAsS samples after oxidation revealed oxidized particles partially or entirely covered by precipitates with different sizes, shapes and compositions (e.g., As-S-bearing ferrihydrite, elemental sulfur, and As-O phases). A fine (3-4 nm thick) amorphous layer of S-As-bearing ferric oxy-hydroxide was also identified on oxidized FeAsS, with Fe(III) and As(III) species.

Ex vivo evaluation of the effects of several root canal preparation techniques and irrigation regimens on a mixed microbial infection.

AIM: To assess the ex vivo effectiveness of the alternated use of 1% NaOCl and 15% citric acid in association with two instrumentation techniques for the disinfection of root canals infected with Enterococcus faecalis and Candida albicans. METHODOLOGY: Eighty human mandibular premolars with straight, oval root canals standardized to 15 mm in length were infected with a mixed culture of E. faecalis and C. albicans for 28 days. Five other teeth were used as controls and were neither contaminated nor instrumented. Specimens were divided into two groups (n = 40), according to whether the canal preparation technique used manual (K-type) or rotary (Protaper Universal) instruments. These groups were further divided into four subgroups (n = 10) according to the irrigation solution used: saline, 1% NaOCl, 1% NaOCl with alternated use of 15% citric acid and 5.25% NaOCl. Root canals were prepared with a crown-down technique until a size 50 K-file or with rotary preparation until an F5 instrument. Microbiological sampling was performed before (S1) and after (S2) the chemomechanical preparation, using sterile paper points. The specimens were split, and 0.02 g of dentine chips was collected from the root thirds to verify the presence of microorganisms in root canal walls. RESULTS: Saline and 1% NaOCl were less effective in reducing microorganisms compared with 1% NaOCl with alternated use of 15% citric acid or 5.25% NaOCl alone (P < 0.05). Both manual and rotary preparations significantly reduced microorganisms regardless of the irrigation solution used (P < 0.05). However, there was no significant difference between the canal preparation techniques (P > 0.05). CONCLUSIONS: Irrigation with 5.25% NaOCl and 1% NaOCl alternated with 15% citric acid reduced microorganisms in infected root canals significantly more than saline and 1% NaOCl.

Determination of pulp vitality in vivo with pulse oximetry.

AIM: To evaluate the use of pulse oximetry as a test for pulp vitality, by comparing in the same patient, the levels of oxygen saturation of the index finger and of the maxillary central incisor and canine teeth without clinically detectable pulp inflammation. METHODOLOGY: Seventeen male and female patients aged between 26 and 38 years participated and a total of 32 maxillary central incisor and 32 canine teeth were analysed. Selection criteria required the teeth to have healthy crowns, or with restorations no more than 2 mm in diameter and no clinical and radiographical signs or symptoms of pulp or periapical inflammatory changes. The negative control group consisted of 10 root filled teeth. Measurements were first taken from the index finger of patients. Their teeth were then subjected to a thermal test with refrigerant gas and then to a vitality test with pulse oximetry. Data were analysed by Pearson's and paired t-tests. RESULTS: There were no significant statistical correlations between blood oxygen levels in the index finger and in the teeth of the patient (P > 0.05). There was a statistically significant difference in the oxygen levels between the two tooth groups studied and the index finger (P