Quantitative Comparison of Calcium Hydroxide Removal by EndoActivator, Ultrasonic and ProTaper File Agitation Techniques: An in vitro Study

Calcium hydroxide （CH） dressing residues can compromise endodontic sealing. This study aimed to evaluate the amount of remaining CH in root canals after mechanical removal by four groups of irrigation techniques including needle irrigation only, ProTaper file, EndoActivator, and ultrasonic file. Fifteen extracted single-rooted teeth were collected and used for all four groups. The samples were firstly prepared by ProTaper rotary instruments, and then sectioned longitudinally through the long axis of the root canals, followed by final reassembling by wires. CH was kept in the canals for 7 days setting. The removal procedure began with 5 mL of 2.5% sodium hypochlorite （NaOC1） followed by 1 mL of 17% ethylenediaminetetraacetic acid and a final irrigation with 5 mL of 2.5% NaOC1 solution for all groups. No additional agitation of the irrigant was performed in group 1, while agitation for 20 s be- tween irrigants was done with F2 ProTaper rotary file in group 2, EndoActivator with tip size 25/.04 in group 3 and by an ultrasonic file 25/.02 in group 4. The total activation time was 60 s. The roots were then disassembled and captured by digital camera. The ratio of CH coated surface area to the surface area of the whole canal as well as each third of the canal was calculated. The data were statistically ana- lyzed by one-way ANOVA using post hoc Tukey test. Results showed that none of the four techniques could remove all CH. No significant difference was found between EndoActivator and ultrasonic tech- niques. However, they both removed significantly more CH than ProTaper and needle irrigation （P=0.0001）. In conclusion, the sonic and ultrasonic agitation techniques were more effective in removing intracanal medicaments than the ProTaper rotary file and needle irrigation in all thirds of the canal.

Calcium Hydroxide Removal in Curved Root Canals with Apical Transportation In Vitro

Calcium hydroxide（CH） is applied to improve disinfection of root canals in most root canal retreatment. This study aimed to analyze the CH removal efficacy using 7 different root preparing files（K file, pre-curved K file, EndoActivator, Ultrasonic file, pre-curved ultrasonic file, F file and needle irrigation alone） with apical transportation. Standardized models of curved canal with such apical transportation or not were set up before applying CH to root canal for 7 days. Seven techniques described above were used for its removal. Then the roots were disassembled and digital photos were taken. The ratio of residual CH in the overall canal surface was calculated using the image analyzer image pro plus 6.0. The data were analyzed using one-way ANOVA with post hoc Tukey test. Results revealed that CH was effectively removed（P〈0.05） by using all 6 mechanical methods except irrigation alone. In curved root canals with apical transportation, EndoActivator, pre-curved ultrasonic file and F file were found to be more effective in removing CH than the other four file（P〈0.001）, while there was no significant difference among EndoActivator, pre-curved ultrasonic file and F file groups（P〉0.05）. The percentage of residual CH in the canal with apical transportation was higher than that in the canal without apical transportation（P〈0.05）. In conclusion, CH can be hardly removed completely. Canal with apical transportation will result in insufficient CH removal. EndoActivator, pre-curved ultrasonic file and F file are more effective in the curved root canal with apical transportation.

Gypsum crystallization and potassium chloride regeneration by reaction of calcium chloride solution with potassium sulfate solution or solid

Gypsum crystallization along with the simultaneous regeneration of KCl was investigated by the reaction of CaCl2 solution with K2SO4.Well developed sheet structure gypsum crystals were produced when K2SO4 solution was added into the CaCl2 solution by slow titration or in multiple stages over 2-8 h followed by 2 h equilibration.In order to regenerate KCl solution as concentrated as possible,K2SO4 solid was added into the given CaCl2 solution instead of K2SO4 solution,obtaining gypsum crystals with almost the same quality by multistage addition with[SO4 2-]/[Ca 2+]molar ratio no larger than 0.8.However,impurity of K2SO4·CaSO4·H2O was detected by XRD and was further confirmed by SEM-EDS in the produced crystals when the[SO4 2-]/[Ca 2+] ratio increased to 1.1.It is proved that appearance of the double sulfate is attributed to the relatively high concentration of K2SO4.So,it is essential to properly control the[SO4 2-]/[Ca 2+]ratio and make sure[Ca 2+ ]in excess to suppress the solubility of CaSO4 even at the expense of low calcium removal rate.

Effect of Calcium on the Vanadium Extraction from High Calcium Type Stone Coal

The high calcium type stone coal from Hubei province was leached by water and dilute acid separately after being roasted with different dosage of Na Cl. The water leaching rate of vanadium（WLRV） was low and only 26.8% of vanadium can be leached by water when 4% Na Cl was added, but the acid leaching rate of vanadium（ALRV） was relatively high. Calcium in the high calcium type stone coal is greatly superfl uous relative to vanadium, hence, the calcium reacts with vanadium to form Ca（VO3）2, Ca2V2O7 and Ca3（VO4）2orderly during the stone coal roasting process and high temperature is beneficial to the reactions between calcium and vanadium, which was validated by simulated reactions between pure calcium carbonate and vanadium pentoxide. These calcium vanadates are all water insoluble but acid soluble and this causes the low WLRV and relatively high ALRV. After calcium removal by HCl, the WLRV is highly enhanced and reaches about 50% when only 2% Na Cl was added. If the HCl content is too high, the stone coal is easily sintered and the formed glass structure can enwrap vanadium, which leads the WLRV to decline. Single water leaching process is not appropriate to extract vanadium from high calcium type stone coal.

Calcium Hydroxide in Endodontics: An Overview

Background: Calcium hydroxide has been used in dentistry since several decades. It has been used in a number of applications in the field of endodontics such as root resorption, intracanal medicament, and root canal sealers. Although this material exhibits several advantages, it also has some limitations. Objectives: To review the role of calcium hydroxide in the field of endodontics, focusing on its mechanism of action, antimicrobial effects, different applications, cytotoxicity or biocompatibility, and its removal from the root canals. Materials and Methods: An electronic search was done using different databases. Out of 2,664 articles, only 33 articles have been selected to be included in this review because they are directly related to the topic and matched the inclusion criteria of this review: “Language: English” and “Year: 2000-2016”. Results: The antimicrobial effect of calcium hydroxide is controversial. Although some studies supported the effectiveness of calcium hydroxide against some bacteria others reported its limitation against fungal infection. Calcium hydroxide can be used effectively as intracanal medicament, root canal sealer, in weeping canals, for perforation management and root resorption. Conclusions: Despite the limitation of antimicrobial activity of calcium hydroxide, it is used effectively in a number of treatment modalities in endodontics. Due to its biological and therapeutical properties, calcium hydroxide is the material of choice for all pulp therapy. However, when using calcium hydroxide as a dressing material in root canal treatment caution should be taken to prevent the overextension of the paste beyond the tooth apex and avoid the harmful side effects.

Difference in calcium ion precipitation between free and immobilized Halovibrio mesolongii HMY2

Biomineralization has become a research focus in wastewater treatment due to its much lower costs compared to traditional methods.However,the low sodium chloride(NaCl)-tolerance of bacteria limits applications to only water with low NaCl concentrations.Here,calcium ions in hypersaline wastewater(10%NaCl)were precipitated by free and immobilized Halovibrio mesolongii HMY2 bacteria and the differences between them were determined.The results show that calcium ions can be transformed into several types of calcium carbonate with a range of morphologies,abundant organic functional groups(C-H,C-O-C,C=O,etc),protein secondary structures(β-sheet,α-helix,3_(10)helix,andβ-turn),P=O and S-H indicated by P2p and S2p,and more negativeδ^(13)C_(PDB)(‰)values(-16.8‰to-18.4‰).The optimal conditions for the immobilized bacteria were determined by doing experiments with six factors and five levels and using response surface method.Under the action of two groups of immobilized bacteria prepared under the optimal conditions,by the 10^(th)day,Ca^(2+)ion precipitation ratios had increased to 79%-89%and 80%-88%with changes in magnesium ion cencentrations.Magnesium ions can significantly inhibit the calcium ion precipitation,and this inhibitory effect can be decreased under the action of immobilized bacteria.Minerals induced by immobilized bacteria always aggregated together,had higher contents of Mg,P,and S,lower stable carbon isotope values and less well-developed protein secondary structures.This study demonstrates an economic and eco-friendly method for recycling calcium ions in hypersaline wastewater,providing an easy step in the process of desalination.

Enrichment of Cd^(2＋) from water with a calcium alginate hydrogel filtration membrane

A new method was developed for effective enrichment of Cd2+ ions from water with a calcium alginate(CaAlg) hydrogel filtration membrane. First, the CaAlg hydrogel filtration membrane was prepared without a pore-forming agent. This membrane was used to remove Cd^(2+) via ion exchange with Ca^(2+), and the Cd^(2+) was preserved in the CaAlg hydrogel. Then, the CaAlg hydrogel containing Cd^(2+) was soaked in a sodium citrate solution, and the hydrogel was fully dissolved. The removal rate of the CaAlg filtration membrane reached almost 100% within 120 min when the Cd^(2+) concentration was under 1 mg/L. Factors affecting the removal rate were investigated, such as NaAlg concentration, operating pressure, operating time and the initial concentration of Cd^(2+). The effects of initial Cd^(2+) concentration, pressure and filtration time on the enrichment factor were also investigated. The results show that the enrichment factor reached 87.3 when the pressure was 0.18 MPa and the filtration time was 240 min. Different enrichment factors could be achieved by adjusting the operating pressure and filtration time.