The purpose of this study was to evaluate the antibacterial efficacy of an intracanal medication composed of calcium hydroxide with 2% chlorhexidine. Dentin from 24 bovine incisors was used. The incisors were made into standardized cylindrical segments of dentin and infected with Enterococcus faecalis. They were then treated with an intracanal paste composed of calcium hydroxide and sterile water or an intracanal paste composed of calcium hydroxide and 2% chlorhexidine for 1 week. Dentin shavings were collected, suspended in solution, and spread on brain-heart infusion agar. After incubation, colony-forming units were enumerated. The amount of bacteria per mg of dentin was determined. The calcium hydroxide paste with 2% chlorhexidine was significantly more effective at killing E. faecalis in the dentinal tubules than calcium hydroxide with water.One of the goals of endodontic therapy is the reduction or elimination of bacteria and their by-products from the root canal system. Proper cleaning, shaping, and irrigation have been shown to significantly reduce and sometimes eliminate bacteria from canals (1). The use of intracanal medications to disinfect the root canal system has been advocated (2). Reasons for the use of intracanal medications are: (a) to eliminate bacteria in the root canal; (b) to prevent bacterial proliferation between appointments; and (c) to act as a physiochemical barrier, preventing root canal reinfection and nutrient supply to the remaining bacteria (3). Calcium hydroxide has been the intracanal medication of choice (4). Calcium hydroxide has been demonstrated to improve dissolution of the pulp tissue by sodium hypochlorite (NaOCl) and provide antimicrobial activity (2, 5). However, the antimicrobial activity of calcium hydroxide seems dependent upon direct contact with bacteria (4). Haapasalo and Ørstavik (6) have demonstrated that it is not effective in eliminating bacteria from dentinal tubules.Recently, chlorhexidine has been shown to be an effective antimicrobial endodontic irrigant (7,8). However, chlorhexidine does not have the ability to dissolve tissue, and gels containing chlorhexidine can be difficult to remove from the canal space.White et al. (9) and Leonardo et al. (10) demonstrated the property of substantivity for chlorhexidine. They demonstrated that chlorhexidine irrigation continued to prevent reinfection of dentin for up to 72 h. Several investigators have demonstrated the antimicrobial effectiveness of chlorhexidine gel or sustained release vinyl ribbons containing chlorhexidine as intracanal medications (11,12). The purpose of this investigation was to evaluate a paste made of calcium hydroxide mixed with 2% chlorhexidine for antimicrobial efficacy against Enterococcus faecalis in the dentinal tubules of bovine incisors. MATERIALS AND METHODSTwenty-four bovine incisors were extracted and prepared according to the methods of Haapasalo and Ørstavik (6) as modified by Lenet et al. (12). The incisors were placed in 5.25% NaOCl after extraction to remove any soft tissue. T...

At the Advanced Light Source an undulator beamline, with an energy range from 6 to 30 eV, has been constructed for chemical dynamics experiments. The higher harmonics of the undulator are suppressed by a novel, windowless gas filter. In one branchline high-flux, 2% bandwidth radiation is directed toward an end station for photodissociation and crossed molecular-beam experiments. A photon flux of 10 16 photon/s has been measured at this end station. In a second branchline a 6.65 m off-plane Eagle monochromator delivers narrow bandwidth radiation to an end station for photoionoization studies. At this second end station a peak flux of 3 ϫ 10 11 was observed for 25 000 resolving power. This monochromator has achieved a resolving power of 70 000 using a 4800 grooves/mm grating, one of the highest resolving powers obtained by a vacuum ultraviolet monochromator.

This work is focused on developing a fast gas chromatograph, time-of-flight mass spectrometer (GC/TOFMS) for man-portable field use. The goal is to achieve a total system solution for meeting performance, size, weight, power, cost, and ruggedness requirements for a laboratory in the field. The core technology will also be adaptable to specific applications including real-time point detection for hazardous chemical releases (e.g., chemical weapons), for biological agent signature identification, and for mobile monitoring platforms (e.g., air, ship, truck). Previously we presented results of a feasibility demonstration for a 30-lb field-portable TOFMS system. In this work we present recent progress in integrating a low-power, high-speed GC and show the capability for accurately recording fast GC transients for targeted compound detection using a quadrupole ion trap, time-of-flight instrument (QitTof). n this paper we review our progress toward developing a field-portable, high performance mass spectrometer (MS) system with applications to a variety of fast screening requirements. Previously we reported on a 30-lb class photoionization, quadrupole ion trap, time-of-flight system (PI/QitTof) [1]. More recently we have been developing a low-power, high-speed gas chromatography (GC) sampling system for the QitTof mass analyzer. The intent is to develop a compact system that can perform direct, real-time air and liquid sampling of targeted compounds in complex mixtures in a GC-bypass mode. If a targeted compound is detected during fast screening, the sample can then be subjected to GC/MS analysis for confirmation. This mode of operation achieves high-throughput molecular detection, while affording the option of confirming the results by GC/MS. We present here an overview of our field-portable MS program and then discuss future plans and directions.The focus of this instrumentation development is to develop a "laboratory-in-the-field" capability to conduct general environmental assessments [2] and a "rapid-response monitor" to quickly and accurately detect toxic compounds, such as chemical agents, resulting from leaks or releases. Other military applications include military force protection and chemical demilitarization. Civilian applications include high-profile event security, emergency first responder protection, and hazardous materials investigations. These applications require systems that can detect in real-time (1-10 s) a host of target compounds at ultralow concentrations (e.g., 1-100 ppb air sampling, 10 -100 pg residue) in the presence of a complex matrix that would otherwise obscure signals of interest due to overlapping signal.Several manufacturers have developed products for field applications with GC capabilities (e.g., Bruker's MEM line [3], Varian's Saturn Air); however, these are not man-portable. Viking Instruments, recently acquired by Bruker, offers a portable GC/MS (SpectraTrak) billed as a "real-time" monitor for toxic air, water, and soil pollutants; however, its portability is limited by weight...

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