Michael T. Flanagan

Effect of canal preparation and residual root filling material on root impedance.

AIM To investigate the effect of root canal preparation and residual root filling material on the impedance characteristics of extracted human roots. METHODOLOGY Thirty extracted, human single-rooted teeth were mounted in a custom-made apparatus that allowed strict temperature control. Impedance measurements of the roots were made with a file acting as the internal electrode, using a frequency response analyser. The measurements were made under three canal conditions: (i) before chemo-mechanical preparation; (ii) after chemo-mechanical preparation; (iii) after root filling removal to re-establish patency (following placement of root filling). The measurements were taken at 0, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10 mm coronal to the apical terminus and also at 0.5 and 1 mm past the apical terminus. Impedance values were viewed using Nyquist plots and comparisons made within each tooth, between measurement points along the length of the canal, as well as under the different canal conditions. Equivalent circuits were modelled for different test conditions. RESULTS The impedance decreased from the coronal to the apical levels in all canal conditions in a characteristic way, with an exaggerated drop at the apical terminus. Impedance decreased after chemo-mechanical preparation, but gave higher values compared with before or after instrumentation, once canal filling had been removed. Equivalent circuits remained consistent at the tested positions within the canal, regardless of canal condition, but the circuit component values changed with the impedance. CONCLUSIONS Impedance was influenced by corono-apical position, chemo-mechanical preparation and residual root canal filling material.

From electronic to opto-electronic biosensors: an engineering view

Abstract Electronic engineering has played a significant role in biosensor design, at the primary transducer level, since the appearance of chemically sensitive field-effect transistors (CHEMFETs) in the seventies. The early promise of CHEMFETs could not easily be carried through into more advanced biosensors, e.g., immunosensors, not have CHEMFETs paved the way for a range of non-sensing bioelectronic devices. However, collaboration of electronic engineers and biosensor designers, at a level more fundamental than simple signal-processing instrumentation, was initiated. Such collaborations have led to the appearance of several very promising opto-electronic biosensors and in the use of micro-electronic fabrication techniques in, otherwise, conventional biosensors. It is now possible to foresee the wide use of integrated micro-optical biosensors in medicine and the possibility that integrated fault-tolerant biosensor arrays may start to address some of the severe problems of using biosensors in process control.

Threshold Concepts in Practice

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A Kalman filter algorithm and monitoring apparatus for at-line control of fractional protein precipitation.

Downstream processing operations are often carried out blind in the process timescale since product monitoring on-line is not common. Knowledge of the location and concentration of the product and key contaminants is complementary to other process information for process development and, if available on-line in conjunction with a suitable model, control. This article sets out to demonstrate a model describing a two-cut fractional protein precipitation process and how this may be used for control of the process to maximize yield in the face of variable process stream conditions. Estimation of the model parameters is achieved by means of data-fitting by least squares and in comparison prediction by a Kalman filter algorithm. A description and error analysis of equipment for at-line monitoring of the soluble product in a pilot plant environment is presented which includes a micro-centrifuge necessary to clarify small volumes of sample prior to analysis. Finally, an account of the successful implementation of this equipment and the Kalman filter algorithm for control at bench scale is given where conditions in the process stream are deliberately disturbed to test the control operation. (c) 1997 John Wiley & Sons, Inc.

An ex vivo investigation of the relationship between apical root impedance and canal anatomy.

AIM To investigate a possible relationship between apical root impedance and canal anatomy. METHODOLOGY Twenty-three roots from human extracted teeth with different apical anatomy (classified by number of apical canal exits) were selected. After impedance measurements, the root canals were stained and the teeth cleared to confirm their division into simple (S - Vertucci type 1; n=12) and complex (C - various Vertucci canal types with multiple exits; n=11) root types. Impedance measurements were taken using a frequency response analyser at seven apico-coronal levels in each root (0.0, 0.5, 1.0, 2.0, 3.0, 4.0, 5.0 mm short of the apical terminus) at 14 frequencies ranging from 1120 to 100,000 Hz. Potential confounding factors were controlled. The impedance characteristics of individual roots were compared with 37 equivalent circuits to select best fit. The association between impedance characteristic (described by the selected equivalent circuit) and canal anatomy (S/C) was investigated using logistic regression with robust standard error to account for multiple data-sets from the same root. RESULTS Canal anatomy had a significant (P= 0.046) effect on the equivalent circuit model. One circuit (model 10) occurred significantly more commonly in the simple canals. The odds of selecting circuit-model-10 were 2.2 times (odds ratio 2.17, 95% confidence interval 1.01-4.63) higher in canals with simple anatomy compared to those with complex anatomy. CONCLUSION Canal anatomy had a significant effect on the equivalent circuit describing its impedance characteristics. It is theoretically possible to use impedance spectroscopy to clinically predict and image apical canal complexities.

Metal phosphate planar waveguides for biosensors.

Hard, impermeable, glassy, metal phosphate films have been fabricated inexpensively by the use of a spin-coating and low-temperature-curing technique. Films that are suitable for use as monomode waveguides in biosensors have been identified through an examination of the optical and chemical properties of films containing Fe, Al, Ga, In, Cr, or V. The refractive index is controlled over the range 1.49-1.78 by varying the film composition. The film thickness is controlled over the range 50-1200 nm by varying the spin speed and the deposition temperature. Films can be patterned by photolithography or by embossing. Input coupling through an embossed grating of 833-nm pitch is demonstrated.

Fluorescence Immunosensors Using Planar Waveguides

This chapter elaborates the fluorescence immunosensors using planar waveguides. Planar and fiber waveguides are competing actively, in the laboratory, as the host transducers of evanescently excited fluorescence immunosensors. In balancing the advantages and disadvantages, the major differences lie in the input coupling efficiency, calibration, and internal referencing, ruggedness, and sample presentation. The development of new materials allowing the inexpensive fabrication of low mode order planar waveguides, their patterning by either conventional processes or by embossing procedures, and their incorporation into evanescent field fluorescence immunoassay is described. One such class of material, spin coated trivalent metal phosphate glassy films, and their use in the fabrication of an hcg immunosensor is described. The use of beam steering, and embossed gratings, and the use of a single internal reflection through a stack of thin film dielectric layers are discussed. A comparison is made of theoretical expectations of the latter with the experimental results obtained for immunoassays using a laser diode at 650 nm.