Fluorescence in the tandem scanning microscope

Clinical applicability of in vivo fluorescence confocal microscopy for noninvasive diagnosis and therapeutic monitoring of nonmelanoma skin cancer

Excisional biopsies and routine histology remains the gold standard for the histomorphologic evaluation of normal and diseased skin. However, there is increasing interest in the development of noninvasive optical technologies for evaluation, diagnosis, and monitoring of skin disease in vivo. Fluorescent confocal microscopy is an innovative optical technology that has previously been used for morphologic evaluation of live human tissue. We evaluate the clinical applicability of a fluorescent confocal laser scanning microscope (FLSM) for a systematic evaluation of normal and diseased skin in vivo and in correlation with routine histology. A total of 40 patients were recruited to participate in the study. Skin sites of 10 participants with no prior history of skin disease served as controls and to evaluate topographic variations of normal skin in vivo. Thirty patients with a suspected diagnosis of nonmelanoma skin cancer were evaluated, whereby FLSM features of actinic keratoses (AK) and basal cell carcinoma (BCC) were recorded in an observational analysis. Selected BCCs were monitored for their skin response to topical therapy using Imiquimod as an immune-response modifier. A commercially available fluorescence microscope (OptiScan Ltd., Melbourne, Australia) was used to carry out all FLSM evaluations. Common FLSM features to AK and BCC included nuclear pleomorphism at the level of the granular and spinous layer and increased vascularity in the superficial dermal compartment. Even though the presence of superficial disruption and mere atypia of epidermal keratinocytes was more indicative of AK, the nesting of atypical basal cells, increased blood vessel tortuosity, and nuclear polarization were more typical for BCC. All diagnoses were confirmed by histology. FLSM allowed a monitoring of the local immune response following therapy with Imiquimod and demonstrated a continuous normalization of diseased skin on repeated evaluations over time. This study illustrates potential applications of FLSM in clinical dermatology for the evaluation of dynamic skin conditions and monitoring of cutaneous response to noninvasive therapies. The findings are of preliminary nature and warrant further investigations in the future.

A novel real-time confocal imaging technique for examining host–implant interfacial shear failure patterns

In clinical practice, implant failure usually occurs at the biomaterial-host tissue interface, typically involving both biomechanical and biochemical mechanisms. By definition, any new 'bioactive' material will bond to living bone but, prior to clinical use, interface formation, performance, longevity and failure pattern characterizations are necessary. The common missing link in many biomaterial interface investigations is imaging at the point of presumed loaded failure. The novel real-time confocal technique described here allows bond strength, formation rate, longevity and bone-material interface failure pattern characterization for a wide range of biomaterials capable of forming tissue interfaces, in one real-time imaged microshear stress process, conducted using imaging frame matched load/displacement data acquisition under relatively normal near in vivo environmental conditions. The technique, validated by post-failure scanning electron microscopy imaging, revealed that more slowly reacting melt-derived 45S5 glass materials produced stronger and more stable long-term interfaces than faster reacting microporous bioactive sol-gel glasses.

Penetration of an antibacterial dentine-bonding system into demineralized human root dentine in vitro

In this study, the penetration of three proprietary dentine-bonding agents (Prime & Bond 2.1, Single Bond, Liner Bond 2) and experimental dentine-bonding systems incorporating an antibacterial monomer, 12-methacryloyloxydodecylpyridinium bromide (MDPB), into artificial root caries lesions was evaluated, and the bactericidal activity of each material against Streptococcus mutans or Lactobacillus casei impregnated into demineralized dentine blocks was assessed. All of the commercial dentine-bonding agents were capable of penetrating into the artificial carious lesions to more than 150 microm. The depth of penetration of the experimental systems, which were based on Liner Bond 2, was not significantly different from that of their parent product. Liner Bond 2 primer exhibited the greatest bactericidal effects among the three proprietary dentine-bonding agents tested. Bactericidal activities of experimental primers containing MDPB were greater than those of any other products, and the application of 4% MDPB-containing primer resulted in complete killing of bacteria in demineralized dentine. The results indicate that the penetration of dentine-bonding agents into extensively demineralized root dentine is possible in vitro, and the experimental dentine-bonding systems containing the antibacterial monomer MDPB are capable of killing bacteria within demineralized dentine. This could be of benefit when managing root caries lesions.

Biocompatibility tests on a novel glass-ceramic system

The aim of this study was to look at the bone bonding potential of six formulations of a novel glass-ceramic system. Cylinders of the ceramics were implanted in rabbit tibiae for 4 and 7 weeks. Histological tests, both quantitative and qualitative, as well as push-out tests, were carried out during the bonding assessment. Bone growth was quite prolific, even at 4 weeks, as evidenced by growth up to and along the implant surfaces. The interfacial shear strengths compared well with other biomaterials in use as endosseous implants. Therefore it seems pertinent to pursue further long-term experimentation with this material.

Interfacial characteristics of resin-modified glass-ionomer materials: a study on fluid permeability using confocal fluorescence microscopy

The tooth interface with resin-modified glass-ionomer cements (RM GICs) is poorly understood. This study examined the interface, especially with dentin. Cervical cavities in extracted teeth were restored with Fuji II LC, Vitremer, Photac-Fil, or a conventional GIC, Fuji Cap II. Fluorescent dye was placed in the pulp chambers for 3 hrs before the specimens were sectioned. Examination of the tooth/material interface with a confocal microscope showed that dye uptake by the restoration varied among materials. A "structureless", non-particulate, highly-stained layer of GIC was observed next to dentin in Fuji II LC. This layer varied in width, was prominent where the dentin tubules were cut "end-on" and in areas closer to the pulp, and was not seen adjacent to enamel. Vitremer showed minimal dye uptake, and the "structureless" layer was barely discernible. Photac-Fil showed more uniform uptake and absence of this layer. Cracking of enamel was also noted with these materials. The conventional GIC did not show any dye uptake, presence of a "structureless" layer, or enamel cracking. We elucidated the potential mechanisms involved in the formation of a "structureless" interfacial layer in Fuji II LC by studying the variables of cavity design, surface pre-treatment, water content of the tooth, time for it to develop, early finishing, and coating of the restoration. This layer, the "absorption layer", is probably related to water flux within the maturing cement, depending on environmental moisture changes and communication with the pulp in a wet tooth. The "micropermeability model" was useful in this study of the interfacial characteristics of RM GICs.

Laser sources in direct-view-scanning, tandem-scanning, or nipkow-disk-scanning confocal microscopy

Laser sources offer a potentially low-cost means of improving thelight throughput in tandem-scanning confocal microscopy because oftheir high beam directionality. We measure and compare the opticalsectioning characteristics of the tandem-scanning microscope (TSM)employing (i) the traditional choice of incoherent light from a Xearc lamp and (ii) a cited alternative-coherent light from a He-Nelaser source. In general the laser source is found to result inaxial responses with pronounced sidelobes, the sizes and locations ofwhich are extremely sensitive to the alignment of the pinholearray. The implications of these results for practical TSM systemsare discussed.

Confocal microscopy as a tool for the investigation of the anterior part of the eye

In recent years, confocal microscopy has become a powerful tool for examining microscopic structures in the living eye. The decisive advantage of this technique is that it permits the investigation of optical sections of relatively thick (> 10 microns) specimens. Because confocal microscopy suppresses the out-of-focus blur, sharp three-dimensional images with excellent resolution can be obtained. Confocal microscopy is therefore able to provide more information than the classic methods--i.e., specular microscopy and slit-lamp biomicroscopy. This paper reviews recent applications of confocal microscopy in three fields of ophthalmology: the observation of the anatomy of the anterior parts of the eye, the investigation of these structures after local administration of drugs and, finally, the use of this technique for the diagnosis of infectious ocular diseases.

4D confocal microscopy for visualisation of bone remodelling

Until recently it was very time consuming and difficult to make three-dimensional (3D) images of newly formed bone. With the advent of confocal technologies and increased computer power, 3D imaging is greatly facilitated. In this paper we demonstrate that enhanced confocal visualisation of newly formed bone is possible when bone is labelled in vivo sequentially with two osteotropic markers (xylenol orange and tetracycline). Computer-assisted reconstruction of the confocal optical sections was achieved through the use of the CONVEX Application Visualisation System (AVS). The computerised image data provides the researcher with ample flexibility in displaying the results. It was found that CSLM combined with AVS is excellent for visualising the remodelling process in three and four dimensions, in which the fourth dimension is time. With this approach visualised bone remodelling has become possible in a manner not easily achieved by other techniques.

3D computed X-ray tomography of human cancellous bone at 8 microns spatial and 10(-4) energy resolution

Human cancellous bone was imaged and its absorptive density accurately measured in three dimensions (3D), nondestructively and at high spatial resolution by means of computerized microtomography (microCT). Essential for achieving the resolution and accuracy was the use of monoenergetic synchrotron radiation (SR) which avoided beam hardening effects, secured excellent contrast conditions including the option of energy-modulated contrast, and yet provided high intensity. To verify the resolution, we selected objects of approximately 8 micron size that could be observed on tomograms and correlated them in a unique manner to their counter images seen in histological sections prepared from the same specimen volume. Thus we have shown that the resolution expected from the voxel size of 8 microns used in the microCT process is in effect also attained in our results. In achieving the present results no X-ray-optical magnification was used. From microCT studies of composites (Bonse et al., X-ray tomographic microscopy (XTM) applied to carbon-fibre composites. In: Materlik G, ed. HASYLAB Jahresbericht 1990. Hamburg: DESY, 1990; 567-568) we know that by including X-ray magnification a resolution below 2 microns is obtained. Therefore, with foreseeable development of our microCT method, the 3D and nondestructive investigation of structures in mineralized bone on the 2 micron level is feasible. For example, it should be possible to study tomographically the 3D distribution and amount of osteoclastic resorption in the surrounding bone structure.

Histochemical and confocal laser scanning microscopy study of the bone-titanium interface: an experimental study in rabbits

The aim of our study was an analysis of the presence of an unmineralized bone matrix between mineralized bone and titanium screws in rabbit tibiae. A microscopical analysis, using a histochemical technique, was performed on the titanium-bone interface of commercially pure titanium implants placed in rabbit tibiae and harvested after 2 months. Thin ground sections of the specimens were prepared by the cutting-grinding system and stained using the von Kossa method for calcium salts and basic fuchsin for osteoid. The microscopical and morphometrical evaluation showed that bone covered about 40% (+/- 7.5%) of all implants. Mineralized bone was, however, in direct contact with the titanium surface on only about 10% of the implant, while in the remaining 30% the mineralized bone was separated from the implant by an unmineralized tissue. This basophilic, probably osteoid matrix, could represent the medium that allows the biochemical exchanges between bone and cells under the influence of the implant. A small, optically translucent gap (1-5 microns), probably an artifact, was present in some areas between titanium and bone. Confocal laser scanning microscopy (CLSM) in a fluorescent mode showed the presence at the interface of a fluorescent material. Results from our study showed that light microscopy of thin ground sections allowed a good analysis of the real nature of the titanium-bone interface. Moreover, this double staining technique showed the presence of an unmineralized bone matrix at most of the bone-titanium interface.

Bone ingrowth into hydroxyapatite coating: a light microscopy and laser scanning microscopy study

The authors present a description of the presence of organic material inside the hydroxyapatite (HA) coating of Calcitek implants inserted in rabbit tibia. Light microscopy showed that in all specimens a granular basophilic material which was not mineralized was present inside the thickness of the coatings. In two specimens out of 40, a bone-like substance was observed in some areas of the coating, at a distance from the interface. Laser scanning microscopy showed in all specimens an autofluorescence of osteocytes, osteoblasts, of the interface, and inside the coating. The presence of bone could either show an ability of the coating to serve as a scaffold for the newly forming osseous tissue or be a sign of an initial degradation of the HA.

The three-dimensional architecture of the mitotic spindle, analyzed by confocal fluorescence and electron microscopy

Fluorescence microscopy techniques have become important tools in mitosis research. The well-known disadvantages of fluorescence microscopy, rapid bleaching, phototoxicity and out-of-focus contributions blurring the in-focus image are obstacles which still need to be overcome. Confocal fluorescence microscopy has the potential to improve our capabilities of analyzing cells, because of its excellent depth-discrimination and image processing power. We have been using a confocal fluorescence microscope for the study of the mechanism of poleward chromosome movement, and report here 1) a cell preparation technique, which allows labeling of fixation sensitive spindle antigens with acceptable microtubule preservation; 2) the use of image processing methods to represent the spatial distribution of various labeled elements in pseudocolour; 3) a novel immunoelectron microscopic labeling method for microtubules, which allows the visualization of their distribution in semithin sections at low magnification; and 4) a first attempt to study microtubule dynamics with a confocal fluorescence microscope in living cells, microinjected with rhodamine labeled tubulin. Our experience indicates that confocal fluorescence microscopy provides real advantages for the study of spatial colocalization of antigens in the mitotic spindle. It does not, however, overcome the basic limits of resolution of the light microscope. Therefore, it has been necessary to use an electron microscopic method. Our preliminary results with living cells show that it is possible to visualize the entire microtubule network in stereo, but that the sensitivity of the instrument is still too low to perform dynamic time studies. It will be worthwhile to further develop this new type of optical instrumentation and explore its usefulness on both fixed and living cells.

Three-dimensional reconstruction of the rat brain cortical microcirculation in vivo

We used confocal laser scanning microscopy (CLSM) to investigate the morphology and three-dimensional relationships of the microcirculation of the superficial layers of the rat brain cortex in vivo. In anesthetized rats equipped with a closed cranial window (dura mater removed), after i.v. injection of 3 mg/100 g of body weight of fluorescein in 0.5 ml of saline, serial optical sections of the brain cortex intraparenchymal microcirculation were taken. Excitation was at a wavelength of 488 nm (argon laser), and emission was collected above 515 nm. CLSM provided images of brain vessels with sufficient signal-to-noise ratio for three-dimensional reconstructions down to a depth of 250 microns beneath the surface of the brain. Compared to conventional fluorescence microscopy, CLSM has a much higher axial resolution and higher depth of penetration. Laser light-induced intravascular aggregates, irregularities of erythrocyte flow, or microvascular occlusions ("light and dye injury") were not apparent in the current experimental paradigm. CLSM is a promising new tool for in vivo visualization of the cerebral microcirculation. Future studies have to characterize the potential damage to the tissue dye mechanisms.

A confocal microscopic study of some factors affecting the adaptation of a light-cured glass ionomer to tooth tissue

Vitrabond consists of a conventional glass ionomer, in conjunction with a light-curing resin and hydroxy-ethylmethacrylate. This study, which used a tandem scanning reflected light microscope for confocal imaging, looked at factors affecting the adaptation of this material to tooth tissue. Wedge-shaped cervical cavities were cut and restored in three ways: (1) Vitrabond was applied as a thin sub-base and either extended onto the enamel margin or kept clear of it. P50 resin composite was then placed, following phosphoric-acid-etching of the enamel margins. (2) The dentin surfaces were conditioned with Scotchprep (maleic acid), then with the Vitrabond, the enamel was etched, and the Scotchbond 2 adhesive applied prior to addition of the P50. (3) Vitrabond was applied alone in bulk, with and without Scotchprep acid-dentin conditioning with a 1:1 (normal) and 3:1 powder:liquid ratio (P:L). Adaptation of the Vitrabond was excellent when maleic acid was used for conditioning of the dentin. When the Vitrabond was used with P50 but extended onto the enamel, the enamel margin occasionally failed. Enamel invariably fractured when the Vitrabond was used alone in bulk. An increase in the P:L ratio decreased contraction gaps when the dentin was not conditioned, but Vitrabond failed cohesively when the dentin was conditioned. The Vitrabond was very susceptible to shrinkage on dehydration. This study suggests that Vitrabond should only be applied to dentin in thin layers, should not be extended onto enamel margins, and should not be allowed to dehydrate. Maleic acid conditioning of the dentin improved adaptation.