Use of Electron Microscopy for Investigating Teeth Erosion - Essay Example

Use of Electron Microscopy for Investigating Teeth Erosion Introduction The advent of electron microscopy began with the development of electron optics by Hans Busch (Klein, Buhr and Frase 2012, 298). This soon gave way to the invention of the first electron microscope by Ruska (Klein, Buhr and Frase 2012, 298). Prior to the invention of electron microscope, light microscope using visible light was the only tool available for magnification of microscopic objects. Theoretically, a light microscope’s magnification power is infinite, while its resolving power is limited to 200 nm because of the fixed wavelength of photons in visible light (Carter & Shieh 2009, 135). Due to this limitation, the magnification of extremely minute objects at the microscale and nanoscale by a light microscope is not possible. On the other hand, electron microscopy uses electrons rather than photons. As electrons have very short wavelengths compared to photons, electron microscopes achieve a much higher resolution than what is achievable by a light microscope. In fact, the resolving power of an electron microscope is 1000 times that of a light microscope (Carter & Shieh 2009, 135). Electron microscopy is of two major types – Transmission electron microscopy (TEM) and Scanning electron microscopy (SEM). While both types employ electrons for magnification, they vary in their design and application. Proprieties and Uses of TEM and SEM Transmission Electron Microscope (TEM) The design of TEM is similar to that of a light microscope. Electrons in the electron beam that is focused on the sample are accelerated up to 200 kV before hitting the specimen (Klein, Buhr and Frase 2012, 300). The specimen is of a very thin section. Electromagnetic lenses are used to condense, focus and guide the electron beam onto the specimen. The specimen is treated chemically for increasing the contrast in the magnified image of the specimen (Carter & Shieh 2009, 136). Heavy metals are usually used for staining. Once the electrons hit the specimen, they pass through it and are then collected and projected via electron optics onto a screen (Klein, Buhr and Frase 2012, 300). A magnified image of the object appears on the screen. The image can also be recorded digitally and viewed on a computer when a scintillator converts the hitting electrons into pulses of light that can be detected using a charge-coupled device (Klein, Buhr and Frase 2012, 300). Two-dimensional images are created according to variations in the intensity of electrons hitting the detector (Carter & Shieh 2009, 136). TEM has a large number of applications in innumerable fields ranging from life sciences to material science. TEM has proved to be a priceless tool for studying the ultrastructure of metals (Egerton 2005, 14). In life sciences, it is used for studying bacteria, viruses, and tissues of plants and animals (Egerton 2005, 14). TEM has great applicability in examining the ultrastructure of cell organelles and membranes. Scanning Electron Microscope (SEM) One of the limitations of TEM is that the specimen to be examined has to be made very thin as thicker specimens absorb electrons instead of transmitting them (Egerton 2005, 17). SEM, on the other hand, can be used for bulky specimens. It is used for a detailed study of the surface of the specimen (Carter & Shieh 2009, 136). In a SEM, the electron beam is scanned over the surface of the specimen that is coated with platinum or gold. As the electrons interact with the specimen surface, different types of signals are emitted based on the surface topography. The sample’s surface reflects secondary electrons of low energy and high-energy backscattered electrons are released from below the surface (Carter & Shieh 2009, 137). The signals are collected and the image is processed. A three-dimensional image of the specimen is obtained pixel by pixel. Using SEM, a specimen’s shape, topography and composition can be studied (Klein, Buhr and Frase 2012, 300). Importance of Electron Microscopy in Studying Biological Samples Electron microscopy has revolutionized the field of biology. Almost all cell inclusions and organelles were either discovered or studied in much greater detail through electron microscopy (Bozzola and Russel 1999, 12). Electron microscopy enabled a better understanding of cellular ultrastructure and function, and aided the understanding of “how cellular structure varies in normal, experimental and diseased states”, which further helped in experimental manipulations (Bozzola and Russel 1999, 12). With the help of electron microscopy, not only the structure but also the “chemical makeup and physical properties” of biological specimens can be studied (Bozzola and Russel 1999, 12). It has also enabled the study of cellular interactions and the surface topology of microscopic and nanoscale objects. It is also being used in dentistry to study teeth erosion and microscopic wear. Electron microscopy also has innumerable applications in forensic sciences. Use of Electron Microscopy in Studying Teeth Erosion In human teeth, the process of erosion or toothwear occurs very slowly. Teaford and Tylenda assert, “Traditionally it (toothwear) has needed months or years to be measurable” (1991, 204). They showed that by studying microscopic changes in the teeth’s wear patterns, tooth erosion can be detected and the rate of wear can be measured. By observing and documenting microscopic changes in the rate of wear in certain locations of the teeth, it would be easier to study teeth erosion in varying contexts. Moreover, it would be possible to monitor minute changes in tooth use such as those changes that occur due to various dental procedures. Scanning electron microscopy enables the investigation of microscopic wear on teeth. It gives a fine picture of the dentine and enamel of tooth, and any striations or pits that result from wear (White and Folkens 2005, 412). Dental erosion occurs as a result of exposure to acidic environments. Various methods, such as electrochemical impedance spectroscopy and atomic force microscopy, have been employed to study dental erosion (Castro et al. 2011). Scanning electron microscopy (SEM) and other forms of electron microscopy have proved to be highly efficient in the study of dental erosion. SEM enables a high-resolution study of the surface of teeth, and has a high depth of field (Addy, Embery and Edgar 2000, 107). There is, however, a possibility of shrinkage of tissue because of fluid loss during specimen preparation. Thus, there may be minor changes in morphology upon observation under SEM (Addy, Embery and Edgar 2000, 107). With the help of SEM, many researchers have investigated the effects of various fluids and lifestyle habits on dental erosion. Absi et al. (1992, cited by Addy, Embery and Edgar 2000) investigated the effects of dietary fluids like wines and fruit juices on toothwear using SEM (107). They found that such fluids have etching effects on the tooth’s dentine. In another technique, Millward et al. (1995, cited by Addy, Embery and Edgar 2000) studied castings created by replica impression technique using SEM (107). Simmelink, Nygaard and Scott (1974) studied enamel dissolution in acid and EDTA under both TEM and SEM. Similarly, Grobler, Toit and Basson (1994) studied the effect of honey on dental erosion. Li and Risnes (2004, 77) compared various resins used for embedding teeth during sample preparation using SEM. They found that high quality embedding of teeth is possible using Spurr and Epon, apart from Epo-kwick that enabled faster embedding. This study is significant because sometimes, the sectioning of teeth for microscopic observation requires embedding for ease of handling and protection of enamel. Sample preparation for electron microscopy always requires embedding in a resin prior to grinding or sectioning. Zheng et al. (2009, 1558) successfully studied the erosion of tooth enamel upon exposure to citric acid. They demonstrated the appearance of a honeycomb like structure on prolonged exposure to acid. Erosive substance loss was also demonstrated. Such an observation was possible only because of the use of electron microscopy. Other electron microscopy techniques for studying dental erosion include environmental scanning microscopy that does not involve the preparation of a specimen (Addy, Embery and Edgar 2000, 107). SEM is expensive and requires specific skills for operation and handling. However, it provides very good quantitative and qualitative information of teeth erosion. Of all the electron microscopy techniques availabe, SEM and TEM have been very popular for studying dental erosion. Bibliography Addy, Martin, Graham Embery, and Michael Edgar. Tooth Wear and Sensitivity: Clinical Advances in Restorative Dentistry (Massachusetts: Taylor & Francis, 2000), 107. Bozzola, John, and Lonnie Russell. Electron Microscopy: Principles and Techniques for Biologists (Canada: Jones & Bartlett Learning, 1999), 12. Carter, Matt, and Jennifer Shieh. Guide to Research Techniques in Neuroscience (Massachusetts: Academic Press, 2009), 135-137. Castro, Pollyana Alex Lima, Tiago Ferreira, and Mauro Bertotti. “Scanning Electrochemical Microscopy as a Tool for the Characterization of Dental Erosion.” International Journal of Electrochemistry, doi:10.4061/2011/952470. Egerton, Ray. Physical Principles of Electron Microscopy: An Introduction to Tem, Sem, and Aem (Canada: Springer, 2005),14. Grobler, S, I Toit, and N Basson. “The effect of honey on human tooth enamel in vitro observed by electron microscopy and microhardness measurements.” Archives of Oral Biology, 39, no. 2, 147-153. Klein, Tobias, Egbert Buhr, and Carl Georg Frase. “TSEM: A Review of Scanning Electron Microscopy in Transmission Mode and Its Applications.” Advances in Imaging and Electron Physics, 171, no. 1 (2012): 297-356. Li, Chunfang, and Steinar Risnes. “A comparison of resins for embedding teeth, with special emphasis on adaptation to enamel surface as evaluated by scanning electron microscopy.” Archives of Oral Biology, 49, no. 1, 77—83. Simmelink, J, V Nygaard, and D Scott. “Theory for the sequence of human and rat enamel dissolution by acid and by EDTA: A correlated scanning and transmission electron microscope study.” Archives of Oral Biology, 19, 183-197. Teaford, M, and C Tylenda. “A New Approach to the Study of Tooth Wear.” Journal of Dental Research, 70, no. 3, 204-207. White, Timothy, and Pieter Folkens. The Human Bone Manual (Massachusetts: Academic Press, 2005), 412. Zheng, J, F. Xiao, L.M. Qian, and Z.R. Zhou. “Erosion behavior of human tooth enamel in citric acid solution.” Tribology International, 42, no. 1, 1558–1564. Read More