Introduction
The knowledge of radiation physics prepares the foundation for the use of modern dental imaging methods, helping the dentist to see structures that lie under the soft tissue. In Dentistry, this science is utilized by certain use of X-rays to identify cavities, measure the bone levels, determine the interference of impacted teeth, and plan therapy. A knowledge of the behavior of radiation increases the understanding of both the student and patient of the great power and safety that can be achieved when dental imaging is used safely and effectively. The use of these principles is an every day occurrence in the field of oral radiology. to help increase diagnostic accuracy with the least amount of radiation exposure possible every day. To get more background on the discipline, read this overview of oral radiology. It explains, in a structured and easy-to-understand manner, how radiation is generated, how it will interact with the human body, and how finally an image is produced. It also explains why the conventional dental radiography is now closely controlled and is safe for use in routine clinical practice.
Basics of Radiation Physics in Dentistry
In dentistry, radiation referred to represents a type of energy, like visible light but possessing greatly higher energy levels and wavelengths of much shorter proportions. This high energy provides the power necessary to create contrast between different structures in the mouth, as well as penetrate soft tissue. Roughly explained, radiation can be thought of as a wave and also as particles given off that are called photons; photons have enough energy to penetrate the body at different levels according to tissue density. The soft tissue, bone, dentin and enamel of the teeth each respond differently to these photons, giving rise to the differences in presentation observed on radiographs. More dense (heavier) structures absorb more radiation to appear lighter in the image and less dense (lighter) structures let more through to appear darker. Students must grasp this interaction when studying dental imaging because it is what allows the likes of X-rays to be such a powerful tool to differentiate normal from abnormal structures.
How dental x-ray machines work.
Dental X-ray machines are designed to produce controlled bursts of radiation only when they are activated or in use to ensure that the amounts of radiation you will be exposed to are limited and deliberate. It starts in a vacuum-tube whose only contents are a cathode and an anode. When current flows through the cell, the cathodes emit electrons and under the influence of a strong electric field, the electrons move rapidly towards the anode. When they collide with other materials, their kinetic energy instigates a process known as Bremsstrahlung radiation in which they emit X-ray photons as well as the characteristic radiation due to electron shell transitions. All these happen within milliseconds, which accounts for the speediness and efficiency of dental X-rays. There are also filters and collimators to control the beam and eliminate any radiation from it that would not contribute to producing an image, and may reduce the amount of radiation dose that would otherwise be given to the patient. Thus only radiation of value to the patient reaches it and image quality and safety are maintained in this controlled production.
Where is the X-ray Tube?
Radiation is carefully controlled within the X-ray tube to maximize the production of radiation. In a vacuum, electrons are not hindered by air molecules, and can move freely towards the anode target, which is usually tungsten, since it has a high atomic number and is heat resistant. The collision of the electrons with the tungsten target causes most of the energy of the electrons to be transferred as heat, and a smaller fraction is transferred as x-ray photons. This is important since the heat generated can cause damage to the tube, hence the need for cooling systems in X-ray tubes. Also crucial is the angle of the anode, for it is important to concentrate the beam in a direction that is useful. The technical design provides stability and predictability of radiation output for consistent diagnostic imaging in dental practice.
How do X-rays not stop a human tissue?
X-ray photons, once produced, pass through the patient’s brain and interact more or less with various brain parts and tissues. Absorption and scattering is the major interaction that dominates this interaction. Higher mineral densities, such as enamel and cortical bone, will absorb more x-rays, and softer tissue, such as a gum or cheer, will pass more x-rays. The differing proportions of the absorption is why a radiographic image has contrast. This phenomenon is called differential attenuation, and it is the principle behind all radiography imaging processes. Some photons are completely absorbed while others do not interact and others are scattered in different directions. The photons that arrive at the detector form the image. When students learn this process they can better appreciate the importance of positioning, exposure setting and the composition of the tissues on the final diagnostic image.
The ability to recognize the difference between the various structures of the mouth is due to Differential Absorption in x-rays of the teeth. A decayed area of a tooth, for instance, looks darker because the density of the decayed enamel is less than that of healthy enamel, and absorbs fewer photons. In the same way, when bone loss occurs with periodontal disease, the X-rays show up as darker areas because the bones are softer and do not absorb the X-rays well. This contrast is very important for diagnosis as it can reveal conditions which are not discernable in the clinical examination. This balance of penetration/absorption has to be carefully controlled; under penetration can result in poor contrast; over penetration can result in under-exposure. It is, therefore, important to select the correct exposure settings as part of the radiographic technique in the dental practice.
How Images Are Formed (Film & Digital)
Dental radiographic images are created when X-ray photons are delivered to a detector (film or a digital sensor). In a film-based system, the X-rays cause a light-sensitive emulsion containing silver halide crystals to develop. These crystals are subject to chemical change when irradiated which is revealed on processing in developer and fixer. In digital radiography, however, charge-couple devices (CCD) or complementary metal-oxide semiconductor (CMOS) devices convert the X-ray energy to electronic signals. The signals are then controlled by software that creates a visual picture on a computer screen. The advantages of a digital system include less radiation to patients, immediate availability of patient images, greater convenience in storage and other attributes. In any case, the final image is all of the shadows caused by the different degree of absorption of the X-rays as they move through the body, resulting in a shadow pattern of the inside structure.
Civil Protection and Radiation Protection
To protect patients from unnecessary radiation exposure and maximize useful diagnostically, strict principles govern radiation safety in dentistry. The ALARA concept (As Low As Reasonably Achievable) is a key aspect of the practise of radiography that allows exposure to be minimised as much as possible whilst maintaining a reliable and accurate diagnosis. Protective measures include lead pieces of apron, thyroid collars and need for lower exposure times with digital sensors. Furthermore, x-ray machines include the use of filters to reduce the amount of low energy photons that pass through the machine because they would not be useful in the image but would contribute to the tissue dose. The operators also adhere to safety practices, including proper distances from the radiation source and exposure control settings. The equipment is regularly calibrated and follows regulatory procedures for safety. Together, these will render dental radiography one of the most controlled modes of imaging in medicine.
Dental X-Rays are safe, explain why.
The radiation dose in dental X-rays is very small and is well controlled, making them safe. The amount of radiation received by the patient at a dentist’s office at a single appointment is roughly equal to background radiation received in a short time span throughout the day. Also, over the years, developments in technology have contributed to a marked reduction in levels of exposure and an increase in image quality. Digital radiography, in part, has been responsible for this decrease in radiation, because it is the most effective way to produce images for diagnosis with only a fraction of the radiation as conventional film radiography. The carcinogenic risk posed by dental X-rays is thus very low in comparison to the diagnostic benefit, such as, early detection of disease, prevention of dental complications and better prognosis of the dental disease. The advantages are clearly numerous, significantly outweighing the risks if the exposure is owed in a logical and scientifically designed way, as carried out by the well-trained personnel.
Conclusion
The Physics of radiation in dentistry offers definite answers to questions on how and how much X-rays are formed and how they affect biological tissues and how they are converted to diagnostic images. Students can be more appreciative of the technical and scientific bases of dental imaging and patients can feel confident that dental imaging procedures are safe. Controlling the generation of X-rays, advanced safety measures and the use of technology have made dental imaging efficient and safe. These principles are fundamental for the proper diagnosis and treatment planning in Oral Radiology. In total, dental x-rays are a great illustration of the interdisciplinary and intelligence-driven application of physics and medicine to better health outcomes in a safe and reliable way.
