Veterinary Dentistry Radiography PDF 2023

Dentistry for the General Practitioner VetCPD 2023 Rachel Perry BSc, BVM&S, MANZCVS (Small Animal Dentistry & Oral Surgery), PG Cert (VetEd), FHEA, Dipl.EVDC, MRCVS EBVS ® European Veterinary Specialist, Ve...

Dentistry for the General Practitioner VetCPD 2023 Rachel Perry BSc, BVM&S, MANZCVS (Small Animal Dentistry & Oral Surgery), PG Cert (VetEd), FHEA, Dipl.EVDC, MRCVS EBVS ® European Veterinary Specialist, Veterinary Dentistry RCVS Specialist, Veterinary Dentistry perryreferrals.co.uk [email protected] 2. RADIOGRAPHY and RADIOLOGY Learning Outcomes By the end of this module you should be better able to: Discuss the equipment required in order to generate dental radiographs in practice, including pros and cons of each system Explain the principles of the parallel and bisecting angle techniques in order to generate dental radiographs. Formulate a routine/process for obtaining full mouth radiographs in both the dog and cat. Analyse dental radiographs in order to detect pathology and obtain a diagnosis. Question: Does your practice have access to dental radiography? If yes, how often is it used? If no, why do you think this is? Dental radiography is an essential tool in veterinary dentistry. No human dentist would begin an extraction of a tooth without a pre-operative radiograph- in fact this could be considered negligent. It is not cost prohibitive to install, nor to the client, it is an easy technique to master, nurses can become actively involved, clients can immediately see the extent of pathology in their pet’s mouth (and therefore perceive better value for money) and the practice can benefit financially. Furthermore, the full extent of disease can be detected in an animal’s mouth, meaning the correct treatment can be provided; ensuring patients are not left with painful and/or infected teeth. Just as importantly, you will feel a much better sense of job satisfaction! © Rachel Perry 2023 Why take dental radiographs? The crown of the tooth can be visually inspected during the oral examination once the patient is anaesthetised. We cannot visualise the root structure, the periodontal ligament or the surrounding alveolar bone. We must have dental radiographs for this. Skull radiographs are good for the TMJs, sinuses and tympanic bullae but no good for teeth due to the inevitable superimposition of structures. Evidence-based veterinary medicine justifies full mouth radiography in every dental patient. Indications for dental radiography: Pre-operative assessment of extent of disease-in one study, radiographs of teeth without clinical lesions revealed clinically relevant information in 42% cats and 28% dogs (Verstraete et al 1998). Treatment planning- especially relevant in cats with tooth resorption (TR- previously known as FORL) Monitoring of disease progression Pre-extraction: anatomical variations- 10% of the maxillary 3rd pre-molar in cats have a third root (essential to know if extracting teeth in chronic gingivostomatitis cats) (Verstraete 1997). Assessment of tooth vitality- upon eruption, teeth are immature and have pulp spaces with thin dentinal walls (below, left). If the pulp remains vital, more dentine is produced throughout life and thus the pulp space reduces as the dentinal walls thicken (below, right). In addition, the apex of the root is not formed in an immature tooth, and only closes if the pulp remains vital. Thus, a wide pulp space in an old animal (compare contralateral tooth if present) indicates a necrotic tooth. © Rachel Perry 2023  Tooth resorption in cats and dogs (TR, previously known as FORL). 7 types have been identified in humans, and 6 of these have been identified in dogs. Two common types are detected in cats, and only radiography can distinguish. Essential for treatment planning. Extent of periodontitis- helpful in decision making regarding whether to extract or not. 50% attachment loss (as measured on a radiograph) is an indication for extraction. It has been shown that the roots of the mandibular 1st molar in small breed dogs take up a much larger proportion of the height of the mandible than large breed dogs (Gioso et al 2001). Small breed dogs are prone to periodontal disease, and periodontitis causes bone loss. This means there is much less bone to destroy before a pathological or iatrogenic fracture is imminent. Essential to radiograph this tooth before attempting extraction of mandibular M1 in small breed dogs. Post-extraction radiographs- essential to prove that you have extracted the entire tooth, and not left anything behind (broken bur, calculus, loose or sharp bone fragment) which could delay healing. Missing teeth- is it truly missing, previously extracted, is the crown fractured but root remaining, is there a dentigerous cyst? (Dentigerous cysts can form around an unerupted tooth (typically the 1st pre-molar in brachycephalic dogs) causing expansile, destructive cysts. Oral masses- essential in diagnostic work up and treatment planning Deciduous teeth-persistent deciduous teeth are persistent for a reason- often that the root has not undergone physiological resorption. These can be very long, slender roots that may break easily. Radiographs allow surgical planning- open or closed extraction? © Rachel Perry 2023 What do we use to obtain dental radiographs? Generate X-rays In order to obtain a dental radiograph, we need a supply of X-rays. 1. Standard X-ray units can be used, but the beam is generally directed vertically down with a few degrees of variation- this means moving the patient into the correct position which is awkward. Furthermore, the X-ray machine is generally in a different room from the dental table, which means disconnecting the anaesthetic circuit and moving the patient completely. Time consuming and frustrating enough to put anyone off taking dental X-rays! 2. Dental X-ray machine- can be wall mounted near the dental table or on wheels. They have a moveable arm and head, which means the X-ray beam can be directed exactly at the correct angle without moving the patient too much. The end of the head is known as the tube head or cone. There is no light for collimation, but the cone is placed in close contact with the patient’s head. Do not point the beam at a person or through a stud wall while taking an image. A safe distance is 6ft behind the back of the head. The wheeled versions take up a large floor space (so they don’t topple over) and are heavy so can be cumbersome to move around and store when not in use. Most have a set kV and mA, and all that is altered is the time of exposure. Many veterinary versions allow you to select species (cat/dog) and tooth, thus automatically setting the time of exposure. © Rachel Perry 2023  3. Hand held dental units are a bit like oversized cameras and allow you to take the X-ray, holding it in the angle you want. This can be difficult for beginners to master, as you cannot see the angle of orientation of the beam whilst holding the unit. In addition, if the image is not diagnostic, you cannot alter the beam angle slightly from the previous position. They can be useful for mobile practitioners (e.g. branch practices, charity work, zoos etc.). e.g. Genoray PORT-X IV, Nomad Portable hand-held dental X-ray unit being used in a zoo to radiograph an Amur leopard. Do involve your Radiation Protection Advisor (RPA) with any planning of equipment. Local rules must be produced and displayed. A Radiation Protection Supervisor (RPS) must be appointed. Capture images In order to capture a permanent image, some sort of film or sensor is required. This must be placed intraorally, so that superimposition of other teeth and skull structures is negated. These will form part of the animal’s clinical record, and must be of archival quality. Digital systems must be backed up. Traditional film systems are possible, but have a lot of drawbacks. When investing in a new system I would strongly recommend you go for a digital system. Film Dental film is non-screen. It is packaged in its own protective plastic envelope, and inside is a paper envelope plus a small sheet of lead. It is therefore imperative to face the correct side of the film towards the X-ray beam, but written guidance is normally on the packet. © Rachel Perry 2023  Film speed The main speeds of dental film are D, E and F differing in the size of the silver halide crystals, thus the amount of radiation required to produce an image. F requires less exposure than E, which requires less than D. ‘Faster’ films therefore reduces the amount of radiation a patient is subjected to, but will provide slightly reduced image resolution. Film size Different sizes of film are available, and termed; 0,1,2,3,4. Size 4 is the largest (57x76mm) and is useful for extra-oral views and radiographing multiple teeth in quadrant (to reduce the overall number of exposures, and time taken). Size 2 (31x41mm) is commonly used, though feline practitioners will also find size 0 (22x35mm) useful. Dental films , size 2 top and size 4 bottom Left: Film sizes (note these are CR sensors. Size 5, (only available for CR7) is longer than the 4, but same width Size 2 dental film. The plastic envelope has been opened to reveal the film within a sleeve of black paper, and also a sheet of lead to prevent scatter. Note the embossed dot in the top let of the film. Films will then require developing. Traditionally, a small box (chairside developer) containing cups to hold developer, fixer and water for wash are available. Light-tight arm holes are provided, plus a light-safe viewing window. Small clips are available to hold films while developing, and then when drying. © Rachel Perry 2023 Films must be thoroughly fixed and rinsed before drying to ensure there is no image deterioration. Chairside developers can be purchased for about £400, or eBay can be a valuable source as human dentists convert to digital systems. Automatic processors are also available, but do be wary of trying to put films through a generic automatic processor as the films have a habit of becoming lost. If a dark room is still available in the practice, developer and fixer can be placed into food cups for hand processing. Dental films are cheap; size 2 are about 30pence each, size 4 are about £1 each. ECO30 is a self-developing film, with film in one end of a pouch and developer in the other end. They do not require a dark room or processor, but are expensive (£1.50 each) and do not archive well. If you use film, consider waste disposal of chemicals. Left and Right markers are not used on dental films, but there is a system for determining left from right. A small, embossed dot is placed on the film and packet (convex one side and concave the other). The convex side is always faced toward the X-ray beam when generating the image, and always faced toward the viewer when reading the X-ray. The dot is always placed toward the front of the mouth. This enables determination of left or right in the exposed image as long as you can identify which teeth are present, and whether the maxilla or mandible has been exposed. Digital systems Digital systems require less radiation than even the fastest film, and have therefore become the standard of care in human dentistry. If purchasing an old X-ray generator, beware, as the time or exposure may not go down low enough for a digital sensor creating over-exposure and thus non-diagnostic images. Digital systems allow manipulation of images using the programme’s software, allowing changes of contrast, saturation and measurements to be made. Direct digital systems (DR) use a sensor (usually size 0 or 2) attached to a wire (wireless versions are available, but more expensive), which is connected to a computer. An immediate image is generated when the sensor is exposed to radiation. The correct side of the sensor must be faced toward the beam. The © Rachel Perry 2023 computer software will orient the image for you, if you have correctly inputted which tooth you are imaging. Due to the expense, you will normally purchase one size sensor, and size 2 will have the most applicability. This, of course, can be frustrating if trying to radiograph multiple teeth in a large dog, as many exposures will be required compared to a size 4. A distinct benefit of this system for beginners is that you can assess the image quality while both X-ray head and sensor are in the same position. If the image is non-diagnostic due to incorrect sensor or X-ray beam placement, then one or both can be altered and the exposure re-taken. Do ensure your patient is at the correct level of anaesthesia before placing the sensor in the mouth, because chewing or dropping can easily cause irreparable damage. A specific cover should be placed on the sensor and changed between patients. Direct digital sensor in the mouth a dog, positioned to radiograph the left mandibular canine tooth. Note the wire exiting the mouth- this is connected to the computer and image software for an instantaneous image. Computed Radiography (CR) systems have a full range of sensor sizes (0 to 4. The CR7 system from IM3 also provides a larger size 5 sensor). The phosphor sensor (‘plate’) is placed within the mouth, irradiated, and then removed from the mouth to be fed through a specific processor. There is a short time delay while the image is obtained, and once the film has been removed from the mouth it can be more difficult to correct any mistakes. However, the range of sensor sizes is a distinct advantage over direct systems. Light-tight envelopes are required to help protect the film not only from light, but also fluids and scratches. Some standard indirect digital systems have dental films available that are fitted into specific cassettes and processed with the same software. © Rachel Perry 2023  CR7 Indirect system- note the laptop with image software, and processor/scanner on the right. How do we obtain diagnostic images? Patient positioning Ideally position the patient with the area to be radiographed uppermost (i.e. to image the maxilla, have the patient in ventral or lateral recumbency). Film/sensor positioning Place the sensor in the mouth as close as parallel as possible to the tooth/teeth being imaged. Ensure that the sensor is not distorted, as this will disrupt the resultant image. Bear in mind the length of the tooth roots- the apex of the canine tooth for instance ends at the 2nd pre-molar. Ensure the correct side of the film or sensor is placed toward the X-ray beam. Hold the sensor in place with paper towel/gauze swabs. The ET tube can actually help stabilise the sensor. There are three ways to place the sensor in the mouth: Parallel to the mandibular teeth on the lingual aspect for parallel technique Parallel to the hard palate for maxillary teeth Parallel to the tongue for mandibular bisecting angle views Tube head positioning Place the end of the tube head/cone close to the teeth being imaged and remember there is no collimating light. © Rachel Perry 2023  1) Parallel technique. In this technique the sensor is placed parallel to the long axis of the tooth. The X-ray beam is then directed perpendicularly to the sensor (just like a limb or chest radiograph). There are usually lines on the side of the tube head to help orientation, but you could also ensure the end of the tube head is parallel to the sensor. You then know the beam is at right angles to the sensor. The only teeth that can be imaged like this are the mandibular teeth caudal to the symphysis. 2) Bisecting angle technique. In this geometric technique, the sensor is placed as parallel as possible to the tooth. The angle formed between the long axis of the tooth root and the sensor is visualised and then bisected in half. This imaginary line becomes the bisecting line. An X-ray beam directed perpendicularly to this line will produce an image that is similar in size to the tooth being radiographed. If the angle of the beam is more perpendicular to the tooth, an elongated image is produced. If the beam more perpendicular to the sensor, a foreshortened image is produced. Another way of visualising this is to consider your shadow that is cast by the sun. You are the object (tooth), the shadow on the ground the image (dental radiograph) and the sun is the X-ray beam. Late evening sun casts a long shadow because the sun’s beams are perpendicular to the person, and parallel to the ground. © Rachel Perry 2023  Early morning or late evening, the sunrays are almost perpendicular to you, resulting in a very long shadow. At midday, the sun is almost perpendicular to the ground resulting in a short shadow. The only time the shadow is your height is when the sun strikes the bisecting line between you and the ground perpendicularly. As you are forming a right angle with the ground, the bisecting line is at 45°. If the teeth in your image are too short, then it is likely the beam is almost parallel to long-axis of tooth, and hitting sensor at right-angles. Conversely, if the image looks as if the teeth are elongated, it is likely the beam is now too parallel to the sensor, and more at right-angles to the long axis of the tooth. This helps you determine in which direction to move the beam. Shortened image/short shadow In this example, the sensor is in the mouth, parallel to the palate, with the beam almost parallel to the incisor teeth, and perpendicular to the sensor. The radiograph will make the teeth look very short, just like the shadow. © Rachel Perry 2023 Elongated image/long shadow In this example, the sensor is in the mouth, parallel to the palate, with the beam almost parallel to the sensor, and perpendicular to the incisor teeth. The radiograph will make the teeth look very long, just like the shadow. Image looks lifelike/correct height shadow In this example, the X-ray beam is directed perpendicularly to the bisecting line. The teeth should look normal size. © Rachel Perry 2023 Which view? When imaging body cavities and limbs it is essential to obtain orthogonal views to ensure full information and lesion localisation is obtained. In the mouth, orthogonal views are only possible for the canine teeth. Thus, rostrocaudal and lateral views are possible (i.e. the X-ray beam is either directed from rostral to caudal, or from left or right lateral). The incisor teeth can only be imaged using a rostrocaudal view. The premolars and molars can only be imaged using a lateral view. Wherever possible, take two views of the canine teeth. Remember though, that the straight rostrocaudal view of the maxillary canine teeth will superimpose them upon rostral pre-molars. To obtain a rostrocaudal view of each maxillary canine, use an oblique rostrocaudal view. Lateral view for imaging canine, premolars and molar Rostrocaudal view for imaging incisors and canines Set the exposure time using a chart, or pre-set buttons on the unit. Expose the radiograph ensuring that all persons are in the ‘safe zone’, which is 6ft/2m from the back of the tube head at a 90-180° angle. Exposure buttons are usually a ‘dead-man’s switch’ which means if your finger is removed from the button (for instance if someone is walking into the unsafe area) then radiation will not be generated. To take the radiograph, keep the button depressed until a beep is heard, signalling exposure has occurred. © Rachel Perry 2023 Develop the film, process the CR plate or stand and admire your DR image! Is the image of diagnostic quality? The tooth should look ‘life-size’ and not be appreciably elongated or foreshortened. The apex/apices of interest should be in the centre of the image with 2-3mm of alveolar bone surrounding them. Images should not be too dark (over-exposed/developed) or pale (under exposed/developed). Scratches or fingerprints on film during developing can make the image non-diagnostic. Similarly, care should be taken not to scratch CR plates otherwise permanent faults will be apparent on each image generated by the plate. Blood streaks will also show up on CR images, and can obscure pathology. Cone cutting (see right) occurs if the beam only partially covers the sensor, and thus only part of the sensor is irradiated. Ensure that the centre of the beam is directed over the centre of the sensor. Positioning guides IM3 dental have produced a set of positioning guides to be used in conjunction with their CR7 system. This is an incredibly useful resource for learners, as it shows you exactly where to position both the sensor and X-ray beam. With experience and practice, it becomes easier to know where to position in order to obtain diagnostic radiographs. Full mouth radiographs should be obtainable in dogs in under 15 minutes and cats in © IM3 Dental Ltd under 10 minutes. © Rachel Perry 2023 SLOB rule The maxillary 4th pre-molar has two mesial roots, which will appear superimposed on a straight lateral view. To separate the roots on the image it is necessary to direct the beam from a more caudal or rostral direction, but the bisecting angle remains the same. To then identify how the roots have shifted apart, we use the SLOB rule, which is an acronym for Same Lingual Opposite Buccal. The root that moves in the Same direction as the beam is the Lingual (palatal) root. The root that moves in the Opposite direction to the beam is the Buccal root. Slob rule. Lateral radiograph of the right maxillary 4th premolar (108). The beam has been directed from a more rostral direction, and thus the root that also appears to have moved rostrally is the yellow one, which is therefore the lingual (palatal) root Slob rule. Lateral radiograph of the right maxillary 4th premolar (108). The beam has been directed from a more caudal direction, and thus the root that also appears to have moved caudally is the yellow root, which is the lingual (palatal). Extra-oral near parallel technique In cats, the zygomatic arch can superimpose upon the maxillary 3rd and 4th premolars. Another technique can be utilised to produce a clearer image. The sensor is placed extra-orally (outside the mouth) on the table. The cat is placed in lateral recumbency upon the sensor, and the head tilted 10-20° around the © Rachel Perry 2023 sagittal plane. The teeth to be imaged are on the sensor. The X-ray beam is directed down onto the sensor at about a 10-20° angle so that the teeth and sensor are almost parallel to each other and the beam almost perpendicular to both. Question: Why are these radiographs non-diagnostic? What needs to be re- positioned, the sensor, the X-ray beam or both? Radiology- the interpretation of radiographs Dental radiographs are viewed as if looking at the animal (imagine you are the X- ray beam), so that maxillary teeth are viewed with roots pointing upwards and mandibular teeth pointing downwards. Digital software often orients the image for you (if you have inputted the correct tooth into the software). If you are using film, you need to distinguish which way round to view the film. The embossed dot is used. The convex side points towards the X-ray beam during exposure, and you should look at the convex (not concave) side when viewing. In addition, the dot is usually placed toward the front of the mouth. Establish if the teeth are maxillary or mandibular, and orient the roots either upwards or downwards. © Rachel Perry 2023 Next, determine left or right you are looking at the X-ray as if looking at the animal. Maxillary teeth may have nasal turbinates in the image, may have 3 rooted teeth (PM4 in dog and cat, and M1&M2 in dog), and have a radiodense line running across the canine and PM roots (alveolar process of the maxilla). In addition rostrally, the palatine fissures are imaged. Mandibular teeth may show the mandibular cortex and mandibular canal (radiolucent shadow above the cortex). Rostrally, the symphysis will be seen. This is a fibrocartilaginous joint and will appear radiolucent. Questions: Can you identify species and quadrants in these radiographs? Knowledge of normal anatomy is essential when interpreting dental radiographs- for instance, the positions of the major foraminae (infraorbital, mental, mandibular) should be known so that their appearance is not mistaken for pathology, such as a periapical lucency. If in doubt, take another image, and move the beam direction slightly. True pathology will move with the root apex, while an anatomical structure such as a foramen will appear to move away from the apex. © Rachel Perry 2023 When viewing radiographs, it is essential to take a systematic approach, just like viewing a chest or abdominal film. Noticing the glaringly obvious and not assessing the rest of the film can mean subtler pathology is overlooked. A useful systematic approach is to assess these separate items one at a time: Anatomy- shape, size, number Periodontal health- around the tooth (periodontal ligament, alveolar bone) Endodontic health- within the tooth, the pulp system Other: bone Anatomy The normal anatomical form of each tooth should be known, and practise helps reinforce this knowledge. Deciduous teeth should be distinguishable from permanent teeth. The crown: root ratio is much smaller for deciduous teeth, that is, they have very long, slender roots and small, delicate crowns. Developing tooth buds can will be seen in dogs and cats