Dental Radiography PDF

Dental radiography Dental radiography is an important diagnostic tool used in dentistry and medicine to help the clinician to see within the body tissues and help to diagnose the cause of dental and medical problems. In dentistry, radiographs are used to detect and diagnose the following lesions and...

Dental radiography Dental radiography is an important diagnostic tool used in dentistry and medicine to help the clinician to see within the body tissues and help to diagnose the cause of dental and medical problems. In dentistry, radiographs are used to detect and diagnose the following lesions and structures: Dental caries: this shows up as a dark area of destruction extending inwards from the enamel surface of a tooth. Presence and extent of periodontal disease: this shows up as a loss of the lamina dura forming the crest of the alveolar bone, loss of height of the alveolar bone, and a widening of the periodontal ligament space. Periodontal and periapical abscesses: chronic alveolar abscesses show up as a dark circular area at the apex of an affected tooth, caused by destruction of the apical lamina dura and spongy bone. Cysts affecting the dental tissues: these can show up as enlarged darker areas surrounding other structures, and can sometimes be seen to be pushing tooth roots out of their normal positions. Iatrogenic problems: that is, those caused by the dentist, such as overhanging restorations or root perforations by posts. To detect supernumerary teeth and unerupted teeth, or to determine the congenital absence of unerupted teeth. To diagnose hard tissue lesions, such as bone cysts and tumours, salivary calculi and jaw fractures. In addition, radiographs are used during the provision of dental treatment to avoid problems occurring and to ensure that the treatment is successful. Examples include: aiding in endodontic treatment determining the number and position of tooth roots before extraction  ensuring the health of a tooth before it undergoes crown or bridge preparation ensuring the health of a tooth before it is used as an abutment during denture construction assisting in the correct placement of implants determining the presence or absence of teeth during orthodontic assessment ensuring the health of teeth before repositioning them during orthodontic treatment. For examination purposes, dental nurses are not expected to interpret radiographs but they should be able to describe both normal and abnormal radiographic appearances of common dental conditions. Nature of ionising radiation Ionising radiation is commonly referred to as ‘X‐rays’. X‐rays are a type of electromagnetic radiation that possess energy, as are ultraviolet light, microwaves and visible light. The radiation types differ from each other in the amount of energy they possess, X‐rays having high energy so that they are capable of passing through target matter such as human tissue. When they do so, one of three events will occur (Figure 12.26). X‐rays pass cleanly between the atoms of the target matter and are unaltered. X‐rays hit the atoms of the target matter and are scattered, releasing their energy as they do so. X‐rays hit the atoms of the target matter and are absorbed, releasing their energy as they do so. Figure 12.26 Passage of X‐rays in human tissue. With larger atoms of target matter, such as some metals (including calcium in bones and teeth), most of the X‐rays are absorbed or scattered, and these are radiopaque substances – they appear light grey to white on radiographs. Those which allow the majority of the X‐rays to pass through unaffected are called radiolucent substances, and include cavities in teeth, and soft tissues – they appear dark grey to black on radiographs. As bone and enamel have a high calcium content, and dentine and cementum also contain calcium hydroxyapatite crystals but to a lesser extent, these four tissues appear as a variable degree of radiopacity on processed radiographs. The more radiopaque tissues will show as the whitest structures, so enamel is whiter than dentine, and dentine is whiter than cementum. Similarly, the outer layer of bone will be whiter than the cancellous inner layer. Effect of ionising radiation on the body The energy released when X‐rays interact with human tissue is capable of causing cellular tissue damage, so it is imperative that X‐ rays are used only as necessary and at the lowest dose possible, to reduce the amount of energy released and therefore reduce the amount of tissue damage which occurs. Effects occur when the X‐rays hit the atoms of the tissue cells and are either scattered or absorbed, because of the energy that is released during these events. The energy released can cause tissue damage to the human tissue cells. The cells contain chromosomes which are made up of our DNA, the building blocks of life that determine exactly the organism that we are, and if the energy hits the chromosomes it can damage them so that they undergo change (mutation) or even die. This ability of X‐ray exposure to cause cell death is used in medicine to treat some types of cancer, during radiotherapy treatment. The cancer cells can be accurately targeted by the ionising radiation beam so that they are killed outright, or so that the cancerous tumour is reduced to a size that can undergo surgical removal. High doses of X‐ rays are used for this treatment, and tissue cells that divide and grow rapidly, such as skin cells and the body cells of children, are more easily affected. However, cell death is an undesirable effect during the production of dental images. As there can be no ‘safe’ level of exposure to ionising radiation (that is, there is always some cell damage caused during X‐ ray exposure), strict legislation and guidelines are in place to ensure that the following occur when X‐rays are used in dentistry. All use of dental imaging has to be clinically justified: there must be a clinical reason why the patient is being exposed to the X‐rays, and this will be one of the diagnostic or treatment reasons listed above.  The dose of X‐rays used must be kept as low as reasonably achievable (ALARA): the minimum dose of X‐rays must be used, for the shortest time, and aimed at the smallest area of tissue possible, to produce a functional image. This technique is now more usually referred to as being as low as reasonably practicable/possible (ALARP). Only the patient should be exposed to the X‐ray beam, so all staff and family members must be outside the controlled zone during the exposure (the only exception being when a parent assists a small child during exposure). Machines must be well maintained and serviced regularly. No untrained personnel can be involved in radiation exposure procedures. Quality assurance (QA) systems must be regularly operated (as audits) to ensure that the dental images produced are to a consistently high standard. Where an audit uncovers a lower standard of image production than expected or desirable, investigations should be carried out to determine the cause of the fault and the method and actions required to correct it. Ionising radiation legislation in detail Despite its valuable uses in the diagnosis and treatment of dental disease, ionising radiation presents a hazard to the whole dental team, their patients and the general public. X‐rays cannot be seen, heard or felt, and therein lie the dangers as it can easily be forgotten that this type of ionising radiation is potentially hazardous to health. There is no ‘safe’ level of use – every exposure can cause some amount of tissue damage in the patient, or in anyone else in the imaging area that is exposed to the X‐ray beam. An overdose can cause serious health effects, ranging from a mild burn to leukaemia and ultimately death. For this reason, specific legislation is in place to ensure full compliance with the health and safety aspects of ionising radiation by all dental workplaces, under the following regulations: Ionising Radiation Regulations 2017 (IRR17, replacing IRR99). Ionising Radiation (Medical Exposure) Regulations 2017 (IR(ME)R 2017, replacing IR(ME)R 2000). While IRR17 is enforced by the HSE for England, Wales and Scotland, specific guidelines have been produced by the HSE for Northern Ireland which affects dental practices there and are available to view or download at www.hseni.gov.uk. IR(ME)R 2017 and IR(ME)R(NI) 2017 is enforced by: CQC for England HIW for Wales IRMER Inspector of the Scottish Ministers and Health Facilities Scotland RQIA for Northern Ireland. While IRR17 is concerned with the regulation of occupational exposures to ionising radiation and therefore with the protection of staff, and IR(ME)R 2017 similarly with the protection of patients, the aim of both sets of regulations is to keep the number of X‐ray exposures, and their dose levels, to the absolute minimum required for clinical necessity at all times. This is the ALARA/ALARP principle referred to above. This applies not only to the actual direct X‐ray beam that is fired at the patient during the film exposure, but also to the scattered radiation that inevitably occurs during this process. Scattered radiation, as its name suggests, is that which bounces off tissue cells during exposure in an uncontrolled manner, and can re‐ expose the patient several times over, thereby increasing their actual radiation dose. In the dental workplace, three simple factors required for the ALARA/ALARP principle to be achieved have helped to reduce by 40% the amount of scattered radiation that is created during a dental exposure.  Use of ‘fast’ films: currently, F‐speed intraoral films require the shortest possible exposure time to create the radiographic image, once processed. Previous films were D‐speed or E‐speed. Short exposure time: achievable with a combination of modern X‐ray machines, fast films and fast intensifying screens in extraoral cassettes (see later). Rectangular collimator tubes: these have replaced the old plastic aiming cones of intraoral machines and provide a parallel X‐ray beam as it leaves the tube end, rather than a disorganised ‘spray’ effect with lots of scattered rays. The rectangular tube end has the same dimensions as a standard intraoral film too (Figure 12.27). Figure 12.27 X‐ray machine head with rectangular collimator. Compliance with IRR17 This set of regulations replaced IRR99 in January 2018 and there have been some dentally relevant changes. The regulations are concerned with the safety of staff in the dental workplace where ionising radiation is used, as well as with ensuring the correct functioning of the radiation equipment. The initial act of compliance under IRR99 was to inform the HSE of its use on the premises: this was referred to as ‘notification’. One of the changes of IRR17 is that a three‐point risk‐based assessment of regulatory control was introduced, and all dental workplaces had to formally ‘register’ with the HSE in January–February 2018, whether previously registered or not. The new ‘graded approach’ to the HSE application depends on the level of risk of the work carried out involving ionising radiation on the work premises: Low risk: applicants must ‘notify’ the HSE that low amounts of radionuclides are in use. Medium risk: applicants must ‘register’ with the HSE as they operate ionising radiation generators, including X‐ray machines. High risk: applicants must receive ‘consent’ from the HSE to carry out work using high levels and/or dangerous types of ionising radiation. Other than the hospital environment, the vast majority of dental workplaces fall into the medium‐risk category and must therefore register with the HSE. The publication Approved Code of Practice and Guidance of IRR17 is available at www.hse.gov.uk/pubns. Reapplication is not required after January–February 2018 unless the information given in the initial re‐registration process changes significantly, such as when new X‐ray machines are installed, and with each change of ownership or location of the business thereafter. The process is quite simple and can be completed online at www.hse.gov.uk, although a fee is now payable, and a copy of the initial application and the return acknowledgement email from HSE should be kept as evidence of compliance with the regulations. Four formal appointments must then be made by the workplace owner. Legal Person: a designated person who ensures the workplace’s full compliance with both sets of regulations (this is the  employer). Radiation protection advisor (RPA): a specialist person/organisation who is formally appointed by the dental workplace to be available to give advice on staff and public safety in relation to both sets of regulations, and normally also provides routine radiation surveys. Medical physics expert (MPE): a specialist who is appointed in writing to give advice on matters of radiation protection concerning medical exposures (diagnostic dental imaging) and non‐medical exposures (for medico‐legal reasons rather than for diagnosis), including the measurement and optimisation of patient doses and QA. The role of the MPE falls under IR(ME)R 2017 and is summarised later. Radiation protection supervisor (RPS): a designated person within the workplace who can assess risks and ensure precautions are taken to minimise them, in accordance with IRR17 (this is usually a senior dentist or a DCP with a post‐ registration qualification in dental radiography). Legal Person The Legal Person must now be the employer/business owner and he or she is legally responsible for implementing the requirements of the new ionising radiation regulations. They may also be the RPS in the same workplace, or this role may be delegated to a suitably qualified member of staff. The Legal Person is responsible for organising a 3‐yearly assessment of radiation safety within the workplace. This involves arranging for an inspection by a competent authority such as the Radiation Protection Division of the Health Protection Agency (which has replaced the previous authority, the National Radiological Protection Board) or by using the workplace’s own X‐ray machine and processing test kit to carry out the necessary checks and then sending them to the competent authority for analysis. In addition, the Legal Person must draw up a set of Local Rules which have to be displayed at each X‐ray machine, so that they can be referred to by all staff. A copy of all must also be held in the radiation protection file. The Local Rules must give all the following information: The name of the designated RPS, RPA and MPE. The identification of each controlled area to all staff and patients, to limit unauthorised entry during exposure. This is usually an area of 1.5 m from the machine head and the patient, and directly in the primary beam of the radiation during exposure. The designation of a 2‐m safety zone from the machine head will then ensure that only the patient remains within the controlled area during X‐ray exposure (Figure 12.28). Show the standard warning sign at each controlled area, indicating the use of ionising radiation; this is a black sign on a yellow background (Figure 12.29). A summary of the correct working instructions for each controlled area, including a ‘No entry’ rule for the designated 2‐m safety zone around the X‐ray machine head. A summary of the contingency plan to be followed in the event of a machine malfunction. Details of the dose investigation level: this is usually anything above 1 mSv per year in most dental workplaces. The use of a red light or display, and an audible buzzer to indicate the actual exposure time. The arrangements in place for the safety of pregnant staff. Figure 12.28 Safety zone (2 m) and controlled area (1.5 m) around the X‐ray machine head. Figure 12.29 X‐radiation warning sign. IRR17 also requires the following two points to be included in the Local Rules: Information about the procedures in place for ensuring staff have received sufficient information, instruction and training in their relevant roles, particularly if the RPS role is to be delegated from the Legal Person to a member of staff. An appropriate summary of the working instructions of the workplace in relation to X‐rays, including the written arrangements relating to non‐classified persons (carers or comforters) entering or working in designated controlled areas (see later). Radiation protection advisor The RPA must hold a Certificate of Competence to be a Radiation Protection Adviser which is recognised by the HSE, and their certificate number must be issued to the dental workplace as part of their formal appointment and included in the Local Rules. The role of the RPA is to give advice on the actions the workplace must take to comply with both sets of regulations and will cover the following points: The correct installation of all new X‐ray machines (acceptance testing, under IR(ME)R 2017). The regular maintenance and certificated checks that are required for each X‐ray machine to ensure that the minimum exposure to radiation occurs (routine testing, under IR(ME)R 2017). The contingency plans that need to be in place in case of a malfunction of an X‐ray machine, so that staff or patients are not exposed to X‐rays unwittingly. The investigation of any malfunction of an X‐ray machine. The designation of a 1.5‐m controlled area around each X‐ray machine and within the primary beam direction, where no one but the patient may be present during an exposure. Advise on risk assessments with regard to restricting staff and patient exposure to ionising radiation and review the assessments every 5 years. Advise on the necessary staff training required so that designated duties are carried out competently and safely. Assess staff protection with regard to the numbers of exposures carried out on the premises. If more than 150 intraoral films or 50 dental pantomographs are taken weekly, staff are legally required to wear a personal monitoring badge. Advise on the appropriate action to take if analysis of the badges indicates excessive exposure to any staff. Advise on the running of QA programmes so that the principle of ALARA/ALARP is maintained at all times. Medical physics expert The MPE must be formally appointed by the dental workplace, and their name and unique reference number must be included in the Department of Health’s List of Medical Physics Experts in the UK. The role of the MPE falls into both sets of regulations and is to provide advice on the following: Matters relating to radiation protection of patients in relation to medical exposures and non‐medical imaging (in relation to the latter, those exposures carried out for health screening or medico‐legal reasons). Measurement and optimisation of patient doses (ensuring exposures result in clinically diagnostic films which are taken at the lowest possible radiation dose to the patient). Making realistic estimates of the exposures to the public for comparison with the dose limit of 1 mSv per calendar year (whole‐body dose). Radiation protection supervisor The RPS may be the Legal Person or the role may be delegated to a suitably qualified member of staff; for dental nurses this is one who holds a post‐registration qualification in dental radiography. Suitable accredited qualifications are available from the NEBDN and the BDA (see Chapter 2). The role of the RPS is to carry out the following: Ensure all staff have suitable training according to the level of their legal responsibility (see later). Carry out risk assessments with regard to restricting radiation exposure. Ensure the Local Rules remain current or are updated as necessary. Maintain the contents of the necessary radiation protection file. Organise and run QA programmes in relation to the safe use of ionising radiation.  Organise and run quality control tests or delegate the tests to suitably trained staff. Can also be made responsible for ensuring that all staff receive the necessary hours of CPD in relation to dental radiography, as it is one of the recommended subjects for all qualified staff working in the dental surgery environment. Compliance with IR(ME)R 2017 This set of regulations replaced IR(ME)R 2000 in February 2018 and there have been some dentally relevant changes. The regulations are concerned with the safety of patients in the dental workplace, and with their protection during exposure to ionising radiation. They are of most concern to those dental personnel who have the qualifications and legal right to actually expose the patient to ionising radiation; that is, the dentist and any DCP holding a recognised dental radiography qualification. The regulations are therefore of less importance to the student dental nurse, and consequently only the basics are covered here. Roles and responsibilities The regulations set out the responsibilities of the various dental personnel who may be involved in taking and processing radiographs within the dental workplace and restricts those responsibilities by referring to each category with specific appointment titles. Referrer: the dentist, or a suitably radiation‐qualified therapist or hygienist, who refers the patient for radiation exposure, either to themselves (in all three cases) or to another dentist or specialist dental radiographer (for dentists only) who can carry out that exposure. IR(ME)R practitioner: the dentist or specialist dental radiographer who takes responsibility for justifying the taking of the radiograph, by determining that the diagnostic benefits gained will outweigh the risks of the exposure to the patient. Operator: any member of the dental team who carries out all or part of the practical duties involved with the exposure and processing of the radiograph, including:  patient identification positioning of the film, the patient, and the machine tube head setting the exposure controls pressing the exposure button processing the film evaluating the quality of the radiograph carrying out test exposures for QA purposes running QA programmes. Except in the hospital setting then, only a dentist can be an IR(ME)R practitioner. Therapists and hygienists are likely to have undertaken study and qualification in dental radiography as part of their training course and will therefore be able to act as referrers to themselves only, and to carry out all the above duties as operators. With suitable and authenticated training, or qualification, the dental nurse can also carry out a variety of duties under the title of ‘operator’, as shown in Table 12.2. Table 12.2 Details of duties allowed to operators. Duty Radiography NEBDN Level 3 Student qualified qualified Diploma* dental dental nurse dental qualified nurse nurse dental nurse Patient Yes Yes Yes Yes identity Positioning Yes No No No Setting Yes No No No exposure Pressing Yes Yes, in the Yes, in the Yes, in the exposure presence of presence of presence of button the set‐up the set‐up the set‐up operator operator operator Processing Yes Yes Yes Yes Quality Yes Yes Yes Yes audit QA test Yes Yes, in the Yes, in the Yes, in the exposures presence of presence of presence of the set‐up the set‐up the set‐up operator operator operator QA Yes Yes Yes Yes programmes *Level 3 Diploma, formerly National Vocational Qualification. Table 12.2 lays out the various duties involved in the exposure of patients to ionising radiation in the dental workplace, and the processing of the images into radiographs. The four other columns then identify which duty can be carried out by each level of experienced dental nurse, from those holding a post‐registration qualification in dental radiography, through a qualified registrant to a student dental nurse. It can be seen that there is no difference between the final three categories: there is no suitable ‘extended duties’ training that will allow any additional duties to be carried out by a dental nurse, whether registered or in training. The risk of potential harm to a patient and others from unnecessary exposure to ionising radiation is so great that only further specialised qualification is recognised as enabling a qualified dental nurse to carry out the additional duties of positioning the patient and setting the exposure. While all categories can press the exposure button, only those dental nurses holding the dental radiography qualification can do so unsupervised. A dental nurse holding the basic registrable qualification will have received documented training in the majority of these duties throughout their training course, supplemented by documented in‐ house training in any additional duties allowed (under the GDC Scope of Practice document) within the workplace. Similarly, the student dental nurse must receive the same documented training to be allowed to carry out any of the duties listed above. The ability of suitably trained personnel to press the exposure button during radiation exposures is of great help in reducing the risks of cross‐infection, as the operator setting up the procedure would otherwise contaminate the exposure button unless they repeatedly removed and replaced their gloves between setting up and retrieving each film from the patient’s mouth. The medico‐legal importance of all personnel receiving adequate documented training in these operator duties cannot be stressed too highly. Patient protection The IR(ME)R regulations are mainly concerned with the protection of patients while undergoing ionising radiation exposure in the dental workplace, so that they are not exposed unnecessarily and that all exposure levels are as low as reasonably possible, to reduce the chance of any tissue damage occurring. The key points covered are summarised below. Patient identification: of particular importance when the dentist referrer is not also the IR(ME)R practitioner, as occurs when patients are referred to hospital or to a specialist practice for dental treatment. To avoid the wrong patient being exposed, name, address and date of birth should be used as a minimum for identification purposes. Referrer: can be a suitably radiation qualified hygienist or therapist when referring to themselves only or can be a dentist. IR(ME)R practitioner: can only be a dentist (unless the patient is referred to a specialist dental radiographer), as only they have the training to determine when an exposure is justified. Justification: the benefit of exposing the patient should outweigh the risk of causing tissue damage (remember, there is no ‘safe’ level of X‐ray exposure), so every exposure should be expected to provide new information to help the patient’s diagnosis, treatment or prognosis as a minimum requirement, otherwise it should not be undertaken. Thus the taking of ‘routine’ bite‐wings for example is no longer acceptable. Optimisation: the dose of radiation used should follow the ALARA/ALARP principle at all times. Pregnant patients: routine dental exposure techniques do not irradiate the pelvic area and involve such low doses that pregnancy is not considered a contraindication to irradiation; for similar reasons, lead aprons are also not required. Staff training: written evidence of all necessary training pertinent to ionising radiation techniques must be kept for all personnel in the radiation protection file, as documented proof of their competence in the duties that they undertake. QA programmes and audits provide a valuable tool in determining whether the systems in place to protect patients (and staff) from any potential harm from ionising radiation are actually working, by looking at the procedures and the results achieved, and analysing any problems encountered so that policies and techniques can be suitably adjusted and updated where necessary. Accidental exposure: all X‐ray machines must have an isolation switch outside the controlled area, an illuminated control panel or switch to indicate when the mains power is on, and an additional light and/or an audible buzzer that is activated  during the exposure time itself. If a machine malfunctions during use, it will then be obvious by the lights and buzzers, and the mains power can be switched off without the operator having to enter the controlled area. The additional changes that have occurred under IR(ME)R 2017 are as follows: Non‐medical imaging: this covers exposures for health screening or medico‐legal reasons, rather than to gain clinical information and diagnosis for the health benefit of the patient. With advice from the MPE, dose constraints for these exposures must now be established and the dental workplace can decide not to carry out non‐medical imaging exposures if they wish, although this must be stated as a written protocol. Carers and comforters: these are people who assist the patient during an exposure, thereby knowingly exposing themselves to the ionising radiation; an obvious example is a parent holding a young child while an exposure is taken. Additional protection for these people is now required, by the provision of written employer’s procedures (with advice from the MPE) that: establish appropriate dose constraints for carers and comforters provide guidance on how they may be exposed and protected have a procedure in place to justify their exposure allow the dental workplace the option to disallow this type of assistance, although this must be stated as a written protocol. Other written procedures: as well as the two points above, written procedures are now required in relation to the following: Where practicable before an exposure, adequate information about the risks and benefits of the radiation dose is given to the patient (or their carer/comforter). Where a clinically significant unintended or accidental exposure occurs, the referrer, practitioner and the patient (or  their carer/comforter) are made aware and are informed of the analysis outcome of the event. In the event of such an occurrence, the RPA must be notified and their advice sought immediately. Estimates of population dose: guidance is to be issued for the employer to collate this information, with the help of the MPE, in readiness for its provision to the Secretary of State if requested. MPE: this person must be formally appointed by the dental workplace and their details held by the Department of Health on the List of Medical Physics Experts in the UK. Equipment testing: both the ‘acceptance testing’ of a new dental imaging set and the ‘routine survey’ of existing equipment is now a requirement under IR(ME)R 2017, rather than under IRR regulations as previously. Radiation protection file Effectively, this acts as a summary document that holds as much information as possible about the procedures in place to ensure radiation protection within the particular workplace and should be reviewed and kept updated annually to ensure that it remains relevant and effective. It should contain all the following information and have references included for any information that is kept elsewhere (such as qualification and relevant training details that are kept in personnel files). Formal appointments of staff on the premises, including referrers, IR(ME)R practitioners and all operators (with details of the range of their duties). Reference to the initial risk assessment carried out by the Legal Person, in consultation with the RPA. Local Rules for each X‐ray set on the premises. Procedures for ensuring patient protection, as required under IR(ME)R. Information on how ALARA/ALARP is achieved.  Details of protocols followed in relation to justification and authorisation of exposures (usually referenced to the FGDP booklet Selection Criteria for Dental Radiography). Details of protocols followed in relation to clinical evaluation of radiographs (so written notes are kept of each radiograph taken and what the findings were). Details of QA programmes to ensure consistently accurate radiographs, including their frequency and the named persons who run them. Quality assurance of films All the faults that may occur during the taking or processing of a radiograph, which may result in the patient having to undergo a retake, are avoidable. However, it may not be realised by the dental team that a recurring problem exists unless radiographs are regularly checked for quality, and this is especially so in large multi‐dentist workplaces. A processing fault may affect the radiographs of several dentists but unless someone is analysing the radiographs from all surgeries, it can easily be overlooked. This is the purpose of a QA system, in which all radiographs are analysed and scored according to a universal system of quality so that commonly occurring problems will be identified. With suitable training, a QA system of radiograph analysis can easily be run by the dental nurse, the aim being to reduce all faults to a minimum or to eliminate them completely. Indeed, in line with the relevant ionising radiation legislation and with clinical governance, the running of a QA system in dental workplaces is now a legal requirement. The types of faults that may occur during the exposure, handling and processing of radiographs are detailed later. To protect both patients and the dental team from unnecessary ionising radiation exposure, it is everyone’s duty to ensure that the occurrence of these faults is kept to a minimum or eliminated completely. To do this involves assessing the quality of the films processed to determine the following points: How readable is the film? Is a fault present?  What is the fault? How has it occurred? How can it be prevented from recurring? Is re‐exposure of the patient necessary? When run correctly, the QA system should achieve the following results: Involve a simple‐to‐use scoring system that is understood and followed by all staff. Easily identify any areas of concern. Develop solutions to the problems identified. Limit the number of patient exposures to the minimum required for clinical necessity. Therefore, to achieve ALARA/ALARP. A simple‐to‐use scoring system set out in clinical governance guidelines is as follows: Score 1: excellent quality radiograph with no errors present. Score 2: diagnostically acceptable quality, with minimal errors present that do not prevent the radiograph from being used for diagnosis. Score 3: unacceptable quality, where errors present prevent the radiograph from being used for diagnosis, and will therefore involve a retake. Score 1 should at a minimum constitute 70% of all exposures, while score 3 should at a maximum constitute 10%. The results need to be easily recorded after every exposure so that they can be analysed on a regular basis and any problems identified. A typical recording system is shown in Figure 12.30. The simple record sheet shows, at a glance, all the information required to enable a retrospective QA audit of the workplace radiographs to be carried out. As the operator is identified (by their initials), the audit can be used to track the performance of individuals, while the identification of the views used (detailed in the fourth column) also allows an audit of each type of radiograph to be carried out. The final column should give the information required to explain the QA score of 2 or 3 that has been awarded in each case, so that trends can be identified. For example, if an operator takes periapical radiographs without using a holder and regularly scores 2 or 3 due to coning or elongation, the audit will identify that this as a recurrent problem and that it can be resolved by the suitable use of film holders. Similarly, when all radiographs begin to score 2 or 3 due to poor processing from a certain date onwards, it may indicate a faulty machine or that the processing chemicals are spent. Figure 12.30 Example of quality assurance radiograph record sheet. When a score 3 occurs the radiograph has to be rejected and the patient irradiated again, as the initial radiograph is deemed clinically unacceptable – the image could not be read and a diagnosis could not be made. Information on score 3 radiographs stored in the image quality log can be transferred to a reject image analysis sheet such as that shown in Figure 12.31 on a 6‐monthly basis. The type of view, the reason for the rejection of the radiograph, the total number of rejects and their percentage of the total number of radiographs taken can then be analysed so that any recurring issues can be investigated. The fewer the number of score 3 radiographs and therefore repeat exposures for patients, the safer the working practices of the workplace, although this reject information is likely to go undetected unless a robust QA and analysis system is in place. Figure 12.31 Reject image analysis sheet. Similar QA systems can be set up to monitor other areas of dental radiography, such as equipment, working procedures or staff training. Dangers of ionising radiation X‐rays cannot be seen, heard or felt, and therein lie the dangers of their use. As they cannot be perceived by any of the senses, it is easily forgotten that they are potentially dangerous to health and it is just as easy to ignore every safety precaution. An overdose can give rise to serious health effects, ranging from a mild skin burn to the onset of leukaemia. This is why the special legal requirements described previously are in force for dental workplaces, and other workplaces where X‐rays are used. In the course of dental radiography the patient never receives an overdose. It is the operator, not the patient, who is most at risk, as the former is continually taking X‐rays and must therefore take strict precautions to avoid their own accidental exposure. Radiation safety must be checked at least every 3 years to ensure that X‐ray sets are adequately shielded to prevent stray radiation and that processing equipment and procedures are satisfactory. All sets must have regular professional maintenance. Use of the fastest film (E and F speed) will allow the shortest possible exposure time. Indeed, there is no justification for using anything but the fastest available film. Cassettes should be fitted with the fastest (rare earth) intensifying screens. Plastic aiming cones on X‐ray sets are no longer acceptable (as they allowed dangerous scatter to occur) and must be replaced by lead‐lined, rectangular collimator tubes to further reduce beam size to the safest level. This combination of fastest film, shortest exposure and narrowest beam will alone reduce the amount of scattered radiation by 40%. In addition, the following are important: Special film‐holder/beam‐aiming devices should be used for periapical and bite‐wing radiographs, so that the paralleling  technique of image production is used in preference to the bisecting angle method. The operator must stand well clear of the X‐ray beam during exposure, at the full length of the cable on the time switch; this should be not less than 2 m. On no account must a dental nurse hold the film in place for a patient. If a child cannot keep still during the exposure, the parent must hold the film packet in place and wear a protective lead apron, if the workplace has opted to allow the assistance of carers and comforters, in line with IR(ME)R 2017 requirements. Exposure of the reproductive organs to X‐rays has produced abnormalities in the offspring of laboratory animals. Similar exposure of humans may occur from scattered radiation during dental radiography. Although it is insufficient to produce such genetic changes in the case of pregnant dental patients, any possibility can be excluded by strict adherence to all the required safeguards. Every radiograph must not only be necessary but also of diagnostic value. There should be no need for retakes because of faulty technique or processing. Retakes mean unnecessary additional exposure of patients and staff. To ensure perfect results the films must be in good condition, taken correctly, processed carefully and mounted properly. X‐ray sets should be disconnected from their electricity supply when not in use. The amount of stray radiation received by staff can be checked by means of a film badge. This is an intraoral film which is worn at waist level for up to 3 months. It is then processed to indicate whether an excessive dosage is being received. If so, expert advice must be sought immediately to trace and eliminate the cause. Staff working in rooms adjacent to the surgery should also wear badges as X‐rays can pass through walls. Film badges are called personal monitoring dosimeters and details of suppliers are available from the Radiation Protection Division (RPD) of the Health Protection Agency or a local medical physics department. The RPD will process the badges, notify the dosage received and can arrange appropriate investigation if it is too high. Principles of dental radiography As stated previously, there are many sound clinical reasons for dental radiographs to be taken in the dental workplace, and their use is particularly invaluable as a diagnostic tool in dentistry. However, to avoid their indiscriminate use, guidelines have been drawn up for the safe prescription of dental radiographs in dental practice, as follows, and must be adhered to by all. A history and a clinical examination must be performed before any radiograph is taken. Only new patients with clear evidence of some dental disease should have full‐mouth radiographs taken. Regularly attending child patients in the mixed dentition stage who have orthodontic problems developing can be radiographed as necessary. Recall patients with a low caries risk should be radiographed no more frequently than every 18 months. Those with a moderate caries risk should be radiographed every 12 months. Those with a high caries risk should be radiographed at 6‐ monthly intervals, gradually reducing this rate as the caries is brought under control. Patients exhibiting evidence of periodontal disease can have selective radiographs taken of problem areas, as necessary. Edentulous patients should only have selective radiographs taken if there are any clinically suspicious areas (such as retained roots or hard tissue lesions). Types of views used in dental radiography Various types of film are used in dental radiography, depending on the reason for taking the dental image, but all are either those taken within the oral cavity – intraoral films – or those taken outside the oral cavity – extraoral films. Intraoral films Intraoral films are supplied in child and adult size packets that contain the following (Figure 12.32): Plastic envelope to protect the contents from saliva contamination. Wrap‐around black paper to prevent exposure of the film to light. Film, which is exposed to the ionising radiation and produces the dental image once processed or loaded onto the computer (digital imaging). Lead foil to prevent scatter of the ionising radiation past the film packet. Raised pimple marker on the film and packet side towards the X‐ ray tube, which is used to correctly determine the left and right side of the image produced (film is mounted with the pimple towards the observer). Figure 12.32 Contents of intraoral film packet. The intraoral views that can be produced using these films are as follows: Horizontal bite‐wing (Figure 12.33): show the posterior teeth in occlusion and are taken to view interproximal areas and diagnose caries in these regions  restoration overhangs in these areas recurrent caries beneath existing restorations occlusal caries. Vertical bite‐wing (Figure 12.34): show an extended view of the posterior teeth, from midroot of the uppers to midroot of the lowers as a minimum, and are taken to view periodontal bone levels of the posterior teeth true periodontal pockets. Periapical (Figure 12.35) show one or two teeth in full length with their surrounding bone, and are taken to view the area and the teeth in close detail. Anterior occlusal (Figure 12.36): show a plane view of the anterior section of either the mandible or the maxilla, and are used especially to view the area for unerupted teeth, supernumerary teeth and cysts. Figure 12.33 Horizontal bite‐wing radiographs. Figure 12.34 Vertical bite‐wing radiograph showing bone levels. Figure 12.35 Upper posterior periapical radiograph. Figure 12.36 Anterior mandibular occlusal radiograph. Extraoral films Extraoral films are used to produce much larger images showing many structures, and are supplied in cassettes that contain the following (Figure 12.37): Cassette case that is loaded into special imaging machines for use. Intensifying screens in both sides of the cassette, to reduce the dose of radiation exposure required to produce a dental image. Film, of a type compatible with the intensifying screens, to produce the dental image once exposed and processed. Marker to correctly determine the left and right side of the image produced. Figure 12.37 Contents of extraoral cassette. Extraoral films are packed differently from intraoral films. The latter are individually packed in lightproof wrappers but extraoral film is not. Packets of extraoral film only contain unwrapped film and can only be opened in a darkroom. On removal from the packet in the darkroom, a film is placed immediately in the special lightproof container or cassette, which is then kept closed ready for use. A typical cassette opens like a book and the film is placed in the middle. On each inside cover of the cassette there is a white plastic sheet called an intensifying screen, and the film is sandwiched between the two screens when the cassette is closed ready for use. The screens fluoresce on exposure to X‐rays, and the brightness of the fluorescence creates the image on the film itself, rather than being produced by the actual X‐ray beam. This allows the use of a reduced exposure time of X‐rays, making the technique safer for the patient. The extraoral views that can be produced using these films are the following: Dental panoramic tomograph (DPT) (Figure 12.38): shows both jaws in full and their surrounding bony anatomy, and is taken for orthodontic and wisdom tooth assessments, as well as to help diagnose pathology and jaw fractures. Lateral oblique: shows the posterior portion of one side of the mandible, including the ramus and angle and the lower molar teeth, and is an alternative to a DPT to view the position of unerupted third molar teeth (it is used infrequently now, as the image produced on a well‐aligned DPT is far superior). Lateral skull radiograph (Figure 12.39): this is a view of the side of the head, taken in a specialised machine called a cephalostat (which may be present as an attachment to a DPT machine or as a stand‐alone device), and is used to monitor jaw growth and determine orthognathic surgery techniques in complicated orthodontic cases where the patient has a severe skeletal discrepancy as well as malocclusion of the teeth. Figure 12.38 Dental panoramic tomograph. Figure 12.39 Lateral skull radiograph. When DPTs initially became widely available to the dental profession, they were called ‘orthopan‐tomographs’ and referred to as OPGs or OPTs; these abbreviations are still in current use in some areas. Radiographic techniques Any dental image is produced by the correct placing of the film on the far side of the area to be exposed from the X‐ray machine. In other words, the radiation beam passes from the machine through the area to be exposed and then hits the film inside either the plastic envelope or the cassette. Intraoral films are held in the correct position by the use of film‐ holder devices where possible, as shown in Figures 12.40 and 12.41. These are correctly loaded with the film packet (pimple towards the tube head) and placed inside the oral cavity for the patient to bite on so that the radiograph can be produced (Figure 12.42). If a digital imaging technique is used, the film is replaced by a special sensor that is positioned in exactly the same way, but instead of an exposed film being produced which is then chemically processed, the digital image is transmitted directly to a computer where it can be viewed immediately (see later). Figure 12.40 Vertical and horizontal bite‐wing holders – loaded. Figure 12.41 Posterior periapical holder – loaded. Figure 12.42 Posterior periapical radiograph. Intraoral films can be exposed in one of two angulations, depending on which is the best technique for the given clinical situation. They are called the paralleling technique and the bisecting angle technique, and wherever possible the paralleling technique is used with the aid of film holders. The paralleling technique holds the film exactly parallel to the long axis of the tooth being exposed, so that the image produced is exactly the same size as the actual tooth (Figure 12.43). This is especially important during endodontic procedures, when the correct diagnostic length of the tooth has to be determined to ensure accurate root filling of the canal. Figure 12.43 Paralleling technique. Sometimes the film cannot be placed parallel to the tooth, because of the size restriction of the patient’s mouth. In this situation the bisecting angle technique is used. The film is placed intraorally and the angulation of the long axis of the tooth against the film is determined by the operator. This angle is then halved (bisected) and the collimator of the tube head is angled to be at right angles to it (Figure 12.44), before the film is exposed. Figure 12.44 Bisecting angle technique. Anterior occlusal views are produced using the bisecting angle technique, with the patient holding the actual film packet between the teeth anteriorly, as illustrated in Figure 12.45. Figure 12.45 Maxillary anterior occlusal position. Source: Smith, N.J.D. (1989) Dental Radiography, 2nd edn, Blackwell Scientific Publications, Oxford. Reproduced with permission of John Wiley and Sons. Lateral oblique cassettes are held in position by the patient’s hand, on the far side of the head from the radiation machine and angled so that the X‐ray beam passes up through the angle of the jaw on that side, so that the third molar teeth on that side only are exposed (Figure 12.46). Figure 12.46 Lateral oblique position. Extraoral DPT film cassettes are loaded into their special radiation machines, and then the patient is accurately placed within the machine and the cassette is revolved around their head during the exposure process (Figure 12.47). Both types of extraoral film are processed in the same way as intraoral films, either manually or by the use of an automatic processing machine, as described later. Figure 12.47 DPT machine with patient positioned. Digital radiography Conventional X‐ray techniques rely on the use of a chemically coated plastic film being exposed to the X‐ray beam, and then processed in a darkroom or an automatic processor, using special chemicals to produce the image permanently onto the film. Digital radiography avoids the use of both the chemically coated plastic film and the need for processing it, as the X‐ray beam is fired at a special sensor plate instead (Figure 12.48), which then relays the image directly to a computer screen on the surgery worktop (Figure 12.49). The reusable intraoral sensor plate is used instead of film and the radiation dose is far less than with ordinary film. It is a technique similar to the use of digital cameras and mobile phones to produce photographic images that can then be loaded onto the computer from a memory card, via email or from a scanner. Figure 12.48 Digital sensor plate without protective sheath in place. Figure 12.49 Digital image on computer screen. The sensor plate is a similar size to whichever intraoral view is being taken: bite‐wing, periapical or occlusal. It is placed within a single‐use protective sheath and then positioned exactly the same in the patient’s mouth, using holders so that a paralleling technique is possible. The plate is connected directly to the computer via a USB cable, and the image produced is visible on the screen within seconds. Extraoral digital views can also be taken with specialised DPT machines, or with three‐dimensional scanning machines (Figure 12.50) with or without a DPT facility incorporated. The three‐ dimensional scans produced (Figure 12.51) are particularly useful in the field of implantology, where the correct positioning of implants can be determined. Figure 12.50 Example of three‐dimensional scanning machine with DPT facility. Figure 12.51 Three‐dimensional digital scan of maxilla. The digital image produced on the computer screen can be treated in the same way as digital photographs from a camera. Stored on the computer hard drive or transferred onto a storage device (disc or flash drive). Printed onto paper and stored as a hard copy in the patient’s record card. Sent via email to be viewed by other colleagues. However, as with digital photographs, the image can be adjusted and edited on the computer screen, and this raises issues in dentolegal situations where an image can be enhanced to make a clinical case look better than it actually was or the image selectively deleted so that poor‐quality treatment is not so apparent. Fortunately, computer experts would be able to detect that alterations had been made by examining the hard drive of the computer. Digital radiographic techniques are now popular but have not fully superseded conventional techniques in the dental workplace, and many still rely on X‐ray films that have been processed either manually or with an automatic processor, such as a Velopex machine. The advantages and disadvantages of digital radiographs are shown below. Advantages Financial savings of not having to buy film packets and processing chemicals and equipment. Avoidance of health and safety issues surrounding COSHH and the handling of the processing chemicals. Help towards achieving ALARA/ALARP as the use of the sensor always ensures a lower dose of radiation than if conventional film is used. The image is produced in seconds at the chairside, rather than several minutes in the processing area. The patient is able to view the magnified image on the computer screen, at the chairside and with the dentist. The magnified image can give greater clarity in some instances. The same sensor can be used repeatedly, as long as adequate infection control techniques (such as single‐use sheaths) are in place to avoid cross‐infection. Disadvantages The issue of adequate infection control to avoid cross‐infection, although there should be no instance where single‐use sheaths are not used. Financial implications of buying the computer with suitable specifications for use with the digital radiography software, the computer software itself (including any updates), and the sensor plates and their attachments.  Financial implications of buying the specialised scanner machine, with or without the DPT facility. The ability to alter the image without detection raises dentolegal concerns in complaint and fraud cases, unless an expert is employed to examine the computer hard drive. Formation of the conventional image An intraoral X‐ray film packet contains a celluloid film coated with light‐sensitive silver bromide salts in an emulsion, surrounded by black paper to protect it from unwanted light and enclosed in a waterproof plastic packet. On one side of the film is a lead foil which prevents the emulsion coat being exposed twice, by absorbing scattered radiation during the actual exposure to X‐rays. The passage of the X‐rays through the tissue causes the energy release discussed earlier, and an exact pattern of the tissue is produced within the chemicals on the film itself, as a latent (hidden) image, with radiopaque tissues causing the most energy release and therefore a clearer (white) image. Unless a digital imaging technique is used, the latent image can only be seen on the film by the use of special chemicals to make it visible during the processing procedure, in much the same way that conventional photographs from a camera are developed before being able to be viewed as prints. Film processing As discussed above, intraoral digital images are transmitted directly to the computer and can be viewed within seconds on the computer screen. All other films require chemical processing to convert the latent image to a visible image for viewing, and this can be done using an automatic processing machine (such as a Velopex machine) or by manual processing, with the film being passed through the chemical tanks by hand and in the correct sequence. Automatic processing The machine consists of a base containing the chemical and water tanks, with a conveyor belt style of rollers that carry the film through the machine during processing (Figure 12.52). These are all beneath a removable, light‐tight lid which has hand entry ports so that the film packet or cassette can be put into the light‐tight environment before being opened. If the film is exposed to visible light before being processed, the image will be permanently lost. Figure 12.52 Velopex processing machine: internal detail. The procedure of automatic processing is as follows: Observe the warning light system to check that the chemical and water levels are adequate, and that the temperature is correct for processing (Figure 12.53). When the temperature and fluid levels are correct, the warning light(s) will go out and the machine is ready for use. Intraoral film packets are taken into the machine through the hand ports, while wearing clean gloves. Extraoral cassettes are placed into this section by lifting and replacing the lid, and then can be opened and handled via the hand ports. The rollers become operational once the processing start button is pressed or automatically when the film is placed at the entrance port. The film packet is carefully opened and the plastic envelope, black paper and lead foil are all dropped to the base of the tank, for removal later. The film is then held by its sides only, as finger marks on the surface will damage the image. The film is carefully inserted into the entrance to the rollers, and it will be gently tugged into the machine as the rollers turn, to be processed. Once the film has passed through the machine, been processed and dried, it will reappear at the delivery port and can be safely handled and viewed. Figure 12.53 Velopex machine and control panel. Manual processing Although the vast majority of dental workplaces use automatic processing machines or digital radiography techniques, it is important for the dental nurse to know about the manual processing technique, so that it can be carried out safely and effectively whenever necessary. Manual processing follows the same procedure as that occurring in an automatic processor, but is carried out by hand and in a darkroom, a light‐tight lockable room containing the processing chemicals and water tanks, which sit in a main water tank that is heated and maintained in the correct temperature range of 18–22 °C. Alternatively, self‐enclosed worktop designs are also available for use with intraoral films only, where small, lidded fluid pots at room temperature are arranged within the unit as for the conventional darkroom layout, and accessed via hand ports (Figure 12.54). Figure 12.54 Self‐enclosed manual processing unit. In the conventional darkroom set‐up, four tanks will be present (Figure 12.55). Lidded developing tank: containing the alkaline developing fluid that produces the initial latent image; the lid is only removed during processing as the solution will deteriorate in air. The image is still unstable in visible light at this point. First water tank: to wash off the developing solution after the correct developing time, using tap water. Fixing tank: containing the acid fixing solution which permanently fixes the image onto the celluloid film, so that it can be viewed in visible light without deterioration. Second water tank: to wash off the fixing solution after the suitable fixing time, again using tap water. Figure 12.55 Darkroom layout. Some vision is required within the room, so an orange or red safe light will be present under which the processing can be carried out without exposing the film to actual visible light, thereby ruining the image. The room must be lockable from within so that the door cannot be opened by anyone else, as this would result in the accidental exposure of the film to light and the destruction of the image before it has been fully processed. The procedure of manual processing is as follows: Check that the chemical and water levels are adequate. Check the temperature of the solutions, and determine the developing and fixing times required from the chemical manufacturers’ guidelines. Check that a timing clock and suitable film hangers are available in the room. Wipe surfaces dry of any previously spilt chemicals or water, if necessary. Lock the door and switch off all lights except the safe light. Open the film packet or cassette, locate the film and clip it to one of the hangers available, carefully handling the film by its edges only, to avoid spoiling it with fingerprints. Remove the developer lid, immerse the hanger in the solution so that the film is completely covered by the solution, and start the timer. When the timer sounds, remove the hanger and film and immerse in the first water tank, agitating the hanger to ensure thorough washing occurs. Shake off excess water, then fully immerse the hanger and film in the fixer solution, and start the timer. Replace the developer lid to prevent the solution being weakened by exposure to air, which would allow oxidation to occur. When the timer sounds, remove the hanger and film and immerse in the second water tank, agitating the hanger to ensure thorough washing occurs. Switch on the ordinary light. Shake off excess water and dry the film: a slow‐running hairdryer is suitable for this, as the radiograph must not be dried too quickly. Once dry, the films can be correctly mounted as necessary and returned to the dentist for viewing. Mounting and viewing films Once the films have been successfully processed, they will be viewed by the dentist so that diagnoses can be made and treatment plans formulated. Ideally, a light box and magnifier will be available for viewing the films (Figure 12.56), but it is imperative that they are mounted and positioned correctly, otherwise the left teeth will be viewed as the right, and vice versa. Figure 12.56 Viewing screen with magnifier. Extraoral cassettes are marked with an ‘L’ to indicate the patient’s left side and unless the cassette has been placed upside down in the machine, the film is easily orientated on the viewer so that it is viewed as if looking at the patient from the front (see Figure 12.38). Various plastic envelope designs are available to mount all types of intraoral films nowadays, but they must be loaded correctly by the dental nurse first. All intraoral films have a raised pimple in one corner which must be facing out to view the film correctly, and not back to front. It is irrelevant which corner of the film the pimple appears in, but it must face out towards the person viewing the radiograph. Also, the dental nurse should use their knowledge of oral anatomy to check themselves: molar teeth are posterior to all other teeth so correct mounting of bite‐wing films, for instance, should result in the molar teeth appearing on the outer side of both films, with their pimples palpable in one corner (see Figure 12.33). Upper periapical films should be mounted with the roots above the crowns of the teeth, as they are in the patient’s maxilla (Figure 12.57), and so on. Figure 12.57 Periapical radiograph, correctly orientated with the roots above the crowns. Dental workplaces are likely to use one of the various different methods of patient identification and storage of films, and the dental nurse has to be aware of the methods in use in their workplace and use them appropriately. These may include any of the following: Digital images will be stored on computer or downloaded onto disks. Intraoral films may be mounted in plastic envelopes, with patient identification details written in indelible ink. These may be stored within each patient’s record card and filed. If clinical notes are computerised, there may be a separate filing system used exclusively for films. Extraoral films may be too large to store within the record cards, so may also have their own exclusive filing system. Whichever system is used, all films must be marked with the patient’s identification details (e.g. name, computer number), the date the image was taken, and a note of the view used, before being stored or filed. Care of processing equipment and film packets One of a dental nurse’s many duties will be to care for all processing equipment, once trained adequately to do so. This is a vital role with regard to patient safety, since poorly maintained equipment will lead to poor‐quality radiographs that may need to be retaken, causing unnecessary X‐ray exposure for the patient. And as stated previously, there is no safe level of X‐ray exposure – each one could cause cell damage. The following list summarises the points that should be included in any care and maintenance protocol. Ensure adequate training in processing techniques has been given. Always carry out the preprocessing checks correctly.  Always wear suitable PPE when handling all processing chemicals, as they are toxic if used inappropriately. Follow the surgery policy on topping up and changing spent solutions; normally all will require full replacement on a monthly basis, if not earlier. Dispose of all waste solutions as hazardous chemical waste, under the health and safety policy (see Chapter 4). Follow the training given and the manufacturer’s guidelines on cleaning the processing area or the automatic processor, to avoid film contamination. This is especially important with regard to the roller system in automatic machines, as films can stick to dirty rollers and their images will be destroyed. Be aware of the correct functioning of the equipment, so that failures can be recognised, the equipment switched off safely and the matter reported to the necessary person for repair. In addition, poor‐quality or unreadable radiographs will be produced if old film stock is used or if the stock has not been stored correctly. Films can still deteriorate before their expiry date if stored in hot or damp places, or if they are kept too near an X‐ray set. Unexposed film packets must be stored as follows: Away from all sources of radiation. Away from all heat sources, and ideally at room temperature. Away from all liquids that may penetrate the packets and destroy the films before use. In stock rotation, so that older films are in front of newer films and therefore used first. If an expiry date is given on a packet of film it should not be used beyond that date. Any remaining films should be discarded, as old film will not expose correctly and the image produced will be of poor quality. Film in poor condition from any of these causes will give a radiograph of poor quality which may have to be retaken. Exposure faults Although many practices have abandoned manual processing in favour of automatic methods, it is still necessary for all dental nurses to understand what happens to a film during exposure and processing. This will help to run QA systems that will trace any causes of error and prevent the need for retakes. Faults that occur during exposure are the responsibility of the operator taking the view. Any part of a film exposed to X‐rays or white light is turned black and opaque by developer. The remaining unexposed part is still sensitive to light and appears green and opaque. Fixer dissolves away the unexposed green part, leaving it completely transparent and no longer sensitive to light. Some common faults that occur during exposure are listed in Table 12.3, some of which are shown in Figure 12.58. Table 12.3 Some common faults that occur during exposure. Fault Reasons Elongation of Collimator angulation is too shallow, producing a image (Figure long image 12.58a) Foreshortening of Collimator angulation is too steep, producing a image (Figure squat image 12.58b) Coning (Figure Collimator angulation is not central to the film, so 12.58c) film is only partly exposed Blurred image Patient or collimator moved during exposure Transparent film Film placed the wrong way around to the or faint image collimator for exposure, with the lead foil pattern with overlying superimposed onto the film; this may not always pattern (Figure appear as the traditional ‘herringbone’ pattern 12.58d) Fogged film Exposed to light before X‐ray exposure (this may occur with extraoral films, as they are being loaded into the cassette) Blank film X‐ray machine not switched on, although this is unlikely to happen with modern machines, as they have exposure lights and audio signals installed Figure 12.58 Radiograph exposure faults. (a) Elongation. (b) Foreshortening. (c) Coning. (d) Reversed film. Handling faults Faults can also occur due to poor handling technique or poor preparation of the processing equipment; these are both the responsibility of the dental nurse tasked with processing the exposed film. All these faults are avoidable by adequate training and by following procedures accurately. Some common handling faults are listed in Table 12.4, some of which are shown in Figure 12.59. Table 12.4 Some common handling faults. Faults Reasons Scratches or fingerprints Catching the film on the tank side (Figure 12.59a) during immersion Not holding the film by the edges Blank spots (Figure 12.59b) Film splashed with fixer before developing Black line across film Film bent or folded during processing Brown or green stains Inadequate fixing due to old solution Crazed pattern on film (Figure Film dried too quickly over a strong 12.59c) heat source Presence of crystals on film Insufficient washing after fixing (Figure 12.59d) Figure 12.59 Radiograph handling faults. (a) Scratched. (b) Splashed. (c) Crazed. (d) Insufficient washing. Processing faults Poor‐quality radiographs can also be produced due to equipment preparation faults, and especially by lack of solution preparation and maintenance of the automatic processor. As the majority of film processing will be undertaken by the dental nurse in the workplace, knowledge of the faults, their occurrence and avoidance, and correct processing techniques should be basic topics of study and understanding for every dental nurse. Some common processing faults are listed in Table 12.5, some of which are shown in Figure 12.60. Table 12.5 Some common processing faults. Faults Reasons Dark film Developer solution too concentrated (Figure 12.60a) Developer solution temperature too high Overdeveloped Blank film Film placed in fixer solution before developer (Figure solution, so the image is destroyed 12.60b) Partly blank Film partially immersed in developer solution film Fogged film Processing room or machine is not light‐tight, so the (Figure 12.60c) film is exposed to light before processing Faint image Developer solution too weak (Figure Developer solution temperature too low 12.60d) Underdeveloped Fading image Inadequate fixing time so image is not permanently held on the film Loss of film Film stuck in roller system due to poor cleaning and maintenance of automatic processor Visible Film contaminated with solution spillages, in artefacts cassettes or on work surfaces Figure 12.60 Radiograph processing faults. (a) Dark film. (b) Blank film. (c) Fogged film. (d) Faint film. Every radiograph must not only be clinically justified but also of diagnostic value, so that an accurate diagnosis can be made and treatment planned accordingly. There should be no need for retakes because of faulty exposure or handling techniques, or poor processing skills. Retakes mean unnecessary additional exposure of patients and staff to X‐rays. To ensure perfect results, the films must be in good condition, exposed correctly, processed carefully and mounted properly. Quality assurance of films As discussed earlier, the faults described previously are avoidable. However, the dental team may not realise that a recurring problem exists unless radiographs are regularly checked for quality, and this is especially so in large multi‐dentist surgeries. A processing fault may affect the radiographs of several dentists but unless someone is analysing the radiographs from all surgeries, it can easily be overlooked. This is the purpose of a QA system, in which all radiographs are analysed and scored according to a universal system of quality so that commonly occurring problems will be identified. The running of a QA system of radiographs is a very important task that is often allocated to the dental nurse, and has been described in detail previously. Conclusion For each patient who attends the dental workplace, an oral health assessment will guide the dentist, therapist or hygienist towards diagnosing the presence of an oral disease, and help to formulate a treatment plan where necessary or to refer on for specialist tests and treatment in some cases. Not every patient will have to undergo every assessment method described, and the assessor will use their professional knowledge and discretion in each case to determine the assessment, diagnosis and treatment planning required. The role of the dental nurse is to understand the need for the various assessments, and to be able to assist the assessor and patient while they are carried out, as well as to accurately record all the findings in each case. Further resources are available for this book, including interactive multiple choice questions and extended matching questions. Visit the companion website at: www.levisonstextbookfordentalnurses.com