RADIOGRAPHY & RADIATION PROTECTION

Transcription

1 RADIOGRAPHY & RADIATION PROTECTION F`` A Guide for the Dental Team CPD Module 020

2 Page 2 Fig.1 RADIOGRAPHY AND RADIATION PROTECTION CPD Module 020 Suitability Dentists Dental Care Professionals Receptionists and Practice Managers Dental technicians Aims and Objectives The aim of this module is to cover the core knowledge required by members of the dental team to fulfil their CPD requirements on radiation protection and radiography. The objective is to review previous knowledge, increase understanding and improve clinical and managerial practice. Learning Outcomes Upon completion, users should understand: Electromagnetic radiation and x-rays Ionising and non-ionising radiation Sources of radiation Health effects of exposure to radiation Radiation protection including health & safety Principles of radiography X-ray machines and techniques Digital radiographs Conventional radiographs and processing techniques Quality assurance Statutory requirements, legislation and best practice Clinical indications for taking radiographs Assessment and CPD Certificate Users who complete this module including the assessment will receive a printed certificate for 10 hours CPD credit. Alternatively, if the user does not want to take the assessment it may count for unverified CPD. Click on the link at the end of this module to complete your online assessment. Your free CPD certificate and module summary will then be available to print.

3 Page 3 Glossary of Terms HSE - The Health and Safety Executive. HPA - The Health Protection Agency. Ionising radiation - A type of radiation released by atoms, as electromagnetic waves or particles which have sufficient energy to ionize an atom. X-rays are a form of ionising radiation. Medical device - An instrument or piece of equipment which is used to diagnose, prevent or treat patients, this includes x-ray machines. MHRA - Medicines and Healthcare Products Regulatory Agency. Medical physics expert A science expert who gives advice on radiation protection. Non-ionising radiation - Radiation which does not have sufficient energy to ionize an atom but which could still be potentially harmful. This includes radio waves and visible light. NRPB - National Radiation Protection Board. Radiation - Particles or waves of energy which can travel through any medium. Radiation protection advisor (RPA) - A person or organisation who advises employers on how to conform to the Ionising Radiations Regulations. Radiation protection supervisor (RPS) - A person or organisation with responsibility for implementing the local rules relating to the use of ionizing radiation equipment and who ensures correct procedures/guidance are followed. Radiography - The process of using x-rays to capture an image for medical or dental diagnostic purposes or treatment. Key Legislation The Health & Safety at Work Act 1974 Reporting of Injuries, Diseases and Dangerous Occurrences Regulations RIDDOR1995 Directive 96/29/Euratom-Basic Safety Standards Directive 1996 Directive 97/43/Euratom 1997 The Provision and Use of Work Equipment Regulations PUWER 1998 Ionising Radiation Regulations 1999 Management of Health and Safety at Work Regulations 1999 Ionizing Radiation (Medical Exposure) Regulations (IR(ME)R 2000 Radiation (Emergency Preparedness and Public Information) Regulations 2001 The Hazardous Waste (England and Wales) Regulations 2005 The Environmental Permitting (England and Wales) (Amendment) Regulations 2011 The Waste (England and Wales) Regulations 2011

4 Page 4 Radiography Overview Radiography is the process of using x-rays to capture an image which can be used for diagnostic purposes. Radiographs play an essential role in dentistry; in diagnosis and treatment planning and in the monitoring of a patient s condition or lesion. In 2008, an estimated 46 million medical and dental radiographs were carried out in the UK; more than 11 million of these were in general dental practice. For the majority of people, their main exposure to ionising radiation (apart from background radiation) is in the form of x-rays from medical or dental radiography. In dentistry, the most common radiographs taken are periapical (fig.2) and bitewing (fig.3) intra oral views and the OPT orthopantomagram (fig.4) extra-oral view. Fig.2 Periapical radiograph Fig. 3 Bitewing radiograph Fig.4 OPT radiograph Radiation Protection Overview Radiation protection is ensuring the safety of staff, patients and the general public when using ionising radiation (including x-rays) by conforming to current best practice, guidance and legislation. Originally developed in the USA in 1946, the trefoil is the international radiation symbol and is used to denote any radiation hazard. It can be black or magenta on a yellow background. Fig.5 The trefoil radiation symbol CPD on the subjects of both radiography and radiation protection are core compulsory subjects for dental professionals on the UK GDC register.

5 Page 5 Statutory Duties of Dentists The UK General Dental Council document Maintaining Standards states, that dentists who own or operate an x-ray machine have a number of statutory duties which include: Compliance with statutory regulations and guidance. The use of safe practices to protect staff, patients and the general public. To ensure anyone they delegate to take radiographs on their behalf has been appropriately trained. Failure to comply with any of these could lead to a charge of professional misconduct. Radiation and the Electromagnetic Spectrum Electromagnetic radiation is a type of energy which is absorbed and/or emitted by charged particles which has both magnetic and electrical properties. The electromagnetic spectrum is the range of frequencies of electromagnetic radiation from radio waves with frequencies in the order of many kilometres, through to gamma rays with frequencies sometimes smaller than an atom. X-rays are part of the electromagnetic spectrum and have a number of features which include: They travel as waves in straight lines. They travel at the speed of light (186,000 miles per second / 300,000 km per second). They are a form of ionising radiation with higher energies. Apart from gamma rays, x-rays have the highest frequencies and energy levels. Shorter wavelength x-rays have a wavelength less than 10 nanometres (1 billionth of a metre), compared to radio waves whose wavelength can be as long as 100km. LOWER ENERGY LONGER WAVELENGTH HIGHER ENERGY SHORTER WAVELENGTH Radio Waves Micro waves Infra- red waves Visible light spectrum Ultraviolet rays X-rays Gamma rays NON IONISING RADIATION IONISING RADIATION THE ELECTROMAGNETIC SPECTRUM Fig.6

6 Page 6 Radiation Radiation is the process where energy waves or particles pass through a media of some kind, including the human body. All waves in the electromagnetic spectrum are a type of radiation and transfer energy in the form of photons. Higher frequency electromagnetic waves (including x-rays) have higher energy photons. Waves with these higher energies are a form of ionising radiation and include higher energy ultraviolet rays, x-rays and gamma rays. Waves with lower energy levels are known as non-ionising radiation. As such, x-rays can be divided into two groups: Ionising Non-ionising Exposure to Radiation Both ionising and non-ionising radiation have the potential to cause harm but ionising radiation has a much greater potential because of its higher energy. People can be exposed to ionising radiation from a number of sources, some of which are naturally present in the environment. This is often termed background radiation. Everyone is exposed to cosmic and UV radiation daily. The amount increases at higher altitudes and being outdoors more of the time. Exposure is greater at higher altitudes such as when travelling by aeroplane and on longer flight times. Some less well known sources are foods including bananas and brazil nuts. In addition, building materials such as concrete and bricks emit radiation. Even some smoke detectors contain a source of radiation. Other sources of radiation include purposeful exposure to undergo a test or scan using x-rays or the rare but serious accidental exposure from nuclear accidents or weapons testing (table below). Sources of Ionising Radiation Natural UV radiation Cosmic rays especially at higher altitudes 60+ naturally occurring radioactive materials in air, soil and water Buildings and bricks Radon gas from rocks and soil Incidental Body scanners in airports Electromagnetic fields Lasers Medical radiation such as x-rays and ultrasound Tanning beds Some smoke detectors Incidents/accidents

7 Page 7 Uses of Ionising Radiation in Medicine and Dentistry Ionising radiation can be used in several ways: 1. Diagnostic radiography - taking x-ray images (fig.7), ultrasound scans, MRI scans (fig.8) 2. Nuclear medicine - radioactive substances injected into a patient for diagnostic scans (fig.9) 3. Radiotherapy - use of x-ray machines or radioactive sources to treat cancers 4. Sterilisation of medical instruments The use of radiation has led to major improvements in the diagnosis and treatment of human diseases. Each year, more than 3,600 million x-ray examinations are carried out. Fig.7 Dental Radiograph Fig.8 MRI scanner Fig.9 Tracer isotope injection Potential Health Risks from Ionising Radiation The photons of an ionising radiation have sufficient energy to ionise atoms or molecules (i.e. make them lose electrons), as they pass through them. Cells which have been ionised can be damaged, may die or undergo changes to their DNA making them prone to becoming cancerous in both the short and long term. Most DNA damage is repaired straight away but occasionally a permanent alteration can take place. This is known as a mutation. Epidemiological evidence has demonstrated links between ionising radiation and the following health conditions: Cancer Cataracts DNA damage Inherited conditions Effects on the immune system Cardiovascular problems Some effects are dose related, for example skin problems are directly related to the skin dose received. However, some effects such as DNA damage or cancer occur randomly. A single x-ray exposure in a person s lifetime could cause cancer in one person whereas a number of exposures in a lifetime on another person might have little or no effect at all.

8 Page 8 Fig.10 DNA helix Fig.11 Cataracts of the eye X-rays and DNA Damage X-rays are well absorbed by bone and other calcified tissues such as teeth but less well by muscle and soft tissues. This feature is the reason for using them to provide diagnostic images in medicine and dentistry. However, they are a type of ionising radiation and when they pass through cells in tissues they have the potential to cause damage. This is why their use must be carefully monitored and controlled. Some risks from x-rays were discovered not long after their use in medicine started. Dr Rollins the inventor of the first dental x-ray unit in the USA in 1896, was one of the first to report the effects of radiation exposure as he suffered burns to his hands, following experimental use. It is important to remember that potential health risks from ionising radiation have no threshold which means the risk is there every time a person is exposed to even the smallest doses. The magnitude of risk is proportional to the dose. Exposure to higher doses and for longer or multiple doses, increases the risk. The risks are also greater in younger people who are more radiosensitive. For example, children aged 10 years or younger have a 3 times greater risk compared to adults exposed to similar doses. Exposure to lower dosages or over a longer period of time can cause immediate damage to cells which may repair successfully or damage to a cell s nuclear DNA in the longer term. DNA alterations which are not repaired have the potential to cause tumours, many years after the exposure occurred. The risk is much greater if the person was a child at the time of exposure to the radiation. There is epidemiological evidence linking an increased risk of brain, salivary gland and thyroid tumours to patient exposure to x-rays in dental radiography. Some health effects will not occur unless a large threshold dose has been reached. Exposure to radiation above a certain threshold can cause acute physical effects such as burns, hair loss and skin redness. The dose threshold for acute radiation syndrome is 1000mSv.

9 Page 9 Other Causes of DNA Damage DNA can be damaged by a number of different processes, chemicals and radiation, including: X-ray radiation UV radiation Chemicals in tobacco Oxidative damage during routine cell chemical reactions Repair of Damaged DNA X-rays can cause single or double strand breaks in DNA. It is estimated that between 1000 and 1,000,000 of these occur in the human body every day. DNA BREAK DNA BREAK Fig.12 DNA helix Most damaged DNA can be repaired, with the majority repaired within one hour. The repair process is triggered by several proteins including P53, tenovins, BRCA1 and BRCA2. DNA which cannot be repaired leads to programmed cell death, known as apoptosis. In healthy humans, billions of cells undergo cell death every day and the number of cells which die each day equals the number of cells undergoing cell division. Non ionising radiation such as visible light, microwaves, infra- red and radio waves do not have sufficient energy to knock electrons from the nucleus of a cell (i.e. ionize directly) but can cause electrons to move or shift position and this has a thermal effect. This increase in temperature can lead to some electrons being energised enough to ionize indirectly. This means that both ionising and non-ionising radiation have the potential to cause health effects and DNA damage. Both ionising and non-ionising radiation have the potential to cause damage to the human body but ionising radiation has the greater potential.

10 Page 10 National Reference Dosages Taking into account expected background radiation dosages as well as safety limits, recommended ionising radiation exposure dosages are published each year. The Health Protection Agency (HPA) is the appointed body who work across organisations to issue recommended national reference dosages for services using different types of radiation. Dose - This is measured for the whole body or particular organs/tissues in milligrays (mgy) Exposure -This is a measure of equipment settings in milliamps(ma) or kilovolts(kv) Effective dose - This can be calculated for any x-ray technique measured in microsieverts (µsv) or millisieverts (msv). Few effective doses have yet been published for dental radiography. Comparison of Radiation Exposures from Different Sources Exposure in millisieverts One dental intra-oral radiograph One dental panoramic radiograph Return flight from London to Glasgow Eating 135g bag of brazil nuts One chest x-ray 0.02 Return flight from London to LA 0.16 One CT scan mandible Table 2 Fig.13 Aeroplane Fig.14 Periapical radiograph Fig.15 Brazil nuts Effective Dose Limits These are advisory limits for exposure to ionising radiation for both staff using them and members of the public. There are lower limits for younger employees and pregnant/nursing women. Radiation exposure from dental radiographs is low. For example, the radiation exposure from 2 bitewing radiographs is around half that experienced on a short plane flight. Examples: Annual Effective Dose Limits: Employee (aged 18+) -20mSv Employee (16-18 years) -6mSv Members of the public -1mSv

11 Page 11 Dose Constraints In dental radiography there are also dose constraints which recommend the upper level limit of an individual s exposure to x-rays. These are 1mSv for employees involved in radiography and 0.3mSv for other staff and the public. The dose limits can be increased in places of work where these normal limits would be impracticable but additional monitoring measures would then be required. This is unlikely to occur in every day dental practice but could occur in busy x-ray departments. Staff Health Surveillance Monitoring There is guidance on protective measures, depending on the effective radiation dose that members of the dental team (who use x-rays) receive each year. Monitoring of staff using ionising radiation is not mandatory, unless they are exposed to more than 100 intra-oral exposures or 50 panoramic films each week. Many dental practices and clinics carry out annual testing with staff wearing x-ray monitoring badges. This can be a useful tool in alleviating staff concerns on the use of x-rays but is not a standard requirement. Employers must ensure that exposure of the foetus of any pregnant member of staff does not exceed 1mSv throughout the course of the pregnancy. Records of personal monitoring must be kept for at least two years and a person has the right to see their results should they request to do so. Diagnostic Reference Levels In order to keep radiation exposures ALARP to a minimum, the doses for each procedure should be compared to a diagnostic reference level. The current recommendation is a patient entry dose of 4mGyA for an adult mandibular molar intra-oral radiograph. Each x-ray view taken will have a different reference level and these may vary slightly between x-ray machines. As such the levels calculated are specific to individual machines. However, to calculate the effective dosages requires the services of an RPA and this must be carried out at least every 3 years. Justification and Referral Criteria Despite the small doses involved, the use of x-rays in dentistry is not without risk. A radiograph should be taken only when the diagnostic benefit outweighs these potential small risks. This is called justification. Radiographs should only be taken after a history (including medical history) and clinical examination have been carried out. The routine use Fig.16 of radiographs for screening is not advised.

12 Page 12 Evaluation Whenever a radiograph has been taken, a clinical evaluation of its outcome and diagnostic findings must be noted in a patient s dental records. The patient dose must also be recorded. Legislation Working with x-rays in everyday dental practice, means conforming to a number of regulatory legislation and guidance documents; including directives from both the European Commission and UK governments. This has been further complicated since some governmental powers were devolved in Scotland and Wales, as some regulations now differ between England, Northern Ireland, Scotland and Wales. It is important to check through the relevant documents for the area you are working in, to ensure you conform. Relevant legislative documents are listed below. European Legislation Directive 96/29/Euratom Directive 97/43/Euratom UK Legislation 1974 Health & Safety at Work Act 1995 Reporting of Injuries, Diseases and Dangerous Occurrences Regulations (RIDDOR) 1998 The Provision and Use of Work Equipment Regulations (PUWER) 1999 Ionising Radiation Regulations (IRR-replaced IRR 1985) 1999 Management of Health and Safety at Work Regulations 2000 Ionizing Radiation (Medical Exposure) Regulations (IR (ME) R 2000) 2001 Radiation (Emergency Preparedness and Public Information) Regulations (REPPIR) 2005 The Hazardous Waste (England and Wales) Regulations 2011 The Waste (England and Wales) Regulations 2011 The Environmental Permitting (England and Wales) (Amendment) Regulations

13 Page 13 Training and Roles All dental team members involved in radiography must have adequate training for their role. Each role has particular responsibilities according to legislation and guidance documents. These roles are: Holder/Employer - An employer with legal responsibility for an x-ray machine. Referrer - A dental practitioner, medical practitioner or other health professional, who is able to refer a patient for a radiograph. In the dental setting this must be a dentist and cannot be a dental care professional. Practitioner - A dental practitioner, medical practitioner or health professional who provides justification for the radiograph to be taken. Operator - A person with responsibility to take a radiograph and process it. This could be a radiographer, student, colleague or dental care professional. A dentist can be referrer, practitioner and/or operator. Radiation Protection Advisor (RPA) - A person or organisation who advises employers on how to conform to the ionising radiation regulations. All dental surgeries including community and hospital services must consult an RPA who must be suitably trained. A dentist can act as RPA, as long as they have completed a suitable training course. This role is usually carried out annually by an outside agency on a consultative basis. A list of RPA s can be found by contacting the Society for Radiological Protection. Radiation Protection Supervisor (RPS) - This must be a named person who is responsible for implementing the local rules relating to the use of ionizing radiation equipment and who ensures that the approved code of practice following IRR 1985 are followed. The RPS can be the same person with RPA duties but is usually a senior dentist or practice manager who is suitably trained. An RPS must be appointed where there is a designated controlled area. Medical Physics Expert -This is an expert who can give advice on radiation protection. Dental practices should consult an expert on a regular base to calculate effective dose received by patients and staff. This is usually carried out under contract with a designated monitoring company.

14 Page 14 Responsibilities of Radiation Employers: Radiation employers are those who own or operate services which use any type of ionising radiation. This includes the owners of dental practices and healthcare trusts who operate dental clinics in hospital and community dental services which use x-ray machines. The responsibilities apply to both NHS and private dental services using x-rays. Radiation employers are required by law to restrict the exposure of their staff and others, including the general public. There is a duty of care to undertake a risk assessment to consider a number of factors related to the use of x-ray units. Dental surgeries and clinics using x-ray machines are classed as an employer working with ionising radiation ; as such they are required to consult with a Radiation Protection Advisor (RPA) in order to complete their risk assessment. Employers must also have written procedures in place for the use of dental x-ray equipment which should include: Protocols for operating x-ray units Staff who are authorised to act as referrer, practitioner and operator Patient dose assessment and diagnostic reference levels Patient ID system for radiographs Procedure to enquire about a patient s pregnancy status Procedure for evaluating each radiograph taken Quality assurance programme Risk Assessment Employers must carry out a risk assessment on the use of ionising radiation and consider: The source of ionising radiation Possible accident situations, their likelihood and severity Management of accidents, incidents and reporting Potential hazards and risks including people who could be affected The estimated radiation dose rates to which anyone could be exposed Precautions to be taken to ensure dosages are as low as possible (ALARP) Design and control features Consequences of failures of control measures PPE that is required Results of any previous personal dosimetry monitoring Manufacturer or supplier advice on equipment, safe use and maintenance Staff training

15 Page 15 MEASURE MANAGE RISK ASSESSMENT ASSESS Fig.17 EVALUATE This risk assessment should enable an employer to determine: What action is needed to ensure that radiation exposure is kept as low as possible Local rules Controlled and supervised areas What control measures are needed Warning devices that are to be used Whether PPE is needed Assess any dosage constraints Consider the need to alter working conditions of pregnant /breastfeeding employees Check restrictions on exposure levels Maintenance and testing schedules Contingency plans Staff training needs Staff dose assessment and testing Management responsibilities Appropriate monitoring or audit and quality assurance programmes Employers with five or more staff, must record any employees especially at risk and significant findings of their risk assessment. All pregnant staff members should have an individual risk assessment carried out at the start of the pregnancy and at further intervals if necessary. Responsibilities and Duties of Employees: Take care to minimise exposure of themselves and others to ionising radiation Wear PPE if required to do so and complete training as requested Gain written informed consent from the patient or for a radiograph to be taken

16 Page 16 Designated Areas After completing a risk assessment, an employer must designate an area in order to manage radiation risk. These areas must be monitored regularly and equipment tested with records kept for 2 years. There are three types of area and they are determined by estimating the expected annual dose. Controlled area This is an area which restricts radiation exposure in the workplace. Entrance into the controlled area needs to be restricted to classified workers who must undergo monitoring and use PPE if required. A controlled area is a place that nobody should enter while the x-ray unit is in use. A dental surgery or X-ray room will be demarcated as a controlled area when the x-ray unit is in use. Only the patient should be in the controlled area. For machines operating up to 70kV, the demarcated area must be 1m from the x-ray tube /patient head in all directions. For machines above 70kv,this should be 1.5m.The operator is advised to stand as far away as possible but at least 2m away and never in line with the beam. The controlled area may need to be bigger if large numbers of films are produced or the effective dose is greater than 6mSv but do not normally extend beyond the walls of the room in dental practice. Additional measures such as protective shields in walls and ceilings may also then be needed. X-ray machines can be used in a designated room or in a surgery or clinic room but its positioning must allow the operator to stand at least 2m away during use so that they comply with the controlled area. The operator must be able to prevent access to the room whilst the x-ray machine is in use and be in a position where they can still see the x-ray tube warning light and the patient while taking the radiograph. Warning Signs If the controlled area extends to the entrance of a room where x-ray equipment is used, then a warning notice must be placed on the outside of the door. Such signs must comply with legal requirements and include the ionising radiation warning symbol as a minimum. For Panoramic X-Ray Machines: Two stage warning light at the entrance to the room stating X-rays Controlled Area when the machine is on and Do Not Enter when in use. For Intra-Oral X-Ray Machines: A warning sign on the door of the surgery or x-ray room stating X-rays Controlled Area and No Unauthorised Entry when in use. Fig.18 Fig.19

17 Page 17 Local Rules /Radiation Protection Files These are a set of rules which should be followed for a particular practice or clinic when using x- rays. They include: Written procedures for controlled or supervised areas (restriction of exposure) Details of the risk assessment including staff pregnancy risk assessment Dose constraints and limitations Details of safety features including visible/audible warning devices Features to keep exposure as low as possible- ALARP Standard operating procedures Contingency and emergency plans The file must have a written protocol for each type of x-ray set including the exposure settings and this should be kept near the x-ray machine. Individual x-ray machines must have their own local rules and radiation protection file. Quality Assurance (QA) Programme All employers using x-ray equipment must follow a quality assurance programme which includes: Regular equipment testing A yearly audit of radiograph quality and justification for requesting radiographs Effective dose calculations every 3 years Most dental practices and services carry out in house equipment testing and auditing. However, the effective dose calculations must be evaluated by a Radiation Protection Advisor (RPA) and this must be carried out every three years. Radiograph Quality Audit IR (ME) R regulations state, that each year a quality audit needs to be carried out on a number of radiographs, to assess image quality and investigate any failures and their causes. The audit can be carried out by any member of the dental team who has been trained adequately. The purpose of the audit is to improve the quality of radiographs in processing and reduce patient doses by minimising the number of retakes required due to poor quality images being produced. The quality ratings should be: 70% or more rated excellent (no errors of patient exposure, positioning, processing or film handling) 20% or less rated acceptable (some errors but which do not prevent the diagnostic value) Less than 10% rated unacceptable (errors which make the radiograph unacceptable) After analysing the results, any measures for improvement need to be outlined in a summary report.

18 Page 18 Reporting of Accidents and Incidents If there is an incident where a patient and/or staff member has been exposed to excessive radiation due to machine malfunction or operator error, the radiation employer must investigate the incident and consult with their designated RPA. In dentistry, the HSE recommends this be any exposure more than 20 times the intended dose. Patients who have been exposed to a higher dose than expected should be informed as a matter of good practice but this is not mandatory. If the patient was not informed, this must be written in their patient record together with a reason for not doing so. Any over-exposure to x-rays must still be reported to the HSE; with a records kept for at least 2 years and a detailed written investigation kept for at least 50 years. Any incidents involving x-ray equipment malfunction must also be reported to the Medical Devices Agency (MDA) as they might need to issue warnings to other users of similar equipment. Use and Sharing of Radiographs Fig.20 OPT Radiograph The sharing of radiographs is considered good practice in order to avoid unnecessary patient exposure to x-rays. For example a dentist carrying out extractions could request to borrow radiographs taken by the orthodontist (if available). Similarly, viewing previous radiographs which show anomalies such as unerupted teeth or anatomical structures might be helpful, rather than repeating. Patients undergoing treatment on referral for example sedation services, could have their radiographs sent from the referring dentist to the operating dentist whilst treatment is being carried out and these could then be returned at the end of treatment on referral.

19 Page 19 Radiography in Dentistry Radiography is the process of using x-rays to capture an image on a film or digital sensor for diagnostic or monitoring purposes. Radiographs play an important role in dentistry; in diagnosis, treatment planning and in monitoring a patient s condition or lesion. Production of a dental radiograph requires: A source of x-rays (x-ray machine) An image detection system (conventional film or digital sensors) Equipment X-ray machines vary by manufacturer and type. In every day dental practice, there are two main types of machine in use: Intra-oral (e.g. periapical, bitewing, occlusal views) Extra-oral (e.g. panoral and lateral cephalogram views) X-ray equipment must be designed and installed in line with UK and EU standards. X-ray machines are classed as medical devices and as such must comply with the Medical Devices Regulations An intra-oral x-ray machine can be found in most dental practices and clinics; not all practices have an extra-oral x-ray machine as these can take up space which may not be available in some smaller surgeries. Some hospital dental departments do not have any x-ray machines in the dental surgeries as they often have a dedicated x-ray department. Within a dental practice or clinic, the location of x-ray machines varies. Some are found in the dental surgery itself whilst others prefer to use a dedicated x-ray room. Each option has advantages and disadvantages and location is related to personal preference and the size and/or location of rooms available. a) Intra-oral x-ray machines Intra-oral machines consist of an x-ray tube, housing, positioning arm and cone/head. They can be wall or floor mounted with mobile machines also available. Settings are altered via a control panel and keypad according to the patient s age and the type of radiograph being taken. Fig.21 Pointed cone x-ray machine Fig.22 Open end cone x-ray machine

20 Page 20 The machine is positioned next to the area being examined with the film or sensor inside the patient s mouth to produce the image required. Depending upon the technique used, a film holder may be used to keep the film in the correct position. In recent years, open ended round or rectangular cones have replaced pointed cones. An open ended tube is sometimes called a position indicator device (PID). Intra-oral dental x-ray machines come with short or long cone heads (some have interchangeable heads). A longer cone increases the source to object distance and improves image sharpness and reduces magnification. Magnification is the enlargement of the actual tooth size projected onto the radiograph. In some machines the x-ray tube is housed further away from the end of the cone and so what might look like a short cone machine may actually have a longer source to object distance. You would need to check the manufacturer s handbook for details. The focal spot in dental x-ray machines is short at 0.5 to 1.2 mm and this can affect the sharpness and magnification of the image. Image Magnification All radiographic images are magnified and this is greater in panoramic views. The amount of magnification is affected by: (i) The Object to Film Distance - This is the distance between the films or digital sensor and the area being radiographed e.g. a tooth. The closer the tooth is to the film or digital sensor, the lower the magnification. (ii) The Target to Film Distance This is the distance from the source of the x-rays in the x-ray machine (the focal spot on the tungsten target) and the film or digital sensor. A shorter cone machine results in greater magnification as mentioned earlier. When using a shorter cone machine, less parallel rays from the middle of the beam and more divergent rays from the edge of the beam hit the object being radiographed and this increases magnification (fig.23). A longer cone reduces magnification of the final image A shorter cone increases magnification of the final image Fig.23 Magnification of image with short and long cone x-ray tubes

21 Page 21 b) Extra-oral x-ray machines There are several different types of extra-oral x-ray machine. The most commonly used in everyday dental practice is the panoramic which produces an orthopantomagram (OPT) radiograph. This machine consists of an x-ray tube mounted on an arm with the x-ray film inside a cassette or digital sensor on another arm on the opposite side of the patient. These machines can be wall or floor mounted. Settings are altered via a control panel and keypad according to the patient s age and the type of radiograph being taken. The patient stands or sits inside the machine with their head and teeth held in the correct positions using a bite block, head rest and positioning guides and/or lights (fig.24). Fig. 24 Panoramic X-Ray machine and the light indicators for patient positioning Another extra-oral view, the lateral cephalogram is used in practices and services providing orthodontic treatment, to produce a skull view allowing measurements to be taken which help in treatment planning. This view can be achieved by using an additional attachment to the panoramic machine or by using a separate specialised x-ray machine. The radiographic image produced by an extra-oral x-ray machine will also be affected by magnification and the sharpness of the images is less than that from intra-oral radiographs. Another useful view, especially for children who are not compliant or patients who have a strong gag reflex, is the lateral oblique view. This involves holding a cassette containing film next to one side of the jaw whilst pointing the x ray beam from the angle of the mandible on the opposite side (fig.25). It can give an excellent view of the upper and lower jaws on one side. CASSETTE The x-ray tube is positioned at the angle of the mandible and pointed towards the opposite side of the face where the cassette is held. The patient will need to hold the cassette flat against the face. Fig.25 Technique for lateral oblique radiograph

22 Page 22 Installation, Replacement and Maintenance X-ray equipment must be designed, constructed and installed in accordance with British Standard Testing and maintenance should be carried out regularly, with details noted in the local rules. There are no specific time intervals required by law. An inventory of equipment must be kept which includes: Installation date Manufacturer name Manufacture date Model number Serial number or unique identifier Record of Defects, Maintenance and Quality Assurance (QA) Tests. An acceptance test must be carried out on all newly installed or replacement x-ray equipment to ensure it is functioning correctly. When opening a new dental practice or clinic which will be using x-ray equipment or installing new x-ray equipment, the Health and Safety Executive must be informed at least 28 days in advance. In addition, an assessment on the adequacy of shielding must be carried out. X-ray Production Inside the x-ray machine metal housing is an inner glass tube encasing x-ray producing unit. This contains insulating oil which helps dissipate the excess heat generated during x-ray production. The tube head has a seal and aluminium filter fitted together with a collimator. The housing and tube head are lined with lead to reduce x-ray scatter. All machines use an x-ray tube to generate x-rays. In summary the process involves: Heating a cathode filament until it emits electrons - process called thermionic emission Using an electrical field to focus and accelerate the electrons into a beam The x-ray beam moving at high speed towards a positively charged tungsten anode The electron beam striking the target at the focal point 99% of the energy in the electron beam is converted to heat The heat is dissipated by a copper stem and bulb in oil in the tube head 1% of the energy is converted into x-rays which are emitted in all directions Useful x-rays travel through the filters and collimator and out of the opening Some x-rays pass through the body whilst others are absorbed An image is formed on a film or an electrical input goes to a sensor which can be processed

23 Page 23 SCATTER X-RAYS METAL HOUSING INSULATING OIL anode X-RAY TUBE cathode anode cathode X-RAY TUBE TUBEHEAD SEAL ALUMINIUM FILTER LEAD COLLIMATOR X-RAY BEAM Fig.26 Intra-oral x-ray machine internal and external views Methods Used to Reduce Patient X-ray Dosage Individual doses of x-rays received by patients can vary even for the same views using the same x-ray machine. This is due to variability in equipment, operator technique and whether digital or conventional film is being used. In radiography, the principle of ALARP - as low a dose as reasonably possible should be followed. Several methods can be used to reduce the patient s skin dose exposure to x-rays during dental radiography. Machine Voltage The kilovoltage (kv) of an x-ray machine is a measure of the potential difference between the cathode and the anode when in use. A higher kv setting produces rays with shorter wavelengths and higher energies. This increases their speed, giving them greater penetration and scatter resulting in a lower skin dose to the patient. It is important to note that films used have an optimal sensitivity and as the machine setting gets higher, the image produced has poorer contrast and less diagnostic value. Settings between 60 and 70kv give the best balance of good quality images but limiting patient dosages.. Fig.27 X-ray control panel

24 Page 24 Filament Temperature The ma setting on a dental x-ray machine is a measure of the level of current in the cathode filament. Increasing this setting increases the level of current and the temperature of the filament, resulting in more electrons being released. A typical setting is 10-15mA. DC and AC Current Machines Traditional x-ray machines use alternating current (AC). Some newer machines generate x-rays using a constant direct current (DC). These DC machines produce less lower energy x-rays and so the skin dose given to patients is reduced. As such, the kilovoltage of the DC machine, is set at a lower level. These machines are therefore recommended when older machines need replacement. Timer The exposure timer controls the time that electrons are produced and affects the number of x-rays. Reducing exposure time is better for the patient, as they are exposed to less x-rays. Each machine will have pre-set exposure times which vary according to film speed, the age of the patient and the view being taken. These can be further adjusted as required, for example exposure times for edentulous patients should be reduced by around 25%. Filters X-ray machines are fitted with an aluminium filter by the manufacturer. A typical filter for a machine above 70kV is 2.5mm of aluminium and for machines of 70kV or less is 1.5mm. X-RAY HOUSING UNIT LEAD COLLIMATOR AT THE BACK OF THE PID ALUMINIUM FILTER AT THE FRONT OF THE HOUSING Fig.28 Position of filter and collimator on dental x-ray machine Filters help remove lower energy x-rays and this reduces the skin dose received by the patient. Additional filters can also be fitted. Their use can help reduce the dose to the patient but this must be balanced against their effect on the image quality and their cost.

25 Page 25 Collimation Use of beam collimators reduces the size of the x-ray beam and helps reduce skin exposure to x- rays. The collimator is a lead disc with a hole in the centre that adjusts the x-ray beam size going out through the open cone (no larger than 2.75cm) and filters out weaker rays. Rectangular collimation at 30 x 40mm is recommended in the UK as it reduces the patient s dose by up to 60% in dental radiography. CIRCULAR COLLIMATION RECTANGULAR COLLIMATION FILM FILM Fig.29 Rounded and rectangular collimation compared to film size If circular beams are used, the beam diameter must not exceed 60mm and be open ended. Beam collimators should be open ended and for machines operating at 60kV or above have a minimum focus to skin distance of 200mm (100mm for machines operating below 60kV). Rectangular collimation can be more difficult to use as the beam size is not much greater than the film size, as such positioning accuracy is essential (fig.29). Film Speeds The size of the crystals in the emulsion on dental films regulate the speed of the film, the larger the crystals the faster the film. Ultraspeed films have crystals approx. 1µm in diameter. Faster film speeds allow the patient s x-ray dose to be reduced. Film speeds E and F reduce the patient dose by more than 50% compared to D speed film. Faster films have a poorer contrast and so a balance between diagnostic use and film speed must be maintained. Instant x-ray films have slower speeds and poorer image quality but can be useful for endodontic or urgent care. around the film, For extra oral radiographs, a rare earth intensifying screen should be used as this can reduce patient x-ray doses by 50%.

26 Page 26 Protective Equipment Lead aprons and/or thyroid collar may be used by patients to protect vital organs during x-ray exposure. They have a layer of lead equivalent to 0.25mm.Current guidance recommends that lead aprons do not need to be used routinely. However, the thyroid gland is one of the most radiosensitive organs in the body it is often exposed to x-rays during dental radiography because of its anatomical position in the neck. Thyroid shielding during dental radiography, using a lead collar can reduce doses by 45% and is recommended for younger people. When not in use, lead aprons must be stored correctly and not folded to ensure they remain in good condition. They also require regular visual inspection. Fig.30 Thyroid gland Fig.31 Thyroid collar and lead apron in use Dental Radiographs There are two types of dental radiographs: 1.Intra-oral 2.Extra-oral Intra-Oral Radiographs These are the most common dental radiographs, where the x-ray beam is fired from an intra-oral x-ray machine at the target tooth or area of the jaw to produce an image on a film or sensor inside the mouth. The exposure time for this type of radiograph varies with the view being taken but is typically short at less than one quarter of a second. They provide excellent detail to check for dental caries, bone and periodontal health, developing teeth, anomalies or pathology. These views can be taken using any intra-oral x-ray machine in any dental practice, clinic or x-ray department.

27 Page 27 There are several types of intraoral radiographs: Periapicals- These should ideally be centred on the object tooth with the whole tooth including the root and approx.3mm of alveolar bone visible. They are used Fig.32 to detect tooth root problems or pathology (fig.32). Fig.33 Fig.34 Bitewings- Ideally these should show the crowns of the teeth from the distal surface of the canine to the mesial surface of the third molar; the crest of the alveolar bone with no overlapping of teeth. The image should centre on the crowns of the teeth with the occlusal plane horizontal. Bitewings are used to detect dental caries and bone levels. They can also be useful in determining the fit of a crown and integrity of restorations (fig.33). Occlusals- These use a larger film and show several teeth in one area. They are often used to assess positioning of growing teeth in children, particularly unerupted teeth (fig.34). A full mouth series is a set of intraoral radiographs which can be taken to show the full range of teeth. The number of films required, will vary from patient to patient but in most cases will be around 20 films- 4 bitewings and 16 periapicals. The full series shows almost the same diagnostic information as a panoral OPT radiograph and at reduced x-ray dose to the patient. Techniques used for Intra-Oral Radiographs There are two different techniques used for taking intra-oral dental radiographs: 1. Paralleling (long cone) 2. Bisecting Angle a) Paralleling Technique This is the technique of choice if possible, as the radiation to the patient is less than that with the bisecting angle technique. It aims to keep the tooth, film and x-ray beam on parallel planes. This requires film holders to achieve correct positioning together with a long cone (figs.35-36). Several manufacturers produce varying models of film holders but each brand has a number of different types for anterior, posterior, bitewing and endodontic radiographs. Film holders for conventional film and digital sensors differ and so the correct one must be used. Film holders are suitable for reprocessing in autoclaves, so they can be re-used. They consist of a plastic section which holds the dental film, attached to a plastic ring which is placed in front of the x-ray machine tube head.

28 Page 28 Fig.35 DENTAL FILM RING FOR FILM HOLDER X-RAY TUBE HEAD X-RAY BEAM PERPENDICULAR TO TOOTH AND FILM HOLDER FILM HOLDER IN MOUTH Fig.36 X-ray film holder For both maxillary and mandibular radiographs, the patient should be positioned with the maxillary occlusal plane parallel to the floor and the sagittal plane perpendicular to the floor. For mandibular radiographs, the patient may need to be tilted back in the chair to achieve this. b) Bisecting Angle Technique This was the original technique used prior to film holders being available. It exposes the patient to greater radiation than the paralleling technique and so should be used as a second choice or on patients who cannot tolerate a film holder. It uses a shorter cone than the paralleling technique. For radiographs of the maxilla or mandible, the patient needs to be positioned with the mandibular occlusal plane parallel to the floor and the sagittal plane of the head should be perpendicular to the floor. This technique involves placement of the dental film or sensor into the correct position in the mouth and getting the patient to steady the film or sensor in position with their finger. For bitewing views using film, the patient bites gently onto a paper tab to hold in place. The key principles are: 1. The central beam should pass through the area being examined 2. The film position should minimise image distortion This means that depending on the view being taken, the beam angle will need to be changed. The table below indicates the required angulations for different views. TABLE MAXILLA MANDIBLE Incisors +40 degrees -15 degrees Canines +45 degrees -20 degrees Premolars +30 degrees -10 degrees Molars +20 degrees +5 degrees

29 Page 29 For periapical views- The centre of the beam should be at right angles to an imaginary line which bisects the long axis of the tooth and the long axis of the film. BISECTOR LINE LONG AXIS OF TOOTH X-RAY HEAD PERIAPICAL INTRAORAL FILM X-RAY BEAM CENTRAL RAY PERPENDICULAR TO THE BISECTOR Fig.37 Periapical radiograph bisecting angle technique For bitewing views- The film is positioned parallel to the long axis of the teeth and the tube head is angled slightly downwards at +10 degrees. X-RAY HEAD BITEWING INTRAORAL FILM X-RAYBEAM CENTRAL RAY AT +10 DEGREES TO BITEWING TAB For occlusal views- Mandibular - The patient should be positioned with the occlusal plane at 45 above the horizontal which will mean tilting the head slightly backwards.they will need to bite gently onto a larger size 4 intra-oral film. The x-ray tube is placed under the chin at an angle of -55 with the central ray aimed at the apices of the mandibular central incisors. Lateral occlusal views are adaptions of this technique. Fig.12 Fig.38 Bitewing Bitewing radio radiograph bisecting angle MANDIBULAR OCCLUSAL- X-RAY TUBE IS PLACED UNDER CHIN POINTING UP AT 55 DEGREES Fig.39 Method for occlusal radiographs VERTEX OCCLUSAL- X-RAY TUBE IS PLACED AT THE TOP OF THE HEAD POINTING FORWARDS TO BE 90 DEGREES TO THE FILM Vertex Occlusal - The patient is seated with the occclusal plane parallel to the floor, biting gently onto a size 4 intra-oral film.the central x-ray is directed through the top of the skull with the beam at 90 to the film.

30 Page 30 Extra-Oral Radiographs These show less detail than intra-oral radiographs but provide more extensive views of the teeth, skull, jaws and anatomical structures. They are taken using a film within a cassette, outside of the mouth and are used to check for the presence of impacted or unerupted teeth, jaw growth, TMJ problems and pathology. Apart from the lateral oblique view, these views can only be taken using specialist dedicated x-ray machines which are not found in every dental practice, clinic or x-ray department. There are several types of extra-oral radiograph used in dentistry. The most common are: Panoramic - the most common view is the OPT (OPG) which shows all the teeth, upper and lower jaws, TM joints and bone. This view is useful in oral surgery and orthodontic treatment planning. Cephalometric views- show the entire side of the skull, jaw and teeth and are often used by orthodontists for measurements and sketches when treatment planning. Fig.40 OPT radiograph Fig.41 Lateral cephalogram Lateral oblique - this gives a view of one side of the jaw.often taken as right and left views using similar cassettes and as an alternative to the OPT. The patient holds the cassette to the side of the face and a regular intra-oral x-ray machine can be used to take the radiograph. Useful in younger children and those patients with a strong gag reflex. It can be taken using a cassette and intra-oral x-ray machine and is therefore of help in practices that do not have an OPT machine. Computed tomography (CT scan) - useful for identifying problems in the face, fractures or tumours as a 3D image is produced. However, specialist equipment in a hospital setting is required. Sialography This involves injection of a radio-opaque dye into the salivary glands followed by an x-ray film. It is used to identify salivary gland problems but can only be carried out in the hospital setting.

31 Page 31 Detection Systems The x-ray beam passes through the patient s body to provide a latent image which must be captured in order to produce a useful image. One of two methods is used: 1. A digital sensor capture system 2. Conventional dental film Digital Radiography In recent years, a number of digital imaging systems have come into use in dental practice. These are used as an alternative to conventional x-ray films and processing. Digital systems use an electronic sensor to capture the image from the x-ray beam. The sensor picks up analogue data in a continuous greyscale and this must be converted to digital data that can be processed by a computer. Digital radiographs also produce an image which can be viewed within a few seconds without the need to use processing chemicals. The disadvantage of this type of system is the initial start-up costs and the small size and thickness of some sensors resulting in placement and image errors. The sensors are expensive and this system also requires dedicated computer software as well as a computer system with sufficient memory to enable it to work. There are two types of intraoral digital systems currently available. a) Charge Coupled Device (CCD) sensor CCD systems convert radiation into visible light. This is transferred to the CCD sensor which then passes the signal on to a computer for conversion into an image. More recent sensors have a smaller pixel size. CCD systems are not cordless. The sensors vary in size and the user must decide which type they prefer when installing equipment. Image production from CCD sensor - Data captured by the sensor can be transmitted to a computer via Bluetooth, Ethernet, USB or wireless. Cross infection issues -As digital sensors are very expensive, they are not single use and so principles of cross infection must be introduced when using them. The majority of dental surgeries will have only one sensor for intra-oral x-rays and in practice tend to use a plastic protective barrier sleeve over the sensor which is changed with each patient use. Fig.42 Digital sensors Fig.43 Digital sensor with protective sleeve Fig.44 Digital radiograph on computer screen

32 Page 32 b) Storage phosphor (PSP) image plates When the image plate is irradiated, the absorbed X-ray energy is stored as a latent image within phosphor crystals. In a scanner, a narrow laser beam causes the release of the stored energy as visible blue light which is then turned into an electronic signal. Scanning is quick and the image can be viewed on a computer. PSP systems are cordless. A PSP is flexible and thinner than a piece of dental film and so can be placed in the mouth using the same film holders that are currently used for film. They also have a service life of approx. 1,000 exposures, making them more affordable than CCD s. PSP plates are placed inside a barrier envelope before placing in the patient s mouth. This barrier envelope needs to be cleaned and dried according to the manufacturer s instructions before the plate is removed for processing. Advantages of digital x-ray systems: Quicker image production Reduction in patient x-ray dosage Environmentally friendly as no processing chemicals required Disadvantages: Difficulty placing sensor in correct position as can be bulky in size Additional equipment costs for sensors, computers and additional software Infection control issues X-ray beam size is smaller and more radiographs may be needed to cover the same number of teeth One of the advertised advantages of using digital, radiography has been that the patient x-ray dosage is said to be lower but this is not always the case. When intra-oral digital systems are used in standard mode, the exposure is approx. 40% that of a standard E speed film. However, when used in high resolution mode, the exposure is actually greater than when using conventional film. In addition, the beam size for digital radiography is smaller, which means more digital pictures need to be taken to provide images for the same number of teeth. In some cases, this is twice as many. This also makes accuracy more difficult and often images need to be repeated due to operator error. In both cases, this can increase the patient x-ray dose. For film based radiographs: X-ray beam size is approx. 28cm 2 (circular tube) and 12cm 2 (rectangular tube). For digital based radiographs: X-ray beam size may be as small as 5cm 2, this means accuracy when positioning is essential as the beam size may be smaller than the sensor.

33 Page 33 CIRCULAR COLLIMATION X-RAY BEAM SIZE FOR CONVENTIONAL DENTAL FILM (ACTUAL LIFE SIZE) RECTANGULAR COLLIMATION X-RAY BEAM SIZE FOR DIGITAL RADIOGRAPHS (ACTUAL LIFE SIZE) Fig.45 X-ray beam sizes in conventional and digital dental radiography Digital X-ray Image Manipulation One advantage of digital radiographs is that the images can be adjusted or manipulated to improve diagnostic quality. Several different options are available, including: Brightness Radiographs that are too dark or too light can be adjusted to improve the image. For conventional radiographs this would involve a re-take but for digital, a poor image can be enhanced and used for diagnostic or monitoring. Colour The normal image (fig.46) can have a colour added (fig.47) and this too helps the human eye to pick up subtle changes which may otherwise be missed. Fig.46 Normal colour Fig.47 Radiograph with colour filter

34 Page 34 Contrast Modification The contrast can also be adjusted, which helps the user to see changes more easily on the image. A higher contrast aids caries detection and a lower contrast makes it easier to see periodontal changes. Reverse Grey Scale The image can be reversed or inverted so that what was radio-opaque appears radiolucent and vice versa. This can help in the visualisation of bone and pulp canals. Noise Reduction Filters can be used remove noise which is unnecessary data and this enhances and sharpens the image. However, overuse can result in blurring of the image. Zoom Digital images are routinely magnified by 4 times. Images can be further magnified to show up more detail. Fig.75 OPT radiograph and zoom into area of interest Digital Subtraction Images taken at different times can be combined and subtracted to show up changes over a period of time. This can be useful when monitoring conditions such as periodontal bone loss or apical healing following endodontic treatment. In order for images to be subtracted, they need to have been taken in exactly the same position which can be difficult to achieve. Computer software can now make slight adjustments if the images are not exact. Studies have shown digital subtraction to be a successful method of detecting and monitoring dental diseases such as bone lesions. Diagnostic Quality and Disease Detection Although the contrast on digital radiographs is not as good as on conventional radiographs, this is not thought to affect their diagnostic usefulness and several studies have shown that digital radiographs are equally as good in detecting dental conditions such as caries and bone loss.

35 Page 35 Image Output For optimum image display, digital radiographs must be viewed on a super VGA monitor (post 1989). The digital images produced are 20mm x 29mm and the number of pixels ranges from 134 x 203 up to 385 x 576. Standard images have an 8 bit grey level resolution. In a digital image with a bit depth of 8, each pixel has 2 8 (256) grey levels. A processor of at least 266 MHz speed is needed to support a digital x-ray system. In addition, care must be taken when choosing paper and printer quality if a hard copy is to be produced. For example, the printer needs to be able to produce an image with 28 or 256 shades of grey. Data Storage and Transfer If digital x-rays are to be sent electronically there are several factors that need to be considered. The software systems used are not always compatible and a digital radiograph taken on one system will not automatically transfer to another. There is an international standard, DICOM (Digital Imaging and Communications in Medicine) and systems that comply with this will allow successful data and image transfer. Several file formats can be used to store images on a computer, including jpg, gif, and png. An intra-oral radiograph requires approx. 200kB and an extra-oral radiograph approx.6mb. Files can be stored or transferred in their original format or compressed into a smaller file which uses less disc space and which are quicker to transfer. Compression of the images is needed otherwise practice computers would run out of computer memory storage. Newer digital systems produce better images and sensors use more bits per pixel to produce these improved images. As such, more data storage is required. In addition, back up storage on disc or tape is also required for dental IT systems including storage of digital radiographic images. Image Compression The compression of images can be either lossless or lossy. a) Lossless compression - The images are compressed unchanged and this process is reversible. The maximum rate of lossless compression is less than 3:1 b) Lossy compression - The images lose some of their quality when being compressed and this is irreversible. Research demonstrates that compression rates of up to 12:1 do not affect caries detection on dental radiographs. In dentistry this does not interfere with their diagnostic quality. Therefore both lossy and lossless files can be used. The most common format for digital radiographs is jpg.films.

36 Page 36 Dental Films Traditional methods using x-rays produce an image on a film which must be processed to capture a permanent image. Unused films need to be stored carefully as they are sensitive to stray radiation, temperature changes and some chemicals. Ideally they should be stored at temperatures lower than 20 C and so keeping them inside a refrigerator is recommended. Unused films should not be left out on a work surface or near an x-ray machine as stray radiation can affect the unused films even when kept inside their outer cardboard packaging. Films can be purchased from a number of manufacturer s in packs of Each pack will have an expiry date and film should be discarded once out of date. There are two types of x-ray films for dental use: 1. Non screen- Films used for intra-oral views are inside a cover of plastic, paper and foil. 2. Screen- Films used for extra-oral views come without any outer covering and must be stored in their box or in a specially designed cassette (screen) to prevent exposure to light prior to use. Size 0-22x 35mm Size 1-24 x 40mm Size 2-31 x 41mm Size 3-27 x 57mm There are several film sizes available and these vary according to the view being taken. The main sizes used for intra-oral views are: Periapical views- size 0,1,2 Bitewing views - size 0,2,3 Occlusal views- size 4 Size 0 films tend to be used more in children as the smaller size makes them easier to tolerate in the mouth. There is a marker dot on the outer plastic and the film itself which by convention should be placed towards the tongue and facing the x-ray tube. This aids identifying correct tooth positioning In the final radiograph. Size 4-57 x 76mm Fig.48 Intra-oral x-ray films life size Films come in differing speeds which has already been outlined. Double films are also available where each packet contains two films which will provide two identical radiographs.

37 Page 37 There are also larger film sizes available without protective packaging for use in cassettes in extra-oral views. These do not have a protective outer cover and so are light sensitive and should only be handled in safelight conditions. Used or unused films should only be removed from their outer packaging or from inside a cassette, in a dark room under safelight conditions. Intra-Oral Dental Film Contents The first pre-wrapped packets were invented by Kodak in Each individual intra-oral film consists of: Outer plastic wrapper to prevent moisture entry Black paper folded around the film Lead foil backing to absorb scattered radiation Fig.49 Intra-oral dental x-ray film contents A 0.2mm cellulose acetate film coated by an emulsion of silver halide crystals in gelatin Used and unused lead foils are considered hazardous waste and must be disposed of according to current waste regulations and guidance. They should be saved in a specialised container and removed by a dedicated waste company. If the lead can be re-used, then the waste company may offer payment according to weight. Extra-Oral Film, Intensifying Screens and Cassettes Screen films are used in conjunction with intensifying screens inside a protective cassette. The screen allows a good quality radiograph to be produced but at a lower radiation dose to the patient. The x-ray film is placed inside a cassette and is replaced under safelight conditions after each use. Cassettes Cassettes are light tight containers which hold x-ray film used for extra-oral dental radiographic views. They have intensifying screens inside. Each cassette has a flat front which faces the x-ray tube and is made of metal or plastic which must be transparent to x- rays. The back of the cassette is made from a stronger metal and is sprayed inside with lead paint to help reduce back scatter. There is also a felt pad at the back, to which are glued the intensifying screens. Spring clips hold the front and back of the cassette securely together during use. Each cassette must be clearly marked left and right using a lead marker on the front side. This is for diagnostic and medico-legal purposes. Faults such as loose clips or inadequate closure may develop with prolonged use and in time they may require repair or replacement.

38 Page 38 Intensifying screens These are plastic sheets coated with phosphors which are fluorescent. They convert x-ray photon energy into light energy. There is one screen on either side of the dental film within the cassette. During the time x-rays are fired, the phosphors in the intensifying screens produce fluorescence i.e. the x-ray photon energy is converted to light energy. There are 3 types of intensifying screens: Standard- calcium tungstate phosphors Rare earth-gadolinium or lanthanum phosphors Combined There are 3 speeds of intensifying screens: Slow Medium Fast Fig.50 X-ray cassette and intensifying screen In dentistry, rare earth intensifying screens tend to be used as they are efficient at converting x-rays to light energy and reduce radiation to the patient. The intensifying screens come already inside a cassette. If required, they can be cleaned using a damp cloth and antistatic solution. With use they can become loose and may need to be re-attached and in time will need replacement. Film Image Production When the silver halide (usually silver bromide) crystals are exposed to x-rays, they store the energy to create a "latent image" depending on the different densities that the x-rays have passed through. Different areas absorb x-rays by differing amounts. During film processing, energised crystals form deposits of metallic silver which appear darker on the film. The developer reacts with the energized crystals to make darker areas and the fixer removes unenergized crystals leaving those areas whiter. The ability for different tissues to absorb radiation is called attenuation. In time, the latent image will disappear and so the film should be processed as soon as possible. Storage in a fridge can slow attenuation, if processing cannot be carried out straight away.

39 Page 39 Film Processing The films must be removed from either the protective layers or cassette under safelight conditions in order to process the image. The resultant image on film must go through a processing system in order to produce a permanent record. Dental x-ray films are processed in either a manual or automatic processing machine in a dark room where the image goes through a series of developer, fixing and rinsing solutions. When this type of processing takes place, there should be a quality assurance system in place to ensure that there are: Records to control and validate the chemical changes Adequate cleaning procedures for automatic processors Solutions are checked every 2/3 days Solution temperatures are checked before use Dark Room Processing in a dark room helps in the production of high quality radiographs. When processing, normal room lights must be switched off and a safelight used. The dark room should have: No light leakage and use of safelight Use equipment which has been installed and maintained correctly Use, store and replace processing chemicals with care Testing for light leakage in a dark room Close the door Switch off normal lighting and switch on the safelight Remove an unused dental film from its protective sleeve and place on work surface Place a coin on top of the film for 2 minutes Process the film If the outline of the coin can be seen, then the darkroom is too bright and needs to be adjusted. Dark rooms must be made light tight to prevent fogging of films. Routine checks should be carried out at least every 12 months with a written log kept. Safelight A safelight is a coloured filter used in a darkroom which does not adversely affect photosensitive film. A safelight should be bright enough to allow the operator to handle and process a radiograph correctly but not too bright otherwise the film may become fogged. For dental radiographs the safe filter to use is dark red GBX-2.

40 Page 40 Ideally, the safelight should be at least 1.2m (4ft) away from the area where the film will be handled. It is also useful to regularly check the integrity of the safelight. Handling of Films Once the safelight is working, dental films need to be removed from their protective plastic, paper and foil coverings. They should be handled carefully by the edges to avoid nail or finger marks and placed correctly into the processor. Films will need to be attached to a hanger if going through a manual processor. Processors and Chemicals Machines which process dental films can be manual where the operator places the film in the different solutions in a set order and timescale or automatic where the operator places the film at the start of the process and collects the film at the end of the machine cycle. Cycles can take 4-6 minutes; the higher the temperature, the shorter the developer time. The ideal temperature range is C. Processors use developer and fixer solutions as well as water and require careful maintenance to ensure they produce good quality radiographs. Typical Contents of Developer and Fixer Solutions Developer contains: Hydroquinone + Elon (reducing agent) Sodium sulphite (preservative) Sodium carbonate (accelerator) Potassium bromide (restrainer) Water Fixer contains: Sodium or ammonium thiosulfate (fixing agent) Sodium sulphite (preservative) Potassium alum (hardening agent) Acetic or sulphuric acid (acidifier) Fig.51 Processing chemicals and x-ray processor Developer solution -has a ph of 7 and contains the reducing agents, hydroquinone and elon which blacken the silver halide crystals on the dental film. These chemicals help give dental film contrast and detail. They are in an alkaline solution of sodium carbonate which helps activate the reducing agents. If the reducing agents work too quickly, the film can fog.

41 Page 41 Therefore, potassium bromide is added to the developer solution to act as a restrainer. Both the alkaline medium and reducing agents can be affected by oxygen and so developer solution also contains sodium sulphite which acts as a preservative, preventing oxidation and increasing life expectancy of the solution. Fixer solution- Fixer stops the development process and removes any unexposed crystals from the film. The sodium thiosulphate is the chemical responsible for this and acetic acid ensures acidic conditions for it to work correctly. As in developer, sodium sulphite acts as a preservative, preventing oxidation and increasing life expectancy of the solution. Potassium alum hardens the gelatin emulsion. This protects the film and helps it dry more quickly. Used fixer solution can stain clothing as it contains silver salts. The quality of radiographs is influenced by the chemical processing potential of the solutions and these can be affected by: Temperature - They become inactive when cold and deteriorate when hot Use - The more they are used, the shorter their life expectancy Exposure to air - The chemicals can oxidise in air which shortens their life expectancy Key rules for Quality Image Production: Change chemicals every 2-4 weeks or sooner if more than 30 films processed daily Top up developer and fixer solutions every day, if they are running low. Summary of Procedure for Manual Processing 1.Set up the processor correctly 2.Check the temperature using a thermometer and check with guidance chart 3.Attach films to film holder 4.Immerse in developer solution, gently moving for 5 seconds then still 5.Remove from developer after the set time 6.Immerse the film into the rinse tank for 30 seconds and keep moving 7.Place film in fixer for up to 4 minutes, agitating every 30 seconds. 8.Allow excess fixer to drain back into the fixer tank before washing 9.Wash film for 10 minutes in clean running water but do not leave in the water for any length of time as the image could be damaged 10.Allow the film to dry on the hanger at room temperature Regulation of Water Temperature Different processors have different water needs with some requiring no water at all.

42 Page 42 Routine Checks for Processors At the start of each day: Check chemical levels and top up if required Turn on the power supply Turn on the water supply (if necessary) Place a trial film through the processor For manual processors a film hanger will be needed. At the end of each day: Turn off the power and water supplies to the processor Wash and dry hangers and clips if used It is important that equipment is used correctly and any accidental chemical spills cleaned immediately according to the surgery or clinic s risk assessment. Disposal of Waste Developer and Fixer Solutions Both developer and fixer solutions (whether used or unused) are considered as hazardous waste and must be disposed of according to current guidance and regulations. They cannot be flushed down the sink as regular waste. Fixer solution contains silver salts. Used solutions should be placed in waterproof containers and removed by a specialised waste company. Film Storage, Mounting and Viewing The radiograph image produced by digital sensors can be easily stored on a computer s memory or mobile device (fig.52). The image can be magnified or manipulated to enhance diagnosis. Radiographs produced using conventional film will need to be correctly stored and mounted if possible. All radiographs must have a patient identifier and date recorded on them. Conventional radiographs are often stored in a paper envelope inside a patient s record card but ideally they should be kept in cardboard or plastic mounts for protection and easier viewing. Radiographs are best viewed on an illuminated light box viewer (fig.53). Fig.52 Fig.53

43 Page 43 Common Factors Affecting Conventional X-ray Film Image Quality A list of common faults on radiographs and their causes is outlined below: FAULT POSSIBLE CAUSES POSSIBLE SOLUTIONS Too dark Film overdeveloped Developer too warm Film exposed to light during processing Check dark room for light leakage Check safety light Use a timer and thermometer Too light Film underdeveloped Developer too cold Developer solution old or diluted Film past expiry date Fogged film Film overdeveloped Film exposed to light during processing Films exposed to radiation after exposure Yellow, green or brown film Fixer solution old or contaminated Poor rinsing of films after fixing Films stuck together Use a timer and thermometer Change processor solutions Check film use by date before use Check dark room for light leakage - Check safety light Use a timer and thermometer Take exposed films out of room when exposing other radiographs Change processor solutions Wash correctly after fixing Unstick the films and put through fixer /rinse stage again Black spots Developer gas splashed onto film Take care not to splatter when changing solutions White spots Water splashed on to film before placing Take care not to splatter in developer solution Lines on film Finger nail marks Keep nails short and take care Bending film during processing Static electricity Do not bend films Use agent to reduce static or humidify processing environment Streaks/artefacts Chemicals exhausted Poor rinsing between developer and fixer solutions Dirty rollers Patient anomalies Change solutions regularly-more frequently in warmer weather and if increased number of radiographs being taken Regularly clean and maintain equipment Check patients for anomalies such as piercings, hair grips, hearing aid Area coned off Incorrect tube and/or film positioning Check alignments Teeth shortened or Incorrect film or tube angulation Use film holder to aid correct elongated positioning Tooth overlaps Central ray mis-angulation Apex missed Incorrect tube and/or film positioning (periapical) Blurred image Patient movement Explain importance of keeping still Film used twice and that a beeping noise will occur during exposure Take care of films once used to avoid mix-up Grainy image blurred Film not tube side in mouth Film past expiry date Ensure correct film placement Check film use by dates

44 Page 44 Radiographs and Patient Records Radiographs are considered to be part of the patient record (figs.54-56). As such their use and storage whether conventional or digital must comply with legislation on data protection, confidentiality and record keeping. Fig.54 Patient record cards Fig.55 Dental radiograph Fig.56 Computer The rules for keeping dental records (including radiographs) are: Children and young people Records must be kept until the patient is aged 25 (or 26 if they are 17 when treatment ends) or eight years after death Records may be kept longer if a child s illness or death could be relevant to an adult condition or have genetic implications for their family Adults At least 11 years Records relating to people with a mental disorder 20 years after the last contact between the patient and a healthcare professional or eight years after the patient's death The NHS Dental Contract requires records to be kept for up to 2 years after a course of treatment has finished but the Consumer Protection Act 1987 requires records to be kept for at least 11 years. The Data Protection Act (1998) prohibits sensitive personal data (dental records) from being kept any longer than necessary. However, the limitation period for starting a negligence claim is 3 years (6 years if private treatment) and for a child until the age of 21; this means claims can arise many years after treatment and having records including radiographs is very helpful.

45 Page 45 Clinical Indications for taking Radiographs in Dentistry Caries Detection For caries risk, bitewing radiographs are recommended. For adults: High caries risk-every 6 months Moderate caries risk-every 12 months Low caries risk-every 24 months For children: High caries risk-every 6 months Moderate caries risk-every 12 months Fig.57 Bitewing radiograph Low caries risk-every 12 months (deciduous teeth) and 24 months (permanent teeth) Early enamel caries progresses slowly (up to two years to reach dentine).early detection of enamel lesions can allow early preventive intervention which is a health benefit. Pregnant Patients IR (ME) R 2000 regulations state that a medical exposure of any woman of child bearing age is prohibited unless she has been asked if she is pregnant. In dental radiography there is little chance of x-rays reaching the pelvic area unless taking a vertex occlusal view. The risks to the developing foetus are very low and there is no contra-indication to radiography for women who are pregnant. The use of a lead apron is not necessary though in some countries it is recommended. Despite this, the use of x-rays during pregnancy is emotive and as such it is recommended that patients be given the option to delay the procedure until after the pregnancy, if they so wish. New Patients Routine radiographic screening of new patients is not recommended. Any radiographs should be taken on an individual basis depending on the history and clinical examination of the patient. Edentulous patients do not normally require any radiographs unless there is concern of retained roots or pathology. A number of studies show that dentists are able to detect caries better from full mouth periapical and bitewing views than from a panoramic radiograph. In addition, full mouth periapical radiographs show periodontal bone loss better than an OPT. Consider a lateral oblique view or OPT if the patient has difficulty in compliance or strong gag reflex, especially in children.

46 Page 46 Recall Patients with High Caries Risk (or clinical caries) Primary and Mixed Dentition -Posterior bitewings every 6 months until no new carious lesions Permanent Dentition up to 18 years - Posterior Bitewings every 6-12 months Permanent Dentition over 18 years - Posterior Bitewings every months Recall Patients with Low Caries Risk (or no clinical caries) Primary and Mixed Dentition - Posterior Bitewings every months Permanent Dentition up to 18 years - Posterior Bitewings every months Permanent Dentition over 18 years- Posterior Bitewings every months Permanent Dentition over 18 years - Posterior bitewings every months Monitoring the Developing Dentition /Orthodontic Assessment Radiographs and particular views should be taken on an individual basis, often dependent upon patient co-operation factors. Occlusal views are useful in showing unerupted or impacted teeth. Lateral oblique views may be easier than taking an OPT view as some children are frightened by the beeping noise of the x-ray machine and may move while taking the radiograph. Fig.58 Periapical radiograph showing impacted canine teeth Fig.59 Periapical radiograph showing midline supernumerary as well as developing permanent teeth Locating the Position of an Unerupted Tooth using Radiographs There are two methods which can be used to help locate the position of an unerupted tooth. The first is by taking two radiographs at 90 to each other. The second is using the tube shift (alternative names Clark s rule, buccal object rule) method. This method involves taking two radiographs where the tube head position has been moved in the second radiograph. When studying the radiographs, if the object (e.g. unerupted tooth) has moved in the same direction as the tube head it is lingually or palatally placed. If the object has moved in the opposite direction it is buccally placed. The acronym SLOB (Same-Lingual-Opposite-Buccal) can be used to remember this.

47 Page 47 Periodontal Assessment Posterior bitewings and vertical bitewings give excellent views of bone loss and are therefore useful views to monitor periodontal disease. Vertical bitewings are very similar to normal posterior bitewings except that the film is turned vertically. Vertical bitewings can be used on anterior and posterior teeth, although it is more difficult on posterior teeth, as the film positioning could be uncomfortable for the patient and difficult to tolerate. The vertical bitewing therefore tends to be used more on anterior teeth. Fig.60 Vertical and horizontal bitewing radiographs using conventional film Fig.61 Vertical and horizontal bitewing radiographs using digital sensor Periapical and panoramic views can also be helpful. The process of subtraction in digital radiography is also beneficial in monitoring periodontal bone loss, as images of the same teeth or area can be critically compared in the long term. Fig.63 Fig.62 Figs Periodontal disease clinically and on radiographs Fig.64

48 Page 48 Endodontic Treatment Periodical radiographs should be taken at the following stages: Pre-operative to check canals and any pathology (fig.65) Apical length determination (fig.66) Post obturation 1 year post obturation (fig.67) Fig.65 Fig.66 Fig.67 Fig Radiographs during endodontic treatment Extractions and Oral Surgery Radiographs are not required for routine extractions except for third molars where proximity to the ID canal (fig.70) and lower border of the mandible are clinically important. However, they may be useful in some cases such as: Orthodontic extractions to check for permanent successors or unerupted teeth Unusual anatomy Previous difficult extractions Medical history concerns To check for position of buried roots Fig.68 Figs Clinical picture and radiograph of root fractures Fig.69 Fig.70 Fig.70 Radiograph showing position of ID canal