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RADIOGRAPHY & RADIATION PROTECTION

A Guide for the Dental Team

CPD Module 020

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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.

RADIOGRAPHY AND RADIATION PROTECTION

CPD Module 020 Fig.1

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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

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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.

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.

CPD on the subjects of both radiography and radiation protection are core compulsory subjects

for dental professionals on the UK GDC register.

Fig.2 Periapical radiograph Fig. 3 Bitewing radiograph Fig.4 OPT radiograph

Fig.5 The trefoil radiation symbol

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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 HIGHER ENERGY LONGER WAVELENGTH 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

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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

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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.

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.

Fig.7 Dental Radiograph Fig.8 MRI scanner Fig.9 Tracer isotope injection

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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.

Fig.10 DNA helix Fig.11 Cataracts of the eye

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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.

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.

DNA BREAK

DNA BREAK

Fig.12 DNA helix

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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 0.001-0.083

One dental panoramic radiograph 0.0038-0.03

Return flight from London to Glasgow 0.004

Eating 135g bag of brazil nuts 0.005

One chest x-ray 0.02

Return flight from London to LA 0.16

One CT scan mandible 0.364-1.202

2.4 Table 2

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

Fig.13 Aeroplane Fig.14 Periapical radiograph Fig.15 Brazil nuts

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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

of radiographs for screening is not advised.

Fig.16

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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 • 1996- Directive 96/29/Euratom

• 1997 -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

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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.

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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

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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

RISK ASSESSMENT

MEASURE

ASSESS

EVALUATE

MANAGE

Fig.17

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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

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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.

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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

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.

Fig.20 OPT Radiograph

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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 1994.

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

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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).

Fig.23 Magnification of image with short and long cone x-ray tubes

A shorter cone increases magnification of the final image

A longer cone reduces magnification of the final image

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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).

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.

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. 24 Panoramic X-Ray machine and the light indicators for patient positioning

Fig.25 Technique for lateral oblique radiograph

CASSETTE

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Installation, Replacement and Maintenance X-ray equipment must be designed, constructed and installed in accordance with British Standard

60601. 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

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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.

.

METAL HOUSING

TUBEHEAD SEAL ALUMINIUM FILTER LEAD COLLIMATOR

INSULATING OIL

SCATTER X-RAYS

X-RAY BEAM

anode

X-RAY TUBE cathode anode cathode

X-RAY TUBE

Fig.26 Intra-oral x-ray machine internal and external views

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

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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.

ALUMINIUM FILTER AT THE FRONT OF THE HOUSING

LEAD COLLIMATOR AT THE BACK OF THE PID

X-RAY HOUSING UNIT

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.

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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.

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%.

FILM FILM

CIRCULAR COLLIMATION RECTANGULAR COLLIMATION

Fig.29 Rounded and rectangular collimation compared to film size

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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.

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.

Fig.30 Thyroid gland Fig.31 Thyroid collar and lead apron in use

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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.

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.

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

to detect tooth root problems or pathology (fig.32).

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).

Techniques used for Intra-Oral Radiographs There are two different techniques used for taking intra-oral dental radiographs:

1. Paralleling (long cone)

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).

Fig.33

Fig.34

Fig.32

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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

X-RAY BEAM PERPENDICULAR TO

TOOTH AND FILM HOLDER

X-RAY TUBE HEAD

RING FOR FILM

HOLDER

DENTAL FILM

FILM HOLDER

IN MOUTH

Fig.35

Fig.36 X-ray film holder

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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.

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.

Fig.12 Bitewing radio

Fig.38 Bitewing radiograph bisecting angle

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.

X-RAY HEAD

PERIAPICAL INTRAORAL

FILM

X-RAY BEAM CENTRAL RAY

PERPENDICULAR TO THE BISECTOR

LONG AXIS OF TOOTH BISECTOR

LINE

X-RAY HEAD

X-RAYBEAM CENTRAL RAY AT +10 DEGREES TO BITEWING TAB BITEWING

INTRAORAL FILM

MANDIBULAR OCCLUSAL- X-RAY TUBE IS PLACED UNDER CHIN POINTING UP AT 55 DEGREES

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.

Fig.39 Method for occlusal radiographs

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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:

Fig.40 OPT radiograph Fig.41 Lateral cephalogram

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.

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.

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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.43 Digital sensor with protective sleeve

Fig.44 Digital radiograph on computer screen Fig.42 Digital sensors

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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. 28cm2 (circular tube) and 12cm2

(rectangular tube). For digital based radiographs: X-ray beam size may be as small as 5cm2, this

means accuracy when positioning is essential as the beam size may be smaller than the sensor.

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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

CIRCULAR COLLIMATION

X-RAY BEAM SIZE FOR CONVENTIONAL DENTAL FILM

(ACTUAL LIFE SIZE)

X-RAY BEAM SIZE FOR DIGITAL RADIOGRAPHS

(ACTUAL LIFE SIZE)

Fig.45 X-ray beam sizes in conventional and digital dental radiography

RECTANGULAR COLLIMATION

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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.

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.

Fig.75 OPT radiograph and zoom into area of interest

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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 28 (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.

P a g e | 36

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 0 - 22x 35mm

Size 2 - 31 x 41mm

Size 1 - 24 x 40mm

Size 3 - 27 x 57mm

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.

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 100+. 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.

P a g e | 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 1913.

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

• 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.

Fig.49 Intra-oral dental x-ray film contents

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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

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.

Fig.50 X-ray cassette and intensifying screen

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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.

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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 20-26.5°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)

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.

Fig.51 Processing chemicals and x-ray processor

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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.

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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

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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

Use a timer and thermometer Change processor solutions Check film use by date before use

Fogged film • Film overdeveloped • Film exposed to light during processing • Films exposed to radiation after exposure

Check dark room for light leakage - Check safety light

Use a timer and thermometer Take exposed films out of room

when exposing other radiographs Yellow, green or brown film

• Fixer solution old or contaminated • Poor rinsing of films after fixing • Films stuck together

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

in developer solution Take care not to splatter

Lines on film • Finger nail marks • Bending film • Static electricity

Keep nails short and take care during processing

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 Use film holder to aid correct

positioning

Teeth shortened or elongated

• Incorrect film or tube angulation

Tooth overlaps • Central ray mis-angulation Apex missed (periapical)

• Incorrect tube and/or film positioning

Blurred image • Patient movement • Film used twice

Explain importance of keeping still and that a beeping noise will occur during exposure

Take care of films once used to avoid mix-up

Grainy blurred image

• Film not tube side in mouth • Film past expiry date

Ensure correct film placement Check film use by dates

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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.

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.

Fig.54 Patient record cards Fig.56 Computer

Fig.55 Dental radiograph

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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

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.

Fig.57 Bitewing radiograph

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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 12 - 18 months

Recall Patients with Low Caries Risk (or no clinical caries)

• Primary and Mixed Dentition - Posterior Bitewings every 12-24 months

• Permanent Dentition up to 18 years - Posterior Bitewings every 18-36 months

• Permanent Dentition over 18 years- Posterior Bitewings every 24-36 months

• Permanent Dentition over 18 years - Posterior bitewings every 24-36 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.

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.

Fig.59 Periapical radiograph showing midline supernumerary as well as developing permanent teeth

Fig.58 Periapical radiograph showing impacted canine teeth

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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.

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.60 Vertical and horizontal bitewing radiographs using conventional film

Figs.62-64 Periodontal disease clinically and on radiographs

Fig.63

Fig.62

Fig.64

Fig.61 Vertical and horizontal bitewing radiographs using digital sensor

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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)

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.65-67 Radiographs during endodontic treatment

Fig.65 Fig.66 Fig.67

Figs 68-69 Clinical picture and radiograph of root fractures

Fig.68 Fig.69

Fig.70 Radiograph showing position of ID canal

Fig.70

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Implants Radiographs are recommended when considering implants for patients. The views taken will

vary on the needs of the individual and the procedure but should include:

Pre-operative

During placement (if needed)

Post-operative

One year review and subsequent reviews if necessary

Pathologies Radiographs can show pathologies which may or may not be symptomatic (figs.73-74). Some

may show up on routine views taken for other reasons. Radiographs can be helpful in

diagnosis especially when a radiologist’s report is given.

Fig.71 Clinical picture of implants Fig.72 Radiograph of implant

Fig.73-74 Radiographs showing cysts in the mandible

Fig.73

Fig.74

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This is the end of the module. Click on the link below to access the online assessment.

https://docs.google.com/forms/d/1BtgoqZmImqr6xHW8mq9Tsv_uVPDLY3IuGz3GSocIVfM/viewform

P a g e | 51

REFERENCES 1. General Dental Council CPD http://www.gdc-uk.org/Dentalprofessionals/CPD/Pages 2. Dental Radiation Safety Handbook 2009 https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/27807/Leaflet25DentalMar09.pdf 3. Hart D, Wall BF, Hillier MC, Shrimpton PC -Frequency and Collective Dose for Medical and Dental X-ray Examinations in the UK 2008 Health Protection Agency 2010 ISBN 978-0-85951-684-6 http://www.hpa.org.uk/webc/HPAwebFile/HPAweb_C/1287148001641-accessed online 12.12.12 4. Report of the United Nations Scientific Committee on the Effects of Atomic Radiation 2010 (UNSCEAR) published May 2011 5. United States Nuclear Regulatory Commission-accessed online 23.12.12 http://www.nrc.gov/reading-rm/basic-ref/glossary/radiation-warning-symbol.html 6. The Environmental Permitting (England and Wales) (Amendment Regulations) 2011 http://www.legislation.gov.uk/uksi/2011/2043/contents/made-accessed online 03.01.13 http://www.legislation.gov.uk/uksi/2001/2975/contents/made 7. Emergency preparedness and public information Regulations 2001 (REPPIR) http://www.legislation.gov.uk/uksi/2001/2975/contents/made-accessed online December 2012 8. Code of practice for radiological protection in Dentistry 1996 Radiological Protection Institute of Ireland. 9. Maintaining Standards General Dental Council 2001 http://www.gdcuk.org/Newsandpublications/Publications/Publications/MaintainingStandards[1].pdf 10. Phinney DJ, Halstead JH Dental assisting a comprehensive approach Thomas Learning 2000 http://books.google.co.uk/books?id=r3E1SujL9IC&pg=PA322&lpg=PA322&dq=what+is+in+dental+x+ray+film+packet&source=bl&ots=ezStn2nekY&sig=fsZ3RLS0kkByo5SDSwrcRrqxMbI&hl=en&sa=X&ei=ftfXUKf3O_OM0wWhlYDYAw&ved=0CIQBEOgBMA0#v=onepage&q=what%20is%20in%20dental%20x%20ray%20film%20packet&f=false -accessed online 23/12/12 11. http://www.radman.co.uk/resources/dental-radiography-and-x-ray.aspx-accessed online December 2012 12. http://www.columbia.edu/itc/hs/dental/sophs/material/screens.pdf-accessed online December 2012 13. European Guidelines on Radiation Protection in Dental Radiology-The Safe Use of Radiographs in Dental Practice 2004http://ec.europa.eu/energy/nuclear/radioprotection/publication/doc/136_en.pdf 14. Rowson J, Slaney A -Dentistry for Lawyers Hardback: 978-1-85941-212-1: Published October 27th 1996 by Routledge-Cavendish 15. Ionizing Radiation (Medical Exposure) Regulations (IR (ME) R 2000 http://www.dentrpa.com/faq.asp#menu6 16. Beaconsfield, T., R. Nicholson, A. Thornton, and A. Al-Kutoubi. 1998. Would thyroid and breast shielding be beneficial in CT of the head? Eur Radiol 8:664-7. 17. http://www.dentalxrays.info/blog/long-and-short-it-all-accessed online 03.01.13 18. Hirschmann, P. N. 1995. Guidelines on radiology standards for primary dental care: a resume. Royal College of Radiologists and the National Radiological Protection Board. Br Dent J 178:165-7. 19. National Radiological Protection Board. 2001. Guidance notes for Dental Practitioners on the Safe Use of x-ray equipment. Department of Health, London. http://www.hpa.org.uk/webc/HPAwebFile/HPAweb_C/1194947310610 20. Reglement gran-ducal du 16 mars 2001 relatif a la protection sanitaire des personnes contre les dangers des rayonnements ionisants lors d'expositions a des fins medicales,. Journal Officiel du Grandduche de Luxembourg, Receuil de Legislation 6 juin 2001, Luxembourg 21.http://www.bda.org/dentists/advice/practice-mgt/laws/ethics/records/storage-retention-disposal.aspx-accessed online 03.01.13 22. Horner, K. 1994. Review article: radiation protection in dental radiology.Br J Radiol 67:1041-9. 23. http://www.carestreamdental.com/film-and-anesthetics/intraoral-film-size.aspx-accessed online 03.01.13

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24.http://www.carestreamdental.co.uk/~/media/Files/FILM%20AND%20ANESTHETICS/Support/Exposure%20and%20Processing%20for%20Radiography.ashx -accessed online 23/12/12 25. http://www.airtechniques.com/userfiles/files/Article_Digital_Radiography_Systems.pdf – accessed online 03.01.13 26. http://www.nhs.uk/chq/Pages/1889.aspx?CategoryID=68-accessed online 03.01.13 27. Directive 96/29/Euratom http://ec.europa.eu/energy/nuclear/radioprotection/doc/legislation/9629_en.pdf 28. Directive 97/43/Euratom http://ec.europa.eu/energy/nuclear/radioprotection/doc/legislation/9743_en.pdf 29. Health & Safety at Work Act 1974 http://www.legislation.gov.uk/ukpga/1974/37 30. The Reporting of Injuries, Diseases and Dangerous Occurrences Regulations 1995 http://www.legislation.gov.uk/uksi/1995/3163/contents/made 31. The Provision and Use of Work Equipment Regulations 1998 http://www.legislation.gov.uk/uksi/1998/2306/contents/made 32. Ionising Radiation Regulations 1999 http://www.legislation.gov.uk/uksi/1999/3232/contents/made 33. Management of Health and Safety at Work Regulations 1999 http://www.legislation.gov.uk/uksi/1999/3242/contents/made 34. The Hazardous Waste (England and Wales) Regulations 2005 http://www.legislation.gov.uk/uksi/2005/894/contents/made 35. 2011-The Waste (England and Wales) Regulations http://www.legislation.gov.uk/ukdsi/2011/9780111506462/contents 36. The Environmental Permitting (England and Wales) (Amendment) Regulations 2011 http: //www.publications.parliament.uk/pa/cm200809/cmindex/495/index-15.htm 37. http://books.google.co.uk/books?d=HO5qCgsYmy0C&pg=PA281&dq=dental+digital+radiography +image+sensors&hl=en&sa=X&ei=TLHjUY61LOPC0QXV84DoCw&ved=0CDkQ6AEwAA#v=onepage&q=dental%20digital%20radiography%20image%20sensors&f=false Except where explicitly stated, all content is © Copyright 2013 of MDMS4U Ltd, all rights are reserved, and content should not be copied, adapted, redistributed, or otherwise used without the prior written permission of MDMS4U Ltd. Any unauthorised publication, copying, hiring, lending or reproduction is strictly prohibited and constitutes a breach of copyright. Third party pictures Fig.1 copyright Tyler Olsen @ Fotolia.com- used under license agreement with Fotolia.com. Figs.2-5,7-16,18-22,24,25,27,30-35,40-44,46,47,49-59,62-74 used under public license from Wikimedia Commons.Copyright resides with the respective owners.