New technology in dental practice offers both advantages and risks. Dr Suk Ng discusses cone beam CT with Susan Field.

From intraoral cameras to 3D printing, there is no shortage of exciting developments with the potential to transform dental practice. Practitioners are usually willing to embrace the latest technology if it means they can provide an even higher standard of care or respond to patient demand, but most recognise the need to weigh up the pros and cons before making an investment decision.

One innovation which requires particularly careful thought is cone beam computed tomography (CBCT), where a cone-shaped X-ray beam provides three-dimensional cross-sectional digital images of the patient's teeth and jaws. Once limited to hospital dentistry, CBCT machines are gradually becoming more common in general dental practice. But while this technology is capable of generating high quality dental images in three dimensions, it should not be regarded as an upgrade for conventional radiography equipment.

Dr Suk Ng is president-elect of the British Society of Dental and Maxillofacial Radiology. As she explains, CBCT is particularly valuable in some treatment planning because the imaged volume can be manipulated in any direction or plane to provide more information about the bone shape and density, the relationship between a tooth and adjacent structures such as the ID canal, etc. This helps avoid serious complications, such as nerve damage when placing an implant or removing an impacted wisdom tooth.

'CBCT can be a fantastic diagnostic tool,' says Dr Ng. 'For instance, a dentist referred a patient to me because the root of an upper tooth had broken off during extraction and they were unable to find it. The CBCT scan allowed us to view the area from multiple angles and we were eventually able to find the missing root in the patient's maxillary sinus.'

CBCT scanners first appeared in hospital dental radiology departments about 10 years ago, but the technology is starting to be adopted more widely. Dr Ng suggests this trend has been driven by a range of factors, particularly the growing popularity of implant treatments, competition between manufacturers (which has driven down the price of machines and components), and the development of dual purpose machines combining panoramic and cone beam capabilities.

At the same time, Dr Ng cautions against CBCT machines becoming a must-have piece of equipment, a trend she has noted in the United States. 'People tend to expect that technology is going to get better all the time,' she reflects, 'but I'd be concerned if CBCT scans were to become routinely given to every patient instead of using conventional intraoral and extraoral radiography.'

She continues: 'While CBCT images can provide much more information for the person interpreting them, this comes at a cost. X-rays are associated with a potential risk for cancers and the radiation dose of CBCT is higher than from conventional dental X-ray equipment. Whenever our radiology department receives a referral, we are first obliged to weigh the risks and benefits for the patient and decide if each exposure can be clinically justified.'

Dr Ng notes that the justification of every medical and dental radiograph is a key principle of the Ionising Radiation (Medical Exposure) Regulations 2000 (commonly referred to as IR(ME)R), which are intended to ensure the safety of patients undergoing any type of X-ray examination during the course of treatment.

Any dentist considering CBCT for their practice must be prepared to invest not just their money but their time.

In its own guidance on the safe use of CBCT, the Health Protection Agency (HPA, but now known as Public Health England) is even more precise: 'Only dental CBCT examinations that will provide extra information to aid the patient's management or prognosis and which cannot be gained from lower dose conventional imaging techniques should be authorised.'

Interpretation and training

In addition, Dr Ng warns that the expanded field of view provided by a CBCT scan poses particular practical and diagnostic challenges. 'When a dentist requests a CBCT scan they usually have a specific purpose in mind such as a wisdom tooth or implant but they have to avoid tunnel vision when interpreting the scan because IRMER requires the dentist to examine the whole imaged volume for pathology, not just the area of interest.

'In my experience, most dentists are apprehensive about missing any potential cancers and have this in mind when interpreting images. A CBCT scan will often include parts of structures immediately surrounding the dental alveolar region such as the maxillary sinus and nasal cavity. Clinical evaluation therefore needs an advanced knowledge of anatomy and an understanding of how to interpret CBCT images, which requires training and experience.

'Even operating a cone beam machine requires sufficient anatomical knowledge in order to position the patient correctly, set the field of view and assess the quality of the scan to ensure it has captured the area of interest declared in the original prescription. For this reason I would argue that operating a machine cannot be delegated to a dental nurse, even if they have completed dental radiography training. Such training would not have covered anatomy and image interpretation to the required standard.'

While dentists do cover anatomy and (conventional) radiography at dental school, the HPA's guidance says that 'the introduction of a new technique such as dental CBCT will require additional training' and recommends minimum training requirements. And more recently, a position paper setting out detailed training criteria for dentists was produced by the European Academy of Dento Maxillo Facial Radiology (EADMFR).

Prism with light refracting through it

Photo credit: Science Photo Library

The British Society of Dental and Maxillofacial Radiology (BSDMFR) has devised a two-part training course based on the EADMFR guidelines. Further information can be found on the BSDMFR website.

'Anyone considering CBCT for their practice must be prepared to invest not just their money but their time,' reflects Dr Ng. 'As well as completing the necessary training themselves, they need to ensure that staff who are not directly involved have enough information to ensure their safety and to respond appropriately to questions from patients.'

Provided practices have already notified the Health and Safety Executive (HSE) that X-ray equipment is being used on the premises, the addition of CBCT does not constitute a 'material change' and further notification is not required.

But even if it is not necessary to inform HSE, CBCT equipment is not something you can just buy and start using, warns Dr Ng. 'You must contact your RPA and consider the level of radiation protection because of the higher doses of radiation emitted by CBCT scanners compared to conventional equipment.' This includes the machine's surroundings as well as the machine itself.

Within the practice, the employer (legal person) has the overall responsibility for the safe and effective use of all X-ray equipment, and ensuring that staff are trained and competent in performing their respective IRMER duties. The practice's Radiation Protection Supervisor (RPS) will usually be responsible for day-to-day overview and implementation of the local rules.

Radiation safety measures should already be in place but it is important to review and augment the local rules and to set up procedures in areas such as Quality Assurance (equipment and image quality), the protocol for justifying and authorising CBCT exposures, the designation of controlled areas, dentist and staff training, audits and record-keeping to ensure they are appropriate for CBCT (see box).

The HPA suggests that the practice's RPS may require further specific training in radiation safety. Where a practice accepts referrals from external dentists, then the referral procedure should be set out clearly and selection or referral criteria should be specified. Published guidelines for selection criteria are available from the Faculty of General Dental Practitioners, the British Orthodontic Society and the SEDENTEX project.

Dr Ng is keen to ensure the risks associated with CBCT are fully understood by all dental professionals. 'The level of interest from practitioners in the BSDMFR's training courses took me by surprise. But while it shows that CBCT is fast becoming a hot topic in general practice, I believe the available guidance has not yet fully caught up. Some of the selection criteria are not supported by evidence-based research.

'Given the risks posed by this emerging technology, my advice for practitioners is to proceed with caution. But I'm confident that dental professionals will want to do everything possible to ensure the safety of their patients and staff.'

Minimising your exposure

  • Before acquiring CBCT equipment, consult your practice's appointed Radiation Protection Adviser. Public Health England (PHE) is recognised by the HSE for RPA services in UK. A list of other recognised RPA organisations can also be found on the HSE website.
  • Consult your RPA or a medical physics expert about the position and construction of the surrounding area, critical and acceptance tests, quality assurance test object, etc.
  • Every dental professional with responsibilities under IR(ME)R must have suitable training and experience to carry out their work competently and safely. The practice should maintain up-to-date records of all relevant training.
  • Reassess the practice's existing local arrangements to ensure they are fit for purpose.
  • Make sure you're able to justify every decision to carry out a CBCT scan, given the higher level of radiation exposure. Take time to weigh up the risks and benefits and be sure that there is not a more suitable alternative.
  • When reporting on CBCT scans, you must report on the whole imaged volume, not just the area of particular interest.
  • Record CBCT exposures in the patient's notes. Dr Ng recommends recording kilovoltage, amperage and exposure time, and whether any repeats were necessary, while the HPA says you should also include the identity of the referrer, practitioner and operator. This is important for patient safety and for audit purposes.
  • Establish appropriate CBCT referral criteria within the practice which are clear and ensure referrers provide all the necessary information. The decision to refer someone for a CBCT scan should also be discussed with the patient and recorded in their notes.
  • If a patient receives a 'much greater than intended' dose of radiation during a CBCT scan, they should be told immediately. The GDC requires you to apologise, explain what has happened and the short and long-term effects (you will usually be able to reassure them that the impact on their health should be negligible). You should make an immediate preliminary investigation. You should then contact your Radiation Protection Adviser for assistance to calculate the dose and to decide whether the incident is reportable to (in England) the Care Quality Commission within two weeks through its notification procedures.
  • In Wales, the appropriate enforcing authority is Healthcare Inspectorate Wales. In Scotland, the arrangements have been changeable but currently notifications should be made to Dr Arthur Johnston, Warranted Inspector for the Medical Exposure Regulations. In Northern Ireland, IRMER incidents are reportable to Hall Graham at the Regulation and Quality Improvement Authority.
Interview by Susan Field

This page was correct at publication on 21/09/2016. Any guidance is intended as general guidance for members only. If you are a member and need specific advice relating to your own circumstances, please contact one of our advisers.