This year is the 130th anniversary of Wilhelm Conrad Roentgen’s publication of the “new kind of ray” in Nature and Science journals along with his first public demonstration of these new x-ray images. He was subsequently and rightly awarded the Nobel Prize in physics for his important work. Interestingly, the technique was then rapidly adopted in dentistry. Within two weeks of Roentgen’s ‘rays’, the first dental images were produced by Friedrich Otto Walkoff and Wilhelm Konig using a photographic plate wrapped in dental rubber dam as the image receptor. Two years later, Walkoff created the first extra-oral radiograph. However, the exposure time was 30 minutes resulting in loss of hair for many patients signalling concerns about large quantities of radiation.
2026 is the thirtieth anniversary of the first commercially available cone-beam CT (CBCT) imaging system. As I am a fan of all forms of 3D imaging, the CBCT anniversary is worthy of a small celebration through this blog. CBCT images are increasingly used for diagnosis, treatment planning and outcome assessment across healthcare with further utility in audit and research. The importance of accurate imaging of the hard tissues should not be underestimated due to the complexity and variability of head and neck anatomy which adds a layer of complexity when assessing unwanted pathology. However, despite radiographic imaging having come a long way, concerns about effective radiation doses remain.
Two-dimensional (2D) dental radiography continues to be at the core of dental imaging and should not be overlooked at this point. These images offer versatility with intra-oral periapical radiographs, bitewing radiographs, and panoramic radiography continuing to underpin dental diagnosis and monitoring of dental diseases. The benefits are well-established and with relatively low, but importantly, not-zero radiation doses, rapid image capture and low equipment costs, these images are unbeaten for assessment and diagnosis of caries, periodontal bone loss, periapical pathology and the assessment of dental development and eruption patterns. However, 2D radiographs are just that, and the compression of three-dimensional anatomy and pathology down to flat images results in anatomical superimposition, geometric distortion, magnification and impairs diagnostic accuracy for where the anatomy is complex.
CBCT offers full scale volumetric three-dimensional imaging of the dento-cranio-facial structures using a cone-shaped X-ray beam and flat-panel detector which has two key advantages over medical-grade CT: hard-tissue optimisation and a lower, but not negligible radiation dose. As time goes on, the utility of CBCT is becoming increasingly valuable (particularly with small-volume CBCT) for specific situations where 2D imaging is inadequate. These include dental implant planning, localisation of impacted teeth and assessment of root resorption of adjacent teeth, complex root canal anatomy, root fractures and defects for endodontics, evaluation of pathology, facial fractures and other bony pathological lesions. The ability to accurately assess individual patient anatomy such as the inferior alveolar nerve and maxillary sinus along with imaging for orthodontics and being able to characterise the temporomandibular joint (TMJ) in all three dimensions is simply fantastic. CBCT is now also increasingly used for imaging the extremities and breast oncology. Being able to visualise our patients in combinations of axial, sagittal, and coronal planes, and to be able to utilise various reconstructive methods to explore the detail has been a game-changer during my professional career. Quite simply, CBCT has had a key influence on improving both accuracy and confidence for diagnosis and treatment planning of patients with a range of clinical complexities.
However, knowledge of the relative strengths, limitations, and appropriate indications for every image format is essential for safe, effective, and proportionate patient care. The key consideration is radiation exposure for our patients and while CBCT imaging invariably produces higher radiation doses than 2D radiographs, overall exposure and impact of the radiation dose varies widely with field of view, voxel size and resolution, exposure parameters along with the age of the patient being crucial. Naturally, all clinicians practice in line with IR(ME)R, ALARA/ALADA, SEDENTEXCT principles and country-specific professional guidance. Nonetheless CBCT examinations must be clinically justified, optimised and restricted to the smallest appropriate field of view.
Image interpretation skills and professional responsibilities are higher for CBCT than 2D radiographs and are often underestimated. All clinicians are required to ensure they have adequate training for image interpretation, the ability to recognise and where necessary, refer when incidental findings are identified, and both report and maintain suitable documentation, particularly when any imaging extends beyond the immediate region of interest. These are all relevant in the field of medico-legal concerns.
Is there reliable data on the numbers of CBCT scans taken across the globe? It is estimated that 4 billion X-ray images are recorded globally each year, with 400 million of these being CT images. Data is far from complete on the exact number of CBCT scans, but around 28,000 dental CBCT units have now been installed globally and it is thought that 20 million dental and medical CBCT images are produced each year. Of interest is the growth trend in CBCT machine sales in relation to overall radiation levels. CBCT is one of the fastest growing methods of imaging. Predictions suggest there will be 5-10% annual growth (5% in higher income and 15% in lower income countries), particularly the Asia-Pacific and Latin America regions which are the fastest growing CBCT regions. Therefore, the current total number of CBCT scans per year is likely to double to 40 million between 2030-2035. CBCT radiation levels will therefore continue to rise.
Evidence is however growing along with a degree of unease within our profession that CBCT is at times overused where conventional 2-dimensional radiography would suffice. Increased accessibility, a perceived desire to practice defensive dentistry, accompanied by commercial and workflow pressures, along with training and gaps in clinical confidence have all unhelpfully contributed to increases in CBCT imaging as well as population expansion and increases in access to dental care in some parts of the world.
Now to answer the question Are we taking too many CBCT scans? You will not be surprised that the answer is both yes and no. Inevitably, CBCT is on occasion over-prescribed in specific clinical contexts, but at the same time, availability and training also limit the clinical situations where 3D imaging would provide clinical benefit. Ultimately, the issue is not CBCT itself, but appropriate case selection. The question we should all ask before considering CBCT is “will this CBCT scan change the treatment plan for the patient?” This helps justify the effective dose of radiation to the patient.
One further concern I have relates to image sharing. Whilst CBCT has been widely adopted in oral surgery, endodontics, orthodontics, implantology, and other disciplines and some radiology centres allow self-referral for all varieties of medical and dental imaging, it is incumbent on all who take CBCT images to share these to avoid scan repetition. Maximising diagnostic yield from every radiological scan is at times overlooked as a key principle of radiation protection.
It seems logical, but CBCT should only be prescribed where it is expected to provide additional diagnostic information that will influence patient management. My view is that CBCT should remain a complementary and not a competitive radiographic imaging modality. Whilst the humble 2D dental radiograph should not be overshadowed by the incredible images that can be produced by CBCT scanning, both should co-exist in imaging of the face, teeth, skull and other anatomical regions. The challenge for clinicians will continue to be to select the most appropriate imaging modality for each individual patient, keeping diagnostic yield and radiation risk in balance.
Imaging has come a long way since the early radiographic pioneers using long exposure times and high radiation doses. Although reassuringly, radiation protection is now carefully controlled, three decades on from the beginnings of CBCT, the total number of CBCT scans continues to grow substantially across the globe. The real issue is of course not simply the sheer volume of CBCT scans, but whether each scan is prescribed according to evidence-based clinical criteria. Whilst cone-beam CT has become one of the most powerful diagnostic tools available in dentistry and healthcare, true power is also restraint.
As usual, feel free to contact me: dental@rcsed.ac.uk.