Comparison of 3D CBCT dental imaging with 2D dental imaging

Dr Gautam Deshpande Wednesday, September 13, 2017, 08:00 Hrs  [IST]

Ever wondered what a doctor feels like while examining your x-ray? Just close your eyes and imagine what your house in its x-ray form will look like through the front door. Room after room, wall after wall, appliances and decoratives in between... all leaving their own mark on the x-ray report. You know that structure in between must be the dining table, but you can’t be sure, as it might as well be your similar-looking study table in the very next room. Superimposition, as the doctors call it, is very problematic during examination. But, superimposition is merely the tip of the iceberg when it comes to 2D dental examinations.

2D radiographic imaging
Two-dimensional intraoral and panoramic radiography are at present the most popularly used 2D imaging techniques for dental examinations. In intraoral radiography, the image receptor is placed inside the patient’s mouth which is used to achieve the desired clinical view, i.e. Bite-wing, Periapical, Occlusal, or FMS (full mouth series). Apart from offering limited view of the dentition, there are multiple other potential disadvantages of such radiography procedures. These include the likelihood of cross-contamination (due to intraoral sensor placement) and a relatively high time requirement for FMS imaging.

These images pose a considerable problem in medical examinations, including cephalometric imaging, due to overlapping of complex osseous structures. It, moreover, provides low-definition imaging of anatomic structures with the inability to accurately assess the width of an alveolar ridge. Panoramic images are also subject to interference which can further depreciate the quality of 2D representations for e.g like in detection of root fractures, which is impossible using this technique until and unless the x-ray beam passes through the fracture line.

For dentists and maxillofacial surgeons, it is essential to identify the problem and plan routine dental treatment procedures and surgeries as per concrete findings. However, two-dimensional radiographs are largely unable to reveal numerous three-dimensional complications and this can subsequently result in poor prognosis and an erroneous treatment plan.

CBCT imaging
CBCT or Cone Beam Computed Tomography, a low radiation three-dimensional imaging modality, has been established to be more efficacious than traditional two-dimensional radiographs. It leverages a cone-shaped ionizing beam which decreases the radiation exposure to the patient while achieving high-quality 3D visuals. As its numerous advantages are coming into the public domain, it is gradually becoming popular for dental procedures.

Scientifically-proven accuracy in 3D representation
CBCT imaging modality, despite its low radiation dosage, also paves the way for a correct three-dimensional representation of the area of concern. Multiple experiments have been conducted that even compared limited volume CBCT to spiral CT scans (including Kobayashi et al). The data of such tests revealed that the limited volume CBCT could measure distances more precisely. In a study conducted by Lascala et al, the accuracy of linear measurement was further analysed using eight dry skulls. The measurement obtained by CBCT was further compared with digital callipers and came out to be statistically similar to the original measurement - thus, making it more apt for dental examinations and prognosis.

Cone Beam CT scans are also advantageous on the below mentioned fronts:

Detailed and accurate images: The maximum image resolution (0.2 mm) provides exceptional detailing & with 90% lesser radiation compared to Medical CTs. Cone Beam CT technology gives a voxel size (3D building block of the representation) of as low as 0.07 mm, making it virtually impossible to miss out on the smallest of pathologies, lesions and fractures.

Quick scanning mechanism: The rotational scan is completed within 15 to 20 seconds. The entire procedure takes less than 5 minutes.

Full 3D volumetric scan: Multiple images are generated in various planes enabling multidimensional assessment in a single attempt.

Non-invasive: It is a non-invasive scanning technique. The x-ray unit and detector rotate around a patient’s head provide plenty of room eliminating the feeling of claustrophobia.

Comfortable positioning: Positioning is more convenient as the patient is seated or standing rather than lying down.

Simplified interface:
CBCT technology comes with an analysis and planning software with a superior diagnostic interface. It also comes equipped with patient education tools which are extended to all referring dentists at zero costs.

Applications and advantages
CBCT scans eliminate an array of problems encountered in the traditional 2D radiographs such as positioning errors, elongation, spine shadows, limited detailing, ghost images, magnifications, distortion, unproportioned imaging, overlapping as well as shortening. This aspect makes the technology pivotal in an array of dental applications, especially for dental implants, wisdom teeth & nerve procedures, pathology, gum & bone diseases, computer-guided surgery, printed anatomical 3D models, and also serves as a vital pre-operative diagnostic tool. In addition to these, the CBCT scan is an immensely helpful tool in endodontic evaluation, root fractures, and periapical lesions.

Let us analyse its applications

Dental implants
3D CBCT scans allow the surgeon and restorative dentist to optimally plan and place dental implants. Their uses and benefits are present throughout the continuum of care from diagnosis to treatment as well as to post-op examinations. It is essential in: Identification and distance determination of vital anatomic structures; Alveolar bone width measurement and bone contours visualization; Determining if a bone graft or sinus lift is required; Optimal implant size and type selection; Optimising the implant location and angulation; Increasing case acceptance; Reducing surgery time and building patient confidence.

Wisdom teeth and nerve
Cone Beam CT scans can provide a more accurate and 3-dimensional assessment to provide more predictable treatment results while reducing the risks associated with any impacted tooth. It helps in visualizing an impacted tooth’s position in relation to surrounding vital structures and nearby teeth and their roots. It is capable of better assessing the risk of treatment or non-treatment based on more accurate 3-dimensional analysis.

CBCT scans provide a superior means for visualization and study of pathological processes in the maxilla and mandible. This information is invaluable when planning any surgical efforts for biopsy or resection. The data can be used to: Render three-dimensional images of hard tissue abnormalities; Provide more accurate information related to size, extent, location, and the relation as well as effect on nearby anatomical structures; Monitor the progression of the pathology and the success of treatment with the use of successive scans.

Gum and bone diseases
The disadvantages of conventional two-dimensional x-rays for accurate periodontal assessment are eliminated by 3D and cross-sectional analysis. It helps to avoid unanticipated discoveries often encountered during periodontal surgery. 3D CBCT, moreover, enables to analyse periodontal bone defects on all sides of each and every tooth. It also aids in: Assessing the extent of every furcation involved;  Tracking the progression of advancing periodontal bone loss; and Evaluating bone parameters such as bone width, depth and density; Visualising vital structures such as the maxillary sinus, mental foramen and mandibular nerve prior to periodontal or implant surgeries.

Computer guided surgery
Computer guided surgery is designed for more confidence and predictability in dental implant and surgical practices. It establishes the option of prosthetic-driven backward planning which supports the predictability in the prosthetic outcome for a patient’s satisfaction. Furthermore, the system allows a seamless communication between surgeon, restorative dentist, and the local dental laboratory. This facilitates: Esthetic dental treatment planning; Dental prosthetic planning; Computer-guided surgery for dental implants; High degree of precision and control; Ease and comfort of surgical procedures; Reduced surgical time; Quick recovery and Zero stitches.

Printed anatomical 3D models
The anatomical 3D modelling service uses the latest technology to produce high-resolution rapid prototype models derived from the CBCT scan. These anatomical models are precise 3D replicas of an imaged area. They find their use in: Case study model; Mock surgery; Reconstruction in trauma cases; Reconstruction in cancer cases; Reconstruction in developmental anomaly cases and Reconstruction in skeletal cosmetic correction.

Dentistry has observed remarkable advancement in terms of technology, something which has tremendously enhanced the way dentists diagnose and deliver care to patients over the past two decades. Thanks to CBCT technology, the field is now observing a new technology-led era of sensors, decreased radiation dosage and evolved digital representation of the dental environment – paving the way for more effective dental care.

(Author is chairman and MD, Scandent Imaging Ltd, Mumbai)