CBCT diagnostics and restoration fabrication – Jonathan Fleet Nobel Biocare

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  Posted by: The Probe      5th October 2018

Dental cone beam computed tomography (or CBCT) is a versatile and powerful technology, which continues to be developed and refined within the area of implant dentistry.

CBCT machines provide similar accuracy to traditional imaging methods such as digitized plaster models and two-dimensional radiographs. The technology is popular for both the quality of the 3D imagery it provides and the speed with which scans can be taken. CBCT scanners can export data in the standardized DICOM format, allowing it to be imported into a range of software where it can be viewed and used. This has greatly benefitted treatment planning and fabrication of restorations using CAD/CAM.

The accuracy of CBCT allows 3D surgical guides to be used to retro-engineer casts and enable the prefabrication of temporary restorations. This information can be used to produce highly precise prosthetics and can even assist dental surgeons with guided surgery techniques.

Other benefits

CBCT offers several advantages over conventional CT, including reduced radiation exposure and higher 3D resolution. The field of view can be set far more narrowly than conventional scans, focusing on an area as small as two or three teeth when necessary. This is more efficient and reduces unnecessary radiation exposure to the patient.

Challenges

Despite this improvement in resolution, CBCT imaging does not always produce flawless imagery. Images can be blurred due to the partial volume effect (a result of resolution limitations) or distorted by artifacting, which can make the gray value of the root difficult to see. The presence of metal, such as metal restorations or titanium implants, is a known cause of artifacts and can present challenges for image processing. Metallic implants cause considerably greater X-ray attenuation than organic tissues, which can result in shadows or beam hardening. As a result of this, the detail of structures close to implants may be difficult to make out.

Although CBCT allows the tooth root structure to be observed, it is not always very clear because the scanner is unable to accurately measure the root dentin. Despite this limitation, the use of 3D models for oral and maxillofacial surgery has increased the predictability of clinical outcomes and reduced operating time.

Choice

The many CBCT machines currently in use vary by age and model in the quality of images they capture, what areas are scanned and the way in which scans are performed (differences in modes, settings, etc.). As such, some units may be less suited to particular applications and challenges than others.

Modern software allows for CBCT data to be combined with other information, taking advantage of the technology’s strengths while compensating for its weaknesses. For example, CBCT alone may not adequately capture enough soft tissue detail to ensure a tight fitting prosthesis. However, it can be combined with intraoral scanning to make up for this deficit. For obvious reasons CBCT alone does not capture color, so photographic reference is useful for determining the shade of the patient’s teeth and soft tissues when designing the implant prosthesis.

Digital advantage

A major benefit of digital modeling over traditional methods, is that they are not as limited in the types of measurements that can be performed. 3D modeling allows for almost limitless measurements to be performed, at angles that would be difficult or impossible by hand.

Unlike panoramic radiographs, CBCT is not subject to distortion, which makes superimposing a digital model over the relevant area both viable and straightforward. With suitable software, this eases treatment planning and prosthetic design by improving visualization for the clinician. By overlaying imagery of the patient’s hard and soft tissues, implant position can be more easily planned and designing a restoration that matches the existing teeth is more achievable.

New techniques continue to be developed. For example, for dentate patients, a possible technique for treatment planning involves combining a CBCT scan with a digitized scan of a cast with a wax-up applied. This approach helps prosthodontists and technicians find the ideal positioning for implant crowns, enabling better esthetics and masticatory load. Software is available that can automatically align these data sets, however, this can fail – necessitating manual alignment by a technician.

To get the most out of your CBCT scans consider the NobelClinicianTM digital treatment planning concept. NobelClinician features SmartFusionTM allowing prosthetic data to be superimposed over anatomical information, without the need for a radiographic template. When used in conjunction, these technologies facilitate powerful treatment visualization, helping to achieve the best post-treatment esthetics.

The accuracy of anatomical data gathered by CBCT, along with its relative ease of use has seen its usage become widespread. By combining this with other data types and intelligent software, a more thorough digital recreation of the patient’s anatomy can be produced. This can and will result in improvements in fabrications and implantation.

For more information, contact Nobel Biocare on 0208 756 3300, or visit www.nobelbiocare.com

REFERENCES

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Arcuri L., De Vico G. Ottria L., Condo R, Cerroni L., Mancini M., Barlattani, A. Smart fusion vs. double scan: a comparison between two data-matching protocols for a computer guided implant planning. La Clinica terapeutica. 2016; 167(3): 55-62. Available at https://www.researchgate.net/publication/311822496_Smart_fusion_vs_Double_scan_A_comparison_between_two_data-matching_protocols_for_a_computer_guided_implant_planning Accessed June 7, 2018.


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