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A technique to minimize CBCT distortion in a highly restored patient using a digital workflow


Mohammad Almutairi, DDS, MS

Yasser Alzahrani, BDS – Resident, Loma Linda Implant Department


Purpose of the Study: Cone-beam computed tomography (CBCT) is a three-dimensional (3D) imaging tool designed to reduce radiation dose to the maxillofacial region. Although CBCT is a great imaging tool in dentistry, it has some drawbacks such as scatter and beam hardening artifacts caused by dense metal structures. The purpose of this case report is to describe how to accurately design a CAD-CAM surgical guide for proper placement of dental implants in a patient with multiple metal restorations.

Methods: A 71-year-old male presented to the Graduate Prosthodontics Clinic with missing #20, 28 and 29. Most of his teeth were restored with gold metal-ceramic crowns (Figures 1a and 1b). Additional procedures were added to the conventional digital workflow to properly merge the CBCT to the digital scan of the oral tissue. A customized 3D printed appliance with radiopaque markers was designed in a CAD software (Meshmixer) and printed with a 3D printer (Form 2, Formlabs). The appliance was adapted to the mandibular arch using bite registration material (Blu-Mousse) and a CBCT was taken with the appliance in the mouth (Figures 2a and 2b). The same appliance and bite registration was placed on the stone cast and another CBCT was taken (Figures 3a and 3b). Implant planning software (Blue Sky Plan) was used to design the surgical guide. The CBCT scans of the appliance in the mouth and on the cast were merged in the implant planning software; this created the first merge (Figure 4a). The stone cast was scanned with an intraoral dental scanner (Trios, 3Shape) (Figure 4b), and the digital scan of the stone cast was then merged with the first merge, creating the second merge (Figure 5a). After the merging process, implants were planned in the proper position based on a digital wax-up, and a fully guided surgical guide was printed (Figure 5b). The surgical guide was used to accurately place implants in sites #20, 28, and 29 (Figure 6a). Second stage surgery was complete after 3 months of healing (Figures 6b and 6c).

Results: Implants were restored with screw-retained PFM crowns.

Conclusion: Using a 3D printed appliance with radiopaque markers that can be identified in implant planning software helps in properly merging the CBCT with the scan of a patient’s soft tissue, particularly when a patient is highly restored with metal or metal-ceramic restorations. Once the merge is completed, the conventional digital workflow of implant planning is followed to fabricate a surgical guide to achieve predictable and accurate implant placement.

Articles: Ozan O, Seker E, Kurtulmus-Yilmaz S, Ersoy AE. Clinical application of stereolithographic surgical guide with a handpiece guidance apparatus: A case report. The Journal of Oral Implantology. 2012; 38:603-609. Nagarajappa AK, Dwivedi N, Tiwari R. Artifacts: The downturn of CBCT image. Journal of International Society of Preventive & Community Dentistry. India: Medknow Publications & Media Pvt Ltd; 2015; 5:440-445.

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