In computer-based NobelGuide™ cases, CT scan data is used as a basis for surgical planning and for the production of a Surgical Template that guides the surgery during installation of dental implants. It is, therefore, important that the CT- scan data is a true representation of the dental anatomy of the patient.
The purpose of the double-scan is to get clear and precise data of the patient's alveolar bone and of the Radiographic Guide. These can then be shown clearly in the Procera Software Planning Program - Surgical application.
CT Scan Protocol
First Scan
The first CT scan in the procedure is a scan of the patient wearing the prepared Radiographic Guide and the Radiographic Index.
The following routine is recommended:
Position the patient in the CT scan with the Radiographic Guide in the proper edentulous place in the mouth.
Ask the patient to lean his or her head forward with the chin close to the chest, while remaining comfortable.
Make sure that the patient is positioned with the occlusal plane and the horizontal laser indicator parallel and coinciding (if the CT scan has a vertical laser indicator, this should be positioned between the central incisors). No gantry tilt is allowed.
The patient should be advised to remain very still during the whole scanning process, and avoid swallowing.
Choose the correct distance between the axial slices, with a recommended maximum distance of 0.5 mm.
When the “scout image” is shown on the screen, correction of the position of the patient should be done to a horizontal position of the hard palate. Then the field of interest for axial slices, parallel with the horizontally positioned hard palate, can be assigned.
Insert the Radiographic Index in the correct position between the Radiographic Guide and the opposing teeth. It is very important that the patient bites firmly on the index and Radiographic Guide during the scanning, to align the guide well to the soft tissue of the patient eliminating any potential air pockets.
Check that the position of the patient remains stable, and start scanning.
Second Scan
After the first CT scan, allow the patient to leave the scanner and remove the Radiographic Guide from his or her mouth in order to scan the guide alone, without the index .
The Radiographic Guide should be scanned in a similar position as the patient scan. Therefore, attach the guide to a suitable object of radiolucent material and position it in the CT scanner, as close to possible as it was located in the patient's mouth during the first scan.
The material used to properly position the Radiographic Guide should be as radiolucent as possible. Make sure that the material is significantly darker after scanning than the Radiographic Guide.
Paper boxes or other head-sized objects made of polyethylene and polyurethane-foam materials are suitable. Use adhesive tape to attach the Radiographic Guide to the material, such as Leukoflex, Leukosilk
(BSNmedical); or Nexcare paper tape series, Durapore tapes(3M).
Apply the same CT settings for the second scan used for the first scan, including the same distance of the axial slices.
