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What are the CBCT requirements for a GuidedSMILE revision case, and why do they change with prosthesis material?

The CBCT is where most revision cases succeed or stall, because the existing prosthesis is often the thing standing between you and a usable scan.

CBCT protocol by scenario

Case type CBCT protocol Prosthesis in the mouth?
Revision fixed, resin only Single CBCT, OPEN position Yes, prosthesis seated
Revision fixed, zirconia or hybrid with bar Single CBCT, OPEN position, with Grammetry or PhotoG scan bodies seated No, prosthesis removed
Revision overdenture, no metal Dual scan protocol, two separate scans Scan 1: denture in the mouth in occlusion. Scan 2: denture alone on foam
Revision overdenture, with metal Dual scan protocol using an ordered scan appliance Scan 1: appliance in the mouth in occlusion. Scan 2: appliance alone on foam

Why the material changes the protocol

Resin scatters very little. A resin-only prosthesis can stay seated during the CBCT and still leave usable anatomy, so a single scan with the prosthesis in place is sufficient.

Zirconia, metal bars, and metal mesh scatter heavily. A metal-based overdenture cannot be usefully CBCT scanned at all, which is precisely why the fourth checklist adds an appointment to fabricate a scan appliance. For fixed zirconia and hybrid cases, the prosthesis comes out and scan bodies go in, because scan bodies are dramatically easier to stack than a prosthesis full of scatter.

Universal CBCT rules

  • Open the bite. Have the patient bite on cotton rolls or the scanner bite fork. A closed bite is not usable.
  • Place cotton rolls between the cheeks and teeth for a better image.
  • If the field of view only allows one arch, send individual scans of each arch.
  • Export DICOM files (.dcm) from the CBCT into a patient folder. This should contain 200 to 400 individual .dcm files. Zip the patient folder and upload it with the Rx.
  • Note "GuidedSMILE Revision Case" on the Rx.

Additional rules for the overdenture dual scan

  • The scan must include the patient from the chin up to the nasal cavity.
  • Do not scan the patient alone without their denture or scan appliance.
  • The denture or appliance must be fully seated with no black voids at the intaglio. Black voids mean the appliance was not seated and the scan is unusable.
  • When scanning the denture or appliance alone, rest it on foam, not plastic.

 

Resources

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