How a CBCT and an intraoral scan become a guide

Guide design needs two different pictures of the same patient, because neither one alone contains what is required.

What the CBCT gives you (DICOM)

A CBCT is a volumetric X-ray dataset, stored as DICOM. It shows what is under the surface: bone volume and shape, the inferior alveolar canal, the maxillary sinuses, roots, and existing restorations. It is the only source for where an implant can safely go.

What it does not give you is an accurate picture of the surface. Metal restorations scatter, and the resolution at the gingival margin is not what a guide needs to seat on.

What the surface scan gives you (STL)

An intraoral scan — or a scanned model — records the shape of the teeth and soft tissue precisely, as a surface mesh in STL. That surface is what the guide is actually built against, because it is what the guide will sit on.

What it does not contain is anything below the surface. On its own it cannot tell you whether there is bone to place into.

Alignment is the step that matters

The two datasets are captured separately, in different coordinate systems, and have to be brought into one. That alignment — matching the surface scan onto the CBCT using features visible in both — is where accuracy is won or lost. Everything downstream inherits it: if the alignment is a fraction off, the plan is correct relative to the wrong anatomy.

This is the main reason scan quality is worth attention. Scatter from metalwork, patient movement during the CBCT, or a surface scan missing the very teeth the guide will seat on all make alignment harder and less certain.

From plan to printed guide

• The datasets are aligned to one another.
• Implant positions are planned against the anatomy and the intended restoration.
• The guide body is designed onto the surface the scan captured, with sleeve positions following the planned axes.
• The design is exported as an STL for printing or milling.