What you lose converting to JPEG
Bit depth: CT/CBCT data is 12 or 16 bits per pixel. JPEG is 8. The dynamic range needed to show air, soft tissue, fat and bone in the same image only fits in the higher bit depth — JPEG forces a fixed window/level burn-in.
Spatial information: the 3D nature of the volume is gone. Each JPEG is just a single 2D plane at one window setting. You can't go back and re-slice in another direction.
When JPEG is fine
For email summaries, patient education printouts, marketing or non-diagnostic reference, an annotated JPEG export from the viewer is fine. Many viewers (CBCTHub included) export labeled screenshots specifically for these uses.
For diagnosis, second opinion, surgical planning or insurance documentation, send the underlying DICOM. Include the JPEG too if it helps point at the finding, but the DICOM is what enables real interpretation.