There are lots of segmentation models for head and neck and dental:
- Whole Head Segmentation model in MONAI Auto3DSeg for facial muscle segmentation
- AMASS module in AutomatedDentalTools extension
- DentalSegmentator extension
- TotalSegmentator extension has 4 models for head and neck muscles, bones, vessels - in the latest Slicer Preview Release (really the latest, released today)