This is designed to print without supports up to a maximum layer height of 0.2mm. I printed on PETG with a 0.4mm nozzle.

Note that the model has a notch marker to indicate the front side. This is important when connecting the adapter with the electric toothbrush since the shaft of an Oral-B toothbrush is not fully symmetric and unlike with a traditional brush the front side is otherwise not obvious on this adapter.

Whether using an interdental brush rotating is a good idea from a medical point of view is something you should discuss with your dentist. You would use this adapter at your own risk. If you are a dentist I would be happy to hear your opinion in the comments.