Is it possible to 3D printing a model with small internal cavity (closed) ?

Hi everyone, I am new to 3D printing. Recently I want to 3D print a mandible model.
The teeth have small internal cavities that imitates the root canal system of teeth. I need to use X-ray to scan the internal cavity and the cavity should be preserved.
Attachment 16273

Attachment 16272
But the internal cavity is very small (the diameter is about ~1mm)
I've consulted several 3D printing shops and they told me it's impossible to 3D print something with closed internal cavity and even if you left exit holes on the teeth surface, most 3D printers are not able to print such small cavities.
So I am wondering is it possible to 3D printing a model with small internal cavity (closed) ? Any help or information would be appreciated !

It would certainly be impossible with SLS there has to be an exit for the unfused powder but I have printed internal passage way down to 2mm diameter but they have always been open ended though with blind bends and intersections in them (they are pressurisation airways so slight distortion of the shape is acceptable ) I was using 0.4mm jet and 0.2 mm layer height using nylon.
So worth a try using a 0.2mm nozzle.

yeah not a problem with fdm printers - you just need to use a 0.25mm nozzle.

I've printed smaller things in the past.