I assume you mean the head of the toothbrush but what about my head? The IMU data is relative to earth (kinda). But toothbrush position over teeth is relative

I assume you mean the head of the toothbrush but what about my head? The IMU data is relative to earth (kinda). But toothbrush position over teeth is relative to my head. Moving around and turning your head gets added to the IMU measurements with no way to tell it apart. Did I turn my head/body 90 degrees left, or did I move the toothbrush 90 degrees from my front teeth to the rear left ones? Impossible to tell these apart.