|Teeth in the tumour, seen during surgery.|
(Cover Asia Press)
Although such tumours are rare, they contain skeletal and dental tissues which could very well survive in archaeological contexts. A brief search of the International Journal of Osteoarchaeology hasn't turned up any clear examples of such a condition in the past, but I think they could be out there. It's certainly something to keep in mind next time I find some teeth where teeth really shouldn't be...
* Wikipedia informs me that a benign tumour of this nature, in the UK is termed a 'mature teratoma', whilst in the US it's simply referred to as a teratoma. In the UK, a 'teratoma' or 'immature teratoma' refers to a malignant tumour.