Here's a extract from a scientific reference to show that teeth discolouration in the dead is normally found after prolonged water immersion and is not normally a conclusive indicator of cause of death.
Full abstract is here -
Medico-legal aspects of postmortem pink teeth. [Int J Legal Med. 1994] - PubMed Result
Borrman H, Du Chesne A, Brinkmann B. Medico-legal aspects of postmortem pink teeth. Int J Legal Med 1994;106(5):225-31.
"Except for very few and poorly documented exceptions, [pink teeth] develop earliest after 1 to 2 weeks postmortem.
...they are most often associated with water immersion.
The phenomenon is very often seen in victims of drowning where the head usually lies in a head-down position.
Since, there is no obvious connection between the occurrence of pink teeth and the cause of death, it may be concluded that pink teeth are not pathognomonic for a specific cause of death and this is therefore an unspecific phenomenon."