I've been gardening grin + clenched teeth off and on since I opened my account. At the time, both wiki entries said the tags are mutually exclusive. To me, the explanations made sense because many characters with clenched teeth and no smile look angry/frustrated/injured while there are plenty of grinning characters that don't display the tension clenched teeth implies. I recently looked at the wiki page for clenched teeth and the wiki now only says "A character clenching their teeth." It was changed 2 days ago by nonamethanks. The grin wiki still says not to use them together.
I couldn't find any discussions about this in the forums, so I have no idea what led to this decision. Since the wiki was edited by an admin, I'd like to know why the wiki was changed before continuing with any more gardening.