How can you really know?
Randomly my 8mo LO woke up twice last night (she's always slept through the night since 2 months old). This morning an armpit temp of 99.4 and a runny nose. Crying, fussy, sad, tired, restless. It broke my heart dropping her off at the sitter's. This is so new to us. I have co-workers say that this is teething. I have some saying that fever and runny nose are not teething symptoms. Needless, to say I've been a wreck at work today. I cannot wait until I can pick her and hold her.
Also, her botten two teeth came in at 6 months and no issues at all. Just a little fussy but nothing a cold wet rag couldn't fix. She's not drooling like she did then. Her gums are red or no sign of anything poking through that I can tell. Then again...like I said, I'm a new mommy and never been around babies.