I think it depends on what's it cut with. I've had good quality coke
and it didn't numb my teeth (which I love), but other baggies did numb my teeth and that's how I knew I was getting good coke. The lack of numbness is probably because it has been cut many times and all you get is a high but there is no high purity.
I remember back in the old days, I'd do a couple key bumps, and it would numb my teeth, as soon as it happened I grinned and thought to myself "this is the kind of coke I like"
Try this, do a couple of key bumps, if you don't get high or get barely high, you have bad quality coke.
Good quality coke is best enjoyed by doing key bumps, so the nasal mucous can absorb it well. Doing lines results in a lot of coke dripping down your throat and it's basically a waste. If you are one of those people who like to do large amounts of coke then chop a line, and instead of snorting
it all at once, do key bumps every few seconds until its over, it'll absorb better and give you a nice high.