Growing up if my mother ever caught me tearing something open with my teeth she’d sternly tell me not to lest I damage my teeth. Childhood dentists said the same thing.
I don’t buy it. The teeth are intended for use in ripping and tearing. I’m not talking about prying open beer bottles here, but as long as the thing I’m tearing is softer with my teeth (for instance a ketchup packet) why should I worry?
Teeth are not ‘intended’ for anything. That being said, I’ve eaten lots of foods that were much much harder on my teeth than that stupid bag of chips that I couldn’t open because my hands were slippery.
I think it is safe to conclude that most things we rip open with our teeth present no more wear and tear than many foods we eat.
Ripping and tearing meat, not hard plastics (and other man made materials). Both of my top front teeth are rough (I’d say chipped, but they’re not chipped, just… rough) from ripping stuff that isn’t food. Even though it may be softer, it can still have a much higher tensile strength.
That, and sometimes mothers and dentists stretch the truth a bit to keep kids from doing “rude” things in public.
Most things are safe to rip open with your teeth, but if you try to tear open some slick, tough plastic, it might slip right out and your teeth will smack into each other, with a risk of chipping.
I can’t think of any kind of food that’d behave that way, but then again, I can’t think of that many things I’d rip with my teeth that do either.
Because if you ruin your teeth you’ll have to pay your mother back for your braces. That’s what I was told, at any rate.
She used to tell me that if I wanted to get in a fight I’d damned well better tell the other kid not to hit me in the mouth because it was too expensive and there would be a bill presented.
I wonder if the real issue isn’t harming your teeth but tearing off a piece of plastic that you might accidentally swallow or choke on.
Due, I’m sure, to early parental warnings I’m deeply inhibited about tearing things like plastic packages open with my teeth. Which makes it all the stranger that I did it without even thinking the other day … with something that it then occurred to me could easily have been handled by twenty other people.
I mouthwashed for like 5 minutes before I could let myself stop. 
I used to twist open the tops of particularly stuck pop bottles with my molars, much to my parents’ horror. Never did anything to my teeth in the long run, from what I could see. I’m sure it’s more of a “better safe than sorry!” feeling.
I see this morning’s post is not here. Surprise on that. Take my word it was good.
Do you get sick quite often? That is some serious germ phobia.
It’s only partly about the teeth. Mostly it’s because we’ve had to clean a ketchup 'splosion off your brand new tshirt, the table, the seat and the floor one time too many. Kids are clumsy. Kids biting into ketchup packets are messy.
Ditto for flying potato chips and spilled soda.