Technically scratches should not be an issue, since teflon is very inert and will go through your systems without affecting anything. Over-heating it will make toxic without a question and I'll throw out any overheated cookingwear and just get new ones.

If you're paying attention it's not difficult to keep the temp below the temperature where teflon starts breaking down (260°C / 533 K): sunseed oil starts smoking at 230°C, butter below 200°C and heating oils to their smoke point is already something you should avoid if you care about your health.