Did you wash the teats properly with the liquid for washing bottles and teats with a small brush?
This not only apply to NUK, it applys to any other bottles. Sticky normally means its not wash properly and oil residues from formula or breastmilk are left on the teats, therefore it bcums sticky. Did you sterilise as well?
Your boy suck till dent, he must be powerful! All my kids use NUK and have not encountered dent besides my daughter bitin it ... Hehe