Sunflower, the recommendation is to change the teats every 3 months, especially the rubber type (yellow ones) as the rubber tends to stick together after repeated sterilising. Silicon ones last longer, I usually change after 6months. You'll also see that different brands have different types of teats, some longer, and some have air vents to prevent bubble build up (colic). My favorite is Nuk bottles, they have airvents and shaped closest to that of our nipple so I understand - will prevent development of bug-bunny teeth. But they are non-BPA free, so I just have to change it more frequently. (Also available in glass, but not suitable for clumsy pp like me).