NUK® offers orthodontic replacement nipples that help promote healthy oral development as your baby grows. Every nipple features the NUK® Air System – a unique venting system – which helps reduce colic. The natural shaped nipple mimic's Mom's to help make baby's transition from breast to bottle a seamless one. This unique nipple also has the drinking hole specially located on the top side – not the tip like round nipples -- which allows the milk to mix more effectively with saliva and promote easier digestion. NUK® Orthodontic Replacement Nipples are silicone, fit all NUK® wide neck bottles and are available in sizes Slow Flow (0-6 months), Medium Flow (6-18 months) and Fast Flow (18+ months). Made by the by the number one selling brand of orthodontic bottles and trusted for 50+ years to nurture babies best.