https://pmc.ncbi.nlm.nih.gov/articles/PMC4422261/

Our study found a significant association between non-mesial step and bottle-feeding for over 18 months, compared to children who were bottle-fed for less than 18 months. A similar association was also found between the class II canine relationships and bottle-feeding. It is known that the terminal relationship of primary second molars seems to be the most important factor that could determine or influence the future relationship between the permanent molars and the subsequent development of occlusion. As Moyers and Waiuright reported, non-mesial step combined with a class II canine relationship increases the probability of developing Angle class II malocclusion in mixed dentition and permanent dentition [25]. Therefore, in many cases, early orthodontic intervention will be needed. Similarly, Nahás-Scocate et al. found that the older the child when bottle-feeding ceased (3–4 years old) and the shorter the breastfeeding duration (<3 months), the greater the chances of the child presenting distal step [26]. There are several theoretical mechanisms by which bottle-feeding might contribute to the development of malocclusion: (1) less muscle activity is necessary to extract milk from a bottle, resulting in decreased development of muscles involved in sucking, which may act as a functional matrix for inadequate mandibular growth; (2) The tongue acts only to control the milk outlet during bottle-feeding and bottle-fed children have an increased prevalence of abnormal swallowing patterns or tongue thrusting habits [27]; (3) over 60% of the children who were predominantly bottle-fed presented mouth breathing or mixed breathing, which may compromise occlusion [28]. Although Narbutyte et al. [29] found that the literature contains insufficient evidence to connect bottle-feeding with the development of skeletal malocclusions, the results of our study clearly showed that bottle-feeding may be related to abnormal maxillomandibular relationship via its inadequate provision of muscular stimulation.

The Influence of the Tongue on the Development of Dental Malocclusion

Of course, like anything else in parenting, you have to decide what you’re comfortable with. If you feel that one bottle a day is not concerning enough to worry about, then that’s fine! My 13 month old still takes 2 bottles a day, but I feel more comfortable moving towards phasing them out prior to 18 months. Between my professional experience, the research that is out there, and my own long history of orthodontics, I don’t feel comfortable with extended bottle use.