The concept of the specific mode of feeding being a risk factor of ear infections (in this case the bottle) is similar to what I have heard also. Some researchers have postulated that the degree of suction bottle feeding necessitates related to the negative pressure in non-ventilated bottles can lead to increased pressures in both the oral cavity and ear canals. A very very small study was done observing middle ear pressure measurements with bottle feeding. I am sorry, I only have the link to the abstract. http://www.ijporlonline.com/article/S0165-5876(00)00330-X/abstract. 

Do you think that another potential factor is that with bottle feeding, a parent may be more prone to prop the bottle or with an older infant just give the bottle to baby to self-feed? And in these cases often the baby is not upright and may even by lying flat on his/her back? Similarly, bottle fed babies may be given bottles to self-feed when they are put to bed. 

And certainly, to Pat's point about contents in the bottle, formula does lack the antibodies present in the breast milk which would act to decrease the presence of bacteria and therefore the occurrence of ear infections among BF babies and even those taking EBM.  

At any rate, it is likely multifaceted as are so many many things... 

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