I ordered the 7550 and received the 7400. so I returned it and requested the correct product. Again the 7400 arrived. This time I called Braun who makes the Oral-B product line. They explained that the 7400 and 7550 are the same toothbrushes, but that the 7550 comes with extra toothbrush heads. I called Amazon and requested a refund for the price difference. They couldn't do it because the 7400 is actually more expensive than the 7550 even though they are the same product except that the 7440 contains fewer replacement brush heads. This is really crummy, but I am starting to travel now and just decided to get wronged and keep the 7400 because I needed a new toothbrush ASAP.