It is hard to answer your question specifically without a little more information. For example, how good is your son's plaque control? The fact that he needs such frequent cleanings suggests he may have a problem keeping his teeth sufficiently clean, which could promote cavities. How old is your son? Could there be some other source of sugar in his diet? Sealants do not protect all surfaces of the teeth, so they do not prevent cavities entirely, although they help. Braces can interfere with oral hygiene and make it hard to keep the teeth clean enough to prevent cavities. Braces can also prevent cavities from being seen, either visually or with x-rays, so it is possible that he had a cavity for some time, but because of the braces it was not detectable until the braces came off and the cavity had gotten large. Finally, you note you changed dentists. Different dentists have different thresholds for recommending fillings, and it is possible some of the five fillings might not have been recommended by the first dentist. It is also possible that the new fillings were diagnosed with x-rays that could not be taken until the braces were removed. If you have any question as to the diagnosis, you should get a second opinion, if the treatment has not already been done. I hope this answers your question. I am sorry to hear that your son has had these problems, but hopefully they can be stabilized. If it's any consolation, I had all my cavities as a teenager, after which I was more careful with my teeth, and have had very few problems since.