Can a person develop 10 small cavities in 6 months, even though they have excellent dental hygiene and get cleanings every 6 months?

Probably not: Are you seeing a different (new) dentist? Some dentists "watch" what they consider very small or "not quite" cavities. Others have a different view and want to treat these lesions before they grow. Seek another opinion if you have any misgivings regarding the diagnosis you've been given.

It is possible: Dental decay can be caused by many factors including acidic drinks. You can have the best dental hygiene habits in the world but if the bodies natural defenses, like salivary flow are compromised or can't balance the oral ph to be more neutral, the decay bacteria have more ability to cause decay. So unfortunately yes it is possible. The diagram on the right can give you many clues to help you.

Yes: But i'd get a second opinion. It is entirely possible, but that is a large number if you have been seeing your dentist regularly and have good oral hygiene. These may be cavaties still in the enamel that could be stopped or even reversed without fillings. However, changes in immunity, diet, dexterity, medications, salivary flow, oral flora, etc could all lead to increased dental decay.

Possible,: But not probable. We're the cavities missed six months ago, or are the teeth being examined more carefully this time? If you have any doubts at all you should get a second opinion.