Please tell me if my dentist is trying to make some more money or is being serious?

I went for dental cleaning on wednesday. He took cavity tests and said there are no cavities and teeth are in very good condition. But then he said that a filling is coming off from my teeth and that needs to be done again. In 1992, i got a cavity filled in my rear tooth. The same filling still exists today too. The dentist said that the filling done in 1992 is dropping off and new filling is needed now or a cavity may result. As i don't have dental insurance, i want to know if the dentist was being serious or just trying to make more money? I don't see anything wrong in the filling and dental x-rays showed no cavities at all.
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Silver fillings "average life span" are 8 to10 yrs. I have had some fillings last much longer than that. I had two fillings replaced a few years ago, that were 20 + years old. The problem with amalgam (silver fillings) is that the fillings can pit and chip. It is especially easy to chip at edges. The dentist may see something that sees as a potential major problem. For example, when I had a filling replaced, not because of decay, but because the old filling was chipped, and compromised the structure and integrety of the tooth (I was risk of cracking that tooth when I chewed (lots of pressure). It is called preventive dentistry. The dentist helps you try to prevent major dental health problems, by fixing the minor, less expensive problems before they escalate. If you are really concerned, get a second opinion. It may help your trust issue.
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