I agree to the tips of marty998 (good diet, brush twice daily, floss) and suggest the modified bass technique as well:
http://www.youtube.com/watch?v=LqCpZm6s_dEFirst do the outside, then the inside, then the chewing surfaces. I recommend a toothbrush with a small head, so that you can reach your back molars properly. It also allows for also applying the technique to the back of your front teeth, which is difficult with a bigger toothbrush because of the curvature of your jaw.
When you're getting older, your gums will often start to recede, which increases the chance of losing teeth. This brushing technique helps against that as it's very thorough in removing any residues from the edges of the gums, while being very gentle (even massaging the gums a little).
By using the modified bass technique, I've stopped my gums from receding, and have reduced plaque to nil. At the last two yearly checkups, my dentist didn't find any plaque at all. And when I asked about my yearly professional cleaning appointment, he actually said I won't need it, there's nothing to clean. Yay, healthier teeth AND $$$ saved.
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As for the original question, I'm not living in the US, but around here, dental prostheses aren't included in health insurance. You can purchase extra "insurance", but I'm planning to pay for this kind of expense out of my own pocket. My family hasn't the greatest teeth, but mine are healthy so far. Also, I think that almost everyone who reaches a certain age will need some kind of dental prosthesis some day, so those "insurances" are really more of a distributed rainy day fund, in which case it's probably cheaper to save up the money yourself.
Treatments like cavities, root canal, etc. are included in our health insurance, however, so I can't give you a lot of advice about those.