I think it is a combination of genetics and care. You can only do so much with what you were given. I happened to have (apparently) been blessed with pretty good genetics in the tooth department. I had a lot of fillings as a child--all in molars in the back, which my own children had sealants applied to avoid. They didn't do sealants back when I was 10. Now they do, so we got it for our kids as preventative to help avoid cavities in those deep crevices in their molars.
Neither have had any cavities to date (ages 14 and 11).
Other than the early cavities in my molars, I am pretty good. The dentist I began seeing after my kids were born asked me if I had had braces, since my teeth were so well aligned, etc.. Nope. Just blessed. We certainly couldn't have afforded it if I had needed it. I have 2 brothers, and they also have similar teeth to me. No braces, and none were needed... No problems with the teeth.
I did have my wisdom teeth removed when I was about 22.
I sometimes get sensitivity issues, since I lost a lot of enamel during my pregnancies. The same dentist who asked me about orthodontic work, asked me if I had ever had an eating disorder, since the enamel damage came from vomiting daily for 18 months (2 kids x 9 months). He said my teeth looked like those of someone who had suffered an eating disorder at some point. So I have to be careful of acidic things that can further damage my teeth.
I brush several times a day. I don't use toothpaste every single time (when I get up and before I go to bed, I do use toothpaste). For the most part, it is a mouth refresher (per my dentist).. just actually brushing properly with the right tooth brush is what matters, not the paste you apply to essentially freshen your breath. Although, using the wrong paste (those with whiteners in particular) can increase sensitivity issues, so I avoid them, which is getting harder to do, since every toothpaste wants to brag about "whitining" your teeth. :(
I floss several times a week, although not daily.
But I go to the dentist 2 x per year for cleanings like clockwork. So do my kids and husband. Any problems are discovered early. My son (the 14 yr old) did have a small pit that was repaired--before it turned into a cavity.
My husband has had some issues with cracking teeth (got in implant for the first one), but another is headed that way. I suspect that he could have benefited from braces when he was younger (his teeth are fairly crowded), but he didn't get braces and his teeth probably do not align correctly, which can contribute to weakened and damaged teeth. Every time you bite, if your teeth do not align properly, you could be adding to damage to your teeth. The pressure is uneven on the teeth, which contributes to wear/damage.
Which is why we opted to go forward with orthodontics for our kids--not aesthetics, but long term health of the mouth.
I don't think I have the prettiest smile... my teeth are not the perfectly rectangles that the models sport and they aren't gleaming white. But I am not embarrassed by my smile, either, and don't anticipate needing a huge amount of dental work in my future.
My dad has had a few cracked teeth/caps over the years. My mom had gum disease in her early 40s and had a bridge/partial installed way back then. (She is 71 now).
Bleeding gums should never be ignored. It is one of the first signs of something awry. Whether it is specific to the mouth is something for you to find out... it could be some other underlying issue, but typically is the first major physical indicator of gingivitis, which progresses to full blown gum disease, lost teeth, receding gums, pain, etc. Please don't ignore it.