Question: I was thinking about how we differ from crocodiles and sharks in terms of teeth. Now of course we don't have carnivore teeth but we also don't grow new teeth unless you are talking about a young child losing his/her baby teeth. But it seems like an omnivore diet, especially one that includes bones would be better suited to growth of new teeth than a carnivore diet.

I mean, there are all kinds of things that would wear down an omnivore's teeth. Here are just some of them:

* Hard fruits
* Nuts and Seeds
* Bones

And these 3 would wear an omnivore's teeth down the most, assuming no crispy processed foods are included.

And wouldn't wearing down of the teeth be a major factor into evolving the ability to grow new teeth?

So, since my Kepler Bb Humanoids are omnivores and they eat bones, especially during these circumstances:

* Pregnancy
* Breastfeeding
* Growth spurts

And they don't get more frail with old age, why wouldn't they evolve to grow new teeth?

Answer: 
If you're able to bend your humanoids anatomy, you may consider giving them open rooted teeth. Essentially they are teeth that don't stop growing, and must constantly be worn down. This is usually an adaptation seen in herbivores eating grass, leaves, and hay.

I think it's usually just front teeth with this trait, but it would probably help increase longevity of the rest of the teeth by grinding tough foods before the back molars get it. It would be a good reason for your humanoids to chew on bones, since failure to wear down teeth leads to painful dental problems.
I had an extra set of adult teeth (four front uppers) and later found out I also had two extra wisdom teeth (upper one on each side). Its called hyperdontia.