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: 
**Growing new teeth endlessly is the norm**, everything with teeth can do it except mammals. 
Mammals kinda traded out that ability for more complex teeth. more complex teeth is a big advantage for insectivores, (insects need to be cut apart to get the most out of them) and all living mammals are descendents from the small insectivorous mammals around turing the time of the dinosaurs. Being small and short lived the limited number of teeth was not much of a problem so the mutation that swapped/transformed the genes for making more teeth into genes for creating more complex teeth was an advantage. Now us as their descendants are stuck with that evolutionary baggage. \*

I would not expect that weird fluke of evolution to occur against in an unrelated evolutionary history. **So your humanoids should grow more teeth continuously (Polyphyodont), it does not need an explanation, having a limited number would be unlikely and would need an explanation.** 

Now if you are continuously growing new teeth it is a little harder to get them to fit tightly, since they are constantly dropping out an leaving gaps. But dinosaurs found a way around that, just grow lots of little tiny [interlocking](http://blogs.plos.org/paleocomm/2016/09/14/all-the-better-to-chew-you-with-my-dear/) teeth where you need a chewing surface, and normal shaped teeth everywhere else. It is called a dental battery. 

[![enter image description here](https://i.stack.imgur.com/EIy4o.jpg)](https://i.stack.imgur.com/EIy4o.jpg) 

The few mammals that have more than one set of replacement teeth (elephant,kangaroo, and manatee) still only grow a limited number, and eventually stop making more. They are not true Polyphyodont they do run out of teeth. They basically don't produce all their teeth in one or two rounds but make them two or four at a time till they run out.
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.