There hasn't been nearly enough time for changes in selective pressure to develop through the population. Orthodontics as we know it was invented in the mid-18th century, and it wasn't affordable until the late 19th century. That's like, four or five generations to the present with access to medical tooth alignment.
I'm not sure what the point you're making is, can you clarify?
My point is orthodontia has a large market because, outside of actual pain and health symptoms associated with malocclusion, we have a predisposition towards well-aligned jaws and teeth.
I'm not making any assessment of the effects of orthodontia on long-term selective biases in human populations.
... but also, four or five generations is not insignificant. Evolution is just a change in allele frequency in a population over time, and five generations is more than enough time to objectively measure a change in frequency with such a large population sample. (I think the better argument would be that that the number of people that have had access to medical tooth alignment is a statistically insignificant fraction of the global population.)
