system
Given the following post, respond as if you're commenting on Reddit:
human
Why is lack of complete enamel coverage of herbivore teeth not a problem?

Deer and horse teeth appear to lack the chewing surface enamel which we're used to seeing in our own teeth. What's the reason for this?

I suppose that since horse teeth grow continuously it is not geometrically possible for their teeth to have enamel caps. How is the absence of complete enamel coverage in horses and deer reconciled against the fact that enamel destruction on the chewing surface of human teeth leads to catastrophic problems if untreated?
gpt
Herbivores such as those mentioned above have dental anatomy that is referred to as hypsodont which essentially means they have long tooth crowns. Humans and carnivores are what we call brachydonts i.e short crowns. This alone allows for a much greater degree of tooth wear to take place before the highly sensitive pulp cavity is exposed. As a tooth is worn extensively and exposure of the pulp cavity begins it is converted into secondary dentine hence losing its innervation and blood supply.

Additionally this arrangement become beneficial to herbivores as the differential rates of wear between enamel and the outer cement and inner dentine create what can best be described as a protruding ridge of enamel. Imagine 3 substances in direct contact with each other in creating a smooth surface, if the middle substance were, say, steel and the outer 2 wood and each of these were to sanded down separately with the same force for the same amount of time you would no longer have a smooth surface across the 3 layers but you would have a protruding peice of steel between the 2 planks of wood. Practically in a horses mouth this creates a series of transverse ridges across the tooth to create a rough, abrasive surface best adapted for masticating their rough, fibrous diet. 

A horses tooth can suitably resist attrition with this arrangement for 25-40 years before developing the condition colloquially referred to in equine dentistry as "smooth mouth" at which point the horses days are numbered.

Source: Veterinary Student

Edit: Accidentally wrote root instead of crown when describing hypsodont.