1802 Straight Talk

So I wonder about words we use sometimes. Every now and then some contrary linguistic streak leaves us with an outrider that makes no sense.
Take the word orthodontia. "Ortho," you would think, is a word that refers to bones. Like an orthopaedic doctor. You go to one when you have bone problems, right?
Very true. But the paed in paedic originally referred to the Greek word "child." And "ortho" doesn't mean bone at all. When used as a prefix it means straight or erect. So orthopaedic actually means straightening the child. At least according to www.MedicineNet.com.
But that's a bonus. The word I was really curious about was orthodontist. Thinking the ortho meant bone and the dontist meant teeth. So now I know ortho means straighten, and dontist means teeth. But why? Every other time we refer to teeth, we use the word dental. From the Latin word "dens," meaning teeth.
So why isn't it orthodental work we pay through the nose for, and which leaves our jaw hanging when we see the bill? And why aren't the practitioners of said specialty known as orthodentists?
On another note, how about the word "downs?" Horseracing places are always called downs. As in Churchill Downs, Emerald Downs, and Kentucky Downs.
To what do the downs refer? I always think of downs as like dales. You got your hills and you got your dales. So if you got your downs, why aren't there any ups?
"I went to Churchill Downs and while I was there took a side trip to Churchill Ups. Great view of the horsetrack."
Strangely, the dictionary defines downs as "an expanse of rolling grassy upland."
Maybe if they straightened the rolling downs out they could race horses on the flats.
A little orthodowntia anyone?
America, ya gotta love it.