Some construction workers here in southern Thailand offered me some green variety, known as Gaan Kiow (whereas Gaan Daeng is red vein this is green vein) I think perhaps this is the same as MaengDa. According to people here there is only 2 types of Kratom. I think I read otherwise online though.
The green is so much more pleasant to chew, I don't know why the Red is so 'spicy', but I think the effects are a bit different. It seems the green is much more of a stimulant, the leaves are smaller, so 2-3 are chewed at a time. The Red Vein is more 'hazy' more of the painkilling side I guess. For people unaccostomed to eating leaves, or eating bitter, I think the Red Vein would make them sick, it is such a strange spicy bitter taste, it really never leaves as well, making it hard to swallow even after keeping it in the cheek for 20 minutes. The green however is nice to chew, it becomes a sweet numbing ball of mush after 20 minutes which you don't want to swallow.
Poultices of the green would work very good for toothaches I believe, perhaps 5-10 leaves would definitely numb, but not sure how long of the effects.
Here in Thailand ancient remedy for toothaches is Betel Nut Paste (aka Hmaak), Areca Catechu Palm nuts, and the effects of Kratom and Maak seem very similar. I have read that Maak is supposedly cancerous? It seems medicinally Kratom is much more promising.
Here in Thailand you might want to know that Thai people blame foreigners for being illegal in Thailand. However the main reason I believe it is illegal while other similar natural herbs remain legal is because of how the youth prepare the Kratom. They boil bags of Kratom with cough syrup, to extract the DMT and other amphetamines into a liquid cocktail. These people high on the drugs always involved with some serious crimes like rape and murder. They blame the drugs, and the cocktail is known as Kratom. However what is really the issue is the amphetamines and DMT, plus I believe almost 80% of the issue comes down to these kids and how they were raised.
I think the law in the USA is definitely on the right path, to not outlaw the plant, but outlaw derivatives and concoctions, this will prevent kids getting hooked on homemade meth marketed as Kratom.