I really like this logo! There are definitely a few issues with it for me though.
Firstly, the text is lost with the strong contrast between the pale green and the strong, vibrant colours of the tree.
I agree with graphicscove that the tree would look better if the two uppermost swirls were the same as the bottom right one. It's not about consistency for me, it just looks better with the swirls going round the branches than through them.
I'm not too sure on the font you've chosen either, apologies for not being more specific, it just doesn't seem to match the design, in my opinion.
I'm undecided on the path, perhaps you could try the hill as just a thick semi circle outline instead of applying a fill colour to it?
If you're going to have the extra swirls around the tree, can I suggest reducing their prominence in some way, try reducing their opacity to around 40%.
As for the other logos, the leaf ones look like clipart, the top right one looks a bit too fruity for a dentist. The bottom right one looks pretty good, again, I'd reduce the prominence of the swirls on the ground. I like the font, but I'm wondering how well it fits the clients brief? As I said, the font looks good but it doesn't scream dentist to me.
Good luck with this promising logo!