For me, also, the interests started well before I had any idea about any sexual links.
I think, for me, it is mainly a case of altered sensations....ie "what would it feel like"....

One of my earlier memories is of visiting friends of the family who we did not see often when i might have been about 8 or 9. The son was perhaps a year older than me. I was instantly captivated by the fact that he was wearing two long metal braces (calipers as his mother called them) on his legs. I don't know why but I remember trying to think of any way that I could get to try them on, but it didn't happen of course. All I can remember is that he couldn't sit cross legged on the floor like me and then we went out in the garden and he couldn't run. So thats one interest which has lasted.
This was reinforced shortly afterwards when I spotted a girl waiting for a bus near our school wearing one extra long leg brace which held her so her foot was off the ground, and a thick shoe on the other foot to lift that leg to the same height. I couldn't take my eyes off her and somehow the best bit was seeing her walking without too much apparent difficulty.

Next I can remember seeing a few people with hearing aids. At that time they were always earpieces with seperate body-worn receivers in shirt pocket etc. I saw someone about the same age as me at the beach with two aids and a harnes to hold them. I wanted to know what it would be like to hear through something like that and couldnt get that thought out of my mind. I had a pocket radio with an earpiece. I bought another earpiece and wore them, pretending. Second interest, still there and stronger.

Next a boy in my class at school (I was now about 10) appeared with what he called a brace, on his teeth. Just a wire around them, as far as I could see. But it got a lot more interesting when he took it out and I could see that it was a large plastic plate etc...a hawley retainer, I suppose.
I couldnt get the idea out of my mind that this must be so good to wear and to feel plastic rather than the roof of your mouth. The third interest now grabbed me....

Each of these things is something that causes a change in sensation. Each of them is restricting in some way, I suppose.

I like to see them on others but, for me it is a case of wanting to experience the altered sensation myself.
The Internet helps us to make some of these things a reality..........

I wonder if this particular type of thinking is familiar to others here?

The "restriction" part of any fetish is always cool for me.  If its "restrictive", I have a liking for it, regardless what that restriction is.  My braces fetish definitely comes from having it myself.  I *know* what it's like to be braced, and that tight feeling in your mouth that on a bad day can feel like potential suicide, but on a good day can be a very interesting and fun feeling.  I know what it's like to sit in a headgear for hour upon hour, day after day, week after week, and the discipline it takes to keep that thing in your mouth.  I love the idea of the "discipline" of it. 

Like Retained, above, I also have a thing for other medical things, but I think it all boils down to "restriction".  A cast/brace/caliper/whatever is just another bondage device.  And because it is medical, its kinda "legitimate".  I cannot take my pal out to dinner to a fancy restaurant in handcuffs, but I can take her in a cast.  Never done that though, but the idea stands.  (Instead, I just have my pals over for dinner at my place, where they can have a meal with handcuffs on!)

Restriction, yes, but also some degree of giving up control. You can't just decide you're done with braces, once they're on you're in for the long run. Same thing with a cast (recreational or medical).

The more the metal the better for me. My partner and I both had braces. She got hers off now.  I still have mine on and love it. But when I had to wear my headgear the ortho told me 20 hours a day but the last I wore it 24/7 and my partner loved it. I am so lucky.

Definitely a fetish for me...my wife has had braces twice (currently wearing them for the second time) now and it's been great! She knows of my fetish and indulges me when and where possible!

Definitely a fetish
I love the metal ones with power chain and if i had to select a color, would be purple 

Hey Cassandra I agree with you completely we have exactly the same fetishes