To the best of my understanding it depends on your DSLR.
1. Least wear and tear.
I believe that some DSLRs have the ability to flip the mirror and open the shutter throughout the timelapse. The images are then captured by activating and deactivating the sensor. If this is the case with your camera, then there shouldn't be any mechanical wear and tear. These cameras probably have modes / overrides specifically for timelapses. I've never seen/used one of these.
2. Moderate wear and tear.
Other cameras can either flip the mirror or open the shutter for a period, reducing the wear on these parts. My 7D will flip the mirror during bracketing, but I haven't managed to get it remain up during continuous shooting.
3. Maximum wear and tear.
Lastly are cameras that aren't able to flip the mirror or open the shutter during continuous shooting. Each image requires both to be activated and this will lead to wear and tear. My Canon 7D and it is in this third category. In my experience the movement also causes camera shake, which isn't very nice, particularly if you use a log lens for your timelapse.
If you are unsure, set up a short test and listen. If you hear the mirror or shutter, and you can't find a way to override them, then I suppose you're in category 3.
Workarounds that I have tried with varying success:
1. Movie mode
This works reasonable well, actually. Shutter and mirror are still (except if the camera adjusts exposure during). Then, use something like
ffmpeg to strip your movie down to individual frames, and hey presto, an image sequence to play with. You're limited by things like your camera's movie resolution and degree of compression, and probably some other movie aspects I'm not aware of. Here's an example with this technique https://vimeo.com/103661603
2. Magic Lantern
If your DSLR is a Canon, Magic Lantern (http://www.magiclantern.fm/) may have a version for you. This opens up your camera to all kinds of fun things, including, in some cases, timelapse modes — careful not to brick your camera though :). I haven't run a timelaspe with ML yet, but I have played with it and it is awesome.