Stretching excercises?...

[DrEvil-]

Is it safe to do excercises to increase the angle between thumb and pinkie?

I'm 18 and can reach tenths sort of comfortably, but my hand only opens up to a little more than 90 degrees.

Thanks!

[jbmajor]

I regularly stretch my hands, but am careful about making sure I don't overdo it.  It helps to run your hands under warm water to loosen up the joints, make them more limber.  I'm not sure how much of an angle increase you are looking for between thumb and forefinger, but it is possible to increase the "spread" of your hand through stretching, so long as you do it gently.  Be careful, as you can seriously hurt your ligaments/tendons if you try to force your joints to stretch too far.  

[xvimbi]

Is it safe to do excercises to increase the angle between thumb and pinkie?

It all depends on how you do it. This has been discussed before. E.g.:

https://www.pianoforum.net/cgi-bin/yabb/YaBB.cgi?board=teac;action=display;num=1090696664;start=0

https://www.pianoforum.net/cgi-bin/yabb/YaBB.cgi?board=stud;action=display;num=1089409817;start=0