Quality Center - User Fields - Regular Expression

Is there a way to apply a Regular Expression to a User Field as Input Mask?

I want to create an input mask for builds: for example '3.15.3.234'

the patter should be:

3digits.3digits.3digits.4digits

I tried to do this:

!990.099.099.0999

but, once it's running the variable looks like '  3.7  .8  .123' it keeps the 'blank spaces'