Rotation of a 3d model

Hi!
I need to solve a problem related to the rotation of a head 3d model.
I've created two sliders: one to control the rotation of the head on the x axis, and one to control the rotation on y axis. The problem is that if i move the x-axis slider, and after i want to move the other one, the model starts the new rotation from the starting position, and don't continue the rotation from the last point.For example:
If i want to rotate the head on the right and after turn the head up, the result is not head "right + up", but only up. Practically when i change from a slider to the other one the position of the head resets.
I would like to mantain the position when i change values between sliders.
Someone have any suggestion?
Thank you