Are the lines/grooves running vertical from the cuticle to the free edge? If so, the nails may just be very dry, which could also account for the twisting when they become free edge. The nail plate rides forward on the nail bed on a series of 'rails' and 'grooves' much lile a train rides forward on its tracks. When the nail plate becomes dried out, these rails and grooves become apparent as lines/furrows in the nail plate. You might try using Solar Oil which is availalbe through fine nail salons and Ulta Cosmetic outlets nationwide, or Botanical Oil which is available in the nail department of your local Sally Beauty Supply. Both oils contain jojoba and vitamin E along with other essential oils that will deep condition and moisturize your nails.