bonding to calcified tissues , including human teeth , tooth dentine and bone , is achieved through the medium of crystal growth adhered to the tissue . the crystals preferably comprise gypsum crystals which are formed by contacting the tissue surface with a mildly acidic solution containing sulphate ions . an uncured liquid resin is applied to the crystal growth and is cured to achieve adhesion by micromechanical interlock with the crystal growth and by superficial penetration of the tissue surface .