had similar issues there too. both clinical and in the laboratory. made that switch a long time ago after wasting a few hundred bucks because ivoclar technical said it must be a bad batch and i had to purchase more. when it happened again, i bailed. had a good few years of enjoying Link-Ace but the replacement for it ended up giving me headaches for the same reason. turned to panavia and its been fantastic. hopefully ill get at least a few years before they screw something up too lol