Due to repeated biting on the cheek there occurs this "linea alba" which is a very common finding. Now as in your case due to repeated biting it seems that some fibrosis
has occured which you can feel as thickening. If its very small in size and almost constant in texture then there is no need to worry and this itching will subseqently subside if you are no longer in habit of biting. Till then you can start with frequent gargles with betadine
after diluting it with water.