Sensitiveness means that suddenly you feel a sharp pain in one or more teeth when eating cold, warm, sweet and salty meals, or when drinking, or when your teeth contact with cool air. It is not rare that the tooth-cleaning itself causes pain.
Many things can be the source of sensitivity but these things have a common feature: the pulp contacts with the oral cavity through little canals. These canals, which run through the dentin, are usually closed by the enamel, the root cementum and the gums. The openings of the little canals can become uncovered, in case of cavity or when the enamel abrades, or the gums withdraw.
In each case it is worth asking for a dentist’s help, who prepares a filling or cures the inflammation of the gums. Sometimes the problem is solved when you clean your teeth gently but thoroughly. Use a toothbrush with soft bristles (e.g. Sensodyne) and a toothpaste the ingredients of which are able to block the little dentin canals (Sensodyne toothpaste or other toothpastes for sensitive teeth). You should try to solve the problem by all means because the tooth can inflame from the many external impacts.