Dentist treated my toothache but on the next day after filling I still had aches when biting something and pressing on that tooth.

So I returned to that dentist and she said that she didn't see the cause of the pain previosly because it was closed, now she opened and saw it, so she drilled what was very painful put the arsenic on Friday evening and told me to come on Monday morning. Usually when dentists put arsenic that stops acheing at once, but this time after 1 day has passed from the time of arsenic putting I still experience pain when biting (though it is bearable) and now I feel that when I just close my mouth and press the upper teeth against the lower teeth the area around the tooth with arsenic is aching. What is the reason of this pain? Has the dentists made any mistake?

[Jerome Tsang, DDS]

I don't know of any dentists that would use arsenic anymore in dental treatment of pulpal infections.  Are you sure that the dentist used arsenic?  

You may want to see your dentist and have your bite adjusted.  Generally after a pulpectomy (opening up the tooth and removing the pulp and root tissue), you shorten the tooth so that they don't put much force on it to relieve the pain on chewing.

[Medinla]

Thanks for your response. Only my perceptions around the tooth remind me of inflammation in it, though the pain is not sharp but not very weak. May it be the inflammation of the root or under the root while the nerve is being killed by the stuff filled in?

[Jerome Tsang, DDS]

What happens sometimes (I'm sorta guessing here) is that with an infection of the pulp, the bacteria can travel down the root into the bone and infect/irritate the ligament of the tooth.  When you bite down, the ligaments are stretched or move.  Since they are irritated by the bacteria, it produces pain on chewing/biting/movement of the tooth.  We diagnose this as a type of periodontitis.  You probably have an acute or chronic apical periodontitis.