Though there is no defect in a particular tooth, I feel something odd in it. Why?

Hello,

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If x-ray also has nothing, it means there is no cavity. So the probable causes for your problem are,

1. Food impaction between teeth, which will cause such feelings for three-four days and will go away on its own. Use warm salt water for rinsing a few times a day for three days.

2. Sometimes sinusitis, i.e. infection or running nose, may cause discomfort of upper posterior teeth. For it, you should show it to a physician.

If you feel there is specific pain which is increasing then show to one more dentist as the previous dentist might have left some finding. If you can, send the x-ray so that I can examine too. Use saltwater and a painkiller for three days and wait if it goes away.