Most probably its the tartar /calculus deposition that has come off ..
Do visit your dentist if the sensitivity gets worse or in case of any pain .
Second trimester that is ,from 4th to 6th month is considered as safer period for dental procedure if any required to be done .
Next Steps
use desensitizing tooth paste just in case sensitivity is more .
Health Tips
maintain proper oral hygiene by brushing twice a day .