Nothing specific. These are just myths that teeth become loose after delivery. Kindly brush well and maintain good oral hygiene.
Manjan is rough. It damages teeth. Stop using manjan.
Kindly go through my blogs mentioned in the links below. It will help you a lot.
Next Steps
"10 Dental Commandments for Happy Teeth!" by Dr.Rashmi Bamane - https://www.practo.com/healthfeed/10-dental-commandments-for-happy-teeth-40426/post
Health Tips
"Side Effects of Wrong Tooth Brushing" by Dr.Rashmi Bamane - https://www.practo.com/healthfeed/side-effects-of-wrong-tooth-brushing-40067/post