The most popular narration on how lord Ganesha lost his tusk is penned in the skanda puranas/tales of gods and goddesses. This is form of lord Ganesha where he is shown having a single tusk. ‘Ekadanta’ means ‘single tooth’. It is believed that Ekadanta is the 22nd form of out of 32 forms of lord Ganesha.
According to the padma purana, once parashuram went to meet lord shiva in kailash. But that time, Lord Shiva was busy meditating. Lord Ganesha stopped parashuram to entering the abode. For this, parashuram became furious and attacked lord Ganesha with his axe. He refrained from blocking the attack of the axe and to chop off one of his tusks. Thus, Ganesha came to be known as lord Ekadanta.
There is yet another myth about lord Ganesha broken tusk goes like this. Once lord Ganesha consumed a large number of laddoos and modaks. The mouse named krauncha, a snake came their way. On seeing this mouse dropped Ganesha and fled away.
All the sweets are come out. Lord Ganesha collects all the sweets and he tied the snake around his belly to hold it together. Seeing this incident, the moon was laughing. Lord Ganesha became anger on seeing the moon laughing. So, he broke one of his tusks and cursed the moon that will never be shine in its glory. After the forgiveness, the lord Ganesha removed the curse of moon and he came to be known as lord Ekadanta.
The broken tusk of the Ganesha signifies that he will be sacrificing anything to grant the wishes of his devotees. So, worship the lord Ekadanta with pure devotion, fulfill all your wishes.