I think it is mucous cyst. It is caused by lip biting, check biting, accidentally rupture of salivary gland, adjacent teeth causing chronic damage. The cyst develops when the mouth salivary gland become plugged with mucus.most cyst are on the lower lip . They usually temporary and painless.if cyst is permanent the treatment is required.
Next Steps
treatment is based upon the severity of the mucous cyst.some time cyst may not required treatment. the treatment is removed the cyst and laser therapy.please consult your dentist