Hi.. Thanks for the query.. Bruising of lower labial frenulum can occur due to a number of causes like traumatic injury like toothbrush trauma, injury with some hard or sharp foods, ulcer formation, infection causing abscess formation etc.. So my suggestion is to consult an Oral Physician and get evaluated and a thorough clinical examination should be done.. In case if there is infection then another course of antibiotic and anti inflammatory painkiller like Ibuprofen can be advised. Along with it topical application of antiseptic ointment like Chlorohexidine and warm saline gargles can help. Do antiseptic mouthwash gargles. Do ice packs over the frenulum.. Hope this helps.. Regards.