Hello. Slight injury to alveolar &/ lingual nerve while giving local anaesthesia may leads to numbness and sensation in lower lip and chin. First of all you have to check is there any alteration in taste perception, as there is a long span of suffering. There are many interventions or treatments available, surgical and non‐surgical, that may enhance recovery, including improving sensation, supplements such as multivitamins, antioxidants, renerve plus for a month.