This is a tough one -- inferior alveolar nerve damage is the most common long-term complication in third molar extraction -- I advise about 1% of my patients against extraction based on the proximity of their lower molar roots to this nerve. However, there is great anatomic variation in the course of the IAN such that damage to it can occur even when pre-op radiographs show that there is little risk of hitting it. (Which is to say... SURPRISE, there's a nerve where you didn't expect it!) Sorry to hear it, OP, AND I hope you don't have permanent lingual paresthesia -- having a numb tongue is nearly impossible to acclimate to...