Hello, Recent dental procedures and keeping your mouth open for a long period of time can cause some stress to the corner of your lips. In addition, if you were numb for your dental procedure, did you bite your lip at all? Does your bite feel different and cause your lip to lay differently against your teeth? Do you have a dry mouth? Medications often have the side effect of a dry mouth and affect the flow of saliva. Some dental procedures require you to adjust your medication prior to treatment. Does this situation apply to you? Contact your dentist if you feel that the numbness is a result of your dental procedure. There is a condition called paresthesia that indicates a delay in the return of normal sensation. This will often disappear with time. There can be the conditions with a salivary gland that affect the flow of saliva. Do you feel you have excessive saliva? This may be irritating to the corner of your mouth as well. I am glad to provide additional information with more details concerning your condition. I recommend that you make a phone call to your dentist and report all symptoms. Your dentist will provide the best advice due to your recent dental visit. I suggest you use some soothing gel for your lip area. Try not to wet the corner of your lips, especially by licking with your tongue.. Avoid irritants and try not to stress the corners of your mouth. Give the area time to heal. Keep well hydrated and make sure you do not have any vitamin deficiencies. I hope you find my suggestions helpful. Thank you for your inquiry.