Hello Dear, Welcome to HCM. Understanding your concern. Thanks for your query .The symptoms you describe in query are indicating that you are not properly rinse your oral cavity with water after hydrogen peroxide rinses. Some times when hydrogen peroxide remains on mucosa or unreacted hydrogen peroxide on mucosa , i make mucosa dry and prone to infection . This will cause infection of mucus membrane of mouth which leads to sores . I would suggest you to properly rinse you mouth with clean water after peroxide rinses ,so tha no peroxide left on your mucosa , avoid carbonated drinks ,smoking and drinking. Do warm saline rinses twice a day. If condition still persists then consult dentist again for proper evaluation to rule out condition like canker sore . Dentist may perform polishing of teethe ,Because sometimes small sharp edges left after scaling that create problem or prescribe you anticeptic mouthwash other then peroxyll like listrine. Hope your concern has been resolved. Get Well Soon. Best Wishes, Dr. Harry Maheshwari