A 23-year-old man has a proximal lesion on the distal of 15. Bitewings taken 2 years apart show it has progressed from the outer half of the enamel to just reach the amelodentinal junction, despite fluoride toothpaste and flossing. After tooth separation with an orthodontic elastic for 2 days, the surface is intact with no cavitation. What is the most appropriate management?