We all see these old composites that are still serviceable but the enamel margins have broken down. That usually is the result of curing the older composites too fast, creating "white lines" which are literally fractured enamel rods. After a while they wash out leaving a void at the margin. Here I was placing a composite on #31 and with the dam on and magnification could see that the margins on 30 needed help. This is a simple technique that "refreshes" these old composites, hopefully extending their serviceability for years.
This is a simple technique that can be done very quickly. Hope this helps.