A root canal filled with calcium hydroxide should appear on a radiograph as if it were completely sclerosed, as in Figure 4. The material is prone to dissolution, which would appear on a radiograph as voids in the canal. In the past, the addition of more radiopaque agents such as barium sulphate has been recommended. As these materials may be resorbed more slowly than the calcium hydroxide a false picture may be given, and this practice has largely been discontinued.