Visible-light curing units: correlation between depth of cure and distance between exit window and resin surface

Study 1) The depth of proximal cavities was measured on previously taken bitewing radiographs. Study 2) By means of a scrape test, the relationship between depth of cure and irradiation distance was examined with four different curing units and two different restorative resins. Study 3) The microhardness of one of the polymerized resins was measured 0.5 mm below the free surface of the filling and then at 1.0 mm, 1.5 mm, 2.0 mm, and so forth until the resin became so soft that no hardness could be recorded. The hardness at each 0.5-mm level was recorded in relation to irradiation distance. 1) The cavity depth was most often 4-5 mm in lower premolars, 5 6 mm in upper premolars and lower molars, and 5-7 mm in upper molars. In the latter teeth, 15% of the cavities were > or =8 mm deep. 2 and 3) The depth of cure decreased moderately and in a linear manner with increasing irradiation distance. An irradiation distance of 12 mm reduced the depth of well-cured resin only by about 1 mm as compared with close contact between exit window and surface of resin.