Visible-Light Curing Units: Correlation Between Depth of Cure and Distance Between Exit Window and Resin Surface

Abstract

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.

A pilot investigation of operator variability during intra-oral light curing

“…14,15 Depth of cure depends on many factors including material composition, light source characteristics, irradiation time and distance of the light guide exit window from the material surface. [16][17][18] When curing the initial increment of material in a tunnel restoration or a deep box-shaped proximal cavity in a molar tooth, a distance of 6 mm frequently occurs between the cusp tips and the cavity surface. 17,18 Problems may also arise in vivo in ensuring normal and stable alignment of the light guide relative to the composite surface throughout the entire irradiation period.…”

“…[16][17][18] When curing the initial increment of material in a tunnel restoration or a deep box-shaped proximal cavity in a molar tooth, a distance of 6 mm frequently occurs between the cusp tips and the cavity surface. 17,18 Problems may also arise in vivo in ensuring normal and stable alignment of the light guide relative to the composite surface throughout the entire irradiation period. Access is further restricted in posterior locations and patients vary in their ability to obtain and sustain a wide-open mouth position.…”

Comparative efficiency of plasma and halogen light sources on composite micro-hardness in different curing conditions

“…Actually, it is well known that the degree of conversion of a given light-curing composite is mainly influenced by the light intensity of the curing device, total exposure duration, and distance between the exit window and resin surface [3,5]. Early advertising of the Apollo 95 E PAC unit advocated a 1 s curing time, which justifies the enormous and immediate interest taken in this device.…”

Effect of thickness of indirect restoration and distance from the light-curing unit tip on the hardness of a dual-cured resin cement

“…According to Pilo et al (15), low degree of conversion and low hardness values can be attributed to poor light exposure, what can explain the influence of composite resin discs interposed between light-curing unit tip and resin cement on resin cement hardness values. Probably, the power density supplied for resin cement during light curing was inadequate to excite photoinitiators at deep areas because of light absorption and scraping by superficial areas (5). The reciprocity between exposure time and light intensity could be also applied to overcome the effects on polymerization depth, once such effects are related to energy supplied for activation (7).…”

“…However, in some clinical situations, some factors such as light intensity, exposure time, thickness, composition, shade and opacity of the indirect restorative material can affect the amount of energy reaching the cement (3). Studies have demonstrated that the distance from the top of the highest cusp to the cavity floor can reach 8 mm at deep cavities (4,5), so the light intensity reaching the deepest region can be strongly attenuated. As a consequence, lower degree of conversion is expected from resin cements when the energy is lower than that required for a proper resin cement polymerization, leading to postoperative sensitivity, staining, marginal breaking, poor adhesion between the tooth and the indirect restoration (6), microleakage, secondary caries, and changes in some cement mechanical properties.…”