Effect of C-factor and LED curing mode on microleakage CEJ. The mesio-distal dimension of the cavities for 15 seconds. After removal of all etchant gel was 4 mm (Figures 1a and 1b). The cavities were with a vigorous water spray for 10 seconds, ex- standardized for depth by a mark on the burs and cess water was removed with high volume evacu- for the diameter by placing a sticker with a 4 mm ation tip placed directly over the preparation for punched hole on the desired area.22 The resulting 1-2 seconds. Then, the dentin bonding agent C-factor for the cavities was calculated as the ra- (Excite, Ivoclar Vivadent, Bendererstrasse 2, FL- tio of the bonded to the unbonded surface area of 9494 Schaan, Liechtenstein) was applied to both the cavity. The cavities in these groups were visu- enamel and dentin with a disposable brush, ac- alized approximately as a triangular prism. The cording to manufacturer instructions. To obtain a surface area of a triangular prism = [ab + (s1 + s2 uniform, glossy appearance and solvent free ad- + s3) h] (a = altitude of the triangle, b = base of the hesive, a high-volume evacuation tip was placed triangle, s = side of the triangle, and h = height of over the preparation for 1-2 seconds, and then the prism) = [2x4 + (2 +2 + 4) 4) = 40 mm2. The un- the adhesive was light cured for 15 seconds. The bonded surface area of the cavity is visualized as cavities were then filled with microhybrid resin- a rectangle, therefore its surface area = length x based composite material (Tetric Ceram, shade width = [4x4] = 16 mm2. The bonded surface area A3, Ivoclar Vivadent, Bendererstrasse 2, FL-9494 = the surface area of the prism – the unbonded Schaan, Liechtenstein) in one increment. surface area = 40 – 16 = 24 mm2. Therefore, the The resin composite in groups I and III was resulting C-factor = 24/16= 1,5. cured for 15 seconds using the fast curing mode In groups III and IV, box-shaped class V cavi- of the LED curing device (light intensity 1100 mW/ ties were prepared on the vestibular surfaces cm2). On the other hand, the resin composite in of the teeth using fissure carbide burs at high groups II and IV was cured for 20 seconds, using speed handpiece and water coolant. The cavi- soft-start curing for 10 seconds from 0 to 1100 ties were prepared in enamel and dentin at the mW/cm2, followed by 1100 mW/cm2 for 10 sec- CEJ. The dimensions of the cavities were: 2 mm onds. The two curing modes resulted in the same in depth, 4 mm mesio-distal in width, and 2 mm radiation energy of 16.5 J/cm2. occluso-gingival in height (Figures 2a and 2b). Immediately after curing, each restoration The cavities were visualized approximately as a was contoured using ET finishing diamonds rectangular prism. The surface area of the rect- (Brasseler USA, Savannah, GA, USA), and then, angular prism= [2(lw) + (2l + 2w) h] (l = length of specimens were placed in distilled water at 37°C the prism, w = width of the prism, and h = height for 24 hours, after which they were thermocycled of the prism) = [2(2x2) + (2x2 +2x2) x4] = 40 mm2. 1000 times at 5°C and 55°C with a dwell time of The unbonded surface area of the cavity is visual- 30 seconds. With the exception of 1 mm around ized as a rectangle, therefore its surface area = the restoration, the entire tooth was covered length x width = [4x2] = 8 mm2. The bonded sur- with two layers of nail varnish. Specimens were face area of the cavity = the surface area of the placed in a solution of 0.5% basic fuchsin dye for prism - the unbonded surface area = 40 – 8 = 32 24 hours, after which they were removed, rinsed mm2. Therefore, the resulting C-factor = 32/8 = 4. with distilled water, and embedded in autopoly- The volume of the V-shaped cavities (the tri- merizing acrylic resin. angular prism) was calculated using the follow- The embedded specimens were sectioned ing formula [½abh] = [1/2 (2x4x4)] = 16 mm3. The longitudinally in the bucco-lingual direction into volume of the box-shaped cavities (rectangular halves using a water-cooled, slow-speed dia- prism) was calculated based on the following mond saw (ISOMET, Buehler Ltd, Lake Bluff, IL, formula [lwh] = 2x2x4 = 16 mm3. The volumes of USA) and a diamond blade (15HC, Buehler Ltd, the cavities were equal for all groups, namely 16 Lake Bluff, IL, USA). Pictures of the sections mm3. were taken with a digital camera (Leica DC 200, One curing unit (Mini L.E.D, Satelec, Merignac, Leica Microsystems, Wetzlar GmbH, Ernst-Leitz- Cedex, France) with a curing guide of 7.5 mm di- Strasse, D-35578 Wetzlar, Germany) attached to ameter was used throughout the study. All the a stereomicroscope (Leica MZ-6, Leica Micro- cavities were treated with 35% phosphoric acid systems, Wetzlar GmbH, Ernst-Leitz-Strasse, 402 European Journal of Dentistry