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    Effect of tree types of light-curing units on 5-year colour changes of light-cured composite
    (SPRINGER HEIDELBERG, 2009) Tak, Onjen; Altıntaş, Subutay Han; Öztürk, Nilgün; Üşümez, Aslıhan
    The purpose of this study was to determine colour changes in a composite cured with tungsten-halogen, light-emitting diode (LED) or a plasma arc after 5 years. Five specimens 10 mm in diameter and 2 mm in height were prepared using Hybrid (Clearfil AP-X) composite for each test group. The corresponding specimens were cured with a tungsten-halogen curing light, a LED unit or with a plasma arc. Specimens were stored in light-proof boxes for 5 years after the curing procedure to avoid further exposure to light and stored in 37A degrees C in 100% humidity. Colorimetric values of the specimens immediately after curing and after 5 years were measured using colorimeter. The Delta E* (ab) values varied significantly depending on the curing unit used (p < 0.001). Curing time did not affect the colour changes of the specimens (p = 0.4). The results of this study suggest that composite materials undergo measurable changes due to the curing unit exposure.
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    Influence of food simulating solutions on the hardness of composite resins
    (SAGE PUBLICATIONS LTD, 2008) Sevimay, Muejde; Yucel, Munir Tolga; Tak, Onjen
    The aim of this in vitro study was to evaluate the influence of food simulating solutions on surface hardness of three different composite resins. A total of 50 specimens were fabricated for each of Filtek Z 250, Clearfil ST, Aelite LS Packable according to the manufacturers' instructions. Ten specimens of each material were randomly selected and stored in 8% ethanol, 50% ethanol, heptane, distilled water, and air at 37 degrees C for 1 week. After one week conditioning period, hardness testing was carried out with a micro hardness tester. The hardness of composite resin materials are strongly influenced by food simulating solutions.
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    Temperature rise during polymerization of three different provisional materials
    (SPRINGER HEIDELBERG, 2008) Altıntaş, Subutay Han; Yöndem, İsa; Tak, Onjen; Üşümez, Aslıhan
    The purpose of this study was to evaluate the temperature rise during polymerization of three different provisional materials by direct method on two different dentin disc thicknesses. Two autopolymerizing; bis-acrylic composite (Fill-in; Kerr), polymethyl methacrylate (Temdent; Weil Dental), and one light polymerizing composite (Revotek LC; GC) provisional restoration materials were used in this study. Sixty dentin discs were prepared from extracted molars (diameter, 5 mm; height, 1 or 2 mm). These dentin discs (1 or 2 mm) were placed on apparatus developed to measure temperature rise. The temperature rise during polymerization was measured under the dentin disc with a J-type thermocouple wire that was connected to a data logger. Statistical analysis was performed with two-way analysis of variance followed by Tukey HSD test (alpha=0.05). Temperature rise values statistically varied according to the provisional restoration material used (light polymerized, auto polymerized; P < 0.001) and the dentin thickness (1 and 2 mm; P < 0.001). The polymethyl methacrylate based provisional material induced significantly higher temperature rise than other provisional restoration materials at 2-mm dentin thickness (P < 0.01). At 1-mm dentin thickness, polymethyl methacrylate and composite induced significantly higher temperature increase than bis-acrylic composite provisional material (P < 0.05). The risk for heat-induced pulpal damage should be taken into consideration during polymerization of provisional materials in deep cavities in which dentin thickness is less than 1 mm.