Early Hardness and Shear Bond Strength of Dual-cure Resin Cement Light Cured Through Resin Overlays With Different Dentin-layer Thicknesses

Abstract

Reducing the dentin-layer thickness while increasing the translucent-layer thickness of resin inlays increases the photopolymerization of dual-cure resin cement, thereby increasing the early bond strength of resin inlays to dentin. SUMMARYThe purpose of this study was to investigate whether dentin-layer thickness of resin overlays could affect the early hardness and shear bond strength of dual-cure resin cement (DCRC, RelyX ARC) after light curing with light curing units (LCUs) of various power densities: Optilux 360 (360), Elipar Freelight 2 (FL2), and Elipar S10 (S10). Resin overlays were fabricated using an indirect composite resin (Sinfony) with a dentin layer, an enamel layer, and a translucent layer of 0.5 mm thickness each (0.5-0.5-0.5) or of 0.2 mm, 0.5 mm, and 0.8 mm thickness (0.2-0.5-0.8), respectively. The DCRC was light cured for 40 seconds through the overlays, and surface hardness and shear bond strength to bovine dentin were tested 10 minutes after the start of light curing. Surface hardness was higher when the DCRC was light cured through the 0.2-0.5-0.8 combination than when the DCRC was light cured through the 0.5-0.5-0.5 combination with all LCUs. The ratio of upper surface hardness of DCRC light cured through resin overlays relative to the upper surface hardness of DCRC light cured directly was more than 90% only when the DCRC was light cured with S10 through the 0.2-0.5-0.8 combination. The shear bond strength value was higher when the DCRC was light cured with S10 through the 0.2-0.5-0.8 combination than when light cured with S10 through the 0.5-0.5-0.5 combination. This study indicates that reducing the dentin-layer thickness while increasing the translucent-layer thickness of

Effects of layering technique on the shade of resin overlays and the microhardness of dual cure resin cement

“…A bolt was attached to the opposite side of the Teflon plate, so that the space inside the hole could be adjusted by the rotation of the bolt, which was marked in 10 steps such that one step corresponded to a downward movement of the Teflon plate by 0.1 mm. 12 Single-layer resin overlays (Group 1L) were fabricated by lowering the Teflon plate by 1.5 mm and filling the empty space with Filtek Z350 (3M ESPE, St Paul, USA), shade A3. The upper surface of the aluminum mold was covered with a polyester film and a glass slab to press the surface for removal of the excess resin composite.…”

“…12 To control the light curing time of the DCRC, the diameter of the DCRC specimen was controlled to be smaller than the diameter of the light guide tip of the LCU. The Teflon plate in the mold was lowered by 1 mm, and DCRC (RelyX Unicem, 3M ESPE, Seefeld, Germany) was mixed according to the manufacturer's instructions and filled into the empty space.…”

“…After removing the glass slab, the DCRC was light cured through the resin overlay with the LCU for 20 seconds according to the manufacturer's instructions. 12 The power density of the LCU was measured at 1040 mW/cm 2 with a handheld dental radiometer (Cure Rite, Kerr, Milford, USA). After 10 minutes from the start of light curing, the Vickers microhardness of the DCRC was measured with a microhardness tester (MHT-10, Anton Paar, Graz, Austria) with a 100 g load for 10 seconds dwell time at 3 points in the center of the upper surface forming a small triangle, and the mean Vickers hardness number (VHN) was calculated.…”

“…11 Higher curing light penetration could enhance the light curing of DCRC beneath the resin overlays. Polymerization of resin cement is usually assessed by hardness tests, 12,13 and many studies on hardness measurements of DCRCs that were light cured through various indirect restorations were performed with one single shade. 14,15 However, in clinical situations, resin inlays are usually fabricated with a layering technique.…”

Microtensile bond strength of a newly developed resin cement to dentin

“…The specimen preparation for TEM observation was based on routine procedures for ultra-structural TEM examination of biological tissues. This involved overnight fixation in 2.5% glutaraldehyde in 0.1 M sodium cacodylate buffer for 1 min with three changes of solution, followed by dehydration in ascending concentrations of ethanol (25,50,75,95, and 100%) for 10 min each, with two changes of solutions every time. The specimens were subsequently immersed in 1:1 absolute ethanol-epoxy embedding resin (Epon 812, Polysciences, PA, USA) for 4 h with rotation at 4 rpm (Taab Rotatortype N, Taab Laboratories Eqt, Aldermaston, UK).…”