Mechanical and Optical Characterization of Single-shade Resin Composites Used in Posterior Teeth
This study aimed to evaluate the optical and mechanical performance of two single-shade resin-based composites (RBCs) compared to those of a conventional RBC for restoring posterior teeth. Two single-shade RBCs, Omnichroma (Tukoyama) and Vittra Unique APS (FGM), and a conventional RBC, Filtek Z350XT shade A2 (3M Oral Care), were evaluated in this study. The optical shade-matching performance was measured using a spectrophotometer. The light emitted by VALO Grand (Ultradent) and transmitted through the 2.0-mm RBC specimens was evaluated using beam profiling. Knoop hardness (KH, N/mm2), degree of conversion (DC, %) at the top and bottom, flexural strength (FS, MPa), elastic modulus (E, GPa), postgel shrinkage (Shr, %), and shrinkage stress (MPa) were evaluated. Scanning electron microscopy (SEM) was used to characterize the filler. Data for FS, E, and Shr were analyzed by one-way analysis of variance (ANOVA) and KH and DC by repeated one-way ANOVA measurement followed by Tukey test (α=0.05). The modified von Mises stress values, light transmission, and SEM images were analyzed qualitatively. All single-shade RBCs exhibited higher chromatic adaptation than the Filtek Z350XT (p<0.001). Omnichroma exhibited less color difference than Vittra Unique APS, irrespective of the shade. The light transmitted through Omnichroma and Vittra Unique APS increased during polymerization. KH and DC values were significantly reduced from the top to the bottom of the specimens for all RBCs (p<0.001); however, the ratio values were always higher than 80%. In general, all RBCs demonstrated similar mechanical properties. All RBCs exhibited a similar FS (p=0.083) and Shr value (p=0.144). Filtek Z350XT exhibited significantly higher E (p<0.001) than both single-shade RBCs. All RBCs exhibited similar shrinkage stress during restoration and similar residual stress during occlusal loading. Single-shade Omnichroma and Vittra Unique APS increased light transmission during light-activation, demonstrating better chromatic adaptation than conventional Filtek Z350XT. In general, Omnichroma and Vittra Unique APS exhibited similar mechanical properties and shrinkage stress distributions as Filtek Z350XT during light-activation and occlusal loading.SUMMARY
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Color of the first mandibular typodont molars (A2, B2, C2, and D3). (A): Without restoration. (B): Teeth restored with Omnichroma. (C): Teeth restored with Vittra Unique APS. (D): Teeth restored with Filtek Z350XT.
Scanning electron microscopy images of tested RBCs. (A): Omnichroma. (B): Vittra Unique APS. (C): Filtek Z350XT. (10,000× magnification)
Two-dimensional (2D) and three-dimensional (3D) beam profile images at the same scale captured at the light-curing unit tip (control) and through 2.0 mm of each resin-based composite.
Three-dimensional beam profile images in same scale captured during light-activation across 2.0 mm of each resin-based composite. (A): Omnichroma. (B): Vittra Unique APS. (C): Filtek Z350XT.
Radiant power (mW) emitted during 20-second exposure time. (A): VALO Grand on standard mode (note, light-curing unit images are in different scales). (B): Radiant power (mW/nm) transmitted through the RBC specimens. Abbreviation: RBC, resin-based composite.
Chromatic adaptation of RBCs according to tooth shade. Different letters indicate significant difference with uppercase letters used for comparing single-shade RBCs and lowercase letters for comparing tooth shades to each RBC. *Indicates significant difference between each single-shade RBC compared with Filtek Z350XT and shade A2 (control) (p<0.05). Abbreviation: RBC, resin-based composite.
Modified von Mises stress distribution generated by shrinkage during the restoration and at occlusal loading for different resin-based composite tested at maximum intercuspidation of molar teeth.
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