2.1

Materials and preparation of the specimens

Three nanocomposites, one hybrid composite and two different polishing systems were tested ( Table 1 ).

Twelve specimens of each material were made using cylindrical metallic molds (5 mm diameter × 3 mm depth). A transparent matrix strip was applied at the top of the surface of each composite with a constant pressure to extrude excess material, to flatten the surface and to reduce voids at the surface. Specimens were then polymerized according to the manufacturer’s recommendations with a Heliolux DLX (Vivadent, Schaan, Liechtenstein).

After curing, all specimens were transferred to other cylindrical metallic molds (5 mm diameter × 2.5 mm depth) and were divided into two groups. Each group was polished using one polishing system. Each abrasive disk was used only once, under dry conditions, for 20 s, using a slow-speed handpiece at a speed according to manufacturer’s instructions.

2.2

Surface roughness analysis

Surface roughness of each composite was assessed quantitatively by optical profilometry with a Chromatic confocal point sensor CHR 150-N (Stil, Aix en Provence, France) with an optical pen of 300 μm.

Each surface was scanned by eleven parallel tracings (length = 1 mm) per area of 1 mm × 1 mm. One area per specimen was analyzed for the samples without any polishing treatment, whereas two areas were analyzed for the polished surfaces. Measurement areas were chosen randomly, excluding a surface of 1 mm from the edge, which was not representative of the polishing. The average surface roughness (Ra) of each specimen was calculated with a cut-off value of 0.08 mm.

One representative zone of 0.3 mm × 0.3 mm of each composite and of each surface treatment (matrix, Sof-Lex, CompoSystem) was scanned by 151 parallel tracings to give a 3D reconstructed image.

2.3

Atomic force microscopy observations

Due to the nature of the composites, AFM microscopy was required to resolve nanocharges present in the material. The surface and filler morphology of the composites tested was investigated using contact mode with a commercial atomic force microscope (AFM) Nanoscope III with controller IV from Digital Instruments (Veeco Metrology Inc., Santa Barbara, CA, USA). Cantilevers with a constant spring of 0.1 N/m and with silicon nitride tips of 20 nm radius, were used (model MLCT-AUHW Park Scientific, Sunnyvale, CA, USA). Several scans over a given surface area were performed to provide reproducible images. Deflection and height mode images were obtained simultaneously at a fixed scan rate (between 1 and 2 Hz) with a resolution of 512 × 512 pixels. Images were acquired with 20 μm × 20 μm, 10 μm × 10 μm and 5 μm × 5 μm sizes. The images were analyzed with specific softwares (Nanoscope v613r1, Veeco Metrology Inc., Santa Barbara, CA, USA and WSxM 4.0 Develop11.1, Nanotec Electronica S.L., Tres Cantos, Spain).

2.4

Scanning electron microscopy observations

Representative specimens of each group of polished composites were analyzed qualitatively by scanning electron microscope (SEM) (XL 30 ESEM FEI Company, Hillsboro, Oregon, USA), following a sputter gold coating (460 Å thickness) (Edwards S 150 Sputter Coater, Edwards High Vacuum International, Wilmington, Massachusetts, USA).

2.5

Statistical analysis

All profilometry results were analyzed by means of two-way analysis of variance (ANOVA, SAS 9.1, SAS Institute, Cary, NC, USA) using a general linear model at a significance level of α = 0.05 with an adjustment for multiple comparisons.

2.1

Materials and preparation of the specimens

Three nanocomposites, one hybrid composite and two different polishing systems were tested ( Table 1 ).

Table 1

Details of the tested materials: bis-GMA: bisphenol-A glycidilmethacrylate; bis-EMA: ethoxylatedbis-phenol-A dimethacrylate; UDMA: urethane dimethacrylate; TEGDMA: triethyleneglycol dimethacrylate.

Material (group)	Type	Shade	Matrix	Filler type and size	Filler average size	Filler loading		Manufacturer	Batch#
						vol%	wt%
List of tested materials
Filtek Supreme XT (FS)	Nanofilled	A3B	Bis-GMA
			Bis-EMA	Zirconia–silica cluster filler	0.6–1.4 μm	59.5	78.5	3M ESPE (St. Paul, MN, USA)	5CT
			UDMA	Nanofillers (SiO 2 )	20 nm
			TEGDMA
Grandio (Gr)	Nanofilled hybrid	A2	Bis-GMA
			Dimethacrylate	Ba–Al–borosilicate glass filler	1 μm	71.4	87	Voco (Cuxhaven, Germany)	700173
			UDMA	Nanofiller (SiO 2 )	20–50 nm
			TEGDMA
Synergy D6 (Syn)	Complex nanofilled hybrid	A3,5/B3	Bis-GMA	PPF (prepolymerized fillers)	20 μm
			Bis-EMA	Barium glass filler <2.5 μm	0.6 μm	65	80	Coltene Whaledent AG (Altstatten, Switzerland)	89438
			UDMA	Microfiller (SiO 2 aggregated)	150 nm
			TEGDMA	Nanofiller (SiO 2 )	20–80 nm
Tetric Ceram (TC)	Hybrid	B3		Barium glass filler	0.7 μm
			Bis-GMA	Ba–Al–fluoroborosilicate glass filler		60	75	Ivoclar Vivadent AG (Schaan, Liechtenstein)	G08059
			UDMA	Microfiller (SiO 2 )	40 nm
			TEGDMA	Mixed oxide (ZrO 2 /SiO 2 )	0.2 μm
				Ytterbium trifluorure

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