Surface roughness and morphology of three nanocomposites after two different polishing treatments by a multitechnique approach

Abstract

Objectives

The purpose of this study was to assess the surface roughness and morphology of three nanocomposites polished with two different polishing systems.

Methods

Specimens made of hybrid composite (Tetric Ceram [TC] as control) and nanocomposites: nanofilled (Filtek Supreme [FS]), nanofilled hybrid (Grandio [Gr]), complex nanofilled hybrid (Synergy D6 [Syn]) were polished with CompoSystem [CS] or Sof-Lex [SL] polishing discs. The average surface roughness (Ra) before and after polishing was measured using optical profilometry. Both AFM and SEM techniques were additionally used to analyze the surface morphology after polishing with the aim of relating the surface morphology and the surface roughness. Statistical analysis was done by ANOVA using a general linear model ( α = 0.05) with an adjustment for multiple comparisons.

Results

Within the same polishing system, FS exhibited the smoothest surface, followed by Syn, TC and Gr ( p < 0.0001). Sof-Lex polishing discs produced the smoothest surface compared to CompoSystem ( p < 0.0001). AFM and SEM observations confirmed that the surface roughness was related to the surface morphology and to the average filler size.

Significance

Positive correlation between the average filler size and the surface roughness suggest that using nanoparticles in the formulation does not necessary improve the surface texture. The nanofilled composite FS, which contains only nanofillers, showed the best results when associated to Sof-Lex polishing discs.

Introduction

Development and advances in the field of filler technology have affected dentistry since the introduction of dental resin composites about forty years ago. Since that time composites with macro-, micro- and nanofiller particles have been successively proposed. Today, only few macrofilled composites are still available in the dental market because of their inadequate surface texture. Compared to macrofilled composites, microfilled composites show better surface properties as well as superior aesthetic qualities, however their poor mechanical properties restrict their usage to non-stress-bearing areas. Microhybrid composites are most widely used as they provide optimal mechanical and physical properties combined with good polishing properties. However, one of the most important advances of the last few years in the field of filler technology is the application of nanotechnology to dental composites. Nanofillers have been developed with the aim of combining the advantages of hybrid and microfilled composites in the same restorative material. Nanofillers are described as “the discrete particles which have all of three dimensions in the range of about 1–100 nm” . Nanocomposites built with these nanofillers have a low shrinkage attributed to the high filler volume loading . They show favorable mechanical properties, which are at least equal to or may surpass those of hybrid materials . They exhibit a higher surface quality, a better polish and gloss, an increased retention as well as an increased wear resistance .

Among these properties, surface roughness is greatly taken into consideration. Roughness has a major impact on the aesthetic appearance and discoloration of restorations , plaque accumulation, secondary caries and gingival irritation , and wear of opposing and adjacent teeth . In addition, a smooth surface ensures patient comfort and facilitates oral hygiene . The smoothest composite surface, as known, is obtained under polyester matrix film . Nevertheless, removal of the resin rich surface layer is necessary because of compromising mechanical properties , biocompatibility and increasing staining . Furthermore, the surface treatment is systematic, following the placement of composite in order to remove excess material, to adjust the anatomic form and the occlusion, and, finally, to obtain a smooth surface. For these purposes, a wide variety of finishing and polishing instruments are available. Among them, aluminum oxide graded abrasive flexible disks were reported to produce the best surface smoothness .

The purpose of the present study was to investigate the surface roughness and the surface morphology of three dental composites containing nanoparticles and one hybrid composite after polishing with two different aluminum oxide-based polishing systems. The formulated hypotheses were: (i) Is there is a significant improvement in surface roughness between nano and hybrid composites? (ii) Is the surface roughness of the tested composites related to their surface morphology? (iii) Is the surface roughness after polishing significantly different depending on the polishing system?

Materials and methods

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
Polishing system Type Composition Filler average size Speed (rpm) Manufacturer Batch#
List of polishing systems investigated
Sof-Lex Discs (SL) 9.5 mm diameter Coarse Al 2 O 3 92–98 μm 10,000 3M ESPE Dental Products (St. Paul, MN, USA) P061121
Medium Al 2 O 3 25–29 μm 10,000
Fine Al 2 O 3 16–21 μm 30,000
Superfine Al 2 O 3 2–5 μm 30,000
CompoSystem (CS) discs 9 mm diameter Medium Al 2 O 3 50 μm 10,000 Komet, Gebr. Brasseler GmbH&Co (Lemgo, Germany) 32788
Fine Al 2 O 3 30 μm 10,000 33452
Ultrafine Al 2 O 3 5 μm 10,000 32393

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.

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.

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).

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).

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.

Materials and methods

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
Only gold members can continue reading. Log In or Register to continue

Nov 30, 2017 | Posted by in Dental Materials | Comments Off on Surface roughness and morphology of three nanocomposites after two different polishing treatments by a multitechnique approach
Premium Wordpress Themes by UFO Themes