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The International Journal of

Vol 38/2 2018 • March/April

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Cogo Rigo et. al:Influence of Polishing System on the Surface Roughness of Flowable and Regular-Viscosity Bulk Fill Composites

Volume 38, Number 4, 2018

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©2018 by Quintessence Publishing Co Inc.

1 Professor, School of Dentistry, FASURGS, Passo Fundo, Rio Grande do Sul, Brazil.2 Professor, Department of Restorative Dentistry, University of Guarulhos, Guarulhos, São Paulo, Brazil.

3 Professor, Department of Prosthodontics, University of Vila Velha, Vila Velha, Espírito Santo, Brazil.

4 Professor, Department of Biomaterials and Biomimetics, New York University, College of Dentistry, New York, New York, USA. Correspondence to: Dr Lindiane Cogo Rigo, 433 First Avenue, 10010, Dept Biomaterials and Biomimetics, New York University, New York, NY, USA. Fax: 212-995-4244. Email: [email protected]

Influence of Polishing System on the Surface Roughness of Flowable and Regular-Viscosity Bulk Fill Composites

This study evaluated the influence of polishing protocols on the surface roughness of flowable and regular bulk fill composites. Five bulk fill composites were tested: SureFil SDR Flow (SDR), Tetric EvoFlow Bulk fill (TEF), Filtek Bulk Fill Flowable (FIF), Tetric EvoCeram Bulk Fill (TEC), and Filtek Bulk Fill Posterior (FIP). Two polishing protocols were tested: Sof-Lex and Astropol. Astropol created a smoother surface for FIP (P < .05); however, the polishing protocol did not influence surface roughness on TEC (P > .05). SDR, TEF, and FIF exhibited rougher surfaces when polished. Sof-Lex created rougher surfaces for bulk fill composites. It was concluded that surface roughness was related to material composition rather than the polishing system. Int J Periodontics Restorative Dent 2018;38:e79–e86. doi: 10.11607/prd.3033

Composites are widely used for ante-rior and posterior restorations due to their ability to closely mimic the natu-ral tooth in terms of color, strength, shape, and texture.1,2 Superficial texture is an important factor in the longevity of composite restora-tions.3 Long-term follow-up stud-ies have demonstrated that a rough composite surface can compromise color and gloss,4–6 lead to increased plaque accumulation,2,4–7 and favor development of secondary caries.2,7–9 Secondary caries are one of the main reasons for failure of a composite res-toration (around 38% in 30 years).8,9

In addition to their beneficial ef-fect on patient comfort, finishing and polishing procedures are required to achieve restoration esthetics and increase longevity.2,4 Finishing is the primary contouring of a restoration to reach a desirable anatomy and occlusion. Polishing reduces rough-ness and removes scratches created in previous steps.2 Many polishing systems (with one or multiple steps) have been introduced over the years, including diamond burs, mul-tifluted carbide finishing burs, and aluminum oxide–coated abrasive discs/wheels.2,3 The goal for manu-facturers and clinicians is to create the smoothest surface in the short-est amount of time.2 A clinically ac-ceptable surface roughness will have values close to enamel-to-enamel contact in occlusal areas (0.64 μm).10

Lindiane Cogo Rigo, DDS, MS1

Dimorvan Bordin, DDS, MS, PhD2

Vinicius Pavesi Fardin, DDS, MS, PhD3

Paulo G. Coelho, DDS, MS, PhD4

Timothy G. Bromage, MA, PhD4

Andre Reis, DDS, MS, PhD2

Ronaldo Hirata, DDS, MS, PhD4

© 2018 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.

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Previous studies suggest that surface roughness and polishing ef-ficiency are dependent on the com-posite resin formulation.2,4 Flowable conventional composites (37% to 53% of the filler’s volume) allow for easier insertion, better adaptation, and improved polishing results.4,11 However, regular conventional com-posites (50% to 70% of the filler’s volume) are generally more difficult to polish and adaptation might be compromised due to their higher viscosity.11 Filler size has also proven to influence the surface roughness of composite materials. For ex-ample, nanoparticles (smaller than 100 nm) exhibit better polishing, im-proved optical characteristics, and better gloss maintenance relative to composites with coarser fillers.2,6

Bulk fill composites were devel-oped to fill caries in one increment.12 Matrix and filler content and size have been modified to improve the clinical performance of materials.13,14 They are commercially available in two viscosities, flowable and regu-lar, which have different indications in clinical practice. Flowable bulk fill composites are recommended as a base in Class I and II restora-tions, which should subsequently be capped with a conventional com-posite to withstand occlusal loading. Regular-viscosity bulk fill composites are recommended for bulk filling the entire caries lesion and do not re-quire a regular composite layer.

Further investigations are war-ranted considering that few studies have assessed the different surface textures produced after polishing bulk fill composites. This in vitro study evaluated the efficiency of

polishing protocols and the surface roughness of flowable and regular-viscosity bulk fill composites. The following two hypotheses were test-ed: (1) flowable and regular-viscosity bulk fill composites will present dif-ferent surface roughness after pol-ishing protocols, and (2) different polishing systems will provide differ-ent surface roughness.

Materials and Methods

Specimen Preparation

A total of 126 composite discs (5 × 2 mm) were prepared according to the seven composites tested. Three flowable bulk fill composites (SureFil SDR Flow [SDR], Tetric EvoFlow Bulk Fill [TEF], and Filtek Bulk fill Flowable [FIF]) and two regular-viscosity bulk fill materials (Tetric EvoCeram Bulk fill [TEC] and Filtek Bulk Fill Posterior [FIP]) were tested, and two conven-tional composites (IPS Empress Di-rect [EMD] and Filtek Supreme Ultra [FIS]) were used as control materials (n = 18). Materials, manufacturers, and composition are shown in Table 1. For each material, composite was inserted into a rubber mold and pressed between two glass micro-scope slides covered by polyester strips. Constant standardized mild pressure was applied on the top to remove excess material and produce a flat surface. Specimens were polym-erized from the top for 20 seconds with a polywave LED light-curing unit (1,200 mW/cm2, Bluephase, Ivoclar Vivadent). All samples were stored in distilled water at 37ºC for 24 hours before polishing procedures.

The samples were subdivided into three groups (n = 6) according to the polishing protocol used. In the control group, no polishing was performed; the polyester strip pro-vided the surface finishing. The oth-er groups were polished using either Sof-Lex discs or Astropol rubber polishers, following manufacturers’ recommendations (Table 2). A metal mold was used to hold the sample during polishing procedures, which were performed by a single opera-tor (L.C.R.). The abrasive discs were used once and discarded. After pol-ishing, samples were ultrasonically cleaned with deionized water for 10 minutes to remove any surface de-bris. All samples were stored under water at 37ºC prior to surface rough-ness evaluation.

Surface Roughness Evaluation

The average surface roughness (Sa) of each specimen was measured in five different areas using optical topom-etry (OTM) (PhaseView ZeeScan, at-tached to a Zeiss Axio Imager M1m) for extended depth of field imaging. An x-y cutoff of 425 μm was used with a ×50 (NA = 0.70) magnification objective lens providing submicron vertical resolution. ZeeScan software (GetPhase) provided z-depth mea-surement and three-dimensional reconstruction of the surface for calculating surface roughness (Sa) as well as two-dimensional images from the surface for qualitative analysis.

The data was statistically ana-lyzed by two-way analysis of vari-ance (ANOVA) considering material and polishing protocols. Post hoc


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comparisons were carried out using Tukey test (α = .05).

Results

Table 3 presents the Sa values and standard deviation for the different groups. Two-way ANOVA revealed significant differences for the factors composite resin (P = .00001) and polishing technique (P = .00001)

and for the interaction between fac-tors (P = .00001).

Regarding polishing protocols, no significant difference was ob-served for the conventional com-posites (FIS and EMD) (P > .05). With the exception of TEC, Sof-Lex increased surface roughness for all bulk fill composites. Astropol creat-ed a smoother surface for the regu-lar bulk fill composites FIP and TEC; however, no significant difference

was observed with respect to TEC in terms of polishing protocol (P > .05). Both polishing protocols created rougher surfaces than the control (polyester strip) for all bulk fill flow-able composites (FIF, TEF, and SDR) (P > .05). Regarding FIF and SDR, no significant difference was observed between Sof-Lex and Astropol. However, regarding TEF, Astropol produced the highest surface roughness values (P < .05). Consid-

Table 1 Materials, Manufacturers, Batch Numbers, Composition, and Filler Loading of the Materials Studied

Material (abbreviation) Composition Batch number

Regular conventional composite

Filtek Supreme Ultra Universal Restorative, 3M ESPE (FIS)

Matrix: bisphenol a diglycidyl ether dimethacrylate (Bis-GMA), modified urethane dimethacrylate resin (UDMA), triethyleneglycol-dimethacrylate (TEGDMA), ethoxylatedbisphenol A dimethacrylate (bis-EMA), and polyethylene glycol dimethacrylate (PEGDMA); Fillers: nonagglomerated silica filler (20 nm), nonagglomerated zirconia filler (4–11 nm), and aggregated zirconia/silica cluster fillers (filler content 78.5% wt/63.3% vol, filler average size = 0.6–1.4 μm)

N709034

IPS Empress Direct, Ivoclar Vivadent (EMD)

Matrix: UDMA, Bis-GMA, tricyclodecane dimethanol dimethacrylate (TCDD); Fillers: barium-alumina-fluorosilicate glass, barium glass filler (0.4 μm), mixed oxide (150 nm), prepolymer (1–10 μm) (filler content 81.2% wt/59% vol)

U26969

Regular bulk fill composite

Tetric EvoCeram Bulk Fill, Ivoclar Vivadent (TEC)

Matrix: Bis-GMA, UDMA, bis-EMA; Fillers: Ba-Al-Si glass (0.4–0.7 μm), ytterbium trifluoride (200 nm), and an Isofiller (prepolymer) (filler content 79%–81% wt/60%–61%vol)

U24443

Filtek Bulk Fill Posterior Restorative, 3M ESPE (FIP)

Matrix: AUDMA, UDMA, 12-dodecane-DMA (DDDMA); Fillers: nonagglomerated silica filler (20 nm), nonagglomerated zirconia filler (4–11 nm), aggregated zirconia/silica cluster filler (20 nm silica/4–11 nm zirconia), and an agglomerate ytterbium trifluoride filler (100 nm) (filler content 76.5% wt/58.4% vol)

N710947

Flowable bulk fill composite

Filtek Bulk Fill Flowable Restorative, 3M ESPE (FIF)

Matrix: Bis-GMA, UDMA, substituted dimethacrylate, (BisEMA-6), and Procrylat resins; Fillers: zirconia/silica particles (0.01–3.5 μm) and ytterbium trifluoride fillers (0.01–5.0 μm) (filler content 64.5% wt/42.5% vol)

N721690

Tetric EvoFlow Bulk Fill, Ivoclar Vivadent (TEF)

Matrix: Bis-GMA, Bis-EMA, TCDD; Fillers: barium glass, ytterbium trifluoride, copolymers (filler content 68.2% wt/46.4% vol)

U27609

SureFil SDR Flow, Dentsply Caulk, Milford (SDR)

Matrix: UDMA, EBPDMA, TEGDMA; Fillers: barium-alumino- fluoro-borosilicate glass fillers (4.2 µm) (filler content 68% wt/45% vol)

1410000822


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ering the materials evaluated, the flowable bulk fill composites TEF and SDR displayed the highest Sa values when polished with Astropol.

In qualitative analysis, OTM two-dimensional surface images (Fig 1) demonstrated that polishing systems created scratches on composite sur-face depending on the materials and polishing technique used. Three-dimensional reconstructions (Fig 2) revealed that for conventional com-posites (FIS and EMD), a similar sur-face was obtained for all polishing groups. A change in the reconstruc-

tion pattern between the polished composites and the control was ob-served for the rest of the compos-ites. Overall, qualitative texture was similar for all polishing protocols.

Discussion

The present study evaluated sur-face roughness of bulk fill compos-ite materials using OTM. OTM is a three-dimensional optical pro-filometry analysis that provides qualitative and quantitative rep-

resentations, making it a useful method to evaluate surface rough-ness.1,2,4,15 OTM is a nondestructive method for sensitive samples that allows general and detailed visual-ization without mechanical contact.16 Three-dimensional optics captures specular light reflection from the material. The apparatus measures topographic relief on the surface with submicron resolution to detect microscale roughness.4

This investigation assessed the surface roughness of flowable and regular-viscosity bulk fill composites

Table 2 Composition and Application Directions of the Polishing Systems Used

Finishing/ polishing material Composition Application directions Batch number

Sof-Lex, 3M ESPE

Extra-thin contouring and polishing discs; aluminum oxide discs (coarse 92–98 μm, medium 25–29 μm, fine 16–21 μm, and superfine 2–5 μm); followed by spiral finishing and polishing wheels—thermoplastic elastomer impregnated with aluminum oxide particles (beige and white)

20 s each, using a low-speed handpiece in circular movements and without water cooling

Coarse N723925; medium N719256; fine N712257; superfine N723924; spiral beige N715950 and white N717535

Astropol, Ivoclar Vivadent

Silicon carbide–coated polishing discs (coarse grey [F] 45 μm; fine green [P] 1 μm; and extra-fine pink [HP] 0.3 μm)

15 s each, using a low-speed handpiece in circular movements and with continuous water cooling (50 mL/min)

Grey (F) UL0368; green (P) TL0806; pink (HP) TL0809

Table 3 Mean ± SD Surface Roughness Sa (μm) for the Composite Resins After Different Polishing Protocols

Composite Control (polyester strip) Sof-Lex Astropol

Filtek Supreme Ultra (FIS) 0.36 ± 0.02Aa 0.44 ± 0.07ABa 0.37 ± 0.04Aa

Empress Direct (EMD) 0.39 ± 0.06Aa 0.40 ± 0.06Ba 0.35 ± 0.04Aa

Tetric Evoceram Bulk Fill (TEC) 0.37 ± 0.06Aa 0.38 ± 0.05Ba 0.37 ± 0.03Aa

Filtek Bulk Fill Posterior (FIP) 0.35 ± 0.06Aa 0.52 ± 0.16ACb 0.41 ± 0.08Aa

Filtek Bulk Fill Flowable (FIF) 0.35 ± 0.05Aa 0.48 ± 0.09ABCb 0.42 ± 0.05Aab

Tetric Evoflow Bulk Fill (TEF) 0.29 ± 0.03Aa 0.58 ± 0.05Cb 0.68 ± 0.07Bc

Surefil SDR Flow (SDR) 0.27 ± 0.02Aa 0.56 ± 0.11ACb 0.55 ± 0.12Cb

Different superscript letters (uppercase: material; lowercase: polishing) are significantly different by Tukey test at the .05 confidence level.


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polished with different pro-tocols. The first postulated hypothesis was accepted be-cause different Sa values were observed for the different materials. For flowable bulk fill composites (FIF, TEF, and SDR), Sof-Lex and Astropol produced higher Sa values. This observation differs from previous studies regarding conventional flowable com-posites, which demonstrated a smoother surface when com-pared to regular-viscosity con-ventional materials because of their lower filler rate.11,17 The filler size for the three flowable bulk fill composites tested in this study was increased by the manufacturers, which modi-fied the surface characteristics of the materials. Manufacturers followed different strategies to increase the depth of cure of bulk fill composites, allowing an adequate degree of con-version in increments ≥ 4 mm thick (ie, reducing the filler amount, increasing filler size, changing the photoinitiator, increasing material translu-cency).5 This study revealed that the Sa of these materials increased after polishing.

Flowable bulk fill compos-ites are indicated to fill Class I cavities as a base, as a Class II box liner, or as a stand-alone restorative material in nonoc-clusal-contact areas.15 A con-ventional composite should be applied on the top fol-lowing the incremental tech-nique.14 Clinical studies have

Fig 1 Two-dimensional images showing composites’ surfaces obtained by optical topometry. Field width = 196 μm, with a ×50 (NA = 0.70) magnification. Unpolished surfaces (left column) exhibited few air voids (white arrows) and reproductions of matrix imperfections (black arrows). Polished samples displayed a rougher and scratchier surface, Sof-Lex (middle) and Astropol (right).


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Fig 2 Three-dimensional surface reconstructions obtained by optical profilometry. Spikes appearing at borders are edge artifacts and were not included in surface roughness measurements.


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demonstrated acceptable perfor-mance after a 3- to 5-year follow-up period when applied according to the manufacturer’s instructions.18,19

Although flowable bulk fill com-posites are not subject to polishing or exposed to occlusal wear resis-tance, their roughness and polishing behavior is an important charac-teristic on the proximal surfaces. In nonstress areas (ie, proximal areas), flowable bulk fill composites tend to be exposed to environmental degradation and plaque accumula-tion. According to the results of this study, FIF, TEF, and SDR revealed rougher surfaces with both polishing systems. However, low Sa values, not significantly different from regular composites, were obtained when the polyester strip was used as control. A polyester strip represents the clinical result when a matrix is used,2,20 and it is considered the smoothest surface obtained on a restoration.2,4 Accord-ingly, when these materials are used, proximal polishing (file strips) should be avoided, if possible.

With respect to regular bulk fill composites, no significant differ-ence was observed among the pol-ishing protocols for the TEC group. Sof-Lex and Astropol revealed smoother surfaces compared to the control polyester strip. Previous studies suggested that TEC exhibits higher Vickers microhardness due to modifications of its composition. The modifications were focused on the substitution of camphorquinone for a more efficient photoinitiator (Ivocerin, Ivoclar Vivadent), the increase in the material’s translucency, and the ad-dition of smaller-size round fillers. These modifications are related to a

deeper and more efficient degree of polymerization and a better polish-ing performance because of the size and shape of the fillers.14

With respect to FIP, Sof-Lex created the roughest surface. Ac-cording to the manufacturer, FIP has the same filler composition as the conventional regular composite FIS. Nevertheless, FIS presented no difference between polishing proto-cols. This may be explained by the modifications made to the FIP ma-trix content. Four monomers were introduced: two low-viscosity mono-mers (DDDMA and UDMA) and two new monomers (AUDMA and AFM). DDMA and UDMA reduce reactive groups in the material to moderate the shrinkage, while AUDMA and AFM react with any methacrylate. This mechanism relaxes the devel-oping material, relieving stress. Pre-vious studies suggested that UDMA elution on Filtek Bulk Fill was consid-erably higher and its degree of cure was lower compared to other bulk fill composites.21 These properties may contribute to a higher abrasion of the matrices during polishing and exposure of superficial fillers, result-ing in increased roughness.20,22

The second postulated hypoth-esis, that polishing systems would provide different surface roughness, was partially accepted. Except for TEC, Sof-Lex increased the surface roughness of all bulk fill materials tested. A possible explanation lies with the smooth surface provided by the polyester strip used as a con-trol.22 The Sof-Lex system created a more abrasive surface because it consists of four gradual files (start-ing from 92 to 98 μm and progress-

ing to 2 to 5 μm) to first finish and then polish the surface, with two ad-ditional silicon wheels impregnated with aluminum oxide particles used at the end of the procedure. Previ-ous studies described the Sof-Lex system as providing a smooth sur-face when a rougher starting surface was evaluated (ie, silicon paper files, diamond or carbide burs).7,11,22–25

In this study, the control was smoother than the last polishing disc, which may have increased the Sa.26 In contrast to Sof-Lex, the Astropol system polishes the sur-face with a sequence of three silicon carbide–coated discs,2,11 which are less abrasive (from 45 to 0.3 μm) and have fewer steps than Sof-Lex. The result was a more uniform and regu-lar surface.

Only discs and rubber polish-ers were tested in this study. From a clinical practice perspective, oth-er finishing protocols (ie, diamond burs, carbide burs) are usually used before finishing and polishing discs or rubber, likely changing the rough-ness results obtained.22 In addition, other factors can influence polishing efficiency, such as pressure, time, abrasive particles hardness, and at-tachment of such particles to the base material.20 The abrasive parti-cles should be harder than the com-posite filler and should not detach during polishing.2,22 The polishing choice should ultimately be based on the finishing/polishing need of each specific clinical case.

Final composite roughness should be similar to enamel-to-enamel contact in occlusal areas (0.64 µm).10 The results obtained from the OTM analysis range from


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0.29 to 0.68 μm, which according to Kakaboura et al15 indicate that all composites presented clinically acceptable results with both polish-ing systems. Additional studies are needed to determine the long-term roughness of these materials.

Conclusions

Flowable bulk fill composites exhib-ited rougher surfaces when polished. The Sof-Lex disc system created rougher surfaces for bulk fill com-posites. Surface roughness was more closely related to material composi-tion than to the polishing system used.

Acknowledgments

The authors are grateful to Ivoclar Vivadent, 3M ESPE, and Dentsply Caulk for donating the materials used in the present investiga-tion. The authors would like to thank Brazil-ian Federal Agency CAPES-PDSE for their support through a scholarship granted to Dimorvan Bordin (process 6780/2015-06). The authors reported no conflicts of interest related to this study.

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