| Abstract|| |
Aim: This in vitro study assessed the surface quality of three nanoparticle composites with four commercially available polishing systems.
Materials and Methods: A total of 180 specimens (10 × 2 mm) were prepared in metal molds using three nanocomposites, Filtek Z-350 XT, Ceram-X Mono, and Tetric N-Ceram. Sixty specimens of each material were then randomly assigned to five study groups. Control specimens were left untreated and the remaining specimens were subjected to polishing with SpinBrite, CompoMaster, AstroPol, and SofLex polishing systems. Average roughness (Ra) and average ten-point roughness (Rz) were calculated using Perthometer, and the data were analyzed by two-way analysis of variance (ANOVA) and post-hoc Tukey's tests.
Results: For all the materials, the roughest surfaces were observed for control specimens, with no statistically significant differences between the material groups. For Filtek Z-350 XT, the decrease in surface roughness after two-step polishing was insignificant. For Ceram-X, SpinBrite specimens showed similar degree of roughness as control specimens. For Tetric N-Ceram, no significant decrease in roughness was observed after one-step polishing. Two-way ANOVA (interaction of subgroups and groups) did not show a significant association with the outcome.
Conclusions: For nanofilled composites (Filtek Z-350 XT), the surface roughness decreased with the increase in number of polishing steps, whereas one-step and multi-step polishing procedures produced similar quality of smoothness for nanohybrid composites (Ceram-X, Tetric N-Ceram). Ra and Rz values of surface roughness are a function of type of finishing/polishing only.
Keywords: Nanocomposites; profilometry; surface roughness
|How to cite this article:|
Sapra V, Taneja S, Kumar M. Surface geometry of various nanofiller composites using different polishing systems: A comparative study. J Conserv Dent 2013;16:559-63
|How to cite this URL:|
Sapra V, Taneja S, Kumar M. Surface geometry of various nanofiller composites using different polishing systems: A comparative study. J Conserv Dent [serial online] 2013 [cited 2020 Jul 11];16:559-63. Available from: http://www.jcd.org.in/text.asp?2013/16/6/559/120949
| Introduction|| |
Surface characteristics determine the success and clinical longevity of a restoration. The surface roughness interferes with a patient's comfort in terms of tactile perception, aesthetic appearance, and stain resistance,  and is of high clinical relevance for wear resistance, plaque accumulation, gingival inflammation, material discoloration (especially in Class-V restorations), and surface gloss.  Conversely, surface smoothness adds to the patients' comfort. 
Surface roughness of a resin composite relates to the composition and porosity of the material, nature of the instruments, and the procedures used in polishing. The resin matrix and filler particles have different levels of hardness that cause variations in removal efficiency during polishing, which leads to differences in surface roughness. Because of composition diversity, types of resin, variations in filler particles, and the size and nature of abrading particles in the polishing instruments, it is of significant importance to pair a resin composite with a matching polishing system. Other factors affecting polishing results may include the amount of pressure used, orientation of the abrading surface, and the amount of time spent with each abrasive instrument. 
Nanocomposites combine the mechanical strength of hybrid composites and superior aesthetic characteristics of microfill composites. These novel composites have many advantages including reduced polymerization shrinkage, improved optical characteristics, better gloss retention, and diminished wear  because of the decrease in differences between the polymer matrix and filler particle size and increased filler loading. ,
One group of these materials, Filtek Z-350 XT, contains zirconia-silica particles, 5-20 nm fillers, and 0.6-1.4 μm nanoclusters. Another group, Ceram-X, comprises organically modified ceramic nanoparticles and nanofillers combined with conventional glass particles of approximately 1 μm. Tetric N-Ceram contains ytterbium trifluoride with particle size ranging from 20 to 40 nm.
For years, finishing/polishing of composites was limited to the use of multistep procedures such as coated abrasives (abrasive disks), cutting devices (carbide burs and stones), and fine diamond burs. Currently, one-step (diamond impregnated- urethane dimethacrylate bristles) and two-step rubberized abrasives (resin- or silicon-impregnated burs) and loose particulate abrasives (polishing pastes) have been advocated. ,,
Although several studies in the literature deal with the surface quality of nanocomposites, to our knowledge, only few studies have evaluated the effect of increasing number of polishing steps on the surface roughness of nanocomposites. Moreover, the effect of SpinBrite and CompoMaster on the surface roughness of nanocomposites has not yet been evaluated.
Thus, the present study was undertaken to quantitatively evaluate the surface roughness of three nanofilled resin composites after polishing with four different polishing systems (one-, two-, three-, and four-step systems) using a contact-type surface profilometer.
| Materials and Methods|| |
Three nanocomposite resins used in this study were Filtek Z-350 XT (3M-ESPE, St. Paul, MN, USA) (Group I), Ceram-X Mono (Dentsply DeTrey, Konstanz, Germany) (Group II), and Tetric N-Ceram (Ivoclar-Vivadent, Schaan, Liechtenstein, UK) (Group III). Control specimens received no polishing (subgroup A). The polishing systems evaluated were SpinBrite (Danville, San Ramon, CA, USA) (one-step system; subgroup B), CompoMaster (Shofu dental corporation, San Marcos, CA, USA) (two-step system; subgroup C), AstroPol (Ivoclar-Vivadent) (three-step system; subgroup D), and SofLex (3M-ESPE) (four-step system; subgroup E).
A total of 180 specimens (60 specimens of each composite) were prepared in stainless steel molds (10 mm × 2 mm). The mold was placed on mylar strip supported by glass slide of 1 mm thickness. The restorative material was placed in one increment and was covered with another mylar strip and a glass slide. The specimens were polymerized with quartz halogen activation light (Spectrum-800, Dentsply DeTrey GmbH, Konstanz, Germany) calibrated at 600 mW/cm 2 , and its intensity checked with an in-built radiometer before curing each specimen for 40 sec each, from both sides. All specimens retrieved were then stored in a container at 37°C and 100% relative humidity for 24 h in an incubator.
After storage, the specimens of each restorative material were subjected to a baseline surface roughening using 600-grit silicon carbide sand paper under water cooling (baseline roughening). The specimens were then subjected to polishing procedures (SpinBrite, CompoMaster, AstroPol, and SofLex), whereas the control group specimens received no further treatment (n = 12 for each subgroup).
Surface roughness was measured quantitatively with a Perthometer S6P (Perthen, Mahr, Germany), which is a contact mode stylus pick-up system, with a 0.5 μm diamond stylus.
The measuring parameters set were as follows:
Surface roughness was described by two parameters: Ra (point measure) being the arithmetic mean of absolute ordinate values (average roughness as per ISO 4287) and Rz (ten-point average roughness; profile measure) averages the height of five highest peaks and depths of the five lowest values over the measuring length.
- transverse length (L T ) = 1.75 mm
- sampling length (L M ) = 1.25 mm
- vertical band width (VB) = ±62.5 μm
- Gauss profile filter (λc) = 0.25 mm
- evaluated area = 1.25 mm
The readings were taken and the data obtained were tabulated and subjected to statistical analysis using SPSS version 15.0. One-way analysis of variance (ANOVA) and post-hoc Tukey's honestly significant difference (HSD) were applied to compare whether a significant difference existed amongst various groups. Multivariate (two-way) ANOVA was applied to check whether surface roughness (Ra and Rz) is a dependent variable of the type of composite material and the type of polishing systems. P < 0.05 was considered as statistically significant.
| Results|| |
[Table 1] shows the mean Ra and Rz (μm) values after application of five polishing systems on groups I, II, and III, respectively.
|Table 1: Mean point measure (Ra) and mean point measure values (Rz) of surface roughness for different composites polished using different polishing systems|
Click here to view
Overall comparisons (of both Ra and Rz) for similar polishing systems amongst material groups did not show a statistically significant difference.
For Filtek Z-350 XT and Tetric N-Ceram groups, SofLex (four-step system) polishers produced smoothest surfaces, whereas for Ceram-X specimens, AstroPol (three-step system) produced the lowest surface roughness both in terms of Ra and Rz. However, for Tetric N-Ceram group, AstroPol (three-step system) resulted in even more roughness than CompoMaster (two-step system) polishers, the difference being statistically insignificant.
ANOVA showed significant inter-subgroup differences, hence between-subgroup comparisons in each material group were performed using Tukey's HSD test.
In Filtek Z-350 XT, all the differences, except between CompoMaster and Astropol, CompoMaster and SofLex, and AstroPol and SofLex, were statistically significant. In Ceram-X, control specimens had significantly higher mean values as compared to all other subgroups, except SpinBrite specimens. In Tetric N-Ceram, control specimens were significantly rougher than the specimens polished with all the other systems.
It was also observed that though subgroup was independently associated with the outcome (Ra and Rz) (P < 0.001), the type of composite material (group) did not show an independent association with the outcome. The interaction between groups and subgroups also did not show a significant association with the outcome. It was observed that both point measure (Ra) and profile measure (Rz) of surface roughness is a function of type of finishing only.
| Discussion|| |
With the advances in the filler technology over the years, various newer polishing systems have been evolved, tested, and tried. It has been shown that one-step systems were superior to or at least comparable to multi-step polishing techniques, ,,,, but in some cases, the results were product related. ,
To describe the surface texture (quantitatively), parameters Ra (arithmetical mean roughness) and Rz (ten-point mean roughness) were selected. The Rz parameter was included (as complementary to Ra) due to the fact that it is more sensitive to distribution of peaks and valleys and their atypical or unusual form, hence minimizing the chances of misinterpretation of the Ra parameter. ,,,
The Ra and Rz values of surface roughness in different subgroups (polishing systems) of the three study groups (nanocomposites) showed that there was no significant inter-group difference. This might be due to the fact that all restorative materials evaluated were nanocomposites, and hence, they behaved in a similar fashion to the different surface treatments. The Ra values obtained were in accordance with study of Guler et al.  who found no statistically significant differences in the surface roughness of nanofilled and nanohybrid composite resins. Erdemir et al.  also reported similar findings while evaluating one-step (PoGo) and multi-step (SofLex) polishing systems on nanofilled (Filtek Supreme XT) and nanohybrid (Ceram-X, Grandio) composites.
In the present study, Rz values obtained were proportional to Ra values. Similar findings amongst both the parameters were also reported by Ozgunaltay et al., Lu et al.,  and Marigo et al. 
For Filtek Z-350 XT (Group I), intragroup comparison of Ra values for surface roughness revealed a gradual decrease in surface roughness with increase in number of polishing steps, though the difference was statistically significant till two-step polishing only.
Jung et al. showed that greater number of polishing steps produced better smoothening effects. They reported that three-step systems were more efficient than two-step and/or one-step polishing systems on the nanocomposites and hybrid resin composites tested. Similar findings were reported by Gulati and Hegde  who found that for nanofilled composite Filtek Z-350, SofLex showed smoother surface than PoGo, which could be attributed to the fact that PoGo points are less flexible than SofLex disks and, therefore, cause more displacement of filler particles. Watanabe et al.  have also demonstrated that the surface finish produced by four-step polishing systems was superior to that obtained with one-step polishing systems. Gupta et al. and Verma et al.  have also shown that SofLex disks produced the best surface finish on the composites tested in their study.
Contradictory findings to the present study were reported by Erdemir et al.  and Uppal et al.  This might be due to the reason that they considered mylar created surfaces as controls, whereas baseline roughening of all the specimens was done in the present study (including controls).
For Ceram-X (Group II), between-subgroup comparison of Ra values for surface roughness revealed that control specimens (with the exception of SpinBrite) had significantly higher values as compared to the other subgroups. This could be due to the fact that Ceram-X contains organically modified ceramic particles that might have been left protruding after polishing with SpinBrite (one-step system) and, hence, is rougher than the controls. Contradictory findings were reported by Erdemir et al.  who reported that one-step (PoGo) and multi-step (SofLex) polishing systems created comparable, clinically acceptable, and similar quality surfaces on Ceram-X. This may be due to the difference in flexibility and composition of PoGo and SpinBrite polishers.
For Tetric N-Ceram (Group III), between-subgroup comparisons of Ra values revealed that control specimens had significantly higher mean values as compared to all other subgroups. Statistically significant differences were not found amongst the other polishing systems tested on Tetric N-Ceram specimens.
When the orders of surface roughness of the point (Ra) and profile (Rz) measurements in different subgroups in the same material group were compared, our study showed that for Filtek Z-350XT and Ceram-X, the two-, three-, and four-step polishers produced a similar degree of surface smoothness, with the exception that one-step polishers caused even more roughness than the controls on Ceram-X. For Tetric N-Ceram (Group III), the order of roughness for point measurement (Ra) values showed that no significant decrease in roughness was achieved with increase in number of polishing steps, after application of one-step polishers.
On determining whether the type of composite material (groups) and type of finishing (polishing systems) had any effect on surface roughness, it was found that surface roughness is a function of type of finishing only. These results are in contrast to the study by Jung et al. who found that the effect of polishing systems on surface finish is material dependent and the effectiveness of one-step polishing system was mostly product dependent. This might be attributed to the differences in the materials tested in their study, that is, nanofilled composites and hybrid composite, whilst the present study evaluated only nanofilled composites.
Further studies are needed to determine which finishing technique is best suited to clinical situations where access is limited and the restoration surfaces are not flat.
| Conclusions|| |
Within the limitations of this study, the following can be concluded:
- There was no difference in surface roughness amongst the polished composite resins.
- For nanofilled composite resin Filtek Z-350 XT, the surface roughness decreased with the increase in number of polishing steps, though the difference was statistically significant till two-step polishing only.
- One-step and multi-step polishing procedures produced similar quality in terms of surface roughness for nanohybrid (Ceram-X, Tetric N-Ceram) composite resins.
- Point measure (Ra) and profile measure (Rz) of surface roughness is a function of type of finishing/polishing only.
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Department of Conservative Dentistry and Endodontics, I.T.S Centre for Dental Studies and Research, Delhi-Merrut Road, Ghaziabad, UP - 201 206
Source of Support: None, Conflict of Interest: None