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Year : 2013 | Volume
: 24
| Issue : 3 | Page : 363-368 |
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Influence of finishing/polishing on color stability and surface roughness of composites submitted to accelerated artificial aging |
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Gustavo Da Col dos Santos Pinto1, Kleber Campioni Dias1, Diogo Rodrigues Cruvinel1, Lucas da Fonseca Roberti Garcia1, Simonides Consani2, Fernanda de Carvalho Panzeri Pires-De-Souza1
1 Department of Dental Materials and Prosthodontics, Ribeirão Preto Dental School, São Paulo University, Ribeirão Preto, SP, Brazil 2 Department of Restorative Dentistry, Dental Materials Area, Piracicaba Dental School, Campinas State University, Piracicaba, SP, Brazil
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Date of Submission | 05-Jan-2010 |
Date of Decision | 08-Jul-2010 |
Date of Acceptance | 13-Nov-2010 |
Date of Web Publication | 12-Sep-2013 |
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Abstract | | |
Aim: To assess the influence of finishing/polishing procedure on color stability (ΔE ) and surface roughness (Ra ) of composites (Heliomolar and Tetric - color A2) submitted to accelerated artificial aging (AAA). Materials and Methods : Sixty test specimens were made of each composite (12 mm × 2 mm) and separated into six groups (n = 10), according to the type of finishing/polishing to which they were submitted: C, control; F, tip 3195 F; FF, tip 3195 FF; FP, tip 3195 F + diamond paste; FFP, tip 3195 FF + diamond paste; SF, Sof-Lex discs. After polishing, controlled by an electromechanical system, initial color (spectrophotometer PCB 6807 BYK GARDNER) and Ra (roughness meter Surfcorder SE 1700, cut-off 0.25 mm) readings were taken. Next, the test specimens were submitted to the AAA procedure (C-UV Comexim) for 384 hours, and at the end of this period, new color readings and R a were taken. Results: Statistical analysis [2-way analysis of variance (ANOVA), Bonferroni, P < 0.05] showed that all composites demonstrated ΔE alteration above the clinically acceptable limits, with the exception of Heliomolar composite in FP. The greatest ΔE alteration occurred for Tetric composite in SF (13.38 ± 2.10) statistically different from F and FF (P < 0.05). For Ra , Group F showed rougher samples than FF with statistically significant difference (P < 0.05). Conclusion: In spite of the surface differences, the different finishing/polishing procedures were not capable of providing color stability within the clinically acceptable limits. Keywords: Artificial accelerated, aging color stability, polishing, surface roughness
How to cite this article: Pinto Gd, Dias KC, Cruvinel DR, Garcia LR, Consani S, Pires-De-Souza FP. Influence of finishing/polishing on color stability and surface roughness of composites submitted to accelerated artificial aging. Indian J Dent Res 2013;24:363-8 |
How to cite this URL: Pinto Gd, Dias KC, Cruvinel DR, Garcia LR, Consani S, Pires-De-Souza FP. Influence of finishing/polishing on color stability and surface roughness of composites submitted to accelerated artificial aging. Indian J Dent Res [serial online] 2013 [cited 2023 Mar 30];24:363-8. Available from: https://www.ijdr.in/text.asp?2013/24/3/363/118010 |
Composite development, in particular, their physical-chemical properties, allied to the characteristic of re-establishing the natural appearance of teeth, concerning color and translucence, makes this material one of the main choices among esthetic restorative materials in Dentistry. [1],[2] However, 30-40% of composite restorations in anterior teeth are substituted in a period of 5 years, [3] and esthetic failure is the most common reason for changing restorations. [4],[5]
There is consensus among researchers that direct composite restorations present color alteration over the course of time [6],[7],[8],[9],[10],[11] and these alterations commonly occur due to surface staining, changes in the material opacity due to bond failure at the matrix/load interface or discoloration of the resin matrix by thermal or photochemical stimuli. [12]
The different types of composite discoloration are usually described in the literature as:
- external discolorations due to plaque accumulation and stains;
- surface or sub-surface alterations involving surface degradation and reaction of coloring agents with the resin composite layer (adsorption); and
- intrinsic discolorations due to physical-chemical reactions in the deep portions of the restoration. [13]
The structure of the composite and the characteristics of the load particles have different effects in surface polishing, and consequently, susceptibility to extrinsic staining of the restoration. [14] The characteristics of the load particles have a direct impact on the surface smoothness of the composite [15] and in the susceptibility to extrinsic staining. [16]
The affinity of the composite for stains is modulated by its degree of conversion and chemical characteristics. [17] Lower the conversion degree, higher is the affinity for some coloring substances. The chemical additives of composites, especially those that do not suffer reactions, such as initiators, accelerators, and ultraviolet filters, may also degrade the color components. [18]
In addition to the material composition, finishing and polishing may also influence the quality of the composite surface and may be related to early staining of the restoration. [19],[20] Surface roughness allows biofilm accumulation that may result in staining the restoration surface. [21]
The surface of a composite restoration may be finished/polished by a variety of techniques, [22],[23],[24] but the problem inherent to the finishing and polishing procedure of a composite restoration is the difference in hardness of the organic matrix and load particles of which it is composed; that is, the matrix and load particles do not wear in the same proportion. [25] Consequently, there are irregularities on the surface of the material, which may mean disparity, particularly in the color of the restoration after polishing. [26]
The polishing capacity of a material with regard to the system used is normally tested in vitro in flat specimens by using dental handpieces at pre-determined rotation speeds and polishing times. However, pressure applied during the procedure is not normally controlled. [27] Few studies in the literature discuss constant pressure used to assess polishing with polishing brushes, and prophylactic and polishing pastes. [28],[29]
Thus, the aim of this study was to evaluate, in vitro, the influence of the different types of finishing/polishing procedures on color stability and surface roughness of composites submitted to accelerated artificial aging (AAA). Since the type and quality of finishing/polishing may interfere directly with the final roughness of the composite restoration, this study tested the hypothesis that rougher finishing/polishing tips will allow greater surface roughness and less color stability for composites.
Materials and Methods | |  |
To obtain the specimens, two composites in shade A2 were used [Table 1], which were placed in a Teflon matrix (12 × 2 mm) in two increments. A glass slide was placed onto the last increment to press the material against the matrix to allow excess material to flow. Photoactivation was performed using LED device (FLASHlite 1401, Discus Dental, Culver City, CA, USA, light intensity ≥ 1100 mW/ cm 2 , wavelength in the range between 460 and 480 nm), for 40 seconds, as recommended by the manufacturers. Next, the specimens were stored at a temperature of 37°C in artificial saliva to simulate the oral conditions and kept in the absence of light for 24 hours.
Sixty test specimens were obtained of each studied composite and separated into six groups (n = 10) according to the type of finishing/polishing procedure to which they were submitted [Table 2].
Electromechanical system for finishing and polishing
Polishing was performed using an electromechanical system that consisted of a mobile and a fixed base. The mobile base had unidirectional movement, but with dual direction, driven by an electrical motor. The fixation base of the test specimen was kept on this mobile base of the appliance. The fixation base is composed of a device that fixes the low-speed handpiece (N270, Dabi Atlante, Ribeirγo Preto, SP, Brazil) or high-speed motor (Silent - MRS 400 FG, Dabi Atlante, Ribeirγo Preto, SP, Brazil) in a single position, used to apply the finishing/polishing systems [Figure 1].
After the test specimen was put into position and fixed to its base on the mobile base by adjusting a screw, the high-speed motor with the appropriate tips or polishing system coupled to it was lowered until the active tip of the appliance touched half the surface of the test specimen. This was considered as the zero point; that is, the initial point of wear to be performed. From this point and at high speed activation, the mobile base began its back and forth movement at a constant and uniform speed. During the run, the finishing/polishing appliances used in each group came into contact with the test specimen, producing uniform wear throughout its entire extension (25 μm). After polishing half the test specimen, it was turned 180° and the other half was polished, following the same protocol described above. Low speed was used to perform polishing in the specimens of Groups FP, FFP and SF. In the first two groups, after using burs, Robinson brushes (Bolton Dental Manufacturing Inc., Buffalo, NY, USA) were used to apply the paste.
After polishing, the samples were submitted to color readings against a black background (Standard for 45°/0° Reflectance and Color Gardner Laboratory Inc., Bethesda, MD, USA) using a spectrophotometer (PCB 6807 BYK GARDNER, Geretsried, Germany), and initial color values of the samples were obtained. The spectrophotometer used in this study had an opening with the exact diameter of the test specimen, not allowing the entry of external light during the color reading procedure. The observation standard simulated by the equipment followed the CIE L*a*b* system.
The surface roughness was measured using SE 1700 Surfcorder (Kosakalab, Tokyo, Japan) at a distance of 0.8 mm, with a 5 mm cut-off and a speed of 0.25 mm/s. Three readings were taken at different locations of the sample surface and the mean of these readings was considered to be the initial roughness value.
Next, the test specimens were submitted to AAA (Accelerated Aging System for non-metal substances C-UV, Comexim Matιrias Primas Ltda, Sγo Paulo, Brazil). The AAA procedure is achieved in a laboratory environment that indicates the behavior of a material under certain conditions and it is widely used for development and control of different properties of materials. [30] The fixed working program was 4 hours of exposure to UV-B at 50°C and 4 hours of condensation at 50°C, totaling 384 hours, corresponding to 8 months of clinical aging. [30]
After AAA, the samples were submitted to a second color and roughness reading, following the same methodology described for the initial readings. The color stability (ΔE) of the materials was calculated using the formula: ΔE* = [(ΔL*) 2 + (Δa*) 2 + (Δb*) 2 ]½, where ΔE represents the color change in all dimensions (L*a*b*) and ΔL*, Δa* and Δb* represent color changes along the individual axes. [31] Values of ΔE ≥ 3.3 were considered clinically unacceptable. [10]
To evaluate roughness alteration, the mean values of the three surface roughness readings in the same test specimen, before and after aging were compared. The values obtained for color stability and surface roughness tests were statistically analyzed by 2-way analysis of variance (ANOVA) and Bonferroni post hoc test (P < 0.05).
Results | |  |
Color stability
[Table 3] presents the mean values for coordinates L*, a* and b*, before and after AAA, for Tetric and Heliomolar composites. Color stability analysis [Table 4] indicated that all studied composites showed unacceptable color alteration, irrespective of the type of finishing/polishing procedure (ΔE ≥ 3.3), except Heliomolar composite in FP, which showed clinically acceptable results (ΔE = 2.90 ± 1.21). The comparison of ΔE mean values (2-way ANOVA, Bonferroni, P < 0.05) indicated lower color stability for Tetric composite (P < 0.05) when compared to Heliomolar [Table 4]. The greatest color alteration occurred for Tetric composite in SF (13.38 ± 2.10), statistically different from F and FF (P < 0.05). For the other groups, there was no statistically significant difference. Heliomolar composite showed the greatest color alteration in C, followed by SF, however, with no statistically significant difference among all groups (P > 0.05). | Table 4: Comparison of ΔE mean values (SD) for the different studied groups (2-way ANOVA, Bonferroni, P < 0.05)
Click here to view |
Surface roughness
The analysis of the surface roughness results for both composites, before AAA [Table 5], allowed one to verify that the use of higher grain diamond tips (F) provided rougher samples than the use of fine grain tips (FF) with statistically significant difference (P < 0.05) among the groups. Furthermore, the use of polishing paste after the diamond tip caused less roughness in Group FP for both composites, with statistically significant different difference (P < 0.05), when compared to Group F. As regards Group FFP, decrease in roughness was significant (P < 0.05) only for Heliomolar composite. | Table 5: Comparison of surface roughness (Ra) mean values (SD) before AAA (2-way ANOVA, Bonferroni, P < 0.05)
Click here to view |
The comparison of surface roughness mean values (2-way ANOVA, Bonferroni, P < 0.05) for Tetric composite before and after AAA [Figure 2] indicated that after AAA, there was an increase in surface roughness for all groups, however, with statistically significant difference only for FP (P < 0.05). | Figure 2: Graphic representation of the comparison of surface roughness means (2-way ANOVA, Bonferroni, P < 0.05) for Tetric composite before and after AAA. Lines on the horizontal bars indicate results with statistically significant difference (P < 0.05)
Click here to view |
For Heliomolar composite [Figure 3], there was an increase in surface roughness after AAA; however, only the samples from Groups F and FP showed statistically significant difference (P < 0.05). | Figure 3: Graphic representation of the comparison of surface roughness means (2-way ANOVA, Bonferroni, P < 0.05) for Heliomolar composite before and after AAA. Lines on the horizontal bars indicate results with statistically significant difference (P < 0.05)
Click here to view |
Discussion | |  |
The value assigned to the esthetic and the need for imperceptible restorations has raised the importance of composites' color stability. The manufacturers of esthetic restorative materials seek to provide dental composites with greater chemical stability, resulting in maintaining the physical, mechanical and optical properties. This latter characteristic will enable better esthetic results to be obtained with dental composites, such as color stability, adequate translucence, opalescence and fluorescence. [5]
Differences in the chemical structure of composites, such as the type of oligomers or monomers used; concentration/type of activators, initiators, inhibitors; oxidation of double-bonded carbons; size/type of particles and the particle/resinous matrix bonding system, may interfere in color stability. [32] According to several authors, [33],[34] dental composites with lower concentration of load particles present higher values of ∆E. However, the results showed in this study contradict this information, since there was greater color alteration for Tetric composite, which has a higher percentage of load particles by volume and larger particles. These results are in agreement with those of Vichi et al.[31]
In the present study, the clinical limit of acceptance of color alteration adopted for esthetic restorative materials was ΔE ≥ 3.3, a value adopted by other authors. [10],[14],[35] Thus, all the ΔE values of Heliomolar and Tetric composites, for all finishing/polishing situations, with exception for Heliomolar in FP (ΔE = 2.90 ± 1.21), were higher than 3.3, indicating clinically unacceptable color alteration, and according to the limit determined, replacement of the restoration would be indicated for esthetic reasons.
Dental literature states that composites allow solvents to penetrate into the resinous matrix or at the matrix/particle interface. [36] According to Ferracane, [20] greater the volume of load particles in the composite composition, lower is the conversion degree presented. Consequently, the polymeric network formed would have a larger quantity of remaining double bonds and lower quantity of formed bonds. Therefore, this composite will be more predisposed to solvents action (water), which will penetrate into the resinous matrix, causing "swelling" or relaxation of these bonds, in an effect known as plasticization. The solvent inside the resinous matrix can cause it and the particle/matrix interface to deteriorate. This phenomenon can explain the color alteration in the composite and higher surface roughness after AAA. [20]
As regards the resinous matrix composition, all the dental composites used in the present study presented Bis-GMA and UDMA in their composition. Tetric also presented TEGDMA in its composition. This monomer is more predisposed to water sorption than UDMA, [37] increasing the solubility of the polymer formed. [38] Greater solubility of composites in water provides lower color stability due to the increase in free volume of the polymer formed, and consequently, larger space for water molecules to diffuse into the polymeric network. [38] Thus, the greatest color alteration for Tetric composite may be related to all these situations.
The load particle size is correlated with color alteration, in which composites with larger particles are more susceptible to water sorption and color alteration. According to Kawaguchi et al., [39] hybrid composite resins present a lower coefficient of light transmission due to the various sizes of their particles. In the present study, Tetric composite contained load particles of mean size of 0.7 μm, which could explain the greater color alteration. With particles ranging from 0.04 to 0.2 μm, Heliomolar composite showed lower color alteration.
The difference between organic matrix hardness and load particles that form a composite makes the polishing process difficult because the matrix and load particles do not wear in the same proportion. [25] This is in agreement with the results of this study, since Tetric composite, which contains larger load particles and a larger volume of particles, presented greater color alteration than Heliomolar composite in all the finishing/polishing situations.
It is important to verify that both composites showed higher ΔE values for control group, the values being higher than those of the other groups, with exception of Group SF for Tetric composite. This proves the need to perform polishing to maintain the color of the restorative material.
As regards surface roughness, it was verified that the higher grain tips provided rougher surfaces in both the tested composites, and the use of pastes improved the quality of polishing, which allows one to accept partially the hypothesis of the study.
It is worth emphasizing, however, that there is a critical value regarding surface roughness (Ra ≥ 0.2 μm). According to Bollen et al., [40] surface roughness values above 0.2 μm allow a greater biofilm retention, which allows an increase in recurrent caries. Another critical value for Ra is 0.3 μm, which can be detected when the patient's lips or tongue enter in contact with the material, causing discomfort. [40] All of the studied composites showed values for surface roughness above the critical limits, irrespective of the finishing/polishing system used, before and after AAA. These values are unacceptable for composites that were submitted to a finishing/polishing procedure.
However, color stability seems to be more related to the material composition than the surface roughness of the material. Therefore, the results contradict the findings of Zanin et al., [41] who verified that indirect composites submitted to 384 hours of AAA showed color alteration as well as increase in surface roughness, and they concluded that these properties are closely related.
It can be concluded that despite the fact that the composites presented differences in their surfaces, according to the type of finishing/polishing procedure used, none of them was capable of providing color stability within the clinically acceptable limits after AAA.
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Correspondence Address: Lucas da Fonseca Roberti Garcia Department of Dental Materials and Prosthodontics, Ribeirão Preto Dental School, São Paulo University, Ribeirão Preto, SP Brazil
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/0970-9290.118010

[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5] |
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