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Acta Odontológica Latinoamericana

versão On-line ISSN 1852-4834

Acta odontol. latinoam. vol.28 no.1 Buenos Aires abr. 2015



Influence of polishing protocol on flexural properties of several dental composite resins


Robert Ramirez-Molina1, Andrea E. Kaplan2

1 Department of Operative Dentistry, University of Los Andes, School of Dentistry, Mérida, Venezuela.
2 Department of Dental Materials, University of Buenos Aires, School of Dentistry, Buenos Aires, Argentina.

CORRESPONDENCE Dra. Andrea E. Kaplan. Catedra de Materiales Dentales Facultad de Odontologia, Universidad de Buenos Aires Marcelo T. Alvear 2142 3B (C1122AAH) Ciudad Autonoma de Buenos Aires Argentina. e-mail:


The aim of this study was to determine the influence of the finishing protocol (FP) on flexural properties of several composites (CR). Twenty composite samples (25x2x2 mm) were prepared: G1 HelimolarR; G2 Filtek™ Z350;G3TetricR N Ceram, G4 Point 4™, G5 Premisa™; G6 Esthet.XR HD, G7 ice, G8 Vit-L-escenceR, G9 GrandioR, G10 TPHR3, G11 AmelogenR Plus, G12 Brilliant Enamel; G13 Filtek™ Z100 and randomly divided into four groups according to the finishing system: C control, J JiffyR, SS Super SnapR, AA AstropolR /AstrobrushR. Each sample was polished for 10 seconds with each sequence instrument, and stored in distilled water for 24 hours, after which a three-point flexure test was applied to determine flexural strength (FS) and modulus (Flexural modulus). Data were analyzed using a two-way multivariate ANOVA and means were compared with Tukey's test. Results were: FS level CR p=0.000 with significant differences. FS level FPp= 0.093 with significant differences. In order: FM level CR p 0.00 with significant differences. FM level PS p=0.001; with significant differences. Under the study conditions, the polishing systems based on silicone rubber decreased the flexural properties of composite resins.

Key words: Composite resins; Elastic modulus; Dental polishing.


Influencia del protocolo de pulido sobre las propiedades flexurales de varias resinas reforzadas

El objetivo de este trabajo fue determinar la influencia del protocolo de pulido sobre las propiedades flexurales de varios composites. Se prepararon veinte probetas de composite (CR) (25x2x2 mm) en cada grupo: G1 HelimolarR; G2 Filtek™ Z350;G3TetricR N Ceram, G4 Point 4™, G5 Premisa™; G6 Esthet.XR HD, G7 ice, G8 Vit-L-escenceR, G9 GrandioR, G10 TPHR3, G11 AmelogenR Plus, G12 Brilliant Enamel; G13 Filtek™ Z100 y se dividieron aleatoriamente en cuatro grupos segun el sistema de pulido (SP) utilizado: C control, J JiffyR, SS Super SnapR, AA AstropolR /AstrobrushR. Cada probeta se pulio durante 10 segundos con cada secuencia de instrumentos, se almaceno en agua destilada durante 24 hs y se aplico un ensayo de resistencia flexural de tres puntos a fin de determinar la resistencia (RF) y el modulo (MF) flexural. Los valores obtenidos fueron analizados con un ANOVA multivariado de dos vias y comparacion de medias de Tukey. Los resultados obtenidos fueron: nivel de RF para CR p=0,000con diferencias significativas. RF nivel SP p= 0,093 con diferencias signi - ficativas. Para MF a nivel de CR p=0,000con diferencias signifi cativas. MF a nivel SP p=0,000, con diferencias signifi - cativas. En las condiciones de este trabajo se puede concluir que el uso de sistemas a base de gomas siliconadas disminuyen las propiedades flexurales de las resinas reforzadas restaura - doras. : composite resins; elastic modulus; dental polishing.

Palabras clave: Resinas reforzadas; Modulo elastico; Pulido dental.



Composite resin is universally accepted as an anterior direct restorative material, even for large restorations. In posterior restorations its application is becoming more popular, probably because of its high esthetic potential, acceptable longevity, tissue preservation potential, tooth structure bonding, low temperature conductivity and increased demand from patients 1. Initially these materials had many disadvantages, such as high polymerization shrinkage; occasional patient-referred post-operative sensitivity and accelerated wear in restorations, mainly located in the molar area, leading to loss of occlusal and proximal anatomy. A meticulous restoration technique, the right case selection, improvement in material formulations and better knowledge of their performance have enabled safe use of these materials. When considering desirable properties for clinical performance, mechanical properties are described as very important, especially because they are closely related to the long-term success of these restorations. Improvement in mechanical properties in recent formulations has led to increased toughness and resistance to abrasion and attrition wear2. Mechanical properties depend mainly on composite microstructure and composition; therefore filler amount, size, morphology and distribution3 are critical for composite selection. In addition, variations in matrix chemistry should be taken into account, since it has been reported that they could significantly affect flexural strength and modulus. Flexural modulus means material stiffness, which is important because it influences composite selection in high stress situations, such us mediumlarge sized restorations in proximal or occlusal locations, or for incisal angle replacement or when used to replace cusps 4.
In a three-year clinical study2, 102 class 4 restorations made with 4 different composite formulations were evaluated and a correlation between mechanical properties and clinical performance was found, which is an association between wear, modulus and defect size. Clinical procedures that may damage or prematurely harm restorations should be accurately performed because the primary cause of failure during the first five years is related to technique and material selection 5. Optimal finishing and polishing of composites is one of the most important steps when performing a restoration, since it not only results in optimal esthetics, but also favors gingival health, restoration of marginal integrity over time and patient comfort 6,7, as well as increasing resistance to pigmentation and wear 8,9 and possibly influencing restoration longevity. Surface roughness creates a favorable microenvironment for bacterial adhesion and growth, which enables the development of secondary caries, gingival inflammation and restoration staining. Polishing aims to reduce surface roughness and lines progressively until they are smaller than visible light wavelength. A traumatic technique might overheat and damage a composite surface, 10-12 resulting in accelerated wear. This research group has published previous data evaluating how filler morphology, matrix composition and finishing protocol correlate with flexural properties and mass loss in several composites13 . We concluded then that all variables evaluated correlate with a stronger weight on modulus.
There is no clear evidence of how different clinical polishing protocols might affect the flexural properties of composite resins reinforced with different fillers; thus, the aim of this study was to evaluate the effect of three polishing protocols on flexural properties of thirteen restorative composites.


Thirteen groups of twenty samples of light cured composite resins, shade A2, from eight manufacturers, were prepared: G1 Heliomolar (Ivoclar- Vivadent, Schaan, Liechtenstein), G2 Filtek Z350 (3M/ESPE. St. Paul, USA), G3 Tetric N Ceram (Ivoclar-Vivadent, Schaan, Liechtenstein), G4 Point 4 (KERRR- Sybron dental Specialties, Orange, USA), G5 Premisa (KERR- Sybron dental Specialties, Orange, USA), G6 Esthet.X HD (DENTSPLYCaulk, Milford, USA), G7 Ice (SDI Limited. Victoria, AU), G8 Vit-L-escence (Ultradent Products, INC. South Jordan, USA), G9 Grandio (VOCO America INC. Sunnyside, USA), G10 TPH3 (DENTSPLYCaulk, Milford, USA), G11 Amelogen Plus (Ultradent Products, INC. South Jordan, USA), G12 Brilliant Enamel (Coltene Whaledent, Altstatten, Switzerland), G13 Filtek Z100 (3M/ESPE. St. Paul, USA). They were randomly divided into four groups of five samples each according to the polishing protocol to be applied: C control, J Jiffy (Ultradent Products, INC. South Jordan, USA), SS Super Snap (Shofu Dental Corporation, San Marcos, USA), AA Astropol /Astrobrush (Ivoclar- Vivadent, Schaan, Liechtenstein-batch H32042). Samples were prepared according to ISO Standard 4049 for flexural strength and ANSI/ADA standard 27, using a standardized 25x2x2 mm aluminum mold and verified by means of a digital micrometer 500 (Mitutoyo Corporation, Japan) with an accuracy of 0.01 mm. Composite was placed in 2 mm increments, each of which was light cured for 40 seconds using an Astralis 3 (Ivoclar-Vivadent, Schaan, Liechtenstein) unit at 600 mW/cm 2. Samples were normalized using moist 400 grit sandpaper. One hour later each sample was submitted to the polishing protocol, applying 10 seconds per step and following the manufacturer's instructions with a handpiece at 10,000 rpm NSK (NAKANISHI, Kanuma, Japan), being very careful to maintain water refrigeration and not to press too hard. Samples were stored in distilled water at 37oC for 24 hours. Sample dimensions were determined, after which they were submitted to a three point flexural test (ISO4049/2000 - 27 ANSI/ADA specification) using a universal testing machine 1011 (INSTRONR, Norwood, USA) with a crosshead speed of 1 mm/min until fracture. Data were recorded and processed applying the equations in Table 1 in order to determine flexural strength and modulus for each sample. Statistical analysis was performed using two-way ANOVA, and DHS Tukey test was applied for multiple comparisons. (Statistical Package for the Social Sciences 15.0R).

Table 1: Flexural strength and modulus. Flexural strength Flexural modulus

Two series of samples of each composite resin were prepared and metalized with gold and argon laser for SEM observation at the Advanced Microscopy Center, University of Buenos Aires, Argentina, with a Supra 40 Scanning Electron Microscope, Carl Zeiss, Germany, with a field emission gun. Micrographs were taken and composites were classified into five groups: spherical, sphericalconglomerates, irregular, irregular + pre polymers and pre-polymers. (Table 2).

Table 2: Classification of the composite according to filler morphology.


Flexural strength: descriptive statistics (mean and standard deviation) are shown in Table 3. ANOVA for flexural strength (FS) showed statistical differences among groups p<0.001 (Table 4). HSD Tukey (Table 3) proved composites reinforced with spherical (G13 Filtek™ Z100) and irregular particles (G9, G7, G10, G6, G12, G8 and G11) to have higher flexural strength than composites with mixes of pre-polymerized/ irregular (G3, G4 and G5), spherical conglomerates (G2 Filtek™ Z350) and pre-polymerized particles (G1 HeliomolarR). When flexural strength was analyzed related to polishing system, ANOVA showed significant differences among groups p<0.05 (Table 4). Descriptive statistics are shown in Table 5 with mean and typical deviation expressed in MPa. HSD Tukey test showed that there was no significant difference among J, SS and AA and only AA differed significantly from C. Composite-polishing system interaction on flexural strength showed p=0.416, indicating that flexural properties are independent from it. Modulus: ANOVA performed for flexural modulus showed significant differences among materials p<0.001. Descriptive statistics (mean and standard deviation in GPa) (Table 5) were G13:15.03(1.09)= G9:14.50(1.50)> G11:9.79(0.52)= G10:9.76(1.27)= G2:9.72(2.20)≥ G12:8.89(0.4)= G7:8.56(0.73)≥ G4:7.98(1.01)= G6:7.88(0.46)= G8:7.57(0.50)= G3:7.19(0.66)≥ G5:6.53(0.71)> G1:4.65(0.38). When modulus was analyzed with relation to polishing system, ANOVA showed significant differences among groups, p<0.001 (Table 6). Descriptive statistics are shown in Table 7 with mean and standard deviation expressed in GPa. Groups were as follows: C= SS≥ AA: > J. HSD Tukey test proved that all experimental groups showed lower modulus values than the control, although SS had no significant difference. JiffyR had the lowest values and differed significantly. Composite-polishing system interaction on flexural modulus showed p<0.001 (Table 4), indicating that flexural modulus is dependent on it.

Table 3: Descriptive statistics and multiple comparisons for flexural strength at composite level.

Table 4: Tests of Between-Subjects Effects (ANOVA).

Table 5: Descriptive statistics and multiple comparisons for flexural modulus at composite level.

Table 6: Descriptive statistics and multiple comparisons for flexural strength at polishing level.

Table 7: Descriptive statistics and multiple comparisons for flexural modulus at polishing level.

Figures 1-5 show SEM photographs taken of each type of composite and their classification in terms of filler morphology.

Fig. 1
: SEM image at 10,000x of Filtek Z100 composite resin reinforced with spherical fillers.

Fig. 2
: SEM image at 10,000x of Filtek Z350 composite resin reinforced withspherical conglomerate fillers.

Fig. 3
: SEM image at 10,000x of composite resin reinforced with irregular fillers. From right to left upper and lower images of Esthet.XR HD, Ice, Vit-L-escence, Grandio, TPH3 and Amelogen Plus.

Fig. 4
: SEM image at 10,000x of composite resin reinforced with irregular fillers + pre-polymer fillings. From right to left upper and lower images of Point 4, Premisa, Tetric N Ceram and Brillant Enamel.

Fig. 5
: SEM image at 10,000x of Heliomolar composite resin reinforced with pre-polymers.


Two out of the three polishing protocols evaluated in this investigation are based on silicone impregnated with varied grain size abrasives, mostly silicon carbide (Jiffy and Astropol). The third (Super Snap) is based on flexible paper discs impregnated with silicon carbide and aluminum oxide. In order to calculate flexural performance, we carried out a three point stress test which applies one force in one sense that generates three types of loads (shear, tensile and compressive)14. Some authors consider that these results cannot be transferred to clinical situations, primarily because failure distribution is different. However, the model we applied in order to determine mechanical properties here is accepted worldwide because it is easy to reproduce, serves in terms of comparative purposes and represents material behavior in biomechanical efforts and determines critical performance during function 15,16. In terms of FS, all evaluated composites comply with ISO Standard 4049. However, there were some differences among commercial brands. In our study, composites with spherical filling proved to be similar to composites with irregular particles. Small variations might be given by filler quantity and mean size because the manufacturing processes are essentially the same. Therefore, it can be speculated that recent formulations with optimized matrix containing nanometric spherical filler do not seem to improve FS. It could be considered that variations (although not significant) in FS occur because irregular particles concentrate stress at dead angles in the polymerized matrix. On the other hand, differences in monomer proportions might significantly change mechanical properties 4, where a slight TEGDMA increase might cause a strength reduction and a UEDMA increase would turn into an increase. Furthermore, BisGMA variations do not seem to affect the final result. It can thus be speculated that TEGMA content may be responsible for preventing Grandio high filling content and spherical particles in FilteK Z-100 from being significantly superior in mechanical properties to the other irregular particles composites. Finally, the lower part of the table shows the results for prepolymerized + irregular reinforced composites (Tetric N Ceram, Point 4, Premisa), spherical conglomerate (Filtek Z-350) and pre-polymerized (Heliomolar). It could be explained by several factors such as their lower sized fillers, which increase the surface to be covered by the matrix, leading to less filler content. Also more silane could be present and diminish the polymerization degree, modifying their mechanical properties18. All composites, with the exception of Tetric N Ceram, have TEGMA in their composition and smaller particles are less effective in preventing crack propagation because they are easier to go around. Regarding composites with pre-polymerized particles, it could be speculated that the high conversion degree might affect bond strength with unpolymerized matrix, leading to lower mechanical properties. In Filtek Z-350, it can be inferred that although the filler keeps its spherical shape, sintered nanometric particles are not bonded enough to alter the course of the fracture, causing a conglomerate separation. Our group has previously reported a part of this research focused on filling morphology, matrix and polishing protocol correlation with flexural properties and surface loss 13. We found that flexural strength, flexural modulus and surface loss were significantly correlated to the composition and morphology of these composite resins. The highest influence was found for modulus at 85.7%, while it was lower for resistance and surface loss, at 41% and 36.3% respectively. Although that paper also analyzed the influence of the matrix composition, we reported, for example, that spherical conglomerates negatively influence mechanical properties. On the other hand, independent spherical particles might turn into a more regular structure that could help distribute tension, thus increasing properties. This might suggest that properties are influenced not only by filler morphology, but also by filler distribution. Finishing refers to the restoration´s adaptation to the tooth and aims to obtain good contour, occlusion, healthy relationship with adjacent teeth and a smooth surface 9, while polishing refers to the elimination of irregularities in order to create a surface which is as smooth as possible, to minimize gingival irritation, biofilm accumulation, pigmentation, and recurrent formation of caries18-21. We carried out the whole process using water cooling in order to avoid some factors that may affect resins when the procedure is performed without water cooling22. It was also finished a few minutes after initial curing, since lack of polymerization and surface roughness in newly cured composite resins 23 have been rejected in recent formulations 24,25.
There are more variables that might influence restoration properties, such as operator, time, humidity and matrixes were controlled, pressure applied to polish the samples. That pressure might increase tension in the sample, and even transmit pneumatic handpiece vibrations, which might induce some kind of initial defect in the material. All these variables were controlled by limiting all procedures to a single operator.
The efficacy of abrasive systems is related to the flexibility of the supporting material. Abrasive hardness in this case is very close in the different systems (2500 Knoop H Kg/mm2 silicon carbide and 2100 Knoop H Kg/mm2 aluminum oxide), instrument geometry and application . Differences between flexible discs and silicone rubber reside in the fact that discs wear filler particle and matrix in a similar way 7, whereas rubbers wear matrix by plastic deformation, leading to temperature increase and either leaving particles on the surface or removing them, both of which leave irregularities that translate into a less bright surface. They also create defects where the cracks initiate, leading the material to its strength limit. Moreover, physical stress caused by temperature increase might result in the formation of micro-cracks, micro-pores or interface spaces between matrix and filler, which might affect physical properties 9. Our results differ from those reported by Gordan et al. 2003 10, who found an increase in FS when polishing maneuvers were carried out.


Under the conditions of this study, flexural properties of composite resins were affected by the polishing systems tested. FS is higher in composites reinforced with spherical and irregular particles. Flexural strength is diminished when the Astropol/ Astrobrush system is used. Regarding stiffness, Filtek Z100 and Grandio proved to be superior to the other resins tested. However, both resins showed lower stiffness when systems based on silicone rubber such as Astropol/Astrobrush and Jiffy were used.


The authors thank Prof. Marc Heft for his assistance in manuscript preparation. This study was supported by UBA Grant 2002009010017 and ULA CDCHTA O-221-08-07-B.


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