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- J Appl Oral Sci
- v.20(5); Sep-Oct 2012
- PMC3881789
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J Appl Oral Sci. 2012 Sep-Oct; 20(5): 510–516.
PMCID: PMC3881789
PMID: 23138735
Gabriela Ulian de OLIVEIRA,1 Rafael Francisco Lia MONDELLI,2 Marcela CHARANTOLA RODRIGUES,1 Eduardo Batista FRANCO,3 Sérgio Kiyoshi ISHIKIRIAMA,4 and Linda WANG2
Author information Article notes Copyright and License information PMC Disclaimer
Abstract
Objectives
Nanofilled composite resins are claimed to provide superior mechanical propertiescompared with microhybrid resins. Thus, the aim of this study was to comparenanofilled with microhybrid composite resins. The null hypothesis was that thesize and the distribution of fillers do not influence the mechanical properties ofsurface roughness and wear after simulated toothbrushing test.
Material and methods
Ten rectangular specimens (15 mm x 5 mm x 4 mm) of Filtek Z250 (FZ2), Admira (A),TPH3 (T),Esthet-X (EX), Estelite Sigma (ES), Concept Advanced (C), Grandio (G) andFiltek Z350 (F) were prepared according to manufacturer's instructions. Half ofeach top surface was protected with nail polish as control surface (not brushed)while the other half was assessed with five random readings using a roughnesstester (Ra). Following, the specimens were abraded by simulated toothbrushing withsoft toothbrushes and slurry comprised of 2:1 water and dentifrice (w/w). 100,000strokes were performed and the brushed surfaces were re-analyzed. Nail polishlayers were removed from the specimens so that the roughness (Ra) and the wearcould be assessed with three random readings (µm). Data were analyzed by ANOVA andTukey's multiple-comparison test (α=0.05).
Results
Overall outcomes indicated that composite resins showed a significant increase inroughness after simulated toothbrushing, except for Grandio, which presented asmoother surface. Generally, wear of nanofilled resins was significantly lowercompared with microhybrid resins.
Conclusions
As restorative materials suffer alterations under mechanical challenges, such astoothbrushing, the use of nanofilled materials seem to be more resistant thanmicrohybrid composite resins, being less prone to be rougher and worn.
Keywords: Composite resins, Toothbrushing, Roughness, Wear
INTRODUCTION
Material properties and technical approaches are two essential factors that havedeveloped together over time in order to allow for a better clinical performance ofcomposite resin restorations2,10,14,18.
Composite resins are so far the most esthetic restorative material applied in directrestorations2,14,18. Filler andorganic matrix have been modified in an attempt to offer satisfactory mechanical andesthetic characteristics, thus allowing its indication to posterior teeth2,7,10,11,12,14,18,20-22. In this sense, nanotechnology has been applied to Dentistry,permitting the incorporation of a larger amount of small-sized filler particles in amore hom*ogeneous distribution into organic matrix5,6,15.
The decreasing filler size over the years resulted in some changes in commercialcomposites, resulting in different implications to their adequate clinical use andperspectives of success. Since the introduction of nanotechnology, these resins (0.1-100µm) are classified as Nanohybrid, NanoMicrohybrid, Microybrid, Microfilled10,19. This classification varies extensively according to manufacturersand cannot be precisely identified5,6,10,15. This scenario pointed out to the needfor investigating optical and mechanical properties of this new generation of compositeresins. As fillers play a major role to reflect the irradiated light, enhanced estheticproperties were previously verified13,15. A perspective of improved material isalso expected as high mechanical properties are attributed to filler load23. However, it should be highlighted thatthe particles are not arranged in the same pattern to all nanotechnology materials.There are composites with nanofillers, nanoclusters and/or microhybrid particles thatare combined in different structures5,6,10,15. Additionally, a larger surface area ofparticles with reduced filler size result in a material more prone to water uptake,which can affect negatively its mechanical properties by degradation8-10. It is believed that as silane-based fillers are susceptible tohydrolytic degradation, it may affect adversely their dynamic mechanical properties overtime9,22.
Surface roughness and wear tests after simulated toothbrushing have been indicated toassess the mechanical features of restorative materials3,4,8,20,25. Simulated toothbrushing can intentionally provoke astress in the organic matrix, fillers and their interfaces, and adhere to an assessmentof their resistance properties16.
As fillers are incorporated into the organic matrix by a chemical treatment of theirsurfaces, this interface can be stressed and be loosened from the matrix in differentpatterns17. Through a three-bodyabrasive action, toothbrushing provokes a mechanical challenge. In consequence, theseparticles can be loosed, fractured or the organic matrix can be removed, exposing theparticles. Thus, roughness and wear readings can establish a comparison of theperformance of these materials.
The aim of this study was to compare mechanical performance of nanotechnologyhigh-density composite resins, according to their dimensions and distribution. The nullhypothesis is that there is no difference of their performance on surface roughness andwear assessments after simulated toothbrushing testing.
MATERIAL AND METHODS
Experimental design
This in vitro study was performed involving two factors: material(in eight levels) and time (in two levels). The quantitative response variables werethe surface roughness and wear analyzed by profilometry (µm). Information aboutmaterials under investigation is presented in Figure1.
Figure 1
Information of tested composite resins
| Material | Manufacturer | Classification | Monomer/Filler | % w/v |
| Filtek Z250 | 3M ESPE, St Paul, MN, USA | Microhybrid | Monomers: Bis-GMA, UDMA, Bis-EMA Filler: Zircon andSiO2 - 0.6 mm (0.01 - 3.5 mm) | 84.5/60 |
| Admira | Voco, GmbH, Cuxhaven,Germany | Microhybrid | Monomers: Ormocer, Additivealiphatic and aromatic dimethacrylate Filler: Glass ceramic SiO2- (mean of 0.7 mm) | 78/56 |
| TPH3 | Dentsply, York, PA, USA | Nanohybrid | Monomers: Bis-GMA; BisEMA Filler: Barium aluminiumborosilicate glass, Fluoro-aluminium borosilicate glass, Silica - (0.02 - 1mm) | 75/* |
| Estelite Sigma | Tokuyama DentalCorporation, Japan | NanoMicrohybrid | Monomers: Bis-GMA/ TEGDMAFiller: Spherical silica/zirconia submicron filler - 0.2 mm (0.1 mm - 0.3mm) | 82/71 |
| Esthet-X | Dentsply, York, PA ,USA | Microhybrid | Monomers: Bis-GMA, BisEMA, TEGDMA Filler: SilanizedFluoro-aluminium borosilicate glass, silanized barium (1 mm) and colloidalsilica (0.04 mm) | 77/60 |
| Concept Advanced | Vigodent S/A Produtos eComércio, Rio de Janeiro, RJ, Brazil | Nanofilled | Monomers: Bis-GMA/UDMAFiller: Alluminium and barium silicate - 0.04mm (0.001 - 2 mm) | 77.5/* |
| Grandio | Voco, GmbH, Cuxhaven, Germany | Nano-hybrid | Monomers: Bis-GMA, TEGMA Filler: glass ceramic filler (1 mm)and SiO2 (20 - 60 nm) | 87/71.4 |
| Filtek Z350 | 3M ESPE, St Paul, MN,USA | Nanofilled | Monomers: Bis-GMA, UDMA,TEGDMA, Bis-EMA Filler: aggregated zirconia (0.6 - 1.4 mm) andSiO2 (20 nm) | 78.5/59.5 |
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All informations were supplied by the manufacturers
*Not informed by manufactures
Bis-GMA=bisphenol-A-glycidyl methacrylate; Bis-EMA=bisphenol-A-ethoxylateglycidyl methacrylate; Bis-PMA=bisphenol-A-polyethylene glycoldietherdimethacrylate; TEGDMA=triethylene glycol dimethacrylate; UDMA=urethanedimethacrylate
Ten specimens of each material were prepared using a previously lubricated steelstainless mold of 15 mm length x 4 mm in width x 5 mm in height placed over a glassslab and polyester strip (TDV Dental LTDA, Pomerode, SC, Brazil). Four individualincrements were inserted which were light-cured according to manufacturers'recommendations, using a halogen lamp VIP (VIP, Bisco Inc, Schaumburg, IL, USA), withirradiance of 600 mW/cm2, as measured with a curing radiometer (CuringRadiometer - Model 100P/N-150503, Demetron Research Corp., Danbury, CT, USA). Thefinal increment was pressed with a polyester strip (TDV Dental LTDA, Pomerode, SC ,Brazil) and glass slab under a constant axial load of 500 g for 30 s. Regardless ofthe recommended time, the last increment of all composite resins was light-cured for40 s to standardize the surface. The specimens were removed from the molds and theexcess was cut off with a #12 Bard-Parker scalpel blade.
Thereafter, the specimens were subjected to mechanical polishing in a metallographicpolishing machine (Arotec - APL 4, Arotec SA Ind. Com., Cotia, SP, Brazil) using thesequence of #600-, #800- and #1200-grit silicon-carbide abrasive papers underwater-cooling. Polishing was performed under a load of 172 g for 20 s for eachgranulation. All specimens were ultrasonically cleaned in deionized water for 10 minand were identified and stored at 37ºC for 1 week.
In order to allow wear analysis, each specimen had half of its surface protected withtwo layers of nail polish that served as control (with no abrasion).
Baseline surface roughness of the specimens was analyzed by a profilometer (HommelTester T1000, Hommelwerke GmbH, Villingen-Schwenningen, Germany) accurate to 0.01 mmand was expressed in mm as a Ra value. Five records of each specimen were randomlyassessed. To record roughness measurements of the surfaces a device containing adiamond needle affixed to the profilometer was used. The average of five randomizedtransversal readings was established as the baseline roughness value. Ra range waspreviously adjusted at 0.01 to 0.8 mm at a cut-off of 0.25 mm. Readings were obtainedfrom 4.8-mm-long measurements.
A specially designed toothbrushing machine was used for the test. It allowedcontrolled performance using soft nylon bristle toothbrush heads (Colgate Classic,Colgate-Palmolive Ind. Com. Ltda, São Paulo, SP, Brazil) under a load of 300 g andtemperature of 37ºC. Slurry was prepared according to ISO specification #14569-1,mixing 2:1 of deionized water and dentifrice (Colgate Total 12, Colgate-PalmoliveInd. Com. Ltda, São Paulo, SP, Brazil) and 0.4 mL amount was injected periodically torenew for fresh slurry. For each specimen, a total of 100,000 strokes were performedand toothbrushes were replaced after 50,000 strokes. At the end of the test, eachspecimen was rinsed under running water and cleaning was completed by sonicating indeionized water for 10 min.
Final roughness was analyzed in the same way as described for baseline. Differencesbetween initial and final readings were registered. For wear assessment, the sameprofilometer was used; allowing a needle to run from the protected half (control) tothe abraded half. Parameters were adjusted to tolerances from 0 to 40 mm, length ofassessment at 4.8 mm and cut off of 0.25 mm. The mean values among three readingswere registered for each specimen.
Random samples of each tested groups, before and after toothbrushing, were selectedfor microscopic examination to illustrate possible events. These specimens wereprepared and mounted on metal stubs, sputter coated with gold, and examined under ascanning electron microscope (JSM T220A, JEOL Ltd., Peabody, MA, USA) at 500xmagnification.
The assumptions of equality of variances and normal distribution of errors werechecked for the tested response variables. Since the assumptions were satisfied, datawere subjected to one-way ANOVA and Tukey's post-hoc test for thecomparison of initial and final roughness and wear among the materials. Paired t-testwas applied for roughness analysis considering a two-time evaluation (p<0.05).
RESULTS
Comparative roughness assessments and wear values after simulated toothbrushing arepresented in Table 1. For all composite resins,initial and final roughness was statistically different (p<0.05).
Table 1
Mean and standard deviation of initial surface roughness (Ra), final surfaceroughness (Ra) and wear after simulated toothbrushing (μm)
| Material | Initialroughess | Finalroughness | Wear |
| FZ2 | 0.08±0.01Ac | 0.19±0.04Bbc | 14.6±4.39d |
| A | 0.05±0.00Aa | 0.06±0.02Ba | 3.17±1.16a |
| T | 0.08±0.01Ac | 0.18±0.10Bab | 8.02±2.51bc |
| ES | 0.05±0.01Aa | 0.30±0.08Bbc | 11.75±3.32cd |
| EX | 0.06±0.01Ab | 0.47±0.15Bd | 12.61±4.26cd |
| C | 0.05±0.01Aab | 0.51±0.17Bd | 13.26±5.29d |
| G | 0.08±0.01Ac | 0.07±0.01Ba | 4.27±1.80ab |
| FZ3 | 0.04±0.06Aa | 0.13±0.05Bab | 5.58±1.46ab |
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Different capital letters indicate differences between columns
Different lower case letters indicate differences between rows
Comparison among the tested materials regarding their initial roughness, showed that thenanofilled resins, Filtek Z350 and Concept Advanced, as well as the microhybrid resins,Admira and Estelite Sigma, presented smoother surfaces while Filtek Z250, TPH3, andEsthet X presented rougher surfaces.
According to the final condition, roughness outcomes revealed a great variability ofperformance after simulated toothbrushing. Admira, Grandio, Filtek Z350 and TPH3 wereless rougher than the other composite resins. Concept and Esthet X were more susceptibleto abrasion, consequently, presented significantly higher roughness. Intermediate valueswere found for Filtek Z250 and Estelite Sigma. According to the presented results, thequalitative analysis of the SEM micrographs of the resins, after the abrasion test,showed more polished surface of the nanofilled and the nanohybrid resins than themicrohybrid resins, as seen in Figure 2.
Figure 2
Qualitative analyzis of different composite resins after abrasion test. A -Nanofilled (Esthet X); B – Nanohybrid (TPH3); C – Microhybrid (Z250)
Comparing each system before and after toothbrushing simulation, except for Grandio, allmaterials became significantly rougher than their initial condition (p<0.05).
The wear assessment values revealed that Admira, Grandio and Filtek Z350 were lesssusceptible to wear after toothbrushing simulation, followed by TPH3, Estelite Sigma andEsthet X. Concept and Filtek Z250 presented the least resistance to wear(p<0.05).
DISCUSSION
Enamel and dentin are directly affected by caries disease. When these tissues arecompromised, teeth lose the ability to absorb the load from mechanical impact. Dentinpresents a mechanical property from a complex arrangement of collagen type-I-fibrilsreinforced with a nanocrystalline apatite mineral in the extra and intrafibrilarspaces1. However, when cariesaffects dentin, it results in a disorganized structure. Thus, when this natural complexis changed, the restorative material needs to present properties that are able torecover it an appropriate manner. In order to reach a satisfactory clinical performance,the composite resin is indicated as a hybrid material composed mainly by fillers andorganic matrix. Thus, mechanical properties are of great interest to allow compositeresins to be well indicated10,19.
Filler particles play an important role in this mechanism. They are responsible for thestrength of the material and also protect organic matrix from wear8,17,25. Nanotechnology provides incorporationof well-distributed and larger amount of fillers compared with othercategories5,6,15. Consequently,a high mechanical resistance is expected. This is essential in posteriorrestorations2,14,18.
Organic matrix is the second point of interest to be focused. There have been severalinvestigations with the purpose to promote modifications to reach betterproperties10. This balance oforganic matrix and fillers is responsible for the determination of long-term clinicaluse2,14.
Therefore, the comparison of the performance of resin-based materials is an essentialparameter to aid clinical indication. Roughness is well accepted as a comparativefeature. Basically, it quantifies surface texture by means of randomized readings of theamplitudes in mm, established as Ra (arithmetical roughness)3,8,20,25.
According to the results of the present study, simulated toothbrushing was a mechanicalprocess able to modify the balance between organic matrix and filler since all compositeresins showed rougher surface after the abrasion challenge as shown in Table 1.
Initial roughness is essential to establish a parameter of comparison. Filtek Z350 andConcept Advanced presented the smoothest surfaces. This was somehow expected as they arecategorized as nanofilled resins. Nanofilled materials have the ability to provide morevolume of filler in hom*ogeneous distribution, which enables it to protect organic matrixwear3,23.
Admira and Estelite were significantly rougher than the nanofilled composite resins. Thepossible explanation relies on the fact that Admira, even classified as a microhybridcomposite, is composed differently than other tested resins as its monomers are based onOrmocer, which is considered a resistant organic matrix10. Long-term clinical studies have shown the superiorityof this matrix regardless of the size of filler2,14. In occlusalstress-bearing cavities, the Ormocer-based composite materials tested performedcomparably to conventional microhybrid Bis-GMA-based composites. This study reveals thatthis organic matrix itself is more resistant than conventional monomers. On the otherhand, the manufacturer of Estelite classifies it as nanomicrohybrid material. Since thevariability between nano-sized materials also includes their distribution, it mightaffect their performance in a not well-clarified manner. It requires moreinvestigation.
Filtek Z250, TPH3 and Grandio were the materials that exhibited rougher initial values.Filtek Z250 is a microhybrid resin while the manufacturers classify TPH3 and Grandio asnanohybrid. Also, it is should be highlight that even Filtek Z250 and Esthet X are bothmicrohybrid, they differed statistically from each other. Despite this samecategorization, it might vary in different levels that are not possible to precise, astheir manufacturers do not supply this information in details. In comparison with theother tested materials, the distribution of the particles in hybrid resins is lesshom*ogeneous, which allows this condition. Additionally, the range of fillers ofnanohybrid resins is large.
When final roughness was analyzed, distinct performances were observed after simulatedtoothbrush testing. Except for Grandio, all resins became rougher after toothbrushing,but Admira, Grandio, Filtek Z350 and TPH3 were less prone to be rougher. Once again, theorganic matrix composition of Admira seemed to determine a good performance. Filtek Z350as nanofilled material attended the expectation of this technology, confirming previousresults9. Likely, toothbrushingabrasion caused a polishing effect on the surface, allowing smother surface comparedwith other resins, even rougher than its initial condition. Concept and Esthet X weremore susceptible to abrasion in terms of roughness as they presented the greatest valuesafter the test. Concept is categorized as a nanofilled composite resin and its organicmatrix is based on conventional BisGMA. Limited information is supplied by itsmanufacturer, and so, with the limitations of this study, we cannot confirm preciselythe reason of this poor performance. Esthet X, on the other hand, as a microhybridresin, was rougher as expected, compared with nanosized resins. Intermediate finalroughness values were detected in Filtek Z250, TPH3 and Estelite Sigma. As thesematerials are classified as micro or nanohybrid materials, their performances aresimilar according to a previous study, which stated that they are both resistantmaterials10.
According to wear values, Admira was the least susceptible to wear after toothbrushingsimulation. The specific performance of this Ormocer-based material seems to confirm therelevance of organic matrix as well as fillers.
Grandio and Filtek Z350 did not differ significantly from Admira. Once again, nanofilledmaterials also attest to the relevance of a combination of reduced size with hom*ogeneousdistribution of filler to reach satisfactory performance. In sequence, TPH3, EsteliteSigma and Esthet X showed moderate resistance to wear. Concept and Filtek Z250 were theresins that had the high level of wear. As also stated, the poor results and lack ofinformation about the organic matrix composition of Concept makes this resin lessreliable.
Manufacturers have produced composites with different filler sizes (ranging from 5 to100 nm) and distributions, in order to enhance performance. The mechanical propertieslike high flexural strength, low abrasion, low polymerization shrinkage and resistanceto fracture are attributed to the high-filler load of these materials because of thesmall size the fillers possess21. Anexplanation for the improvement of the wear resistance with the smaller particles isthat the mean distance between neighboring particles was smaller than that with thecoarsest filler particles24. This sizeand distribution is favorable to protect organic matrix against wear, resulting ingreater durability. From the observations of Admira, it can be stated that theOrmocer-based composite is relevant to resist wearing and roughness changes, which iscomparable to the performance of the nanofilled composite resins compared with the othertested materials.
CONCLUSIONS
With the limitations of this study, the null hypothesis is rejected. Comparison ofdifferent categories of direct composite resins revealed that all materials becamerougher after simulated toothbrushing. Different levels of wear occurred according tofiller size and distribution. In general, nanofilled systems and the Ormocer-based resinshowed better performance than the microhybrid and conventional organic matrixcomposites. This comparison can be helpful to predict the performance of these materialsunder clinical service.
ACKNOWLEDGMENTS
This study was performed by G.U.O. as fulfillment of her Master’s degree researchthat was supported by grant 136375/2006-5 from CNPq (Conselho Nacional deDesenvolvimento Científico e Tecnológico), Brazil. Authors are also thankful for 3MESPE, Voco, Dentsply, Tokuyama Dental Corporation and Vigodent S/A Produtos eComércio for donation of the tested products.
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Articles from Journal of Applied Oral Science are provided here courtesy of Bauru School of Dentistry
