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Sliding wear of 19 commercially available composites and compomers
Dental Materials (2004) 20, 277–285
http://www.intl.elsevierhealth.com/journals/dema
Sliding wear of 19 commercially available composites and compomers Catharina Zantnera,*, Andrej M. Kielbassaa, Peter Martusb, Karl-Heinz Kunzelmannc a
Department of Operative Dentistry and Periodontology, University School of Dental Medicine, ¨t Berlin, Berlin, Germany Freie Universita b ¨t Berlin, Berlin, Germany Institute for Medical Informatics, Biometry and Epidemiology, Freie Universita c Department of Operative Dentistry and Periodontology, Dental School of the Ludwig-Maximilians-University, Munich, Germany Received 28 May 2002; received in revised form 12 December 2002; accepted 12 March 2003
KEYWORDS Wear; Composites; Compomers; Particle size
Summary Objectives. The aim of this study was to determine the influence of particle size, particle material and morphology on the sliding wear of 19 light curing, commercially available composites (Durafill VS, Metafil CX, Heliomolar RO, Solitaire, Arabesk, Artglass, Charisma F, Pertac II, Charisma, Degufill Ultra, TPH Spectrum, Z100, Tetric classic, Pertac Hybrid, Estilux Hybrid, Dyract AP, Compoglass F, Compoglass and Hytac). Methods. The materials were applied to an aluminum sample holder (7.5 mm diameter, 2 mm depth) in one layer and polymerized in a Dentacolor XS light curing unit for 180 s. The surface was ground flat (#1000) to remove any matrix rich surface layer. Then samples were stored in Ringer’s solution for 24 h at 37 8C. Occlusal contact wear was simulated in a sliding wear tester (Munich Artificial Mouth). Eight specimens of each material were tested in a pin-on-block design with oscillating sliding of a Degussit antagonist (5 mm diameter) at a vertical load of 50 N. The horizontal excursion of the antagonist was 8 mm. Wear was quantified by a replica technique every 6000, 10,000, 30,000 and 50,000 cycles using a 3D-laser scanner. The materials were compared by their mean wear after 50,000 cycles. Comparisons of different composites and compomers were performed using analysis of variance and t-tests including the Bonferroni correction. Results. The microfiller composites (Durafill VS, Metafil CX, Heliomolar RO) revealed the lowest, and the compomers (Dyract AP, Compoglass F, Compoglass and Hytac) showed the highest contact wear ðp , 0:05Þ: The wear of the hybrid composite (Estilux Hybrid) and the micro hybrid composites (Solitaire, Arabesk, Artglass, Charisma F, Pertac II, Charisma, Degufill Ultra, TPH Spectrum, Z100, Tetric classic, Pertac Hybrid) was higher than that of the microfiller composites ðp , 0:05Þ: The results showed additional significant differences within the three groups of composites. The coefficient of determination between loss of height and maximum particle size was r2 ¼ 0:41: Significance. Both particle size and morphology have a high influence on the wear properties concerning the two-body wear in the occlusal contact area. Q 2003 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.
*Corresponding author. Universita ¨tsklinik fu ¨t Berlin, Poliklinik fu ¨r Zahn-, Mund- und Kieferheilkunde, der Freien Universita ¨r Zahnerhaltungskunde und Parodontologie, Aßmannshauser Straße 4-6, 14197 Berlin, Germany. Tel.: þ49-30-8445-6129; fax: þ49-308445-6204. E-mail address: [email protected] 0109-5641/$ 30.00 Q 2003 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved. doi:10.1016/S0109-5641(03)00104-0
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Introduction Alleged adverse health effects and environmental concerns regarding the release of mercury gave rise to a controversial discussion about the use of amalgam in several countries, especially in Sweden and Germany.1,2 Thus, the use of composite resins for restoring posterior stress-bearing cavities has increased enormously in the last few decades. Early attempts to place composites in posterior teeth as an alternative to amalgam revealed only limited success because of insufficient properties of the materials used. Nowadays, light cured tooth colored composites feature the advantage of good esthetics for restorations, are able to bond to tooth structures, and have a successful clinical performance. The main reasons for failure have been shown to be secondary caries.3 In addition, inadequate resistance to wear and fracture may be significant concerns, resulting in a loss of anatomic form under masticatory abrasion and attrition and fractures within the body of the restoration and/or at its margins.3 Thus further investigation of wear mechanisms of composite materials is necessary. Wear can be defined as unwanted removal of solid material from surfaces due to mechanical action.4 This indeed is a simple definition; namely, wear is a very complex process. The only way to predict wear is to understand the single mechanisms contributing to the wear that is observed.4 Moreover, wear is not a specific material property as elastic modulus, fracture toughness, or tensile bond strength are.5 Unfortunately, in vivo testing is costly and time consuming.6 For these reasons it seems necessary to investigate the different types of composite wear in vitro. Due to its complicity, wear should be evaluated by a multilevel investigation method.6 – 8 There are several current test devices for this purpose4,14,32 producing results that correlate well with published clinical data for commercial composites. Another possibility is to use a complex of different, more simple test devices to simulate the wear mechanism: These are tooth brushing machines7,8 to simulate the wear in the contact free areas (CFA),9 and the ACTA machine10,11 which has been constructed to simulate simultaneously many clinical variables being active in the occlusal wear; furthermore, pin-on-disc-12 and pin-on-block devices7 have been described. Regarding the results of one of these tests it is noteworthy, that one kind of test only simulates one aspect of the complex wear mechanisms in vivo. Both the pin-on-disc12 and the pin-on-block devices as used in this study7 simulate sliding wear in the occlusal contact area
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(OCA). Artificial mouths use the pin-on-block design with unidirectional8,13 or bi-directional sliding.4,7,14 Furthermore, in scratch tests bi-directional sliding causes more wear than unidirectional sliding.15 In contrast, impulse load, simulated in an artificial mouth does not affect the wear.5 Concerning the composition of composite materials filler content, filler material, filler size, as well as the distribution of the filler particles influence the physical and mechanical properties of the composites. The wear resistance of composite resins has been significantly improved by decreasing the average filler particle size and increasing the filler loading.16 In general, higher wear rates in the contact area are related to the larger filler particles in composite materials.17 Therefore, new composites may have smaller particle size, but they do not have higher filler volumes. These new materials show a lower abrasive wear, but also generally have lower properties compared to many of the preceding composites. On the contrary, besides the filler system the resin matrix also has an important influence on the properties of the composite materials.18,19 However, in the past 30 years the mostly used monomer systems for composites since the introduction of dimethacrylates by Bowen in 1962 has been the BisGMA. One new approach concerning different monomer systems was the introduction of the polyacid-modified resin composites (PMRC), commonly termed as compomers. The monomer of the PMRC contains acidic carboxylate groups and polymerizable methacrylate groups, which enables a free-radical polymerization by light curing and an acid-base reaction if water is present.33 Concerning the antagonist used in occlusal contact simulations many varying types of antagonists can be found in the dental literature. The most important aspect concerning the used antagonist is using a standardized material without biological variation to obtain comparable wear rates. Such materials are aluminum oxide and Steatite. However, Steatite is a very soft material and would have been quickly abraded by the composites.7 As a consequence, the contact area would increase during the tests, thus leading to a decreased pressure per area resulting in less wear.7 All in all, comparison of commercially available composites is difficult because information regarding the material composition is often not available,20 and there will usually be simultaneous differences in both filler composition and loading, and resin matrix composition for different products. The aim of this study was to investigate the specific wear mechanisms of commercially available composites caused by mechanical stress in
Sliding wear of 19 commercially available composites and compomers
the OCA under standardized conditions. The influence of the particle size on the sliding wear, and the particle material, as well as the morphology (porous particles, range of particle size) were to be determined.
Materials and methods The composite resins used were three heterogeneous microfiller composites (Durafill VS, Metafil CX, Heliomolar RO), one hybrid composite (Estilux Hybrid), nine micro hybrid composites containing bariumaluminiumsilicate glass with different particle sizes (Arabesk, Charisma F, Charisma, Degufill Ultra, TPH-Spectrum, Z 100, Tetric classic) or quartz fillers (Pertac Hybrid, Pertac II), four compomers (Dyract AP, Compoglass F, Compoglass, Hytac) with different particle sizes and two micro hybrid composites with special composition, one with large and porous particles (Solitaire), and one with a high level of microfillers (Artglass). Manufacturers and compositional information (given by the manufacturers) of the tested materials are summarized in Table 1. Aluminum specimen holders (7.5 mm diameter and 2 mm depth; Mu ¨ ller, Schwarzenbruck, Germany) were silicated (Rocatector; ESPE, Seefeld, Germany) and silanized (ESPE-Sil; ESPE) to obtain an adhesive bond between the sample holder and the composite. All materials were applied in one increment into the specimen holders covered by a matrix band (Sachs, Tettnang, Germany) and polymerized (Dentacolor XS lightcuring unit; Heraerus Kulzer, Wehrheim, Germany) for 180 s. The surface was ground flat (#1000) with wet silicon carbide paper (LD 40; LECO, St. Joseph, USA) to remove any matrix rich surface layer and stored in Ringer’s solution for 24 h at 37 8C before testing. Occlusal contact wear was simulated in a sliding wear tester (Munich Artificial Mouth; Festo, Denkendorf, Germany). Eight specimens of each material were tested in a pin-on-block design with oscillating sliding of a spherical Degussit antagonist (Al2O3, 5 mm diameter; Degussit AL 23; FRIATEC, Mannheim, Germany) under permanent contact to the specimens at a vertical load of 50 N for 50,000 cycles. The machine operated in a forward and backward motion. Thus 50,000 cycles represent 100,000 wear events. The Degussit antagonists were fixed with self and light curing composite (Twinlock cement; Heraeus Kulzer, Wehrheim, Germany) into the aluminum antagonist holders (6 mm diameter; Mu ¨ller) before being silicated and
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silanized in the same way as the aluminum specimen holders. The horizontal excursion of the antagonist on the specimen was 8 mm. During the wear simulation the samples were continuously rinsed with distilled water with a temperature of 37 8C. Each composite was tested in each of the eight test stands (Latin Square Design). All tests were accomplished within 24 h. The wear of each specimen was quantified with a special replica technique (Permadyne Garant; ESPE/GC New Fuji Rock White; GC, Heverlee, Belgium) used after each 6000, 10,000, 30,000 and 50,000 cycles, and the surface was digitized with a 3D-laser scanner with an accuracy of 6.0 mm and a precision of 2.2 mm (Laser Scan 3D; Willytec, Munich, Germany). Wear analysis was performed using the software package Match3D, which has been developed for this purpose at the Department of Operative Dentistry (Dental School of LudwigMaximilians-University, Munich, Germany). The wear volume was calculated by laying a virtual plane over the surface of the material and another one on the wear track according to the least square method. To enable a comparison to previous studies, volumetric wear (mm3) was converted to loss of height (mm). To obtain approximately normally distributed data, a logarithmic transformation was applied. In the descriptive analysis, including boxplots, untransformed data are given. In the confirmative analysis, the scatterplots, and the correlation analyses between the average particle size, log-transformed data are used. Mean wear (MW), standard deviations (SD), and coefficients of variation (COVA) were evaluated after 6000, 10,000, 30,000, and 50,000 oscillating load cycles. Overall differences of loss of height were tested using an analysis of variance for the factor ‘composites’ with 19 levels. Subsequent pairwise comparisons were applied using the ttest for independent samples. The Bonferroni correction was used to adjust for multiple testing, using the factor 19 £ 18/2 ¼ 171. Thus, every pvalue was multiplied by 171. Only those p-values smaller than 0.05/171 ¼ 0.00029 (t . 4.78) were considered to be significant. The sample size of 8 measurements per composite required a standardized difference of 5.25 to be detectable with the power of 80%. Thus, non-significant results definitely do not provide evidence of no difference between composites. The method of Pearson was used to calculate correlation coefficients. All analyses were performed using a commercially available software package (SPSSWIN 11.0; SPSS, Chicago, USA).
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Table 1 Investigated materials (all data corresponding to data as given by manufacturer). The materials are identified by their filler type. Material
Hytac1
Batch number
Manufacturer
Categorization
Filler type
Particle size (average particle size)
Filler weight/ volume (%)
25
ESPE, Seefeld, Germany Vivadent, Schaan, Liechtenstein Vivadent, Schaan, Liechtenstein Dentsply DeTrey, Konstanz, Germany Heraeus Kulzer, Wehrheim, Germany
Compomer
max. 19 mm (10 mm)
85 (wt)
0.2 –3.0 mm (1 mm), 0.2 –3.0 mm (0.24 mm), 0.2 –3.0 mm (0.20 mm) 0.2 –1.6 mm (1 mm), 0.2 –1.6 mm (0.24 mm), 0.2 –1.6 mm (0.20 mm) D10 0.35 mm, D90 1.5 mm (0.8 mm)
79 (wt) 55 (vol)
0.04 – 5.2 mm, 0.04 –5.2 mm, 0.01 – 0.04 mm
84 (wt) 68 (vol)
ESPE, Seefeld, Germany Vivadent, Schaan, Liechtenstein
Micro hybrid composite
max. 4 mm (1.5 mm)
80.0 (wt)
Micro hybrid composite
0.04 – 3.0 mm (1.5 mm), 0.04 – 3.0 mm (0.24 mm), 0.04 – 3.0 mm (0.20 mm), 0.04 – 3.0 mm (0.04 m) 0.01 – 3.5 mm (0.6 mm)
79.5 (wt) 61 (vol)
3 M Medica, Borken, Germany Dentsply DeTrey, Konstanz, Germany Degussa, Hanau, Germany Heraeus Kulzer, Wehrheim, Germany ESPE, Seefeld, Germany Heraeus Kulzer, Wehrheim, Germany Heraeus Kulzer, Wehrheim, Germany
Calciumaluminiumflouridsilicate glass, dispersed silicon dioxide, yttriumfluorid Bariumaluminiumfluorid silicate glass, ytterbiumfluoride, spheroid mixed oxide Bariumaluminiumfluorid silicate glass, ytterbiumtrifluoride, spheroid mixed oxide Strontiumaluminiumsodiumfluoridphosphorsilicate glass, strontiumfluoride Bariumaluminiumsilicate glass, lithiumaluminiumsilicate glass, highly dispersed silicon dioxide Fine milled quartz, dispersed silicon dioxide, yttriumfluoride Barium glass, ytterbiumtrifluoride, spheroid mixed oxide, highly dispersed silicon dioxide Synthetic mineral of zirconium/silicon
84.5 (wt) 66 (vol)
max. 5 mm (1 mm), 0.01 – 0.04 mm
77 (wt) 57 (vol)
0.01 – 3.5 mm (1 mm)
78 (wt)
D50 0.7 mm, D99 2.0 mm, D99 0.01 – 0.04 mm max. 1.8 mm (0.9 mm)
, 72 (wt) , 60 (vol)
1,3,4,6
800065
Compoglass F4,6,7
905702
Compoglass
Dyract AP
4,9,10
9706000779
Estilux Hybrid
29
Pertac Hybrid1
120
Tetric1,3*
825971
Z 1001,4
19950224
TPH-Spectrum1,4,8 Degufill ultra
1,3
Charisma1,4 Pertac II
1
9607182 1016 044 002
Compomer Compomer Compomer Hybrid composite
Micro hybrid composite
Micro hybrid composite Micro hybrid composite Micro hybrid composite Micro hybrid composite (quartz fillers) Micro hybrid composite
27
Artglass2
103
Arabesk
70500
Voco, Cuxhaven, Germany
Solitaire2
22
Heraeus Kulzer, Wehrheim, Germany
Micro hybrid composite (with porous fillers)
Heliomolar RO1,3,5
823373
Metafil CX
70301
Vivadent, Schaan, Liechtenstein J. Morita Europe, Dietzenbach, Germany Heraeus Kulzer, Wehrheim, Germany
Microfilled composite (heterogeneous) Microfilled composite (only organic fillers) Microfilled composite (heterogeneous)
1,4
Durafill VS
47
Micro hybrid composite (with a high level of microfiller) Micro hybrid composite
Micro silicon dioxide, chip formed prepolymerisates
75 (wt) 50 (vol)
80 (wt)
D50 0.7 mm, D99 2.0 mm, D99 0.01 – 0.04 mm D50 0.7 mm, D99 2.0 mm, D50 4 mm, D99 10 mm
, 75 (wt) , 62 (vol)
D90 2.0 mm (1.0 mm)
76.5 (wt) 59.0 (vol)
D50 0.7 mm, D99 2.0 mm, D50 8.0 mm, D99 22.0 mm, D50 0.8 mm, D99 2.0 mm, D99mm
, 66 (wt) , 90 (vol)
0.04 – 0.2 mm (0.04 mm), 0.04 –0.2 mm (15 mm), 0.04 –0.2 mm (0.24 mm) 1 –100 mm (20 mm)
76.5 (wt) 64 (vol) 66 (wt) 54 (vol)
0.01 – 0.04 mm (0.04 mm) (30 mm)
, 60 (wt) , 50 (vol)
, 69 (wt) , 54 (vol)
* Tetric Classic Monomer-Systems: 1Bis-GMA, 2Polymerglasmatrix, 3UDMA, 4TEGDMA, 5Descandioldimethacrylat, 6Cycloaliphat. Dicarbonsa ¨uredimethacrylat, 7Polyethylenglycoldimethacrylat, 8Bis-EMA, 9Tetracarbonacid-hydroxyethylenmethacrylat-ester, 10Alkanoy-poly-methacrylat.
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Charisma F1,4
Bariumaluminiumboronsilicate glass, highly dispersed silicon dioxide Bariumaluminiumboronsilicate glass, pyrogenic silicic acid (agglomerated) Bariumaluminiumboronsilicate glass (67%), pyrogenic silicon dioxide (5%) Ultra fine milled quartz, highly dispersed silicon dioxide, yttriumfluoride Bariumaluminiumboronfluorid-silicate glass (70%), pyrogenic silicon dioxide (5%) Bariumaluminiumboronsilicate glass (55%), specific silicon dioxide (14%) (no pyrogenic) Bariumaluminiumsilicate glass, lithiumaluminiumsilicate glass ceramic, highly dispersed silicon dioxide Bariumaluminiumboronfluorid-silicate glass (26%), highly porous silicon dioxide (30%), aluminiumfluorid silicate glass (5%), fluoride salt (5%) Highly dispersed silicon dioxide copolymers, ytterbiumtrifluoride Prepolymerisates of organic fillers
77 (wt) 55 (vol)
Sliding wear of 19 commercially available composites and compomers
Results The wear rates in material groups for the microfiller composites, the micro hybrid composite and the compomers after 50,000 cycles are shown in Fig. 1(a) – (c). The micro hybrid composite Tetric classic had the lowest coefficient of variation (COVA 6%), while the compomer Hytac revealed the highest coefficient of variation (COVA 49%). Except for two compomers the coefficient of variation for all tested materials was lower than 23%. The coefficient of
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variation for the three microfilled composites was lower than 15% after 50,000 cycles. The overall differences between groups were significant ðp , 0:0005Þ: After 50,000 cycles, the microfilled composites showed the lowest mean wear (Durafill VS MW 4.02 ^ 0.59 mm; Metafil CX MW 6.65 ^ 0.76 mm; Heliomolar RO MW 6.79 ^ 1.03 mm). For all comparisons versus hybrid/micro hybrid composites and compomers significant differences were observed (corrected p , 0:05), except for Solitaire (MW
Figure 1 (a) Wear of microfiller composites after 50,000 cycles. (b) Wear of hybrid and micro hybrid composites after 50,000 cycles. (c) Wear of compomers after 50,000 cycles.
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7.39 ^ 0.76 mm), where no significant difference was observed (corrected p . 0:05). The highest wear was observed for the compomers (Hytac MW 284.95 ^ 138.92 mm; Compoglass MW 163 ^ 56.92 mm; Compoglass F MW 96.36 ^ 6.37 mm; Dyract AP MW 83.04 ^ 11.96 mm) with significant differences between the compomer group and the hybrid/micro hybrid composite group. The microfiller composites (except for Estilux Hybrid MW; 56.31 ^ 9.3 mm) differed significantly from Compoglass and Dyract AP (corrected p . 0:05). Within the compomers, only Hytac showed significantly higher wear compared to Dyract AP and Compoglass F (corrected p . 0:05). Within the hybrid/micro hybrid composites, no differences (p . 0:05) were detected between Arabesk (MW 12.49 ^ 2.71 mm), Artglass (MW 12.72 ^ 2.98 mm), Charisma F (MW 13.23 ^ 1.19 mm), Pertac II (MW 13.24^2.19 mm), Charisma (MW 13.56 ^ 1.56 mm) and Degufill Ultra (MW 14 ^ 1.45 mm). Moreover, no significant difference was obtained for the comparisons between Artglass and Solitaire or TPH-Spectrum (MW 20.34 ^ 2.25 mm). Z100 (MW 21,64 ^ 1.96 mm) did not differ significantly from TPH-Spectrum. Again, no differences between Tetric classic (MW 26,01 ^ 1.69 mm) and Pertac Hybrid (MW 31.35 ^ 4.39 mm) were observed. All other differences were statistically significant (Bonferroni correction). In particular, the hybrid composite Estilux Hybrid showed a significantly more pronounced wear than all other micro hybrid composites. The compomer with the highest filler level (determined as wt%) showed the highest wear (Hytac MW 284.95 ^ 138.92 mm) of all compomers. The compomer with the lowest filler level (determined as wt%) (Dyract AP MW 83.04 ^ 11.96 mm) had the lowest wear in the compomer group. This correlation could also be found for the microfiller composites. The microfiller composite with the highest filler level (determined as wt%) showed the highest wear (Heliomolar RO MW 6.79 ^ 1.03 mm) of all microfiller composites. The microfiller composite with the lowest filler level (determined as wt%) (Durafill VS MW 4.02 ^ 0.59 mm) had the lowest wear in the microfiller composite group. This correlation could not be found for the hybrid and micro hybrid composites. The coefficient of determination between loss of height and maximum particle size was r2 ¼ 0:41: Separate correlation analysis within the three groups of composites revealed an r2 value of 0.37 for the microfiller composites, an r2 value of 0.65 for the micro hybrid and hybrid composites, and an r2 value of 0.81 for the compomers. However, in
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the last group the correlation was mainly produced by the extreme result of Hytac (Fig. 2(a) and (b)). Moreover, the wear over time showed that the wear was almost exactly linear in the time course during the test, after a running-in phase up to 10,000 cycles, except for the micro hybrid composites Pertac Hybrid and Z 100. However, individual values did not correlate equally high for the composites, as
Figure 2 (a) Correlation between the wear of the microfiller composite and the micro hybrid composites and particle size of the composite materials (as given by manufacturer). (b) Correlation between the wear of the compomers and the particle size of the compomers (as given by manufacturer).
Sliding wear of 19 commercially available composites and compomers
Pertac Hybrid ðr2 ¼ 0:76Þ; Compoglass ðr2 ¼ 0:75Þ and Hytac ðr2 ¼ 0:56Þ showed considerable deviations, and the remaining composites varied between r2 ¼ 0:81 (Estilux Hybrid) and r2 ¼ 0:99 (Tetric classic).
Discussion Two aspects should be mentioned concerning the method of preparation and evaluation of the samples. The specimens were polymerized in a laboratory light curing unit for 3 min to overcure the composite, corresponding to the recommendation of the ADA.7 This method of polymerization does not reflect clinical practice for direct restoration, but standardizes the specimens for the wear simulation. The specimens were stored wet only for 24 h before testing. Thus the clinical situation has been simulated, since the patients use the restoration immediately. Concerning the average filler size and the microfiller compomers, the filler volumes have been determined to obviously affect the wear properties of the composite materials. Composites with small filler particles and high filler fraction volumes were suggested to wear less in earlier studies.16,21 In the present study the microfiller composites Durafill VS, Heliomolar RO and Metafil CX demonstrated significantly less wear compared to the hybrid and micro hybrid composites (except for Solitaire). Different hypotheses exist for the low wear of microfiller composites compared to hybrid and micro hybrid composites. Wear basically depends on different parameters such as preparation of specimens, type of antagonist, or load used. A further hypothesis is, that the interparticle spacing could influence the wear behavior of dental composites, because small particles are more embedded in the surface and as a consequence they will not be torn out of the matrix by the oscillating antagonist when compared to large fillers.22 Using small interparticle spacing, the soft matrix is protected from wear.23 Furthermore, the number of micro contacts between the filler particle and the antagonist, influences the wear behavior. The smaller the particles, the smaller is the load on the individual particle. Depending on the number of particles the load is distributed more homogeneously among the particles. In consequence the load on the matrix is distributed over a larger area.24 According to the manufacturer, Estilux Hybrid contains fillers which are 5.2 mm in diameter. In agreement with previous conclusions
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that related a higher wear rate to the larger filler particles in a composite material,17 the larger sized particles are more likely to be responsible for the high abrasion wear of Estilux Hybrid in the present study. The surface of the microfiller composites and the microhybride composite could become more polished and glossy during the test and this may limit wear as the coefficient of friction actually changes during the test in the absence of a third body abrasive. However, the SEM for the microhybrid composite, Tetric classic, as a representative example (Fig. 3), does not show a polished surface. Compared with the clinical situation this would concern only the movement without food. The present results suggest that the filler plucking as well as the size of the wear particles placed between the specimens and the antagonist, appear to have major effects on the wear of the composites. The larger filler particles and the larger wear particles of the hybrid and micro hybrid composites obviously do cause more wear than the smaller fillers and the smaller wear particles of microfiller composites. This theory is corresponding to the behavior of wear of composites by an abrasive paper, with rising particle size producing more wear.25 In another previous investigation26 the highest wear was observed when the abrasives had the same particle size as the filler particles. A further simulation of wear in the contact area using a pinon-disc design showed high wear rates for hybrid composites and low wear rates for microfiller composites according to the present study.27 The evaluation of wear resistance in a three-body simulation using the ACTA machine or the Leinfelder wear simulator, showed contrary results
Figure 3 Scanning electron micrograph of the wear track of the hybrid composite Tetric classic after 50,000 load cycles (magnification 4000 £ ). Note, that the surface has not become polished and glossy.
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with higher wear rates for the microfiller composites.28,29 However, the higher wear may be due to the method of test because the Leinfelder machine can be used in low and high stress conditions, correlating with abrasive and attrition wear. In previous studies, Leinfelder17 and Condon and Ferracane21 also showed low wear for the microfiller composites in three-body abrasion. The ACTA machine can also vary the load, but the wear of the microfiller composites is still high. Finally, in vivo wear of microfiller composites is, in general, low. It is at the contact sites, where these materials experience higher wear. However, this does not oppose the findings in this study, because the socalled two body wear in the OCAs, comparable to the contact wear in the contact area without food, simulated in the present study, is as important as the three body wear because contact areas should stabilize the vertical distance between the mandible and the maxillae in every case.7 It is interesting, that the wear of Solitaire is as low as the wear of the three investigated microfiller composites. Here, probably the porous filler is the reason for this excellent wear behavior. 30 A possible explanation could be that Solitaire wears in a similar way to the microfiller composites. Thus, only small particles are abraded from the large smooth filler and these small particles cause only low wear under the sliding of the antagonist. This model of wear would also explain why the three microfiller composites and the micro hybrid composite with a high level of small particles showed a lower wear than the micro hybrid composites. Corresponding to the microfiller composites, the wear for Solitaire in vivo, in contrast, is high in the contact area. However, this discrepancy can be explained in that this study has simulated only twobody wear in the OCA and not three-body wear. All investigated compomers, Dyract AP, Compoglass F, Compoglass and Hytac, showed higher wear rates than the microfiller composites, the micro hybrid composites, and the hybrid composite. This could be caused in part by the different matrix system of compomers. The compomers contain a relatively hydrophilic monomer in their organic matrix. The interaction between the matrix and water is probably the reason for the high wear of the compomers compared to all other examined microfiller composites.31 However, the ranking of wear of the four compomers is also obviously determined by the different particle size (Table 1). It has been suggested31 that another reason for the high wear rate of compomers could be the low volume filler fraction (Dyract AP 50 vol%) compared to the composites (Tetric classic 61 vol%). Nevertheless, this hypothesis would not explain the high
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wear rate of the other investigated compomers (Compoglass 55 vol%, Compoglass F 55 vol%). These indeed have the same high filler volume as one of the investigated micro hybrid composites (Artglass 54 vol%) and one of the microfiller composites (Durafill VS 50 vol%). Another explanation could be, that the antagonist abraded and the abraded material caused more wear under the sliding of the antagonist. The visual inspection of the antagonist did assist this hypothesis. Obviously, further investigation and evaluation of the antagonists in a separate study are necessary. Concerning the loss of height over time: two composites (Pertac Hybrid, Z 100) showed a decreasing wear curve; a probable explanation for this finding could be that these two composite materials have either extremely hard quartz particles (Pertac Hybrid) or an extremely high filler content (determined as wt%), both of which could produce more wear on the antagonists and increase the contact surface. In consequence the load per area decreases and the wear should increase, respectively. The results suggest that all tested composites have an inevitable, remarkable wear regardless of the particle size, the filler volume fraction and modification of the particle morphology. Furthermore, the influence of these filler qualities on the antagonist should be evaluated in a following study.
Conclusions Comparison of the wear rates over time is not straight forward, because not all materials wear exactly linearly over time after the running in phase. Thus the comparison of wear after 50,000 cycles is useful. Concerning two-body wear in the OCA; composites with small particles are more wear resistant in the two-body wear than composites with large particles. A large but porous filler probably wears in two-body occlusal contact, comparable to microfillers. Thus, both particle size and morphology have a high influence on the wear properties concerning two-body wear in the OCA. Because the simulation in the artificial mouth represents only two-body wear on the OCA and as in the clinical situation there is also three-body wear in the OCA and the CFA, these results reflect only one aspect concerning the clinical situation. They can only be used with the limitations of an in vitro study to predict clinical wear behavior of definitive restoration in load bearing cavities in permanent teeth.
Sliding wear of 19 commercially available composites and compomers
References 1. Peters MCRB, Roeters JJM, Frankenmolen FWA. Clinical evaluation of Dyract in primary molars: 1-year results. Am J Dent 1996;9:83—7. 2. Roulet JF. Benefits and disadvantages of tooth-colored alternatives to amalgam. J Dent 1997;25:459—73. 3. Hickel R, Manhart J. Longevity of restorations. In: Wilson NHF, Roulet J-F, Fuzzi N, editors. Advances in operative dentistry— challenges of the future. Chicago: Quintessence; 2001. 4. Roulet JF. Degradation of dental polymers. Mu ¨nchen: Karger; 1987. 5. Powell JM, Philips RW, Norman RD. In vitro wear response of composite resin, amalgam and enamel. J Dent Res 1975;54: 1183—95. 6. Krejci I, Reich T, Albertoni M, Lutz F. In-vitro-Testverfahren zur Evaluation dentaler Restaurationssysteme 1. Computergesteuerter Kausimulator. Schweiz Monatsschr Zahnmed 1990;100:953—60. 7. Kunzelmann K-H. Verschleißanalyse und -quantifizierung von Fu ¨llungsmaterialien in vivo und in vitro. Aachen: Shaker; 1998. 8. Krejci I, Albertoni M, Lutz F. In-vitro-Testverfahren zur ¨rsten/ Evaluation dentaler Restaurationssysteme 2. Zahnbu Zahnpastenabrasion und chemische Degradation. Schweiz Monatsschr Zahnmed 1990;100:1164—8. 9. Lutz F, Phillip RW, Roulet JF, Sectos JC. In vivo and in vitro wear of potential posterior composites. J Dent Res 1984;63: 914—20. 10. De Gee AJ, Pallav P, Davidson CL. Effect of abrasion medium on wear of stress-bearing composites and amalgam in vitro. J Dent Res 1986;65:654—9. 11. De Gee AJ, Pallav P. Occlusal wear simulation with the ACTA wear machine. J Dent 1994;22(Suppl 1):21—7. 12. Bailey WF, Rice SL. Comparative sliding-wear behavior of a dental amalgam and a composite restorative as a function of contact stress. J Dent Res 1981;60:731—2. 13. DeLong R, Douglas WH. Development of an artificial oral environment for the testing of dental restoratives: bi-axial force and movement control. J Dent Res 1983;62:32—6. 14. Leinfelder KF, Beaudreau RW, Mazer RB. An in vitro device for predicting clinical wear. Quintessence Int 1989;20:755—61. 15. Powers JM, Ludema KC, Craig RG. Wear of fluorapatite single crystal: VI. Influence of multiple-pass sliding on surface failure. J Dent Res 1973;52:1032—40. 16. Li Y, Swartz ML, Phillips RW, Moore BK, Roberts TA. Effect of filler content and size on properties of composites. J Dent Res 1985;64:1396—401.
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17. Leinfelder KF. Posterior composites. State-of-the-art clinical application. Dent Clin North Am 1993;37:411—8. 18. Kawaguchi M, Fukushima T, Horibe T. Effect of monomer structure on the mechanical properties of light-cured composite resins. Dent Mater J 1989;8:40—5. 19. Peutzfeld A. Resin composites in dentistry: the monomer systems. Eur J Oral Sci 1997;105:97—116. 20. Braem M, Finger W, Van Doren VE, Lambrechts P, Vanherle G. Mechanical properties and filler fraction of dental composites. Dent Mater 1989;5:346—8. 21. Condon JR, Ferracane JL. In vitro wear of composites with varied cure, filler level and treatment. J Dent Res 1997;76: 1405—11. 22. Mair LH, Stolarski TA, Vowles RW, Loyds CH. Wear: mechanisms, manifestations and measurement. Report of a workshop. J Dent 1996;24:141—8. 23. Bayne SC, Taylor DF, Heymann HO. Protection hypothesis for composite wear. Dent Mater 1992;8:305—9. 24. Axe ´n N, Jacobson S. A model for the abrasive wear resistance of multiphase materials. Wear 1994;174:187—99. 25. Harrison A, Moores GE. Influence of abrasive particle size and contact stress on wear rate of dental restorative materials. Dent Mater 1985;1:14—19. 26. Draughn RA, Harrison A. Relationship between abrasive wear and microstructure of composite resin. J Prosthet Dent 1978;40:220—4. 27. Rice SL, Bailey WF, Wayne SF, Burns JA. Comparative in vitro sliding-wear study of conventional, microfilled and lightcured composite restoratives. J Dent Res 1984;63:1173—6. 28. Barkmeier WW, Wilwerding TM, Latta MA, Blake SM. In-vitro wear assessment of high density composite resins. J Dent Res 1999;78(448). Abstr. No. 2737. 29. Suzuki S. In vitro wear of condensable resin composite restoratives. J Dent Res 1999;78(447). Abstr. No. 2734. 30. Manhart J, Kunzelmann K-H, Chen HY, Hickel R. Mechanical properties and wear behavior of light-cured packable composite resins. Dent Mater 2000;16:33—40. 31. Sindel J. Simulation des Verschleißverhaltens von Komposi¨rztl Mitt 1998;5:514—6. ten. Zahna 32. Condon JR, Ferracane JL. Evaluation of composite wear with a new multimode oral wear simulator. Dent Mater 1996;12: 218—26. 33. Hammesfahr PD. Developments in resionomer systems. In: Hunt PR, editor. Glass inomers: the next generation. Proceedings of the second International Symposium on Glass Ionomers, Philadelphia: International Symposium in Dentistry; 1994. p. 47—54.
http://www.intl.elsevierhealth.com/journals/dema
Sliding wear of 19 commercially available composites and compomers Catharina Zantnera,*, Andrej M. Kielbassaa, Peter Martusb, Karl-Heinz Kunzelmannc a
Department of Operative Dentistry and Periodontology, University School of Dental Medicine, ¨t Berlin, Berlin, Germany Freie Universita b ¨t Berlin, Berlin, Germany Institute for Medical Informatics, Biometry and Epidemiology, Freie Universita c Department of Operative Dentistry and Periodontology, Dental School of the Ludwig-Maximilians-University, Munich, Germany Received 28 May 2002; received in revised form 12 December 2002; accepted 12 March 2003
KEYWORDS Wear; Composites; Compomers; Particle size
Summary Objectives. The aim of this study was to determine the influence of particle size, particle material and morphology on the sliding wear of 19 light curing, commercially available composites (Durafill VS, Metafil CX, Heliomolar RO, Solitaire, Arabesk, Artglass, Charisma F, Pertac II, Charisma, Degufill Ultra, TPH Spectrum, Z100, Tetric classic, Pertac Hybrid, Estilux Hybrid, Dyract AP, Compoglass F, Compoglass and Hytac). Methods. The materials were applied to an aluminum sample holder (7.5 mm diameter, 2 mm depth) in one layer and polymerized in a Dentacolor XS light curing unit for 180 s. The surface was ground flat (#1000) to remove any matrix rich surface layer. Then samples were stored in Ringer’s solution for 24 h at 37 8C. Occlusal contact wear was simulated in a sliding wear tester (Munich Artificial Mouth). Eight specimens of each material were tested in a pin-on-block design with oscillating sliding of a Degussit antagonist (5 mm diameter) at a vertical load of 50 N. The horizontal excursion of the antagonist was 8 mm. Wear was quantified by a replica technique every 6000, 10,000, 30,000 and 50,000 cycles using a 3D-laser scanner. The materials were compared by their mean wear after 50,000 cycles. Comparisons of different composites and compomers were performed using analysis of variance and t-tests including the Bonferroni correction. Results. The microfiller composites (Durafill VS, Metafil CX, Heliomolar RO) revealed the lowest, and the compomers (Dyract AP, Compoglass F, Compoglass and Hytac) showed the highest contact wear ðp , 0:05Þ: The wear of the hybrid composite (Estilux Hybrid) and the micro hybrid composites (Solitaire, Arabesk, Artglass, Charisma F, Pertac II, Charisma, Degufill Ultra, TPH Spectrum, Z100, Tetric classic, Pertac Hybrid) was higher than that of the microfiller composites ðp , 0:05Þ: The results showed additional significant differences within the three groups of composites. The coefficient of determination between loss of height and maximum particle size was r2 ¼ 0:41: Significance. Both particle size and morphology have a high influence on the wear properties concerning the two-body wear in the occlusal contact area. Q 2003 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.
*Corresponding author. Universita ¨tsklinik fu ¨t Berlin, Poliklinik fu ¨r Zahn-, Mund- und Kieferheilkunde, der Freien Universita ¨r Zahnerhaltungskunde und Parodontologie, Aßmannshauser Straße 4-6, 14197 Berlin, Germany. Tel.: þ49-30-8445-6129; fax: þ49-308445-6204. E-mail address: [email protected] 0109-5641/$ 30.00 Q 2003 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved. doi:10.1016/S0109-5641(03)00104-0
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Introduction Alleged adverse health effects and environmental concerns regarding the release of mercury gave rise to a controversial discussion about the use of amalgam in several countries, especially in Sweden and Germany.1,2 Thus, the use of composite resins for restoring posterior stress-bearing cavities has increased enormously in the last few decades. Early attempts to place composites in posterior teeth as an alternative to amalgam revealed only limited success because of insufficient properties of the materials used. Nowadays, light cured tooth colored composites feature the advantage of good esthetics for restorations, are able to bond to tooth structures, and have a successful clinical performance. The main reasons for failure have been shown to be secondary caries.3 In addition, inadequate resistance to wear and fracture may be significant concerns, resulting in a loss of anatomic form under masticatory abrasion and attrition and fractures within the body of the restoration and/or at its margins.3 Thus further investigation of wear mechanisms of composite materials is necessary. Wear can be defined as unwanted removal of solid material from surfaces due to mechanical action.4 This indeed is a simple definition; namely, wear is a very complex process. The only way to predict wear is to understand the single mechanisms contributing to the wear that is observed.4 Moreover, wear is not a specific material property as elastic modulus, fracture toughness, or tensile bond strength are.5 Unfortunately, in vivo testing is costly and time consuming.6 For these reasons it seems necessary to investigate the different types of composite wear in vitro. Due to its complicity, wear should be evaluated by a multilevel investigation method.6 – 8 There are several current test devices for this purpose4,14,32 producing results that correlate well with published clinical data for commercial composites. Another possibility is to use a complex of different, more simple test devices to simulate the wear mechanism: These are tooth brushing machines7,8 to simulate the wear in the contact free areas (CFA),9 and the ACTA machine10,11 which has been constructed to simulate simultaneously many clinical variables being active in the occlusal wear; furthermore, pin-on-disc-12 and pin-on-block devices7 have been described. Regarding the results of one of these tests it is noteworthy, that one kind of test only simulates one aspect of the complex wear mechanisms in vivo. Both the pin-on-disc12 and the pin-on-block devices as used in this study7 simulate sliding wear in the occlusal contact area
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(OCA). Artificial mouths use the pin-on-block design with unidirectional8,13 or bi-directional sliding.4,7,14 Furthermore, in scratch tests bi-directional sliding causes more wear than unidirectional sliding.15 In contrast, impulse load, simulated in an artificial mouth does not affect the wear.5 Concerning the composition of composite materials filler content, filler material, filler size, as well as the distribution of the filler particles influence the physical and mechanical properties of the composites. The wear resistance of composite resins has been significantly improved by decreasing the average filler particle size and increasing the filler loading.16 In general, higher wear rates in the contact area are related to the larger filler particles in composite materials.17 Therefore, new composites may have smaller particle size, but they do not have higher filler volumes. These new materials show a lower abrasive wear, but also generally have lower properties compared to many of the preceding composites. On the contrary, besides the filler system the resin matrix also has an important influence on the properties of the composite materials.18,19 However, in the past 30 years the mostly used monomer systems for composites since the introduction of dimethacrylates by Bowen in 1962 has been the BisGMA. One new approach concerning different monomer systems was the introduction of the polyacid-modified resin composites (PMRC), commonly termed as compomers. The monomer of the PMRC contains acidic carboxylate groups and polymerizable methacrylate groups, which enables a free-radical polymerization by light curing and an acid-base reaction if water is present.33 Concerning the antagonist used in occlusal contact simulations many varying types of antagonists can be found in the dental literature. The most important aspect concerning the used antagonist is using a standardized material without biological variation to obtain comparable wear rates. Such materials are aluminum oxide and Steatite. However, Steatite is a very soft material and would have been quickly abraded by the composites.7 As a consequence, the contact area would increase during the tests, thus leading to a decreased pressure per area resulting in less wear.7 All in all, comparison of commercially available composites is difficult because information regarding the material composition is often not available,20 and there will usually be simultaneous differences in both filler composition and loading, and resin matrix composition for different products. The aim of this study was to investigate the specific wear mechanisms of commercially available composites caused by mechanical stress in
Sliding wear of 19 commercially available composites and compomers
the OCA under standardized conditions. The influence of the particle size on the sliding wear, and the particle material, as well as the morphology (porous particles, range of particle size) were to be determined.
Materials and methods The composite resins used were three heterogeneous microfiller composites (Durafill VS, Metafil CX, Heliomolar RO), one hybrid composite (Estilux Hybrid), nine micro hybrid composites containing bariumaluminiumsilicate glass with different particle sizes (Arabesk, Charisma F, Charisma, Degufill Ultra, TPH-Spectrum, Z 100, Tetric classic) or quartz fillers (Pertac Hybrid, Pertac II), four compomers (Dyract AP, Compoglass F, Compoglass, Hytac) with different particle sizes and two micro hybrid composites with special composition, one with large and porous particles (Solitaire), and one with a high level of microfillers (Artglass). Manufacturers and compositional information (given by the manufacturers) of the tested materials are summarized in Table 1. Aluminum specimen holders (7.5 mm diameter and 2 mm depth; Mu ¨ ller, Schwarzenbruck, Germany) were silicated (Rocatector; ESPE, Seefeld, Germany) and silanized (ESPE-Sil; ESPE) to obtain an adhesive bond between the sample holder and the composite. All materials were applied in one increment into the specimen holders covered by a matrix band (Sachs, Tettnang, Germany) and polymerized (Dentacolor XS lightcuring unit; Heraerus Kulzer, Wehrheim, Germany) for 180 s. The surface was ground flat (#1000) with wet silicon carbide paper (LD 40; LECO, St. Joseph, USA) to remove any matrix rich surface layer and stored in Ringer’s solution for 24 h at 37 8C before testing. Occlusal contact wear was simulated in a sliding wear tester (Munich Artificial Mouth; Festo, Denkendorf, Germany). Eight specimens of each material were tested in a pin-on-block design with oscillating sliding of a spherical Degussit antagonist (Al2O3, 5 mm diameter; Degussit AL 23; FRIATEC, Mannheim, Germany) under permanent contact to the specimens at a vertical load of 50 N for 50,000 cycles. The machine operated in a forward and backward motion. Thus 50,000 cycles represent 100,000 wear events. The Degussit antagonists were fixed with self and light curing composite (Twinlock cement; Heraeus Kulzer, Wehrheim, Germany) into the aluminum antagonist holders (6 mm diameter; Mu ¨ller) before being silicated and
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silanized in the same way as the aluminum specimen holders. The horizontal excursion of the antagonist on the specimen was 8 mm. During the wear simulation the samples were continuously rinsed with distilled water with a temperature of 37 8C. Each composite was tested in each of the eight test stands (Latin Square Design). All tests were accomplished within 24 h. The wear of each specimen was quantified with a special replica technique (Permadyne Garant; ESPE/GC New Fuji Rock White; GC, Heverlee, Belgium) used after each 6000, 10,000, 30,000 and 50,000 cycles, and the surface was digitized with a 3D-laser scanner with an accuracy of 6.0 mm and a precision of 2.2 mm (Laser Scan 3D; Willytec, Munich, Germany). Wear analysis was performed using the software package Match3D, which has been developed for this purpose at the Department of Operative Dentistry (Dental School of LudwigMaximilians-University, Munich, Germany). The wear volume was calculated by laying a virtual plane over the surface of the material and another one on the wear track according to the least square method. To enable a comparison to previous studies, volumetric wear (mm3) was converted to loss of height (mm). To obtain approximately normally distributed data, a logarithmic transformation was applied. In the descriptive analysis, including boxplots, untransformed data are given. In the confirmative analysis, the scatterplots, and the correlation analyses between the average particle size, log-transformed data are used. Mean wear (MW), standard deviations (SD), and coefficients of variation (COVA) were evaluated after 6000, 10,000, 30,000, and 50,000 oscillating load cycles. Overall differences of loss of height were tested using an analysis of variance for the factor ‘composites’ with 19 levels. Subsequent pairwise comparisons were applied using the ttest for independent samples. The Bonferroni correction was used to adjust for multiple testing, using the factor 19 £ 18/2 ¼ 171. Thus, every pvalue was multiplied by 171. Only those p-values smaller than 0.05/171 ¼ 0.00029 (t . 4.78) were considered to be significant. The sample size of 8 measurements per composite required a standardized difference of 5.25 to be detectable with the power of 80%. Thus, non-significant results definitely do not provide evidence of no difference between composites. The method of Pearson was used to calculate correlation coefficients. All analyses were performed using a commercially available software package (SPSSWIN 11.0; SPSS, Chicago, USA).
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Table 1 Investigated materials (all data corresponding to data as given by manufacturer). The materials are identified by their filler type. Material
Hytac1
Batch number
Manufacturer
Categorization
Filler type
Particle size (average particle size)
Filler weight/ volume (%)
25
ESPE, Seefeld, Germany Vivadent, Schaan, Liechtenstein Vivadent, Schaan, Liechtenstein Dentsply DeTrey, Konstanz, Germany Heraeus Kulzer, Wehrheim, Germany
Compomer
max. 19 mm (10 mm)
85 (wt)
0.2 –3.0 mm (1 mm), 0.2 –3.0 mm (0.24 mm), 0.2 –3.0 mm (0.20 mm) 0.2 –1.6 mm (1 mm), 0.2 –1.6 mm (0.24 mm), 0.2 –1.6 mm (0.20 mm) D10 0.35 mm, D90 1.5 mm (0.8 mm)
79 (wt) 55 (vol)
0.04 – 5.2 mm, 0.04 –5.2 mm, 0.01 – 0.04 mm
84 (wt) 68 (vol)
ESPE, Seefeld, Germany Vivadent, Schaan, Liechtenstein
Micro hybrid composite
max. 4 mm (1.5 mm)
80.0 (wt)
Micro hybrid composite
0.04 – 3.0 mm (1.5 mm), 0.04 – 3.0 mm (0.24 mm), 0.04 – 3.0 mm (0.20 mm), 0.04 – 3.0 mm (0.04 m) 0.01 – 3.5 mm (0.6 mm)
79.5 (wt) 61 (vol)
3 M Medica, Borken, Germany Dentsply DeTrey, Konstanz, Germany Degussa, Hanau, Germany Heraeus Kulzer, Wehrheim, Germany ESPE, Seefeld, Germany Heraeus Kulzer, Wehrheim, Germany Heraeus Kulzer, Wehrheim, Germany
Calciumaluminiumflouridsilicate glass, dispersed silicon dioxide, yttriumfluorid Bariumaluminiumfluorid silicate glass, ytterbiumfluoride, spheroid mixed oxide Bariumaluminiumfluorid silicate glass, ytterbiumtrifluoride, spheroid mixed oxide Strontiumaluminiumsodiumfluoridphosphorsilicate glass, strontiumfluoride Bariumaluminiumsilicate glass, lithiumaluminiumsilicate glass, highly dispersed silicon dioxide Fine milled quartz, dispersed silicon dioxide, yttriumfluoride Barium glass, ytterbiumtrifluoride, spheroid mixed oxide, highly dispersed silicon dioxide Synthetic mineral of zirconium/silicon
84.5 (wt) 66 (vol)
max. 5 mm (1 mm), 0.01 – 0.04 mm
77 (wt) 57 (vol)
0.01 – 3.5 mm (1 mm)
78 (wt)
D50 0.7 mm, D99 2.0 mm, D99 0.01 – 0.04 mm max. 1.8 mm (0.9 mm)
, 72 (wt) , 60 (vol)
1,3,4,6
800065
Compoglass F4,6,7
905702
Compoglass
Dyract AP
4,9,10
9706000779
Estilux Hybrid
29
Pertac Hybrid1
120
Tetric1,3*
825971
Z 1001,4
19950224
TPH-Spectrum1,4,8 Degufill ultra
1,3
Charisma1,4 Pertac II
1
9607182 1016 044 002
Compomer Compomer Compomer Hybrid composite
Micro hybrid composite
Micro hybrid composite Micro hybrid composite Micro hybrid composite Micro hybrid composite (quartz fillers) Micro hybrid composite
27
Artglass2
103
Arabesk
70500
Voco, Cuxhaven, Germany
Solitaire2
22
Heraeus Kulzer, Wehrheim, Germany
Micro hybrid composite (with porous fillers)
Heliomolar RO1,3,5
823373
Metafil CX
70301
Vivadent, Schaan, Liechtenstein J. Morita Europe, Dietzenbach, Germany Heraeus Kulzer, Wehrheim, Germany
Microfilled composite (heterogeneous) Microfilled composite (only organic fillers) Microfilled composite (heterogeneous)
1,4
Durafill VS
47
Micro hybrid composite (with a high level of microfiller) Micro hybrid composite
Micro silicon dioxide, chip formed prepolymerisates
75 (wt) 50 (vol)
80 (wt)
D50 0.7 mm, D99 2.0 mm, D99 0.01 – 0.04 mm D50 0.7 mm, D99 2.0 mm, D50 4 mm, D99 10 mm
, 75 (wt) , 62 (vol)
D90 2.0 mm (1.0 mm)
76.5 (wt) 59.0 (vol)
D50 0.7 mm, D99 2.0 mm, D50 8.0 mm, D99 22.0 mm, D50 0.8 mm, D99 2.0 mm, D99mm
, 66 (wt) , 90 (vol)
0.04 – 0.2 mm (0.04 mm), 0.04 –0.2 mm (15 mm), 0.04 –0.2 mm (0.24 mm) 1 –100 mm (20 mm)
76.5 (wt) 64 (vol) 66 (wt) 54 (vol)
0.01 – 0.04 mm (0.04 mm) (30 mm)
, 60 (wt) , 50 (vol)
, 69 (wt) , 54 (vol)
* Tetric Classic Monomer-Systems: 1Bis-GMA, 2Polymerglasmatrix, 3UDMA, 4TEGDMA, 5Descandioldimethacrylat, 6Cycloaliphat. Dicarbonsa ¨uredimethacrylat, 7Polyethylenglycoldimethacrylat, 8Bis-EMA, 9Tetracarbonacid-hydroxyethylenmethacrylat-ester, 10Alkanoy-poly-methacrylat.
C. Zantner et al.
Charisma F1,4
Bariumaluminiumboronsilicate glass, highly dispersed silicon dioxide Bariumaluminiumboronsilicate glass, pyrogenic silicic acid (agglomerated) Bariumaluminiumboronsilicate glass (67%), pyrogenic silicon dioxide (5%) Ultra fine milled quartz, highly dispersed silicon dioxide, yttriumfluoride Bariumaluminiumboronfluorid-silicate glass (70%), pyrogenic silicon dioxide (5%) Bariumaluminiumboronsilicate glass (55%), specific silicon dioxide (14%) (no pyrogenic) Bariumaluminiumsilicate glass, lithiumaluminiumsilicate glass ceramic, highly dispersed silicon dioxide Bariumaluminiumboronfluorid-silicate glass (26%), highly porous silicon dioxide (30%), aluminiumfluorid silicate glass (5%), fluoride salt (5%) Highly dispersed silicon dioxide copolymers, ytterbiumtrifluoride Prepolymerisates of organic fillers
77 (wt) 55 (vol)
Sliding wear of 19 commercially available composites and compomers
Results The wear rates in material groups for the microfiller composites, the micro hybrid composite and the compomers after 50,000 cycles are shown in Fig. 1(a) – (c). The micro hybrid composite Tetric classic had the lowest coefficient of variation (COVA 6%), while the compomer Hytac revealed the highest coefficient of variation (COVA 49%). Except for two compomers the coefficient of variation for all tested materials was lower than 23%. The coefficient of
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variation for the three microfilled composites was lower than 15% after 50,000 cycles. The overall differences between groups were significant ðp , 0:0005Þ: After 50,000 cycles, the microfilled composites showed the lowest mean wear (Durafill VS MW 4.02 ^ 0.59 mm; Metafil CX MW 6.65 ^ 0.76 mm; Heliomolar RO MW 6.79 ^ 1.03 mm). For all comparisons versus hybrid/micro hybrid composites and compomers significant differences were observed (corrected p , 0:05), except for Solitaire (MW
Figure 1 (a) Wear of microfiller composites after 50,000 cycles. (b) Wear of hybrid and micro hybrid composites after 50,000 cycles. (c) Wear of compomers after 50,000 cycles.
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7.39 ^ 0.76 mm), where no significant difference was observed (corrected p . 0:05). The highest wear was observed for the compomers (Hytac MW 284.95 ^ 138.92 mm; Compoglass MW 163 ^ 56.92 mm; Compoglass F MW 96.36 ^ 6.37 mm; Dyract AP MW 83.04 ^ 11.96 mm) with significant differences between the compomer group and the hybrid/micro hybrid composite group. The microfiller composites (except for Estilux Hybrid MW; 56.31 ^ 9.3 mm) differed significantly from Compoglass and Dyract AP (corrected p . 0:05). Within the compomers, only Hytac showed significantly higher wear compared to Dyract AP and Compoglass F (corrected p . 0:05). Within the hybrid/micro hybrid composites, no differences (p . 0:05) were detected between Arabesk (MW 12.49 ^ 2.71 mm), Artglass (MW 12.72 ^ 2.98 mm), Charisma F (MW 13.23 ^ 1.19 mm), Pertac II (MW 13.24^2.19 mm), Charisma (MW 13.56 ^ 1.56 mm) and Degufill Ultra (MW 14 ^ 1.45 mm). Moreover, no significant difference was obtained for the comparisons between Artglass and Solitaire or TPH-Spectrum (MW 20.34 ^ 2.25 mm). Z100 (MW 21,64 ^ 1.96 mm) did not differ significantly from TPH-Spectrum. Again, no differences between Tetric classic (MW 26,01 ^ 1.69 mm) and Pertac Hybrid (MW 31.35 ^ 4.39 mm) were observed. All other differences were statistically significant (Bonferroni correction). In particular, the hybrid composite Estilux Hybrid showed a significantly more pronounced wear than all other micro hybrid composites. The compomer with the highest filler level (determined as wt%) showed the highest wear (Hytac MW 284.95 ^ 138.92 mm) of all compomers. The compomer with the lowest filler level (determined as wt%) (Dyract AP MW 83.04 ^ 11.96 mm) had the lowest wear in the compomer group. This correlation could also be found for the microfiller composites. The microfiller composite with the highest filler level (determined as wt%) showed the highest wear (Heliomolar RO MW 6.79 ^ 1.03 mm) of all microfiller composites. The microfiller composite with the lowest filler level (determined as wt%) (Durafill VS MW 4.02 ^ 0.59 mm) had the lowest wear in the microfiller composite group. This correlation could not be found for the hybrid and micro hybrid composites. The coefficient of determination between loss of height and maximum particle size was r2 ¼ 0:41: Separate correlation analysis within the three groups of composites revealed an r2 value of 0.37 for the microfiller composites, an r2 value of 0.65 for the micro hybrid and hybrid composites, and an r2 value of 0.81 for the compomers. However, in
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the last group the correlation was mainly produced by the extreme result of Hytac (Fig. 2(a) and (b)). Moreover, the wear over time showed that the wear was almost exactly linear in the time course during the test, after a running-in phase up to 10,000 cycles, except for the micro hybrid composites Pertac Hybrid and Z 100. However, individual values did not correlate equally high for the composites, as
Figure 2 (a) Correlation between the wear of the microfiller composite and the micro hybrid composites and particle size of the composite materials (as given by manufacturer). (b) Correlation between the wear of the compomers and the particle size of the compomers (as given by manufacturer).
Sliding wear of 19 commercially available composites and compomers
Pertac Hybrid ðr2 ¼ 0:76Þ; Compoglass ðr2 ¼ 0:75Þ and Hytac ðr2 ¼ 0:56Þ showed considerable deviations, and the remaining composites varied between r2 ¼ 0:81 (Estilux Hybrid) and r2 ¼ 0:99 (Tetric classic).
Discussion Two aspects should be mentioned concerning the method of preparation and evaluation of the samples. The specimens were polymerized in a laboratory light curing unit for 3 min to overcure the composite, corresponding to the recommendation of the ADA.7 This method of polymerization does not reflect clinical practice for direct restoration, but standardizes the specimens for the wear simulation. The specimens were stored wet only for 24 h before testing. Thus the clinical situation has been simulated, since the patients use the restoration immediately. Concerning the average filler size and the microfiller compomers, the filler volumes have been determined to obviously affect the wear properties of the composite materials. Composites with small filler particles and high filler fraction volumes were suggested to wear less in earlier studies.16,21 In the present study the microfiller composites Durafill VS, Heliomolar RO and Metafil CX demonstrated significantly less wear compared to the hybrid and micro hybrid composites (except for Solitaire). Different hypotheses exist for the low wear of microfiller composites compared to hybrid and micro hybrid composites. Wear basically depends on different parameters such as preparation of specimens, type of antagonist, or load used. A further hypothesis is, that the interparticle spacing could influence the wear behavior of dental composites, because small particles are more embedded in the surface and as a consequence they will not be torn out of the matrix by the oscillating antagonist when compared to large fillers.22 Using small interparticle spacing, the soft matrix is protected from wear.23 Furthermore, the number of micro contacts between the filler particle and the antagonist, influences the wear behavior. The smaller the particles, the smaller is the load on the individual particle. Depending on the number of particles the load is distributed more homogeneously among the particles. In consequence the load on the matrix is distributed over a larger area.24 According to the manufacturer, Estilux Hybrid contains fillers which are 5.2 mm in diameter. In agreement with previous conclusions
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that related a higher wear rate to the larger filler particles in a composite material,17 the larger sized particles are more likely to be responsible for the high abrasion wear of Estilux Hybrid in the present study. The surface of the microfiller composites and the microhybride composite could become more polished and glossy during the test and this may limit wear as the coefficient of friction actually changes during the test in the absence of a third body abrasive. However, the SEM for the microhybrid composite, Tetric classic, as a representative example (Fig. 3), does not show a polished surface. Compared with the clinical situation this would concern only the movement without food. The present results suggest that the filler plucking as well as the size of the wear particles placed between the specimens and the antagonist, appear to have major effects on the wear of the composites. The larger filler particles and the larger wear particles of the hybrid and micro hybrid composites obviously do cause more wear than the smaller fillers and the smaller wear particles of microfiller composites. This theory is corresponding to the behavior of wear of composites by an abrasive paper, with rising particle size producing more wear.25 In another previous investigation26 the highest wear was observed when the abrasives had the same particle size as the filler particles. A further simulation of wear in the contact area using a pinon-disc design showed high wear rates for hybrid composites and low wear rates for microfiller composites according to the present study.27 The evaluation of wear resistance in a three-body simulation using the ACTA machine or the Leinfelder wear simulator, showed contrary results
Figure 3 Scanning electron micrograph of the wear track of the hybrid composite Tetric classic after 50,000 load cycles (magnification 4000 £ ). Note, that the surface has not become polished and glossy.
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with higher wear rates for the microfiller composites.28,29 However, the higher wear may be due to the method of test because the Leinfelder machine can be used in low and high stress conditions, correlating with abrasive and attrition wear. In previous studies, Leinfelder17 and Condon and Ferracane21 also showed low wear for the microfiller composites in three-body abrasion. The ACTA machine can also vary the load, but the wear of the microfiller composites is still high. Finally, in vivo wear of microfiller composites is, in general, low. It is at the contact sites, where these materials experience higher wear. However, this does not oppose the findings in this study, because the socalled two body wear in the OCAs, comparable to the contact wear in the contact area without food, simulated in the present study, is as important as the three body wear because contact areas should stabilize the vertical distance between the mandible and the maxillae in every case.7 It is interesting, that the wear of Solitaire is as low as the wear of the three investigated microfiller composites. Here, probably the porous filler is the reason for this excellent wear behavior. 30 A possible explanation could be that Solitaire wears in a similar way to the microfiller composites. Thus, only small particles are abraded from the large smooth filler and these small particles cause only low wear under the sliding of the antagonist. This model of wear would also explain why the three microfiller composites and the micro hybrid composite with a high level of small particles showed a lower wear than the micro hybrid composites. Corresponding to the microfiller composites, the wear for Solitaire in vivo, in contrast, is high in the contact area. However, this discrepancy can be explained in that this study has simulated only twobody wear in the OCA and not three-body wear. All investigated compomers, Dyract AP, Compoglass F, Compoglass and Hytac, showed higher wear rates than the microfiller composites, the micro hybrid composites, and the hybrid composite. This could be caused in part by the different matrix system of compomers. The compomers contain a relatively hydrophilic monomer in their organic matrix. The interaction between the matrix and water is probably the reason for the high wear of the compomers compared to all other examined microfiller composites.31 However, the ranking of wear of the four compomers is also obviously determined by the different particle size (Table 1). It has been suggested31 that another reason for the high wear rate of compomers could be the low volume filler fraction (Dyract AP 50 vol%) compared to the composites (Tetric classic 61 vol%). Nevertheless, this hypothesis would not explain the high
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wear rate of the other investigated compomers (Compoglass 55 vol%, Compoglass F 55 vol%). These indeed have the same high filler volume as one of the investigated micro hybrid composites (Artglass 54 vol%) and one of the microfiller composites (Durafill VS 50 vol%). Another explanation could be, that the antagonist abraded and the abraded material caused more wear under the sliding of the antagonist. The visual inspection of the antagonist did assist this hypothesis. Obviously, further investigation and evaluation of the antagonists in a separate study are necessary. Concerning the loss of height over time: two composites (Pertac Hybrid, Z 100) showed a decreasing wear curve; a probable explanation for this finding could be that these two composite materials have either extremely hard quartz particles (Pertac Hybrid) or an extremely high filler content (determined as wt%), both of which could produce more wear on the antagonists and increase the contact surface. In consequence the load per area decreases and the wear should increase, respectively. The results suggest that all tested composites have an inevitable, remarkable wear regardless of the particle size, the filler volume fraction and modification of the particle morphology. Furthermore, the influence of these filler qualities on the antagonist should be evaluated in a following study.
Conclusions Comparison of the wear rates over time is not straight forward, because not all materials wear exactly linearly over time after the running in phase. Thus the comparison of wear after 50,000 cycles is useful. Concerning two-body wear in the OCA; composites with small particles are more wear resistant in the two-body wear than composites with large particles. A large but porous filler probably wears in two-body occlusal contact, comparable to microfillers. Thus, both particle size and morphology have a high influence on the wear properties concerning two-body wear in the OCA. Because the simulation in the artificial mouth represents only two-body wear on the OCA and as in the clinical situation there is also three-body wear in the OCA and the CFA, these results reflect only one aspect concerning the clinical situation. They can only be used with the limitations of an in vitro study to predict clinical wear behavior of definitive restoration in load bearing cavities in permanent teeth.
Sliding wear of 19 commercially available composites and compomers
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