IN VITRO WEAR OF THREE BULK FILL COMPOSITES AND ENAMEL
Original Articles
Round No. 1 2 3 4 5 6 7 8 9
Table 2. Number of mechanical cycles and time intervals for scanning.
10 11 12 13 14 15 16 17
Table 3. Wear rate of the tested materials. Same superscript letters mean same statistical group( p < 0.001).
Material
Enamel X-tra Tetric QuiXX
No. of cycles
1x10 2
4x10 2
5x10 2
1x10 3
3x10 3
5x10 3
1x10 4
1x10 4
1x10 4
1x10 4
1x10 4
1x10 4
1x10 4
1x10 4
1x10 4
1x10 4
1x10 4
Wear rate( x10 3 µ m 3 / cycle) Mean ± SD 2.23 ± 0.28 4.64 ± 0.41 5.38 ± 0.63 11.19 ± 1.12
Total
1x10 2
5x10 2
1x10 3
2x10 3
5x10 3
1x10 4
2x10 4
3x10 4
4x10 4
5x10 4
6x10 4
7x10 4
8x10 4
9x10 4
1x10 5
1.1x10 5
1.2x10 5
Stat. Group
3. Results One-way ANOVA of the volumetric wear of the composites and enamel, and respective wear of the antagonists after 1.2x10 5 load cycles showed there were statistically significant differences between the four materials tested and the respective antagonists( p < 0.0001). The results of Tukey’ s wear ranking for each material and respective antagonist along with the mean and standard deviation of the wear are shown in Fig 1. With exception of QuiXX, the antagonist wear was less than half of the wear of the materials. The wear-loading cycle plots of each test showed that a linear correlation could be identified between volumetric wear and number of load cycles in the range of 5x10 3 to 1.2x10 5 load cycles. Linear regression was performed for each test and the slope of the line was considered as the wear rate of each individual test. The degree of fit of linear regression
A B B C was greater than 98 % for each specimen. ANOVA of the wear rates showed there was statistically significant difference between the tested materials( p < 0.0001). Fig. 2 shows the plot of mean wear vs the number of loading cycles. The straight lines associated with each material are the result of linear regression based on the mean wear values of 8 specimens for each material. The mean wear rates along with the standard deviation and Tukey’ s ranking are shown in Table 3. The wear behavior of Tetric N Ceram Bulk Fil and X-tra fil were almost identical, while QuiXX showed statistically significant more wear.
4. Discussion 4.1. Methodology The new bulk fill materials selected for this study were from the group of the high viscosity ones, designed to be used as a regular filling material, but being easier and faster in their application, and thus being exposed to the occlusal stress of antagonists. When looking at mechanical properties of composites, it is important to make sure that the composite is well cured, which means that the polymer network has reached its optimal degree of conversion. Thus one can expect the best possible mechanical properties of the material. Therefore, in this study it was decided to use the curing times recommended by the manufacturers. Furthermore, the total energy delivered to the composites was determined to be 14.5 J / cm 2. It is in agreement with the recommendations found in literature, showing that to adequately cure resin composites of 2-mm thickness, between 12 and 24 J / cm 2 16, 17
of energy is needed. Wear is a very complex process; therefore, there is no single standard procedure for wear testing. Many wear testers use different approaches; however, lately two-body wear with a sliding component and preferably computer controlled forces and movements are the preferred approach. 18 Since every wear tester has a different operational approach 18 different antagonists regarding material, shape and dimensions are used. 19-24 In the present study steatite antagonists with a spherical shape and 6 mm diameter were used due to their hardness, reproducibility, standard form similar to a cusp, and easy availability. Furthermore, most chewing simulator users prefer these antagonists which allow better comparisons with other studies. Standard parameters were used for operating the chewing simulator. Therefore, our data are well comparable for instance with the ones obtained by the Ivoclar Vivadent group in Schaan. 13 The slight difference in the measured wear between the Ivoclar group and the values presented in this study may be explained with the different antagonists used. In the present experiment spherical steatite antagonists were used, while Ivoclar Vivadent used standardized Empress( leucite ceramic) antagonists which had the shape of a molar cusp. 13 The wear values obtained in this experiment were almost half as high as the ones obtained with similar composites in a former experiment using the same chewing simulator. 25 This difference may be explained by the different loads used. In the present experiment 49.05 N load was used as others do,
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Stoma Edu J. 2017; 4( 4): 248-253 http:// www. stomaeduj. com