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 ,
250
Stoma Edu J . 2017 ; 4 ( 4 ): 248-253 http :// www . stomaeduj . com