IN VITRO WEAR OF THREE BULK FILL COMPOSITES AND ENAMEL
Figure 1. Total wear of 3 Bulk-fill composites and enamel( control) as well as the steatite antagonists after 12 x 10 5 cycles. Letters below the columns indicate Tuckey’ s group.
while in the former experiment the load was 58.86 N, which seems to be too much since fractures of the samples had occurred. It is difficult to determine the actual chewing force under function. Literature data show high variability( 20 – 120 N). The decision to use 49.05 N was based on a paper by Gibbs et al. 26 who reported that value to be the average chewing force under normal function. To measure the wear facets a laser scanner was used. Heintze et al. 27 have indeed shown that there was no significant difference between a mechanical or optical profilometer and a laser scanner. As in a former experiment, 25 the wear behavior in the first 5x10 3 cycles was inconsistent and had a higher variability. This is a known effect called“ running in”. Therefore, the analysis of the data began at 5x10 3 cycles. From that point on, the wear development was linear with an excellent fit( R2 > 0.98; Fig 2), which confirms the findings from Heintze et al., 21, 27 Wang et al. 28 and Matias et al. 25 It allows to calculate a wear rate(= volume loss / cycle) which is best expressed in µ m3 / cycle( Table 3). It is thus possible to make direct comparisons independently from the number of cycles run. Nevertheless, it is recommended to run at least 1.2x10 5 cycles, to exclude an unnoticed change in the slope of the wear rate. The latter may be in fact due to fatigue-induced catastrophic failure, as we have seen with a glass ionomer cement( unpublished data). 4.2. Results With the exception of QuiXX, the results of this study can confirm Heintze’ s, 21, 27 and Matias’ s et al data 25 that the antagonist’ s wear is about half the wear of the composite materials( Fig. 1). This may be explained by a different composition of QuiXX compared to the other composites, especially in its glass filler. That filler seems to be less hard than the fillers used in the other composites, thus being easier abraded, but at the same time being gentler with the antagonists. QuiXX was worn three times more than the other two materials( p < 0.001). Looking at the composition of QuiXX as indicated in the directions for use, one can see that besides UDMA and TEGDMA, Di-
Figure 2. Linear regression of wear vs cycles for the tested composites and enamel( p < 0.0001). Superscript letters next to the name of the materials in the legend show Tuckey’ s group.
and Trimethacrylate resins, also a Carboxilic acidmodified dimethacrylate resin has been added. In addition, silanated strontium aluminum sodium fluoride phosphate silicate glass was used as filler. Furthermore, the material is delivered in a blister, obviously to prevent a ionomeric reaction between the carboxylic acid hydrolyzed by water that may diffuse into the material and the glass, which would make the material harden in its package The manufacturer claimed fluoride release as well. Both facts lead to the suspicion that compomer technology was used for that product, and that could at least partly explain the increased wear of that material. 29-32 X-tra fill is characterized by the manufacturer as a hybrid composite with 70.1 % vol filler content and BiS-GMA, UDMA, BHT and TDMA as resins. Multimodal filler distributions with prepolymerized composite particles have been used for that material. Similar composition can be found in Tetric N Ceram Bulkfil, which could explain the same wear behavior. It is not known by the authors, if Voco uses similar filler technology. Looking at the antagonist wear one may speculate that the filler used by Voco might be of a conventional type, and in average coarser than the one used in the bulk-filled material by Ivoclar Vivadent. An interesting fact, the composite with the highest wear( QuiXX) has worn the antagonists the least and the composite with the least wear( Xtra) has worn the antagonist the most. This could be partly explained by the particle size, particle size distribution, the properties of the fillers( composition, hardness) and the filler load. If the particle distributions and the composition of the fillers used were known, this statement could be verified. Besides showing the least wear, enamel also showed the least antagonist wear. This can be explained with the structure of enamel, which is very dense. The size of the hydroxyapatite crystals is much smaller than the ones of the fillers used in the tested bulkfill composites. Once polished, the enamel surface is very smooth and generates low friction. Since there are considerable differences in the
Original Articles
Stomatology Edu Journal
251