IN VITRO WEAR OF 4 DIFFERENT UNIVERSAL COMPOSITES
Figure 3a. Wear facette of Filtek Z 350 after 120.000 cycles. Note the white line perpendicular to the direction of the wear
Figure 3b. Wear facet of Tetric N-Ceram after 120,000 cycles
Figure 3c. Wear facet of Herculite Precis after 120,000 cycles
Figure 3d. Wear facet of Charisma Opal after 120,000 cycles. Note the multiple white lines perpendicular to the direction of the wear scratches pressed under constant force onto a rotating disk 26 or oscillated against a flat surface. 27 Using a pin on block approach, scientists have tried to simulate chewing movements by having an antagonist lowered on a surface, then slid sideways under load, disengaged from the load and being moved to starting point to begin the next cycle. 28 Such devices are the Willitec Chewing simulator, 29 the Minnesota artificial mouth, 30 the CoCom Chewing simulator, 31 the TE88, 32 the Tokyo Medical Dental University Chewing simulator 33 or the Mechatronik Chewing simulator used in the present study. We decided to use a Pin on block chewing simulator, because the load and movements are well controlled and there is no third body to deal with, which makes interpretation of the results less problematic. Chewing forces are reported in the literature to vary from 20 – 120N. 34 Most researchers use 5 Kg( 49N), which has been reported by Gibbs et al. 35 to be the average chewing force under normal function. For the present study, 6 kg( 58.9N) was chosen, with the idea to be able to better discriminate between the materials having a slightly higher load. However, the higher load apparently was incapable of discriminating the wear rate among the four material groups. Therefore, 5 kg load should be adopted as a standard for future study for ease of comparison. All wear facets exhibited typical grooves resulting from abrasive wear by harder antagonists with unique feature for each material. For Charisma( Fig. 3d), the white lines common for that group of material are not cracks on the surface but wear debris being folded perpendicular to the direction of horizontal movement. Some worn surfaces of Tetric-N-Ceram samples appear to have a round tab to the oval wear spot( Fig. 3b). The likely cause is that samples had shifted in the
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