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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