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IN VITRO WEAR OF 4 DIFFERENT UNIVERSAL COMPOSITES

Table 2. Settings of Chewing Simulator

Load

Upstroke

Downstroke

Horizontal movement

Upward speed

Downward speed Horizontal speed Frequency

Thermocycling

Direction

6 Kg

2 mm

1 mm

0.7 mm

60 mm / s

60 mm / s 40 mm / s 1.2HZ

5 ° C-55 ° C; 116 s / cycle; total 860 cycles

Back and Forth

Figure 2. Mean wear of the four groups of composites up to 120,000 cycles. The respect straight for each material group represents the results of linear regression of wear between 2,000 and 120,000 cycles( R 2 > 0.99).

Table 3. Wear of composite and respective Steatie antagonists at 120 K cycles

Materials

Wear of composite, mm 3 Wear of Steatie antagonist, mm 3 Composite wear rate, μm 3 / cycle

4. Discussion

The wear of all composites investigated were in a linear relationship with respect to the number of chewing cycles after wear-in period and thestatistical analyses showed that there is significant difference among the composites in wear rate at p = 0.0448 and no significant difference( p = 0.1183) in final volumetric wear. Therefore, the first hypothesis was accepted and the second hypothesis was rejected. Various wear testers have been used to investigate the wear behavior of composites since their introduction. Wear simulation is a very complex process and over the last 40 years scientists have tried to build devices capable of simulating the wear of dental restorative materials. The outcome is heavily influenced by a multitude of factors, such as wear type reflected by the wear testing equipment, the load used, the antagonist material and shape, the use of thermocycling and finally of the material that is worn. One family of wear devices uses 3-body wear. This means that a third body, mimicking food, is forced between the two bodies which stress the material with wear. Such devices are the ACTA wear machine, 18 the Oregon Health Science University( OHSU) machine, 19 the Alabama wear simulator, 20 and the CW3 of Peking University 21 and multiple toothbrushing machines. 22, 23 Common to these devices is the introduction of a third body in suspension that affects the results heavily and it is not known which quality of the third body would be clinically relevant for wear of the occlusal surface. The ACTA machine can be run as a two body wear tester as well, having the two wheels run in contact. Osiewicz et al. 24 have reported differences in wear between 1 and 62.5 fold more wear for moving from 2-body wear to 3-body wear using the same abrasive, but different material combinations( 4 composites for antagonist wheel and 6 composites for other wheel). Another approach is to use a two body wear. A simple and widely used device is the Taber abraser, 25 which comprises two abrasive wheels engaging on a rotating disk under constant pressure. Two body wear can be induced as a pin on block principle where a pin( antagonist) is