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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