Tribological Behavior of Dental Restorative Materials - Dental Biotribology - page 142

Fig. 6.1 Steady-state values
of the coeffi cient of friction
(COF) for the fi ve tested resin
composites under different
kinds of lubrication [ 22 ]
For most resin-based restorative materials, water has a negative impact on those
mechanical properties. However, the oral cavity is a relatively wet environment, and
its relative humidity ranges from 78 % to 90 %. The resin matrices can decompose
after water absorption; this energy is transferred through the bonded interface to the
inorganic fi ller, causing destruction at the fi ller-matrices interface and in turn a
decrease in the material's durability. Previous studies have suggested that a water
environment signifi cantly enhances the three-body wear, especially for the compos-
ite resin made of silica fi llers [ 28 ]. The silicon-oxygen bonding was interrupted,
causing materials to be more vulnerable to damage from stress. In addition, resin-
based restorative materials may suffer from corrosive wear in a relatively wet envi-
ronment, which is often ignored in experimental abrasion studies [ 4 ]. Corrosive
wear is initiated by water-induced decomposition; when water penetrates through
the matrices, fi llers, and other weak links, the fi ller-matrices interface degrades,
resulting in a fl accid layer, which is easily exfoliated upon stress caused by chew-
ing. Depending on the environment and timing, the thickness of the fl accid layer is
mostly determined by the permeability of the resin complex [ 29 , 30 ].
The oral chemical mediator, such as saliva, food, and drink, plays an extremely
important role in the tribological behavior of resin composites. An acidic environ-
ment was found to reduce the wear resistance of composite resins, and ethanol
might soften the resin matrix, undermining the interfacial bond between the fi ller
and the matrix [ 29 ]. As a result, the wear resistance of resin material was reduced,
and the wear loss increased. However, the results of our recent research suggested
that artifi cial saliva and a cola soft drink could play important roles in lowering the
friction coeffi cient and wear loss of dental composites, as shown in Figs. 6.1 and 6.2
[ 22 ]. The cola soft drink was found to display a better lubrication effect. The degree
of sensitivity to changes in lubrication conditions varied with different dental
composites.