NANOINDENTATION OF TOOTH TISSUES - Nanoindentation with Biological Applications - page 257

3.6. Nanoindentation measurements on cementum

Nanoindention investigations of cementum generate the baseline
knowledge of the mechanical properties of sound cementum and allow
for an understanding of abnormal behavior due to various pathologic
conditions. It is anticipated that changes in the mechanical properties of
cementum may be related to its mineral levels and porosity resulting
from cellular activities surrounding the root.
The mechanical properties of cementum have been shown to vary
significantly due to the local anatomy and cementum type ( Table 8-4 ) .
Unlike enamel and dentin, only limited data on cementum are available
in the literature. Poolthong 36 reported that cementum has a hardness
equivalent to dentin, but lower elastic modulus. The hardness and elastic
modulus of the apical third range from 0.8 - 0.9 and 9.2 - 9.4 GPa,
respectively, while the cervical two third were 1.4 - 1.6 and 11.5 - 12.1
GPa, respectively. 36 Using a 20 m spherical indenter, Malek and

coworkers 75 were able to investigate the mechanical properties of the
unpolished surfaces of the outer cementum. They found that the
mechanical behavior of the outer cementum is root site dependant
ranging from 0.18 - 0.6 and 1.7 - 10.8 GPa, for hardness and elastic
modulus respectively, which are noticeable lower than the previous data.
The outer surface has more organic material as a result of the presence of
Sharpey fibers compared to the rest of the cementum. 22 Due to the
enriched presence of protein and collagen fibers, cementum is highly
viscoelastic, especially when hydrated. 76 The cemento-dentinal junction
was shown to have large quantities of proteins including collagens that
contribute to hydration and significantly reduced the mechanical
properties. It has decreased mechanical properties compared to the
adjacent hard tissues, cementum and dentin. 77
The mechanical preparation required for nanoindentation as well as
the storage media were shown to affect the mechanical properties of the
cementum measured. It was suggested that an ultra-sectioning technique
using a microtome generates a flat surface of cementum with the
advantage of clear visualization of its microstructure. The later is not
evident in polished specimens possibly due to the smear layer generated
from polishing procedures. 76 As a result more diverse data are obtained

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