NANOINDENTATION OF TOOTH TISSUES - Nanoindentation with Biological Applications - page 240

2.3. Structure of cementum
Cementum is a thin layer of dental calcified tissue that covers the tooth
root by firmly adhering to dentin. Similar to bone tissue, it consists of an
inorganic component (65 wt%) mainly comprising hydroxyapatite, an
organic component of collagen type I (23 wt%) and the remainder is
water (12 wt%). Based on the presence or absence of cells, cementum is
grouped into cellular and acellular cementum. The cellular cementum
develops a relatively thicker layer on the apical third of the root
particularly the outer region, while the acellular cementum, which is
more highly calcified, but structureless, covers the cervical two-thirds of
the root. The fibers found in cementum could be extrinsic (Sharpey)
fibers from periodontal ligaments, or intrinsic fibers originating from
cementoblasts, or both types of fibers. The cementum facilitates the
attachment of collagen fibers of periodontal ligament to tooth root,
whereby the tooth is physically maintained and supported in an alveolar
socket. 27 Cementum responds to mechanical loadings to which the tooth
is subjected, and is continuously modified through life. Excessive forces
may lead to a pathological condition resulting in either a resorption or a
hyperplasia of the cementum. Dental disease such as caries can affect the
cementum as well as other pathologic conditions involving dental pulp
and periodontium. Chemical substances from dental procedures may also
initiate pathosis in the cementum.
3. Nanoindentation Behavior of Teeth
As enamel is the outmost layer of tooth, its mechanical properties are
more important and significant to us in developing restorative materials.
Moreover, the implication of its hierarchical microstructure in regulating
mechanical behaviour of biocomposites has attracted considerable
attention of materials scientists. Therefore, more nanoindentation
investigations have been done on enamel than dentin. In the following
sections, we will take enamel as a sample to summarize and discuss the
nanoindentation of teeth.