NANOINDENTATION OF TOOTH TISSUES - Nanoindentation with Biological Applications - page 263

Similarly, another nanoindentation mapping showed the hardness and
elastic modulus of hypomineralized region ranged from 0.07 - 1.7 GPa
and 3.2 - 40.9 GPa, respectively, which are less than a quarter of that of
the normal enamel. 89 It was also suggested that this reduction is not only
due to variations in mineralization, but more likely from differences in
the apatite crystalline and crystal orientations of the hypoplastic enamel.
Moreover, a newly published report showed that hypomineralized
enamel also showed a size effect on nanoindentation elastic modulus,
as described in Section 3.1 of this chapter, but the decreasing trend
was more significant than sound enamel. 90 The corresponding TEM
observation illustrated thicker interrod structures and higher levels of
organic content surrounding the HAP crystals within both rod and
interrod regions. 90 By employing Spears' finite element model, the
inferior mechanical properties can be reasonably explained in respect of
the microstructure of the hypomineralized enamel.
4. Dental Applications of Nanoindentation Techniques
4.1 . Evaluation of dental materials
With the technique of nanoindentation, small regions of material can be
tested accurately. Due to this advantage, the technique has been
employed in dental material development, evaluation and selection. A
good example is the increasing reports on the measurement of dental
composite materials with nanoindentation. 91-98 An investigation on fiber-
reinforced composites tested the mechanical properties of reinforcement
fibers and polymer matrix separately and reported the influence of water
storage. 98 The effects of coupling agents on hydroxyapatite (HA) before
incorporating into polymer matrix to form bioactive composite materials
were investigated with nanoindentation, 99 in which the hardness and
elastic modulus of small HA particles, the polymer matrix and the
particle-matrix interface were tested and reported separately. Different
surface finish methods were also compared with nanoindentation on
dental composite materials. 100 Nanoindentation also helped in the
evaluation of different coatings on dental alloys, systems that have a
range of potential dental applications. 101