Biomedical Engineering Reference
In-Depth Information
fulfill the mechanical requirements
[42,43]
. However, an important clinical problem related to carbon
material
incorporated products in oral application is the poor esthetics because of their black color.
As a phenomenon, with the fast development of nanocomposites application in dentistry
[44]
,sparse
report can be found on using CNTs/CNFs in oral cavity.
Zhang et al.
[45]
have developed a process to improve the application of SWCNTs in dental
resin-based composites. To achieve uniform dispersion of SWCNTs in matrix, they deposited a thin
shell of nano-SiO
2
onto the oxidized surface of SWCNTs, and then surface modified this
SWCNTs/SiO
2
with organosilane (allyl triethoxysilane, ATES). Finally, the authors blended this
SWCNTs/SiO
2
/ATES into a resin monomer. Although the composite resin specimens with the
modified SWCNTs exhibited improved flexural strength, the nanocomposite resin specimens pre-
pared as described above were still grayish black, which was disharmonious with the color of natu-
ral teeth and was therefore not suitable for direct oral use. The authors suggested the application of
other inorganic additives such as sol-gel-based opalescent fillers or chromophoric xerogel pigment
particles to achieve the desired esthetic requirements. In one of our previous studies, a composite
fibrous network consisting of poly(
L
-lactic acid) (PLLA), MWCNTs, and HA (PLLA/MWCNT/HA)
was fabricated to develop novel guided tissue regeneration (GTR) membranes for periodontal
defects
[34]
. Its unique feature is the selective promotion of attachment and proliferation of
PDLCs, while inhibition of GECs making it a potential candidate for GTR application, which is
suggested as the inner layer of functional-graded membranes to face the periodontal defects directly
(
Figure 18.6
).
For application in implant dentistry, CNTs also can be used as a coating on titanium implants.
An earlier study showed that osteoblasts synthesized more ALP and calcium on the surfaces of non-
functionalized MWCNTs grown from anodized nanotubular titanium surface than on anodized
nanotubular titanium without MWCNTs and currently used unanodized commercial titanium sur-
face for implant manufacturing
[46]
. This study concluded that bone growth could possibly be
enhanced on currently used titanium implants coated with MWCNTs. In a recent study, titanium
plates were aminated and coated with collagen. Carboxylated MWCNTs were coated onto this
collagen surface and mouse osteoblasts were cultured on the nanotubes. The results of this study
showed increased cell proliferation and adhesion on the MWCNTs
[47]
. The reason for these
results was thought due to the similarity of the dimensions of SWCNTs/MWCNTs to that of the tri-
ple helix collagen fibers in bone, which makes these nanotubes ideal candidates as substrates for
bone growth and as a coating on titanium implants.
Another possible application of CNTs/CNFs in dentistry might be the use of CNT/CNF-rein-
forced ceramic to improve fracture toughness. Over the past three decades, considerable research
has been devoted to the development of HA acting as a coating material for titanium or other
metals used as implants. The metal substrates are able to provide mechanical properties, while the
biocompatibility is usually rendered by HA coating. Although plasma-sprayed HA coatings have
successfully improved the aspects of bone attachment and integration of the implants, the long-term
stability of these coatings is still a very challenging issue since these coatings tend to have uncon-
trollable dissolution and sometimes exhibit insufficient fracture toughness and bond strength to the
metal substrate
[48,49]
. Due to their outstanding mechanical properties and excellent chemical sta-
bility, introducing small amounts of CNTs to ceramic are envisioned to produce tougher ceramic
materials
[50
52]
. Kobayashi et al.
[51]
used CNFs as reinforcement for HA composites. The frac-
ture toughness values for CNF/HA composites were around 1.6 times higher than those obtained
