Biomedical Engineering Reference
In-Depth Information
8.7
Nanosized calcium fluoride
Calcium fluoride (CaF
2
) preparations are of significant interest in preventive dentistry due to their role
as labile fluoride reservoir in caries prophylaxis. Low concentrations of fluoride in the oral fluid in the
range of 0.1 ppm F
2
derived from dentifrices or mouth rinses have been shown to reveal a profound
effect on the progression of dental caries. However, the low salivary calcium concentration provides a
limited driving force for the formation of CaF
2
deposits. Nano-CaF
2
powder containing clusters of
10
15 nm sized crystallite particles has been prepared from Ca(OH)
2
and NH
4
F solutions using a
spray drying technique
[91]
. The advantage of this technique over conventional solution precipitation
methods is that the nanoparticles, once formed, are not subject to further washing, and thus maintain
the high surface reactivity, innate to nanosized particles
[91]
. Interestingly, the nano-CaF
2
powder dis-
played much higher solubility and reactivity than its macrosized counterpart
[91]
. Thus, nano-CaF
2
might be used as an effective anticaries agent in increasing the labile fluoride concentration in the oral
fluid, thereby enhancing the process of remineralization. The nanosized calcium fluoride will be more
effectively retained in the mouth due its high affinity to oral substances, thereby serving as a long-
lasting source for ambient fluoride than that produced by currently used NaF products
[91]
. Results of
a pilot in vivo study indicate that a 1-min application of this nano-CaF
2
rinse produces a significantly
greater 1-h postrinse salivary fluoride content (158
μ
mol/L) than a NaF rinse (36
μ
mol/L)
[91]
.
8.8
Dentin hypersensitivity
Dentin hypersensitivity is a widespread and increasing problem especially in the dentate elderly
population. Due to the loss of the root cement, the dentinal tubules are exposed. Liquid movement
in these tubules induced by cold and hot beverages or osmotically active substrates provokes irrita-
tion of the subodontoblastic plexus
[10]
. According to this hydrodynamic theory, some kind of bio-
mimetic sealing of
the dentin surface and especially of
the open tubules is demandable.
Carbonate
HA nanocrystals with size, morphology, chemical composition and crystallinity similar
to that of dentin were synthesized and are available as preparation for clinical application
[92]
.
TEM (transmission electron microscopic) analysis indicates that the nanocrystals present a length
ranging from 20 to 100 nm and a thickness ranging from 5 to 10 nm
[92]
. It has been shown by
in vitro experiments that patent dentinal
tubules can be sufficiently closed by application of
carbonate
HA nanocrystals for 10 min
[92]
. These in vitro effects were confirmed in a double-blind,
randomized clinical trial with 70 patients
[93]
. A dentifrice based on zinc carbonate
HA nanocrystals
was adopted at regular intervals and repeatedly applied. It reduced dentinal hypersensitivity signifi-
cantly and yielded greater improvement than a conventional fluoride-based preparation, if an airblast
test was conducted
[93]
. It might be postulated that the preparation also obturated the openings of the
dentinal tubules in vivo. In contrast, singular application of CPP
ACP (Tooth-Mousse) revealed insuf-
ficient effectiveness in treating hypersensitivity in a clinical study, and the therapeutic effect was short
termed
[94]
. Accordingly, repeated application of the material is necessary. Besides these preparations
which are available on the market, other experimental preparations were tested in vitro. A composite
material based on nanostructured calcium phosphate and collagen yielded successful sealing of dentin
