Biomedical Engineering Reference
In-Depth Information
8.6 Erosion
For treatment of eroded tooth surfaces, carbonate
HA nanocrystals were synthesized by precipita-
tion from an aqueous suspension of Ca(OH) 2 by slow addition of H 3 PO 4 [86,87] . The nanocrystals
were allowed to form clusters of dimensions ranging from 0.5 to 3.0
m. They are quite similar as
compared to dentinal apatite crystals. Enamel surfaces etched with phosphoric acid for 1 min were
treated by aqueous slurries containing these experimental carbonate
μ
HA nanocrystals for 10 min
under in vitro conditions [86] and washed. After application of the nanoparticles to the etched
enamel surface, a coating of carbonate
HA is deposited on the enamel surface [86] . This coating
is less crystalline than native enamel apatite and consists of apatite mineral depositions which fill
the micro-rough surface pattern of the etched enamel [86] . Commercially available toothpastes con-
taining comparable HA nanoparticles have been shown to remineralize experimental erosive enamel
defects in vitro [33,63] . Despite these promising in vitro observations, the effects have to be con-
firmed by in situ or in vivo investigations considering the pellicle and the dynamic environment of
the oral cavity.
Another approach for treatment of the demineralized enamel surface is also based on HA nano-
particles, however with a smaller particle size of only 20 nm [40] . It has been shown by in vitro
experiments that adsorption of these nanoparticles onto the tooth surface strongly reduced the pro-
cess of erosive demineralization of natural enamel. This observation indicated that the 20-nm HA
particles themselves are comparatively resistant to dissolution in the acidic milieu which can be
understood by a nanodissolution model [40] . Briefly, this model suggests that active dissolution
pits cannot be produced on nanoparticles. Thus, the nanostructured materials will be kinetically pro-
tected due to their size and remain relatively stable even in case of undersaturated conditions [40] .
Therefore, not only repair but also prevention of enamel erosion might be enhanced by the applica-
tion of nanosized HA [40] .
However, concerning the protective effect of ACP
CPP-containing agents against dental ero-
sion, the published data are controversial [88] . On the one hand, it had been reported that applica-
tion of CPP
ACP paste is effective in preventing dental erosion produced by a soft drink in vitro
[88] . On the other hand, according to measurements of the surface nanohardness, tooth erosion
could not be prevented or repaired by CPP
ACP pastes in an in vitro cyclic erosion model regard-
less of the paste's fluoride content [88] .
Apatite nanoparticles or calcium phosphate nanocomplexes had been also applied to reduce
the erosive potential of acidic beverages such as sport and soft drinks [88] . Addition of 0.25%
or 0.5% of nano-HA to a low-pH sport drink (pH 2.96) will increase the pH (up to 4.38 or
4.63, respectively), thereby significantly reducing the erosive effect of the acidic drink [88] .
A follow-up study indicated that adding 0.25% nano-HA to Powerade sport drink could prevent
erosion in vitro [89] . Furthermore, addition of 0.2% w/v of CPP
ACP to commercially avail-
able soft drinks has been shown to significantly reduce the erosivity of these beverages under
in vitro conditions [90] .
In summary, based on the results from in vitro experiments it can be proposed that HA nanopar-
ticles are able to fill microdefects on the enamel surface and might modify the process of erosive
tooth destruction. However, up to now in vivo evidence for these effects is lacking.
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