Biomedical Engineering Reference
In-Depth Information
microscale can be generated, their formation often requires high pressure, or is at least very time
consuming. All these experiments are still on the pure in vitro level, and the entire regeneration of
micronsized defects or even of small cavities is not accomplishable at the moment.
Busch et al.
[107,108]
have studied fluoroapatite formation in gelatin matrices. It could be
shown that the morphogenesis of hierarchically ordered spherical aggregates of fluoroapatite/gelatin
nanocomposites starts from elongated hexagonal prismatic seed crystals. At later stages of minerali-
zation, fractal branching and the development of growing dumbbell states were observed. Based on
these results, a technique was developed to form dense fluorapatite layers on the human enamel
surface, using the diffusion of calcium ions from solution into a glycerin-enriched gelatin gel con-
taining phosphate and fluoride ions at 37
C
[107,108]
. To induce mineralization of fluorapatite on
the tooth surface, samples were immersed in a neutral calcium solution
[107,108]
. The similarity of
the biomimetically grown mineral layer with the natural enamel suggests that the experimental
setup is an attractive model for resembling mineralization of enamel, but the formation rate of
approximately 500 nm/day is very low. Interestingly, one time overnight application of this BIMIN
in patients for at least 8 h caused—according to the authors' interpretation—deposition/precipita-
tion of a smooth enamel-like layer on the tooth enamel under in vivo conditions
[97]
.
Even if the formation of hierarchically structured and durable minerals would be possible, there
is still the challenge of bonding this biomineral tenaciously to the surrounding dental hard tissue. It
has to be pointed out that the physiological binding between dentin and enamel has not been under-
stood in detail until now
[30]
.
8.10
Discussion and clinical recommendations
The research on the application of nanobiomaterials in preventive dentistry is just beginning, and
there are numerous open questions, though there are many promising ideas. At the moment, most
of these novel approaches are at the theoretical level or at the experimental stage, and only few pre-
parations are already available on the market
[9]
. However, it is not evident at the moment whether
the adoption of these nanomaterials means an improvement in preventive dentistry as compared
with conventional dentifrices or mouthwashes. This has to be proved in broad clinical studies. If
this would be the case, biological and biomimetic nanomaterials without adverse effects could
potentially substitute fluorides. This would be of special interest for young children to improve car-
ies prophylaxis without running the risk of dental fluorosis. Dental fluorosis occurs in a dose-
dependent manner, and low-dose fluoridated toothpastes suitable for children are of limited efficacy
for prevention of caries
[109
111]
.
The nanomaterials' mode of action is based on surface interactions. This applies for the effects
on biomineralization as well as for the modulation of bioadhesion
[9]
. In this context, it has to be
pointed out that many aspects of these physiological processes are not even approximately under-
stood. Accordingly, extensive basic research is necessary in this field. One example are fluorides—
their clinical efficacy has been proven but the in vivo interactions are not fully understood until
now
[112]
. For conventional as well as for nanotechnology based preparations, it is necessary to
understand their mode of action besides the evaluation of clinical efficacy. This is also of relevance
for rating the toxicology of the very different materials. It is very difficult to assess potential
