Biomedical Engineering Reference
In-Depth Information
of the plant's leaves only sporadically comes in contact with water, whereas the teeth are rather in
a marine environment, which means completely different requirements. However, there are other
unexplored or even undetected strategies in the fauna and the flora which could also mean new
stimuli for dental research. These biological phenomena of self-cleaning surfaces are usually based
on certain nanoscaled surface textures as well as on a specific chemical composition
[75]
. These
biological surface structures with a hierarchical nanostructure may serve as archetype for the estab-
lishment of new easy-to-clean surfaces in preventive dentistry. However, this requires further
research in the field of bionics. Presumably, a combination of special physical surface structures
and chemical surface coating is the key to biomimetic and therewith biological biofilm manage-
ment on the nanoscale.
8.5
Effects on de- and remineralization
De- and remineralization are critical to the formation of dental caries and tooth erosion. Both
demineralization and remineralization occur on the tooth surface, and thus can be considered as
highly dynamic processes, characterized by the flow of calcium and phosphate out of and back into
the tooth enamel. Fluoride promotes remineralization and this has been suggested as the main
mechanism by which fluoride protects the teeth. The essence of the remineralization concept of
demineralized tooth surfaces might be achieved by simultaneously supplying calcium, phosphate,
and fluoride ions to the teeth in order to induce formation of various apatites that remineralize and
strengthen the tooth. Therefore, intensive investigations on the remineralizing potential of new
toothpastes and fluid formulations based on nanotechnology are in progress. Nanomaterials might
optimize the process of remineralization. On the one hand, they could fit to the nanoscopic defects
of the enamel which are to be reconstituted; on the other hand, they can serve as carriers for remi-
neralizing ions with high affinity to the pellicle. Thereby, a supersaturation at the tooth surface or
in the pellicle layer would be achieved; this means a slow-release depot.
Biomimetic HA nanocrystals have been designed and synthesized in order to facilitate reminera-
lization of the altered enamel surface. HA nanocrystals provide excellent biological properties such
as biocompatibility, lack of toxicity, as well as lack of inflammatory and immunological responses.
In early in vitro studies, the effects of nano-HA on enamel remineralization were evaluated in static
models
[50,76
78]
. These pilot studies reveal that nanosized HA possess a certain potential to
remineralize incipient caries lesions. More recently, the potential of an experimental 10 wt% nano-
HA aqueous slurry (HA crystals with a length of 60
80 nm and a diameter of 10
20 nm) or a
toothpaste containing 20 wt% clustered zinc carbonate
nano-HA to remineralize initial caries
lesions under dynamic pH-cycling conditions in vitro has been demonstrated
[33,79]
. Detailed
investigations indicated that application of nanosized HA under these in vitro conditions promotes
preferential mineral deposition in the outer layer of the initial caries lesion and had a limited capac-
ity to reduce lesion depth or to increase the mineral content in the body of the lesion
[33,79]
.
Interestingly, the remineralization effect strongly depends on the pH during application of the nano-
sized HA: under neutral conditions, full remineralization effect is not achievable, while under
acidic conditions (pH of 4.0) nano-HA can significantly increase the depth of penetration and the
extent of remineralization of artificial incipient caries lesions
[79]
.
