Nanobiomaterials in Preventive Dentistry - Nanobiomaterials in Clinical Dentistry - page 168

tubules in vitro [95] . Another in vitro study showed that tenacious occlusion of the dentinal tubules
could be achieved with nanosized carbonate apatite [96] .
Currently, Guentsch et al. (2012) [97] could provide evidence that a biomimetic mineralization
system (BIMIN, Heraeus Kulzer, Wehrheim, Germany) based on the diffusion of calcium ions
from solution into a glycerine-enriched gelatine gel containing phosphate and fluoride ions is as
effective as the clinically established application of a glutaraldehyde containing agent (Gluma) in
treatment of patients suffering from dentin hypersensitivity [97] . SEM (scanning electron micro-
scopic) analysis performed on replica models which had been produced from impressions of the
patients' teeth demonstrates that a single BIMIN application (over 8 h) caused deposition of a
mineral-like layer on the dentinal surfaces and occlusion of the dentinal tubules and that this layer
(effect) was stable over the observation period of 12 months [97] .
8.9 Regeneration of dental hard substances
Several recent studies have documented the formation of enamel-like structures from mineral solu-
tions under ambient conditions. Various strategies for self-assembling one-dimensional HA crystal-
lites or nanorods resulting in an enamel-like organized rod array suprastructure have been
described [9,32,98,99] . However, only very thin layers at the micron- or even nanoscale are
obtained; the process of guided mineral formation is quite time consuming. In general, there are
two different approaches to achieve these mineral layers: with and without the application of
organic scaffolds [100] . Especially for the formation of thicker structures, these scaffolds seem to
be necessary in many models [100] . Controlled binding and assembly of proteins onto inorganics is
the core of biological materials science and tissue engineering [101] .
A typical scaffold protein used widely is amelogenin. It has been suggested that this predomi-
nant enamel matrix protein has self-assembling properties, thereby facilitating the organization of
organic nanostructures in developing enamel crystallites [102,103] . Higher order HA nanocrystals
were observed, if crystal formation emerged from aggregates of nanospheres with HA cores and
amorphous calcium phosphate shells [104] . Thereby, enamel-like HA architecture was achieved in
the presence of amelogenin or glycine, respectively [104] .
In a follow-up study, an oriented amelogenin fluoridated HA layer could be precipitated on
etched enamel indicating a synergistic interaction of fluoride and enamel [105] . This cooperating
role of amelogenin and fluoride ions in formation of oriented apatite-like crystals was also proven
in a cation-selective membrane system as a model for enamel formation [106] . Under in vitro con-
ditions, amelogenin accelerates HA nucleation kinetics, thus decreasing the induction time in a
concentration-dependent manner [32] . Hierarchically organized apatite microstructures are achieved
by self-assembly involving nucleated nanocrystallites and amelogenin oligomers and nanospheres
at low supersaturation and protein concentrations. This in vitro observation provides direct evidence
that amelogenin promotes apatite crystallization and organization [32] .
It has been demonstrated recently by in vitro experiments on apatite nucleation in the presence
of amelogenin that hierarchical self-assembly, by a nucleation-growth pathway, gives rise to a
remarkably high degree of cooperativity, mimicking the self-organized microstructure of tooth
enamel [32] . However, also with the aid of organic structures only very thin layers on the