Biomedical Engineering Reference
In-Depth Information
To the best knowledge of the authors, up to now only one randomized, double-blind, cross-
over, in situ study has been published concerning the efficacy of nano-HA dentifrices on caries
remineralization and demineralization
[51]
. Demineralized enamel specimens were exposed
to dentifrices containing 5% or 10% nano-HA, or 1100 ppm fluoride, respectively, via an
intraoral appliance worn by 30 adults over a 28-day period. Treatment with all three dentifrices
caused significant reduction of the lesion depth and extent of demineralization detected at base-
line. In addition, no demineralization occurred in sound enamel specimens exposed intraorally
over 28 days, while using the 10% nano-HA toothpaste. From these in situ data, the authors con-
cluded that a nano-HA containing dentifrice canbeaneffectivealternativetofluoridetooth-
pastes
[51]
.
Also CPP
ACP nanocomplexes have been tested with respect to remineralizing properties, and
considerable effects were observed. For this preparation, not only in vitro but also clinical data are
available
[11,80
82]
. In particular, a special chewing gum has been tested in vivo
[81,82]
.
Remarkably a clinical 2-year-study showed that application of a chewing gum containing
CPP
ACP significantly diminished the progression of carious lesions and promoted regression of
initial proximal carious
lesions. More than 2500 children were enrolled in this project.
Furthermore, CPP
ACP has been combined with fluoride to enhance the remineralizing properties
[34,83,84]
.
Most studies focus on the remineralization of enamel. However, the remineralization of demi-
neralized dentin is even more challenging, as it represents a biological compound structure with
inorganic and organic components. The organic matrix is mainly composed of type-I collagen
fibrils forming a three-dimensional matrix that is reinforced by HA nanocrystallites. Though demi-
neralized collagen fibrils may serve as some kind of scaffold for mineral crystallites in the reconsti-
tution of the dentin, they are quite prone to proteolytic degradation if exposed to oral fluids.
However, remineralization of carious dentin has as its ultimate goal the reestablishment of the func-
tionality of the affected tissue
[31]
.
Remineralization of dentin can occur either by precipitation of mineral between collagen fibrils
or functionally bound to its structure
[31]
. Therefore, simple precipitation of mineral into the loose
demineralized dentinal matrix means an increased mineral content but may not necessarily provide
an optimal interaction with the organic components of the dentin matrix
[31]
. Partial recovery and
remineralization of human carious dentin were achieved in vitro using colloidal HA and
β
-trical-
cium phosphate over a period of 10 days
[85]
. Treatment with
β
-tricalcium phosphate yielded better
reconstitution of the dentin's micromechanical properties. The
-tricalcium phosphate is assumed
to be partially dissolved in the acidic carious regions recovering intermolecular collagen cross-
linking by combining with corresponding intrafibrillar sites. However, intrafibrillar remineralization
of dentin is difficult due to the denaturation of collagen fibrils by proteolytic enzymes of cariogenic
bacteria
[85]
.
Also nanosized bioactive glass particles for remineralization of the demineralized dentin
were investigated in vitro
[49]
. After treatment of demineralized dentin for 10
β
30 days, an
increase in mineral content was observed, but the mechanical properties were below native
dentin. These examples and the required application time illustrate the difficulties of dentin
remineralization. However, also under pure in vitro conditions, toothpastes containing HA nano-
particles revealed better remineralizing effects when compared to a conventional amine fluoride
toothpaste
[33]
.
