Biomedical Engineering Reference
In-Depth Information
9.3
Phosphates micro- and nanoparticles and caries prevention
9.3.1
De- and remineralization process
Dental caries is a dietobacterial disease resulting from the slow but progressive dissolution of the
tooth surfaces by acids produced by bacteria in the dental biofilm
[26]
. It has a multifactorial
nature, in which the concomitant interaction of dietary sugars, dental biofilm, and the host is
needed
[27]
. In order to understand the dynamics of dental enamel demineralization (DE) and remi-
neralization (RE) processes, a few biochemical aspects of
the oral environment must be
highlighted.
In general terms, tooth enamel is mostly composed by hydroxyapatite (HAP) and fluoro
hydroxyapatite (FAP). The supersaturation of saliva with respect to these minerals has important
clinical implications, as HAP and FAP will not dissolve unless significant changes in the oral pH
occur. When the dental biofilm is exposed to fermentable sugars, the pH in the biofilm fluid rapidly
decreases to values below the critical pH for HAP (5.5) and/or FAP (4.5), so that saliva becomes
undersaturated with respect to these minerals. This leads to enamel DE. With time, the pH in the
biofilm fluid begins to rise, due to the action of salivary buffers. When the pH in the biofilm fluid
reaches values above the critical pH for HAP and FAP, enamel RE occurs
[28]
. The equilibrium
between DE and RE processes will determine that the enamel structure will not dissolve. However,
when DE episodes occur at a higher frequency and intensity, RE cycles will not be able to reverse
enamel dissolution, causing dental caries lesion.
Among the strategies to shift the balance from DE to RE, fluoride therapy is the most widely
used, as it reduces the enamel acid solubility (by converting HAP in FAP after acid challenges) and
increases the RE process (by promoting the reprecipitation of calcium and phosphates into the den-
tal mineral)
[26,29]
. However, due to the increase in dental fluorosis prevalence observed over the
last few decades, the search for nonfluoride therapeutic agents have been studied, which include
calcium and phosphate salts. These have been studied in association or not with fluoride in denti-
frices, gels, varnishes, and rinses, and include CaCl
2
, calcium lactate, calcium glycerophosphate,
sodium trimetaphosphate (TMP), nanocomplexes of casein phosphopeptide
amorphous calcium
phosphate, among others.
9.3.2
Nanophosphates and microbial adhesion
Phosphates have great affinity with HAP, preventing the release of calcium and phosphate ions and
reducing the surface area available for dissolution
[30,31]
. In vitro studies showed that it is possible
to reduce the concentration of fluoride in dentifrices and mouth rinses, yet maintaining their protec-
tive action against both dental caries and erosion by adding inorganic phosphate (sodium TMP) to
the products
[32
36]
. Given the high adsorption of phosphates to the enamel surface, it would be
interesting to investigate whether the use of phosphate would influence bacterial adhesion to tooth
enamel, as well as on mineral loss. The effects of TMP on dental biofilm and its efficacy when
combined to different antimicrobials effect on biofilm were analyzed by colony forming unit
(CFU) counts and lactic acid production. The data presented in that study demonstrated that the
biofilm model used was suitable to grow biofilm on different substrata, both in microcosm and
single species biofilms. The model allows the evaluation of antimicrobial agents and TMP on
