Spectroscopic evaluation of native, milled, and functionalized β-TCP seeding into dental enamel lesions

Excerpt

Infrared (IR) spectroscopy has been used extensively to probe chemical and structural aspects of synthetic calcium phosphate-based mineral and biological hard tissue, including bone and enamel, due to the IR active modes pertaining to phosphate and/or carbonate [1‐5]. Distinction among these vibrational modes allows one to identify and contrast tricalcium phosphate and apatite mineral phases, [2] for instance, or the similarities between prehistoric and extant reptile enamel [6]. The apatite in tooth enamel manifests both carbonate and hydroxyl groups, which are susceptible to demineralization, or weakening, when exposed to acidic events that naturally arise during eating events, for example [7]. The body’s natural repair mechanism is saliva, which contains critical minerals, such as calcium and phosphate, that can help repair weakened tooth structure [8]. Because the mineral content in saliva may be too low to adequately remineralize weakened enamel, studies have shown the use of fluoride, calcium, and other minerals can help restore the lesions created through the loss of enamel mineral (i.e., calcium, hydroxyls, carbonate, and phosphate) [9‐11]. Of considerable interest from an efficacy point of view is the ability to obtain structural information demonstrating inclusion of the seed mineral into enamel lesions. For instance, enamel uptake of fluoride, the most clinically renowned anti-cavity remineralizing agent, [12] can be performed by making measurements on biopsies extracted from enamel lesions using a fluoride-sensitive electrode [13] as outlined in the United States Food and Drug Administration’s ‘Anticaries Drug Products for Over-the-Counter Human Use’ monograph [14]. The effects of calcium phosphate (CaP) seeding into enamel tissue are particularly challenging and have been primarily limited to atomic absorption spectroscopy [15, 16] or ⁴⁵Ca radiolabeling [17]. These methods, however, do not provide chemical and structural insight into enamel remineralization stimulated by a given CaP salt/mineral (i.e., calcium lactate, calcium phosphate, etc.); hence, there exists a fundamental disconnect in how CaP agents affect enamel tissue. Recently, we reported on the novel solid-state synthesis and dental application of a functionalized tricalcium phosphate (fTCP) mineral comprised of β-TCP and sodium lauryl sulfate (SLS) in remineralizing weakened enamel (98% β-TCP + 2% SLS) [18]. In efforts to further our understanding of fTCP and its remineralizing effects on enamel, in this letter we use IR spectroscopy to probe the ensuing enamel structure when weakened enamel is seeded with native β-TCP, milled β-TCP, and fTCP. Our observations reveal significant structural differences in enamel arising from each β-TCP system and confirm the novelty of fTCP as a promising mineralizing agent. While we show this approach resolves modifications in dental tissue structure when seeded with CaP minerals, we also believe this can be extended to growth processes in the mineralization of teeth and bone. …