Enhanced Delivery of F-, Ca2+, K+, and Na+ Ions into Enamel by Electrokinetic Flows.

As the outermost layer of the tooth crown, dental enamel is the most mineralized tissue in mammals, consisting of hydroxyapatite crystallites separated by long and narrow nanochannels. A major challenge in dentistry is how various molecules can be infiltrated into these nanopores in an efficient and controlled way. Here we show a robust method to transport various ions of interest, such as fluoride (F-), potassium (K+), calcium (Ca++), and sodium (Na+), into these nanopores by electrokinetic flows. It is verified by fluorescence microscopy, laser-scanning confocal microscopy, mass spectrometry, and ion selective electrode technique. Different ions are demonstrated to infiltrate through the entire depth of the enamel layer (~1 mm), which is significantly enhanced penetration compared with diffusion-based infiltration. Meanwhile, transport depth and speed can be controlled by infiltration time and applied voltage. This is the first demonstration of reliably delivering both anions and cations into the enamel nanopores. This technique opens opportunities in caries prevention, remineralization, tooth whitening, and nanomedicine delivery in clinical dentistry, as well as other delivery challenges into various biomaterials such as bones.

Synthesis of carboxylic block copolymers via reversible addition fragmentation transfer polymerization for tooth erosion prevention.

Dental professionals are seeing a growing population of patients with visible signs of dental erosion. The approach currently being used to address the problem typically leverages the enamel protection benefits of fluoride. In this report, an alternative new block copolymer with a hydrophilic polyacrylic acid (PAA) block and a hydrophobic poly(methyl methacrylate) (PMMA) block was developed to similarly reduce the mineral loss from enamel under acidic conditions. This series of PMMA-b-PAA block copolymers was synthesized by reversible addition fragmentation transfer (RAFT) polymerization. Their structures were characterized by gel permeation chromatography (GPC) and (1)H nuclear magnetic resonance (NMR) spectra. The molar fractions of acrylic acid (AA) in the final block copolymer were finely controlled from 0.25 to 0.94, and the molecular weight (Mn) of PMMA-b-PAA was controlled from 10 kDa to 90 kDa. The binding capability of the block copolymer with hydroxyapatite (HAP) was investigated by ultraviolet-visible spectroscopy (UV-Vis) and Fourier transform infrared (FTIR) spectroscopy. FTIR spectra confirmed that the PMMA-b-PAA block copolymer could bind to HAP via bridging bidentate bonds. Both UV-Vis and FTIR spectra additionally indicated that a high polymer concentration and low solution pH favored the polymer binding to HAP. The erosion-preventing efficacy of the PMMA-b-PAA block copolymer in inhibiting HAP mineral loss was quantitatively evaluated by atomic absorption spectroscopy (AAS). Based on the results, polymer treatment reduced the amount of calcium released by 27% to 30% in comparison with the unprotected samples. Scanning electron microscope (SEM) observations indicated that PMMA-b-PAA polymer treatment protected enamel from acid erosion. This new amphiphilic block copolymer has significant potential to be integrated into dentifrices or mouthrinses as an alternative non-fluoride ingredient to reduce tooth erosion.

Characterizing the composition of underarm and forearm skin using confocal raman spectroscopy.

Many studies have reported differences in skin composition as a function of body site and age. However, rarely has axilla (underarm) skin been included in these studies. This report highlights the results of a clinical study where confocal Raman spectroscopy was used to assess the differences between underarm and volar forearm skin. In the reported study, the concentration of natural moisturizing factor (NMF), urea, lactic acid, cholesterol, trans urocanic acid (t-UCA) and ceramide 3 (N-octadecanoyl-phytosphingosine) was evaluated as a function of depth, body site (underarm vs. forearm) and age. Two age groups of women were included: (i) between 20 and 30 years and (ii) older than 55 years (post-menopause). The levels of cholesterol, ceramide 3 and lactic acid were highest in the underarm regardless of the age group whereas the forearm contained higher amounts of NMF. Ceramide 3, urea and lactic acid were significantly lower for women 55 years or older in the underarm. No age-related differences were detected within the forearm site..