In vitro surface analysis of the brushing resistance of orthodontic sealants using two different profilometric evaluation methods.

The enamel can be protected by applying orthodontic sealants at the bracket base to avoid the development of white spot lesions caused by inadequate oral hygiene. The aim of this study was to investigate the mechanical resistance of five commonly used orthodontic sealants against brushing in comparison to a positive group. Hydroxyapatite discs were bonded with a metal bracket and a piece of arch-wire was ligated in order to simulate a daily clinical situation (n = 48). Samples were divided into 6 groups of respectively 8 specimens. Sealants were applied around the bracket base according to manufacturer's instructions. Following sealants were used: Group 1: Pro Seal (Reliance Orthodontic Products, Itasca, Illinois, USA); 2: Light Bond (Reliance Orthodontic Products, Itasca, Illinois, USA); 3: ClinproXT Varnish (3M ESPE, Seefeld, Germany); 4: ProtectoCaF2 Nano (BonaDent GmbH, Frankfurt am Main, Germany); 5: Fluor Protector and 6: Tetric EvoFlow (both Ivoclar Vivadent AG, Schaan Liechtenstein). Tooth brushing were simulated for 6 weeks and 6 months with an electric toothbrush. The sealant thickness was measured by mechanical (MP) and optical profilometry (OP) at baseline, after 6 weeks and after 6 months of brushing. Statistical analysis was performed according to two mixed linear models and post hoc Tukey-Kramer comparisons. The significance level was set at 5% (α ≤ 0.05). Pro Seal (MP: 9%; OP: 22%) and Light Bond (MP: 19%; OP: 16%) showed the lowest changes in sealant thickness after 6 months of simulated brushing. ClinproXT Varnish and Tetric EvoFlow recorded no statistically significant results (p > 0.05). The fluoride varnishes ProtectoCaF2 Nano and Fluor Protector could not be conclusively evaluated since the thickness of the sealants could not be determined at baseline. The results of both evaluation methods MP and OP are in good agreement. Pro Seal and Light Bond were resistant against tooth brushing and were able to adequately keep the bracket environment sealed even after 6 months. The two different measuring methods, MP and OP, provide a precise impression of the changes in the surface.

Impact of self-assembling peptides in remineralisation of artificial early enamel lesions adjacent to orthodontic brackets.

Enamel demineralisation can occur as a side effect during orthodontic treatment with fixed appliances. This study aimed to evaluate the efficacy of the self-assembling peptide P11-4 for remineralisation combined with fluorides, compared to application of fluoride varnish alone. De- and remineralisation was assessed by Quantitative light-induced fluorescence (QLF). Orthodontic brackets were bonded on 108 human enamel samples and white spot lesions were created. The samples were allocated randomly into three groups: Group I received no treatment, group II had a single application of fluoride varnish (22,600 ppm), and group III was treated with P11-4 following a single application of fluoride varnish. Quantitative light-induced fluorescence (QLF) measurements were performed at baseline, after demineralisation and after storage in remineralisation solution for 7 and 30 days. Non-parametric tests (Kruskal-Wallis test and Friedman test) were used for further analysis. After demineralisation, all samples showed a median ΔF -9.38% ± 2.79. After 30 days median ΔF values were as followed: group I = -9.04% ± 2.51, group II = -7.89 ± 2.07, group III = -6.08% ± 2.79). The median ΔF values differed significantly between all groups at all investigation times (p < 0.00001). Application of P11-4 with fluoride varnish was superior to the use of fluorides alone for remineralisation of enamel adjacent to brackets.

Interaction of water with different cellulose ethers: a Raman spectroscopy and environmental scanning electron microscopy study.

Different non-ionic cellulose ethers like methyl cellulose (MC), hydroxypropyl cellulose (HPC) and hydroxypropylmethyl cellulose (HPMC) were investigated. The characterization of the cellulose ethers was carried out by thermogravimetry and sorption/desorption isotherms. Differences in the properties of the cellulose ether films were described by time-dependent contact angle measurements. Changes in molecular structure of the raw materials, gels and films caused by water contact were studied using Raman spectroscopy. Differences between the substitution types and changes due to the gel or film formation were observed. An environmental scanning electron microscopy (ESEM) technique was used to distinguish the morphological behaviour of the cellulose ether films in contact with water. Based on in-situ ESEM experiments, the swelling and drying behaviour of the various stages of cellulose ether films (film-hydrated film-dried film) were quantified by using image analysis.

Nanoporous aluminum oxide as a novel support material for enzyme biosensors.

To construct novel amperometric sensors for the detection of hydrogen peroxide and pyruvate, peroxidase and pyruvate oxidase were immobilized in self-supporting nanoporous alumina membranes those made by anodic oxidation. Pyruvate oxidase and other enzymes were enclosed in poly(carbamoylsulfonate) hydrogel and sucked into the nanoporous alumina structure before polymerization. The alumina membranes were investigated by scanning electron microscopy before and after the enzyme immobilization. In an amperometric flow detector cell, pyruvate and hydrogen peroxide were detected under flow injection analysis conditions in concentration ranges from 1 microM to 100 microM and 5 microM to 500 microM, respectively. The achieved operational stability showed that alumina membranes can be used to construct enzyme-modified electrodes.

Raman spectroscopic surface characterization of cellulose derivatives.

First results of experiments on the surface characterization of cellulose derivatives are presented. Different water contents of the surface of microcrystalline cellulose have been investigated by means of Raman spectroscopy, SERS, and environmental scanning electron microscopy (ESEM).

Laser microstructuring and scanning microscopy of plasmapolymer-silver composite layers.

Laser-induced coalescence of silver nanoparticles embedded in thin plasma polymer films has been used to generate permanent submicrometer structures in the films, which exhibit unusual optical properties. Scanning-electron-microscope images and spatially resolved optical transmission spectra reveal the changes in the nanostructure of the films that are due to the irradiation. The structural modifications result from thermally induced coalescence of the irradiated nanoparticles and are accompanied by significant changes in the optical transmission spectra. A planar micro-optical element has been generated in this way, and its optical properties have been characterized by means of the depth resolution of a confocal microscope.