Evaluation of the re-bond strength of debonded metal and ceramic brackets following Er: YAG laser treatment.

BACKGROUND: Failure of orthodontic bracket bonds is a common occurrence during orthodontic treatment. This study investigated the impact of Er: YAG laser-based removal of adhesive from the bases of metal and ceramic brackets for re-bonding. METHODS: A total of 168 extracted premolars were collected from patients. 84 metal brackets were used to be bonded on the buccal surface of the premolars in Groups 1, 2, 3 and 4, while 84 ceramic brackets were applied in Groups I, II, III and IV. Group 1/I represented the initial bonding group, with Group 2/II being the re-bonding group with new brackets, while Groups 3/III and 4/ IV received recycled brackets treated by Er: YAG laser or flaming respectively. Both the first and second de-bonding were performed in all samples using a universal testing machine to determine the shear bond strength (SBS). The adhesive remnant index (ARI) was evaluated using a stereo-microscope. The new and the treated bracket bases were evaluated using scanning electron microscopy (SEM). Differences in initial bonding and re-bonding ability were analyzed through one-way ANOVAs, and differences in ARI were assessed with the Kruskal-Wallis test. RESULTS: Greater amounts of adhesive residue were observed on ceramic brackets treated by laser. The SBS values for recycled metal brackets in Group 3 (26.13 MPa) were comparable to Group 1 (23.62 MPa) whereas they differed significantly from Group 4 (12.54 MPa). No significant differences in these values were observed when comparing the 4 groups with ceramic brackets. ARI score in Group 4 (2-3 points) differed significantly from the three other groups (P < 0.05). For Group I, II, III and IV, similar ARI scores were observed (P > 0.05). SEM analysis didn't show apparent damage of bracket bases consisting of either metal or ceramic material treated by Er: YAG laser. CONCLUSIONS: Er: YAG laser treatment was superior to flame treatment as a means of removing adhesive without damaging the brackets. SBS values and ARI scores following Er: YAG laser treatment were similar to those for new brackets, offering further support for Er: YAG laser treatment as a viable means of recycling debonded brackets.

A Novel Air-Cooled Nd:YAG Laser for the Treatment of the Venous Lakes of the Lips.

Objective: To evaluate the therapeutic effect of a novel air-cooled Nd:YAG laser in the venous lakes of the lips (VLL). Background: The thermal injury is one of the most important issues during laser therapy for venous lakes. Methods: Six pieces of fresh pork livers were used to provide 30 regions with a diameter of 6 mm for experiment in vitro, among which 15 regions were treated by Nd:YAG laser with air cooling until the tissue turned gray-white, whereas the rest were treated without air cooling as control. The operation time of laser irradiation, the degree of temperature increase, and the depth of coagulation tissue were compared between two groups. Then, 60 VLL patients were selected for Nd:YAG laser treatment with or without air cooling. The operation time of laser irradiation, the degree of temperature increase, the postoperative pain visual analog scale (VAS) score, and the percentage of lesions removed within 1 month were compared. Results: In tissue studies, the treated group showed a longer operation time of laser irradiation (p < 0.01), a lower degree of temperature increase (p < 0.01), and there was no significant statistical difference in the depth of coagulation tissue (p = 0.624). In clinical studies, the treated group showed a longer operation time of laser irradiation (p < 0.01), a lower degree of temperature increase (p < 0.01), and a lower VAS score on the 1st and 2nd day, compared with the control group (p < 0.01). Conclusions: Air cooling during Nd:YAG laser for the treatment of VLL can prolong the surgical time, but lowered tissue temperature and reduced patient pain within 2 days under the premise of ensuring the treatment effect.

A Comparison Between Phosphoric Acid- and Er:YAG Laser-Mediated Re-Etching of Enamel for Orthodontic Bracket Re-Bonding.

Objective: This study sought to compare enamel surface morphology and orthodontic bracket re-bonding strength after phosphoric acid- or erbium-doped yttrium aluminum garnet (Er:YAG) laser-mediated re-etching. Methods: A total of 81 extracted premolars were obtained from patients undergoing orthodontic procedures. Conventional etching with 35% phosphoric acid was first used to bond brackets to the enamel surface. Then brackets were de-bonded 1 week later. These samples were then separated randomly into three groups (n = 27 teeth each group) and re-bonded with new brackets after one of the following re-etching manners: Group A-35% phosphoric acid, Group B-Er:YAG laser (200 mJ, 30 Hz), and Group C-Er:YAG laser (250 mJ, 30 Hz). The enamel surface and the interface of enamel and adhesive were then analyzed through scanning electron microscopy. Shear bond strength (SBS) and adhesive remnant index (ARI) were also measured. Results: Samples in Group A exhibited significant residual adhesive at the enamel surface, whereas samples in Groups B and C showed a cleaner surface with more distinct and evenly distributed honeycomb-like structures. Further, samples in Group C displayed a larger average SBS value between the two laser-etching groups, although there were no significant differences in SBS values or ARI scores between the acid and laser re-etching groups (p > 0.05). Conclusions: Er:YAG laser-based enamel re-etching (250 mJ, 30 Hz) produces an uniform honeycomb-like structure and a trend of similar SBS compared with 35% phosphoric acid-mediated re-etching. Er:YAG laser-mediated re-etching seems to be a promising alternative approach for bracket re-bonding.

Broadband high-sensitivity current-sensing device utilizing nonlinear magnetoelectric medium and nanocrystalline flux concentrator.

A broadband current-sensing device with frequency-conversion mechanism consisting of Terfenol-D/Pb(Zr.Ti)O3 (PZT)/Terfenol-D magnetoelectric laminate and Fe73.5Cu1Nb3Si13.5B9 nanocrystalline flux concentrator is fabricated and characterized. For the purpose of acquiring resonance-enhanced sensitivity within broad bandwidth, a frequency-modulation mechanism is introduced into the presented device through the nonlinearity of field-dependence giant magnetostrictive materials. The presented configuration provides a solution to monitor the weak currents and achieves resonance-enhanced sensitivity of 178.4 mV/A at power-line frequency, which exhibits ∼3.86 times higher than that of direct output at power-line frequency of 50 Hz. Experimental results demonstrate that a weak step-change input current of 1 mA can be clearly distinguished by the output amplitude or phase. This miniature current-sensing device provides a promising application in power-line weak current measurement.

Structural requirements of the ASBT by 3D-QSAR analysis using aminopyridine conjugates of chenodeoxycholic acid.

The human apical sodium-dependent bile acid transporter (ASBT) is a validated drug target and can be employed to increase oral bioavailability of various drug conjugates. The aim of the present study was to investigate the chemical space around the 24-position of bile acids that influences both inhibition and uptake by the transporter. A series of 27 aminopyridine and aminophenol conjugates of glutamyl-chenodeoxycholate were synthesized and their ASBT inhibition and transport kinetics (parametrized as K(i), K(t), and J(max)) measured using stably transfected ASBT-MDCK cells. All conjugates were potent ASBT inhibitors. Monoanionic conjugates exhibited higher inhibition potency than neutral conjugates. However, neutral conjugates and chloro-substituted monoanionic conjugates were not substrates, or at least not apparent substrates. Kinetic analysis of substrates indicated that similar values for K(i) and K(t) implicate substrate binding to ASBT as the rate-limiting step. Using 3D-QSAR, four inhibition models and one transport efficiency model were developed. Steric fields dominated in CoMFA models, whereas hydrophobic fields dominated CoMSIA models. The inhibition models showed that a hydrophobic or bulky substitute on the 2 or 6 position of a 3-aminopyridine ring enhanced activity, while a hydrophobic group on the 5 position was detrimental. Overall, steric and hydrophobic features around the 24 position of the sterol nucleus strongly influenced bile acid conjugate interaction with ASBT. The relative location of the pyridine nitrogen and substituent groups also modulated binding.

Why we should be vigilant: drug cytotoxicity observed with in vitro transporter inhibition studies.

From routine in vitro drug-transporter inhibition assays, observed inhibition is typically assumed from direct interaction with the transporter. Other mechanisms that possibly reduce substrate uptake are not frequently fully examined. The objective of this study was to investigate the association of transporter inhibition with drug cytotoxicity. From a pool of drugs that were identified as known ASBT or OCTN2 inhibitors, 21 drugs were selected to screen inhibitory potency of their prototypical substrate and cytotoxicity against three human sodium-dependent solute carrier (SLC) transporters: apical sodium-dependent bile acid transporter (ASBT), organic cation/carnitine transporter (OCTN2), and the excitatory amino acid transporter 4 (EAAT4) in stable cell lines. Twenty drugs showed apparent inhibition in OCTN2-MDCK and ASBT-MDCK. Four dihydropyridine calcium channel blockers were cytotoxic to MDCK cells, and the observed cytotoxicity of three of them accounted for their apparent OCTN2 inhibition, and consequently were classified as non-OCTN2 inhibitors. Meanwhile, since their cytotoxicity only moderately contributed to ASBT inhibition, these three were still considered ASBT inhibitors. Four other drugs showed apparent inhibition in EAAT4-HEK cells, and cytotoxicity of three drugs corresponded with their inhibition of this transporter. Therefore, cytotoxicity significantly affected EAAT4 observations. Results showed the potential of cytotoxicity as a mechanism that can account for apparent in vitro transporter inhibition. Drug cytotoxicity varied in different cell lines, which could increase false positives for pharmacophore development.

Synthesis and in vitro evaluation of potential sustained release prodrugs via targeting ASBT.

The objective was to synthesize prodrugs of niacin and ketoprofen that target the human apical sodium-dependent bile acid transporter (ASBT) and potentially allow for prolonged drug release. Each drug was conjugated to the naturally occurring bile acid chenodeoxycholic acid (CDCA) using lysine as a linker. Their inhibitory binding and transport properties were evaluated in stably transfected ASBT-MDCK monolayers, and the kinetic parameters K(i), K(t), normJ(max), and P(p) were characterized. Enzymatic stability of the conjugates was evaluated in Caco-2 and liver homogenate. Both conjugates were potent inhibitors of ASBT. For the niacin prodrug, substrate kinetic parameter K(t) was 8.22microM and normJ(max) was 0.0917. In 4h, 69.4% and 26.9% of niacin was released from 1microM and 5microM of the conjugate in Caco-2 homogenate, respectively. For the ketoprofen prodrug, K(t) was 50.8microM and normJ(max) was 1.58. In 4h, 5.94% and 3.73% of ketoprofen was released from 1microM and 5microM of the conjugate in Caco-2 homogenate, and 24.5% and 12.2% of ketoprofen was released in liver homogenate, respectively. In vitro results showed that these bile acid conjugates are potential prolonged release prodrugs with binding affinity for ASBT.

Identification of inhibitor concentrations to efficiently screen and measure inhibition Ki values against solute carrier transporters.

The objective was to identify inhibitor concentrations to efficiently screen and measure inhibition K(i) values of solute carrier (SLC) transporters. The intestinal bile acid transporter and its native substrate taurocholate were used as a model system. Inhibition experiments were conducted using 27 compounds. For each compound, the inhibition constant K(i) was obtained from the comprehensive inhibition profile, and referred as the reference K(i). K(i) values were also estimated from various partial profiles and were compared to the reference K(i). A screening K(i) was estimated from one data point and also compared to the reference K(i). Results indicate that K(i) can be accurately measured using an inhibitor concentration range of only 0-K(i) via five different inhibitor concentrations. Additionally, a screening concentration of 10-fold the substrate affinity K(t) for potent inhibitors (K(i)<20K(t)) and 100-fold K(t) for nonpotent inhibitors (K(i)>20K(t)) provided an accurate K(i) estimation. Results were validated through inhibition studies of two other SLC transporters. In conclusion, experimental conditions to screen and measure accurate transporter inhibition constant K(i) are suggested where a low range of inhibitor concentrations can be used. This approach is advantageous in that minimal compound is needed to perform studies and accommodates compounds with low aqueous solubility.

Computational models for drug inhibition of the human apical sodium-dependent bile acid transporter.

The human apical sodium-dependent bile acid transporter (ASBT; SLC10A2) is the primary mechanism for intestinal bile acid reabsorption. In the colon, secondary bile acids increase the risk of cancer. Therefore, drugs that inhibit ASBT have the potential to increase the risk of colon cancer. The objectives of this study were to identify FDA-approved drugs that inhibit ASBT and to derive computational models for ASBT inhibition. Inhibition was evaluated using ASBT-MDCK monolayers and taurocholate as the model substrate. Computational modeling employed a HipHop qualitative approach, a Hypogen quantitative approach, and a modified Laplacian Bayesian modeling method using 2D descriptors. Initially, 30 compounds were screened for ASBT inhibition. A qualitative pharmacophore was developed using the most potent 11 compounds and applied to search a drug database, yielding 58 hits. Additional compounds were tested, and their K(i) values were measured. A 3D-QSAR and a Bayesian model were developed using 38 molecules. The quantitative pharmacophore consisted of one hydrogen bond acceptor, three hydrophobic features, and five excluded volumes. Each model was further validated with two external test sets of 30 and 19 molecules. Validation analysis showed both models exhibited good predictability in determining whether a drug is a potent or nonpotent ASBT inhibitor. The Bayesian model correctly ranked the most active compounds. In summary, using a combined in vitro and computational approach, we found that many FDA-approved drugs from diverse classes, such as the dihydropyridine calcium channel blockers and HMG CoA-reductase inhibitors, are ASBT inhibitors.

Method to screen substrates of apical sodium-dependent bile acid transporter.

Human apical sodium-dependent bile acid transporter (hASBT) is a potential prodrug target under study. Development of prodrugs that target hASBT may yield compounds with low solubility and/or susceptibility to hydrolysis. A transport uptake method is needed that increases compound solubility and avoids NaOH for cell lysis during postexperimental cell sample preparation. The overall goal was to develop an assay method to screen for hASBT uptake of novel compounds. The first objective was to determine the maximum cosolvent concentrations that are compatible with an hASBT active transport assay. The second objective was to develop a NaOH-free cell lysis method to process cell samples from these uptake studies. The following cosolvents were studied: dimethylacetamide (DMAC), dimethylformamide (DMF), dimethylsulfoxide (DMSO), ethanol, methanol, polyethylene glycol-400, propylene glycol, and dioxane. Initial studies included taurocholate flux studies across hASBT-Madin-Darby canine kidney monolayers using up to 10% cosolvent, as well as cytotoxicity studies. The effect of selected cosolvent concentrations on the hASBT Michaelis-Menten kinetic parameters was evaluated. Additionally, two acetonitrile-based cell lysis methods that do not use NaOH were evaluated in terms of percent sample recovery and hASBT kinetic parameters. Results showed that the maximum permissible cosolvent concentrations for hASBT uptake studies, without compromising assay results or causing cytotoxicity, are 1% DMAC, 1% DMF, 2.5% DMSO, 2.5% methanol, and 2.5% ethanol. Additionally, both NaOH-free, acetonitrile-based cell lysis methods provided similar recovery and hASBT results, compared to NaOH method. Hence, an assay method was developed to screen for active transport, allowing for cosolvents that can solubilize compounds and avoid NaOH sample treatment, which can otherwise degrade compound.