Coagulative Nucleation in the Copolymerization of Methyl Methacrylate-Butyl Acrylate under Monomer-Starved Conditions.

Coagulative nucleation in the copolymerization of methyl methacrylate-butyl acrylate (MMA-BA) via semicontinuous emulsion heterophase polymerization (SEHP) under monomer-starved conditions in latexes with high solid content (50.0 wt %) and low concentrations of surfactant is reported. The SEHP technique allows the obtention of latex with high colloidal stability and has potential industrial application in polymer synthesis. High instantaneous conversions (>90%) and a high-ratio polymerization rate/addition rate (Rp/Ra) ≥ 0.9 were obtained at low times until the final copolymerization, which confirmed the starved conditions in the systems at the highest surfactant concentrations. The particle size exhibited a linear size increment at conversions between 0 and 40% induced by homogeneous nucleation, a transition region between 40 and 50%, and non-linear behavior at higher conversions by coagulative nucleation. These three behaviors were also observed in the particle surfactant coverage area (Sc), Z-potential, particle coagulation rate (dNp/dt) by the Smoluchowski model, final particle size (Dpz), and number particle (Np) through the reaction. By means of transmission electron microscopy (TEM) images, the onset of coagulation was observed from 50% of conversion until the end of the reaction. In addition, in both processes of copolymerization, tacticity was displayed (mainly syndiotacticity).

Drug Delivery from Stimuli-Responsive Poly(N-isopropylacrylamide-co-N-isopropylmethacrylamide)/Chitosan Core/Shell Nanohydrogels.

The synthesis of stimulus-responsive poly(N-isopropylacrylamide-co-N-isopropylmethacrylamide)/chitosan core/shell nanohydrogels made by batch emulsion polymerization in the presence of chitosan (CS) micelles is reported. The ratio of monomers required to obtain copolymers with a volume phase transition temperature (TVPT) in the range of the temperatures observed in the human body in response to an infection (38 to 40 °C) was estimated with the Fox equation. The conversion was determined by gravimetry; mean particle size, size distribution, and thermal response were measured by quasi-elastic light scattering (QLS). The core/shell structure was confirmed by TEM, and FTIR showed the presence of N-isopropyl acrilamide (NIPA), N-isopropyl methacrylamide (NIPMA), and CS in the nanohydrogels. The nanohydrogels were loaded with the drug doxycycline hyclate, and their release kinetic profile was determined at pH = 2.0 and 7.4 at their volume phase transition temperatures (TVPT). A higher amount of drug was released at acidic pH. Some mathematical models described in the literature were used to fit the experimental drug release data.

Characterization and Electrical Properties of PVA Films with Self-Assembled Chitosan-AuNPs/SWCNT-COOH Nanostructures.

Nanostructured films with electrical conductivity in the semiconductor region were prepared in a polymeric matrix of poly(vinyl alcohol) (PVA) with nanostructures of chitosan-gold nanoparticles (AuNPs)/single-wall carbon nanotubes carboxylic acid functionalized (SWCNT-COOH) (chitosan-AuNPs/SWCNT-COOH) self-assembled. Dispersion light scattering (DLS) was used to determine the average particle sizes of chitosan-AuNPs, z-average particle size (Dz) and number average particle size (Dn), and the formation of crystalline domains of AuNPs was demonstrated by X-ray diffraction (XRD) patterns and observed by means of transmission electron microscopy (TEM). The electrostatic interaction was verified by Fourier transform infrared spectroscopy (FTIR). The electrical conductivity of PVA/chitosan-AuNPs/SWCNT-COOH was determined by the four-point technique and photocurrent. The calculated Dn values of the chitosan-AuNPs decreased as the concentration of gold (III) chloride trihydrate (HAuCl4·3H2O) increased: the concentrations of 0.4 and 1.3 mM were 209 and 90 nm, respectively. Average crystal size (L) and number average size (D) of the AuNPs were calculated in the range of 13 to 24 nm. Electrical conductivity of PVA/chitosan-AuNPs/SWCNT-COOH films was 3.7 × 10-5 σ/cm determined by the four-point technique and 6.5 × 10-4 σ/cm by photocurrent for the SWCNT-COOH concentration of 0.5 wt.% and HAuCl4·3H2O concentration of 0.4 mM. In this investigation, the protonation of the amine group of chitosan is fundamental to prepare PVA films with nanostructures of self-assembled chitosan-AuNPs/SWCNT-COOH.

Analysis of Electronic Apex Locators in Human Teeth Diagnosed With Apical Periodontitis.

Electronic apex locators (EAL) have been used to establish the working length (WL) in root canal treatment. In teeth diagnosed with apical periodontitis, resorption of tooth apical structures can lead to difficulties to obtain an appropriate WL. The aim was to compare the capacity of three EAL's (Root ZX II, Raypex 6 and Endo-Eze Quill) to locate the tip of the K-file between 0 to -0.5 mm from the apical foramen (AF) on teeth diagnosed with asymptomatic apical periodontitis (AAP). Electronic working length was performed on 60 roots with AAP. A K-file #15 was inserted in the root canal until the apical foramen (AF) was located, and followed was re-adjusted to -0.5 mm through observation in EAL display. The K-file was fixed to the tooth with composite and teeth were extracted. The 4 apical millimeters were worn out until the K-file could be seen and were prepared and measured its distance to AF in a scanning electron microscope. Appropriate WL was when the tip of the K-file was located between 0 to -0.5 mm from AF. Results: Root ZX II showed significant difference (p<0.01) with the other two EALs. Root ZX II presented the better performance than Raypex 6 or Endo-Eze Quill in teeth with AAP.

Analysis of electronic apex locators in human teeth diagnosed with apical periodontitis

Abstract Electronic apex locators (EAL) have been used to establish the working length (WL) in root canal treatment. In teeth diagnosed with apical periodontitis, resorption of tooth apical structures can lead to difficulties to obtain an appropriate WL. The aim was to compare the capacity of three EAL's (Root ZX II, Raypex 6 and Endo-Eze Quill) to locate the tip of the K-file between 0 to -0.5 mm from the apical foramen (AF) on teeth diagnosed with asymptomatic apical periodontitis (AAP). Electronic working length was performed on 60 roots with AAP. A K-file #15 was inserted in the root canal until the apical foramen (AF) was located, and followed was re-adjusted to -0.5 mm through observation in EAL display. The K-file was fixed to the tooth with composite and teeth were extracted. The 4 apical millimeters were worn out until the K-file could be seen and were prepared and measured its distance to AF in a scanning electron microscope. Appropriate WL was when the tip of the K-file was located between 0 to -0.5 mm from AF. Results: Root ZX II showed significant difference (p<0.01) with the other two EALs. Root ZX II presented the better performance than Raypex 6 or Endo-Eze Quill in teeth with AAP.

Resumo Os localizadores eletrônicos apicais têm sido usados ​​para estabelecer o comprimento de trabalho no tratamento do canal radicular. Nos dentes diagnosticados com periodontite apical, a reabsorção das estruturas apicais dos dentes pode levar a dificuldades na obtenção de uma odontometria apropriada. Este estudo comparou três localizadores apicais (Root ZX II, Raypex 6 e Endo-Eze Quill) para localizar a ponta do instrumento K-file entre 0 a -0,5 mm do forame apical em dentes com diagnóstico de periodontite apical assintomática. O comprimento de trabalho eletrônico foi realizado em 60 dentes com periodontite apical assintomática. Uma lima K-file de número 15 foi inserida no canal radicular até a localização do forame apical, e seguida foi reajustada para -0,5 mm por meio de observação no visor do localizador eletrônico apical. A lima K-file foi fixada ao dente usando compósito, e a seguir os dentes foram extraídos. Os 4 milímetros apicais foram desgastados até que a lima K-file pudesse ser visualizada para as medidas de distância no forame apical por meio de microscópio eletrônico de varredura. O comprimento de trabalho apropriado foi determinado quando a ponta do instrumento estivesse localizada entre 0 a -0,5 mm do forame apical. O Root ZX II apresentou o melhor desempenho (p<0,01) que o Raypex 6 ou Endo-Eze Quill em dentes humanos com periodontite apical assintomática.

Biomechanical anchorage evaluation of mini-implants treated with sandblasting and acid etching in orthodontics.

PURPOSE: The purpose of this study was to assess the stability of sandblasted and acid-etched miniscrew implants based on orthodontic mechanics for space closure after tooth extraction. MATERIALS AND METHODS: Twenty-four orthodontic mini-implants were placed in 13 patients, for a skeletal anchorage purpose, all prepared by the manufacturer (3M Unitek-IMTEC Ortho USA) with sandblasting and acid treatment. Anchorage measurements were made on occlusal radiographs, on a monthly basis in a 6-month period. RESULTS: All the mini-implants were effective for the clinical trial; but 65% of the mini-implants, after been loaded, showed up to 1 degree, or less, of displacement, while 35% showed ≥2 degrees shift. The mandible mini-implants resulted in a smaller amount of displacement than the ones located in the maxilla. The ones located at the anterior maxilla displaced less than the posterior. The best results were obtained with the 8-mm mini-implants, followed by the 6-mm and 10-mm mini-implants. CONCLUSIONS: Modifying the mini-implant surface with sandblasting and acid treatment offers good bone anchoring for orthodontic purposes.

Resin replica in enamel deproteinization and its effect on acid etching.

PURPOSE: The goal of this in vitro study was to identify the topographical features of deproteinized (NaOCl) and etched with phosphoric acid (H3PO4) enamel surface, compared to phosphoric acid surface alone with a Resin Replica model. MATERIALS: Ten extracted lower first and second permanent molars were polished with pumice and water, and then divided into 3 equal buccal sections having similar physical and chemical properties. The enamel surfaces of each group were subjected to the following treatments: Group A: Acid Etching with H3PO4 37% for 15 seconds. Group B: Sodium Hypochlorite (NaOCl) 5.25% for 60 seconds followed by Acid Etching with H3PO4 37% for 15 seconds. Group C; No treatment (control). All the samples were treated as follow: Adhesive and resin were applied to all groups after A, B and C treatment were performed; Then enamel/dentin decalcification and deproteinization and topographic SEM Resin Replica assessment were used to identify resin tags enamel surface quality penetration. RESULTS: Showed that group B reached an area of 7.52 mm of the total surface, with a 5.68 mm2 (73%) resin tag penetration equivalent type I and II etching pattern, 1.71 mm2 (26%) equivalent to type III etching pattern and 0.07 mm2 (1%) unaffected surface. Followed by group A with 7.48 mm2 of the total surface, with a 3.47 mm2 (46 %)resin tag penetration equivalent to type I and II etching pattern, 3.30 mm2 (45%)equivalent to type III etching pattern and 0.71 mm2, and (9%) unaffected surface. Group C did not show any resin tag penetration. A significant statistical diference (P < 0.001) existed between groups A and B in resin quality penetration, leading to the conclusion that when the enamel is deproteinizated with 5.25% NaOCl for 1 minute prior H3PO4, the surface and topographical features of the replica resin penetration surface increases significantly with type I-II etching pattern.