Quantum Dots as Nonagglomerated Nanofillers for Adhesive Resins.

Nanoparticles used in adhesive resins are prone to agglomeration, turning the material susceptible to physical failure. Quantum dots are nonagglomerated inorganic nanoparticles (1 to 10 nm) when in equilibrium. The aim of the present study was to synthesize and characterize zinc oxide quantum dots (ZnOQDs) and to develop and evaluate an adhesive resin with the addition of ZnOQDs. ZnOQDs were formulated by self-organization in chemical reaction with isopropanol and added to 2-hydroxyethyl methacrylate (HEMA). HEMA containing ZnOQDs was used for the experimental group and neat HEMA for the control group. Mean ZnOQD diameter was evaluated in isopropanol and in HEMA by ultraviolet-visible spectroscopy. The adhesives were evaluated for degree of conversion ( n = 5), softening in solvent ( n = 5), ultimate tensile strength ( n = 5), microtensile bond strength ( n = 20) at 24 h and after 6 mo, SEM-EDS (scanning electron microscopy-energy-dispersive x-ray spectroscopy; n = 3), and superresolution confocal microscopy ( n = 3). Data of microtensile bond strength after 6 mo and Knoop hardness after solvent immersion were evaluated by paired t test with a 0.05 level of significance. The other data were evaluated by independent t test with a 0.05 level of significance. Ultraviolet-visible spectroscopy indicated that the mean ZnOQD diameter remained stable in isopropanol and in HEMA (1.19 to 1.24 nm). Fourier transform infrared spectroscopy analysis showed the peak corresponding to zinc and oxygen bond (440 cm-1). The experimental group achieved a higher degree of conversion as compared with the control group and presented dentin/adhesive interface stability after 6 mo without altering other properties tested. SEM-EDS indicated 1.54 ± 0.46 wt% of zinc, and the superresolution confocal microscopy indicated nonagglomerated nanoparticles with fluorescence blinking in the polymerized adhesive. The findings of this study showed a possible and reliable method to formulate composites with nonagglomerated nanoscale fillers, shedding light on the nanoparticle agglomeration concern.

The effect of antimicrobial agents on bond strength of orthodontic adhesives: a meta-analysis of in vitro studies.

Antimicrobial orthodontic adhesives aim to reduce white spot lesions' incidence in orthodontic patients, but they should not jeopardizing its properties. Systematic review and meta-analysis were performed to answer the question whether the association of antimicrobial agents with orthodontic adhesives compromises its mechanical properties and whether there is a superior antimicrobial agent. PubMed and Scopus databases. In vitro studies comparing shear bond strength of conventional photo-activated orthodontic adhesives to antimicrobial photo-activated orthodontic adhesives were considered eligible. Search terms included the following: orthodontics, orthodontic, antimicrobial, antibacterial, bactericidal, adhesive, resin, resin composite, bonding agent, bonding system, and bond strength. The searches yielded 494 citations, which turned into 467 after duplicates were discarded. Titles and abstracts were read and 13 publications were selected for full-text reading. Twelve studies were included in the meta-analysis. The global analysis showed no statistically significant difference between control and experimental groups. In the subgroup analysis, only the chlorhexidine subgroup showed a statistically significant difference, where the control groups had higher bond strength than the experimental groups. Many studies on in vitro orthodontic bond strength fail to report test conditions that could affect their outcomes. The pooled in vitro data suggest that adding an antimicrobial agent to an orthodontic adhesive system does not influence bond strength to enamel. It is not possible to state which antimicrobial agent is better to be associated.

The influence of methodological variables on the push-out resistance to dislodgement of root filling materials: a meta-regression analysis.

The aim of this systematic review was to evaluate the influence of several methodological variables on the push-out resistance to dislodgment of root filling materials by a meta-regression analysis of the literature. A systematic review was performed by searching the PubMed database using the terms 'push-out' and 'pushout'. Laboratory studies published before March 2015 were included. Two reviewers extracted data regarding country of origin, year of publication, tooth type, smear layer removal, root canal sealer, core material, obturation technique, sample storage, tooth portion, test machine load velocity and slice thickness. Pooled mean resistance to dislodgement of all groups from the included studies was used in a linear meta-regression of random effects (α = 0.05). Of the 850 identified studies, 53 met the inclusion criteria. A meta-regression of the 341 groups extracted from these articles was performed to analyse the influence of each variable on resistance to dislodgement (in MPa). The sealer, core material, obturation technique, slice thickness, storage time, load velocity and tooth portion significantly influence the results (P < 0.05). Irrigant solution and smear layer removal did not influence the resistance to dislodgement of the root filling materials (P > 0.05). Methodological variables such as sealer, core material, root filling technique, tooth type, tooth portion, slice thickness, storage time and load velocity influenced the resistance to dislodgment. The inclusion and standardization of all related variables could lead to a more comparable and reproducible analysis of the resistance to dislodgment of the root canal sealers.

Synthesis and characterization of a glycerol salicylate resin for bioactive root canal sealers.

AIM: To develop and characterize a salicylate resin with potential use in bioactive endodontic sealers. METHODOLOGY: Methyl salicylate, glycerol and titanium isopropoxide were added in a closed system for the transesterification reaction. The resin obtained was characterized by proton nuclear magnetic resonance spectroscopy (1H NMR) and size exclusion chromatography (SEC). To verify the applicability of the resin to the development of endodontic sealers, experimental cements were prepared by mixing glycerol salicylate resin, calcium hydroxide and methyl salicylate in the ratios of 2 : 1 : 1, 1 : 2 : 1, 1 : 1 : 2, 1 : 1 : 1, 4 : 1 : 1, 1 : 4 : 1 and 1 : 1 : 4. Setting times were measured according to ISO 6876. Features of the hardening reaction were described by micro-RAMAN spectroscopy. RESULTS: The transesterification reaction had a 72% efficiency. The (1) H NMR analysis revealed the presence of the expected functional groups (hydroxyls and aromatic rings), and the SEC confirmed the molar mass of the resin produced. The setting times of experimental sealers ranged from 70 min (ratio 1 : 1 : 1) to 490 min (ratio 1 : 1 : 4). The conversion of the salicylic groups (1 613 cm(-1) ) to salicylate salt (1 543 cm(-1) ) and the reduction in calcium hydroxide peaks (1084 and 682 cm(-1) ) were confirmed by micro-RAMAN spectroscopy, which showed the calcium chelation by the resin. CONCLUSION: The new glycerol salicylate resin was successfully synthesized and revealed a potential application in the development of endodontic sealers.

Niobium pentoxide as a new filler for methacrylate-based root canal sealers.

AIM: To evaluate the influence of several niobium pentoxide (Nb(2) O(5) ) concentrations on the radio-opacity, flow, film thickness, microhardness and degree of conversion of an experimental root canal sealer. METHODOLOGY: An experimental dual-cured root canal sealer was produced with a methacrylate-based comonomer blend. Nb(2) O(5) was added at four different concentrations: 0, 80, 100 and 120 wt%. Radio-opacity was evaluated according to ISO 6876 using a digital system (n = 5). Flow and film thickness were determined in accordance with ISO 6876 (n = 3). Microhardness was evaluated with 50 g for 15 s (n = 5). Degree of conversion was evaluated with FTIR immediately after photocuring and after 1, 7 and 14 days. The data were analysed using anova and Tukey's test. The degree of conversion over time was evaluated using RM-anova (α = 0.05). RESULTS: The groups with 80 wt% and 100 wt% of filler showed no significant difference in radio-opacity from that of equivalent 2 mmAl (P > 0.05). The addition of 120 wt% resulted in radio-opacity values higher than 2 mmAl (P < 0.05). The flow was not significantly different amongst the different groups (P > 0.05). All groups had a film thickness of <50 µm (ISO 6876). All groups with Nb(2) O(5) were associated with higher values of microhardness than the control group. The group with 0 wt% was associated with a higher degree of conversion at all times. All groups except those with 80 wt% had higher values for degree of conversion after 14 days than immediately after photocuring. CONCLUSION: The addition of Nb(2) O(5) increases radio-opacity and microhardness; this material may be a promising filler for the production of a new endodontic sealer.

Nanostructured hydroxyapatite as filler for methacrylate-based root canal sealers.

AIM: To evaluate the effect of different concentrations of nanostructured hydroxyapatite on the radiopacity, flow and film thickness of an experimental root canal sealer. METHODOLOGY: An experimental dual-cured root canal sealer was produced with a methacrylate-based co-monomer blend. Nanostructured hydroxyapatite/calcium tungstate solutions (ratios 10:90, 20:80, 30:70 and 40:60) were added to produce the sealer. Radiopacity was evaluated using a digital system and an aluminium step wedge (n=5). Flow and thickness tests were conducted in accordance with ISO 6876 (n=3). The data were analysed using one-way anova and Tukey's test (α=0.05). RESULTS: All groups had levels of radiopacity in accordance with ISO 6876. The flow of the experimental sealers was not significantly different (P=0.204). All groups had a film thickness in accordance with ISO 6876 and with no statistical difference (P = 0.654). CONCLUSION: The addition of up to 40% HA(nano) to root canal sealers did not alter their radiopacity and film thickness.

Ytterbium trifluoride as a radiopaque agent for dental cements.

AIM: To evaluate the radiopacity, degree of conversion (DC) and flexural strength of an experimental dental cement, with several added radiopaque substances. METHODOLOGY: Titanium dioxide, quartz, zirconia, bismuth oxide, barium sulphate and ytterbium trifluoride were added to the experimental cement in five different concentrations. Radiopacity was evaluated with a phosphor plate system, and the radiodensity of specimens was compared with an aluminium step-wedge. DC was evaluated with FT-infrared spectroscopy following 20 s of photo-activation. Specimens with dimensions of 12 x 2 x 2 mm were used for the flexural strength test. Data were analysed with two-way anova and Tukey's post hoc test. RESULTS: Radiopacity of the experimental dental cements with barium sulphate and bismuth oxide at 40% and ytterbium fluoride at 30% and 40% showed no significant differences in comparison with 3 mm of Al (181, 96). CONCLUSIONS: The experimental dental cements with at least 30% added ytterbium trifluoride had satisfactory radiopacity without influencing other properties.