Addition of ammonium-based methacrylates to an experimental dental adhesive for bonding metal brackets: Carious lesion development and bond strength after cariogenic challenge

Debonding Characteristic and Survival Probability of Adhesive Flash-Free Ceramic Orthodontic Brackets Following pH Cycling

OBJECTIVES

 Orthodontic bracket bond failure is an obstacle in clinical orthodontics. This study investigated the influence of pH cycling on the shear bond strength (SBS), adhesive remnant index (ARI), and survival probability of adhesive-precoated flash-free ceramic brackets.

MATERIALS AND METHODS

 Forty mandibular premolars were randomly divided into two groups (n = 20): C: noncoated orthodontic brackets, and F: flash-free adhesive-precoated orthodontic brackets. Each group was subdivided into two subgroups according to storage medium solutions (n = 10): in subgroup AS, specimens were immersed in artificial saliva for 24 hours, and in Subgroup ASL, specimens were recycled between a demineralizing solution and an artificial saliva for 42 days. Within each subgroup, specimens were subjected to SBS and ARI testing. SBS data were analyzed using one-way ANOVA (analysis of variance) and Tukey's post-hoc test. Weibull analysis was performed on the SBS data to determine the characteristic SBS and their survival probabilities.

RESULTS

 Flash-free adhesive-precoated brackets had higher significant (p < 0.001) SBS values in both the AS group (17.74 ± 1.74 MPa) and the ASL group (12.61 ± 1.40 MPa) compared with the noncoated bracket (10.67 ± 1.55 and 7.89 ± 1.39 MPa, respectively). The ARI scores for the noncoated brackets in the AS group were 70% occurrence for score 1, while 90% for score 1 in the ASL group. For the flash-free precoated brackets, ARI scores were 70% occurrence for score 2 in the AS group, while 80% for score 2 in the ASL group. Flash-free brackets had higher SBS in both AS and ASL groups (14.07 and 9.76 MPa, respectively), at 95% survival probability.

CONCLUSION

 Flash-free orthodontic brackets performed better in terms of significantly higher bond strength and higher ARI scores. Meanwhile, noncoated brackets revealed acceptable SBS results in both storage medium groups. Flash-free brackets showed higher survival than the noncoated brackets in both storage medium groups at 90% survival probability.

Brazilian red propolis as a potential antimicrobial additive in orthodontic primers

This study evaluated the effect of adding ethanolic extract of red propolis (EERP) on antimicrobial activity, polymerization kinetics (PK), degree of conversion (DC), and shear bond strength (SBS) of the orthodontic adhesive system. Transbond XT Primer was the control group (G1). The experimental adhesives contained 3.25 mg/mL (G2) and 6.50 mg/mL (G3) EERP. Minimum inhibitory concentration and biofilm assay against Streptococcus mutans, and bacterial and exopolysaccharide (EPS) evaluation by confocal laser scanning microscope were performed. PK and DC were evaluated by Fourier Transform Infrared Spectroscopy. The bracket-tooth SBS was evaluated by a universal testing machine. Both antimicrobial and SBS results were analyzed by ANOVA and Tukey's post-hoc test (p<0.05). PK and DC data were submitted to ANOVA and Bonferroni post-hoc test. G3 presented better antimicrobial activity, inhibiting more than 95% of planktonic S. Mutans, 25% of biofilm dry-weight, and 50% of EPS production (p<0.05). PK was different among the groups. DC after 40 seconds of photoactivation ranged from 68.62% for G1 to 76.85% for G2 (p<0.05). SBS data was not presented as statistically significant (p>0.05). Transbond XT Primer modified with 6.5 mg/mL EERP demonstrated antimicrobial activity with no reduction of the bracket-tooth SBS. Propolis-modification did not influence the physic-chemical properties of the orthodontic adhesive.

Remineralization and anti-demineralization effect of orthodontic adhesives on enamel surrounding orthodontic brackets: a systematic review of in vitro studies

OBJECTIVE

White spot lesions are initial sign of enamel caries that compromise esthetic appearance following orthodontic treatment. Thus, the systematic review was conducted to evaluate the remineralization potential of orthodontic adhesives on early-enamel lesions surrounding orthodontic bracket.

METHODS

Search strategy was performed through three databases (PubMed, Web of Science, and Scopus). A total number of 1712 studies were identified for being potentially relevant, 62 among them were further assessed. Finally, 24 studies were included in this systematic review after adopting the eligibility criteria. The methodologies used to assess enamel remineralization were micro-computed tomography, cross-sectional microhardness, and polarized light microscopy for evaluating remineralization extent; surface microhardness, color change, and laser-induced fluorescence for evaluating superficial surface mineralization; Fourier Transform InfraRed, and Energy Dispersive Spectroscopy technique for chemical characterization.

RESULTS

Bioactive glass (BAG), nano-hydroxyapatite (n-HAP), nano-amorphous calcium phosphate (n-ACP), nano-calcium fluoride (n-CaF2), fluorinated amorphous calcium phosphate nanoparticles (AFCP), and ammonium-based methacrylate monomer were incorporated into orthodontic adhesives. Seven out of the 24 included studies utilized commercially available orthodontic adhesives. While the remaining studies utilized experimental bioactive adhesives; 13 studies evaluated adhesives containing (BAG), two studies evaluated adhesives containing (n-ACP), one study evaluated adhesives containing (AFCP), and one study evaluated adhesives containing (n-HAP). Orthodontic adhesives containing the previously mentioned additives showed significant remineralization power compared to control group. Majority of studies that evaluated bioactive-based orthodontic adhesives revealed significant remineralization effect in comparison with their corresponding control groups. Out of 24 studies, 8 have assessed ion-release. However, few numbers of included studies evaluated the ion-release peak values. The output of most studies reported a significant increase of ion-release over time. Only one study reported a mark decrease of calcium and phosphate ions after 72 h. Following the high risk of bias in the majority of studies, and lack of standard evaluation protocol, meta-analysis was not conducted.

CONCLUSION

The outcome of the included studies supports the effectiveness of incorporation of remineralizing agents into orthodontic adhesives.

Effect of strontium fluoride on mechanical and remineralization properties of enamel: An in-vitro study on a modified orthodontic adhesive

OBJECTIVES

Evaluate the ability of strontium fluoride on bond strength and enamel integrity after incorporation within orthodontic adhesive system as a delivery vehicle.

METHODS

Experimental orthodontic adhesive system Transbond™ XT were modified with 1% Sr2+, 0.5% SrF2, 1% strontium, 0.5% Sr2+, 1% F-, 0.5% F-, and no additions were control. Mixing of formulation was monitored using Fourier transform infrared spectroscopy. Small-molecule drug-discovery suite was used to gain insights into Sr2+, F-, and SrF2 binding. Shear bond testing was performed after 6-months of ageing. Enamel blocks were cut, and STEM pictures were recorded. Specimens were indented to evaluate elastic modulus. Raman microscope was used to collect Raman spectra and inspected using a scanning electron microscope. Crystal structural analysis was performed using X-ray diffraction. Effect of material on cellular proliferation was determined. Confocal was performed to evaluate the effect of formulation on biofilms.

RESULTS

FTIR of modified adhesives depicted peak changes within range due to various functional groups existing within samples. TEM represented structurally optimized hexagonal unit-cell of hydroxyapatite. Mean shear bond strength is recorded highest for Transbond XT with 1% SrF2. Dead bacterial percentage appeared higher in 0.5% SrF2 and 1% F- specimens. Crystal lengths showed an increase in 0.5% and 1% SrF2 specimens. Phase contrast within TEM images showed a union of 0.5% SrF2 crystal with enamel crystal with higher elastic modulus and highly mineralized crystalline hydroxyapatite. Intensity of ν1 PO43- and ν1 CO32- along with carbonate - / ν1PO43- ratio displayed good association with strontium fluoride. The formulation showed acceptable cell biocompatibility (p < 0.353). All specimens displayed characteristic diffraction maxima of different apatite angles within XRD.

SIGNIFICANCE

Experimental results suggested good biocompatibility, adequate mechanical strength, and far-ranging crystallization ability. This would provide a new strategy to overcome the two major challenges of fixed orthodontics, biofilm growth, and demineralization of enamel.

Application of an Antibacterial Coating Layer via Amine-Terminated Hyperbranched Zirconium-Polysiloxane for Stainless Steel Orthodontic Brackets

The massive growth of various microorganisms on the orthodontic bracket can form plaques and cause diseases. A novel amine-terminated hyperbranched zirconium-polysiloxane (HPZP) antimicrobial coating was developed for an orthodontic stainless steel tank (SST). After synthesizing HPZP and HPZP-Ag coatings, their structures were characterized by nuclear magnetic resonance spectroscopy, scanning electron microscopy, thickness measurement, contact angle detection, mechanical stability testing, and corrosion testing. The cell toxicity of the two coatings to human gingival fibroblasts (hGFs) and human oral keratinocytes (hOKs) was detected by cell counting kit eight assays, and SST, HPZP@SST, and HPZP-Ag@SST were cocultured with Staphylococcus aureus, Escherichia coli, and Streptococcus mutans for 24 hr to detect the antibacterial properties of the coatings, respectively. The results show that the coatings are about 10 μm, and the water contact angle of HPZP coating is significantly higher than that of HPZP-Ag coating (P < 0.01). Both coatings can be uniformly and densely distributed on SST and have good mechanical stability and corrosion resistance. The cell counting test showed that HPZP coating and HPZP-Ag coating were less toxic to cells compared with SST, and the toxicity of HPZP-Ag coating was greater than that of HPZP coating, with the cell survival rate greater than 80% after 72 hr cocultured with hGFs and hOKs. The antibacterial test showed that the number of bacteria on the surface of different materials was ranked from small to large: HPZP@SST < HPZP-Ag@SST < SST and 800 μg/mL HPZP@SST showed a better bactericidal ability than 400 μg/mL after cocultured with S. aureus, E. coli, and S. mutans, respectively (all P < 0.05). The results showed that HPZP coating had a better effect than HPZP-Ag coating, with effective antibacterial and biocompatible properties, which had the potential to be applied in orthodontic process management.

Antimicrobial and cytotoxic capacity of pyroligneous extracts films of Eucalyptus grandis and chitosan for oral applications

Chitosan films containing distilled pyroligneous extracts of Eucalyptus grandis (DPEC), characterized and developed by Brazilian Agricultural Research Corporation-Embrapa Temperate Agriculture (EMBRAPA-CPACT), were evaluated for antimicrobial activity against Candida albicans, Streptococcus mutans, and Lactobacillus acidophilus by direct contact test. Further, their capacity for the prevention of teeth enamel demineralization and cytotoxicity in vitro were also determined. The natural polymers were tested at different concentrations (1500-7500 µg mL-1) and the formulation of an experimental fluoride varnish with antimicrobial activity was evaluated by direct contact test, whereas cytotoxicity was analyzed through the colorimetric MTT assay. Preliminary data showed no statistically significant differences in cytotoxicity to NIH/3T3 cell line when DPEC is compared to the control group. On the other hand, the antimicrobial capacity and demineralization effects were found between the test groups at the different concentrations tested. Chitosan films containing distilled pyroligneous extracts of E. grandis may be an effective control strategy to prevent biofilm formation related to dental caries when applied as a protective varnish. They may inhibit the colonization of oral microorganisms and possibly control dental caries through a decrease in pH and impairment of enamel demineralization.

Physicochemical properties and biological effects of quaternary ammonium methacrylates in an experimental adhesive resin for bonding orthodontic brackets

METHODOLOGY

Fixed orthodontic appliances may lead to biofilm accumulation around them that may increase caries risk. This study aimed to evaluate the influence of quaternary ammonium methacrylates (QAMs) on the physicochemical properties, cytotoxicity, and antibacterial activity of adhesive resins for orthodontic purposes. A base resin was prepared with a comonomer blend and photoinitiator/co-initiator system. Two different QAMs were added to the base adhesive: dimethylaminododecyl methacrylate at 5 wt.% (DMADDM) or dimethylaminohexadecyl methacrylate (DMAHDM) at 10 wt.%. The base adhesive, without QAMs, (GC) and the commercial Transbond™ XT Primer 3M (GT) were used as control. The resins were tested immediately and after six months of aging in the water regarding the antibacterial activity and shear bond strength (SBS). The antibacterial activity was tested against Streptococcus mutans via metabolic activity assay (MTT test). The groups were also tested for the degree of conversion (DC) and cytotoxicity against keratinocytes.

RESULTS

The resins containing QAM showed antibacterial activity compared to the commercial material by immediately reducing the metabolic activity by about 60%. However, the antibacterial activity decreased after aging (p<0.05). None of the groups presented any differences for SBS (p>0.05) and DC (p>0.05). The incorporation of DMADDM and DMAHDM significantly reduced the keratinocyte viability compared to the GT and GC groups (p<0.05).

CONCLUSION

Both adhesives with QAMs showed a significant reduction in bacterial metabolic activity, but this effect decreased after water aging. Lower cell viability was observed for the group with the longer alkyl chain-QAM, without significant differences for the bonding ability and degree of conversion. The addition of QAMs in adhesives may affect the keratinocytes viability, and the aging effects maybe decrease the bacterial activity of QAM-doped materials.

Cutting-edge filler technologies to release bio-active components for restorative and preventive dentistry

Advancements in materials used for restorative and preventive treatment is being directed toward "bio-active" functionality. Incorporation of filler particles that release active components is a popular method to create bio-active materials, and many approaches are available to develop fillers with the ability to release components that provide "bio-protective" or "bio-promoting" properties; e.g. metal/calcium phosphate nanoparticles, multiple ion-releasing glass fillers, and non-biodegradable polymer particles. In this review paper, recent developments in cutting-edge filler technologies to release bio-active components are addressed and summarized according to their usefulness and functions, including control of bacterial infection, tooth strengthening, and promotion of tissue regeneration.

Ionic liquid as antibacterial agent for an experimental orthodontic adhesive

OBJECTIVE

The aim of this study was to formulate and evaluate experimental orthodontic adhesives with different concentrations of 1-n-butyl-3-methylimidazoilium bis(trifluoromethanesulfonyl)imide (BMIM.NTf₂).

METHODS

The experimental orthodontic adhesives were formulated with methacrylate monomers, photoinitiators and silica colloidal. The ionic liquid BMIM.NTf₂ was synthesized and characterized. BMIM.NTf₂ was added at 5 (G_5%), 10 (G_10%) and 15 (G_15%) wt.%. One group contained no BMIM.NTf₂ to function as control (G_Ctrl). The adhesives were evaluated for polymerization kinetics, degree of conversion (DC), Knoop hardness and softening in solvent, ultimate tensile strength (UTS), shear bond strength (SBS), thermogravimetric analysis (TGA), antibacterial activity and cytotoxicity.

RESULTS

BMI.NTf₂ showed the characteristic chemical peaks. The polymerization kinetics were different among the groups. G_10% and G_15% showed higher DC (p < 0.05). G_5% and G_Ctrl had no differences for softening in solvent (p > 0.05). There were no differences for UTS (p > 0.05) and SBS (p > 0.05). TGA showed one different peak for G_15%. All groups with BMIM.NTf₂ showed antibacterial activity compared to G_Ctrl (p < 0.05) without cytotoxicity (p > 0.05).

SIGNIFICANCE

To reduce biofilm formation around brackets and to prevent demineralization at susceptible sites, materials have been developed with antibacterial properties. In this study, a new experimental orthodontic adhesive was formulated with an imidazolium ionic liquid (BMIM.NTf₂) as antibacterial agent. The incorporation of 5 wt.% of ionic liquid decreased biofilm formation without affecting the physico-chemical properties and cytotoxicity of an experimental orthodontic resin.