Bond Strength of Methacrylate-based Blends Containing Elastomeric Monomers and Alternative Initiators after Thermomechanical Cycling.

PURPOSE: To evaluate the bond strength to dentin produced by experimental adhesives formulated with an elastomeric methacrylate monomer (EMM) and an alternative initiator system based on a Thioxanthone derivative (QTX). MATERIALS AND METHODS: A self-etching primer was used. For the bonding resin, a model adhesive (G1) was formulated containing bis-GMA/TEG-DMA/HEMA (co-monomeric blend) + CQ/EDAB (initiator system). The other groups were formulated by adding to this formulation: EMM only (G2), QTX (G3), or EMM and QTX (G4). Clearfil SE Bond was used as the commercial control group. Fifty bovine teeth (n = 5) were restored with each one of the five adhesives. After restorative procedures, half of the specimens were stored in distilled water at 37°C for 24 h. The other half was fixed on a metal stub and subjected to 200,000 mechanical (50 N loading at 2 Hz frequency) and 1000 thermal cycles (5°C and 55°C). Afterwards, specimens were serially sectioned into beams and tested in tension until fracture. Bond strengths were statistically analyzed by two-way ANOVA and Tukey's test (α = 5%). RESULTS: After 24 h, significantly higher µTBS was observed for the formulation containing EMM and QTX (G4) when compared to Clearfil SE Bond (p < 0.05). No significant differences in µTBS were detected among the experimental groups after 24 h (p>0.05). After thermomechanical cycling, no significant differences were observed among groups. CONCLUSION: The addition of EMM and QTX can be considered as possible alternative in dental adhesive formulations.

Acid etching concentration as a strategy to improve the adhesive performance on Er:YAG laser and bur-prepared demineralized enamel.

OBJECTIVE: This study investigated the effect of phosphoric acid concentration on microshear bond strength (µSBS) of an etch-and-rinse adhesive system to demineralized irradiated enamel. BACKGROUND DATA: Er:YAG laser irradiation may increase acid resistance of enamel; however, its use is associated with reduced bonding effectiveness. MATERIALS AND METHODS: Three experimental etching agents and one bonding agent were fabricated. Enamel pretreatment was tested in two levels (bur and laser) and phosphoric acid was tested in four levels (control and at 35, 45, or 55%). Commercially available phosphoric acid and a bonding agent were used as control. Enamel samples were submitted to a pH-cycling model to induce demineralization. Half of the exposed demineralized enamel area was prepared with diamond bur and half was prepared with an Er:YAG laser (λ=2.94 µm, 300 mJ, 2 Hz). Specimens were randomly allocated to receive different acid etching concentrations and either the experimental or the commercial adhesive system. Microshear bond strength and the adhesive remnant index (ARI) scores were determined. µSBS's data were evaluated by two way analysis of variance (ANOVA) and Tukey's test. Kruskal-Wallis followed by Dunn's method and Mann-Whitney test were used for ARI comparisons (α=5%). RESULTS: For µSBS, no significant difference among the groups was found, either for phosphoric acid concentration or surface preparation. For ARI scores, statistically higher resin retention was found for lased groups (p<0.001). CONCLUSIONS: The increase of phosphoric acid concentration did not impair bond strength regardless of surface preparation; however, increased retention was found when demineralized enamel was prepared with laser.

Preferences on Vital and Nonvital Tooth Bleaching: A Survey Among Dentists from a City of Southern Brazil

This study evaluated the preferences of general dentists regarding vital and nonvital tooth bleaching therapies and investigated whether the time of clinical practice and post-graduate training influence these options. A cross-sectional study was conducted using a questionnaire with closed questions applied to dentists (n=276) of a mid-sized city of the southern Brazil (Pelotas, RS). Information was collected regarding sociodemographic variables, level of specialization and time since graduation. In addition, options regarding bleaching therapies including the first choice of material, technique and clinical practice for vital and nonvital tooth bleaching therapies were included. Data were submitted to descriptive analysis and the associations were evaluated using chi-square and Fisher exact tests (α=0.05). The response rate was 68% (n=187). At-home bleaching therapy was broadly preferred (78.1%) over in-office (21.9%) bleaching. For at-home bleaching, most dentists answered to use 10% carbamide peroxide (CP) (40.2%) and >30% hydrogen peroxide (HP) (31.7%) for nonvital therapies. The majority of dentists with post-graduation training preferred at-home bleaching techniques (p=0.003). At-home bleaching therapy was also more indicated by younger dentists. No association was found between the choice for nonvital bleaching therapies and time since graduation (p=0.532) or continuous education (p=0.083). In conclusion, at-home bleaching was preferred over in-office therapies; 10% CP and >30% HP were chosen as first option agents to treat discolored vital and nonvital teeth, respectively. The time in clinical practice and the level of specialization affected dentists' choices only for vital tooth bleaching treatment.

Este estudo avaliou as preferências de cirurgiões-dentistas sobre o clareamento de dentes vitais e não-vitais. Também investigou a possível relação entre o grau de formação profissional e as decisões clínicas tomadas por estes profissionais. Para isso, realizamos um estudo transversal. Cirurgiões-dentistas (n=276) de uma cidade de médio porte do sul do Brasil (Pelotas, RS) receberam um questionário contendo perguntas sobre informação sócio-demográfica, nível de especialização e ano de graduação. Adicionalmente, foram realizadas perguntas sobre o material de primeira escolha, técnicas e práticas clínicas relacionadas a clareamento de dentes vitais e não vitais. Os dados obtidos foram submetidos à análise descritiva e as possíveis associações entre variáveis foram avaliadas utilizando o teste Qui-Quadrado e teste Exato de Fisher (p<0,05). A taxa de resposta foi de 68% (187). A técnica de clareamento caseiro supervisionada foi preferida (78,1%) em detrimento da técnica em consultório (21,9%). Os dentistas escolheram preferentemente o peróxido de carbamida (PC) a 10% para clareamento vital caseiro (40,2%) e o peróxido de hidrogênio (PH) >30% para o clareamento de dentes despolpados (31,7%). A maioria dos dentistas que realizaram cursos de pós-graduação preferiram o clareamento caseiro (p=0,003). Além disso, o clareamento caseiro foi mais indicado pelos dentistas mais jovens. Não foi encontrada relação entre as escolhas para clareamento de dentes despolpados e ano de graduação (p=0,532) ou grau de formação (p=0,083). O clareamento vital caseiro foi escolhido em detrimento das técnicas de consultório; CP a 10% e HP > 30% foram os agentes de escolha para o tratamento de dentes vitais e não vitais escurecidos, respectivamente. O tempo de prática clínica e o nível de especialização foram associados com as escolhas dos dentistas somente para clareamento de dentes vitais.

Preferences on vital and nonvital tooth bleaching: a survey among dentists from a city of southern Brazil.

This study evaluated the preferences of general dentists regarding vital and nonvital tooth bleaching therapies and investigated whether the time of clinical practice and post-graduate training influence these options. A cross-sectional study was conducted using a questionnaire with closed questions applied to dentists (n=276) of a mid-sized city of the southern Brazil (Pelotas, RS). Information was collected regarding sociodemographic variables, level of specialization and time since graduation. In addition, options regarding bleaching therapies including the first choice of material, technique and clinical practice for vital and nonvital tooth bleaching therapies were included. Data were submitted to descriptive analysis and the associations were evaluated using chi-square and Fisher exact tests (α=0.05). The response rate was 68% (n=187). At-home bleaching therapy was broadly preferred (78.1%) over in-office (21.9%) bleaching. For at-home bleaching, most dentists answered to use 10% carbamide peroxide (CP) (40.2%) and >30% hydrogen peroxide (HP) (31.7%) for nonvital therapies. The majority of dentists with post-graduation training preferred at-home bleaching techniques (p=0.003). At-home bleaching therapy was also more indicated by younger dentists. No association was found between the choice for nonvital bleaching therapies and time since graduation (p=0.532) or continuous education (p=0.083). In conclusion, at-home bleaching was preferred over in-office therapies; 10% CP and >30% HP were chosen as first option agents to treat discolored vital and nonvital teeth, respectively. The time in clinical practice and the level of specialization affected dentists' choices only for vital tooth bleaching treatment.

Polymerization kinetics and reactivity of alternative initiators systems for use in light-activated dental resins.

OBJECTIVES: The purpose of this study was to evaluate the reactivity and polymerization kinetics behavior of a model dental adhesive resin with water-soluble initiator systems. METHODS: A monomer blend based on Bis-GMA, TEGDMA and HEMA was used as a model dental adhesive resin, which was polymerized using a thioxanthone type (QTX) as a photoinitiator. Binary and ternary photoinitiator systems were formulated using 1mol% of each initiator. The co-initiators used in this study were ethyl 4-dimethylaminobenzoate (EDAB), diphenyliodonium hexafluorophosphate (DPIHFP), 1,3-diethyl-2-thiobarbituric acid (BARB), p-toluenesulfinic acid and sodium salt hydrate (SULF). Absorption spectra of the initiators were measured using a UV-Vis spectrophotometer, and the photon absorption energy (PAE) was calculated. The binary system camphorquinone (CQ)/amine was used as a reference group (control). Twelve groups were tested in triplicate. Fourier-transform infrared spectroscopy (FTIR) was used to investigate the polymerization reaction during the photoactivation period to obtain the degree of conversion (DC) and maximum polymerization rate (R(p)(max)) profile of the model resin. RESULTS: In the analyzed absorption profiles, the absorption spectrum of QTX is almost entirely localized in the UV region, whereas that of CQ is in the visible range. With respect to binary systems, CQ+EDAB exhibited higher DC and R(p)(max) values. In formulations that contained ternary initiator systems, the group CQ+QTX+EDAB was the only one of the investigated experimental groups that exhibited an R(p)(max) value greater than that of CQ+EDAB. The groups QTX+EDAB+DPIHFP and QTX+DPIHFP+SULF exhibited values similar to those of CQ+EDAB with respect to the final DC; however, they also exhibited lower reactivity. SIGNIFICANCE: Water-soluble initiator systems should be considered as alternatives to the widely used CQ/amine system in dentin adhesive formulations.

Influence of water concentration in an experimental self-etching primer on the bond strength to dentin.

PURPOSE: To investigate the influence of different water concentrations in the solvents of self-etching primers on microtensile bond strength (LTBS) of an experimental adhesive system. MATERIALS AND METHODS: Five experimental self-etching primers with 0, 5, 10, 20 and 40 (wt%) water as solvent were formulated. An experimental adhesive resin (AD-50) was also synthesized to create one experimental self-etching adhesive system. Clearfil SE Bond (CSEB) was used as the commercial reference. Sixty bovine incisors were randomly separated into 6 groups. Buccal enamel was removed to expose the superficial coronal dentin; this surface was polished wet to create a standardized smear layer. After rinsing, water was removed, leaving the surface visibly dried. The dentin surfaces were etched with primer and air dried, adhesive resin was applied and photoactivated, then the composite resin restoration was placed. After storage for 24 h, the specimens were sectioned with a cooled diamond saw at low speed. Microtensile bond strength was measured and data were analyzed with one-way ANOVA/Tukey's test (alpha = 0.05). RESULTS: ANOVA showed that primer composition was a significant factor for bond strength. There was no significant difference in bond strengths between the primers with a water concentration of 40% (53.9 +/- 12.7 MPa), 20% (51.1 +/- 11.5 MPa, and 10% (47.5 +/- 11.4 MPa), and CSEB (50.7 +/- 9.8 MPa). The groups with 5% (38.6 +/- 12.9 MPa) and 0% (31.5 +/- 7.5 MPa) water presented similar bond strengths amongst themselves but were statistically significantly lower than that of the other groups. CONCLUSION: The water concentration in the primer solvent exercises a significant influence on the bond strength of this experimental self-etching adhesive system.

Onium salt reduces the inhibitory polymerization effect from an organic solvent in a model dental adhesive resin.

This study evaluated the effect of organic solvent concentration on the polymerization kinetics for a model dental adhesive resin containing a ternary photoinitiator system. A monomer blend based on the bis-GMA, TEGDMA, and HEMA was used as a model dental adhesive resin, which was polymerized using a binary system [camphorquinone (CQ) and ethyl 4-dimethylamine benzoate (EDAB)] and a ternary system [CQ, EDAB, and diphenyliodonium hexafluorphosphate (DPIHFP)]. Additionally, these blends had 0, 10, 20, 30, and 40 wt % ethanol added. Real-time Fourier transform infrared spectroscopy was used to investigate the polymerization reaction over photoactivation time. Data were plotted, and Hill's three-parameter nonlinear regression was performed for curve fitting. The addition of a solvent to the monomer blends decreased the polymerization kinetics, directly affecting the rate of polymerization, delaying vitrification, and attenuating the Trommsdorf effect. The introduction of DPIHFP displayed a strong increase in reaction kinetics, reducing the solvent inhibition effect. After 10 s of photoactivation, the binary system obtained in 0, 10, 20, 30, and 40% of ethanol, a degree of conversion of 44.6, 26.3, 13.4, 1.15, and 0.0%, respectively, whereas when a ternary system was used, the values were 54.6, 40.5, 27.4, 14.5, and 3.4%. An improvement was observed in the polymerization kinetics of a model dental adhesive resin when using a ternary photoinitiation system, making the material less sensitive to the residual presence of a solvent before photoactivation.

Influence of chain extender length of aromatic dimethacrylates on polymer network development.

OBJECTIVE: To investigate the role of chain extender size from Bis-EMA monomers on the polymerization profiles and properties of the crosslinked polymers. Additionally, the influence of Bis-GMA was also evaluated. METHODS: The polymer network from homopolymers Bis-EMA4, Bis-EMA10 and Bis-EMA30 was characterized, as well as copolymers formed among these monomers and Bis-GMA. The degree of conversion from neat and blended monomers as a function of photo-activation time was evaluated by FTIR. Rate of polymerization, network parameter and cross-link density from materials were demonstrated. Water sorption and solubility were determined according to ISO 4049 specification and the data obtained were analyzed by two-way ANOVA/Tukey's test (alpha=0.05). Flexural strength and Young's modulus from polymerized monomers/co-monomers were measured after 24h water storage at 37 degrees C and the results were analyzed by one-way ANOVA/Tukey's test (alpha=0.05). RESULTS: Monomers with larger ethylene oxide units presented the highest values regarding the degree of conversion and cross-link density. The effect of the chain extender length was also observed in water sorption and solubility polymer characteristics, with Bis-EMA4 being the most hydrophobic polymer. Bis-EMA10 and Bis-EMA30 homopolymers were not able to be tested with the three point bending test due to their great flexibility. The addition of Bis-GMA produced stronger and more rigid Bis-EMA polymers (p<0.05). SIGNIFICANCE: Aromatic dimethacrylates with different chain extender lengths can be a useful alternative in controlling the properties of a dental material, adjusting those to specific applications.

Onium salt improves the polymerization kinetics in an experimental dental adhesive resin.

The aim of this study was to evaluate the influence of an onium salt in the polymerization kinetics of a dental adhesive model resin. A monomer mixture, based on Bis-GMA, TEGDMA and HEMA, was used as a model dental adhesive resin, which was polymerized using camphorquinone (CQ) as a photo-initiator in addition to either binary or ternary photo-initiator systems. The binary systems were formulated with different concentrations of diphenyliodonium hexafluorphosphate or ethyl 4-dimethylaminobenzoate in relation to the monomer and 1mol% of CQ. The ternary system was a blend of 1mol% of CQ, 2mol% of ethyl 4-dimethylamino benzoate and 0.25, 0.5, 1, 2 or 4mol% of onium salt. Real time Fourier Transform infrared spectroscopy was used to investigate the polymerization reaction over the photo-activation time. When CQ was used as photo-initiator, a slow polymerization reaction was observed and a lower monomer conversion. The addition of a second component (onium salt or amine) increases the polymerization rate and conversion independent on the co-initiator concentration. Ternary photo-initiator system showed an improvement on the polymerization rate of the dental adhesive model resin leading to high conversion in short photo-activation time. Also, a mechanism for initiating polymerization using an amine or onium salt as a co-initiator component is proposed.