Effect of handling, time of use and photoactivation on the contamination of dental composite resins

This study evaluated the effect of contamination of composite resins (CRs) handled by undergraduate students during restorative procedures, varying the time (baseline, 30 days and 60 days) and experimental condition (before and after handling, contamination with saliva [positive control] and photoactivation). Eight CR tubes were randomly distributed at the dental clinic and the samples were organized into four groups: CR fragments collected before (GB) and after (GA) the restorative procedure; CR fragments contaminated with saliva (GS) and photoactivated (GP) both collected after the procedure. These 4 groups were evaluated in 3 different times: baseline (after sealing), 30 days and 60 days of use of the CR. Samples that had positive turbidity in Brain HeartInfusion (BHI) broth were sown in BHI and Sabouraud Dextrose (SB) agars for subsequent counting of Colony Forming Units (CFU mL-1). The results showed that the handling was responsible for increasing contamination (p < 0.05) at the baseline (GB [n = 0] and GA [n = 3]), as well as after 30 (GB [n = 1] and GA [n = 6]) and 60 (GB [n = 1] and GA [n = 5]) days of use. Photoactivation was responsible for the reduction for microorganisms in T0 and T60. Additionally, the time use and conservation did not influencethe contamination of CRs. Handling was responsible for the increase of contamination of CR, the photoactivation seems to reduce the number of viable microorganisms and the time of use seems not to potentiate the effect of tube contamination.

Influence of modulated photo-activation on shrinkage stress and degree of conversion of bulk-fill composites

Abstract This study aimed to evaluate the polymerization properties of bulk-fill materials (low and high-viscosity) by using high-intensity continuous light and intermittent photo-activation in terms of polymerization shrinkage stress and degree of conversion (DC). The following Bulk-fill and Conventional nanofilled resin composites were evaluated: Filtek Z350XT Flow (3M/ESPE), SureFil SDR Flow (Dentsply), Filtek Bulk Fill Flow (3M/ESPE), Filtek Z350XT (3M/ESPE) and Filtek Bulk Fill Posterior (3M/ESPE). A LED device (DB 685, Dabi Atlante) was used for both protocols: continuous uniform and intermittent photo-activation (light-on and light-off cycles) with identical radiant exposure (14 J/cm2). The polymerization shrinkage stress (n=6) was evaluated by inserting a single increment of 12 mm3 between two stainless steel plates (6×2 mm) adapted to a Universal Testing Machine (UTM), at different times. Measurements were recorded after photo-activation. The degree of conversion was evaluated by Fourier transformed infrared spectroscope (FTIR) with an attenuated total reflectance (ATR) accessory (n=5). Data were analyzed by three-way ANOVA and Tukey's HSD (α=0.05) tests. Bulk Fill Posterior presented higher shrinkage stress values when photo-activated with the intermittent technique (p<0.05). The intermittent photo-activation increased the degree of conversion for the low-viscosity bulk-fills (p<0.05). Therefore, the use of modulated photo-activation (intermittent) must be indicated with caution since its use can influence the shrinkage stress and degree of conversion of composites, which varies according to the resin formulations.

Resumo O presente estudo teve como objetivo avaliar as propriedades de polimerização de materiais bulk-fill (baixa e alta viscosidade) utilizando luz contínua de alta intensidade e fotoativação intermitente em relação ao estresse de contração de polimerização e grau de conversão (DC). As seguintes resinas compostas Bulk-fill e nanohíbridas convencionais foram avaliadas: Filtek Z350XT Flow (3M/ESPE), SureFil SDR Flow (Dentsply), Filtek Bulk Fill Flow (3M/ESPE), Filtek Z350XT (3M/ESPE) e Filtek Bulk Fill Posterior (3M/ESPE). Um dispositivo de LED (DB 685, Dabi Atlante) foi utilizado nos dois protocolos: fotoativação contínua e intermitente contínua (ciclos de liga e desliga) com exposição idêntica (14 J/cm2). A tensão de contração de polimerização (n=6) foi avaliada através da inserção de um incremento único de 12 mm3 entre duas placas de aço inoxidável (6×2 mm) adaptadas a uma Máquina de Ensaio Universal (UTM), em tempos diferentes. As medições foram registradas após a fotoativação. O grau de conversão foi avaliado por FTIR-ATR (n=5). Os dados foram analisados ​​pelos testes ANOVA a três fatores e teste de Tukey (α=0,05). A resina Bulk Fill Posterior apresentou maiores valores de tensão de contração quando fotoativadas com a técnica intermitente (p<0,05). A fotoativação intermitente aumentou o grau de conversão nas resinas bulk-fill de baixa viscosidade (p<0,05). Portanto, o uso de fotoativação modulada (intermitente) deve ser indicado com cautela, uma vez que seu uso pode influenciar a tensão de contração e o grau de conversão dos compósitos, o que varia de acordo com as formulações da resina.

Influence of pre-curing different adhesives on the color stability of cemented thin ceramic veneers

Abstract The objective was to evaluate the color stability of thin ceramic veneers as a function of the curing mode (with and without pre-cure) of different adhesive systems applied to the internal surface of ceramics. Five adhesive systems (Scotchbond Multi-Purpose, Single Bond Universal, Gluma 2 Bond, Ambar, and Ambar APS) and photo-cured resin cement (Allcem Veneer) were used for cementing 0.6 mm-thick feldspathic veneers (Mark II) on composite resin substrates (Charisma Diamond). The groups, according to adhesive system, were divided into two subgroups (n=10): i) adhesive and resin cement were polymerized separately (pre-cure of the adhesive), ii) adhesive and resin cement were polymerized simultaneously. The CIELab color parameters were determined with a spectrophotometer at 24h (baseline), 7 days, 30 days and 12 months. Data were analyzed by two-way ANOVA and Tukey's test (α=0.05). The results indicated statistically significant differences for adhesive systems and time. The mode of curing of the adhesive system was not statistically significant: pre-cured adhesives (2.6±1.3) and not pre-cured adhesives (2.8±1.4). For the adhesives, ΔE values varied in the following order: Ambar-APS (1.6±0.5) < Scotchbond Multi-Purpose (2.6±1.2) = Gluma 2 Bond (2.7±1.2) = Ambar (2.9±1.2) < Single Bond Universal (3.5±1.5). For time, ΔE values were: 7 days (1.7±0.7), 30 days (3.5±1.2) and 12 months (2.9±1.3). It can be concluded that the different adhesive systems used for cementing thin ceramic veneers influenced the final color of the indirect restorations. The adhesives curing mode did not present a significant effect in the color stability of thin ceramic veneers.

Resumo O objetivo deste estudo foi avaliar a estabilidade de cor de laminados cerâmicos de espessura fina em função do momento de ativação de diferentes sistemas adesivos na superfície interna das cerâmicas. Foram utilizados 5 sistemas adesivos (Scotchbond Multiuso, Single Bond Universal, Gluma 2 Bond, Ambar and Ambar APS) e o cimento resinoso fotoativado (Allcem Veneer) para cimentação de lâminas de cerâmica feldspática (Mark II) com 0,6 mm de espessura, sobre substratos de resina composta (Charisma Diamond). Os grupos, de acordo com o sistema adesivo utilizado, foram divididos em dois subgrupos (n=10): i) adesivo e cimento resinoso foram polimerizados separadamente (polimerização isolada do adesivo), ii) adesivo e cimento resinoso foram polimerizados ao mesmo tempo (polimerização simultânea). Os parâmetros de cor do sistema CIELab foram determinados com um espectrofotômetro nos tempos de 24 h (baseline), 7 dias, 30 dias e 12 meses. Os dados foram analisados por ANOVA a dois fatores e teste de Tukey (α=0,05). Os resultados indicaram diferenças estatísticas significantes para os sistemas adesivos e tempo. O momento da fotoativação do sistema adesivo não foi estatisticamente significante: polimerização prévia (2,6±1,3) e polimerização simultânea (2,8±1,4). Para o sistema adesivo, os valores médios de ΔE variaram na seguinte ordem: Ambar APS (1,6±0,5)<Scotchbond Multi-Purpose (2,6±1,2)=Gluma 2 Bond (2,7±1,2)=Ambar (2,9±1,2)<Single Bond Universal (3,5±1,5). Para o fator tempo o ΔE foi: 7 dias (1,7±0,7), 30 dias (3,5±1,2) e 12 meses (2,9±1,3). Pode-se concluir que os diferentes sistemas adesivos utilizados na cimentação de laminados cerâmicos de espessura fina influenciaram na cor final das restaurações. O momento da fotoativação, isolada ou simultânea ao cimento resinoso, não apresentou efeito significativo na estabilidade de cor dos laminados cerâmicos de espessura fina.

Influence Of Different Bleaching Systems On The Bond Strength Of Laminate Veneer To Enamel

Purpose:The objective of this in-vitro study was to examine the microtensile bond strength of a porcelain laminate veneer (PLV) to tooth surface bleached with photoactivation by blue light-emitting diode (LED) or diode laser. Methods:Eigthteen extracted human central incisors were randomly divided into three groups. Two sticks were obtained from each tooth (n=12). Before surface treatments; teeth were prepared to provide space for PLVs. The first group teeth were bleached with Whiteness HP which is contain 35% hydrogen peroxide (HP) and then photoactivated with a LED for 20 seconds. The second group were bleached with Laserwhite 20 which is contain 46% HP and photoactivated with a diode laser for 30 seconds. The third group received no surface treatment and served as the control group. IPS Esthetic ceramic veneers were luted with Variolink II veneer cement . The teeth were sectioned to obtain porcelain-resin-enamel/dentin sticks and submitted to a MTB testing device. The maximum load at fracture was recorded. Data were analyzed using one-way ANOVA followed by the Tukey HSD post-hoc test at a preset α of 0.05. Results:One-way ANOVA revealed that there was significant difference between LED unit group and control group (p<.05) but no statistical differences were observed with diode laser group (p>.05) The LED unit group presented significantly lower bond strength value (6.49±2.3 MPa) than diode laser (8.49±3.1 MPa) and control groups (9.53±2.7 MPa). Conclusion:The results suggested that bleaching therapy with activation by LED or diode laser reduced the bond strength of IPS Esthetic ceramic veneers to tooth surfaces.

Avaliação da microdureza superficial de resinas compostas, variando os métodos de fotoativação / Microhardness evaluations of composite resins using different polymerization methods

Objetiva-se avaliar a eficiência de três métodos de fotoativação sobre quatro resinas compostas, através do ensaio de microdureza Knnop. Quatro resinas compostas foram selecionadas: R1-NaturalLook®- DFL, R2-Opallis®-FGM, R3-Ice®-SDI e R4-FiltekTMZ350XT 3M/ESPE. Um total de 120 amostras, divididas em 4 grupos experimentais (n=30), sendo 10 fotoativadas com luz halógena contínua (F1), 10 com o LED (F2) e 10 com luz halógena pulsátil (F3). A microdureza Knnop da superfície foi determinada em microdurômetro, sob uma carga de 50g por 15s, perfazendo um total de três indentações por amostra. Os dados obtidos foram analisados por ANOVA e teste de Tukey com 5% de significância. Para todos os materiais testados e métodos de fotoativação, a microdureza dos materiais R1 e R2 não foram influenciados pelos diferentes métodos (p>0,05), a microdureza do material R3 foi maior quando do uso da luz halógena contínua do que com luz halógena pulsátil (p<0,05) e a microdureza do material R4 quanto ao uso do LED foi inferior aos outros métodos. Das resinas microhíbridas a que apresentou microdureza superior foi a R3. A resina R4 obteve a melhor microdureza no estudo independente do método de fotoativação. A luz halógena continua apresentou resultado superior ao sistema de LED.

Objective is to evaluate the efficiency of three activation methods on four composite resins by testing microhardness Knnop. Four composites were selected: R1-NaturalLook®-DFL, R2-Opallis®-FGM, R3-Ice®-SDI and R4-FiltekTMZ350XT 3M/ESPE. A total of 120 samples were divided into 4 groups (n = 30), 10 light-cured with halogen light continuous (F1), 10 with LED (F2) and 10 with halogen light pulsed (F3). Microhardness Knnop surface was determined by microhardness under a load of 50g for 15s, for a total of three indentations per sample. Data were analyzed by ANOVA and Tukey's test at 5% significance. For all tested materials and methods of curing, the hardness of materials R1 and R2 were not influenced by different methods (p> 0.05), the hardness of the material R3 was greater when using halogen continuous light than halogen light pulsatile (p <0.05) and R4 microhardness of the material as the use of LED was less than other methods. Microhybrid resins that showed higher hardness was R3. The resin R4 achieved best in independent study hardness of polymerization method. The halogen light continuous showed superior results to LED system.

The effect of photoactivation time and light tip distance on the degree of conversion of light and dual-cured dentin adhesives.

Background: The degree of conversion of dental adhesive is an important parameter since poor mechanical properties are related to low percentage of monomer-to-polymer conversion within resin-based materials. Objectives: To evaluate the influence of polymerization time and light guide distance on the degree of conversion (DC) of three contemporary dental adhesives. Materials and Methods: The spectral data of ExciTE DSC, Single Bond ® , and Adper ® Prompt L-Pop were analyzed using FTIR spectroscopy after 20 s, 40 s, and 60 s of photoactivation times. Light tip distances were kept at 1, 3, and 6 mm during the exposures. Statistics: Data were analyzed using ANOVA and Tukey's test (α = 0.05). Results: Within groups, greater DC values were found using a tip distance of 1 mm or a 60-s curing time for Single Bond ® (59%) and Adper ® Prompt L-Pop (65%). No statistically significant difference (P > 0.05) was found using either 1 mm or 3 mm tip distances after 20 s, 40 s, and 60 s of light curing time for Single Bond ® . ExciTE ® DSC showed the greatest DC values with light tip distances of 1 mm (90%) and 3 mm (89%), using 60 s of light curing. Conclusion : The self-etch adhesive Adper ® Prompt L-Pop could be applied in shallow cavity preparations and must be light cured for at least 40 s. The light-cured total-etch adhesive ExciTE ® DSC could be applied in every restorative scenario if the curing time is extended up to 60 s or if the tip distance is extended up to 3 mm.

A técnica de fotoativação pulso-espera pode substituir a técnica convencional? -bavaliação através de ensaios de microdureza / Can the pulse-delay photoactivation technique substitute the conventional technique? - evaluation by microhardness tests

Introdução:A contração de polimerização é uma propriedade inerente às resinas compostas a qual pode ser responsável por eventos como infiltração marginal, sensibilidade pós operatória e trincas na estrutura dental. Com o intuito de minimizar tais efeitos adversos, técnicas de polimerização alternativas podem ser utilizadas. Objetivo: Avaliar a eficácia da técnica pulso-espera na ativação de resinas compostas através da microdureza Vickers. Material e método: Trinta e cinco corpos de prova foram confeccionados e distribuídos em sete grupos: De acordo com o grupo, os corpos de prova tinham espessura de 2 ou 4 mm, inseridos como único incremento ou incrementos de 1 mm, e foram fotoativados com 500 mW/cm2 durante 40 s (fotoativação convencional) ou com ativação de 250 mW/cm2 durante os primeiros 3 s, seguido de intervalo de 1 min para a ativação de cada incremento, e espera de 5 min para ativação final por 40 s (técnica pulso-espera). A microdureza foi medida na superfície oposta à fotoativação, exceto para o grupo controle que foi medido na superfície irradiada. Resultado: A média (VHN) das durezas encontradas foram: G1- 86,5 ± 2,0 ; G2- 52,8 ± 2,3; G3- 92,3 ± 1,4; G4- 86,9 ± 1,7; G5- 91,2 ± 2,4; G6- 66,2 ± 1,7; Controle- 101,3 ± 2,7. O teste ANOVA para dois fatores de variação, espessura do incremento e técnica de fotoativação (F = 404,79) e o teste de Tukey (T = 4,56) evidenciaram diferenças significativas entre os grupos (p < 0,01), exceto entre os grupos 3 e 5. Conclusão: Os resultados mostraram que, com 2 mm de profundidade, todas as técnicas de inserção e fotoativação empregadas apresentaram polimerização adequada. No entanto, a 4 mm de profundidade, apenas a técnica incremental com ativação convencional apresentou polimerização satisfatória.

Introduction: The polymerization shrinkage is an inherent property of the resins which may be responsible for events such as microleakage, postoperative sensitivity and microcracks in the dental structure. In order to minimize such adverse effects, alternative polymerization techniques can be used. Objective: Evaluate the efficacy of the pulse-delay technique in the activation of composites by Vickers microhardness. Material and method: Thirty-five samples were created and divided into seven groups: According to the group, the specimens had thickness of 2 or 4 mm, could be inserted as single increment or 1mm increments, and were photoactivated with 500 mW/cm2 for 40 s (conventional photoactivation) or received activation of 250 mW/cm2 during the initial 3 s, with 1 min delay for activation of each increment, and 5 min delay to final activation for 40 s (pulse-delay technique). Vickers microhardness was measured on the bottom surface, except for the control group which was measured at the top surface. Result: The hardness (VHN) found were: G1- 86.5 ± 2.0 ; G2- 52.8 ± 2.3; G3- 92.3 ± 1.4; G4- 86.9 ± 1.7; G5- 91.2 ± 2.4; G6- 66.2 ± 1.7; Control- 101.3 ± 2.7. ANOVA for two variation factors, increment thickness and photoactivation technique (F = 404.79) and Tukey test (T = 4.56) showed significant differences among groups (p < 0.01), except between groups 3 and 5. Conclusion: Results showed that, with 2 mm in depth, all insertion/photoactivation techniques employed presented suitable polymerization. However, at 4 mm in depth, only incremental technique with conventional polymerization showed to be efficient.

Effect of different light curing units on Knoop hardness and temperature of resin composite.

Aim: To evaluate the influence of quartz tungsten halogen and plasma arc curing (PAC) lights on Knoop hardness and change in polymerization temperature of resin composite. Materials and Methods: Filtek Z250 and Esthet X composites were used in the shade A3. The temperature increase was registered with Type-k thermocouple connected to a digital thermometer (Iopetherm 46). A self-cured polymerized acrylic resin base was built in order to guide the thermocouple and to support the dentin disk of 1.0 mm thickness obtained from bovine tooth. On the acrylic resin base, elastomer mold of 2.0 mm was adapted. The temperature increase was measured after composite light curing. After 24 h, the specimens were submitted to Knoop hardness test (HMV-2000, Shimadzu, Tokyo, Japan). Data were submitted to ANOVA and Tukey's test (a = 0.05). Results: For both composites, there were no significant differences (P > 0.05) in the top surface hardness; however, PAC promoted statistically lower (P < 0.05) Knoop hardness number values in the bottom. The mean temperature increase showed no significant statistical differences (P > 0.05). Conclusion: The standardized radiant exposure showed no influence on the temperature increase of the composite, however, showed significant effect on hardness values.

Polymerization shrinkage stress of composites photoactivated by different light sources

The purpose of this study was to compare the polymerization shrinkage stress of composite resins (microfilled, microhybrid and hybrid) photoactivated by quartz-tungsten halogen light (QTH) and light-emitting diode (LED). Glass rods (5.0 mm x 5.0 cm) were fabricated and had one of the surfaces air-abraded with aluminum oxide and coated with a layer of an adhesive system, which was photoactivated with the QTH unit. The glass rods were vertically assembled, in pairs, to a universal testing machine and the composites were applied to the lower rod. The upper rod was placed closer, at 2 mm, and an extensometer was attached to the rods. The 20 composites were polymerized by either QTH (n=10) or LED (n=10) curing units. Polymerization was carried out using 2 devices positioned in opposite sides, which were simultaneously activated for 40 s. Shrinkage stress was analyzed twice: shortly after polymerization (t40s) and 10 min later (t10min). Data were analyzed statistically by 2-way ANOVA and Tukey's test (a=5 percent). The shrinkage stress for all composites was higher at t10min than at t40s, regardless of the activation source. Microfilled composite resins showed lower shrinkage stress values compared to the other composite resins. For the hybrid and microhybrid composite resins, the light source had no influence on the shrinkage stress, except for microfilled composite at t10min. It may be concluded that the composition of composite resins is the factor with the strongest influence on shrinkage stress.

Este estudo comparou a contração de polimerização de resinas compostas fotoativadas por luz halógena (QTH) e diodo emissor de luz (LED). Foram confeccionados bastões de vidro (5,0 mm x 5,0 cm), e uma de suas extremidades sofreu jateamento com óxido de alumínio, sobre a qual foi aplicado um adesivo e fotoativado com luz halógena. Os bastões de vidro foram acoplados verticalmente, em pares, em uma máquina universal de ensaios (EMIC DL-2000) e as resinas compostas aplicadas no bastão inferior. A distância entre os bastões foi padronizada em 2 mm e um extensômetro foi acoplado a eles. As resinas foram fotoativadas (n=20), sendo 10 por QTH e 10 por LED utilizando dois aparelhos posicionados em lados opostos, acionados simultaneamente por 40 s. A tensão de contração foi analisada em dois momentos: logo após a polimerização (t40s) e 10 min após (t10min). A tensão de contração apresentada por todas as resinas foi maior em t10min do que em t40s, independente da fonte ativadora. A resina de micropartículas apresentou menores valores de tensão de contração com valores estatisticamente significantes em relação às demais resinas. Para as resinas híbrida e microhíbrida não houve influência da unidade ativadora sobre a tensão de contração, com exceção para a resina de micropartículas em t10min. Concluiu-se que a composição da resina composta foi o fator que mais interferiu na tensão de contração da resina composta.

Influence of light-curing units on the flexural strength and flexural modulus of different resin composites

Aim: This study aimed to evaluate the flexural strength and flexural modulus of different resin composites (MasterFill, Opallis, Z250, Supreme) after photoactivation with quartz-tungsten-halogen (QTH - XL2500) or light-emitting diode (LED - Radii and Ultrablue Is) light-curing units (LCUs). Methods: The irradiance and spectral emission of each unit were evaluated using a power meter and a spectrometer. Flexural strength (MPa) was determined in a three-point bending test in accordance with the ISO4049 standard specifications. Flexural modulus (GPa) was measured from the linear-elastic range on the stress-deformation profile. Data were submitted to two-way ANOVA and Tukey’s test (p<0.05). Results: Different values for irradiance (850, 780 and 590 mW/cm2) and peak of emission (484, 456, 467 nm) were detected for XL2500, Radii and Ultrablue Is, respectively. Flexural strength and modulus were dependent on both material and LCU. Among the resins, Z250 and Supreme showed significantly higher strength and modulus than MasterFill and Opallis. Comparing the LCUs, Ultrablue Is showed significantly lower flexural strength and modulus than the others. Conclusion: Flexural strength and modulus were dependent on the irradiance and the spectral emission of the curing units, as well on the resin composite tested.

Mechanism of reductive photoactivation of enzymes of C4 pathway.

Light, besides initiating primary photochemical processes, alters the redox state of soluble components in chloroplast. The present review attempts to cover the mechanism of reductive photoactivation of enzymes of photosynthetic carbon reduction cycle using key enzymes as examples. The reduced soluble components — ferredoxin, thioredoxin and NADPH, in turn, cause the reduction of disulphides to dithiols of chloroplastic enzymes. NADP-malate dehydrogenase is subject to activation by light through changes in NADPH/NADP. The key enzyme of C4 photosynthesis-PEP carboxylase, though cytosolic, has been shown to be activated by disulphide/sulphhydryl interconversion by reductants generated in light through chloroplast electron transport flow. Pyruvate Pi dikinase activity is controlled by the adenylate energy charge. It remains unclear how light controls the activation of cytosolic enzymes.