Selective carious tissue removal and glass ionomer liner reduction of pulp stress in bulk fill resin composite restorations

Abstract: To evaluate the effect of selective or nonselective carious tissue removal and the use of a resin-modified glass ionomer (RMGIC) liner under bulk fill resin composite restoration on the stress at the pulp chamber, the elastic moduli of hard, firm, soft and intact dentin were calculated using nanoindentation. Post-gel shrinkage of the bulk fill resin composite and RMGIC were determined using the strain-gauge method. Six finite element models were created by using digital radiography with the combination of two study factors: a) carious tissue removal: selective removal or nonselective removal of carious tissue, and b) use of RMGIC liner: with or without 1.0 mm of RMGIC liner. The modified von Mises stresses (mvm) (MPa) were extracted on the nodes of the internal wall of the pulp ceiling chamber at 100 N occlusal loading. Data were analyzed descriptively and recorded quantitively. Both study factors influenced the stress distribution. The mvm stress during the restorative procedure was higher for nonselective carious tissue removal without RMGIC (25.9 MPa) and lower for selective carious tissue removal associated with RMGIC (13.5 MPa). The dentin elastic modulus increased from soft carious (3.6 ± 0.3 MPa) to firm carious (5.2 ± 1.0 MPa) to hard carious (10.9 ± 1.2 MPa) to intact dentin (22.7 ± 3.0 MPa). Molars with carious lesions showed high mvm stress at the pulp ceiling (89.6 MPa) and at fragilized coronal structure remaining. Selective carious tissue removal followed by restoration using a Vitrebond liner and Tetric N-Ceram Bulk fill reduced the stress at the pulp chamber ceiling.

Direct resin composite restoration of endodontically-treated permanent molars in adolescents: bite force and patient-specific finite element analysis

Abstract Objective To evaluate the influence of three levels of dental structure loss on stress distribution and bite load in root canal-treated young molar teeth that were filled with bulk-fill resin composite, using finite element analysis (FEA) to predict clinical failure. Methodology Three first mandibular molars with extensive caries lesions were selected in teenager patients. The habitual occlusion bite force was measured using gnathodynamometer before and after endodontic/restoration procedures. The recorded bite forces were used as input for patient-specific FEA models, generated from cone-beam computed tomographic (CT) scans of the teeth before and after treatment. Loads were simulated using the contact loading of the antagonist molars selected based on the CT scans and clinical evaluation. Pre and post treatment bite forces (N) in the 3 patients were 30.1/136.6, 34.3/133.4, and 47.9/124.1. Results Bite force increased 260% (from 36.7±11.6 to 131.9±17.8 N) after endodontic and direct restoration. Before endodontic intervention, the stress concentration was located in coronal tooth structure; after rehabilitation, the stresses were located in root dentin, regardless of the level of tooth structure loss. The bite force used on molar teeth after pulp removal during endodontic treatment resulted in high stress concentrations in weakened tooth areas and at the furcation. Conclusion Extensive caries negatively affected the bite force. After pulp removal and endodontic treatment, stress and strain concentrations were higher in the weakened dental structure. Root canal treatment associated with direct resin composite restorative procedure could restore the stress-strain conditions in permanent young molar teeth.

Irradiance and radiant exposures delivered by led light-curing units used by a left and right-handed operator

Abstract The combination of the restoration location, the hand preference of the operator using the light-curing unit (LCU), and the design of the LCU all can have an impact on the amount of the light delivered to the restoration. To evaluate the effect of left-handed or right-handed users, the position of the operator (dentist or assistant), and the LCU design on the irradiance, radiant exposure and emission spectrum delivered to the same posterior tooth. Two light emitting diode (LED) LCUs were tested: an angulated monowave LCU Radii-Cal (SDI, Victoria, Australia) and a straight aligned multi-peak LCU Valo Cordless (Ultradent, South Jordan, UT, USA). The irradiance values (mW/cm2), radiant exposure (J/cm2) and emission spectrum were measured using a sensor in maxillary left second molar tooth. The irradiance and radiant exposure were analyzed using three-way ANOVA followed by Tukey test (a=0.05). The emission spectra (nm) were analyzed descriptively. The interaction between LCU design, operator position, and hand preference significantly influenced the irradiance and radiant exposure (P<0.001). In all cases, Valo delivered significantly higher irradiance than Radii-Cal. The handedness and the operator position affected the irradiance and radiant exposure delivered from Valo. Operator position and access affect the irradiance and radiant exposure delivered to the maxillary left second molar. The irradiance and radiant exposure can be greater when a right-hand operator is positioned on the right side of the chair and a left-hand operator is positioned on the left side of the chair. This may result in better resin composite polymerization.

Resumo A combinação da localização da restauração, a preferência de mão do operador ao utilizar aparelhos fotopolimerizadores (AFP) com luz emitida por diodo (LED) e o formato do AFP podem afetar a quantidade de luz fornecida à restauração. O objetivo foi avaliar o efeito de operadores canhotos e destros, a posição do operador (dentista ou auxiliar), e o formato do AFP na irradiância, energia radiante e espectro de luz entregue ao mesmo dente posterior. Dois AFP foram testados: um com formato angulado, onda única Radii-Cal (SDI, Victoria, Australia) e um formato reto multi-pico Valo Cordless (Ultradent, South Jordan, UT, USA). Os valores de irradiância (mW/cm²), energia radiante (J/cm²) e espectro de luz foram medidos utilizando um sensor no segundo molar superior esquerdo. A irradiância e energia radiante foram analisados utilizando ANOVA 3 fatores seguido por teste de Tukey (a=0.05). O espectro de luz (nm) foi analisado de forma descritiva. A interação entre o formato do AFP, posição do operador e preferência de mão foram significativamente influentes na irradiância e energia radiante (P<0.001). Em todos os casos, Valo teve irradiância significativamente maior que Radii-Cal. A mão dominante e a posição do operador afetaram a irradiância e energia radiante com o Valo. Posição do operador e acesso afetou a irradiância e exposição radiante entregue ao segundo molar superior esquerdo. A irradiância e exposição radiante teve melhores resultados quando AFP foi utilizado com a mão direita pelo operador posicionado na cadeira do lado direito e mão esquerda do operador posicionado do lado esquerdo da cadeira. Estes resultados podem levar a uma melhor polimerização da resina composta.

Polymerization shrinkage stress of composite resins and resin cements - What do we need to know?

Abstract Polymerization shrinkage stress of resin-based materials have been related to several unwanted clinical consequences, such as enamel crack propagation, cusp deflection, marginal and internal gaps, and decreased bond strength. Despite the absence of strong evidence relating polymerization shrinkage to secondary caries or fracture of posterior teeth, shrinkage stress has been associated with post-operative sensitivity and marginal stain. The latter is often erroneously used as a criterion for replacement of composite restorations. Therefore, an indirect correlation can emerge between shrinkage stress and the longevity of composite restorations or resin-bonded ceramic restorations. The relationship between shrinkage and stress can be best studied in laboratory experiments and a combination of various methodologies. The objective of this review article is to discuss the concept and consequences of polymerization shrinkage and shrinkage stress of composite resins and resin cements. Literature relating to polymerization shrinkage and shrinkage stress generation, research methodologies, and contributing factors are selected and reviewed. Clinical techniques that could reduce shrinkage stress and new developments on low-shrink dental materials are also discussed.

An Evaluation of the Light Output from 22 Contemporary Light Curing Units

Abstract This study measured the radiant power (mW), irradiance (mW/cm2) and emission spectra (mW/cm2/nm) of 22 new, or almost new, light curing units (LCUs): - Alt Lux II, BioLux Standard, Bluephase G2, Curing Light XL 3000, Demetron LC, DX Turbo LED 1200, EC450, EC500, Emitter C, Emitter D, KON-LUX, LED 3M ESPE, Led Lux II, Optilight Color, Optilight Max, Optilux 501, Poly Wireless, Radii cal, Radii plus, TL-01, VALO Cordless. These LCUs were either monowave or multiple peak light emitting diode (LED) units or quartz-tungsten-halogen LCUs used in anterior and posterior teeth. The radiant power emitted by the LCUs was measured by a laboratory grade laser power meter. The tip area (cm²) of the LCUs was measured and used to calculate the irradiance from the measured radiant power source. The MARC-Patient Simulator (MARC-PS) with a laboratory grade spectrometer (USB4000, Ocean Optics) was used to measure the irradiance and emission spectrum from each LCU three times at the sensor located on the facial of the maxillary central incisors and then separately at the occlusal of a maxillary second molar. The minimum acceptable irradiance level was set as 500 mW/cm2. Irradiance data was analyzed using two-way ANOVA and the radiant power data was analyzed by one-way ANOVA followed by Tukey test (a=0.05). In general, the irradiance was reduced at the molar tooth for most LCUs. Only the Valo, Bluephase G2 and Radii Plus delivered an irradiance similar to the anterior and posterior sensors greater than 500 mW/cm2. KON-LUX, Altlux II, Biolux Standard, TL-01, Optilux 501, DX Turbo LED 1200 LCUs delivered lower irradiance values than the recommended one used in molar region, KON-LUX and Altlux II LCUs used at the maxillary incisors. Bluephase G2 and Optilight Max delivered the highest radiant power and KON-LUX, Altlux II and Biolux Standard delivered the lowest power. The emission spectrum from the various monowave LED LCUs varied greatly. The multi-peak LCUs delivered similar emission spectra to both sensors.

Resumo Este estudo mediu a potência (mW), irradiância (mW/cm2) e espectro da luz (mW/cm2/nm) emitida por 22 fontes de luz (Alt Lux II, BioLux Standard, Bluephase G2, Curing Light XL 3000, Demetron LC, DX Turbo LED 1200, EC450, EC500, Emitter C, Emitter D, KON-LUX, LED 3M ESPE, Led Lux II, Optilight Color, Optilight Max, Optilux 501, Poly Wireless, Radii cal, Radii plus, TL-01, VALO Cordless) disponíveis comercialmente. A potência emitida pelas fontes de luz foi medida usando um medidor laboratorial de potencia com grade a laser. A área (cm²) da ponta ativa efetiva das fontes de luz foi medida com paquímetro digital e utilizada para calcular a irradiância emitida. O simulador de paciente-MARC (MARC - PS) com espectrómetro (USB4000, Ocean Optics) foi usado para medir a irradiância e o espectro de luz emitida por cada fonte de luz na região anterior e posterior. Esta medição foi repetida por três vezes em dois sensores localizados na região anterior e posterior da arcada dentária. Os dados de irradiância foram analisados utilizando análise de variância em dois fatores, e os dados de potência foram analisados com análise de variância em fator único seguido pelo teste de Tukey (a=0,05). As fontes de luz Valo, Bluephase G2, Radii Plus emitiram irradiância semelhante tanto na região anterior como posterior com valores superiores ao mínimo de 500 mW/cm2. Seis fontes de luz emitiram irradiância menor que o recomendado (500 mW/cm2) quando usadas na região posterior: Kon-lux, Altlux II, Biolux Standard TL-01, Optilux 501, DX Turbo LED 1200 e duas quando usadas na região anterior: Kon-lux e Altlux II LCUs. As fontes Bluephase G2, Optilight Max emitiram os maiores valores de potência e as fontes de luz Altlux II e Biolux Standard emitiram os menores valores de potência. O espectro de luz das fontes LED de espectro único variou de forma evidente entre as fontes. As fontes LED multi pico de espectro emitiram espectros de luz similar para ambos os sensores. A fotoativação na região posterior tende a reduzir substancialmente a irradiância da maioria das fontes de luzes testadas.

Evaluation of Eye Protection Filters Used with Broad-Spectrum and Conventional LED Curing Lights

Abstract The high irradiance and the different emission spectra from contemporary light curing units (LCU) may cause ocular damage. This study evaluated the ability of 15 eye protection filters: 2 glasses, 1 paddle design, and 12 dedicated filters to block out harmful light from a monowave (HP-3M ESPE) and a broad-spectrum (Valo, Ultradent) LED LCU. Using the anterior sensor in the MARC-Patient Simulator (BlueLight Analytics) the irradiance that was delivered through different eye protection filters was measured three times. The LCUs delivered a similar irradiance to the top of the filter. The mean values of the light that passed through the filters as percent of the original irradiance were analyzed using two-way ANOVA followed by Tukey test (a= 0.05). The emission spectra from the LCUs and through the filters were also obtained. Two-way ANOVA showed that the interaction between protective filters and LCUs significantly influenced the amount of light transmitted (p< 0.001). Tukey test showed that the amount of light transmitted through the protective filters when using the HP-3M-ESPE was significantly greater compared to when using the Valo, irrespective of the protective filter tested. When using the HP-3M-ESPE, the Glasses filter allowed significantly more light through, followed by XL 3000, ORTUS, Google Professional, Gnatus filters. The Valo filter was the most effective at blocking out the harmful light. Some protective filters were less effective at blocking the lower wavelengths of light (<420 nm). However, even in the worst scenario, the filters were able to block at least 97% of the irradiance.

Resumo A alta irradiância e diferentes espectros de luz emitidos por aparelhos fotopolimerizadores (Fp) podem causar danos oculares. Este estudo avaliou a capacidade de 15 filtros de proteção ocular em bloquear a luz prejudicial de um Fp convencional (HP-3M ESPE) e outro de largo espectro (Valo, Ultradent). Utilizando sensor anterior do equioamento MARC-Patient Simulator (BlueLight Analytics inc.) a irradiância que passou através dos diferentes filtros protetores foi mensuradas três vezes. Os valores médios da irradiância que passaram pelos filtros foram analisados usando Análise de variância fatorial e pelo teste de Tukey (a= 0.05). O espetro emitido dos Fps através dos filtros também foi obtido. A análise de variância mostrou que a interação entre os filtros protetores e Fps influenciou significantemente a quantidade de luz transmitida (p<0,001). O teste de Tukey mostrou que a quantidade que luz transmitida através dos protetores oculares quando usado o HP-3M ESPE foi significantemente maior quando comparado aos valores para o Valo, independentemente do filtro testado. Quando foi utilizado a fonte de luz HP-3M ESPE, o filtro de proteção ocular permitiu significativamente maior passagem de luz, seguido por XL 3000, ORTUS, Google Professional, e pelo filtro Gnatus. O filtro do Valo foi o mais eficiente ao bloquear a luz prejudicial. Alguns filtros foram menos eficazes ao bloquear menores comprimentos de onde (<420 nm). No entanto, mesmo no pior cenário dos resultados deste estudo, os filtros foram capazes de bloquear ao menos 97% da irradiância emitida pelas fontes de luz testadas.

Effect of Resin Cement Porosity on Retention of Glass-Fiber Posts to Root Dentin: An Experimental and Finite Element Analysis

The aim of this study was to evaluate the effect of porosity of self-adhesive resin on the stress distribution, post retention and failure mode of fiber post cemented to human root dentin. Ten human central upper incisors with circular root canal were selected. They were sectioned with 15 mm and were endodontically filled. The roots were scanned using micro-CT after post space preparation for root filling remaining evaluation. Fiber posts were cemented using self-adhesive resin cement (Rely X U200, 3M-ESPE). Two 1-mm-thick slices from the cervical, medium and apical thirds were scanned for resin cement bubbles volume measurements and submitted to a push-out test (PBS). Three operators using stereomicroscopy and confocal laser microscopy classified the failure mode. Stress distributions during the push-out test were analyzed using 3D finite element analysis. PBS values (MPa) were submitted to one-way ANOVA and Tukey's post hoc tests and the failure modes using the Kappa coefficient to assess inter-operator agreement. Chi-square test was used to determine significant differences between the methods ( = 0.05). Push-out bond strength was significantly affected by the bubbles presence in all root depth (p<0.05). The stress concentration was higher when the bubbles were present. Adhesive dentin/resin cement interface failure was the most frequent type of failure. Confocal microscopy was better than stereomicroscopy for failure analysis. Bubbles generated during resin cement insertion into the root canal negatively affect the stress distribution and the bond strength. The use of confocal microscopy is recommended for failure analysis.

Resumo O objetivo deste estudo foi avaliar o efeito da integridade do cimento resinoso autoadesivo, expresso pela presença de bolhas, sobre a distribuição de tensão, resistência adesiva e modo de falha de pinos de fibra cimentados à dentina radicular humana. Dez incisivos centrais superiores humanos com canais radiculares circulares foram selecionados. Os mesmos foram seccionados com 15 mm e tratados endodonticamente. As raízes foram digitalizadas utilizando micro-CT após preparo do pino para avaliação de remanescentes de material obturador. Pinos de fibra foram cimentados utilizando cimento autoadesivo (Rely X U200, 3M-ESPE). Duas fatias de 1 mm de espessura dos terços cervical, médio e apical foram escaneados para mensuração do volume de bolhas no cimento resinoso e submetidos ao teste de push-out. Três operadores classificaram o modo de falha utilizando microscopia confocal à laser e lupa estereoscópica. Distribuição de tensão foi analisada pelo método de elementos finitos 3D. Os valores de resistência adesiva (MPa) foram submetidos ao teste ANOVA em fator único seguido do teste de Tukey. Foi utilizado o coeficiente de Kappa para avaliar a concordância entre operadores. O teste Qui-quadrado foi utilizado para determinar diferenças significativas entre os métodos (α=0,05). A resistência adesiva foi significativamente afetada pela presença de bolhas independentemente da profundidade radicular (p<0,05). A concentração de tensão foi maior na presença de bolhas. Maior frequência de falha adesiva ocorreu na interface cimento/dentina. A microscopia confocal foi melhor do que estereomicroscopia para análise de falhas. A presença de bolhas afetou negativamente a distribuição de tensão e a resistência de união. Recomenda-se uso de microscopia confocal para análise de falhas.