Effects of ionizing radiation and different resin composites on shear strength of ceramic brackets: an in vitro study.

INTRODUCTION: Head and neck cancer is considered one of the most common types, and its treatment includes radiotherapy, which can trigger side effects and undesirable sequelae in the oral cavity and dental tissues. OBJECTIVE: This study aimed to make an in vitro evaluation of the shear strength and failure mode of ceramic orthodontic brackets bonded with two different composites in enamel submitted to ionizing radiation. METHODS: After the study was approved by the Research Ethics Committee, 60 healthy human premolars were selected and divided into two groups, based on the absence or presence of ionizing irradiation of the enamel. The fragments were thermocycled and then randomly subdivided into two subgroups, according to the composite used for bonding the ceramic brackets (Inspire Ice - Ormco) to the enamel (n = 15): Transbond XT composite (3M), and Light Bond composite (Reliance). After 24 hours, the specimens were submitted to the shear strength test, and the failure mode was analyzed using a stereomicroscope and confocal microscopy. The shear strength data were submitted to two-way ANOVA, considering a significance level of 5%. RESULTS: The groups submitted to radiation presented lower shear strength values (4.48MPa) than those not irradiated (9.23MPa) (p< 0.001), and the tested composites were not statistically different (p= 0.078). Regarding the fracture mode, all the groups presented mostly adhesive fractures. CONCLUSION: It was concluded that ionizing radiation negatively affects the adhesion of ceramic brackets, regardless of the composite used for bonding.

Effect of freezing/irradiation/thawing processes and subsequent aging on tenderness, color, and oxidative properties of beef.

This study evaluated the use of gamma irradiation (3, 6 and 9 kGy) in frozen vacuum-packed beef and subsequent thawing and aging for up to 14 days. The effects on tenderness, color, and oxidative properties were determined and compared to non-irradiated controls for frozen/thawed and chilled vacuum-packed beef. The combined irradiation and freezing/thawing processes increased total exudate loss and reduced the meat water-holding capacity, regardless of the dose used. Myofibrillar fragmentation was favored by the freezing/thawing processes and negatively affected by irradiation. Lower shear force values were observed in the non-irradiated frozen/thawed samples. Frozen samples irradiated at 9 kGy had a higher percentage of soluble collagen, lipid peroxidation, and a more reddish color tone. The meat reducing capacity and oxygen consumption were reduced by freezing and further by irradiation, which also included accumulation of metmyoglobin. It was concluded that irradiation of frozen meat and its subsequent thawing and aging does not confer any additional advantages for beef technological quality.

Radiotherapy impairs adhesive bonding in permanent teeth.

OBJECTIVES: To evaluate the in vitro effects of radiotherapy (RT) on the morphological surface of the enamel and dentin and to determine the best adhesive system and most appropriate time to restore teeth in head and neck cancer patients. METHODS: Sixty third molars were cut into 120 enamel fragments and 120 dentin fragments and divided into four groups (n = 30): G1 (control): nonirradiated, only restorative procedure; G2: restorative procedure immediately before RT; G3: restorative procedure immediately after RT; and G4: restorative procedure 6 months after RT. Each group was divided into two subgroups: Adper™ Single Bond 2 (SB) and Clearfill SE Bond (CL) based on the material used. After RT and restorative procedures, the specimens were subjected to confocal microscopy and shear bond strength test. Data were analyzed using a two-way ANOVA followed by Tukey's test at a significance level of 5%. RESULTS: Morphological changes were observed in both substrates after a cumulative dose of 40 Gy, and after 60 Gy, the changes were more evident in both substrates. CL had the highest strength values in both substrates (p < 0.05), and G2 had the lowest strength values for the enamel and dentin (p < 0.05). CONCLUSIONS: Based on the in vitro study results, we can conclude that RT substantially changes the morphological surface of enamel and dentin and impairs the bond strength. The Clearfill system yielded better results than Adper Single Bond 2, and restoring teeth before RT resulted in the worst results in both substrates.

Energia interfacial para fratura entre novas zircônias de diferentes translúcidez e o cimento resinoso / Interfacial energy to fracture between between new zirconia of different translucency and resin cement

O objetivo do presente estudo foi determinar a energia interfacial para fratura e a distribuição de tensões usando espécimes Brazil-nuts. Esses espécimes foram usinados em zircônia de alta translucidez (Vita YZ HT, Vita Zahnfabrik), super translucidez (Vita YZ ST, Vita Zahnfabrik) e extra translucidez (Vita YZ XT, Vita Zahnfabrik) usando uma máquina de alta precisão, de forma que apresentaram um defeito de forma elíptica no centro de cada hemi-disco totalmente padronizado. As superfícies de cimentação foram preparadas com tratamentos de superfície (jateamento com partícula de óxido de alumínio e aplicação de silano), em seguida seguirão o protocolo de cimentação com cimento resinoso com metacriloiloxi-decil-dihidrogenofosfato (MDP). Os espécimes cimentados foram armazenados em água destilada em estufa 37 °C por 7 dias, em seguida, metade dos espécimes foi ensaiada e a outra metade foi colocada em envelhecimento térmico em uma com banhos de 5- 55 °C (sendo ensaiada logo após o término do envelhecimento). O teste de energia interfacial para fratura (EIF ou tenacidade à fratura interfacial) foi realizado em uma máquina de ensaios universal usando um teste de compressão com a interface adesiva do espécime posicionada em cinco ângulos diferentes (0°, 5°, 15°, 25° e 30°), pois dessa forma foi possível mensurar a EIF em pura tração, puro cisalhamento e em modos mistos de falha. Todas as interfaces foram observadas após a fratura para determinação dos padrões de falha e crescimento de trinca na interface adesiva. Foi realizada também a análise da distribuição de tensões nesses espécimes com o método de elementos finitos (FEA). Foi realizado o teste de normalidade Kolmogorov- Smirnov, Shapiro-Wilk e o Teste de Levene (95%), que concluíram que os dados não apresentam comportamento normal e não são homocedásticos (p=0,000). Desta forma, foi realizado o teste Kruskal-Wallis e post hoc Teste de Dunn, ambos com nível de significância de 5%. Entretanto, não houve diferença estatisticamente significante entre os materiais não envelhecidos (p0=0,485, p10=0,8580, p20=0,4027, e p30=0,650) e envelhecidos (p0=0,6976, p10=0,3505, p20=0,7565, e p30=0,1469). Adicionalmente, foi aplicado o Teste de Mann-Whitney, também com nível de significância de 5%, para comparar cada um dos grupos quanto ao fator envelhecimento; essa análise mostrou diferença estatisticamente significante entre os materiais envelhecidos e não envelhecidos em cada um dos ângulos usados (p>0,05). De acordo com o FEA, o carregamento compressivo de espécimes Brazil-nut em diferentes inclinações permitiu a predominância de tensões de tração ou cisalhamento, conforme o ângulo de posicionamento da interface adesiva. Pode ser concluído que, os valores de energia interfacial para fratura sob tensões predominantemente de cisalhamento são maiores do que quando as amostras estão submetidas somente à tensões de tração. Todas zircônias translúcidas cimentadas com cimento resinoso possuem energia para fratura semelhantes e o envelhecimento térmico afeta negativamente essas interfaces(AU)

The objective of the present study will determine the interfacial energy to fracture and stress distribution using the Brazil-nut specimens. These specimens will be milled in high translucent zirconia (Vita YZ HT, Vita Zahnfabrik), super translucent (Vita YZ ST, Vita Zahnfabrik) and extra translucent (Vita YZ XT, Vita Zahnfabrik) using a high precision machine, so that there will be an elliptical shape defect in the center of each hemi-disk. The cementing surfaces will be prepared with surface treatment (sandblasting with aluminum oxide particles), after that a cleaning, application of Silane, drying and application of resin cement with MDP will hold the cementing protocol. The cemented specimens will be stored in a stove with distilled water at a temperature of 37°C for 7 days after the adhesive cementation, after that the specimens will be aged in a thermal cycling bath machine with temperature varying within 5-55° C and will be tested shortly after the aging. The interfacial energy to fracture test (IEF or interfacial fracture toughness) will be held in a universal testing machine using a compression test with the adhesive interface of the specimen placed in five different angles (0°, 5°, 15°, 25° and 30°) this way it will be possible to measure the IEF in its pure form of tensile, pure shear and mixed modes of failure. All interfaces will be observed after the fracture to determine the patterns of failure and crack growth in the adhesive interface. Also, there will be held the stress distribution analysis in these specimens with the finite element method. The data obtained will be discussed in front of the relevant literature. Kolmogorov-Smirnov, Shapiro-Wilk and Levene Test normality test (95%) were preformed, these concluded that the data do not present normal behavior and are not homocdatic (p=0.000). Thus, the Kruskal-Wallis test and dunn's post hoc test were performed, both with a significance level of 5%. However, there was no statistically significant difference among the non-aged materials (p0=0.485, p10=0.8580, p20=0.4027, and p30=0.650) and aged materials (p0=0.6976, p10=0.3505, p20=0.7565, and p30=0.1469) were analyzed. Additionally, the Mann- Whitney Test was applied, also with a significance level of 5% to compare each of the groups regarding the aging factor. Thus, there was a statistically significant difference between aged and non-aged materials at each angle (p>0.05). According to FEA, the compressive loading of Brazil-nut specimens at different inclinations allowed the predominance of tensile or shear stresses, according to the positioning angle of the adhesive interface. It can be concluded that the values of interfacial energy to fracture under predominantly shear stresses are higher than when the samples are subjected only to tensile stresses. All translucent zirconia resin cement-bonded have similar interfacial energy to fracture, and thermal aging negatively affects these interfaces(AU)

Effect of Surface Treatment with CO2 Laser on Bond Strength in Composite Resin Restorations.

Objective: Evaluate the bond strength of repairs made on composite resin following the treatment of the surface of the flaw with different bonding agents and/or CO2 laser. Background: The influence of CO2 laser and its interaction with other bonding agents on the surface of the flaw is not yet known. In this study, CO2 laser was chosen to treat the surface of the flaw due to its capacity to promote irregularities on the surface that enhance mechanical micro-retention. Methods: A block was created with Vitra APS nanohybrid composite resin (color: A3; FGM, Joinville, Brazil) measuring 5 mm in width, length, and depth (volume: 125 mm3). The surface of the flaw was treated before the repair with an adhesive, silane bonding agent, and/or CO2 laser. Six specimens were created in composite resin for each group (total: n = 36): G1: resin+resin; G2: adhesive+resin; G3: laser+adhesive; G4: laser+silane+adhesive; G5: silane+adhesive; G6: laser+silane. After the repair, the surfaces of the fracture of all specimens, which were submitted to the microtraction test, were analyzed under an optical microscope. Bond strength values obtained according to the type of surface treatment were tabulated and submitted to the Kruskal-Wallis test. Dunn's test was used to compare means. Results: G3 and G4 had significantly higher bond strength values compared to all other groups tested. Adhesive fractures predominated in all groups. However, G3 and G4 had a higher percentage of cohesive fractures compared to the other groups. Conclusions: The application of CO2 laser as a surface treatment led to greater bond strength of composite resin repairs in comparison with the groups that only received treatment with a burr and silanization. The groups submitted to CO2 laser also had a significantly lower number of adhesive failures when submitted to the microtraction test.

Effect of 830 nm Diode Laser Irradiation of Root Canal on Bond Strength of Metal and Fiber Post.

OBJECTIVE AND BACKGROUND: The correct selections of the cementing agent, the endodontic post material and placement protocol are critical to provide an increased longevity of the teeth that went through endodontic treatment. The irradiation with diode laser before post cementation, can promote an antimicrobial effect. However, there is a lack of information about the effect of 830 nm diode laser on the post bond strength. This study analyzed the effect of dentin root canal irradiation with high-intensity diode laser, at 830 nm, operating in continuous or pulsed mode, on the retention of metal or fiber posts, cemented with self-etching resinous composite (Panavia F) and zinc phosphate cement (ZnPO4). MATERIALS AND METHODS: Human roots were irradiated with diode laser (continuous and pulsed mode). The fiber posts were luted with Panavia F and the metal posts with Panavia F or ZnPO4 cement. Specimens were sectioned into three sections (cervical, middle, and apical). The bond strength was measured by a push-out mechanical analysis. For the statistical analysis, a three-way ANOVA test was applied following a Tukey's pairwise comparison with a significance level of p = 0.05. RESULTS: The irradiated groups presented higher bond strength compared with nonirradiated group (p < 0.05), and the cervical and middle thirds presented higher on bond strength than the apical. The association of metal post and Panavia F presented higher bond strength when irradiated on continuous mode (p < 0.05). Fiber post and Panavia F presented higher bond strength associated to pulsed mode. The mode seems not to make a significant difference. CONCLUSIONS: These results corroborate the importance of the post bond to dentin and root canal debris removal to increase the tooth longevity. It was shown that the dentin to post bond strength were enhanced by the diode laser irradiation either on continuous or pulsed modes.

Does the CO2 laser reduce bond strength in different types of ceramic brackets?

OBJECTIVE:: The aim of this study was to assess in vitro the influence of the CO2 laser and of the type of ceramic bracket on the shear bond strength (SBS) to enamel. METHODS:: A total of 60 enamel test surfaces were obtained from bovine incisors and randomly assigned to two groups, according to the ceramic bracket used: Allure (A); Transcend (T). Each group was divided into 2 subgroups (n = 15): L, laser (10W, 3s); C, no laser, or control. Twenty-four hours after the bonding protocol using Transbond XT, SBS was tested at a crosshead speed of 0.5 mm/min in a universal testing machine. After debonding, the Adhesive Remnant Index (ARI) was evaluated at 10 x magnification and compared among the groups. Data were analyzed by one-way ANOVA, Tukey's, Mann-Whitney's and Kruskal-Wallis tests (α = 0.05). RESULTS:: Mean SBS in MPa were: AL = 0.88 ± 0.84; AC = 12.22 ± 3.45; TL = 12.10 ± 5.11; TC = 17.71 ± 6.16. ARI analysis showed that 73% of the specimens presented the entire adhesive remaining on the tooth surfaces (score 3). TC group presented significantly higher SBS than the other groups. The lased specimens showed significantly lower bond strength than the non-lased groups for both tested brackets. CONCLUSION:: CO2 laser irradiation decreased SBS values of the polycrystalline ceramic brackets, mainly Allure.

Does the CO2 laser reduce bond strength in different types of ceramic brackets?

ABSTRACT OBJECTIVE: The aim of this study was to assess in vitro the influence of the CO2 laser and of the type of ceramic bracket on the shear bond strength (SBS) to enamel. METHODS: A total of 60 enamel test surfaces were obtained from bovine incisors and randomly assigned to two groups, according to the ceramic bracket used: Allure (A); Transcend (T). Each group was divided into 2 subgroups (n = 15): L, laser (10W, 3s); C, no laser, or control. Twenty-four hours after the bonding protocol using Transbond XT, SBS was tested at a crosshead speed of 0.5 mm/min in a universal testing machine. After debonding, the Adhesive Remnant Index (ARI) was evaluated at 10 x magnification and compared among the groups. Data were analyzed by one-way ANOVA, Tukey’s, Mann-Whitney’s and Kruskal-Wallis tests (α = 0.05). RESULTS: Mean SBS in MPa were: AL = 0.88 ± 0.84; AC = 12.22 ± 3.45; TL = 12.10 ± 5.11; TC = 17.71 ± 6.16. ARI analysis showed that 73% of the specimens presented the entire adhesive remaining on the tooth surfaces (score 3). TC group presented significantly higher SBS than the other groups. The lased specimens showed significantly lower bond strength than the non-lased groups for both tested brackets. CONCLUSION: CO2 laser irradiation decreased SBS values of the polycrystalline ceramic brackets, mainly Allure.

RESUMO OBJETIVO: o objetivo deste estudo foi avaliar in vitro a influência do laser de CO2 sobre a resistência ao cisalhamento da colagem (RCC) no esmalte dentário, usando diferentes tipos de braquetes cerâmicos. MÉTODOS: no total, 60 superfícies de esmalte de incisivos bovinos foram obtidas e aleatoriamente divididas em dois grupos, de acordo com o braquete cerâmico utilizado: Allure (A) e Transcend (T). Cada grupo foi dividido em dois subgrupos (n = 15): L, laser (10W, 3s); C, sem laser, ou controle. Vinte e quatro horas após a colagem dos braquetes com o sistema Transbond XT, foi realizado o teste de resistência ao cisalhamento, com velocidade de 0,5 mm/min, em máquina universal de ensaios mecânicos. Após a descolagem, o Índice de Remanescente de Adesivo (IRA) foi avaliado com aumento de 10X e comparado entre os grupos. Os dados foram analisados pelo ANOVA one-way, testes de Tukey’s, Mann-Whitney’s e Kruskal-Wallis (α = 0,05). RESULTADOS: as médias da RCC em MPa foram: AL = 0,88 ± 0,84; AC = 12,22 ± 3,45; TL = 12,10 ± 5,11; TC = 17,71 ± 6,16. A análise do IRA mostrou que 73% dos corpos de prova apresentaram todo o compósito remanescente aderido à superfície do esmalte (escore 3). O grupo TC apresentou valor significativamente maior de RCC do que os outros grupos. Os corpos de prova dos grupos com laser obtiveram valores adesivos significativamente menores do que os corpos de prova dos grupos sem laser, com ambos os tipos de braquetes. CONCLUSÃO: a irradiação com laser de CO2 diminuiu os valores de RCC dos braquetes policristalinos testados, principalmente do Allure.

Does the light source affect the repairability of composite resins?

The aim of this study was to examine the effect of the light source on the microshear bond strength of different composite resins repaired with the same substrate. Thirty cylindrical specimens of each composite resin--Filtek Silorane, Filtek Z550 (3M ESPE), Gradia Direct Anterior (GC), and Aelite Posterior (BISCO)--were prepared and light-cured with a QTH light curing unit (LCU). The specimens were aged by thermal cycling and divided into three subgroups according to the light source used--QTH, LED, or PAC (n = 10). They were repaired with the same substrate and a Clearfil Repair Kit (Kuraray). The specimens were light-cured and aged for 1 week in distilled water at 37 °C. The microshear bond strength and failure modes were assessed. There was no significant difference in the microshear bond strength values among the composite resins, except for the Filtek Silorane group that showed significantly lower bond strength values when polymerized with the PAC unit compared to the QTH or LED unit. In conclusion, previously placed dimethacrylate-based composites can be repaired with different light sources; however, if the composite to be repaired is silorane-based, then using a QTH or LED device may be the best option.

Evaluation of self-etching adhesive and Er:YAG laser conditioning on the shear bond strength of orthodontic brackets.

The purpose of this study was to evaluate the shear bond strength, the adhesive remnant index scores, and etch surface of teeth prepared for orthodontic bracket bonding with self-etching primer and Er:YAG laser conditioning. One hundred and twenty bovine incisors were randomly divided into four groups. In Group I (Control), the teeth were conditioned with 35% phosphoric acid for 15 seconds. In Group II the teeth were conditioned with Transbond Plus SEP (5 sec); III and IV were irradiated with the Er:YAG 150 mJ (11.0 J/cm²), 150 mJ (19.1 J/cm²), respectively, at 7-12 Hz with water spray. After surface preparation, upper central incisor stainless steel brackets were bonded with Transbond Plus Color Change Adhesive. The teeth were stored in water at 37°C for 24 hours and shear bond strengths were measured, and adhesive remnant index (ARI) was determined. The conditioned surface was observed under a scanning electron microscope. One-way ANOVA and chi-square test were used. Group I showed the significantly highest values of bond strength with a mean value of 8.2 megapascals (MPa). The lesser amount of adhesive remnant was found in Group III. The results of this study suggest that Er:YAG laser irradiation could not be an option for enamel conditioning.

Shear bond strength of orthodontic brackets bonded using halogen light and light-emitting diode at different debond times.

The aim of this in vitro study was to compare the photoactivation effects of QTH (Quartz-Tungsten-Halogen) and LED (Light-Emitting Diode) on the SBS (Shear Bond Strength) of orthodontic brackets at different debond times. Seventy-two bovine lower incisors were randomly divided into two groups according to the photoactivation system used (QTH or LED). The enamel surfaces were conditioned with Transbond self-etching primer, and APC (Adhesive Pre-Coated) brackets were used in all specimens. Group I was cured with QTH for 20 s and Group II with LED for 10 s. Both groups were subdivided according to the different experimental times after bonding (immediately, 24 h and 7 days). The specimens were tested for SBS and the enamel surfaces were analyzed according to the Adhesive Remnant Index (ARI). The statistical analysis included the Tukey's test to evaluate the main effects of photoactivation and debond time on SBS. The Chi-square test was used to compare the ARI values found for each group, and no statistically significant difference was observed. The debond time of 7 days for QTH photoactivation showed statistically greater values of SBS when compared to the immediate and 24 h periods. There was no statistically significant difference between the QTH and LED groups immediately and after the 24 h period. In conclusion, bonding orthodontic brackets with LED photoactivation for 10 s is suggested because it requires a reduced clinical chair time.

Shear bond strength of orthodontic brackets bonded using halogen light and light-emitting diode at different debond times

The aim of this in vitro study was to compare the photoactivation effects of QTH (Quartz-Tungsten-Halogen) and LED (Light-Emitting Diode) on the SBS (Shear Bond Strength) of orthodontic brackets at different debond times. Seventy-two bovine lower incisors were randomly divided into two groups according to the photoactivation system used (QTH or LED). The enamel surfaces were conditioned with Transbond self-etching primer, and APC (Adhesive Pre-Coated) brackets were used in all specimens. Group I was cured with QTH for 20 s and Group II with LED for 10 s. Both groups were subdivided according to the different experimental times after bonding (immediately, 24 h and 7 days). The specimens were tested for SBS and the enamel surfaces were analyzed according to the Adhesive Remnant Index (ARI). The statistical analysis included the Tukey's test to evaluate the main effects of photoactivation and debond time on SBS. The Chi-square test was used to compare the ARI values found for each group, and no statistically significant difference was observed. The debond time of 7 days for QTH photoactivation showed statistically greater values of SBS when compared to the immediate and 24 h periods. There was no statistically significant difference between the QTH and LED groups immediately and after the 24 h period. In conclusion, bonding orthodontic brackets with LED photoactivation for 10 s is suggested because it requires a reduced clinical chair time.