The effect of ionizing radiation on properties of fluoride-releasing restorative materials.

The purpose of this study was to evaluate the effect of ionizing radiation from high energy X-ray on fluoride release, surface roughness, flexural strength, and surface chemical composition of the materials. The study groups comprised five different restorative materials: Beautifil II, GCP Glass Fill, Amalgomer CR, Zirconomer, and Fuji IX GP. Twenty disk-shaped specimens (8x2 mm) for fluoride release and 20 bar-shaped specimens (25 x 2x 2 mm) for flexural strength were prepared from each material. Each material group was divided into two subgroups: irradiated (IR) and non-irradiated (Non-IR). The specimens from IR groups were irradiated with 1.8 Gy/day for 39 days (total IR = 70.2 Gy). The amount of fluoride released into deionized water was measured using a fluoride ion-selective electrode and ion analyzer after 24 hours and on days 2, 3, 7, 15, 21, 28, 35, and 39 (n = 10). The flexural strength was evaluated using the three-point bending test (n = 10). After the period of measurement of fluoride release, seven specimens (n = 7) from each group were randomly selected to evaluate surface roughness using AFM and one specimen was randomly selected for the SEM and EDS analyses. Data were analyzed with two-way ANOVA and Tukey tests (p = 0.05). The irradiation significantly increased fluoride release and surface roughness for Amalgomer CR and Zirconomer groups (p < 0.05). No significant change in flexural strength of the materials was observed after irradiation (p > 0.05). The ionizing radiation altered the amount of fluoride release and surface roughness of only Amalgomer CR and Zirconomer. The effect could be related to the chemical compositions of materials.

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.

The effect of ionizing radiation on properties of fluoride-releasing restorative materials

Abstract The purpose of this study was to evaluate the effect of ionizing radiation from high energy X-ray on fluoride release, surface roughness, flexural strength, and surface chemical composition of the materials. The study groups comprised five different restorative materials: Beautifil II, GCP Glass Fill, Amalgomer CR, Zirconomer, and Fuji IX GP. Twenty disk-shaped specimens (8x2 mm) for fluoride release and 20 bar-shaped specimens (25 x 2x 2 mm) for flexural strength were prepared from each material. Each material group was divided into two subgroups: irradiated (IR) and non-irradiated (Non-IR). The specimens from IR groups were irradiated with 1.8 Gy/day for 39 days (total IR = 70.2 Gy). The amount of fluoride released into deionized water was measured using a fluoride ion-selective electrode and ion analyzer after 24 hours and on days 2, 3, 7, 15, 21, 28, 35, and 39 (n = 10). The flexural strength was evaluated using the three-point bending test (n = 10). After the period of measurement of fluoride release, seven specimens (n = 7) from each group were randomly selected to evaluate surface roughness using AFM and one specimen was randomly selected for the SEM and EDS analyses. Data were analyzed with two-way ANOVA and Tukey tests (p = 0.05). The irradiation significantly increased fluoride release and surface roughness for Amalgomer CR and Zirconomer groups (p < 0.05). No significant change in flexural strength of the materials was observed after irradiation (p > 0.05). The ionizing radiation altered the amount of fluoride release and surface roughness of only Amalgomer CR and Zirconomer. The effect could be related to the chemical compositions of materials.

Longevity of bond strength of resin cements to root dentine after radiation therapy.

AIM: To evaluate the bond strength and adhesive interface between several resin cements and root dentine immediately and 6 months after radiotherapy. METHODOLOGY: Sixty maxillary canines were selected and randomly assigned to two groups (n = 30): one group was not irradiated and the other one was subjected to a cumulative radiation dose of 60 Gy. The teeth were sectioned to obtain roots 16 mm long and the canals were prepared with the Reciproc system (R50) and filled using a lateral condensation technique with an epoxy resin sealer. Each group was divided into three subgroups (n = 10) according to the resin cement used for fibreglass fibre post cementation: RelyX-U200, Panavia-F2.0 and RelyX ARC. The posts were cemented in accordance with the manufacturer's recommendations. Three 1-mm-thick dentine slices were then obtained from each root third. The first two slices in the crown-apex direction of each third were selected for the push-out test. The failure mode after debonding was determined with a stereo microscope. The third slice from each root third was selected for scanning electron microscopy (SEM) analyses to examine the resin cement-dentine interface with 100, 1000, 2000 and 4000× magnification. Bond strength data were analysed by anova and Tukey's test (α = 0.05). RESULTS: Significantly lower bond strength (P < 0.0001) was obtained after irradiation compared to nonirradiated teeth. RelyX-U200 cemented fibre posts had the higher bond strength (15.17 ± 5.89) compared with RelyX ARC (P < 0.001) and Panavia-F2.0 (P < 0.001). The evaluation after 6 months revealed lower bond strength values compared to the immediate values (P < 0.001) for irradiated and nonirradiated teeth. Cohesive failures occurred in the irradiated dentine. SEM revealed fractures, microfractures and fewer collagen fibres in irradiated root dentine. RelyX-U200 and Panavia-F2.0 were associated with a juxtaposed interface of the cement with the radicular dentine in irradiated and nonirradiated teeth, and for RelyX ARC, hybrid layer formation and tags were observed in both irradiated and nonirradiated teeth. CONCLUSION: Radiation was associated with a decrease in the push-out bond strength and with lower resin cement/root dentine interface adaptation. Self-adhesive resin cement was a better alternative for fibre post cementation in teeth subjected to radiation therapy. The bond strength decreased after 6 months.

Structural and mechanical properties of a giomer-based bulk fill restorative in different curing conditions.

The main goal of this study was to compare the polymerization degree of bulk-fill giomer resin cured with three different light-curing units (LCUs): a polywave third-generation (Valo); a monowave (DemiUltra: DU); and a second-generation LED (Optima 10: Opt) LCUs by using structural and mechanical properties. Giomer samples of 2 and 4 mm cured with three LCUs were employed in vitro analysis. The degree of curing (DC%) was determined with Fourier-Transform Infrared Spectroscopy (FTIR). Microstructural features were observed with scanning electron microscopy (SEM). Flexural strength (FS), compression strength (CS), elastic modulus and fracturing strain were determined for mechanical properties. Surface microhardness (SMH) values were also measured. Oneway ANOVA, two-way analysis of variance and Tukey multiple comparison tests were used for statistically analyzing the FS and SMH. DC% values were 58.2, 47.6, and 39.7 for the 2 mm samples cured with DU, Opt., and Valo LCUs, respectively. DC% values of the 4 mm samples were 50.4, 44.6, and 38.2 for DU, Opt, and Valo, respectively. SMH values were Valo, Opt

Structural and mechanical properties of a giomer-based bulk fill restorative in different curing conditions

ABSTRACT Objective: The main goal of this study was to compare the polymerization degree of bulk-fill giomer resin cured with three different light-curing units (LCUs): a polywave third-generation (Valo); a monowave (DemiUltra: DU); and a second-generation LED (Optima 10: Opt) LCUs by using structural and mechanical properties. Material and methods: Giomer samples of 2 and 4 mm cured with three LCUs were employed in vitro analysis. The degree of curing (DC%) was determined with Fourier-Transform Infrared Spectroscopy (FTIR). Microstructural features were observed with scanning electron microscopy (SEM). Flexural strength (FS), compression strength (CS), elastic modulus and fracturing strain were determined for mechanical properties. Surface microhardness (SMH) values were also measured. Oneway ANOVA, two-way analysis of variance and Tukey multiple comparison tests were used for statistically analyzing the FS and SMH. Results: DC% values were 58.2, 47.6, and 39.7 for the 2 mm samples cured with DU, Opt., and Valo LCUs, respectively. DC% values of the 4 mm samples were 50.4, 44.6, and 38.2 for DU, Opt, and Valo, respectively. SMH values were Valo, Opt<DU at top of the samples; Valo<DU, Opt at 2 mm, and DU, Valo<Opt at 4 mm depth. Giomer samples cured with Opt and DU exhibited higher FS values than Valo. CS values were similar but compressive modulus and fracturing strain (%) varied depending on the curing protocol. Conclusions: Based on the results, it can be concluded that curing device and protocol strongly affect crosslinking reactions and thus DC%, SMH, compressive modulus and strain at break values. Consequently, it can be deduced that curing protocol is possibly the most important parameter for microstructure formation of highly-filled composite restoratives because it may bring some structural defects and physical frailties on restorations due to lower degree of polymerization.

Delayed photo-activation and addition of thio-urethane: Impact on polymerization kinetics and stress of dual-cured resin cements.

OBJECTIVE: 1) to determine the moment during the redox polymerization reaction of dual cure cements at which to photo-activate the material in order to reduce the polymerization stress, and 2) to evaluate possible synergistic effects between adding chain transfer agents and delayed photo-activation. METHODS: The two pastes of an experimental dual-cure material were mixed, and the polymerization kinetics of the redox phase was followed. The moment when the material reached its maximum rate of redox polymerization (MRRP) of cement was determined. The degree of conversion (DC) and maximum rates of polymerization (Rpmax) were assessed for materials where: the photoactivation immediately followed material mixing, at MRRP, 1min before and 1min after MRRP. Thio-urethane (TU) additives were synthesized and added to the cement (20% wt), which was then cured under the same conditions. The polymerization kinetics was evaluated for both cements photo-activated immediately or at MRRP, followed by measurements of polymerization stress, flexural strength (FS) and elastic modulus (EM). Knoop hardness was measured before and after ethanol storage. RESULTS: Photo-activating the cement at or after MRRP reduced the Rpmax and the polymerization stress. Addition of TU promoted additional and more significant reduction, while not affecting the Rpmax. Greater hardness loss was observed for cements with TU, but the final hardness was similar for all experimental conditions. Addition of TU slightly reduced the EM and did not affect the FS. CONCLUSION: Delayed photo-activation and addition of TU significantly reduce the polymerization stress of dual-cured cements.

Enamel shear bond strength of two orthodontic self-etching bonding systems compared to Transbond™ XT.

OBJECTIVE: The aim of this in vitro study was to compare the shear bond strength (SBS) and Adhesive Remnant Index (ARI) scores of two self-etching no-mix adhesives (Prompt L-Pop™ and Scotchbond™) for orthodontic appliances to the commonly used total etch system Transbond XT™ (in combination with phosphoric acid). MATERIALS AND METHODS: In all, 60 human premolars were randomly divided into three groups of 20 specimens each. In group 1 (control), brackets were bonded with Transbond™ XT primer. Prompt L-Pop™ (group 2) and Scotchbond™ Universal (group 3) were used in the experimental groups. Lower premolar brackets were bonded by light curing the adhesive. After 24 h of storage, the shear bond strength (SBS) was measured using a Zwicki 1120 testing machine. The adhesive remnant index (ARI) was determined under 10× magnification. The Kruskal-Wallis test was used to statistically compare the SBS and the ARI scores. RESULTS: No significant differences in the SBS between any of the experimental groups were detected (group 1: 15.49 ± 3.28 MPa; group 2: 13.89 ± 4.95 MPa; group 3: 14.35 ± 3.56 MPa; p = 0.489), nor were there any significant differences in the ARI scores (p = 0.368). CONCLUSIONS: Using the two self-etching no-mix adhesives (Prompt L-Pop™ and Scotchbond™) for orthodontic appliances does not affect either the SBS or ARI scores in comparison with the commonly used total-etch system Transbond™ XT. In addition, Scotchbond™ Universal supports bonding on all types of surfaces (enamel, metal, composite, and porcelain) with no need for additional primers. It might therefore be helpful for simplifying bonding in orthodontic procedures.

Effects of Different Radiation Doses on the Bond Strengths of Two Different Adhesive Systems to Enamel and Dentin.

PURPOSE: To evaluate the effects of three different radiation doses on the bond strengths of two different adhesive systems to enamel and dentin. MATERIALS AND METHODS: Eighty human third molars were randomly divided into four groups (n = 20) according to the radiation dose (control/no radiation, 20 Gy, 40 Gy, and 70 Gy). The teeth were sagittally sectioned into three slices: one mesial and one distal section containing enamel and one middle section containing dentin. The sections were then placed in the enamel and dentin groups, which were further divided into two subgroups (n = 10) according to the adhesive used. Three restorations were performed in each tooth (one per section) using Adper Single Bond 2 (3M ESPE) or Universal Single Bond (3M ESPE) adhesive system and Filtek Z350 XT (3M ESPE) resin composite and subjected to the microshear bond test. Data were analyzed using a two-way ANOVA followed by Tukey's test. Failure modes were examined under a stereoscopic loupe. RESULTS: Radiotherapy did not affect the bond strengths of the adhesives to either enamel or dentin. In dentin, the Universal Single Bond adhesive system showed higher bond strength values when compared with the Adper Single Bond adhesive system. More adhesive failures were observed in the enamel for all radiation doses and adhesives. CONCLUSION: Radiotherapy did not influence the bond strength to enamel or dentin, irrespective of the adhesive or radiation dose used.

Effect of a third-generation LED LCU on microhardness of tooth-colored restorative materials.

OBJECTIVE: To assess the effects of different modes of a third-generation light-curing unit (LCU) (VALO) on the microhardness of restorative materials. DESIGN: A microhybrid composite resin (Filtek(™) Z550), a giomer (Beautifil II), a compomer (Dyract eXtra) and a RMGIC (Photac(™) Fil) were used in the study. Three different modes of VALO were tested and a second-generation LCU (Elipar S10) was used as a control. The microhardness (VHN) was measured using a Vickers Hardness tester. Data were analyzed using two-way anova and post hoc Tukey's test (P < 0.05). RESULTS: The Filtek Z550 group had the highest VHN values followed by Photac Fil, Beautifil II and the Dyract eXtra at both top and bottom surfaces, however the difference between Filtek Z550 and Photac Fil was not statistically significant for the bottom surfaces (P > 0.05). Of the different curing protocols tested, the VALO LCU in Mode 3 resulted in the lowest VHN values at both top and bottom surfaces (P < 0.05). CONCLUSION: Based on the results of this study, it can be concluded that the high-power mode of the VALO LCU can be recommended for clinical applications especially in pediatric patients, as it can shorten the time required to adequately polymerize resin-based tooth-colored restorative materials.

Effect of a broad-spectrum LED curing light on the Knoop microhardness of four posterior resin based composites at 2, 4 and 6-mm depths.

OBJECTIVE: To measure the Knoop microhardness at the bottom of four posterior resin-based composites (RBCs): Tetric EvoCeram Bulk Fill (Ivoclar Vivadent), SureFil SDR flow (DENTSPLY), SonicFill (Kerr), and x-tra fil (Voco). METHODS: The RBCs were expressed into metal rings that were 2, 4, or 6-mm thick with a 4-mm internal diameter at 30°C. The uncured specimens were covered by a Mylar strip and a Bluephase 20i (Ivoclar Vivadent) polywave(®) LED light-curing unit was used in high power setting for 20s. The specimens were then removed and placed immediately on a Knoop microhardness-testing device and the microhardness was measured at 9 points across top and bottom surfaces of each specimen. Five specimens were made for each condition. RESULTS: As expected, for each RBC there was no significant difference in the microhardness values at the top of the 2, 4 and 6-mm thick specimens. SureFil SDR Flow was the softest resin, but was the only resin that had no significant difference between the KHN values at the bottom of the 2 and 4-mm (Mixed Model ANOVA p<0.05). Although the KHN of SureFil SDR Flow was only marginally significantly different between the 2 and 6-mm thickness, the bottom at 6-mm was only 59% of the hardness measured at the top. CLINICAL SIGNIFICANCE: This study highlights that clinicians need to consider how the depth of cure was evaluated when determining the depth of cure. SureFil SDR Flow was the softest material and, in accordance with manufacturer's instructions, this RBC should be overlaid with a conventional resin.

Efeito da variação dos parâmetros de potência e energia por pulso na resistência de união à dentina de sistema adesivo irradiado com laser de diodo / Effect of the variation of the parameters of output power and pulse energy on bond strength to dentin irradiated of conventional adhesive system with diode laser

O uso do laser previamente à polimerização de sistemas adesivos aplicados sobre a dentina tem sido proposto para melhorar a resistência de união à dentina. O objetivo foi avaliar o efeito da variação da potência (P) e da energia por pulso (Ep) na resistência de união à dentina de um sistema adesivo convencional irradiado com laser previamente à fotoativação. Duzentos terceiros molares foram distribuídos aleatoriamente em 10 grupos (n=20) sendo um grupo sem irradiação (Controle) e nove grupos irradiados com laser de Diodo (970 nm) (SiroLaser - Sirona Dental Systems - Benshein, Alemanha), de acordo com a potência (P) e energia por pulso (Ep) utilizados: 1 - 0,5W/0,05J; 2 - 0,5W/0,08J; 3 - 0,5W/0,1J; 4 - 0,8W/0,05J; 5 - 0,8W/0,08J; 6 - 0,8W/0,1J; 7 - 1W/0,05J; 8 - 1W/0,08J; 9 - 1W/0,1J. Em todos os grupos fez-se o condicionamento com ácido fosfórico, aplicação do sistema adesivo convencional de dois passos AdperTM Single Bond 2 (3M ESPE, St Paul, MN, EUA) e restauração com resina composta Z250 (3M). Para avaliar a resistência de união foi realizado teste de microtração obtendo-se os valores em MPa. Os resultados foram analisados pelo ANOVA a dois critérios, seguido de Dunnett t (p < 0,001) para comparação entre os grupos. Os grupos irradiados foram avaliados pelo ANOVA a um critério, seguido dos testes de comparações múltiplas Bonferroni e Tamhane. Os valores de resistência de união ± desvio padrão de todos os grupos foram, respectivamente: 0 - Controle (34,60±10,76); 1 - (19,62±8,65); 2 - (27,56±9,20); 3 - (30,34±7,92); 4 - (23,31±5,96); 5 - (20,93±7,46); 6 - (24,67±8,59); 7 - (23,61±7,04); 8 - (25,94±6,82) e 9 - (21,48±3,59). O laser de Diodo influencia na resistência de união entre os grupos irradiados e não irradiado. A potência de 0,5W e energia por pulso de 0,1J influenciam positivamente nos valores de resistência de união quando o sistema adesivo é irradiado previamente a sua fotoativação.(AU)

The use of the laser prior to polymerisation of adhesive systems applied to the dentin has been proposed to improve the bond strength of dentin. The aim of this study was to investigate the effect of the variation of the output power (P) and pulse energy (Ep) on bond strength to dentin irradiated of conventional adhesive system with laser. Two hundred third molars were randomly distributed in 10 groups (n = 20): a group without laser irradiation (group control) and nine groups irradiated with diode laser (970 nm) (SiroLaser Sirona Dental Systems-Benshein, Germany), according to the output power (P) and pulse energy (Ep): 1 - 0,5W/0,05J; 2 - 0,5W/0,08J; 3 - 0,5W/0,1J; 4 - 0,8W/0,05J; 5 - 0,8W/0,08J; 6 - 0,8W/0,1J; 7 - 1W/0,05J; 8 - 1W/0,08J; 9 - 1W/0,1J. It was used in all groups etching with phosphoric acid, application of conventional adhesive system AdperTM Single Bond 2 (3M ESPE, St. Paul, MN, USA) and restoration with composite resin Z250 (3M). Microtensile test was performed obtaining bond strength values in MPa. Results were analyzed by two-ways ANOVA test, followed by Dunnett t (p < 0.001) for comparison between groups. The groups laser irradiated were assessed by one-way ANOVA test and subsequent t test with Bonferroni and Tamhane corrections. Bond strength values ± standard deviation for the groups were, respectively: 0 ­ group control (34.60 ± 10.76); 1 - (19.62 ± 8.65); 2 - (27.56 ± 9.20); 3 - (30.34 ± 7.92); 4 - (23.31 ± 5.96); 5 - (20.93 ± 7.46); 6 - (24.67 ± 8.59); 7 - (7.04 ± 23.61); 8 - (25.94 ± 6.82) and 9 - (3.59 ± 21.48). The Diode laser influences on bond strength between irradiated and without irradiated groups. The output power 0.5W and energy per pulse 0.1J influence positively in the bond strength values when the adhesive system is irradiated prior to their light curing.(AU)

Can Increasing the Manufacturer's Recommended Shortest Curing Time of High-intensity Light-emitting Diodes Adequately Cure Sealants?

PURPOSE: To investigate sealant depth of cure after increasing the curing times of high-intensity light-emitting diode units (LEDs). METHODS: Three sealants (opaque-unfilled, opaque-filled, and clear-filled) were light cured in a covered-slot mold with: (a) three LEDs (VALO, SmartLite, Fusion) for six to 15 seconds; and (b) a quartz-tungsten halogen (QTH) light for 40 seconds as a control (N=10). Twenty-four hours after light curing, microhardness was measured at the sealant surface and through the depth at 0.5 mm increments. Results were analyzed via analysis of variance followed by the Student-Newman-Keuls test (significance level 0.05). RESULTS: The opaque-filled and clear-filled sealants cured with VALO for six or nine seconds had hardness values that were statistically equivalent to or better than the QTH to a depth of 1.5 mm. Using Fusion for 10 seconds (exposure limit) did not adequately cure the three sealants beyond one mm. SmartLite at 15 seconds (maximum exposure period without overheating) did not adequately cure the sealants beyond 0.5 mm. CONCLUSIONS: Among the tested high-intensity LEDs, only VALO at double or triple the manufacturers' shortest curing time (six or nine seconds) provided adequate curing of opaque-filled and clear-filled sealants at 1.5 mm depth compared to the 40-second QTH light.

In vitro comparison of polymerisation kinetics and the micro-mechanical properties of low and high viscosity giomers and RBC materials.

OBJECTIVES: The study aims to characterise a low and high viscosity giomer bulk fill resin restorative with established low and high viscosity resin-based composite (RBC) restoratives at simulated clinical relevant specimen depths. METHODS: The irradiance of a light curing unit (Bluephase 20i) was measured on a laboratory-grade spectrometer at distances up to 10mm from the light tip (in 1mm increments). Polymerization kinetics (real-time decrease of CC double bond and degree of cure, DC) and micro-mechanical properties (Vickers hardness/HV; Depth of cure/DOC; Indentation modulus/E) were assessed at varying specimen depths (0.1-6mm in 100µm steps for E, DOC and HV and 0.1, 2, 4 and 6mm for DC) for a 20s irradiation. RESULTS: One and two-way ANOVA (α=0.05) were performed. The parameter material has a significant (p<0.001) effect on DC (ηP(2)=0.839), HV (ηP(2)=0.683), and E (ηP(2)=0.536), whereas the specimen depth influenced only DC (ηP(2)=0.584) but not HV (p=0.093) or E (p=0.133). The polymerisation kinetic could be described by an exponential sum function, distinguishing between the gel and the glass phase. The hardness drop out was lower than 20%, indicated a depth of cure of 6mm for all materials. CONCLUSIONS: The low and high viscosity giomer bulk-fill restoratives fulfil the requirements of bulk-fill placement, since under the analysed irradiation conditions an adequate depth of cure of >4mm was identified. Variation of DC with specimen depth was low, with little variation at specimen depths of <4mm. The micro-mechanical properties of the giomer materials were higher compared with the conventional RBC materials.

Curing profile of bulk-fill resin-based composites.

OBJECTIVE: To evaluate the curing profile of bulk-fill resin-based composites (RBC) using micro-Raman spectroscopy (µRaman). METHODS: Four bulk-fill RBCs were compared to a conventional RBC. RBC blocks were light-cured using a polywave LED light-curing unit. The 24-h degree of conversion (DC) was mapped along a longitudinal cross-section using µRaman. Curing profiles were constructed and 'effective' (>90% of maximum DC) curing parameters were calculated. A statistical linear mixed effects model was constructed to analyze the relative effect of the different curing parameters. RESULTS: Curing efficiency differed widely with the flowable bulk-fill RBCs presenting a significantly larger 'effective' curing area than the fibre-reinforced RBC, which on its turn revealed a significantly larger 'effective' curing area than the full-depth bulk-fill and conventional (control) RBC. A decrease in 'effective' curing depth within the light beam was found in the same order. Only the flowable bulk-fill RBCs were able to cure 'effectively' at a 4-mm depth for the whole specimen width (up to 4mm outside the light beam). All curing parameters were found to statistically influence the statistical model and thus the curing profile, except for the beam inhomogeneity (regarding the position of the 410-nm versus that of 470-nm LEDs) that did not significantly affect the model for all RBCs tested. CONCLUSIONS: Most of the bulk-fill RBCs could be cured up to at least a 4-mm depth, thereby validating the respective manufacturer's recommendations. CLINICAL SIGNIFICANCE: According to the curing profiles, the orientation and position of the light guide is less critical for the bulk-fill RBCs than for the conventional RBC.

Curing behaviour of high-viscosity bulk-fill composites.

OBJECTIVES: This study aimed to assess the effect of curing conditions--exposure time, mode, energy density, and exposure distance--on the mechanical properties of high-viscosity bulk-fill resin-based composites (RBCs) measured at simulated clinical relevant filling depths. METHODS: Three high-viscosity bulk-fill RBCs were investigated by assessing the variation in micromechanical properties in 200µm steps (Vickers hardness [HV] and indentation modulus [E]) within simulated 6-mm deep fillings (n=5) polymerized under 16 different curing conditions. The exposure duration was 5, 20, and 40s in the standard power mode; 3, 4, and 8s in the high power mode; and 3 and 6s in the plasma mode; the exposure distance was 0 and 7mm. Energy density ranged from 2.63 to 47.03J/cm(2). Measurements were performed after 24h of storage in distilled water at 37°C. The depth of cure (DOC) was calculated as the 80% hardness drop-off. RESULTS: The results were compared using one- and multiple-way ANOVAs and Tukey's HSD post hoc test (α=0.05). The effect of the parameter material was significant and strong on all measured properties (p<0.05, partial eta-squared ηP(2)=0.492 for E, 0.562 for HV, and 0.087 for DOC). Energy density exerted the strongest influence on the measured properties in all materials, whereas the influence of the exposure distance was strong on DOC, low on E and not significant on HV. The high-viscosity bulk-fill RBCs respond heterogeneously to variations in curing conditions. CONCLUSIONS: A lower energy density limit was identified, allowing for a 4mm material bulk placement (5.88J/cm(2) for EvoCeram Bulk Fill, 7.0J/cm(2) for x-tra fil, and 23.51J/cm(2) for SonicFill). This limit increased to 47.03J/cm(2) for a 5mm bulk placement, as claimed for SonicFill. To maintain mechanical properties in depth, however, an energy density of at least 23.51J/cm(2) is recommended for EvoCeram Bulk Fill and x-tra fil and 47.03J/cm(2) for SonicFill, respectively. This energy density should be achieved at moderate irradiance and increased curing time. CLINICAL SIGNIFICANCE: An exposure time of 20s at moderate irradiance is recommended for all materials for a 4 mm bulk placement.

The effect of time between handling and photoactivation on self-adhesive resin cement properties.

PURPOSE: To evaluate the degree of conversion, absorption, and solubility in water of self-adhesive resin cements subjected to different time intervals between material preparation and the photoactivation procedure. MATERIALS AND METHODS: Two dual self-adhesive resin cements were tested: RelyX Unicem and SmartCem2. The degree of conversion as a function of time was evaluated by Fourier-transformed infrared spectroscopy using the attenuated total reflectance technique. Three time intervals between handling and photoactivation were applied: Group 1 = immediately; Group 2 = a 1-minute interval; Group 3 = a 4-minute interval. All specimens were irradiated with a light-emitting diode source for 40 seconds. Thirty discs of each cement (1 mm thick × 6 mm diameter, n = 10) were prepared for the absorption and solubility tests. These specimens were stored in distilled water at 37°C for 90 days. The results were subjected to ANOVA with two factors (material and activation time intervals) and Tukey's test (95% significance). RESULTS: The 4-minute interval significantly reduced the degree of conversion of SmartCem2 (30.6% ± 8.3%). No other significant changes were observed for the degree of conversion; however, the time intervals before photoactivation interfered significantly in the water absorption of the RelyX Unicem specimens but not the SmartCem2 specimens. The time intervals did not affect the solubility of either cement. In all cases, SmartCem2 had higher solubility than RelyX Unicem. CONCLUSION: The time interval between handling and photoactivation significantly influenced the degree of conversion and water sorption of the resin-based cements. In general, one can say that the self-adhesive resin cements should be photoactivated as soon as possible after the material handling process.

Effects of plasma-emulating light-emitting diode (LED) versus conventional LED on cytotoxic effects and polymerization capacity of orthodontic composites.

OBJECTIVES: The aim of this study was to evaluate, the cytotoxicity of orthodontic composites in vitro as a function of degree of conversion (DC) and the light curing units (LCU) employed on mouse fibroblast (L929). MATERIALS AND METHODS: Cured samples of the composites Light bond (Reliance Orthodontic Products, Itasca, Illinois, USA), Ortho bracket paste (Bisco, Schaumburg, Illinois, USA), Opal bond MV (OPAL, South Jordan, Utah, USA), and Transbond XT (3M, Monrovia, California, USA) were prepared. Polymerization was performed with two LCUs: VALO Ortho (Ultradent, South Jordan, Utah, USA) is a third-generation LCU and Elipar S10 (3M, USA) is a second-generation LCU. Four samples were immersed in cell culture medium to obtain composite extracts. After incubation of L929 cell cultures with the extracts obtained, cytotoxicity was determined using the methyl tetrazolium test. Fourier transform infrared spectroscopy (FTIR) was used to evaluate DC for five samples. A multivariate analysis of variance (ANOVA), two-way ANOVA, and Tukey's honestly significant difference test were utilized for statistical analyses. RESULTS: Cytotoxicity and DC of all tested composites (p < 0.001) and the interaction between composites and LCUs (p < 0.01) were significantly different. LCUs had no significant influence on the cytotoxicity and DC of composite materials (p > 0.05). The correlations between cell viability and DC were positive for three composites but statistically insignificant. CONCLUSION: Composites and LCUs must be matched with one another to result in satisfactory maximal biocompatibility and DC. Opal Bond plasma light-emitting diode combination was a better choice for cell viability. Three composites showed a positive correlation between cytotoxicity and DC. Therefore high-intensity LCUs can be said to efficiently affect polymerization, and so, higher DC rates may achieve higher cell viability rates.

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.

Influence of different photo-activation distances on cytotoxicity of a dental adhesive model resin.

AIM: This study evaluated the cytotoxicity of a dental bonding model resin (DBMR) submitted to different photo-activation distances. METHODS: A monomer mixture based on Bis-GMA and HEMA was used to assess the cytotoxicity in a mouse fibroblast-cell line. To promote different photo-activation distances glass slides were interposed between DBMR surface and halogen light curing unit (LCU) tip. Afterwards, the specimens were immersed in RPMI culture medium for 24 h to obtain extracts. The extracts were incubated in contact with the cells for 24 h. Finally, an MTT colorimetric assay was used to assess the cytotoxicity. The cell viability data (absorbance) were analyzed by one way ANOVA followed by Tukey's test (P<0.05). RESULTS: The light output decreased according to the increase in the number of glass slides between the halogen LCU tip and DBMR surface. Yet, the distance between the tip of the curing light system and the specimens had significant influence on the cytotoxicity. All extracts produced by groups submitted to different photo-activation distances showed cytotoxic effect after 24h of incubation. CONCLUSION: The photo-activation distance and the interposition of glass slides between LCU tip and DBMR was shown to play an important role in the cytotoxic effect.