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.

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.

Microhardness of glass carbomer and high-viscous glass Ionomer cement in different thickness and thermo-light curing durations after thermocycling aging.

BACKGROUND: The objective of our study was to compare the upper and lower surface microhardness and surface changes of Glass Carbomer Cement (GCP) and EQUIA Forte (EF) in different thickness after thermo-light curing durations and aging. METHODS: A total of 504 samples (5 mm-diameter) were prepared by using GCP-252 (GCP Dental, and Vianen, Netherlands) and EF-252 (EQUIA Forte, GC, Tokyo, Japan). Three different thickness samples (2, 4, and 6 mm) were prepared with 84 samples in each subgroup. The samples were prepared by three curing procedures (Non-exposed, 60s, 90s). Their varnishes were applied to the upper surfaces of half of each subgroup (n = 7). The upper microhardness measurements were evaluated before and after aging. To compare the effect of different thicknesses, the bottom surfaces of the samples were evaluated before aging in terms of microhardness measurements. Also, the upper surfaces were analyzed in the SEM before and after aging. RESULTS: The upper surface values of all the samples were higher than the bottom values (p < 0.05). There were no significant differences between the varnished and non-varnished samples in both materials (p > 0.05). Although this increase was not significant in some groups, temperature variations increased the surface microhardness values of both materials except for the non-exposed-varnished EF samples. The highest microhardnesses values were recorded in the non-exposed-varnished EF (125.6 ± 6.79) and unvarnished GCP (88.1 ± 7.59) samples which were thermo-light cured for 90 s before aging. The bottom hardness values were affected by thickness variations in both GCP and EF materials (p < 0.05). The sample deformations and microcracks after aging were greater than before in all the materials. Thermo-light curing in 90 s to the samples reduced the cracks in both the materials before and after aging. CONCLUSIONS: Thermal aging adversely affected the microhardness of the materials, which is important for clinical success. The thermo-light curing process improved the microhardness of the GCP group without varnish application. Varnish application increased the microhardness of the EF group without applying thermo-light curing. The microhardness of the bottom surfaces decreased with increasing thickness. The thermo-light curing did not increase the bottom surface microhardness of all the samples.

The Impact of Radiotherapy in the in Vitro Remineralization of Demineralized Enamel

Objective: To evaluate the impact of radiotherapy on enamel around restorations of glass ionomer cement (GIC) and fluoride tooth paste (FTP). Material and Methods: Eighty enamel blocks were made and randomly distributed into two groups, according to the fluoride therapy, non-fluoride tooth paste (NFTP) and FTP (n=40) and in subgroups in conformity with radiation dose (0, 10, 30 and 60 Gy). Roughness and microhardness enamel analyses were conducted before radiotherapy. Enamel cavities were made and restored with two GIC (Ketac Molar Easy Mix or Vitremer). Enamel blocks were submitted to 10, 30 and 60 Gy. Then, artificial enamel caries lesions were created by a pH-cycling procedure and FTP or NFTP were used as treatment. The restored enamel blocks were submitted to final roughness and microhardness analyses. Roughness increase (ΔR) and hardness loss (ΔH) values of enamel were submitted to ANOVA and Tukey test (p=0.05). Results: The irradiated enamel group showed statistically higher ΔR (0.44 ±0.2) and ΔH (99.26±7.0) values compared to non-irradiated group (ΔR = 0.051±0.02; ΔH=66.16±12.7) when a resin-modified GIC and NFTP were used. Conclusion: Higher radiation dose increased dissolution of bovine enamel. The use of GIC associated with FTP decreased roughness and increased enamel hardness after radiotherapy.

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.

Effect of ionizing radiation on properties of restorative materials.

OBJECTIVE: To evaluate the effect of ionizing radiation from high energy X-ray on properties of restorative materials. METHODS: Study materials (3M-ESPE) were: Z250-microhybrid resin-based composite (Filtek Z-250); Z350-nanofilled resin-based composite (Filtek Z-350XT); VIT-resin-modified glass ionomer cement (Vitremer); and KME-conventional glass ionomer cement (Ketac Molar Easymix). Sixty bar-shaped and cylinder-shaped specimens were fabricated from each material. Specimens were light activated (980mW/cm2, Radii, SDI) for 60s (3×20s for Z250 and Z350) and 120s (3×40s for VIT) and thirty specimens from each shape were irradiated (IR) with 1.8Gy/day for 39days (total IR=70.2Gy). IR and non-irradiated (NI) specimens were evaluated for flexural strength (σ, n=30) followed by fractography (SEM), diametral tensile strength (DTS, n=30), hardness (H, n=10), surface roughness (Ra, n=10) and chemical composition (n=3). The IR effect on each material property was statistically analyzed using Student's t test (α=0.05). Data from σ and DTS were also analyzed using Weibull statistics. RESULTS: IR significantly increased the mean σ values of VIT and KME and the mean DTS value of VIT (p<0.05). IR increased Ra and H values for VIT and decreased H value for Z-250 (p<0.05). The remaining materials and properties were not significantly affected by IR (p>0.05). There was no significant change on materials composition after IR. SIGNIFICANCE: The recommended radiotherapy protocol for head and neck cancer altered some material properties, mainly for glass ionomer cements. Such variations on material properties are not related to chemical composition changes.

Effect of Three Clinical Curing Treatments on Fluoride Release and Surface Hardness of Glass-Ionomer Cements.

The purpose of this study was to investigate the effect of radiant heat, ultrasonic treatment, and 42.7 wt% CaCl2 solution on fluoride release and surface hardness in three conventional glass-ionomer cements (GICs). The fluoride release patterns of each GIC were evaluated during a 28-day period using a fluoride ion-selective electrode. The surface hardness of the tested GICs was evaluated 24 hours after preparation of the specimens using Vickers hardness test. Statistical analysis of the data was made using analysis of variance and Bonferroni post hoc test (α = .05). Radiant heat, ultrasonic, and CaCl2 solution treatments reduced fluoride release and increased the surface hardness of the tested GICs (P < .05). Among the tested GICs, differences in fluoride release and surface hardness were observed (P < .05). The clinical treatments investigated may be effective methods for improving the setting reaction of GICs and may achieve sufficient initial mechanical properties earlier. Although a reduction in fluoride release occurs after the treatments, anticariogenic properties of the GICs may not be significantly affected.

Effect of different thermo-light polymerization on flexural strength of two glass ionomer cements and a glass carbomer cement.

STATEMENT OF PROBLEM: Whether polymerization lights can be used for heating glass ionomer cements (GICs) or glass carbomer (GCP) to improve their mechanical properties is not well established. PURPOSE: The purpose of this in vitro study was to assess the effect of thermo-light polymerization on the flexural strength (FS) of 2 GICs (Fuji IX GP Fast, Ketac Molar) and a GCP. MATERIAL AND METHODS: Specimens (n=10) were prepared in stainless steel molds (2×2×25 mm), compressed, exposed to 3 polymerization lights (500, 1000, 1200 mW/cm2) for 2 cycles of 40 seconds on each side, and stored in petroleum jelly (37°C, 24 hours). RESULTS: Significant FS differences were detected among groups after different thermo-light polymerization regimens (F=50.926, df=11, P<.001). GCP showed the highest mean FS (∼5 times, P<.001) after thermo-light polymerization with power outputs of 1000 (127.1 ±25.8 MPa) and 1200 mW/cm2 (117.4 ±18.5 MPa), with no significance difference between them (P=.98), compared with 500 mW/cm2 (24.1 ±1.7 MPa). For Ketac Molar, compared with autopolymerization setting (15.5 ±3.1 MPa), a significant increase in mean FS (∼2.5 times) was only observed in specimens treated with 1200 mW/cm2 polymerization light (P=.03). For Fuji IX GP Fast, only the light with 1000 mW/cm2 output significantly increased the FS (98.9 ±23.4 MPa, P<.001) compared with the autopolymerization setting (34.9 ±6.4 MPa). CONCLUSIONS: Thermo-light polymerization accelerated the development of FS in the tested GICs, potentially protecting against saliva contamination during the first 3 to 4 minutes after mixing GIC. Thermo-light polymerization of the glass carbomer with power outputs of 1000 and 1200 mW/cm2 also substantially increased FS. The clinical advantages of the findings should be validated by in vivo studies.

Intrapulpal Thermal Changes during Setting Reaction of Glass Carbomer® Using Thermocure Lamp.

Objectives. To measure the temperature increase induced during thermocure lamp setting reaction of glass carbomer and to compare it with those induced by visible light curing of a resin-modified glass ionomer and a polyacid-modified composite resin in primary and permanent teeth. Materials and Methods. Nonretentive class I cavities were prepared in extracted primary and permanent molars. Glass carbomer (GC) was placed in the cavity and set at 60°C for 60 sn using a special thermocure lamp. Resin-modified glass ionomer (RMGIC) and polyacid-modified composite resin (PMCR) were placed in the cavities and polymerized with an LED curing unit. Temperature increases during setting reactions were measured with a J-type thermocouple wire connected to a data logger. Data were examined using two-way analysis of variance and Tukey's honestly significant difference tests. Results. The use of GC resulted in temperature changes of 5.17 ± 0.92°C and 5.32 ± 0.90°C in primary and permanent teeth, respectively (p > 0.05). Temperature increases were greatest in the GC group, differing significantly from those in the PMCR group (p < 0.05). Conclusion. Temperature increases during polymerization and setting reactions of the materials were below the critical value in all groups. No difference was observed between primary and permanent teeth, regardless of the material 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.

Color stability of mineral trioxide aggregate and calcium enriched mixture cement.

AIM: To assess the effect of light irradiation and different immersion media on discoloration of white mineral trioxide aggregate (WMTA) and calcium enriched mixture (CEM) cement at different time intervals. METHODS: Enamel sections of 12 teeth were removed and six cavities were prepared in each tooth. The cavities were filled randomly either with WMTA or CEM and covered with transparent sealant. Half the specimens were irradiated for 160 sec (eight exposures of 20 sec each) and the remaining were irradiated for 40 sec (two exposures of 20 sec each); digital images were taken after each exposure. The teeth were stored in phosphate buffer saline, oxygen-rich medium and glycerin (n = 4). Digital images were obtained after 1, 3, 7, 14, and 28 days. Commission Internationale de I'E'clairage (CIE) color space system and Photoshop CS5 software were used to evaluate the discoloration. The color change (ΔE) and lightness (ΔL) values was analyzed using repeated measures anova and Tukey's Tukey's honest significant difference (HSD) test. RESULTS: The materials tested showed significant discoloration over time (WMT > CEM; P < 0.001). ΔE increased significantly while ΔL decreased in three media over time (P < 0.001). Greater duration of light curing caused a significant decrease in ΔL and ΔE values in both materials (WMTA > CEM; P < 0.001). CONCLUSION: Color stability of WMTA was inferior to CEM samples after exposure to different duration of irradiation and media over time.

Avaliação in vitro e in vivo de um cimento de ionômero de vidro incorporado com diacetato de clorexidina e radiado sob condições de tratamento radioterápico / In vitro and in vivo assessments of a glass ionomer cement embedded with chlorhexidine diacetate and radiated under radiotherapy conditions

Radiotherapy (RXT) is one of the main treatments in cases of head and neck cancer and effects of radiation, such as radiation caries, xerostomia and oral mucositis are among the most observed effects after treatment. Chlorhexidine association to glass ionomer cement (GIC) has shown effective antimicrobial activity against the Streptococcus mutans in vitro conditions. However it has only been tested without the use of radiation. The objective of this work is to study the antibacterial effect against S. mutans, the biocompatibility and the pro-inflammatory process induced by a GIC with or without incorporation of chlorhexidine diacetate (dCHX) before and after being radiated under radiotherapy treatment conditions. Test specimens were made in dimensions of 2.5 mm radius x 2 mm thick with GIC incorporated with dCHX percentages at 0%, 0.5%, 1.0% and 2.0%. Half of the samples of each concentration were irradiated with 60 Gy. Antimicrobial activity was tested after exhaustion, with daily changes of sterile distilled water for 270 days. The cytotoxicity was performed by MTT assay according to ISO 10993-5/2009. The pro-inflammatory response was evaluated histologically from the implantation of the samples in subcutaneous tissue of rats. Statistical analysis was performed by Kruskal-Wallis and Dunn tests (p <0.05). All experimental groups were able to inhibit the growth of S. mutans. Cytotoxicity was higher in irradiated groups, regardless of the percentage of incorporation of dCHX. The group without dCHX and subjected to radiation was the condition with higher pro-inflammatory effects, whereas the group with 0.05% dCHX and also submitted to radiation showed less pro-inflammatory effect was (p <0.05). Considering the limitations of this work the following conclusions can be made: 1- radiation or incorporation of dCHX not interfere with the antimicrobial activity against S. mutans for up to 270 days of exhaustion; 2 - the radiation influenced the cytotoxicity, reducing cell viability in all groups, suggesting the use of GIC incorporated with less than 2% dCHX if there is submission to radiation under the conditions of this study; 3 - the proinflammatory analysis also adivse that, in radiation exposure cases, to choose the use of GIV embedded with dCHX and, otherwise, to choose GIC without dCHX.

Radiotherapy (RXT) is one of the main treatments in cases of head and neck cancer and effects of radiation, such as radiation caries, xerostomia and oral mucositis are among the most observed effects after treatment. Chlorhexidine association to glass ionomer cement (GIC) has shown effective antimicrobial activity against the Streptococcus mutans in vitro conditions. However it has only been tested without the use of radiation. The objective of this work is to study the antibacterial effect against S. mutans, the biocompatibility and the pro-inflammatory process induced by a GIC with or without incorporation of chlorhexidine diacetate (dCHX) before and after being radiated under radiotherapy treatment conditions. Test specimens were made in dimensions of 2.5 mm radius x 2 mm thick with GIC incorporated with dCHX percentages at 0%, 0.5%, 1.0% and 2.0%. Half of the samples of each concentration were irradiated with 60 Gy. Antimicrobial activity was tested after exhaustion, with daily changes of sterile distilled water for 270 days. The cytotoxicity was performed by MTT assay according to ISO 10993-5/2009. The pro-inflammatory response was evaluated histologically from the implantation of the samples in subcutaneous tissue of rats. Statistical analysis was performed by Kruskal-Wallis and Dunn tests (p <0.05). All experimental groups were able to inhibit the growth of S. mutans. Cytotoxicity was higher in irradiated groups, regardless of the percentage of incorporation of dCHX. The group without dCHX and subjected to radiation was the condition with higher pro-inflammatory effects, whereas the group with 0.05% dCHX and also submitted to radiation showed less pro-inflammatory effect was (p <0.05). Considering the limitations of this work the following conclusions can be made: 1- radiation or incorporation of dCHX not interfere with the antimicrobial activity against S. mutans for up to 270 days of exhaustion; 2 - the radiation influenced the cytotoxicity, reducing cell viability in all groups, suggesting the use of GIC incorporated with less than 2% dCHX if there is submission to radiation under the conditions of this study; 3 - the proinflammatory analysis also adivse that, in radiation exposure cases, to choose the use of GIV embedded with dCHX and, otherwise, to choose GIC without dCHX.

Degree of conversion and hardness of two different systems of the Vitrebond™ glass ionomer cement light cured with blue LED.

This study investigated the physicochemical properties of the new formulation of the glass ionomer cements through hardness test and degree of conversion by infrared spectroscopy (FTIR). Forty specimens (n = 40) were made in a metallic mold (4 mm diameter x 2 mm thickness) with two resin-modified glass ionomer cements, Vitrebond™ and Vitrebond™ Plus (3M/ ESPE). Each specimen was light cured with blue LED with power density of 500 mW/cm(2) during 30 s. Immediately after light curing, 24h, 48h and 7 days the hardness and degree of conversion was determined. The Vickers hardness was performed by the MMT-3 microhardness tester using load of 50 gm force for 30 seconds. For degree of conversion, the specimens were pulverized, pressed with KBr and analyzed with FT-IR (Nexus 470). The statistical analysis of the data by ANOVA showed that the Vitrebond™ and Vitrebond™ Plus were no difference significant between the same storage times (p > 0.05). For degree of conversion, the Vitrebond™ and Vitrebond™ Plus were statistically different in all storage times after light curing. The Vitrebond™ showed higher values than Vitrebond™ Plus (p < 0.05). The performance of Vitrebond™ had greater results for degree of conversion than Vitrebond™ Plus. The correlation between hardness and degree of conversion was no evidence in this study.

Influence of photo-activation source on enamel demineralization around restorative materials

This study evaluated the effects of the photoactivation source and restorative material on the development of caries-like lesions on human enamel after an in vitro pH challenge. Enamel cavities were prepared in 36 blocks, which were assigned to two groups according to the restorative material: resin-modified glass ionomer (RMGI) and composite resin (CR). Samples were exposed to quartz-tungsten-halogen lamp, argon-ion laser, or light-emitting diode (n = 6). The Knoop microhardness (KHN) values of the top surface of all materials were evaluated. Restored enamel blocks were thermocycled and subjected to 10 demineralization-remineralization cycles at 37°C. KHN analysis of the superficial enamel was performed by four indentations located 100 mm from the restoration margin. The material KHN was not affected by the photoactivation source. No significant difference in KHN was noted between CR and RMGI. The enamel surface around RMGI exhibited a higher KHN (272.8 KHN) than the enamel around CR (93.3 KHN), regardless of the photoactivation source. Enamel demineralization around the dental restoration was not influenced by the photoactivation source. Less enamel demineralization was observed around the RMGI than around the CR restoration.

Influence of photo-activation source on enamel demineralization around restorative materials.

This study evaluated the effects of the photoactivation source and restorative material on the development of caries-like lesions on human enamel after an in vitro pH challenge. Enamel cavities were prepared in 36 blocks, which were assigned to two groups according to the restorative material: resin-modified glass ionomer (RMGI) and composite resin (CR). Samples were exposed to quartz-tungsten-halogen lamp, argon-ion laser, or light-emitting diode (n = 6). The Knoop microhardness (KHN) values of the top surface of all materials were evaluated. Restored enamel blocks were thermocycled and subjected to 10 demineralization-remineralization cycles at 37°C. KHN analysis of the superficial enamel was performed by four indentations located 100 µm from the restoration margin. The material KHN was not affected by the photoactivation source. No significant difference in KHN was noted between CR and RMGI. The enamel surface around RMGI exhibited a higher KHN (272.8 KHN) than the enamel around CR (93.3 KHN), regardless of the photoactivation source. Enamel demineralization around the dental restoration was not influenced by the photoactivation source. Less enamel demineralization was observed around the RMGI than around the CR restoration.

Effects of refractive index solutions on the color of different luting cements.

PURPOSE: The purpose of this study is to determine the effects of refractive index solutions on the color of different luting cements at different periods. MATERIALS AND METHODS: Fourteen disc-shaped specimens were prepared for three different universal shade luting cements. All specimens were divided into two groups and a phthalate ester and glycerol refractive index solution was applied to the specimens at different periods. Color differences (ΔE*) were calculated for before and after 5, 15, 60 min and 24 h periods of applying refractive index solutions. Data were analyzed with multiple analysis of variance (ANOVA) and mean values were compared by the Tukey HSD test (α = 0.05). RESULTS: Periods and periods-cement interaction were statistically significant (p ≤ 0.05). There was no statistically significant difference between the mean ΔE values of refractive index solutions and cement groups (p > 0.05). CONCLUSION: Refractive index solutions affected the color of luting cements.

Effect of light-emitting diode and halogen light curing on the micro-hardness of dental composite and resin-modified glass ionomer cement: an in vitro study.

AIMS: This in vitro study was conducted to evaluate and compare the micro-hardness of composite resin and resin-modified glass ionomer cement using light-emitting diode (LED) and halogen curing and also to inter-compare the effect of LED and halogen curing. MATERIALS AND METHODS: The study sample comprised of 4 stainless steel plates with a thickness of 2 mm. For these stainless steel plates, holes were made to a diameter of 3 mm. The samples were divided into 4 groups of 8 each and labeled as group I, group II, group III, group IV, thus making provision for the two different modes of light exposure. In each group, the hole was restored with its respective restorative material and cured with light-curing unit according to manufacturer instructions. The results were statistically analyzed using Mann-Whitney test. RESULTS AND CONCLUSION: It was concluded that the curing efficacy of the LED lamp was comparable to that of conventional halogen lamp, even with a 50% reduction in cure time, and resin composite (Filtek Z-250) presented the highest hardness values, whereas complete hardening of resin-modified glass ionomer cement (RMGIC) (Vitremer) was observed because of its self-curing system even after the removal of light source.

The effect of pre-warming and delayed irradiation on marginal integrity of a resin-modified glass-ionomer.

Recent studies have indicated that the acid-base reactions and polymerization of resin-modified glass-ionomers (RMGIs) compete with and inhibit each other; however, external energy can also influence the properties of RMGIs. This in vitro study evaluated the effect of pre-warming and/or delayed light irradiation on marginal integrity of RMGIs in cervical restorations. Standard Class V cavities were prepared on the buccal aspects of 60 human maxillary premolars. Each cavity was treated with a cavity conditioner for 10 seconds, rinsed, and gently air-dried. An RMGI was applied to the prepared cavities as dictated by the study protocol. Group 1 samples were treated per manufacturers' instructions. Group 2 samples were photocured after a delay of 2 minutes. For samples in Group 3, the encapsulated material was pre-warmed (at 40° C) for 90 seconds; for Group 4 samples, capsules were pre-warmed and photocuring was delayed for 2.4 minutes. Microleakage scores were determined using dye penetration technique; Kruskal-Wallis and Mann-Whitney U tests were used for statistical analysis (α = 0.05). The enamel groups exhibited statistically significant differences (P = 0.036), while the dentin groups did not (P = 0.122); however, in both cases, Group 2 demonstrated the highest marginal integrity. Based on the results of this study, pre-warming could jeopardize the marginal integrity of RMGIs in cervical restorations, while delaying the curing process might improve it (particularly for enamel).

Effect of light activation on resin-modified glass ionomer shear bond strength.

OBJECTIVE: Recent studies confirmed that resin-modified glass ionomers (RMGIs) set on the basis of two competing mechanisms, an acid-base reaction and a light-activated resin polymerization. This study evaluated the effect of the setting mechanism on bond strength by measuring the shear bond strength of three RMGIs to dentin with and without light activation. METHODS: Sixty human molars were ground to midcoronal dentin and randomly divided into six even groups: 1) Ketac Nano (KN), 2) KN without light cure (woLC), 3) Fuji Filling LC (FF), 4) FF woLC, 5) Fuji II LC (FII), and 6) FII woLC. The dentin surfaces of the specimens were conditioned/primed according to the manufacturers' instructions. A 1.54-mm diameter plastic tube was filled with RMGI material and affixed to the dentin surface. Groups 1, 3, and 5 were light cured for 20 seconds, and groups 2, 4, and 6 were immediately placed in a damp dark box with no light curing at 37°C for 24 hours. Shear bond strength testing was performed in an Instron device at 1 mm/min. Data were analyzed with a one-way analysis of variance (ANOVA) and Tukey/Kramer test (α=0.05). RESULTS: Mean ± standard deviation shear bond strength values (MPa) are: 7.1 ± 4.2 (KN), 11.7 ± 3.9 (FF), 10.2 ± 3.2 (FF woLC), 12.5 ± 5.1 (FII), and 0.3 ± 0.4 (FII woLC). Two KN, all KN woLC, and seven FII woLC specimens debonded before testing. Tukey/Kramer analysis revealed no significant differences in bond strength between the three light-cured RMGIs. KN and FII showed significantly lower bond strength without light cure, but no significant difference was observed between FF and FF woLC. CONCLUSIONS: The results of this study strongly suggest that light activation is necessary to obtain optimal bond strength between RMGI and dentin. FF may contain components that chemically activate resin polymerization. Clinically, KN and FII need to be light cured after placement of these RMGIs.

Influence of ultrasound or halogen light on microleakage and hardness of enamel adjacent to glass ionomer cement.

BACKGROUND: The use of external sources of energy may accelerate the setting rate of glass ionomer cements (GICs) allowing better initial mechanical properties. AIM: To investigate the influence of ultrasound and halogen light on the microleakage and hardness of enamel adjacent to GIC restorations, after artificial caries challenge. DESIGN: Cavities were prepared in 60 primary canines, restored with GIC, and randomly distributed into three groups: control group (CG), light group (LG) - irradiation with a halogen light-curing unit for 60s, and ultrasonic group (UG) - application of ultrasonic scaler device for 15s. All specimens were then submitted to a cariogenic challenge in a pH cycling model. Half of sample in each group were immersed in methylene blue for 4h and sectioned for dye penetration analysis. The remaining specimens were submitted to Knoop cross-sectional microhardness assessments, and mineral changes were calculated for adjacent enamel. RESULTS: Data were compared using Kruskal-Wallis test and two-way ANOVA with 5% significance. Higher dye penetration was observed for the UG (P<0.01). No significant mineral changes were observed between groups (P=0.844). CONCLUSION: The use of halogen light-curing unit does not seem to interfere with the properties of GICs, whereas the use of ultrasound can affect its marginal sealing.