Impact of optical fiber-based photo-activation on dental composite polymerization.

OBJECTIVES: The study aimed to introduce a novel two-step optical fiber-based photo-activation of dental resin-based composites (RBCs) for reducing polymerization shrinkage stress (PSS). METHODS: Proposed protocol design - in the first step, two flexible plastic optical fibers connected to a dental light curing unit (LCU), were used as light guides inserted into the filling to initiate low-irradiance polymerization from within; in the second step, fibers were extracted and remaining voids were filled with RBC, followed by conventional high-irradiance curing to finalize polymerization. Three bulk-fill RBCs were tested (Beautifil-Bulk Restorative, Filtek Bulk-fill Posterior, Tetric PowerFill) using tooth cavity models. Three non-invasive examination techniques were employed: Digital Holographic Interferometry, Infrared Thermography, and Raman spectroscopy for monitoring model deformation, RBC temperature change, and degree of conversion (DC), respectively. A control group (for each examined RBC) underwent conventional photo-activation. RESULTS: The experimental protocol significantly reduced model deformation by 15 - 35 %, accompanied by an 18 - 54 % reduction in RBC temperature change, emphasizing the impact of thermal shrinkage on PSS. Real-time measurements of deformation and temperature provided indirect insights into reaction dynamics and illuminated potential mechanisms underlying PSS reduction. After a 24-hour dark-storage period, DC outcomes comparable to conventional curing were observed, affirming the clinical applicability of the method. CONCLUSIONS: Protocol involving the use of two 1.5 mm fibers in the first step (300 mW/cm2 x 10 s), followed by a second conventional curing step (1000 mW/cm2 x 10 s), is recommended to achieve the desired PSS reduction, while maintaining adequate DC and ensuring efficient clinical application. CLINICAL SIGNIFICANCE: Obtained PSS reduction offers promise in potentially improving the performance of composite restorations. Additionally, leveraging the flexibility of optical fibers improves light guide approach for restorations on posterior teeth. Meanwhile, implementation in clinical practice is easily achievable by coupling the fibers with commercial dental LCUs using the provided plastic adapter.

Polymerization efficiency of different bulk-fill resin composites cured by monowave and polywave light-curing units: a comparative study.

OBJECTIVES: The objective was to evaluate the polymerization efficiency of different bulk-fill resin-based composites cured by monowave and polywave light-curing units, by assessment of the degree of conversion and Vickers microhardness at different depths. METHOD AND MATERIALS: Two commercially available bulk-fill resin-based composites were used: Filtek One Bulk Fill Restorative (3M ESPE) and Tetric N-Ceram Bulk Fill (Ivoclar Vivadent). The light-curing units utilized were two LED light-curing units: a monowave LED light-curing unit (BlueLEX LD-105, Monitex) and a polywave LED light-curing unit (Twin Wave GT-2000, Monitex). For each test, 20 cylindrical specimens (4 mm diameter, 4 mm thickness) were prepared from each bulk-fill resin-based composite using a split Teflon mold. Ten specimens were light-cured by the monowave light-curing unit and the other ten were light-cured by the polywave light-curing unit according to the manufacturer's recommendations. Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) was used to assess the degree of conversion, and a Vickers microhardness tester was used to assess Vickers microhardness. Statistical analysis was performed using three-way ANOVA and Tukey post-hoc tests (P < .05). RESULTS: The degree of conversion and Vickers microhardness in bulk-fill resin-based composites containing only camphorquinone as photoinitiator were similar when cured with either monowave or polywave light-curing units. However, bulk-fill resin-based composites containing a combination of photoinitiators exhibited significantly higher degree of conversion and Vickers microhardness when cured with a polywave light-curing unit. Although all groups showed statistically significant differences between the top and bottom surfaces regarding degree of conversion and Vickers microhardness, all of them showed bottom/top ratios > 80% regarding degree of conversion and Vickers microhardness. CONCLUSION: The polywave light-curing unit enhanced the polymerization efficiency of bulk-fill resin-based composites especially when the latter contained a combination of photoinitiators, but does not prevent the use of a monowave light-curing unit.

Effect of Two Different Ultrafast Curing Exposure Durations on the Surface Hardness of Bulk Fill Composite - An In-Vitro Study.

AIM: The aim of the present study is to assess the microhardness of resin-based composites (RBCs) cured with ultrafast curing mode at two different exposure durations. STUDY DESIGN: This is an experimental in-vitro study. Forty-five cylindrical composite specimens were prepared to a dimension of 5 mm height and 4 mm diameter. Curing was done using three different exposure modes and duration with dual mode LED curing light as follows: Group I: Ultrafast curing mode for 1 second at 2300 mW/cm2 (n = 15); Group II: Ultrafast curing mode for 3 second at 2300 mW/cm2 (n = 15) and Group III: Standard exposure mode for 20 second at 1000 mW/cm2 (n = 15). Vicker's microhardness measurement was done on both the curing and non-curing sides of the specimen using a motorised diamond-faced micro-indenter (Wilson Wolpwert, Germany) using a load of 50 gram and a dwell time of 30 second. STATISTICAL ANALYSIS: Kruskal Wallis ANOVA was used to test for difference between the three groups followed by Mann-Whitney U test for post-hoc analysis. RESULTS: The microhardness values of the composite cured with a conventional curing unit were significantly higher than the ultrafast cured specimens. CONCLUSION: Low-intensity conventional curing lights were found to perform better than the high-intensity ultrafast curing units.

Polymerization and shrinkage kinetics and fracture toughness of bulk-fill resin-composites.

OBJECTIVES: To determine degree of conversion (DC), maximum polymerization rate (RPmax), polymerization shrinkage (PS), maximum shrinkage rate (PS Rmax) and fracture toughness (KIC) of different types of bulk-fill (BF) composites plus the effect of viscosity reduction techniques. METHODS: BF specimens were created in 2 mm deep molds: SonicFill 3 (SF3), Viscalor (VC), One Bulk Fill (OBF) and Beautifil Bulk (BBR). SF3 was applied via sonic insertion using a SonicFill handpiece (Kerr Corp. USA). Viscalor was pre-heated in a Caps Warmer in T3 mode (at 68 °C) for 30 s (T3-30 s) and 3 min (T3-3 min), respectively. Specimens were irradiated at zero distance from the upper surface with an Elipar S10 LED unit (3 M ESPE, USA) of mean irradiance 1200 mW/cm2 for 40 s. Real-time polymerization kinetics and DC at 5 min and 24 h post-irradiation (DC5 min and DC24 h) were measured using ATR-FTIR (n = 3). PS was measured up to 1 h on 1 mm thick discs via the bonded-disk technique (n = 3) and PS Rmax obtained by numerical differentiation (n = 3). For fracture toughness, single-edge-notched specimens (32 × 6 ×3 mm) of each BF composite were prepared and measured by three-point bending after 7 d water storage (n = 5). Data were analysed using One-way ANOVA, independent T-tests and Tukey post-hoc tests (p < 0.05). RESULTS: SF3 showed the significantly highest DC5 min, DC24 h and RPmax (p < 0.05), followed by OBF (p < 0.05). Regardless of pre-heating, VC showed comparable conversion kinetics to BBR (p > 0.05). There was no significant difference in PS of these BF composites, except OBF had the highest PS (p > 0.05). However, PS Rmax significantly varied among materials (p = 0.047) and SF3 had the highest PS Rmax. Regarding fracture toughness, BBR had the lowest KIC (p < 0.05), whereas other composites showed similar KIC (p > 0.05). Strong correlations of filler content (wt%)-PS/KIC were found. Different pre-heating times had no significant influences on DC %, RPmax, PS, PS Rmax and KIC of VC (p > 0.05). SIGNIFICANCE: Different types of bulk-fill composites showed comparable shrinkage. A highly filled BF giomer composite (BBR) had the lowest fracture toughness, whereas others had similar KIC. Pre-heating had no adverse effects on Viscalor properties. Sonication and pre-heating are beneficial techniques to enhance composite flowability without either increasing shrinkage or reducing fracture toughness.

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.

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 effect of 1.5 T and 3 T magnetic resonance imaging on microleakage of amalgam restorations.

The aim of this article is to compare the effects of 1.5 T and 3 T MRI on microleakage of amalgam restorations. A total of 90 extracted molar teeth were used in this study. Amalgam was used to restore standard Class V preparations (5 × 3 × 2 mm). Following the restoration, the teeth were divided into three groups according to magnetic resonance imaging (MRI) protocol (Group I: Control, Group II: 1.5 T MRI, and Group III: 3 T MRI). A total of 6,000 thermal cycles at 5°C-55°C were applied on all samples. Microleakage values were measured in millimeters using the ImageJ program. Microleakage values were higher in the gingival region compared to the occlusal region in all groups and the differences were statistically significant (p < .05). Microleakage values were not statistically different among the groups in the occlusal region (p > .05), while there were statistically significant differences among the groups with respect to microleakage values in the gingival region (p < .01). The highest mean microleakage amount in the gingival region was measured in Group III (1.192 ± 0.941 mm). This was followed by Group II (0.519 ± 0.813 mm) and Group I (0.347 ± 0.726 mm), respectively. Within the limitations of this in vitro study, we observed that higher microleakage values in amalgam restored teeth in which were exposed to MRI procedure. We also found that the teeth exposed to the stronger magnetic field showed higher microleakage amount.

Effect of Polymerization Time and Home Bleaching Agent on the Microhardness and Surface Roughness of Bulk-Fill Composites: A Scanning Electron Microscopy Study.

OBJECTIVE: The aim of this study is to evaluate the microhardness and surface roughness of two different bulk-fill composites polymerized with light-curing unit (LCU) with different polymerization times before and after the application of a home bleaching agent. MATERIALS-METHODS: For both microhardness and surface roughness tests, 6 groups were prepared with bulk-fill materials (SonicFill, Filtek Bulk Fill) according to different polymerization times (10, 20, and 30 s). 102 specimens were prepared using Teflon molds (4 mm depth and 5 mm diameter) and polymerized with LCU. 30 specimens (n = 5) were assessed for microhardness. Before home bleaching agent application, the bottom/top (B/T) microhardness ratio was evaluated. After bleaching agent application, the microhardness measurements were performed on top surfaces. Roughness measurements were performed in 72 specimens (n = 12) before and after bleaching application. Additionally, for SEM analyses, two specimens from all tested groups were prepared before and after bleaching agent application. The data B/T microhardness ratio before bleaching was analyzed by two-way ANOVA and Tukey's HSD test. The data from the top surface of specimens' microhardness before and after bleaching were analyzed using Wilcoxon signed-rank test, Kruskal-Wallis, Mann-Whitney U tests. The data from surface roughness tests were statistically analyzed by multivariate analysis of variance and Bonferroni test (p < 0.05). RESULTS: The B/T microhardness ratio results revealed no significant differences between groups (p > 0.05). Comparing the microhardness values of the composites' top surfaces before and after bleaching, a significant decrease was observed exclusively in FB30s (p < 0.05). No significant differences in surface roughness values were observed when the groups were compared based on bulk-fill materials (p > 0.05) while the polymerization time affected the surface roughness of the SF20s and SF30s groups (p < 0.05). After bleaching, surface roughness values were significantly increased in the SF20s and SF30s groups (p < 0.05). CONCLUSION: The clinicians should adhere to the polymerization time recommended by the manufacturer to ensure the durability of the composite material in the oral environment.

Underperforming light curing procedures trigger detrimental irradiance-dependent biofilm response on incrementally placed dental composites.

OBJECTIVES: Insufficient radiant exposure (J/cm2) may provide an early trigger in a cascade of detrimental responses on incrementally-place composite, especially the bottom layer. This study aimed to assess the influence of poor radiant exposure, the degree of conversion (%DC), water sorption/ solubility and S. mutans biofilm formation on conventional, incrementally placed composites and to establish a relationship between these factors. METHODS: Two light units operating at 600 and 1000 mW/cm2 and four most common operator-dependent curing conditions had the radiant exposure (RE) recorded. All the specimens were subjected to S. mutans biofilm model for 14 days. The %DC, biofilm formation expressed by colony-forming units (CFU), water sorption/ solubility and surface roughness/ SEM were assessed. Data were submitted to two-way ANOVA and Tukey post-hoc test (α = 0.05). Pearson correlation was also determined. RESULTS: The influence of RE on S. mutans CFU values and DC are dependent on the curing conditions and irradiance (p < 0.05). A negative relationship was observed between RE and biofilm formation. The operator-dependent curing conditions have shown RE reduction varying from 49.4% to 73.5% in relation to control. The difference in DC between top/bottom of cylinder varied from 13% to 21% for 1000 mW/cm2and from 29% to 53% for LCU600. The roughness, solubility and salivary sorption were greater for low RE. CONCLUSION: Poor, deficient curing procedures provide an early trigger in a negative pathway of events for incrementally-place dental composite including a biological response by increased biofilm formation by S. mutans, a relevant factor for secondary caries development. SIGNIFICANCE: The susceptibility to variation in the outcomes was RE -dependent. The optimization of the curing procedures ensures the maximum performance in the chain of events involved in the light curing process of resin-based materials and potentially reduce the risk factors of secondary caries development.

Investigation of the reliability of light-curing units in Sivas City, Turkey.

BACKGROUND: The number of studies investigating the physical properties of light-curing units used in city centers in terms of the light intensity, presence of residues fractures at the tips, how long they have been used, and hardness measurements of the composite resins polymerized by these is limited. There is no such study in Turkey and Sivas province. The objective of this study is to examine the light-curing units used in Sivas city center and determine the reliability of light-curing units by measuring the surface hardness of composite samples polymerized with these devices. MATERIALS AND METHODS: The power of the light-curing units that used in all private clinics in Sivas city center was measured. Then, the Vickers surface hardness measurements of the composite resin samples polymerized with these devices were made, and they were statistically evaluated. RESULTS: The light intensity was found to be below from the acceptable value of 400 mW/cm2 in 10.7% of the devices. It was observed that with increasing years of usage, the light intensity of light-curing units decreased (P < 0.05). CONCLUSION: It was observed that as the power of light-curing units increased, the hardness values of the bottom and top surfaces increased significantly.

Evaluation of intensity standards of tungsten-halogen and led curing units / Evaluación de estándares de intensidad de unidades de curado tugsteno-halógenas y leds

Current evidence indicates that the minimum light intensity of photo curing units required to polymerize in a reliable way a composite resin, in increments of 2mm, is 300mW/cm2. The recent introduction of new generations of composite resin materials for large volume increments, partially contrasts with ISO 4049 (2009), calling for the use of light intensity of 1,000mW/cm2. Therefore, it is considered relevant to carry out periodic measurements of the emission intensity of light-curing units of clinical use. The aim of this study was to test the intensity [mW/cm2] of a representative sample of tungsten-halogen and LED photopolymerization units used in private and public health service in different areas of the Valparaíso Region in Chile. This was achieved through the use of dental radiometers, without considering the variables of intensity modification over time (either spontaneously, by undesirable inherent characteristics of the device, or by programs of intensity modification in time), or the density of accumulated power needed. This in vitro diagnostic test, evaluated a sample of 507 units, 107 halogen and 400 LED, for a period of around one month, using two radiometers as measuring instruments. For LED units the Bluephase Meter® radiometer, from Ivoclar-VivadentTM was used, and for halogen units we used the Coltolux® from ColténeTM. As a result, 85% of the LED and halogen units achieved the minimum requirements of intensity needed for the polymerization of conventional dental biomaterials. However, only 25% from the tested units achieved a power density of 1,000mW/cm2.

Characterization of the transmission behavior of dental filling materials and cements for the diode lasers' and the Nd:YAG laser's wavelengths.

OBJECTIVES: Diode lasers and the Nd:YAG laser are used in periodontal therapy and soft tissue surgery. Dental filling materials or cements might be inadvertently damaged. The underlying mechanism of the damage is based on the dental material's specific transmission and thus absorption behavior. MATERIALS AND METHODS: Twenty-four material representatives for composites, glass ionomer cements and other material classes (e.g., compomer) were processed to 100 µm and 200 µm planar specimens and spectroscopically measured for their collimated transmission in the photo spectrometer Varian Cary 5000. The (1) mean intensity of transmitted light was determined for the laser wavelengths of interest (810 nm, 940 nm, 980 nm, 1,064 nm) and used to calculate the (2) absorption lengths. RESULTS: The (1) mean intensity of transmitted light ranged between 9.51 % (Panavia F 2.0 for 810 nm) and 96.79% (Artegral Cem for 1,064 nm) for the composite specimens (100 µm) and was-with few exceptions-near zero for the representatives of glass ionomer cement and the other material classes. The (2) absorption lengths were between 0.06 mm (Panavia F 2.0 for all wavelengths of interest) and 1.33 mm (Coltène Duo Cement Plus for 1,064 nm) for the composites and below or equal 0.15 mm (PermaCem for 1,064 nm) for the few representatives of glass ionomer cements and the other material classes with mean intensities of transmitted light, which were not near zero and thus permitted to calculate absorption lengths. CONCLUSIONS: The transmission behavior varied between the different material classes and even within, albeit less pronounced. Composites generally showed the highest intensities of transmitted light and are thus least susceptible to surface damage by laser light (810 nm, 940 nm, 980 nm, 1,064 nm). The results can be used to improve and develop laser applications involving purposeful interactions between laser light and dental materials. Lasers Surg. Med. © 2019 Wiley Periodicals, Inc.

Effect of radiant exposure and UV accelerated aging on physico-chemical and mechanical properties of composite resins.

Currently, there is no consensus in terms of defining the minimum radiant exposure values necessary for achieving adequate properties of composite resin. In addition, the long-term influence that radiant exposure has on the properties of composite resins is still questionable. OBJECTIVE: The objective of this study was to evaluate the effect of radiant exposure and UV accelerated aging on the physico-chemical and mechanical properties of micro-hybrid and nanofilled composite resins. MATERIAL AND METHODS: A nanofilled (Filtek Supreme; 3M ESPE) and a micro-hybrid composite resin (Filtek Z250; 3M ESPE) were investigated under different radiant exposures (3.75, 9, and 24 J/cm2) and UV accelerated aging protocols (0, 500, 1000, and 1500 aging hours). The degree of conversion (DC), flexural strength (FS), modulus (M), water sorption (WS), and solubility (WL) were evaluated. The results obtained were analyzed using two-way ANOVA and Tukey's test. Comparisons were performed using a significance level of α=0.05. RESULTS: The DC, FS, and M were found to be significantly influenced by both radiant exposure and accelerated aging time. The DC and EM increased with radiant exposure in the no-aging group (0-hour aging) for both micro-hybrid and nanofilled composites, whereas no correlation was found after accelerated aging protocols. WS and WL of micro-hybrid and nanofilled composite resins were scarcely affected by radiant exposure (p>0.05), whereas they were significantly reduced by accelerated aging (p<0.001). CONCLUSIONS: Although increasing radiant exposure affected the degree of conversion and mechanical properties of micro-hybrid and nanofilled composites, no influence on the hydrolytic degradation of the material was observed. In contrast, UV accelerated aging affected both the physico-chemical and mechanical properties of the composites.

Quality and Survival of Direct Light-Activated Composite Resin Restorations in Posterior Teeth: A 5- to 20-Year Retrospective Longitudinal Study.

PURPOSE: To analyze the clinical success of direct light-activated composite resin restorations in posterior teeth. The quality of the margins and occlusal surfaces were evaluated, as well as their survival, according to their extensions and locations. The clinical performance of posterior composite resin restorations with different compositions were compared. All restorations were performed by the first author in his private practice, in a 5- to 20-year period. MATERIALS AND METHODS: Several types of composite resins, provided by different manufacturers, were placed in posterior teeth, after isolation with rubber dams. To be included in the study, the restorations had to have been in function for at least 5 years and had to have been placed between October 1993 and October 2008 by the first author. The established failure criteria were: tooth and/or restoration fracture, secondary caries, endodontic treatment, or tooth loss. Included patients must have been treated in the first author's office for at least 7 years and still in the practice through 2013; all patients had complete dental arches. Patients with removable dental prostheses or disabilities, who had moved, or who had died were excluded. Of 210 patients who fulfilled the inclusion criteria, 138 randomly selected subjects were clinically examined between November 2013 and April 2014. Of these 138 patients, 61 had received 105 direct-light-activated composite resin restorations in posterior teeth, which met the inclusion criteria. Twenty-nine patients (47.5%) underwent annual maintenance therapy. The patient-based data collected from clinical exams and personal records were recorded on a specially designed form. Age, gender, period of clinical attendance, tooth preparation, location, size, quality and longevity of the restorations, restorative materials, adhesive systems, parafunctional habits, secondary caries, and maintenance therapy were the variables evaluated. Authors were blinded to the clinical assessments. Cohen's Kappa coefficient of the quality analysis of the margins and occlusal surfaces of the restorations ranged from 0.78 to 1. Data processing was performed using Epidat software, v3.1, developed by the Consellería de Sanidade de la Xunta de Galicia with the support of PAHO-WHO and SPSS software v13.0. If the number of complete values was too small, a Kaplan-Meier curve could not be used. Therefore the Fisher's exact test, Chi-square test, Kruskal-Wallis test, and Mann-Whitney non-parametric test were indicated to analyze significant differences. RESULTS: At the time of the examinations, 103 (98%) restorations were in function, and 98 (95.1%) were rated as clinically successful. Two restorations failed (2%). The observed mean survival time of restorations that remained functional was 11 years and 7 months. CONCLUSIONS: In the present report, direct light-activated composite resin restorations in posterior teeth showed a high clinical success rate and long-term mean survival time. These composite resins might be considered the material of choice to restore medium, extended, and in some clinical situations, large preparations in posterior teeth.

Effectiveness of photopolymerization in composite resins using a novel 445-nm diode laser in comparison to LED and halogen bulb technology.

Challenges especially in the minimal invasive restorative treatment of teeth require further developments of composite polymerization techniques. These include, among others, the securing of a complete polymerization with moderate thermal stress for the pulp. The aim of this study is to compare current light curing sources with a blue diode laser regarding curing depth and heat generation during the polymerization process. A diode laser (445 nm), a LED, and a halogen lamp were used for polymerizing composite resins. The curing depth was determined according to the norm ISO 4049. Laser output powers of 0.1, 0.5, 1, and 2 W were chosen. The laser beam diameter was adapted to the glass rod of the LED and the halogen lamp (8 mm). The irradiation time was fixed at 40 s. To ascertain ΔT values, the surface and ground area temperatures of the cavities were simultaneously determined during the curing via a thermography camera and a thermocouple. The curing depths for the LED (3.3 mm), halogen lamp (3.1 mm) and laser(0.5/1 W) (3/3.3 mm) showed no significant differences (p < 0.05). The values of ΔTsurface as well as ΔTground also showed no significant differences among LED, halogen lamp, and laser(1 W). The ΔTsurface values were 4.1LED, 4.3halogen lamp, and 4.5 °C for the laser while the ΔTground values were 2.7LED, 2.6halogen lamp, and 2.9 °C for the laser. The results indicate that the blue diode laser (445 nm) is a feasible alternative for photopolymerization of complex composite resin restorations in dentistry by the use of selected laser parameters.

Effect of radiant exposure and UV accelerated aging on physico-chemical and mechanical properties of composite resins

Abstract Currently, there is no consensus in terms of defining the minimum radiant exposure values necessary for achieving adequate properties of composite resin. In addition, the long-term influence that radiant exposure has on the properties of composite resins is still questionable. Objective: The objective of this study was to evaluate the effect of radiant exposure and UV accelerated aging on the physico-chemical and mechanical properties of micro-hybrid and nanofilled composite resins. Material and Methods: A nanofilled (Filtek Supreme; 3M ESPE) and a micro-hybrid composite resin (Filtek Z250; 3M ESPE) were investigated under different radiant exposures (3.75, 9, and 24 J/cm2) and UV accelerated aging protocols (0, 500, 1000, and 1500 aging hours). The degree of conversion (DC), flexural strength (FS), modulus (M), water sorption (WS), and solubility (WL) were evaluated. The results obtained were analyzed using two-way ANOVA and Tukey's test. Comparisons were performed using a significance level of α=0.05. Results: The DC, FS, and M were found to be significantly influenced by both radiant exposure and accelerated aging time. The DC and EM increased with radiant exposure in the no-aging group (0-hour aging) for both micro-hybrid and nanofilled composites, whereas no correlation was found after accelerated aging protocols. WS and WL of micro-hybrid and nanofilled composite resins were scarcely affected by radiant exposure (p>0.05), whereas they were significantly reduced by accelerated aging (p<0.001). Conclusions: Although increasing radiant exposure affected the degree of conversion and mechanical properties of micro-hybrid and nanofilled composites, no influence on the hydrolytic degradation of the material was observed. In contrast, UV accelerated aging affected both the physico-chemical and mechanical properties of the composites.

Multiple-peak and single-peak dental curing lights comparison on the wear resistance of bulk-fill composites.

The effects of tooth brushing could affect the long-term esthetic outcome of composite restorations. This study evaluated the effect of two different emission spectrum light-curing units on the surface roughness, roughness profile, topography and microhardness of bulk-fill composites after in vitro toothbrushing. Valo (multiple-peak) and Demi Ultra (single-peak) curing lights were each used for 10s to polymerize three bulk-fill resin composites: Filtek Bulk Fill Posterior Restorative (FBF), Tetric EvoCeram Bulk Fill (TET) and Surefil SDR Flow (SDR). After 30,000 reciprocal strokes in a toothbrushing machine, the roughness profile, surface roughness, surface morphology, and microhardness were examined. Representative SEM images were also obtained. When light-cured with the Demi Ultra, SDR showed the most loss in volume compared to the other composites and higher volume loss compared to when was light-cured with Valo. The highest surface roughness and roughness profile values were found in SDR after toothbrushing, for both light-curing units tested. FBF always had the greatest microhardness values. Light-curing TET with Valo resulted in higher microhardness compared to when using the Demi Ultra. Confocal and SEM images show that toothbrushing resulted in smoother surfaces for FBF and TET. All composites exhibited surface volume loss after toothbrushing. The loss in volume of SDR depended on the light-curing unit used. Toothbrushing can alter the surface roughness and superficial aspect of some bulk-fill composites. The choice of light-curing unit did not affect the roughness profile, but, depending on the composite, it affected the microhardness.

Intracoronal stress transfer through enamel following RBC photopolymerisation: A synchrotron X-ray study.

OBJECTIVES: To measure the spatial distribution of crystallographic strain in tooth enamel induced by the photo-polymerisation of a dimethacrylate resin based composite cavity restoration. METHODS: Six sound first premolar teeth, allocated into two groups (n=3), were prepared with mesio-occlusal distal cavities. The enamel was machined at the point of maximum convexity on the outer tooth to create a vertical fin of thickness 100µm and 0.5mm depth to allow for synchrotron X-ray diffraction measurements. 2D diffraction patterns were used to determine crystallite orientation and quantify changes in the hydroxyapatite crystal lattice parameters, before and after photo-polymerisation of a composite material placed in the cavity, to calculate strain in the respective axis. The composite was photo-polymerised with either relatively high (1200mWcm-2, group 1) or low (480mWcm-2, group 2) irradiances using LED or quartz halogen light sources, respectively. A paired t-test was used to determine significant differences in strain between irradiance protocols at ɑ=0.001. RESULTS: Photo-polymerisation of the composite in the adjacent cavity induced significant changes in both the crystallographic c and a axes of the enamel measurement area. However the magnitude of strain was low with ∼0.1% difference before and after composite photo-polymerisation. Strain in enamel was not uniformly distributed and varied spatially as a function of crystallite orientation. Increased alignment of crystallites perpendicular to the cavity wall was associated with higher c axis strain. Additionally, strain was significantly greater in the c (p<0.001) and a axis (p<0.001) when using a high irradiance photo-polymerisation protocol. SIGNIFICANCE: Although cuspal deflection is routinely measured to indirectly assess the 'global' effect of composite shrinkage on the tooth-restoration complex, here we show that absolute strains generated in enamel are low, indicating strain relief mechanisms may be operative. The use of low irradiance protocols for photo-polymerisation resulted in reduced strain.