Effect of short LED lamp exposure on wear resistance, residual monomer and degree of conversion for Filtek Z250 and Tetric EvoCeram composites

Emerging technologies for the evaluation of spatio-temporal polymerisation changes in flowable vs. sculptable dental resin-based composites

BACKGROUND

This study presents a novel multi-technique approach that integrates micro-CT and optical photothermal infrared spectroscopy (O-PTIR) to evaluate polymerisation differences, so-called spatio-temporal polymerisation properties, between flowable and sculptable dental resin-based composites.

METHODS

Ten commercially available dental composites were investigated, including flowable and sculptable counterparts from the same manufacturer. Eight parameters were evaluated: short-term polymerisation characteristics (degree of conversion after 5 min, maximum polymerisation rate, time to reach maximum polymerisation rate) was measured using ATR-FTIR with real-time monitoring; changes in the degree of conversion with depth were evaluated with O-PTIR, 3D visualisation of shrinkage patterns, overall volumetric shrinkage, depth-specific shrinkage, and porosity were measured using micro-CT; surface morphology with detailed measurements of elemental composition was characterised using SEM/EDX; light transmittance was analysed with a NIST-referenced spectrometer.

RESULTS

The study found that the increase in filler weight and volume ratio reduced the degree of conversion and polymerisation shrinkage, while moderately influencing the maximum polymerisation rates. The time to reach maximum polymerisation rates and light transmittance were not dependent on the filler amount. O-PTIR assessed a depth-dependent decrease in the degree of conversion for both composite types, with flowable composites generally showing a greater decrease in the degree of conversion than sculptable composites, except for bulk-fill composites. Micro-CT scans showed significantly higher flowable shrinkage values than their sculptable counterparts, highlighting the performance differences between the two types of composites.

CONCLUSIONS

The findings of this study have practical implications for the selection and use of dental composites. Flowable composites, despite their higher degrees of conversion and polymerisation rates, also exhibit higher volumetric shrinkage, which can be detrimental for clinical applications. The new measurement methods used in this study provide a comprehensive overview of the polymerisation behaviour of commercially available dental composites, offering valuable insights for material optimisation.

Validation of a human saliva model for the determination of leachable monomers and other chemicals from dental materials

This study aimed to prove the validity of a mixture of chemicals, including salts, small organic molecules, mucin, and α-amylase, as saliva surrogate ("artificial saliva") for assessing leakage of methacrylate monomers and other constituents from dental materials. To achieve this, we developed and validated a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the quantification of 2-hydroxyethyl methacrylate (HEMA), triethylene glycol dimethacrylate (TEGDMA), diurethane dimethacrylate (UDMA), bisphenol A glycerolate dimethacrylate (BisGMA), diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO), bisphenol A (BPA), and five homologues of ethoxylated bisphenol A dimethacrylate (BisEMA EO2-6) in unstimulated and artificial saliva, and compared their concentrations in the two saliva media following either spiking with a mixture of the compounds or incubation of test specimens of printed biomaterials. Test specimens were immersed in unstimulated/artificial saliva, incubated at 37 °C for 24 h, and saliva aliquots were extracted with methanol and subsequently analyzed by LC-MS/MS. The method was validated with regard to matrix effects, linearity, selectivity, lower limits of quantification (LLOQ), precision, bias and combined measurement uncertainty (u'). The performance characteristics of the method were comparable for unstimulated and artificial saliva samples. The combined u' for individual chemicals at a concentration of 10 × LLOQ were within the range of 5.3-14 % for unstimulated saliva and 6.9-16 % for artificial saliva, except for the BisEMA homologues. Combined u' for the latter were 27-74 % in unstimulated saliva, and 27-79 % in artificial saliva. There was no detectable release of BPA from the test specimens, and the TPO concentrations were mainly below the LLOQ. TEGDMA and UDMA were detected in the highest quantities, and at comparable concentrations in the unstimulated and artificial saliva. For all BisEMA homologues, the release was higher in unstimulated saliva than in artificial saliva. The study showed that the artificial saliva model can be a suitable replacement for native saliva, but might underestimate leakage of more lipophilic methacrylates.

Interfacial integrity of bulk-fill resin composite restorations in deep Class-II cavities

This study evaluated the interfacial integrity of deep (6 mm) Class-II (OM/OD) restorations placed using different bulk-fill resin composites [Filtek™ Bulk Fill Flowable Restorative (BF) and Filtek™ Bulk Fill Posterior Restorative (BP) (3M ESPE, St. Paul, MN, USA)] of different increment thicknesses (2 or 4 mm). BP was used for capping in all cases, while Filtek™ Z250 Universal Restorative (3M ESPE) was used as the control material. Interfacial debonding was measured during curing through acoustic emission (AE), followed by image analysis using micro-computed tomography and scanning electron microscopy. Microhardness testing was also conducted to assess degree of conversion. Depth of cure was adequate in all restorations. Specimens with 4-mm thick first increment of BF, which had a higher shrinkage strain, produced most AE events and debonding. Thus, bulk filling of deep cavities using bulk-fill resin composites with a high shrinkage strain should be avoided.

The effect of high-irradiance rapid polymerization on degree of conversion, monomer elution, polymerization shrinkage and porosity of bulk-fill resin composites

OBJECTIVE

The purpose was to compare the degree of conversion (DC), monomer elution (ME), polymerization shrinkage (PS) and porosity of two addition-fragmentation chain transfer (AFCT) modified resin-based composites (RBC) light-cured with rapid- (RP), turbo- (TP) or conventional polymerization (CP) settings.

METHODS

Cylindrical samples (6-mm wide, 4-mm thick) were prepared from Tetric PowerFill (TPF) and Filtek One Bulk (FOB). Four groups were established according to the polymerization settings: 3s-RP, 5s-TP, 10s-CP and 20s-CP. Samples in 1 mm thickness with 20s-CP settings served as controls. The DC at the top and bottom surfaces was measured with micro-Raman spectroscopy. ME was detected with high-performance liquid chromatography. PS and porosity were analyzed by micro-computed tomography. ANOVA and Tukey's post-hoc test, multivariate analysis and partial eta-squared statistics were used to analyze the data (p < 0.05).

RESULTS

FOB showed higher DC values (61.5-77.5 %) at the top compared to TPF (43.5-67.8 %). At the bottom TPF samples achieved higher DCs (39.9-58.5 %) than FOB (18.21-66.18 %). Extending the curing time increased DC (except the top of FOB) and decreased ME. BisGMA release was the highest among the detected monomers from both RBCs. The amount was three-fold more from TPF. The factor Material and Exposure significantly influenced DC and ME. PS (1.8-2.5 %) did not differ among the groups and RBCs except for the lowest value of TPF cured with the 3s_RP setting (p = 0.03). FOB showed 4.5-fold lower porosity (p < 0.001). Significantly higher pore volume was detected after polymerization in 3s_RP (p < 0.001).

SIGNIFICANCE

High-irradiance rapid 3-s curing of AFCT modified RBCs resulted in inferior results for some important material properties. A longer exposure time is recommended in a clinical situation.

Using Copper-Doped Mesoporous Bioactive Glass Nanospheres to Impart Anti-Bacterial Properties to Dental Composites

Experimental dental resin composites containing copper-doped mesoporous bioactive glass nanospheres (Cu-MBGN) were developed to impart anti-bacterial properties. Increasing amounts of Cu-MBGN (0, 1, 5 and 10 wt%) were added to the BisGMA/TEGDMA resin matrix containing micro- and nano-fillers of inert glass, keeping the resin/filler ratio constant. Surface micromorphology and elemental analysis were performed to evaluate the homogeneous distribution of filler particles. The study investigated the effects of Cu-MBGN on the degree of conversion, polymerization shrinkage, porosity, ion release and anti-bacterial activity on S. mutans and A. naeslundii. Experimental materials containing Cu-MBGN showed a dose-dependent Cu release with an initial burst and a further increase after 28 days. The composite containing 10% Cu-MBGN had the best anti-bacterial effect on S. mutans, as evidenced by the lowest adherence of free-floating bacteria and biofilm formation. In contrast, the 45S5-containing materials had the highest S. mutans adherence. Ca release was highest in the bioactive control containing 15% 45S5, which correlated with the highest number of open porosities on the surface. Polymerization shrinkage was similar for all tested materials, ranging from 3.8 to 4.2%, while the degree of conversion was lower for Cu-MBGN materials. Cu-MBGN composites showed better anti-bacterial properties than composites with 45S5 BG.

Meta-analytical analysis on components released from resin-based dental materials

OBJECTIVES

Resin-based materials are applied in every branch of dentistry. Due to their tendency to release substances in the oral environment, doubts have been raised about their actual safety. This review aims to provide a comprehensive analysis of the last decade literature regarding the concentrations of elutable substances released from dental resin-based materials in different type of solvents.

MATERIALS AND METHODS

All the literature published on dental journals between January 2010 and April 2022 was searched using international databases (PubMed, Scopus, Web of Science). Due to strict inclusion criteria, only 23 papers out of 877 were considered eligible. The concentration of eluted substances related to surface and volume of the sample was analyzed, considering data at 24 h as a reference. The total cumulative release was examined as well.

RESULTS

The most eluted substances were HEMA, TEGDMA, and BPA, while the less eluted were Bis-GMA and UDMA. Organic solvents caused significantly higher release of substances than water-based ones. A statistically significant inverse correlation between the release of molecules and their molecular mass was observed. A statistically significant positive correlation between the amount of released molecule and the specimen surface area was detected, as well as a weak positive correlation between the release and the specimen volume.

CONCLUSIONS

Type of solvent, molecular mass of eluates, and specimen surface and volume affect substances release from materials.

CLINICAL RELEVANCE

It could be advisable to rely on materials based on monomers with a reduced elution tendency for clinical procedures.

Thermal shrinkage reveals the feasibility of pulse-delay photocuring technique

OBJECTIVES

To resolve the feasibility of the pulse-delay photocuring technique as a clinical strategy for reducing the detrimental polymerization stress induced in dental composites during the photocuring process.

METHODS

Model dental composites with high and low-filler contents were cured with the pulse-delay photocuring technique using different combinations of photocuring variables (irradiance, exposure time, and delay time). Irradiance used ranged from 0.1W/cm² to 4W/cm². The exposure time of the first pulse varied from 0.2s to 27.2s and the delay times ranged from 10s to 120s. The radiant exposure was varied from 4J/cm² to 20J/cm². A cantilever-beam based instrument (NIST Standards Reference Instrument 6005) was used to implement the photocuring technique for the measurement of the polymerization properties (the degree of monomer conversion, polymerization stress induced due to shrinkage, and temperature change due to the reaction exotherm and curing light absorbance) simultaneously in real-time. These properties were compared with those obtained using the conventional photocuring technique (i.e., using a constant irradiance for a fixed exposure time, a uniform exposure).

RESULTS

There exists a minimum radiant exposure, such that a reduction in the polymerization stress can be achieved without sacrificing the degree of monomer conversion by using the pulse-delay over the conventional photocuring technique. More specifically, stress reductions of up to 19% and 32% was observed with the pulse-delay when compared with the conventional photocuring technique at an irradiance of 0.5W/cm² and 4W/cm², respectively. The reduction occurred when the exposure time of the first pulse was greater than, but closer to, the gelation time (i.e., lower than the vitrification time) of the composite, regardless of the delay time used. Lower thermal shrinkage (contraction) during the post-curing time, rather than the stress relaxation during the delay time or lower degree of monomer conversion as claimed in the literature, is the cause of the reduction in the polymerization stress.

SIGNIFICANCE

The study clarifies a long-standing confusion and controversy on the applicability of the pulse-delay photocuring technique for reducing the polymerization stress and promotes its potential clinical success for dental restorative composites.

Effect of Polymerization Time on Residual Monomer Release in Dental Composite: In Vitro Study

Light activated resin-based composites are the most accepted and used materials among clinicians. The aim of this study is to determine the amount of residual monomer released from nanofiller composite resins for different polymerization times and storage periods in vitro. To this purpose, Tetric Ceram (Ivoclar, Liechtenstein), Clearfil Majesty Posterior (Kuraray, Japan), Grandio (VOCO, Germany), and Filtek Ultimate Universal (3M, USA) were used as nanofiller resin composites samples. Four groups ( $n=40$ , diameter: 5 mm, thickness: 2 mm) of each material were fabricated, and each group was exposed to three different polymerization time (10, 20 and 40 sec). High-performance liquid chromatography (HPLC) was used to measure the amount of monomers released over 1, 15, and 30 days. The highest amount of monomer release was seen in Tetric EvoCream composite, while the least monomer release was seen in Clearfil Majesty composite. Regardless of the polymerization time, material, or storage period, the highest amount of eluted monomer was Bis-GMA. It is observed that there is no statistically significant difference between various polymerization times. Monomer release reached its highest level on the 15th day and decreased on the 30th day for all composites. Polymerization time did not affect the monomer release from the composites, but the type of the monomers and concentration of the filler used in the composites affected the amount of released monomers. The use of TEGDMA (co)monomer reduced the monomer release.

Correlation of the mechanical and biological response in light-cured RBCs to receiving a range of radiant exposures: Effect of violet light

OBJECTIVE

This study correlates the mechanical and biological response of commercially available resin-based composites (RBCs) to clinically relevant light-curing conditions.

METHODS

Two RBCs (Venus and Venus Pearl; Kulzer) that use different monomer and photo-initiator systems, but have a similar filler volume and shade, were exposed to either just blue light, or violet and blue light from two different LCUs (Translux Wave and Translux 2Wave; Kulzer). Distance and exposure times were adjusted so that both LCUs delivered 5 similar levels of radiant exposures (RE) between 1.5 J/cm²-25 J/cm² in the blue wavelength range. Thus, the violet light was additional light. The top and bottom of 2-mm thick specimens were subjected to a depth-sensing indentation test (Martens hardness/HM, Vickers hardness/HV, indentation modulus/Y_HU, mechanical work/W_total, plastic deformation work/W_plas, creep/Cr). The viability of human gingival fibroblasts was assessed after three days of exposure to RBC eluates. One and multiple-way analysis of variance (ANOVA), the Tukey honestly significant difference (HSD) post-hoc tests (α = 0.05), t-test and a Spearman correlation analysis were used.

RESULTS

As the RE increased, the mechanical properties increased at a greater rate at the top compared to the bottom of the RBCs. Values measured at the bottom of 2-mm increments approached the values measured at the top only when RE > 25 J/cm² of blue light was delivered. Toxicity decreased with RE and elution cycles and was lower for Venus Pearl. Within one RE level, addition of violet light resulted in significantly improved properties (in 131 out of 150 comparisons, p < 0.05). This effect was stronger for Venus Pearl. There was a good correlation between mechanical and biological parameters. This correlation decreased as the number of eluates increased.

CLINICAL SIGNIFICANCE

The mechanical and biological response to variation in RE is interrelated. The addition of violet light has a positive effect, particularly at low RE.

Bulk Fill Composites Have Similar Performance to Conventional Dental Composites

The aim of the study was to perform comprehensive characterization of two commonly used bulk fill composite materials (SDR Flow (SDR) and Filtek™ Bulk Fill Flowable Restorative (FBF) and one conventional composite material (Tetric EvoCeram; TEC). Eleven parameters were examined: flexural strength (FS), flexural modulus (FM), degree of conversion, depth of cure, polymerisation shrinkage (PS), filler particle morphology, filler mass fraction, Vickers hardness, surface roughness following simulated toothbrush abrasion, monomer elution, and cytotoxic reaction of human gingival fibroblasts, osteoblasts, and cancer cells. The degree of conversion and depth of cure were the highest for SDR, followed by FBF and TEC, but there was no difference in PS between them. FS was higher for bulk fill materials, while their FM and hardness were lower than those of TEC. Surface roughness decreased in the order TEC→SDR→FBF. Bisphenol A-glycidyl methacrylate (BisGMA) and urethane dimethacrylate were found in TEC and FBF eluates, while SDR released BisGMA and triethylene glycol dimethacrylate. Conditioned media accumulated for 24 h from FBF and TEC were cytotoxic to primary human osteoblasts. Compared to the conventional composite, the tested bulk fill materials performed equally or better in most of the tests, except for their hardness, elastic modulus, and biocompatibility with osteoblasts.

The Effect of Finishing and Polishing Sequences on The Surface Roughness of Three Different Nanocomposites and Composite/Enamel and Composite/Cementum Interfaces

The purpose of this study was to investigate the effect of final surface treatment and dental composite type on the roughness of the composite surface, composite/enamel interface, and composite/cementum interface, as well as on the polishing time. Class V cavities prepared in extracted teeth (n = 126) were restored using one of the three nanohybrid composites with different filler sizes. The specimens were randomly assigned to three different finishing and polishing sequences. The roughness (Ra) of the investigated surfaces was measured using the contact profilometer. The time required to achieve visible gloss was documented. The data were analyzed using ANOVA with Tukey's post hoc test (p < 0.05). There was no significant influence of the composite type on the restoration surface roughness (p = 0.088), while the polishing method had a significant impact (p < 0.001). The Ra of the composites ranged between 0.08 µm and 0.29 µm, with the lowest values (0.09 µm ± 0.05 µm) found in the aluminum oxide disc group (p < 0.001). The time to achieve a visible composite gloss was influenced by the polishing method, composite type, and interactions between these factors (p < 0.001). The interface roughness was significantly greater than that of the composite surface (p < 0.001), and depended on the composite type and polishing system employed.

Depth-dependence of Degree of Conversion and Microhardness for Dual-cure and Light-cure Composites

CLINICAL RELEVANCE

New dual-cure bulk-fill composites show promise for uniform degree of conversion and microhardness throughout the entire depth of direct restorations.

SUMMARY

Color stability of Lucirin-photo-activated resin composite after immersion in different staining solutions: a spectrophotometric study

INTRODUCTION

Exceptional optical properties characterize teeth. As such, an esthetic restorative material should enable the dental professional to imitate the optical properties of natural teeth accurately. IPS Empress Direct was introduced to the market with the claim that it can mimic optically dental tissues with superior clinical performance.

AIM

To evaluate the ability of IPS Empress Direct to mimic tooth appearance and color and resist staining.

MATERIALS AND METHODS

Three disc specimens were prepared for each shade of enamel and dentin of Lucirin-based composite, IPS Empress Direct (Ivoclar Vivadent) (A1, A2, A3, B1, and B2) (total of 60). The specimens were submitted to colorimetric evaluation in comparison after immersion in 10 different solutions (coffee, coffee with sugar, coffee with milk, red tea, red tea with sugar, red tea with milk, tomato juice, pomegranate juice, coke, and distilled water as a control group) for 4 weeks using spectrophotometric analysis.

RESULTS

After plotting the data and conducting linear regression analyses, IPS Empress showed high potential in mimicking the optical properties of natural tooth color according to the CIE color space. Three solutions showed a change in color higher than 3, coffee, coffee with sugar, and red tea. All other solution showed changes in color that are acceptable clinically.

CONCLUSION

IPS Empress Direct can satisfactory mimic teeth appearance and color while manifesting high stability of color resisting staining upon clinical aging.

Infection Control Barrier and Curing Time as Factors Affecting the Irradiance of Light-Cure Units

Objective

The objective of the study is to investigate the effect of infection control barrier (ICB) and curing time on irradiance of light cure units (LCUs).

Methods

Irradiance (mW/cm²) of the LCUs at a government dental school were recorded with and without ICB at 0 (T₀), 10 (T₁₀), and 20 (T₂₀) seconds using a digital radiometer. Data were analyzed using IBM^® SPSS^® Statistics Version 17 for Windows software for the analysis of variance and Bonferroni methods at 0.05 significance level.

Results

Using ICB resulted in a statistically significant effect on the irradiance mean (P < 0.01). A significant difference existed between the four different brands of LCUs at different time intervals, irrespective of the use of ICB. At T₀ and T₁₀, the mean output of Acteon mini-light-emitting diode (LED) was significantly higher than that of either the Kerr Demi Ultra or the Kavo Polylux II. At T₂₀, E-Morlit's mean irradiance was significantly higher than that of Kerr Demi Ultra, which in turn was significantly higher than that of the Kavo PolyLux II. The mean irradiance of the LEDs was significantly higher than that of the halogens irrespective of barrier placement and at all-time points.

Conclusion

The ICB used in this study resulted in a statistically significant reduction in the irradiance output. No significant difference in the irradiance was found at different curing time intervals for the tested units regardless of ICB usage.

Efficacy of Modern Light Curing Units in Polymerizing Peripheral Zones in Simulated Large Bulk-fill Resin-composite Fillings

The variation in micro-hardness (HV) within simulated large cavities (10 × 6 mm) filled in one increment with three bulk-fill resin-based composites (BF-RBC) was assessed by means of a universal hardness device. Modern blue and violet-blue light curing units (LCUs) were applied in three different positions, by rotating the LCU in 120° steps. The exposure distance was 3 mm. One center and two peripheral (4-mm apart from the center) HV line profiles were measured in 0.5-mm steps at 24 hours postpolymerization to calculate the depth of cure (DOC). Incident light, irradiance, and spectral distribution were recorded. A multivariate analysis (general linear model) assessed the effect of the varied parameters as well as their interaction terms on HV and DOC. The effect of LCU rotation was not significant ( p=0.109). The DOC varied between 3.46 mm and 5.50 mm and was more strongly influenced by the BF-RBC ( p<0.001, η_P²=0.774), followed by the width of specimen ( p<0.001, η_P²=0.554), while the influence of the LCU was very low ( p<0.06, η_P²=0.070). Whether a BF-RBC filling is cured as well in the periphery as in the center depends more on the material than on the curing unit used.

Own brand label restorative materials-A false bargain?

OBJECTIVES

This study aims at evaluating and comparing mechanical, chemical, and cytotoxicological parameters of a commercial brand name composite material against two 'own brand label' (OBL) composites.

METHODS

Parameters included depth of cure, flexural strength, degree of conversion, polymerization shrinkage, filler particle morphology and elemental analyzes, Vickers hardness, surface roughness parameters after abrasion, monomer elution, and cytotoxicity.

RESULTS

The conventional composite outperformed the OBLS in terms of depth of cure (p<0.001), degree of cure at the first and last time intervals (p<0.001), hardness (p<0.001), and post-abrasion roughness (p<0.05). The polymerization volumetric shrinkage ranged from 2.86% to 4.13%, with the highest shrinkage seen among the OBLs. Both Monomer elution from the OBLs was statistically significantly higher (p<0.001). Statistically significantly higher cytotoxicity combined with altered morphology and loss of confluence was detected in the cells exposed to extracts from the OBLs.

CONCLUSIONS

The OBLs were in general outdone by the conventional composite.

CLINICAL SIGNIFICANCE

OBLs restorative materials have become pervasive in the dental market. Manufacturers often promise equal or better characteristics than existing brand-name composites, but at a lower price. Dentists are highly recommended to reconsider utilization of OBLs lacking sound scientific scrutiny, and our findings underscore this recommendation.

Effect of High Irradiance on Depth of Cure of a Conventional and a Bulk Fill Resin-based Composite

OBJECTIVES

This study evaluated the effect of using three commercial light curing units (LCUs) delivering a range of irradiance values, but delivering similar radiant exposures on the depth of cure of two different resin-based composites (RBCs).

METHODS

A conventional hybrid RBC (Z100 shade A2, 3M ESPE) or a bulk fill RBC (Tetric EvoCeram Bulk Fill shade IVA, Ivoclar Vivadent) was packed into a 10-mm deep semicircular metal mold with a 2-mm internal radius. The RBC was exposed to light from a plasma-arc-curing (PAC) light (Sapphire Plus, DenMat) for five seconds, a quartz-tungsten-halogen (QTH) light (Optilux 501, Kerr) for 40 seconds, or a light-emitting-diode (LED) light (S10, 3M ESPE) for 20 seconds and 40 seconds (control). The Knoop microhardness was then measured as soon as possible at the top surface and at three points every 0.5 mm down from the surface. For each RBC, a repeated measures analysis of variance (ANOVA) model was used to predict the Knoop hardness in a manner analogous to a standard regression model. This predicted value was used to determine at what depth the RBC reached 80% of the mean hardness achieved at the top surface with any light.

RESULTS

The PAC light delivered an irradiance and radiant exposure of 7328 mW/cm(2) and 36.6 J/cm(2), respectively, to the RBCs; the QTH light delivered 936 mW/cm(2) and 37.4 J/cm(2) and in 20 seconds the LED light delivered 1825 mW/cm(2) and 36.5 J/cm(2). In 40 seconds, the control LED light delivered a radiant exposure of 73.0 J/cm(2). For Z100, using 80% of the maximum hardness at the top surface as the criteria for adequate curing, all light exposure conditions achieved the 2.0-mm depth of cure claimed by the manufacturer. The LED light used for 40 seconds achieved the greatest depth of cure (5.0 mm), and the PAC light used for five seconds, the least (2.5 mm). Tetric EvoCeram Bulk Fill achieved a 3.5-mm depth of cure when the broad-spectrum QTH light was used for 40 seconds delivering 37.4 J/cm(2). It required a 40-second exposure time with the narrow-spectrum LED, delivering approximately 73 J/cm(2) to reach a depth of cure of 4 mm.

CONCLUSIONS

When delivering a similar radiant exposure of 37 J/cm(2), the QTH (40 seconds) and LED (20 seconds) units achieved a greater depth of cure than the PAC (five seconds) light. For both resins, the greatest depth of cure was achieved when the LED light was used for 40 seconds delivering 73 J/cm(2) (p<0.05).

Ultra-fast light-curing resin composite with increased conversion and reduced monomer elution

OBJECTIVES

To test the null hypotheses that photoactive resin composites containing a Type I photoinitiator would exhibit reduced DC or increased monomer elution at substantially short curing times compared with materials based on a Type 2 ketone/amine system.

METHODS

Two experimental resin composites were prepared, using either Lucirin-TPO or camphorquinone/DMAEMA. Specimens were light-cured using appropriate spectral emission that coincided with the absorption properties of each initiator using different irradiation protocols (0.5, 1, 3, 9s at 500, 1000 and 2000mW/cm(2) for Lucirin-TPO based composites and 20 or 40s at 1000mW/cm(2) for Lucirin-TPO and camphorquinone-based composites). Degree of conversion (DC) was measured by Raman spectroscopy, propagating radical concentrations were collected by means of electron paramagnetic resonance (EPR) and monomer leaching was characterized using high-performance liquid chromatography (HPLC).

RESULTS

The null hypotheses were rejected, except for a single irradiation protocol (0.5s @ 500mW/cm(2)). Lucirin-TPO-based composites could cure 20 times faster and release at least 4 times less monomers in comparison to camphorquinone-based composites. At 1000mW/cm(2), and 1s irradiation time for curing times of 1s, Lucirin-TPO based composites displayed 10% higher DC. The difference in polymerization efficiency of Lucirin-TPO compared with camphorquinone-based resin composites were explained using EPR; the former showing a significantly greater yield of radicals which varied logarithmically with radiant exposure.

SIGNIFICANCE

Lucirin-TPO is substantially more efficient at absorbing and converting photon energy when using a curing-light with an appropriate spectral emission and otherwise a limitation noted in several previous publications. At concentrations of 0.0134mol/L, Lucirin-TPO-based composites require a minimum light intensity of 1000mW/cm(2) and an exposure time of 1s to provide significantly improved DC and minimal elution compared with a conventional photoinitiator system. The use of a wide range of curing protocols in the current experiment has realized the significant potential of Lucirin-TPO and its impact for clinical applications, in replacement to materials using camphorquinone.