Effect of exposure time and pre-heating on the conversion degree of conventional,bulk-fill,fiber reinforced and polyacid-modified resin composites

Objective

To determine the degree of conversion (DC) of different type of resin-based composites (RBC) in eight-millimeter-deep clinically relevant molds, and investigate the influence of exposure time and pre-heating on DC.

Analysis of the dentin–resin interface by use of laser Raman spectroscopy

OBJECTIVES: Adhesion of resin-bonding agents to dentin is currently believed to result from impregnation of adhesive resin into superficially demineralized dentin. The purpose of this study was to investigate the chemical composition of the resin-impregnated dentin (hybrid) layer using a micro-Raman spectroscopy. METHODS: Resin composites were bonded to bovine dentin with the two-step bonding systems, and specimens were sectioned parallel to dentinal tubules. These surfaces were then polished down to 1 microm diamond pastes. Raman spectra were successively recorded along a line perpendicular to the dentin-adhesive interface by steps of 0.2 microm on a computer controlled X-Y stage. The relative amounts of hydroxyapatite (960 cm(-1), P-O), adhesive resin (640 cm(-1), aromatic ring), and organic substrate (1450 cm(-1), C-H) in the dentin-adhesive bonding area were calculated. RESULTS: From the Raman spectroscopy results, the hybrid layer represents a gradual transition in the relative amount of adhesive from the resin side to dentin side. Evidence of poor saturation of the adhesive resin in the demineralized dentin with the one-bottle adhesive system was detected. SIGNIFICANCE: From the results of this study, inhomogeneity of the hybrid layer composition was detected, and the degree of resin impregnation was found to be different between the bonding systems tested.     

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

ObjectiveThe 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.MethodsCylindrical 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).ResultsFOB 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).SignificanceHigh-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.     

Degree of conversion of two dual-cured resin cements light-irradiated through zirconia ceramic disks

PURPOSE

The aim of this Fourier transform infrared (FTIR) spectroscopic study was to measure the degree of conversion (DC) of dual-cured resin cements light-irradiated through zirconia ceramic disks with different thicknesses using various light-curing methods.

MATERIALS AND METHODS

Zirconia ceramic disks (KT12) with three different thicknesses (1.0, 2.0, and 4.0 mm) were prepared. The light transmittance of the disks was measured using ultraviolet visible near-infrared spectroscopy. Four different light-curing protocols were used by combining two curing light modes (Elipar TriLight (standard mode) and bluephase G2 (high power mode)) with light-exposure times of 40 and 120 seconds. The DCs of the two dual-cured resin cements (Duo-Link and Panavia F2.0) light-irradiated through the disks was analyzed at three time intervals (3, 7, and 10 minutes) by FTIR spectroscopy. The data was analyzed using repeated measures ANOVA (α=.05).Two-way ANOVA and Tukey post hoc test were used to analyze the 10 minute DC results.

RESULTS

The 1.0 mm thick disk exhibited low light transmittance (<25%), and the transmittance decreased considerably with increasing disk thickness. All groups exhibited significantly higher 10 minute DC values than the 3 or 7 minute values (P<.05), but some exceptions were observed in Duo-Link. Two-way ANOVA revealed that the influence of the zirconia disk thickness on the 10 minute DC was dependent on the light-curing methods (P<.001). This finding was still valid even at 4.0 mm thickness, where substantial light attenuation took place.

CONCLUSION

The curing of the dual-cured resin cements was affected significantly by the light-curing technique, even though the additional chemical polymerization mechanism worked effectively.     

The adhesive system and root canal region do not influence the degree of conversion of dual resin cement

Objectives

The aim of this study was to evaluate the influence of two adhesive systems and the post space region on the degree of conversion of dual resin cement and its bond strength to root dentin.

Material and Methods

One three-step etch-andrinse (All-bond 2, Bisco) and another one-step self-etch (Xeno III, Dentsply) adhesive systems were applied on 20 (n=10) crownless bovine incisors, at 12-mm-deep post space preparation, and a fiber post (DT Light Post, Bisco) was cemented using a dual cure resin cement (Duo-Link, Bisco). Three transverse sections (3 mm) were obtained, being one from each study region (cervical, middle and apical). The degree of conversion of the dual cure resin cement was determined by a micro-Raman spectrometer. The data (%) were submitted to repeated-measures analysis of variance and Tukey''s test (p<0.05).

Results

For both groups, the degree of conversion means (%) (All bond 2_cervical = 69.3; All bond 2_middle = 55.1; All bond 2_apical= 56; Xeno III_cervical = 68.7; Xeno III_middle = 68.8; Xeno III_apical = 54.3) were not significantly different along the post space regions (p<0.05).

Conclusion

Neither the adhesive nor the post space region influenced the degree of conversion of the cement layer.     

Effect of temperature on post-cure polymerization of bulk-fill composites

Objectives

To investigate the 24 h post-cure polymerization and the effect of temperature on the post-cure polymerization of one conventional and three bulk-fill composite materials.

Methods

A conventional composite GrandioSO (GR) and three bulk-fill composites: Tetric EvoCeram Bulk Fill (TECBF), Quixfil (QF) and X-tra fil (XF) were investigated. The samples were cured for 20 s with irradiance of 1090 mW/cm². Composite samples were divided into two groups: the “room-temperature” group (RT, n = 5) and the “body-temperature” group (BT, n = 5) and they were stored in dark at 20 °C and 37 °C, respectively. Measurements of degree of conversion (DC) were made immediately after curing (0 h) and 24 h post-cure (24 h). To analyse the extent of post-cure DC increase, the DC values of 0 h-RT/24 h-RT and 0 h-BT/24 h-BT were compared. To analyse the difference in DC between RT and BT, the DC values of 0 h-RT/0 h-BT and 24 h-RT/24 h-BT were compared.

Results

DC increase 24 h post-cure was significant for all composites and ranged between 6.3% and 8.2% in RT and between 12.5% and 15.7% in BT. All composites demonstrated a higher DC in 24 h-BT compared to 24 h-RT. The difference was statistically significant for GR, TECBF and QF.

Conclusions

All composites demonstrated a significant post-cure effect after 24 h. Post-cure temperature increase from 20 °C to 37 °C yielded a higher post-cure DC increase.

Clinical significance

Due to the temperature effect on the final DC, studies performed at composite samples at room temperature may record more inferior properties than these attained in the oral cavity.     

Effect of the degree of conversion of resin-based composites on cytotoxicity,cell attachment,and gene expression

ObjectiveThis study investigated the influence of the degree of conversion (DC), resin-based composites (RBC) composition, and the effect of additional violet light from one light curing unit (LCU) on cell attachment/growth, eluate cytotoxicity, and gene expression.MethodsThe effect of different DC of RBCs on human gingival fibroblasts (HGFs) when cultured directly onto cured RBCs, and when exposed afterwards to eluates in cell culture medium was examined. Venus^® (RBC-V; Bis-GMA-based) and Venus Pearl^® (RBC-P; TCD-DI-HEA and UDMA-based) were cured using a single emission peak (blue) light, Translux Wave^®; TW and a dual emission peak (blue-violet) light, Translux 2 Wave^®; T2W. To determine the value of the additional violet light from the T2W, exposure times and distances were adjusted to deliver similar radiant exposures (RE) from the blue region of both lights at five different RE levels from 1.5 J/cm² to 28.9 J/cm².ResultsBoth RBCs light-cured with the T2W at higher REs resulted in higher DC, increased cell adhesion and decreased eluate cytotoxicity. RBC-V induced greater cell adhesion, lower mRNA levels of pro-inflammatory markers, and higher mRNA levels of a proliferation marker than RBC-P. Wettability was the same for both RBCs. Toxicity decreased with increasing number of elution cycles. The initial eluates from RBC-P had a lower toxicity than from RBC-V.SignificanceRBCs cured with T2W (delivering both blue and violet light) at higher RE had greater DCs. The greatest DC and the least cell reactions were observed when the RE was >25 J/cm².     

Relationship between contraction stress and degree of conversion in restorative composites

OBJECTIVES: To verify the relationship between contraction stress and degree of conversion (DC) in different composites (Filtek Z250, Filtek A110, Tetric Ceram and Heliomolar). METHODS: For the contraction stress test, composite (2 mm thick) was applied between two 5-mm diameter glass rods, mounted in a tensilometer. DC was determined by Infrared Photoacoustic spectroscopy in specimens with similar dimensions and geometry, submitted to identical curing conditions. Specimens were exposed to different energy densities (4.5, 13.5, 27.0, 54.0 and 108.0 J/cm2) by varying exposure time. Contraction stress and DC were recorded 10 min after the beginning of photoactivation. Results were analyzed by ANOVA/Tukey's test and regression analysis. RESULTS: For contraction stress, the interaction between composite and energy density was significant. Stress values ranged between 0.6+/-0.2 and 2.0+/-0.3 MPa at 4.5 J/cm2, 2.3+/-0.5 and 4.3+/-0.4 MPa at 13.5 J/cm2, 3.8+/-0.5 and 5.8+/-0.9 MPa at 27.0 J/cm2, 4.2+/-0.8 and 7.9+/-0.9 MPa at 54.0 J/cm2 and 6.6+/-0.8 and 8.1+/-0.9 MPa at 108.0 J/cm2. Tetric Ceram (39+/-5.8%) showed a higher average DC than the other materials. Heliomolar (28+/-5.2%) showed an average DC similar to Filtek Z250 (32+/-6.6%) and to Filtek A110 (24+/-7.5%) regardless of the energy density level. No significant increase in DC was observed above 27 J/cm2. CONCLUSIONS: At high energy levels, DC had a tendency to level off earlier than contraction stress values. SIGNIFICANCE: Using high energy densities may cause a significant increase in stress values, without producing a significant increase in conversion.     

Degree of conversion and in vitro temperature rise of pulp chamber during polymerization of flowable and sculptable conventional,bulk-fill and short-fibre reinforced resin composites

ObjectiveDetermine the degree of conversion (DC) and in vitro pulpal temperature (PT) rise of low-viscosity (LV) and high-viscosity (HV) conventional resin-based composites (RBC), bulk-fill and short-fibre reinforced composites (SFRC).MethodsThe occlusal surface of a mandibular molar was removed to obtain dentine thickness of 2 mm above the roof of the pulp chamber. LV and HV conventional (2 mm), bulk-fill RBCs (2–4 mm) and SFRCs (2–4 mm) were applied in a mold (6 mm inner diameter) placed on the occlusal surface. PT changes during the photo-polymerization were recorded with a thermocouple positioned in the pulp chamber. The DC at the top and bottom of the samples was measured with micro-Raman spectroscopy. ANOVA and Tukey’s post-hoc test, multivariate analysis and partial eta-squared statistics were used to analyze the data (p < 0.05).ResultsThe PT changes ranged between 5.5–11.2 °C. All LV and 4 mm RBCs exhibited higher temperature changes. Higher DC were measured at the top (63–76%) of the samples as compared to the bottom (52–72.6%) in the 2 mm HV conventional and bulk-fill RBCs and in each 4 mm LV and HV materials. The SFRCs showed higher temperature changes and DC% as compared to the other investigated RBCs. The temperature and DC were influenced by the composition of the material followed by the thickness.SignificanceExothermic temperature rise and DC are mainly material dependent. Higher DC values are associated with a significant increase in PT. LV RBCs, 4 mm bulk-fills and SFRCs exhibited higher PTs. Bulk-fills and SFRCs applied in 4 mm showed lower DCs at the bottom.     

Micro-Raman spectroscopic analysis of the degree of conversion of composite resins containing different initiators cured by polywave or monowave LED units

Objectives

To determine the degree of conversion (DC) over 48 h post-curing of resin mixtures containing trimethylbenzoyl-diphenylphosphine oxide (TPO) initiator cured by a polywave or a monowave LED light-curing unit (LCU).

Methods

In resin mixtures based on equal weight percent (wt%) of BisGMA and TEGDMA the following initiators were added: 0.2 wt% camphorquinone (CQ) + 0.8 wt% ethyl-4-dimethylaminobenzoate (EDMAB) (Group 1); 1 wt% TPO (Group 2) and 0.1 wt% CQ + 0.4 wt% EDMAB + 0.5 wt% TPO (Group 3). Half of the samples in each group (n = 5) were cured using a polywave (bluephase^® G2, Ivoclar Vivadent) or a monowave LED LCU (bluephase^®, Ivoclar Vivadent). The DC was measured using micro-Raman spectroscopy within 5 min and then 1, 3, 6, 24 and 48 h post-irradiation. The data were analysed using general linear model and two-way ANOVA for the factors ‘time’, ‘material’, ‘surface’ and ‘LCU’ at α = 0.05.

Results

The initial DC values obtained upon light curing remained similar over a 48 h period. bluephase^® G2 produced the highest DC in Group 2 followed by Group 3, and Group 1. bluephase^® resulted in the highest DC in Group 1, followed by Group 2 and Group 3 (p < 0.05).

Conclusions

Unfilled resin materials containing both TPO– and CQ–amine initiators are effectively cured using bluephase^® G2. Resin mixture with the same wt% of initiators is better cured when TPO is the only initiator, compared to CQ–amine only or combined TPO and CQ–amine system. After initial light cure, no additional conversion of uncured monomers was detected in an unfilled resin material over 48 h at 37 °C.     

How light irradiance and curing time affect monomer conversion in light-cured resin composites

We tested the hypothesis that the degree of conversion of a light-cured dental composite relates to the calculated (s x mW cm-2 = mJ cm-2) rather than to the irradiance value (mW cm-2) of the light source. Two light-curable composite resins were cured with three different light irradiance values over different curing times. The specimens tested were 2, 4 or 6 mm thick, and the degree of conversion values were measured with Raman spectroscopy on the top and the bottom surfaces of the specimens. The highest conversion value of one of the materials was just below 60%, while the maximal conversion value of the other material was just below 65%. That difference in conversion values could be related to differences in monomer systems used in the two composites. By considering light energy per square centimeter (J cm-2) rather than light irradiance (mW cm-2), we found that equivalent energy values gave similar conversion values for a certain sample thickness. From these findings, we conclude that our experimental results support our hypothesis.     

Conversion kinetics of rapid photo-polymerized resin composites

ObjectiveTo measure the degrees of conversion (DC), conversion kinetics, and the effect of post-irradiation time on rapid photo-polymerized bulk-fill resin composites under conditions equivalent to clinical depths of 1 and 4 mm.Methods36 specimens (n = 3), based on two resin composites incorporating PowerCure rapid-polymerization technology in two consistencies (PFill; PFlow) and two comparators with matching consistencies (Eceram; EFlow), were investigated from the same manufacturer (Ivoclar AG, Liechtenstein). Specimens were prepared within 4 mm diameter cylindrical molds, of either 1 mm or 4 mm depths respectively, to simulate near-surface and deep locations in a bulk-fill restoration. The independent variables in this study were: materials, thickness and time. Two high irradiance polymerization protocols were utilized for PowerCure materials: 2000 and 3050 mW/cm² for 5 and 3 s, respectively. A standard (1200 mW/cm²) polymerization protocol was used with control materials. FTIR was utilized to measure DC in real-time for 24 h post-irradiation. The data were analyzed using Welch’s-ANOVA, Games-Howell post-hoc test, kinetic dual-exponential sum function and independent sample t-tests (p = 0.05).ResultsThe DC of the materials ranged between 44.7–59.0 % after 5 min, which increased after 24 h reaching 55.7–71.0 % (p < 0.05). Specimen thickness did not influence the overall DC. At 5 min, the highest DC was shown in EFlow. But PFlow, irradiated for 3 s and 5 s exhibited comparable results (p > 0.05). PFill composite irradiated with the 3 s and 5 s protocols did not differ from ECeram (p > 0.05). Specimen thickness and material viscosity affected polymerization kinetics and rate of polymerization (RP_max). Faster polymerization occurred in 1 mm specimens (except PFill-5 s and ECeram). PFill and PFlow exhibited faster conversion than the controls. RP_max varied across the specimen groups between 4.3–8.8 %/s with corresponding DC _RPmax between 22.2–45.3 %.SignificancePolymerization kinetics and RP_max were influenced by specimen thickness and material viscosity. PFill and PFlow materials produced an overall comparable conversion at 5 min and 24 h post-irradiation, despite the ultra-short irradiation times, throughout the 4 mm specimen thickness.     

Heat curing of UTMA-based hybrid resin: effects on the degree of conversion and cytotoxicity

This study was designed to determine the effects of the heat curing time on a urethane tetramethacrylate (UTMA)-based hybrid resin and specifically on the degree of conversion (DC) and cytotoxicity. The materials used in this study were Estenia, a new-generation hybrid resin, and an experimental fiber reinforcement, Br-100. The DC values of the hybrid resin samples were measured using a Fourier transform infrared (FTIR) spectrophotometer after 180s of light curing followed by heat curing (0, 15, 30, and 60min). A method comparing intensities of C = C and N—H vibrations of the sample was used to calculate the final DC values. FTIR spectra were measured both inside and on the surface of the sample. The calculated DC values increased by increasing the heat curing times. After light curing only and after 15-min heat curing, the DC values inside the samples were smaller than the corresponding DC values at the surfaces of the samples. After 60min of heat curing, the samples achieved homogeneous polymerization (DC% = 65). The cytotoxicity of the material was studied from the glass fiber-reinforced hybrid resin samples, which were first light cured and then heat cured (15, 30, and 60min). Cytotoxicity was tested using both direct contact and extract methods. For the extract tests, the test specimens were incubated in a cell culture media at 37°, 54°, or 72°C for 24h. The heat curing times used had no effect on cytotoxicity. The incubation temperature, however, did have a significant effect. The extract obtained from 72°C incubation showed a cytotoxic effect whereas the others did not. The direct contact test did not show cytotoxicity.     

Bond strengths, degree of conversion of the cement and molecular structure of the adhesive-dentine joint in fibre post restorations

Objectives

Because fibre post restorations are influenced by multiple factors such as the types of bonding materials, the dentine region and the time under moist exposure, this study sought to determine the bond strength of endodontic restorations and its relation to the degree of conversion of the cement layer and the molecular structure of the dentine-bonded joints.

Methods

The performance of 2 etch-and-rinse (All-Bond 2 and One-Step Plus) and 2 self-etch (Clearfil SE Bond and Xeno III) adhesives at post spaces regions, after 7 d or 4 m, was evaluated. FRC Postec Plus posts were cemented to the root canal with a dual-cure resin cement (Duo-Link). Transverse sections of the tooth were subjected to push-out testing, to degree-of-conversion measurements and to hybrid layer evaluation through μ-Raman spectroscopy.

Results

Coronal bonding was higher than cervical and middle bonding. The hybrid layer was thicker for the etch-and-rinse systems, with thicknesses decreasing towards the middle region. The degree of conversion measured for the 3-step etch-and-rinse group after 4 m was significantly higher than that for the self-etching groups.

Conclusions

Although not totally stable at the adhesive–dentine interface, the 3-step etch-and-rinse adhesive in the coronal dentine provided the best bond strength, degree of conversion of the cement and hybrid layer thickness in post restorations, in both short- and long-term analyses.     

Degree of conversion of bulk-fill compared to conventional resin-composites at two time intervals

Objective

The purpose of this study was to assess the degree of conversion (DC) over time, using FTIR spectroscopy for bulk-fill flowable resin composite materials compared to conventional flowable and regular resin composite materials.

Methods

Eight resin composites were investigated including flowable bulk-fill materials SureFil SDR (SDR), Venus bulk-fill (VBF), x-tra base (XB), and Filtek Bulk Fill (FBF). Conventional flowable and regular composite materials included: Venus Diamond flow (VDF), Grandioso flow (GRF), Venus Diamond (VD), and Grandioso (GR). Degree of conversion (DC) was assessed by Fourier transform infrared spectroscopy using attenuated total reflectance technique. DC was measured for samples immediately post-cure (n = 3), and after 24 h storage period at 37 °C (n = 3). Results were analysed using one-way analysis of variance (ANOVA), Bonferroni post hoc test, and independent-samples t-test at α = 0.05 significance level.

Results

Immediately post-cure, the mean DC values of the different materials were in the following order: GRF > VDF > SDR > VBF > XB > GR > FBF < VD and ranged from 34.7 to 77.1%. 24 h post-cure, DC values were in the following order: GRF > VBF > VD > SDR > VDF > GR > XB < FBF and ranged from 50.9 to 93.1%. GRF showed significantly higher DC values than all other materials at both time intervals while XB and FBF showed significantly lower values at 24 h post-cure.

Significance

The 24 h post-cure DC values of the bulk-fill composites SDR and VBF are generally comparable to those of conventional composites studied; however, the 24 h post-cure DC values of XB and FBF were lower compared to the other materials.     

原花青素预处理对全酸蚀粘接系统双键转化率的影响

将葡萄籽提取物原花青素(proanthocyanidin,PA)分别用乙醇、丙酮、蒸馏水配制成不同浓度的预处理剂,利用傅里叶红外光谱测试PA预处理对Single Bond 2和Prime＆Bond NT两种全酸蚀粘接系统双键转化率的影响.结果发现不同溶剂、浓度的PA预处理剂组2种全酸蚀粘接剂的双键转化率与阴性对照组均无统计学差异(P＞0.05).提示原花青素预处理对全酸蚀粘接系统固化性能无显著影响.     

Effect of temperature on composite polymerization stress and degree of conversion

Objective

To test the following hypotheses: (1) degree of conversion (DC) and polymerization stress (PS) increase with composite temperature (2) reduced light-exposure applied to pre-heated composites produces similar conversion as room temperature with decreased PS.

Methods

Composite specimens (diameter: 5 mm, height: 2 mm) were tested isothermally at 22 °C (control), 40 °C, and 60 °C using light-exposures of 5 or 20 s (control). DC was accessed 5 min after light initiation by FTIR at the specimen bottom surface. Maximum and final PS were determined, also isothermally, for 5 min on a universal testing machine. Non-isothermal stress was also measured with composite maintained at 22 °C or 60 °C, and irradiated for 20 s at 30 °C. Data were analyzed using two-way ANOVA/Tukey and Student's t-test (α = 5%).

Results

Both DC and isothermal maximum stress increased with temperature (p < 0.001) and exposure duration (p < 0.001). Isothermal maximum/final stress (MPa) were 3.4 ± 2.0b/3.4 ± 2.0A (22 °C), 3.7 ± 1.5b/3.6 ± 1.4A (40 °C) and 5.1 ± 2.0a/4.0 ± 1.6A (60 °C). Conversion values (%) were 39.2 ± 7.1c (22 °C), 50.0 ± 5.4b (40 °C) and 58.5 ± 5.7a (60 °C). The reduction of light exposure duration (from 20 s to 5 s) with pre-heated composite yielded the same or significantly higher conversion (%) than control (22 °C, 20 s/control: 45.4 ± 1.8b, 40 °C, 5 s s: 45.1 ± 0.5b, 60 °C, 5 s s: 53.7 ± 2.7a, p < 0.01). Non-Isothermal conditions showed significantly higher stress for 60 °C than 22 °C (in MPa, maximum: 4.7 ± 0.5 and 3.7 ± 0.4, final: 4.6 ± 0.6 and 3.6 ± 0.4, respectively).Clinical significance: Increasing composite temperature allows for reduced exposure duration and lower polymerization stress (both maximum and final) while maintaining or increasing degree of conversion.     

Effect of exposure time and moving the curing light on the degree of conversion and Knoop microhardness of light-cured resin cements

ObjectiveTo evaluate the effect of exposure time and moving the light-curing unit (LCU) on the degree of conversion (DC) and Knoop microhardness (KH) of two resin cements that were light-cured through ceramic.MethodsTwo resin cements: AllCem Veneer APS (FGM) and Variolink Esthetic LC (Ivoclar Vivadent) were placed into a 0.3 mm thick matrix in 6 locations representing the canine to canine. The resins were covered with 0.5 mm thick lithium disilicate glass-ceramic (IPS e.max CAD, Ivoclar Vivadent). A motorized device moved the LCUs over the ceramic when the LCU was on. Two single-peak LCUs: Elipar DeepCure-L (3M Oral Care) and Emitter C (Schuster), and one multi-peak: Bluephase G2 (Ivoclar Vivadent) were used with 3 different exposure protocols: a localized exposure centered over each tooth for 10 or 40 s; moving the tip across the 6 teeth for a total exposure time of 10 or 40 s; and moving the tip across the 6 teeth resins for a total exposure time of 60 or 240 s. After 24 h, the DC and KH were measured on the top surfaces and the data was analyzed using three-way ANOVA and Tukey’s tests (α = 0.05).ResultsInterposition of 0.5 mm of ceramic reduced the irradiance received by the resin by approximately 50%. The 40 s localized exposure over each tooth always produced significantly higher DC and KH values. Moving the LCUs with a total exposure time of 10 s resulted in the lowest DC and KH. There was no beneficial effect on the DC or KH when the multi-peak (violet-blue) LCU (Elipar DeepCure-L or Bluephase G2), but the lower light output from a small tip LCU reduced the DC and KH values (Emitter C).SignificanceMoving the LCUs when photo-curing light-cured resin cements is not recommended. This study showed that a single-peak LCU could activate a resin cement that uses Ivocerin™ as well as the multi-peak LCU.     

Influence of resin matrix on the rheology,translucency, and curing potential of experimental flowable composites for bulk-fill applications

ObjectiveTo propose monomer formulations that show an optimal degree of conversion as a function of depth for bulk-fill applications.MethodsFour resin blends were formulated with methacrylate-based monomers: BisGMA + TEGDMA (control); BisEMA + BisGMA + TEGDMA (BisEMA-based); UDMA + BisGMA + TEGDMA (UDMA-based) and BisEMA + UDMA + BisGMA + TEGDMA (BisEMA + UDMA-based). For each material, a photoinitiating system and silanized filler particles were added. The rheological analyses were performed with a rotational rheometer using the cone/plate geometry. CIELab coordinates were assessed over black and white backgrounds using a bench spectrophotometer (SP60, X-Rite) to calculate the translucency parameter (TP) for samples with 0.5, 4, and 6 mm thickness. The degree of CC conversion (DC) was determined by infrared spectroscopy (FTIR/ATR) at 0.05 mm (top), 4, and 6 mm depths (bottom), and the bottom-to-top ratio was considered. A broad spectrum–based LED was used for light activation. Analysis of variance and Tukey’s test (95%) were performed on the results.ResultsThe materials tested showed pseudoplastic and thixotropic behavior and a predominance of viscous effects over elastics. The control resin yielded the lowest viscosity for the entire shear rate investigated, followed by the BisEMA-based, BisEMA + UDMA-based, and UDMA-based group, which had the highest viscosity. The UDMA-based material showed the lowest TP as a function of thickness. Both the materials’ formulations and depths significantly influenced the DC. The UDMA-based group promoted the highest DC ??on the top (71 ± 1%) and 4 mm depth (68 ± 1%) but exhibited lower bottom-to-top DC ratio. The BisEMA + UDMA-based material promoted the highest bottom-to-top DC ratio at 4 mm (99%) and 6 mm (97%).SignificanceThe resin matrix interferes in the rheological behavior, translucency parameter, and polymerization capacity as a function of depth. The material formulated with the addition of UDMA and BisEMA demonstrated the highest curing potential as a function of depth and can be useful for bulk-fill applications.     

The influence of bis-EMA vs bis GMA on the degree of conversion and water susceptibility of experimental composite materials

Objective. The aim of this work was to assess the influence of the bis-EMA content on the degree of conversion (DC) and its effect on the water sorption and solubility. Materials and methods. In a polytetrafluorethylene (PTFE) mould, 30 samples (Ø = 5 mm, height = 2 mm) of four experimental dental composite resins were cured for 10 s, 20 s and 40 s. The DC was analysed by Fourier Transform (FT)-Raman spectroscopy. To analyse sorption and solubility, six samples (Ø = 15 mm and thickness = 1 mm) of each composite (n = 72) were stored in water at 37°C for different storage periods: 24 h, 7 days and 30 days. Results. When cured for 20 or 40 s the DC increased with the increasing content of bis-EMA. However, the presence of 15 wt% of bis-GMA did not affect the DC, except when cured with 10 s irradiation time. This study also found a correlation between the content of bis-EMA and the reduced values for sorption and solubility, for all storage times used, when the materials were cured with 20 s. Conclusions. The DC of mixtures with higher content of bis-EMA is affected by the presence of bis-GMA at lower energy density delivered from the curing device, suggesting that the restrictions caused by the presence of hydrogen bonds is dependent of the irradiation time used.