Significant Differences In Degree Of Conversion Research Articles

Impact of Battery Levels of a Cordless LED Curing Unit on Resin Cement under Varied Lithium Disilicate Thicknesses and Translucencies.

This study aimed to evaluate the impact of battery levels on the emission of a multi-peak cordless LED light-curing unit (LCU) and the effect on the degree of conversion (DC) and Knoop hardness (KH) of a light-cure resin luting agent activated through varying lithium disilicate (LiS2) ceramic thicknesses and translucencies. High and low translucency LiS2 discs (IPS e.max Press HT and LT, respectively; shade A1) with thickness of 0.5, 1.0, 1.5, and 2.0 mm were fabricated. Resin luting agent specimens (Variolink Esthetic LC) were prepared and cured using a Bluephase G2 LCU at different battery levels (100%, 50%, and 10%) through the LiS2 ceramics. The transmitted irradiance was evaluated using USB4000 MARC, while FTIR and a microhardness tester assessed DC and KH, respectively. After ensuring homoscedasticity, the data wee analyzed using analysis of variance and Tukey HSD test (α=0.05). The study found strong positive correlations between battery levels and irradiance, particularly with no ceramic interposition and through HT ceramics (R2=0.9471), although this correlation diminished with thicker HT (R2=0.7907) and LT ceramics (R2<0.2980). Both battery levels and ceramic thickness significantly influenced transmitted irradiance (p<0.0001), resulting in lower values with decreased battery levels and increased ceramic thicknesses (p<0.0001). LT ceramics showed lower transmittance than HT. DC was significantly affected by both battery levels and ceramic thicknesses, with generally lower DC values except for LT ceramics at a 10% battery level (p<0.0001). No significant differences in DC were observed between HT and LT translucencies (p=0.548). KH was higher in HT than LT ceramics at 100% and 50% battery levels, with thicker ceramics showing lower KH values at 10% battery level (p<0.0001). Conclusion: Reduced battery levels in cordless LED curing units significantly affect the irradiance, degree of conversion, and hardness of light-curable resin luting agents. Maintaining battery levels above 50% is recommended for optimal performance. Thicker and more opaque ceramics significantly impacted incident irradiance. However, preserving radiant energy could potentially mitigate these limitations.

Carbon nanotube-modified adhesive to caries affected dentin conditioned with Nd: YAP laser, phosphoric acid, and photoactivated-erythrosine

AimDentin conditioned with phosphoric acid (PA) Nd: YAP laser, and photoactivated-Ery(Erythrosine) on microleakage, shear bond strength (SBS) degree of conversion (DC), and rheological assessment of adhesive-infused with carbon nanotubes (CNTs). Material and methodCarious ninety-six human mandibular molars were included. Specimens were disinfected and allocated into three groups based on surface pretreatment (n = 32) Group 1 (PA), Group 2 (Nd: YAP) laser, and Group 3 (Photoactivated-Ery). Conditioned groups were further divided into two 2 subgroups based on the application of unmodified ERA and CNTs-modified ERA. Composite restorations were placed on the CAD surface and thermal aging of the samples was performed. The microleakage assessment was conducted using a dye penetration test. Universal testing machine (UTM) assessed SBS bond failure was evaluated using a stereomicroscope. Scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) analyses of CNT, and Fourier Transform Infrared FTIR of adhesives were performed. One-way ANOVA and Tukey post hoc analyzed the outcomes. ResultsGroup 1B samples (PA+ CNTs modified adhesive) presented the minimum marginal leakage and highest bond integrity. Group 2A (Nd:YAP laser+Unmodified adhesive) displayed the maximum scores of microleakage and lowest bond strength. ConclusionPhotoactivated Ery-PS can serve as an alternative to phosphoric acid for conditioning CAD. Incorporating CNT in adhesive significantly enhanced bond integrity and marginal seal with no significant difference in DC.

Effect of preheating and curing lamp distance on the degree of conversion of four nanohybrid resins: An in vitro study.

Inadequate polymerization of resins is a major cause of failure in dental restorations. This study aimed to evaluate the hypothesis that both polymerization distance and preheating of four nanohybrid resins significantly affect their degree of conversion (DC). Four A2-colored nanohybrid resins were selected: Filtek Z250 XT (3M), Tetric N-Ceram (Ivoclar), Zafira (New Stetic), and Spectra Smart (Dentsply). These resins were chosen due to their varied compositions. Forty-eight discs (6 mm diameter, 2 mm thickness) were manufactured, with 24 discs preheated to 39°C. All discs were polymerized for 40 seconds at distances of 1 mm and 6 mm using the Bluephase N lamp (Ivoclar Vivadent), operating at 385-515 nm and 1200 mW/cm². The polymerized discs were stored in distilled water at 37°C for 24 hours, and the DC was measured using Fourier-transform infrared spectroscopy (FTIR). Statistical analysis was performed using one-way ANOVA and independent samples t-tests. No statistically significant differences in DC were observed between samples preheated to 39°C and those at room temperature (p> 0.05). Zafira exhibited the highest DC, significantly higher than Z250 XT in all groups (p< 0.005) and higher than Tetric N-Ceram on the surface (p< 0.05). Significant differences were also found between Zafira and Spectra Smart in specific conditions (p< 0.05). No significant differences in DC were found between polymerization distances of 1 mm and 6 mm. Uniform polymerization was achieved throughout the resin discs. Preheating nanohybrid resins to 39°C had no statistically significant impact on their degree of conversion. Acceptable DC values were achieved using a high-intensity lamp for 40 seconds, even at a curing distance of 6 mm. Among the tested resins, Zafira demonstrated the highest DC under various conditions, significantly outperforming Z250 XT, Tetric N-Ceram, and Spectra Smart in specific comparisons. Key words:Nanohybrid composite, polymerization, degree of conversion.

Pretreatment of enamel with Riboflavin activated photodynamic therapy and Er, Cr: YSGG laser for bonding of orthodontic bracket with adhesive modified with cerium oxide nanoparticles

AimTo assess the degree of conversion (DC) and shear bond strength (SBS) of experimental adhesive (EA) infused with and without 1 % Cerium oxide (CeO₂)-NPs on metallic bracket bonded to enamel conditioned with three different pretreatment regimes PDT-activated (Riboflavin) RF, ECY (Er, Cr: YSGG), and Phosphoric acid (PA). Material and MethodEA and EA modified with 1 % CeO₂-NPs were prepared. Characterization of CeO2NPs was assessed using a scanning electron microscope (SEM). Seventy-two premolars extracted due to periodontal or orthodontic reasons were disinfected. Samples were mounted and allocated into three groups according to enamel surface treatment before bracket bonding. Samples in Group 1 were pretreated with Traditional 37 % PA-gel; Specimens in Group 2 surface treated with RF-activated PDT, and samples in Group 3 were conditioned using ECY. Brackets were placed on conditioned surfaces and samples were aged and underwent SBS testing using UTM. ARI index was used to assess bond failure. DC was evaluated for both adhesives using FTIR. ANOVA and Tukey post hoc test were used to compare the means and standard deviation (SD) of SBS and DC in different experimental groups. ResultsEnamel conditioned with PA and RF activated by PDT demonstrated comparable bond values with 1 % CeO2 infused in EA and EA (p>0.05).ARI analysis shows that enamel conditioned with PA and RF activated by PDT showed the majority of failure types between 1 and 2 irrespective of the type of adhesive. DC value in EA (73.28±8.37) was the highest and comparable to 1 % CeO2 infused in EA (66.48±6.81) ConclusionRF-activated PDT can be used alternatively to 37 % PA for enamel conditioning when bonding metallic brackets. Infiltration of 1 % CeO2 NPs in EA improves SBS irrespective of the type of enamel conditioning. Infusion of 1 % CeO2 NPs in EA demonstrates no significant difference in DC compared to EA.

Degree of conversion of light-polymerized composite resin in implant prosthesis screw access opening.

The mechanical and physical properties of implant screw access opening deteriorate if composite resin is not polymerized properly. Therefore, this study aimed to analyze the effect of using composite resin in implant access opening on the degree of conversion (DC). Two prosthetic materials (Co-Cr and zirconia), two types of composite resin (low and high viscosity), two light-cured resin depths (2 and 3mm), and two polymerization methods (max-mode 10s and mid-mode 20s: 16 and 22J/cm2 , respectively) were considered (n=192). The DC of the polymerized composite resin was measured through Fourier-transform infrared spectroscopy. The top and bottom surfaces of the polymerized composite resin body were observed through scanning electron microscopy. Multiple linear regression analysis and analysis of variance were used to identify significant differences in DC (α=0.05). The DC was lower when the low-viscosity composite resin (β=-0.431), light-polymerized resin depth of 2mm (β=-0.430), zirconia prosthesis (β=-0.191), and mid-mode polymerization method (β=-0.164) were used. The resin type, depth of resin to be light-cured, prosthesis material, and polymerization method had an effect on the DC. Low-viscosity composite resin should be polymerized at a low irradiance and long polymerization time (such that the light-cured resin depth does not exceed 2mm) to ensure proper composite resin polymerization in implant screw access opening.

Acid neutralizing and remineralizing orthodontic adhesive containing hydrated calcium silicate

ObjectivesThe objective of this study was to evaluate an orthodontic adhesive containing hydrated calcium silicate (hCS) in terms of its bond strength with the enamel surface and its acid-neutralization and apatite-forming abilities. MethodsThe experimental orthodontic adhesives were composed of 30 wt.% resin matrix and 70 wt.% filler, which itself was a mixture of silanized glass filler and hCS in weight ratios of 100% glass filler (hCS 0), 17.5% hCS (hCS 17.5), 35% hCS (hCS 35.0), and 52.5% hCS (hCS 52.5). The degree of conversion (DC) and shear bond strength (SBS) of bovine enamel surfaces were tested. pH measurements were performed immediately upon submersion of the specimens in a lactic acid solution. The surface precipitates that formed on specimens immersed in phosphate-buffered saline (PBS) were analyzed by scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) and Raman spectroscopy after 15, 30, and 90 days. ResultsThe experimental groups exhibited no significant differences in DC and had clinically acceptable SBS values. The hCS-containing groups showed increasing pH values as more hCS was added. hCS 52.5 produced Ca- and P-containing surface precipitates after PBS immersion, and hydroxyapatite deposition was detected after 15, 30, and 90 days. ConclusionsThese results suggest that orthodontic adhesives containing hCS are effective for acid neutralization. Furthermore, hCS has an apatite-forming ability for enamel remineralization. Clinical significanceThe novel orthodontic adhesive containing hCS exhibits a potential clinical benefit against demineralization and enhanced remineralization of the enamel surface around or beneath the orthodontic brackets.

Flowable fiber-reinforced versus flowable bulk-fill resin composites: Degree of conversion and microtensile bond strength to dentin in high C-factor cavities.

To compare flowable fiber-reinforced and flowable bulk-fill resin composites regarding their degree of conversion (DC) and microtensile bond strength (μTBS) to dentin in high C-factor class I cavities. One flowable fiber-reinforced (EverX Flow, GC) and two flowable bulk-fill composites (SDR, Dentsply, and Tetric N-flow Bulk fill, Ivoclar Vivadent) were tested. Regarding DC, 10 cylindrical-shaped specimens were prepared from each material (N= 30), measured using Fourier-Transform Infrared Spectroscopy (FTIR). Regarding , class I cavities (4.5× 4.5× 3) were prepared on flat dentin surfaces of 30 molars, divided into three equal groups, restored with the three restorative materials, thermocycled, sectioned to create 1 mm × 1 mm cross-sectional beams, then tested using a universal testing machine. Failure mode was assessed using a stereomicroscope. Two-way ANOVA and Tukey's HSD post-hoc tests were used in DC, while One-way ANOVA was used for . The used materials showed statistically significant differences in DC with the fiber-reinforced composite having the highest value. No statistically significant differences were found between the materials regarding their . Flowable fiber-reinforced composite provided the most DC performance compared to the flowable bulk-fill composites. The three used restorative materials provided comparable bonding ability to dentin in high C-factor cavities. Flowable fiber-reinforced resin composite is preferred as a dentin-replacement material in high-stress bearing areas. However, both flowable fiber-reinforced and bulk-fill resin composites are equally effective in bonding to dentin in high C-factor cavities.

Degree of conversion and water sorption of self-adhesive and conventional flowable composites

Aim: Self-adhesive flowable composite resins have been recently introduced to the market. Degree of conversion (DC) and water sorption (WS) are two important parameters affecting the properties of restorative materials. This study aimed to assess the DC and WS of a self-adhesive flowable composite resin in comparison with two conventional flowable composite resins. Methods: Vertise Flow (VF) self-adhesive and Tetric-N Flow (TF) and Grandio Flow (GF) conventional flowable composites were evaluated in this in vitro, experimental study. The DC (n=3) was determined by attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR). The WS (n=7) was measured after 7 days of immersion in artificial saliva according to ISO 4049 specifications. Data were analyzed by one-way ANOVA and a post-hoc test (p&lt;0.05). Results: VF showed the highest DC percentage (84.3%) followed by GF (72.79%) and TF (68.7%). The latter two had no significant difference (p=0.8). WS was the highest in VF (55.2 μg/mm3), and the two conventional flowable composites had a significant difference in WS (19.5 μg/mm3 in TF and 11 μg/mm3 in GF; p&lt;0.001). Conclusions: Flowable composite resins had significant differences in DC and WS, and VF demonstrated the highest DC and WS.

Effects of the light tip position on the degree of conversion and dentin bond strength of a universal adhesive

Introduction/Objectives. To measure the degree of conversion (DC), immediate and long-term microshear bond strength (?SBS) to dentin of a universal adhesive relative to the light tip position and adhesive application protocol. Methods. Mid-coronal flat dentin of 48 human third molars was exposed and split in halves. Single Bond Universal (SBU; 3M) adhesive was applied to each half following ?total-etch? (TE) or ?self-etch? (SE) approach. Depending on the light tip (Bluephase G2, Ivoclar Vivadent, Schaan, Liechtenstein) angle and distance from adhesive surface, three groups were compared: ?1 mm_90?? (control); ?8 mm_90?? and ?8 mm_60??. Cylindrical composite build-ups (o1.7mm, Filtek Z250, 3M) were prepared in each half. DC was measured using Raman spectroscopy. ?SBS was measured after 24 hours and six months storage in distilled water at 37?C. Fracture types were analyzed. Results. No significant difference in DC was detected between groups ?1 mm_90?? (89.1 ? 6.2%) and ?8 mm_90?? (94.6 ? 1.2%) (p &gt; 0.05), both showing significantly higher DC (p &lt; 0.05) than ?8 mm_60?? group (74.9 ? 9.5%) (p &lt; 0.05). Initially, there were no significant differences in ?SBS between groups (p &gt; 0.05). Group ?1 mm_90?? TE (12.8 ? 4.3 MPa) and group ?8 mm_60?? TE (14.7 ? 5.7 MPa) showed significantly lower ?SBS after aging (8.4 ? 4.3 MPa and 9.2 ? 2.6 MPa, respectively) (p &lt; 0.05). Adhesive fractures were predomintantly detected. Conclusion. Initially, both application protocols resulted in similar bond strength to dentin of a universal adhesive in suboptimal curing conditions. In the long-term, SE showed greater adhesive resistance to degradation resulting in smaller decrease in bond strength compared to TE. Light tip angulation affected DC and ?SBS more than tip-to-surface distance.

Evaluation of the influence of light-curing units on the degree of conversion in depth of a bulk-fill resin.

BackgroundIt is known that bulk-fill have been widely studied and used by dentists in the clinic. However, the use of light-curing units that do not have the ability to adequately light-cure these materials at the appropriate depth can affect their clinical performance. The aim of this study was evaluating the influence of 5 different light curing units (LCUs) on the degree of conversion (DC) of a bulk-fill resin at depths of 0 to 4 mm and determined the effect of using 20s exposure and 40s. Material and MethodsCylinders of composite were made in a stainless steel matrix (n=10). The specimens were exposed from the top surface using 5 LCUs: Valo® Cordless (VA); Radii Plus (RA); Emitter.D (EM), Biolux Plus (BI), Woodpecker® (WO). The emission wavelength and the power density was determined. After the photoactivation, the Raman vibrational modes were calculated taking as reference the peaks at 1,601 (aromatic bonds C=C) and 1,640 cm-1 (aliphatic bonds C=C). ResultsThe largest difference in DC in 20s, comparing the values obtained in the first and last layer is for BI, with a variation from 61.24% to 53.86%. Comparing the LCUs, the last layer in 40s DC values are 57.40% (BI), 58.21% (WO), 58.97% (VA), 60.90% (RA) and 62.42% (EM). The higher the dose (J/cm²) and the close the λmax is to the maximum CQ absorption length (λmax ~ 470 nm) the better the DC value. ConclusionsThere was a significant difference in the DC values between the LCUs with increasing depth of the bulk-fill increments. Results indicate significant differences in DC among the different LCUs as well as enhanced DC when using 40s exposure compared to 20s. It is suggested that for DC improvement using lower power photoactivator increase the exposure time the exposure time should be 20s to 40s. Key words:Polymerization, Composite Resins, Raman spectroscopy.

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

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

The Influence of Distance on Radiant Exposure and Degree of Conversion Using Different Light-Emitting-Diode Curing Units.

To investigate the influence of curing distance on the degree of conversion (DC) of a resin-based composite (RBC) when similar radiant exposure was achieved using six different light-curing units (LCUs) and to explore the correlation among irradiance, radiant exposure, and DC. A managing accurate resin curing-resin calibrator system was used to collect irradiance data for both top and bottom specimen surfaces with a curing distance of 2 mm and 8 mm while targeting a consistent top surface radiant exposure. Square nanohybrid-dual-photoinitiator RBC specimens (5 × 5 × 2 mm) were cured at each distance (n=6/LCU/distance). Irradiance and DC (micro-Raman spectroscopy) were determined for the top and bottom surfaces. The effect of distance and LCU on irradiance, radiant exposure, and DC as well as their linear associations were analyzed using analysis of variance and Pearson correlation coefficients, respectively (α=0.05). While maintaining a similar radiant exposure, each LCU exhibited distinctive patterns in decreased irradiance and increased curing time. No significant differences in DC values (63.21%-70.28%) were observed between the 2- and 8-mm distances, except for a multiple-emission peak LCU. Significant differences in DC were detected among the LCUs. As expected, irradiance and radiant exposure were significantly lower on the bottom surfaces. However, a strong correlation between irradiance and radiant exposure did not necessarily result in a strong correlation with DC. The RBC exhibited DC values >63% when the top surface radiant exposure was maintained, although the same values were not reached for all lights. A moderate-strong correlation existed among irradiance, radiant exposure, and DC.

Evaluation of degree of conversion and the effect of thermal aging on the color stability of resin cements and flowable composite.

Purpose:The aim of this in vitro study was to evaluate the color stability and degree of conversion (DC) of dual-cure and light-cure cements and flowable composites after thermal aging.Materials and Methods:A total of 50 human incisors were prepared and divided into six groups (n = 10). Veneers were fabricated using IPS Empress Direct composite resin were bonded with three types of luting agents: Light-cured, conventional dual, and flowable composite according to the manufacturer's instructions. The groups were as follows: Filtek Z350XT Flow/Single Bond 2, RelyX ARC/Single Bond 2, RelyX Veneer/Single Bond 2, Tetric N-Flow/Tetric N-Bond, and Variolink II/Tetric N-Bond. Commission Internationale de l'Éclairage L*, a* and b* color coordinates were measured 24 h after cementation procedure with a color spectrophotometer and reevaluated after 10,000 thermal cycles. To evaluate the DC 50 specimens (n = 10) of each resin material were obtained and Fourier transform infrared spectroscopy was used to evaluate the absorption spectra. Statistical analysis was performed with one-way ANOVA and Tukey's test (α = 0.05).Results:No statistically significant differences in ΔE* occurred after aging. The greatest change in lightness occurred in the Variolink II resin cement. Changes in red–green hue were very small for the same cement and largest in the Tetric N-Flow flowable resin composite, while the greatest change in blue–yellow hue was a yellowing of the RelyX ARC luting cement. RelyX ARC exhibited the highest DC, and there were no statistically significant differences in DC among the other cements.Conclusions:Resin-based luting agent might affect the final of ceramic veneer restorations. The thermal aging affected the final color of the evaluated materials, and these were regarded as clinically unacceptable (ΔE >3.3).

Degree of Conversion and Polymerization Shrinkage of Bulk-Fill Resin-Based Composites.

This study evaluated the degree of conversion (DC) and polymerization shrinkage (PS) of contemporary bulk-fill resin-based composites (RBCs) including giomer materials. Two giomer bulk-fill (Beautifil Bulk Restorative [BBR], Beautifil Bulk Flowable [BBF]), two nongiomer bulk-fill (Tetric N-Ceram Bulk-fill [TNB], Smart Dentin Replacement [SDR]), and three conventional non-bulk-fill (Beautifil II [BT], Beautifil Flow Plus [BF], Tetric N-Ceram [TN]) RBCs were selected for the study. To evaluate the DC, disc-shaped specimens of 5-mm diameter and 2-mm, 4-mm, and 6-mm thickness were fabricated using customized Teflon molds. The molds were bulk filled with the various RBCs and cured for 20 seconds using a light-emitting diode curing light with an irradiance of 950 mW/cm2. The DC (n=3) was determined by attenuated total reflectance Fourier transform infrared spectroscopy by computing the spectra of cured and uncured specimens. PS (n=3) was measured with the Acuvol volumetric shrinkage analyzer by calculating specimen volumes before and after light curing. The mean DC for the various materials ranged from 46.03% to 69.86%, 45.94% to 69.38%, and 30.65% to 67.85% for 2 mm, 4 mm, and 6 mm, respectively. For all depths, SDR had the highest DC. While no significant difference in DC was observed between depths of 2 mm and 4 mm for the bulk-fill RBCs, DC at 2 mm was significantly greater than 6 mm. For the conventional RBCs, DC at 2 mm was significantly higher than at 4 mm and 6 mm. Mean PS ranged from 1.48% to 4.26% for BBR and BF, respectively. The DC at 2 mm and PS of bulk-fill RBCs were lower than their conventional counterparts. At 4 mm, the DC of giomer bulk-fill RBCs was lower than that of nongiomer bulk-fill materials.

Indirect Restoration Thickness and Time after Light-Activation Effects on Degree of Conversion of Resin Cement.

This study evaluated the effects of indirect restorative materials, curing conditions and time on the degree of conversion (DC) of a dual-cured resin cement using infrared spectroscopy. The resin cement (RelyX Unicem 2, 3M ESPE) was applied to the diamond surface of a horizontal attenuated-total-reflectance unit and activated using one of following conditions: self-cure, direct light exposure, light exposure through indirect restorative materials (resin nano-ceramic: Lava Ultimate, 3M ESPE or feldspathic ceramic: Vita Blocks Mark II, Vita Zahnfabrik). Four thicknesses (0.5, 1.0, 1.5 or 2.0 mm) of each indirect material were analyzed, and the light-activation was performed using a blue LED light. Data (n=5) were analyzed by three-way ANOVA, Tukey's post hoc and Dunnett's tests (α=5%). No significant differences in DC were observed between indirect materials of similar thickness. All groups exhibited higher DC after 10 min than after 5 min. At both times points, the self-cure group exhibited significantly lower DC than all the light exposure groups. Only when the overlying indirect restoration had a thickness of 2 mm did DC decrease significantly. The presence of a thick, indirect restoration can decrease the DC of resin cement. DC after 10 min was higher than after 5 min. The self-cure mode yielded lower DC than the light-activating one.

Monomer-to-polymer conversion and micro-tensile bond strength to dentine of experimental and commercial adhesives containing diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide or a camphorquinone/amine photo-initiator system

ObjectivesTo compare the degree of conversion (DC) of adhesives initiated by diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO) or a camphorquinone/tertiary amine system (CQ/Amine) as well as their ‘immediate’ micro-tensile bond strength (μTBS) to bur-cut dentine. MethodsDC of Scotchbond Universal (‘SBU’; 3M ESPE), its experimental counterpart containing TPO as photo-initiator system, an experimental G-aenial Bond (‘Ga-B’; GC) adhesive formulation, and an experimental LUB-102 adhesive formulation (‘LUB’, Kuraray Noritake), containing as photo-initiatior system either 2wt% CQ along with 2wt% tertiary amine (‘SBU_CQ/Amine’; ‘Ga-B_CQ/Amine’; ‘LUB_CQ/Amine’), or 2wt% TPO (‘SBU_TPO’; ‘Ga-B_TPO’; ‘LUB_TPO’), was determined using Fourier-transform infrared spectroscopy (FTIR), after being cured with a dual-wavelength light-curing unit (bluephase 20i, Ivoclar Vivadent). The same adhesive formulations were applied to bur-cut mid-coronal dentine of intact human molars, and subjected to a μTBS test after 1-week water storage. Besides being applied following a self-etch (SE) application mode, the adhesive formulations SBU_CQ/Amine and SBU_TPO were also applied following an etch-and-rinse (E&R) mode, this both for DS and μTBS measurement. ResultsNo significant difference in DC was found for any of the adhesive formulations, except for SBU_CQ/Amine_SE and SBU_TPO_SE. For both SBU formulations, a significantly higher DC was reached for the E&R than the SE approach. Regarding μTBS, no significant differences were recorded, except for the significantly higher μTBS measured for SBU_CQ/Amine_E&R and SBU_TPO_E&R. ConclusionsIn self-etch adhesives, the photo-initiator TPO may be used instead of CQ/Amine. The curing and ‘immediate’ bonding efficiency depended on the application protocol (E&R versus SE), but not on the photo-initiator system. Clinical significanceThe photo-initiator TPO may be used in self-etch adhesives instead of CQ/Amine with similar curing and ‘immediate’ bonding efficiency.

The influence of irradiation potential on the degree of conversion and mechanical properties of two bulk-fill flowable RBC base materials

ObjectiveTo assess the depth of cure claims of two bulk-fill flowable RBC bases (SDR and x-tra base) using Fourier transform infrared (FTIR) spectroscopy, biaxial flexure strength (BFS), and Vickers hardness number (VHN) for specimen depths of 8mm (in 1mm increments). MethodsThe degree of conversion (DC) was measured by monitoring the peak height (6164cm−1) of specimens (11.0±0.1mm diameter, 1.0±0.1mm thickness) during light irradiation for 20s using a quartz tungsten halogen light curing unit at 650±26mW/cm2. DC was measured up to 120s post irradiation and repeated (n=3) for irradiation depths up to 8mm (in 1mm increments). Further series (n=20) of eight discs were prepared, stacked, light irradiated and numbered from one to eight (distance from the LCU). The specimens were stored at 37±1°C for 24h and BFS tested with the fracture fragments used to determine the VHN for each specimen. ResultsX-tra base can be irradiated to 8mm without a change in DC, something the SDR material cannot claim. However, the DC results confirm both bulk-fill flowable RBC bases have a depth of cure in excess of 4mm. One-way ANOVAs of BFS and VHN data showed significant differences between irradiation depths for x-tra base and SDR with increasing irradiation depth (4mm) resulting in significant reductions in mean BFS and VHN. SignificanceThe claims that the bulk-fill flowable RBC bases have a depth of cure in excess of 4mm can be confirmed but the differing chemistry of the resin formulations and filler characteristics contribute to significant differences in DC, BFS and VHN data between the two materials tested.

Effect of sodium sulfinate salts on the polymerization characteristics of dual-cured resin cement systems exposed to attenuated light-activation

Objectives To evaluate the effectiveness of sodium sulfinate salt co-initiators on the degree of conversion (DC) of dual-cured cementing systems [combination of bonding agent (BA) and resin cement (RC)] when the activating light is attenuated or not available. Methods Two 5th generation products [Prime&Bond NT Dual-Cure/Calibra (Dentsply), and Excite DSC/Variolink II (Ivoclar/Vivadent)] were applied, either with or without co-initiators (sodium sulfinate salts) added to the bonding agents, to the surface of a horizontal attenuated-total-reflectance unit, and were polymerized using one of four conditions: self-cure (SC), or direct light exposure (DLE/XL3000/3 M) through a glass slide or through pre-cured resin discs (shades A2 or A4/2 mm-thick) (Z250/3M-ESPE). Real-time infrared spectra were obtained after placing components (uncured) and during 10 min (cured) (16 scans at 2 cm −1, FTS-40/Digilab/Bio-Rad) to obtain polymerization kinetics. DC and maximum rate of polymerization (Rpmax) were calculated using standard techniques of observing changes in aliphatic-to-aromatic peak ratios pre- and post-curing. Data ( n = 5) were analyzed by two-way ANOVA and Tukey's test ( p = 0.05). Results The addition of co-initiators increased the DC in most of the groups. No significant difference in DC was observed between Prime Bond NT Dual-Cure/Calibra and its version without co-initiator using the DLE curing mode. All DLE groups exhibited the highest DC after 10 min. No significant difference in DC was observed between A2 and A4 pre-cured overlay groups. The SC groups exhibited lower DC than the light-activated groups regardless of the presence of co-initiator. Use of co-initiators increased the Rpmax only in the SC groups. The A2 and A4 groups exhibited lower Rpmax than DLE groups, regardless of the presence of co-initiator. Conclusion The detrimental effects of light attenuation on the DC were not avoided by inclusion of sodium sulfinate salts, despite their ability to eliminate the chemical incompatibility between acidic monomers and self-curing components.

Remaining unreacted methacrylate groups in resin‐based composite with respect to sample preparation and storing conditions using micro‐Raman spectroscopy

The aim of this study was to measure degree of conversion (DC) of resin-based composites (RBCs) using micro-Raman spectroscopy followed by different sample preparation procedures and storing conditions. Ninety samples of Tetric EvoCeram (Ivoclar Vivadent, Schaan, Liechtenstein) were prepared in standardized molds and cured with a high powered LED light-curing unit, bluephase (Ivoclar Vivadent, Schaan, Liechtenstein) for 20 s. Samples were allocated to eight groups. DC of groups 1 and 2 was recorded without or after polishing. DC in groups 3 and 4 was recorded from vertically sectioned samples versus "split" samples. DC in groups 5-8 was recorded after storing samples at room temperature and humidity, in 90 +/- 2% humidity at 37 +/- 1 degrees C, distilled water at 37 +/- 1 degrees C or buffered incubation medium (BIM) at 37 +/- 1 degrees C for 24 h. Mean values of DC in polished and unpolished samples were 63.6% (+/-3.2%) and 54.7% (+/-5.2%), respectively (p < 0.0001). There was no significant difference in DC after sample-sectioning (p > 0.05). Significantly higher DC values were obtained after storing samples in BIM (76.8% +/- 2.1%) than in distilled water (59.7% +/- 5.7%), extreme humidity (60.3% +/- 3.9%) or in room conditions (63.6% +/- 3.2%) (p < 0.001). DC of an RBC measured by micro-Raman spectroscopy may be affected by differences in sample preparation and storing conditions, making it difficult to extrapolate data from in vitro studies into clinically relevant information.

Effect of curing mode on the polymerization characteristics of dual-cured resin cement systems

Objectives To evaluate the effects of different curing conditions on the degree of conversion (DC) of dual-cured cementing systems [combination of bonding agent (BA) and resin cement (RC)] using infrared spectroscopy. Methods Four fourth generation products [Scotchbond Multipurpose Plus/RelyX (3M ESPE), Optibond/Nexus 2 (Kerr), All Bond2/Duolink (Bisco), and Bond-It!/Lute-It! (Pentron)], and three fifth generation materials [Bond1/Lute-It! (Pentron), Prime&Bond NT Dual-Cure/Calibra (Dentsply), and Optibond Solo Dual Cure/Nexus 2 (Kerr)] were applied to the surface of a horizontal attenuated-total-reflectance unit, and were polymerized using one of four conditions: self-cure (SC), direct light exposure through glass slide (DLE, XL3000/3M ESPE) or through pre-cured resin discs (shades A2;A4/2 mm thick/Z250/3M ESPE). Infrared spectra of the uncured cementing systems were recorded immediately after application to the ATR, after the system was light-cured or left to self-cure, and spectra were obtained 5 and 10 min later. DC was calculated using standard techniques of observing changes in aliphatic-to-aromatic peak ratios pre- and post-curing. Data ( n = 5) were analyzed by two-way repeated measures ANOVA and Tukey's test ( p = 0.05). Results Changes in aliphatic-to-aromatic peak ratios before and after placing RC onto the BA demonstrated that a combined layer was created. All groups exhibited higher DC after 10 min than after 5 min, except the DLE group of Bond-it!/Lute-it!. No significant differences in DC were observed among light-activated groups regardless of the resin disc shade in three of the four fourth generation cementing systems. The SC groups exhibited lower DC than the DLE groups for both fourth and fifth generation products either after 5 or 10 min. Conclusion The chemistry of the bonding interface changed when RCs were applied to uncured BAs. The presence of an indirect restoration can decrease the DC of some cementing systems and the self-curing mode leads to lower DC than the light-activating one.