Lower Degree Of Conversion Research Articles

Does the Transillumination Technique Using a Diagnostic White Tip Influence the Degree of Conversion of the Infiltrant Resin? A Case Report With InVitro Insights: A New Technique to Improve the Predictability During the Application of Resin Infiltration: Transillumination Using a Diagnostic White Tip.

This study aimed to evaluate, through a case report combined with invitro study, whether a new diagnostic white tip for the transillumination technique during resin infiltration influences the procedure and degree of conversion (DC). A clinical case report demonstrated resin infiltration using the transillumination technique with a new white diagnostic tip (Radii Xpert LED diagnostic tip, SDI, Bayswater, VIC, AU) along with a light-curing device to enhance aesthetic results. An invitro study assessed the DC of two diagnostic white tips (Radii Xpert LED diagnostic tip [SDI, Bayswater, VIC, AU] and Valo Grand White Light Lens [Ultradent Prod., South Jordan, UT, USA]) compared to that achieved using conventional tips of both light-curing devices. Statistical analysis was performed using two-way ANOVA and Tukey's test (α = 0.05). The clinical case achieved complete masking of the white spot lesion. Invitro, the diagnostic white tips exhibited significantly lower DC values compared to conventional tips (p = 0.001), regardless of the light-curing unit. The diagnostic white tip used in the transillumination technique improves resin infiltration visibility without compromising the degree of conversion. The transillumination technique with the diagnostic white tip enables monitoring of resin infiltration while maintaining effective polymerization.

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.

Photoactivated riboflavin-doped hydroxy apatite nanospheres infiltered in orthodontic adhesives.

To assess micro-tensile bond strength (μTBS), degree of conversion (DC), microleakage (ML) antibacterial efficacy, and adhesive remnant index (ARI) of orthodontic brackets to enamel with different concentrations of photoactivated riboflavin-doped hydroxyapatite (HA) nanospheres (NS) (0%,1%,5% and 10%) and 0.5 wt% RF alone in orthodontic adhesive. Samples were included on the predefined inclusion criteria and positioned up to the cementoenamel junction (CEJ). Hydroxy apatite nanospheres (HANS) commercially bought were doped with RF. Surface characterization of HANS and RF-doped HANS were assessed along with EDX analysis. Samples were grouped based on experimental orthodontic adhesive modification. Group 1: Transbond XT no modification, Group 2: experimental Transbond XT 0.5 wt% RF, Group 3: experimental Transbond XT 0.5 wt% RF-doped 1% HANS, Group 4: experimental Transbond XT 0.5 wt % RF-doped 5% HANS and Group 5: Experimental Transbond XT 0.5 wt% RF-doped 10% HANS. Brackets were placed based on different adhesive modifications and samples underwent thermocycling. Samples were evaluated for μTBS, DC, and ML. The type of failure was assessed using ARI. Adhesive modified and un-modified in four different concentrations (0%, 1%, 5%, and 10%) and 0.5 wt% RF only were used to test efficacy against Streptococcus mutans (S.mutans). The survival rate of S.mutans and ML was determined using the Kruskal-Wallis Test. For the analysis of μTBS, ANOVA was employed, followed by a post-hoc Tukey HSD multiple comparisons test. The highest μTBS and lowest ML were observed in Group 2 experimental Transbond XT 0.5 wt% RF only. The lowest μTBS, highest ML, and lowest DC was seen in Group 5 experimental Transbond XT 0.5 wt% RF-doped 10% HANS. Samples in Group 1 in which Transbond XT was used as adhesive demonstrated significantly the highest microbial count of S.mutans and DC. Photoactivated RF-doped HANS in 1% and 0.5 wt% Riboflavin alone in orthodontic adhesive for metallic bracket bonding improved micro tensile bond strength, ML, DC, and antibacterial scores. RESEARCH HIGHLIGHTS: The highest μTBS and lowest ML were observed in Group 2 experimental Transbond XT 0.5 wt% RF only. The lowest μTBS, highest ML, and lowest DC was seen in Group 5 experimental Transbond XT 0.5 wt% RF-doped 10% HA-NS. Samples in Group 1 in which Transbond XT was used as adhesive demonstrated significantly the highest microbial count of S.mutans and DC.

The Effect of the Initiator/Activator/Accelerator Ratio on the Degree of Conversion, Film Thickness, Flow, and Cytotoxicity of Dual-Cured Self-Adhesive Resin Cements.

Although self-adhesive resin cements are convenient and less technique-sensitive materials for dental clinicians, they exhibit a lower degree of conversion due to acidic components in their composition. Supplementation of the initiator, accelerator, and activator in self-adhesive resin cements has been suggested to compensate for the lower degree of conversion. This study aimed to evaluate the effects of different combinations of self-curing initiators, self-curing activators, and accelerators on the degree of conversion (DC) of self-adhesive resin cements. A dual-cured self-adhesive resin was prepared using six combinations of initiators, activators, and accelerators. The change in the DC over time was evaluated with and without light curing. The film thickness, flow properties, and cytotoxicity of each formulation were assessed. The results showed that all supplemental components had an effect on increasing the DC, but a greater increase in the DC was observed in the following order: activator, accelerator, and initiator. The cytotoxicity of the resin cements was related to the DC values, as resin cements with lower DC values exhibited higher cytotoxicity. The film thickness met the ISO standards for all groups. The results suggest that utilizing an activator is the most effective approach to enhance the DC in self-adhesive resin cement and that cytotoxicity tended to increase with lower DC values, whereas film thickness and flow properties demonstrated no correlation with DC values.

Engineering Interfacial Integrity with Hydrolytic-Resistant, Self-Reinforcing Dentin Adhesive.

The leading cause of composite restoration failure is secondary caries, and although caries is a multifactorial problem, weak, damage-prone adhesives play a pivotal role in the high susceptibility of composite restorations to secondary caries. Our group has developed synthetic resins that capitalize on free-radical polymerization and sol-gel reactions to provide dental adhesives with enhanced properties. The resins contain γ-methacryloxypropyltrimethoxysilane (MPS) as the Si-based compound. This study investigated the properties of methacrylate-based resins containing methacryloxymethyltrimethoxysilane (MMeS) as a short-chain alternative. The degree of conversion (DC), polymerization kinetics, water sorption, mechanical properties, and leachates of MMeS- and MPS-resins with 55 and 30 wt% BisGMA-crosslinker were determined. The formulations were used as model adhesives, and the adhesive/dentin (a/d) interfaces were analyzed using chemometrics-assisted micro-Raman spectroscopy. The properties of the 55 wt% formulations were comparable. In the 30 wt% BisGMA formulations, the MMeS-resin exhibited faster polymerization, lower DC, reduced leachates, and increased storage and loss moduli, glass transition (Tg), crosslink density, and heterogeneity. The spectroscopic results indicated a comparable spatial distribution of resin, mineralized, and demineralized dentin across the a/d interfaces. The hydrolytically stable experimental short-chain-silane-monomer dental adhesive provides enhanced mechanical properties through autonomous strengthening and offers a promising strategy for the development of restorative dental materials with extended service life.

Effects of different LED light curing units on the degree of conversion and microhardness of different composites: FT-IR and SEM-EDX analysis

The aim of this study was to evaluate the degree of conversion (DC), Vickers microhardness (VHN), main components and surface properties of a microhybrid and two bulk-fill composite resins polymerized with second and third generation light emitting diodes (LED). Sixty cylindrical specimens of Filtek™ Bulk-Fill, everX Posterior (bulk technique) and Filtek Z250 (incremental technique) were prepared in plexiglass molds (5 mm in diameter and 4 mm in thickness) and cured with second-generation LED (Woodpecker LED.B) and third-generation LED (Valo) resulting in six groups (n = 10). DC was determined using Fourier transform infrared spectroscopy (FT-IR), and VHN with Vickers microhardness tester. The main components were identified by means of energy-dispersive X-ray spectroscopy (EDX) microanalysis; whereas filler particles and surface properties were analyzed by scanning electron microscopy (SEM). VHN and DC data were analyzed using two-way ANOVA, followed by t-test with Bonferroni correction for pairwise comparison (p < 0.05). When DC and VHN values were evaluated, after polymerization with second and third generation LED, there was a statistical difference in bulk-fill composites, while there was no statistical difference in microhybrid composite. While, the highest DC and VHN values were obtained after polymerization of Filtek Z250 with Valo, the lowest DC and VHN values were obtained with Filtek Bulk-Fill with Woodpecker LED.B. The degree of conversion and microhardness are affected by the structure of the composite resin and LEDs.

Tuning conditions for the amine-functionalization of carbonyls formed in biobased polyfurfuryl alcohol

Biobased furan resins (furfuryl alcohol based) are functionalized by taking advantage of a side-reaction occurring during its polymerization. The furan ring-opening reactions yields carbonyls which can be functionalized by reaction with primary amines. Light is shed on unexplored parameters impacting the properties of PFA/Amine systems. First, PFA/Amines were prepared using PFA resins at conversion degree between 0.3 and 0.95. Overall, high conversion degrees (0.9 and above) are best suited to produce rigid materials. In addition, a precipitation process may be used to reach high Tg biobased materials (145 °C). Finally, the impact of the amines’ basicity on the properties of PFA/Amines was investigated. The results highlighted that PFAs at conversion degrees above 0.9 are little affected by the basicity. However, the properties of PFA functionalized at lower conversion degrees are strongly affected by the bases, i.e. high brittleness. This can be circumvented by limiting the functionalization degree to 0.25 and below.

The experimental study of the kinetics and modes of polymethyl methacrylate thermal degradation in argon flows

The experimental study of the kinetics and modes of the thermal degradation of polymethyl methacrylate (PMMA) in an argon flow was carried out. During thermogravimetric analysis the sample heating rates were 2, 5, 8, 20 and 35 K/min. Based on the integral isoconversional method the values of the kinetic rate constants of the PMMA thermal degradation were determined. When modeling the decomposition process of PMMA for low conversion degrees, it is advisable to use the reaction rate constant obtained for the conversion degree equal to 20 %, and for modeling the whole process – 50 %. Therefore, for evaluation calculations, it is possible to describe the process of PMMA decomposition with one gross reaction. Also, the investigation of the thermal degradation of PMMA particles under conductive heating conditions (680, 700, 720 K) in an argon and air was carried out. Based on the analysis of the data obtained, a scheme for the decomposition of PMMA, consisting of four stages, was established.

Preheating and "snow-plow" composite application technique affect double bond conversion but not bond strength to dentine.

To measure degree of conversion (DC) of a flowable composite, microtensile bond strength (MTBS) to dentine in the snow-plow technique with/without preheating and temperature in the preheated composite. For DC, snow-plow specimens of Filtek Ultimate Flowable (Flow) and Filtek Bulk Fill (Bulk) (3M) were prepared by light-curing composites simultaneously in standardized molds while in control groups light-curing was separate. DC of Flow was measured using micro-Raman spectroscopy. For MTBS, specimens were prepared on dentine of human extracted molars by simultaneous (snow-plow) or separate (control) light-curing. MTBS was measured using a universal testing machine after 24 h and 6 months. Data were analyzed using ANOVA with Tukey's post hoc (α = 0.05). Increased curing time significantly increased DC in snow-plow from 13.4% ± 11.6% (10 s) to 31.8% ± 4.4% (40 s) albeit significantly lower than controls (p < 0.05). Preheated Bulk improved conversion in snow-plow (44.3% ± 1.7%) and control (50.5% ± 2.6%) (p < 0.05). No significant differences occurred in MTBS between groups (p > 0.05). MTBS values ranged between 66.7 ± 8.4 MPa (snow-plow group_21°C_baseline) and 54.1 ± 15.8 MPa (control_21°C_long-term). Temperature in the preheated Bulk dropped to ~38°C after 30 s. Snow-plow technique, irrespective of preheating, resulted in lower DC of Flow than separate light-curing of composite increments. Snow-plow, irrespective of preheating, resulted in similar initial and long-term MTBS to dentine. Clinicians with preference for flowable composite liners in Class II restorations should be aware that the snow-plow technique of simultaneous light-curing of flowable and bulk-fill composite increments affects monomer-to-polymer conversion, albeit no effect on immediate, and long-term bonding to dentine was detected. Preheating sculptable bulk-fill composite improves conversion of the flowable liner in the snow-plow technique but has no detectable effect on bond strength to dentine.

Influence of Thickness and Translucency of Lithium Disilicate Ceramic on the Degree of Conversion of Resin Cements with Different Initiators.

The degree of conversion (DC) of resin cements can be affected by ceramics, and by the type of resin cement. The purpose was to evaluate the influence of thickness and translucencies of lithium disilicate ceramic on the DC of resin cements: two light-cure (Variolink LC; NX3 LC) and one dual-cure (NX3 Dual). IPS e.max Press ceramic (A2) discs were prepared in 4 thicknesses (0.3, 0.5, 1.0, and 1.5 mm) and in 3 translucencies: HT (high translucency), LT (low translucency), and MO (medium opacity). Subsequently, 234 samples of resin cement (5 x 1 mm) were light-cured through those ceramic discs. The DC was assessed by Fourier Transform Infrared Spectroscopy (FTIR). Ceramic thicknesses decreased DC of NX3 Dual through HT-1.0 and HT 1.5 (p=0.005). Between translucencies, only MO-0.3 affected Variolink LC DC (p=0.018). There was difference among light- and dual-cured resin cements (p=0.001). Increasing thickness and opacity lead to a decrease in the DC of all resin cements, with a significantly lower DC value in NX3 Dual (HT-1.0; HT-1.5), and in Variolink LC (MO- 0.3). Light- and dual-cured resin cements were different among each other. NX3 Dual achieved a significantly lower value than its counterpart NX3 LC.

Modeling of the evolution of the porous structure during a physical activation process for the production of activated biocarbon: A novel low conversion approach

Many experimental studies have shown the feasibility of using biomass precursors to produce activated carbon, often improving the properties obtained from traditional materials. However, hardly any models focus on the development of porosity during the process. Among the so-called pore models, the random pore model (RPM) is the most popular and accurately predicts the evolution of the porous structure due to pore growth and coalescence. However, in activation processes with a low degree of conversion, in which pore formation is the dominant mechanism, the RPM does not correctly predict the evolution of the specific surface area since it does not consider the appearance and creation of new porosity. In this work, a new model is proposed that predicts the specific surface area created due to the formation of new pores. Subsequently, it is combined with the determination of the variation of the specific surface area predicted by the RPM due to the growth and coalescence of existing pores. The validation of the new pore evolution model with activated carbon samples obtained at different conversions shows that the model proposed adequately predicts the specific surface area and pore distribution evolution throughout the activation process.

Influence of the Bracket Material on the Post-Cure Degree of Conversion of Resin-Based Orthodontic Adhesive Systems.

The aim of this study was to examine the influence of the orthodontic bracket material on the short-term and long-term post-cure development of the degree of conversion (DC) of resin-based orthodontic adhesive systems. Five commercially available materials characterized by different compositions and curing modes (light-curable or dual-curable) were tested under three different light curing conditions: without brackets (control group, CO), and in the presence of metal brackets (MB group) or ceramic brackets (CB group). Fourier-transform infrared spectroscopy was used to determine the post-cure DC development, both after "short-term" periods (2, 6, and 10 min) and "long-term" periods (1, 7, and 28 days). The short-term DC values ranged from 43.9% to 76.1%, and the long-term DC values were higher and ranged from 54.3% to 85.3%. The MB group demonstrated significantly lower short-term DC values compared to the CO and the CB groups, while the CB group had statistically similar or slightly lower DC values compared to the CO group. Long-term DC values in the MB and the CB groups were statistically lower or similar compared to the CO group, which depended on the post-cure time. The results indicated that the post-cure DC development was highly material-dependent and affected by the presence of different types of bracket material.

Cytotoxicity evaluation, antibacterial effect, and degree of conversion of QAM-containing adhesives.

The aim of this study was to evaluate the influence of adding quaternary ammonium methacrylates (QAMs) to experimental adhesives by assessing the degree of conversion (DC), cytotoxicity against keratinocytes and fibroblasts, and antibacterial activity against biofilm formation. Two QAMs were added to an experimental adhesive: dimethylaminododecyl methacrylate bromododecane (DMADDM) or dimethylaminododecyl methacrylate bromohexadecane (DMAHDM) at three concentrations each: 1, 2.5, and 5 wt.%. Experimental adhesive without QAMs (control group) and commercially available Transbond XT Primer (3M Unitek, Monrovia, California, USA) were used for comparisons. The adhesives were tested for DC, cytotoxicity against keratinocytes and fibroblasts, and antibacterial activity against biofilm formation. DC, cytotoxicity against fibroblasts, and antibacterial activity were analyzed using one-way ANOVA and Tukey's multiple comparisons. Cytotoxicity against keratinocytes was evaluated using the Kruskal Wallis and Dunn's post-hoc (α = 5%) tests. Transbond showed lower DC as compared to 5% DMAHDM, 1% DMADDM, and 5% DMADDM (p < 0.05). However, all groups presented proper DC when compared to commercial adhesives in the literature. In the evaluation of cytotoxicity against keratinocytes, Transbond induced higher viability than 2.5 wt.% groups (p < 0.05). Against fibroblasts, Transbond induced higher viability as compared to 5 wt.% groups (p < 0.05). DMAHDM at 5 wt.% reduced biofilm formation when compared to all the other groups (p < 0.05). Despite their cytotoxic effect against keratinocytes, gingival fibroblasts showed higher viability. DMAHDM at 5 wt.% decreased Streptococcus mutans viability. The incorporation of DMAHDM at 5 wt.% may be a strategy for reducing the development of white spot lesions.

Effect of a Diode Laser (445 nm) on Polymerization Efficiency of a Preheated Resin Composite Used for Luting of Indirect Composite Restorations.

The aim of this study was to evaluate the polymerization efficiency of a preheated resin composite used as a luting agent for indirect restorations light-cured by a blue diode laser (445 nm). Bronze molds were used to prepare cylindrical specimens of a laboratory composite (Ceramage) with dimensions 2, 3, and 4 mm in height and 8 mm in diameter. The molds had additional height of 120 μm for the placement of the preheated resin composite. A nanohybrid resin composite (Enamel Plus HRi) was preheated at 55°C to use as a luting agent. Photopolymerization was followed for 20 seconds using three light sources: a diode laser emitting at 445 nm (SiroLaser Blue) and two light-emitting diode (LED) units (Bluephase Style and Valo). Degree of conversion (DC) of the preheated resin composite was evaluated using Fourier transform infrared spectroscopy. The results indicated that the main effects of the analysis were significant for both material thickness (p<0.001) and polymerization method (p<0.001). The preheated resin composite was not polymerized under 4-mm-thick specimens, independent of the light-curing unit. For 2-mm material thickness, there was no difference among the three light-curing units (p=0.383), while 3-mm Bluephase Style presented very low DC. Diode laser (445 nm) achieved better polymerization efficiency at the same fluence compared to the LED unit at 3-mm depth, implying a better mechanical behavior and potential improved adhesion of the luting material to dentin.

Efficient Photopolymerization of Dental Resin Composites Using the Photoluminescent Long Afterglow of Sr2MgSi2O7:Eu2+,Dy3.

Dental curing light with blue emission acts as the excitation source for the photopolymerization of the dental composite resin to achieve dental repairing. However, the current repair methods still suffer from a low monomer conversion degree and incomplete resin curing. In this study, novel dental resin composites (DRCs) were prepared by combining Sr2MgSi2O7:Eu2+,Dy3+ (SMSED), a photoluminescent material with a blue long afterglow, and dental resin composites. The curing depth, double bond conversion, elastic modulus, compressive strength, water absorption and solubility, and cytotoxicity were investigated systematically. The results suggest that adding 1 wt % SMSED to dental resin composites can maximize the curing depth and double bond conversion rate of DRCs and reduce its water absorption capacity without affecting the mechanical properties and biological toxicity. This work explores the practical applications of SMSED in dental resin composites, which provides an important reference for further improving the effect of dental caries repair.

Effect of pendant ester groups on gas transport property of 6FDA-BAPP/6FAP copolyimide membrane

Despite the various methods that have been developed, controlling the microstructure of polyimide membranes to achieve excellent separation performance based on target gases remains a challenge. One such method involves rearranging polyimides containing ortho-hydroxyl groups into polybenzoxazoles at temperatures above 400 °C, which can effectively distort the backbones and improve gas diffusion. However, this approach is limited by the extremely high conversion temperatures required and low conversion degrees achieved. The esterification process of the polyimide, which contains ortho-hydroxyl groups to the imide ring, represents a simple and effective approach to enhance the membrane's competitiveness in gas separation without undergoing thermal rearrangement at high temperatures. The polyimide was prepared by the polycondensation of 4,4'-(Hexafluoro isopropylidene) diphthalic anhydride (6FDA), 2,2-double (4,4-amino phenoxy) propane (BAPP), and 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane (6FAP). Microstructures and gas transport coefficients were analyzed when the esterification of 6FDA-BAPP/6FAP was conducted using acetic anhydride and caproic anhydride. In CO2/N2 separation, a-6FDA-BAPP/6FAP exhibits CO2 permeability of 1279.41 ± 66.93 Barrer and perm-selectivity of 40.80 ± 2.27, owing to the significantly improved affinity to CO2. The membrane of c-6FDA-BAPP/6FAP exhibit the further improved CO2 permeability and deteriorated perm-selectivity, due to a leveling effect on the diffusion of CO2 and N2 caused by the pendant caproates with longer alkyl chains. The results confirmed that the gas separation performance of polyimide membrane containing ortho-hydroxyl groups is sensitive to the pendant group.

Incomplete Polymerization of Dual-Cured Resin Cement Due to Attenuated Light through Zirconia Induces Inflammatory Responses.

Zirconia restorations are becoming increasingly common. However, zirconia reduces the polymerization of dual-cured resin cement owing to light attenuation, resulting in residual resin monomers. This study investigated the effects of dual-cured resin cement, with incomplete polymerization owing to attenuated light through zirconia, on the inflammatory response in vitro. The dual-cured resin cement (SA Luting Multi, Kuraray) was light-irradiated through zirconia with three thickness diameters (1.0, 1.5, and 2.0 mm). The light transmittance and the degree of conversion (DC) of the resin cement significantly decreased with increasing zirconia thickness. The dual-cured resin cement in 1.5 mm and 2.0 mm zirconia and no-irradiation groups showed significantly higher amounts of hydroxyethylmethacrylate and triethyleneglycol dimethacrylate elution and upregulated gene expression of proinflammatory cytokines IL-1β and IL-6 from human gingival fibroblasts (hGFs) and TNFα from human monocytic cells, compared with that of the 0 mm group. Dual-cured resin cement with lower DC enhanced intracellular reactive oxygen species (ROS) levels and activated mitogen-activated protein (MAP) kinases in hGFs and monocytic cells. This study suggests that dual-cured resin cement with incomplete polymerization induces inflammatory responses in hGFs and monocytic cells by intracellular ROS generation and MAP kinase activation.

Revealing substrate-induced structural changes in active site of human CYP51 in the presence of its physiological substrates

The human sterol 14α-demethylases (CYP51, CYP is an abbreviation for cytochrome P450) catalyze three-step oxidative removal of 14α-methyl group of lanosterol by first forming an alcohol, then an aldehyde, and finally conducting a CC bond cleavage reaction. This present study utilizes a combination of Resonance Raman spectroscopy and Nanodisc technology to probe the active site structure of CYP51 in the presence of its hydroxylase and lyase substrates. Ligand-binding induced partial low-to-high-spin conversion is observed by applying electronic absorption spectroscopy and Resonance Raman (RR) spectroscopy. This low degree of spin conversion of CYP51 is contributed by the retention of the water ligand coordinated to the heme iron as well as direct interaction between the hydroxyl group of lyase substrate and the iron center. No significant changes in active site structure are found between detergent-stabilized CYP51 and nanodisc-incorporated CYP51, nevertheless, it is demonstrated that nanodisc-incorporated assemblies provide much more well-defined active site RR spectroscopic responses, which induces a larger conversion from low-to-high-spin state in presence of the substrates. Moreover, a positive polar environment around the exogenous diatomic ligand is detected, providing insight into the mechanism of this essential CC bond cleavage reaction.

A Scoping Review on the Polymerization of Resin-Matrix Cements Used in Restorative Dentistry.

In dentistry, clinicians mainly use dual-cured or light-cured resin-matrix cements to achieve a proper polymerization of the organic matrix leading to enhanced physical properties of the cement. However, several parameters can affect the polymerization of resin-matrix cements. The main aim of the present study was to perform a scoping review on the degree of conversion (DC) of the organic matrix, the polymerization, and the light transmittance of different resin-matrix cements used in dentistry. A search was performed on PubMed using a combination of the following key terms: degree of conversion, resin cements, light transmittance, polymerization, light curing, and thickness. Articles in the English language published up to November 2022 were selected. The selected studies' results demonstrated that restorative structures with a thickness higher than 1.5 mm decrease the light irradiance towards the resin-matrix cement. A decrease in light transmission provides a low energy absorption through the resin cement leading to a low DC percentage. On the other hand, the highest DC percentages, ranging between 55 and 75%, have been reported for dual-cured resin-matrix cements, although the polymerization mode and exposure time also influence the DC of monomers. Thus, the polymerization of resin-matrix cements can be optimized taking into account different parameters of light-curing, such as adequate light distance, irradiance, exposure time, equipment, and wavelength. Then, optimum physical properties are achieved that provide a long-term clinical performance of the cemented restorative materials.

Curing profile and marginal gap formation using a liner containing long-wavelength-absorbing photoinitiator: an in vitro study.

The aim was to evaluate the marginal-gap formation and curing profile of a new restorative technique using a liner with long-wavelength-absorbing photoinitiator (LWAP). Box-shaped preparations (6mm × 4mm × 4mm) were made in third molars. All samples were treated with Clearfill SE Bond and divided into 4 groups (n = 5), according to restorative technique used: (1) incremental technique (INC-Technique); (2) camphorquinone-based liner (CQ-Liner) + bulk-fill resin composite; (3) LWAP-based liner (LWAP-Liner) + bulk-fill resin composite; and (4) bulk-fill technique without liner (BF-Technique). The marginal gaps (%) for all the samples were measured using micro-computed tomography. The restorations were cross-sectioned, and the degree of conversion (DC) and Knoop microhardness were evaluated at different depths (0.3, 1, 2, 3, and 4mm). INC-Technique, CQ-Liner, and LWAP-Liner groups showed significantly fewer marginal gaps than those from the BF-Technique group. The BF-Technique specimens had the lowest DC and microhardness in depth. All the other techniques presented similar degree of conversion and microhardness at all the depths. The use of liners, regardless of the photoinitiator system, decreased the marginal-gap formation and improved the curing profile of bulk-filling restoration technique.