New Perspectives in Overcoming Bulk-Fill Composite Polymerization Shrinkage: The Impact of Curing Mode and Layering.

BACKGROUND: The purpose of this study was to investigate the effect of different light curing modes on the polymerization shrinkage of a bulk-fill composite and to evaluate the impact of two layering techniques on the cuspal deflection. METHODS: Nine different light curing modes were tested on bulk-fill composite samples in aluminum MOD cavities. Intensity, duration, and illumination distance were the factors that changed during the different curing modes. The digital image correlation method was used to visually represent the displacement of carbon particles on the materials' surface caused by shrinkage along both the horizontal and vertical axes. For simulating cuspal deflection, a separate protocol was used, with a bulk and horizontal layering technique. RESULTS: The results showed that the largest horizontal displacements were present in the soft start group (6.00 ± 0.82 µm) and in the X-tra power group (5.67 ± 1.21 µm). The smallest horizontal displacements were detected in normal curing modes (4.00 ± 1.58 µm; 4.00 ± 2.68 µm). The largest vertical displacements, at the bottom layer, were present in the normal curing mode group with a 20 s curing time (5.22 ± 1.56 µm), while the smallest vertical displacements were shown in the X-tra power group (2.89 ± 0.60 µm). The observed particle displacements showing the shrinkage of the composite were correlated with the curing mode. The bulk-fill group showed less cuspal deflection than the horizontal layering group did, but the difference was not statistically significant (p = 0.575). CONCLUSIONS: Within the limitations of this in vitro study, it can be concluded that lower intensities of curing lights (1200 mW/cm2) may perform better from the point of view of material shrinkage than high and extreme light intensities do. The pulse delay mode might be recommended in the case of bulk-fill materials. The number of layers did not significantly affect the cuspal deflection in the case of the studied composite.

Characterization of dental light-curing resin composites incorporating multiple modified low-shrink monomers.

OBJECTIVE: Polymerization shrinkage poses a significant challenge in dental resin composites. The objective of this study is to introduce spiroorthocarbonate monomer 3,9-dimethylene-1,3,5,7-tetraoxa-spiro[5,5]undecane (BMSOC) and epoxy resin monomer 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate (ECHM-ECHC) into bisphenol-S-bis(3-methacrylato-2-hydroxy propyl)ether (BisS-GMA) based resin composites to develop composites with reduced shrinkage properties. METHODS: BMSOC and BisS-GMA were synthesized and thoroughly mixed with ECHM-ECHC, followed by inorganic fillers and photoinitiators. Based on the composition of the resin matrix, five groups of experimental composites were prepared, with traditional bisphenol A-dimethacrylate glycidyl ester (Bis-GMA)/triethylene glycol dimethacrylate (TEGDMA) based composite serving as the control. The polymerization properties, including degree of conversion (DC) and polymerization shrinkage (PS), as well as marginal microleakage, wettability, flexural strength (FS), flexural modulus (FM), and biocompatibility were evaluated. RESULTS: The results demonstrated that compared with the control group, the PS of BisS-GMA based composites containing BMSOC and ECHM-ECHC were significantly reduced (P < 0.05), and the lowest PS (0.96 ± 0.08 %) was observed when the ratio of BisS-GMA: (Epoxy + BMSOC) was 4:6. Additionally, the experimental composites also exhibited improved DC, minimal microleakage, low hydrophilicity, enhanced mechanical properties, qualified in vivo biocompatibility, and slight/moderate in vitro biocompatibility. SIGNIFICANCE: The resin composites incorporating multiple modified low-shrink monomers are promising for dental applications to prevent various clinical problems caused by PS and extend restoration longevity.

Evaluation of pre-heated composite resins with soft-start polymerization and conventional composite restorations in class-I carious lesions - A randomized clinical trial.

Background: By increasing fluidity and conversion, pre-heated composites enhance adaptability and strength, while soft-start polymerization decreases internal stresses. Aim: Over a period of a year, this split-mouth design, randomized controlled clinical trial (RCT) compared pre-heated composites with soft-start polymerization to conventional composites in class-I lesions, with the goal of improving restoration outcomes. Methods: and Findings: Immediately following ethical approval and registration with CTRI, 37 patients with in-formed permission who met specified inclusion and exclusion criteria for class-I lesions were chosen for enrollment. Using a 1:1 ratio, teeth were randomly assigned to Group-A (pre-heated composite with soft-start polymerization) or Group-B (traditional composite restoration). At three-time intervals, the evaluation was blinded and calibrated using Modified United States Public Health Service (USPHS) criteria: baseline, six-month, and one-year marks. Statistical analysis was performed using SPSS 21.0 and the Mann-Whitney U test for inter-group comparisons and the Friedman test for intra-group comparisons. Interpretation: Pre-heated composites with soft-start polymerization performed better in terms of marginal adaptation with a statistically significant difference (p = 0.019) and in terms of color match they performed better clinically (p = 0.062) at 12 months. Other variables like marginal discolouration, sec-ondary caries, anatomic form, post-operative sensitivity, surface texture and retention showed no statistically significant difference (p < 0.05). Pre-heated composites with soft-start mode performed marginally better than nanofilled composites. However, both techniques can be used to successfully restore simple class-I carious lesions.

Effect of Polywave and Monowave Light Curing Units on the Microtensile Bond Strength and Failure Types of Different Bulk-Fill Resin Composites: An in vitro Study.

Aim: This study aimed to evaluate the effects of polywave and monowave light-emitting diode curing units on the microtensile bond strength and failure types of three bulk-fill resin composites. Materials and Methods: This in vitro experimental study was performed on 180 microbars obtained from human third molars and were distributed into 12 groups according to the type of bulk-fill resin composite and the light-curing unit. Third molars were restored using Filtek One Bulk Fill Restorative, Tetric® N-Ceram Bulk Fill, and Opus Bulk Fill resin composites was light-cured with Elipar Deep Cure L and Valo in three modes: standard, high power, and extra power. Subsequently, microtensile analysis was carried out with a universal testing machine and the type of failure with an optical stereomicroscope. For statistical analysis, the Kruskal-Wallis H-test was used, with the Bonferroni post hoc test and Fisher's exact test, considering a significance of p<0.05. Results: There were significant differences in the microtensile bond strength between the Filtek One Bulk Fill restorative and Opus Bulk-Fill (p = 0.042) when light was cured with the polywave unit at standard power. On the other hand, the Filtek One Bulk Fill Restorative and Opus Bulk Fill resins showed significant differences in microtensile bond strength when light was cured with the monowave unit compared with the polywave unit (p<0.05). Conclusion: The presence of alternative photoinitiator systems that are more reactive than camphorquinone produced higher microtensile bond strength in Tetric N-Ceram Bulk Fill and Opus Bulk Fill resins when light-cured with a high and standard polywave unit, respectively, compared to Filtek One Bulk Fill resins. Finally, Tetric N-Ceram Bulk Fill and Opus Bulk Fill resins had the highest percentage of mixed failures, while Filtek One Bulk Fill resin had adhesive failures, which was related to its lower microtensile bond strength.

Tunable and fast-cured hyaluronic acid hydrogel inspired on catechol architecture for enhanced adhesion property.

Hyaluronic acid-based hydrogels have been broadly used in medical applications due to their remarkable properties such as biocompatibility, biodegradability, super hydroscopicity, non-immunogenic effect, etc. However, the inherent weak and hydrophilic polysaccharide structure of pure hyaluronic acid (HA) hydrogels has limited their potential use in muco-adhesiveness, wound dressing, and 3D printing. In this research, we developed in-situ forming of catechol-modified HA hydrogels with improved mechanical properties involving blue-light curing crosslinking reaction. The effect of catechol structure on the physicochemical properties of HA hydrogels was evaluated by varying the content (0-40 %). The as-synthesized hydrogel demonstrated rapid prototyping, excellent wetting adhesiveness, and good biocompatibility. Furthermore, an optimized hydrogel precursor solution was used as a blue light-cured bio-ink with high efficiency and good precision and successfully prototyped a microstructure that mimicked the human hepatic lobule by using DLP 3D printing method. This catechol-modified HA hydrogel with tunable physicochemical and rapid prototyping properties has excellent potential in biomedical engineering.

Monowave vs. Polywave Light - Curing Units: Effect on Light Transmission of Composite without Alternative Photoinitiators.

Objective: The aim of this study was to compare the light transmission of monowave and polywave-curing devices by a bulk-fill composite containing only camphorquinone as a photoinitiator. Materials and methods: Three light-curing devices were used to cure bulk-fill composite QuiXfil: one monowave (Translux® Wave) and two polywave (VALO Cordless and Bluephase® PowerCure. The NIST-calibrated spectrometer (MARC Resin Calibrator, BlueLight Analytics Inc.) was used to measure the incident and transmitted light through a 2-mm composite specimen over 20 s. Light transmittance was calculated from the ratio of the amount of transmitted and incident light. For data analysis (ANOVA, α = 0.05), total irradiation of the entire spectrum, irradiation with wavelengths of 360-420 nm for the violet spectrum, and 420-540 nm for the blue spectrum were selected. Results: Monowave curing unit Translux® Wave had the lowest light transmission (13.78 ± 0.5%), similar to the violet light transmission of polywave devices (12.02 ± 0.94% and 13.81 ± 1.72% for Valo Cordless and Bluephase PowerCure, respectively). Blue light transmittance (32.15-23.70%) was more than twofold higher than for the wavelengths in the violet region of the spectrum (13.81-12.02%) for the two polywave devices. VALO Cordless showed the highest total and blue light transmission (p<0.001). There was no significant difference in the transmission of the violet part of the spectrum between VALO Cordless and Bluephase® PowerCure (p = 0.465). Conclusion: Within the limitations of this study, we could conclude that polywave curing devices can be used for the polymerization of the bulk-fill composite with camphorquinone as the sole photoinitiator.

Post-polymerization of three-dimensional printing resin using a dental light curing unit.

Background/Purpose: In vat photopolymerization, post-polymerization of the three-dimensional (3D) printing resin is necessary to ensure the optimum physical properties of the printed objects. This study aimed to evaluate the potential use of a handheld polywave light-emitting diode (LED) dental light-curing unit (LCU) for post-polymerizing 3D printed resins by measuring the microhardness and biaxial flexural strength of the post-polymerized resin. Material and methods: 3D printed 1- and 2-mm-thick disks were irradiated with a dental LCU at 3200 mW/cm2. Post-polymerization was repeated either on one side from the top surface: two cycles (T2), four cycles (T4), and eight cycles (T8), or on both sides from the top and bottom surfaces: one cycle (T1B1), two cycles (T2B2), and four cycles (T4B4) for each side. The microhardness and biaxial strength of the disks were compared to those post-polymerized by a conventional desktop polymerizing unit (PC) and those without post-polymerization (NC). Results: Microhardness of the disks varied between the top and bottom surfaces of the 1-mm and 2-mm-thick disks, depending on the post-polymerization methods. T8 and T4B4 produced comparable microhardness on the top surface to PC for both thicknesses. In contrast, PC, T2B2, and T4B4 exhibited the highest microhardness on the bottom surface. Except for NC, the 1-mm-thick disks had a higher biaxial flexural strength than the 2-mm-thick disks. T4B4 resulted in the highest biaxial flexural strength for both thicknesses, which was comparable to that of the desktop polymerizing unit. Conclusion: The microhardness and biaxial flexural strengths of the post-polymerized 3D-printed disks increase with polymerization time. With sufficient polymerization from both sides, the polywave LCU has the potential to be a viable alternative to desktop polymerization units.

Automotive Technology Revolutionized Restorative Dentistry Discovery of Alpha-diketone/Amine Catalyst: Part II -Reflections on Photopolymerization from Conception to Development of Composite Resin and Activator Light.

A full account of the preceded early research tribulation that led to the development of the first visible light activated composite resin and the first visible light activator source is documented. The events took place over four years since early 1974 when a raw industrial composite resin that was radiolucent, stiff paste, universal optically opaque white color, polymerized by exposure to a prototype visible light for 120 seconds was given to developed. Four years later, the developed restorative composite resin ended up as a radiopaque, optically translucent, universal color with an additional three shades that possessed the biologic, esthetic, mechanical and physical characteristics with proven efficacy be used for esthetic zone. This conservative account of early development of a technology that must count as one of a small number of inventions during the seventies, over the years has revolutionized restorative dental practice. We were privileged and very lucky to be associated with developmental stages, stumbling blocks, and final success of the first LC Composite resin that ignited the thought process worldwide and laid the foundation for modern esthetic restoratives practiced today.

Assessment of a Bracket-Bonding System's Shear Bond Strength after it has been Cured using Various Light-Curing Units at Different Time Intervals.

Objectives: To assess a bracket-bonding system's shear bond strength cured with dissimilar light-curing units at different time intervals. Materials and Method: Sixty premolar teeth removed for orthodontic purposes were categorized into four types based on the light-curing unit and exposure times used. The specimens in the halogen group were exposed to light for 15 (Group I) and 30 (Group II) sec, respectively. The specimens were exposed to light for 10 (Group III) and 15 sec in the LED group (Group IV). The amount of adhesive still present on the teeth was measured using a stereomicroscope at a magnification of 10 and was then assessed with the help of adhesive remnant index (ARI). Result: The group with the highest mean SBS was in Group II followed by Group I, Group III, and the group with the lowest mean SBS. The ARI was unaffected by the light-curing technique, with score 2 predominating. Conclusion: In all groups, polymerization using halogen and LED led to SBS values that were clinically suitable for orthodontic procedures.

The power of light - From dental materials processing to diagnostics and therapeutics.

Harnessing the power of light and its photonic energy is a powerful tool in biomedical applications. Its use ranges from biomaterials processing and fabrication of polymers to diagnostics and therapeutics. Dental light curable materials have evolved over several decades and now offer very fast (≤ 10 s) and reliable polymerization through depth (4-6 mm thick). This has been achieved by developments on two fronts: (1) chemistries with more efficient light absorption characteristics (camphorquinone [CQ], ~30 L mol-1 cm1 [ʎmax 470 nm]; monoacylphosphine oxides [MAPO], ~800 L mol-1 cm-1 [ʎmax 385 nm]; bisacylphosphine oxide [BAPO], ~1,000 L mol-1 cm-1 [ʎmax 385 nm]) as well mechanistically efficient and prolonged radical generation processes during and after light irradiation, and; (2) introducing light curing technologies (light emitting diodes [LEDs] and less common lasers) with higher powers (≤ 2 W), better spectral range using multiple diodes (short: 390-405 nm; intermediate: 410-450 nm; and long: 450-480 nm), and better spatial power distribution (i.e. homogenous irradiance). However, adequate cure of materials falls short for several reasons, including improper selection of materials and lights, limitations in the chemistry of the materials, and limitations in delivering light through depth. Photonic energy has further applications in dentistry which include transillumination for diagnostics, and therapeutic applications that include photodynamic therapy, photobiomodulation, and photodisinfection. Light interactions with materials and biological tissues are complex and it is important to understand the advantages and limitations of these interactions for successful treatment outcomes. This article highlights the advent of photonic technologies in dentistry, its applications, the advantages and limitations, and possible future developments.

Biofabricated poly (γ-glutamic acid) bio-ink reinforced with calcium silicate exhibiting superior mechanical properties and biocompatibility for bone regeneration.

Background/purpose: The modification in 3D hydrogels, tissue engineering, and biomaterials science has enabled us to fabricate novel substitutes for bone regeneration. This study aimed to combine different biomaterials by 3D technique to fabricate a promising all-rounded hydrogel for bone regeneration. Materials and methods: In this study, glycidyl methacrylate (GMA)-modified poly γ-glutamic acid (γ-PGA-GMA) hydrogels with calcium silicate (CS) hydrogel of different concentrations were fabricated by a 3D printing technique, and their biocompatibility and capability in bone regeneration were also evaluated. Results: The results showed that CS γ-PGA-GMA could be successfully fabricated, and the presence of CS enhanced the rheological and mechanical properties of γ-PGA-GMA hydrogels, thus making them more adept at 3D printing and implantations. SEM images of the surface structure showed that higher CS concentrations (5% and 10%) contributed to denser surface architectures, thus achieving improved cellular adhesion and stem cell proliferation. Furthermore, higher concentrations of CS resulted in elevated expressions of osteogenic-related markers such as alkaline phosphatase (ALP) and osteocalcin (OC), as well as enhanced calcium deposition represented by the increased Alizarin Red S staining. In vivo studies referring to critical defects of rabbit femur further showed that the existence of hydrogels alone was able to induce partial bone regeneration, demonstrated by the results from quantitative and qualitative analysis of micro-CT scans. However, CS alterations caused significant increases in bone regeneration, as indicated by micro-CT and histological staining. Conclusion: These results robustly suggest combining different biomaterials is crucial to producing a well-rounded hydrogel for tissue regeneration. We hope this study could be applied as a platform for others to brainstorm potential out-of-the-box solutions, contributing to developing high-potential biomaterials for bone regeneration.

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

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

Evaluation of the ceramic laminate veneer-tooth interface after different resin cement excess removal techniques.

OBJECTIVES: To compare, in vitro, resin cement excess removal techniques at the veneer-tooth interface. MATERIALS AND METHODS: Anterior human teeth were restored with ceramic veneers and randomly divided according to the following techniques (n = 10): removal of excess resin cement with brush and dental floss, followed by light-curing with Valo (Group 1) or Elipar (Group 2) for 1 min and 40 s; tack-curing with Valo (Group 3) or Elipar (Group 4) for 1 s; and tack-curing with Valo (Group 5) or Elipar (Group 6) for 5 s. The tack-curing was followed by removal of excess with probe and dental floss and light-curing for 1 min and 40 s. The area of excess resin cement (mm2) was measured in micro-CT images using AutoCAD program. The failures at the cervical margin in the X, Y, and Z axes (µm) of greater value were measured using the DataViewer program. The specimens were submitted to microleakage with 2% basic fuchsin. RESULTS: According to the Kruskal-Wallis and multiple comparison test, the highest area of excess resin cement was found in Group 1 (5.06 mm2), which did not differ statistically from Groups 2 (3.70 mm2) and 5 (2.19 mm2). Groups 2, 3 (1.73 mm2), 4 (1.14 mm2), and 5 (2.18 mm2) did not differ statistically. Group 6 (0.77 mm2) obtained the lowest value, which did not differ statistically from Groups 3 and 4. According to the Kruskal-Wallis and Dunn test, there was no significant difference in failures in X (p = 0.981), Y (p = 0.860), and Z (p = 0.638) axes and no significant difference in microleakage (p = 0.203) among the groups. CONCLUSIONS: Tack-curing for 1 s or 5 s, followed by removal of excess resin cement using a probe and a dental floss, tended to result in a lower amount of excess material around the margin. CLINICAL RELEVANCE: The technique used for resin cement excess removal influences the amount of excess leaved at the veneer-tooth interface. Tack-curing for 1 s or 5 s is recommended to mitigate the excess resin cement.

Urethane dimethacrylate-based photopolymerizable resins for stereolithography 3D printing: A physicochemical characterisation and biocompatibility evaluation.

Vat photopolymerisation (VP) three-dimensional printing (3DP) has attracted great attention in many different fields, such as electronics, pharmaceuticals, biomedical devices and tissue engineering. Due to the low availability of biocompatible photocurable resins, its application in the healthcare sector is still limited. In this work, we formulate photocurable resins based on urethane dimethacrylate (UDMA) combined with three different difunctional methacrylic diluents named ethylene glycol dimethacrylate (EGDMA), di(ethylene glycol) dimethacrylate (DEGDMA) or tri(ethylene glycol) dimethacrylate (TEGDMA). The resins were tested for viscosity, thermal behaviour and printability. After printing, the 3D printed specimens were measured with a digital calliper in order to investigate their accuracy to the digital model and tested with FT-IR, TGA and DSC. Their mechanical properties, contact angle, water sorption and biocompatibility were also evaluated. The photopolymerizable formulations investigated in this work achieved promising properties so as to be suitable for tissue engineering and other biomedical applications.

Shedding light on the problem: Proficiency and maintenance practices of light-curing units among dental assistants.

BACKGROUND: Proper light curing is crucial for the success of restorative dentistry and to bond brackets to teeth, yet the responsibility is often delegated to dental assistants (DAs). This study assessed the proficiency and maintenance protocols of DAs when using light-curing units (LCUs) in Saudi Arabia. METHODS: Self-administered questionnaires were distributed to practicing DAs. The questionnaire contained sections on knowledge, adherence to best practices, and how to maintain the LCU. Demographic data were collected as well. Descriptive statistics and linear regressions at a significance level of (p = 0.05) were conducted to identify any relationships that influenced the DAs' LCU knowledge, practice, and maintenance protocols. RESULTS: Among the surveyed DAs, 66% were responsible for using the LCU during treatment, 16% used their fingers for support when light curing, 50% held the LCU tip 1-2 mm from the restoration during curing, and 51% did not have a specific maintenance protocol at their workplace. 70% did not know the output from the LCU, and their educational background correlated with knowledge (b = -14.42, p < 0.001). The type of institution type correlated with adherence to best practices (b = -13.65, p = 0.011), and level of knowledge and adherence to maintenance protocols showed a direct correlation (b = 0.002, p = 0.041). CONCLUSIONS: The findings revealed that a significant percentage of the DAs who replied had insufficient knowledge and did not follow the best practices and maintenance protocols for the LCUs they were using. Their educational background and workplace factors influenced this knowledge gap, while the absence of a maintenance protocol and suboptimal practices were associated with the type of institution. CLINICAL SIGNIFICANCE: To maintain the best practice, clinicians and institutions should improve the education and training of DAs. Otherwise, inadequate light curing by the DAs may jeopardize the long-term success of many dental procedures.

Influence of universal adhesives and silane coupling primer on bonding performance to CAD-CAM resin-based composites: A laboratory investigation.

OBJECTIVE: Obtaining strong resin bonds to computer-aided design and computer-aided manufacturing (CAD-CAM) resin-based composites with dispersed fillers (CCRBCs) poses a challenge. Therefore, this study aimed to assess the effect of three universal adhesives and a two-component silane coupling agent on the shear bond strength to three (CCRBCs). MATERIALS AND METHODS: Eight hundred and sixty-four specimens of Brilliant Crios, Lava Ultimate, and Tetric CAD were polished or grit blasted, bonded with Adhese Universal DC, One Coat 7 Universal (OC7), and Scotchbond Universal Plus Adhesive (SBU) with or without a silane primer. Shear bond strength was measured after 24 h and 10,000 thermocycles. Linear regressions were performed (α = 0.05). RESULTS: After thermocycling, bond strengths were similar for the universal adhesives on polished Brilliant Crios and Lava Ultimate (p ≥ 0.408). Grit blasted Tetric CAD showed no significant differences (p ≥ 0.096). The silane primer had minimal impact on grit blasted Tetric CAD (p ≥ 0.384). The silane primer increased the bond strength of OC7 to Brilliant Crios (p = 0.001) but decreased the adhesion of SBU to Brilliant Crios and Lava Ultimate (p ≤ 0.018). CONCLUSIONS: Bond strength of universal adhesives varied with CCRBC type. The two-component silane coupling agent showed mixed effects on adhesive performance. CLINICAL SIGNIFICANCE: Selecting universal adhesives from the same CCRBC product line does not always guarantee superior bond strength. The efficacy of silane coupling agents differs based on the bonding substrate.

Effect of four different mono and multi-wave light-curing units on the Knoop hardness of veneer resin composites.

OBJECTIVES: To evaluate the effect of mono and multi-wave light-curing units (LCUs) on the Knoop hardness of resin-based composites (RBC) that use different photoinitiators. METHODS: Central incisor-shaped specimens 12 mm long, 9 mm wide, and 1.5 mm thick were made from 2 RBCs that use different photoinitiators: Tetric N-Ceram (Ivoclar Vivadent) - and Vittra APS (FGM), both A2E shade. They were light-cured with 4 different LCUs: two claimed to be multi-wave - VALO Grand (Ultradent) and Emitter Now Duo (Schuster); and two were monowave - Radii Xpert (SDI) and Elipar DeepCure-L (3 M Oral Care) using 2 different light exposure protocols: one 40 s exposure centered over the specimen; and two 20 s light exposures that delivered light from two positions to better cover the entire tooth. 16 groups with 10 specimens in each group were made. The Knoop hardness (KH, kg/mm2) was measured at the top and bottom of the specimen in the center and at the cervical, incisal, mesial, and distal peripheral regions. The active tip diameters (mm) and spectral radiant powers (mW/nm) of the LCUs were measured with and without the interposition of the RBC, as well as the radiant exposure beam profiles (J/cm²) delivered to the top of the RBCs. The data was analyzed using Three-way ANOVA and Tukey's tests (α = 0.05). RESULTS: The VALO Grand (1029 mW) emitted twice the power of the Radii Xpert (500 mW). The KH values of VI and TN resin composite specimens were significantly affected by the LCU used (p < .001), the measurement location (p < .001), and the surface of the specimen (p < .001). LCUs with wider tip diameters produced greater Knoop hardness values at the peripheries of the 12 mm of long, 9 mm wide specimens. In general, the VALO Grand produced the highest KH values, followed by Elipar DeepCure-L, then by Radii Xpert. The Emitter Now Duo LCU produced the lowest values. Exposing the veneers from two locations reduced the differences between the LCUs and the effect of the measurement location. Only the VALO Grand could fully cover the composite veneer with light when the two locations were used. SIGNIFICANCE: The light tip must cover the entire restoration to photocure the RBC beneath the light tip.

Ultraviolet Light Debondable Optically Clear Adhesives for Flexible Displays through Efficient Visible-Light Curing.

With growing sustainability concerns, the need for products that facilitate easy disassembly and reuse has increased. Adhesives, initially designed for bonding, now face demands for selective removal, enabling rapid assembly-disassembly and efficient maintenance across industries. This need is particularly evident in the display industry, with the rise of foldable devices necessitating specialized adhesives. A novel optically clear adhesive (OCA) is presented for foldable display, featuring a unique UV-stimulated selective removal feature. This approach incorporates benzophenone derivatives into the polymer network, facilitating rapid debonding under UV irradiation. A key feature of this method is the adept use of visible-light-driven radical polymerization for OCA film fabrication. This method shows remarkable compatibility with various monomers and exhibits orthogonal reactivity to benzophenone, rendering it ideal for large-scale production. The resultant OCA not only has high transparency and balanced elasticity, along with excellent resistance to repeated folding, but it also exhibits significantly reduced adhesion when exposed to UV irradiation. By merging this customized formulation with strategically integrated UV-responsive elements, an effective solution is offered that enhances manufacturing efficiency and product reliability in the rapidly evolving field of sustainable electronics and displays. This research additionally contributes to eco-friendly device fabrication, aligning with emerging technology demands.

Biobased Resin for Sustainable Stereolithography: 3D Printed Vegetable Oil Acrylate Reinforced with Ultra-Low Content of Nanocellulose for Fossil Resin Substitution.

The use of biobased materials in additive manufacturing is a promising long-term strategy for advancing the polymer industry toward a circular economy and reducing the environmental impact. In commercial 3D printing formulations, there is still a scarcity of efficient biobased polymer resins. This research proposes vegetable oils as biobased components to formulate the stereolithography (SLA) resin. Application of nanocellulose filler, prepared from agricultural waste, remarkably improves the printed material's performance properties. The strong bonding of nanofibrillated celluloses' (NFCs') matrix helps develop a strong interface and produce a polymer nanocomposite with enhanced thermal properties and dynamical mechanical characteristics. The ultra-low NFC content of 0.1-1.0 wt% (0.07-0.71 vol%) was examined in printed samples, with the lowest concentration yielding some of the most promising results. The developed SLA resins showed good printability, and the printing accuracy was not decreased by adding NFC. At the same time, an increase in the resin viscosity with higher filler loading was observed. Resins maintained high transparency in the 500-700 nm spectral region. The glass transition temperature for the 0.71 vol% composition increased by 28°C when compared to the nonreinforced composition. The nanocomposite's stiffness has increased fivefold for the 0.71 vol% composition. The thermal stability of printed compositions was retained after cellulose incorporation, and thermal conductivity was increased by 11%. Strong interfacial interactions were observed between the cellulose and the polymer in the form of hydrogen bonding between hydroxyl and ester groups, which were confirmed by Fourier-transform infrared spectroscopy. This research demonstrates a great potential to use acrylated vegetable oils and nanocellulose fillers as a feedstock to produce high-performance resins for sustainable SLA 3D printing.

Evaluation of the effect of high-intensity light-curing device on micro-leakage of pits and fissure sealants.

Reducing treatment time is one of the most important trends in modern dentistry. This study aimed to compare the micro-leakage around the resin sealants when using both high and conventional intensity light-curing systems. The study sample consisted of 30 extracted human maxillary premolar teeth that were divided into two equal groups according to the light-curing system used: Group 1, High-Intensity Light-Curing System and Group 2, Conventional Light-Curing System. Light-curing by Woodpecker I-LED device with two intensities (high and conventional) has been used. All teeth were subjected to 500 cycles of thermocycling. Then, a methylene blue dye microleakage test was performed, and the teeth were sectioned longitudinally and studied under a stereo microscope. The mean of micro-leakage in the high-intensity group (1.33 ± 1.29) was less than in the conventional intensity group (1.63 ± 1.29) without any statistically significant differences (p = 0.320). The high-intensity light-curing system mode may be a good and acceptable alternative to conventional intensity light-curing system mode in polymerization of pits and fissure sealants.