Search Results (64)

With the growing use of high-intensity LED units in orthodontics, the effect of ultra-fast curing protocols on polymerization efficiency remains unclear. This study aimed to evaluate the influence of conventional and rapid high-intensity light curing protocols on the degree of conversion (DC) of orthodontic adhesive systems. Three commercially available materials were tested under two conditions, without bracket interference (control group, CG) and with a metal bracket present during curing (metal bracket group, MBG). Two light-curing protocols were employed: conventional curing, using two consecutive 10 s exposures at 1100 mW/cm², and rapid curing, with two consecutive 3 s exposures at 2900 mW/cm². The DC was assessed via Fourier-transform infrared (FTIR) spectroscopy at short-term intervals (2, 6, and 10 min) and after 24 h. The results showed that rapid high-intensity curing yielded significantly lower DC values at both the short term and 24 h period compared to the conventional protocol. Short-term DC values ranged from 44.4% to 64.4% for conventional curing and from 43.0% to 60.0% for rapid curing. At 24 h, DC values increased for all materials, reaching 54.4–82.8% in the conventional group and 49.7–81.4% in the rapid curing group. The largest difference in DC values between curing protocols was observed in the MBG, with reductions of up to 5.9% (short-term) and 4.7% (24 h). The 24 h DC values were mostly material-dependent, while external factors (curing protocol and the presence of a bracket) had more impact on the short-term DC values. Full article

Purpose: The aim of this in vitro study was to evaluate the influence of different models of commercially available portable dental radiometers on the measurement of light irradiance emitted by light-emitting diode (LED) photocuring units. Materials and Methods: Eight LED photocuring units, all emitting light in a single-wavelength spectrum, were tested. Light irradiance (mW/cm²) was measured using six portable dental radiometers: four digital models (D1–D4) and two analog models (A1, A2). Digital model D1 was used as the reference (control). All measurements were conducted under standardized conditions, and each LED–radiometer combination was tested in triplicate. Data were analyzed using Sigma Plot 12.0 (Palo Alto, CA, USA) to verify the assumptions of normality and homogeneity of variances. A one-way analysis of variance (ANOVA) was used to assess the effect of the radiometer model on irradiance values, followed by Tukey’s post hoc test for multiple comparisons. The significance level was set at α < 0.05. Results: No statistically significant difference in irradiance was found between D1 (control) and D2. However, significantly lower values were recorded with A2, while D3, D4, and A1 produced significantly higher irradiance values compared to the control (p < 0.05). Conclusion: Irradiance measurements can vary significantly depending on the radiometer model used. Clinicians should be aware of this variability and are encouraged to regularly check the irradiance of the light-curing units used in daily practice, ensure their proper maintenance, and implement periodic monitoring to maintain effective clinical performance. Full article

The development of high-impact denture base formulations that are suitable for digital light processing (DLP) 3D printing is demanding. Indeed, a combination of high flexural strength/modulus and high fracture toughness is required. In this contribution, eight urethane macromonomers (UMs1-8) were synthesized in a one-pot, two-step procedure. Several rigid diols were first reacted with two equivalents of trimethylhexamethylene diisocyanate. The resulting diisocyanates were subsequently end-capped with a free-radically polymerizable monomer bearing a hydroxy group. UMs1-8 were combined with the monofunctional monomer (octahydro-4,7-methano-1H-indenyl)methyl acrylate and a poly(ε-caprolactone)-polydimethylsiloxane-poly(ε-caprolactone) (PCL-PDMS-PCL) triblock copolymer (BCP1) as a toughening agent. The double-bond conversion, glass transition temperature (T_g), and mechanical properties (flexural strength/modulus, fracture toughness) of corresponding light-cured materials were measured (cured in a mold using a light-curing unit). The results showed that the incorporation of BCP1 was highly efficient at significantly increasing the fracture toughness, as long as the obtained networks exhibited a low crosslink density. The structure of the urethane macromonomer (nature of the rigid group in the spacer; nature and number of polymerizable groups) was demonstrated to be crucial to reach the desired properties (balance between flexural strength/modulus and fracture toughness). Amongst the evaluated macromonomers, UM1 and UM2 were particularly promising. By correctly adjusting the BCP1 content, light-cured formulations based on those two urethane dimethacrylates were able to fulfill ISO20795-1:2013 standard requirements regarding high-impact materials. These formulations are therefore suitable for the development of 3D printable high-impact denture bases. Full article

(1) Background: The work aims to determine different chemical and mechanical properties with and without BPA dental resin–matrix composites under the same curing and testing conditions. (2) Methods: Disc-shaped specimens were prepared from six resin–matrix composites used in dentistry, three with BPA (BE-Brilliant EverGlow^TM, ED-IPS Empress Direct, FS-Filtek^TM Supreme XTE) and three without (AF-Admira Fusion, BF-Enamel Plus HRi Bio Function Enamel, N/C). Specimens were photoactivated using an LED light-curing unit. The chemical and mechanical properties were analysed. (3) Results: The FS group exhibited the most significant water sorption (31.17 µg/mm³), while the BF showed the lowest (12.23 µg/mm³). Regarding the diffusion coefficient, the result recorded for the group AF is faster-absorbing water, and the group NC is slower. In both test methods (biaxial flexural strength and compressive strength), the resistance to flexural loading of the AF group was significantly lower than all other resin composites evaluated. (4) Conclusions: According to all the parameters studied, we verified that the BF presents the best chemical–mechanical behaviour. Resins free of BPA may not influence chemical–mechanical performance. However, the inorganic matrix has more influence on mechanical properties than the organic matrix. Full article

Dental researchers and manufacturers use the ISO 4049 standard to determine the depth of cure (DoC) of resin-based composites (RBCs). This standard uses a 4 mm diameter stainless-steel mold and subsequently divides the length of the remaining hard RBC by 2. However, the DoC values obtained using this mold have been challenged. Six bulk-fill RBCs (Tetric plus Fill, Tetric plus Flow, Tetric PowerFill, Tetric PowerFlow, Filtek One, and Aura Bulk Fill) were used to investigate the limitations of the 4 mm diameter mold used in the ISO 4049 standard when compared to a 6 mm diameter metal mold that represented the dimensions of a large cavity in a tooth. Two distinct light curing units were used. One light (Elipar S10) emitted a single peak wavelength of light, while the other (Bluephase G4) was a broad-spectrum, multiple-peak curing light. After 10 s of photocuring, the uncured RBC was immediately removed using acetone. The maximum length of the hard RBC remaining was measured and divided by two so that the effect of these two mold diameters on the DoC results could be compared. The DoC of all six RBCs tested was consistently greater in the 6 mm diameter mold (p < 0.0001). Sectioning revealed that the solvent-dissolved specimens had a clear internal boundary between the apparently well-cured RBC and a peripheral, solvent-resistant, “frosty” region. Using a 4 mm diameter stainless-steel mold resulted in a reduced depth of cure values compared to those obtained when the 6 mm diameter mold was used. The use of a broad-spectrum, multiple-peak LED curing light proved unnecessary for photocuring the six RBCs used in this study. Full article

This study aimed to investigate the impact of varying concentrations of graphene oxide (GO) combined with two surface coating agents (SCAs) and two dental adhesives (DAHs) used as SCAs on microhardness. Two SCAs, Resin Glaze (ReG) and Coat-It (CoI) (Shofu Inc., Kyoto, Japan), along with two DAHs, Adper^TM Scotchbond^TM Multi-purpose Adhesive (AdA) (3M ESPE, Seefeld, Germany) and OptiBond^TM FL Adhesive (OpA) (Kuraray Noritake Dental Inc., Okayama, Japan), were tested. The ten concentrations of GO—0 wt % (control), 0.05 wt %, 0.1 wt %, 0.3 wt %, 0.5 wt %, 0.7 wt %, 1 wt %, 2 wt %, 5 wt %, and 10 wt %—were incorporated into the SCAs and DAHs to create the experimental formulations. These mixtures underwent centrifugation for homogenization, followed by sonication for dispersion. The mixture was poured into the 3D-printed resin mold (10 mm in diameter and 1 mm in height) and then cured with a light curing unit for 180 s. The cured specimens were then kept in distilled water at 37 ± 1 °C for 24 h. All specimens were then subjected to evaluation of their microhardness properties using a Knoop hardness testing machine. Data were collected, and the statistical analysis was conducted using Two-way ANOVA followed by Tukey’s post-hoc tests at a 0.05 level of significance. According to the results, surface hardness was significantly increased (p < 0.05) when 0.3–0.7 wt % of GO was added to ReG, CoI, and AdA, compared to the control group. However, surface hardness was significantly increased (p < 0.05) when 0.05–0.3 wt % of GO was added to OpA compared to the control group. In the control groups, the microhardness of OpA was significantly higher than that of the other groups (p < 0.05). In the 0.1 wt % groups, the microhardness of OpA was significantly higher than that of the other groups (p < 0.05). At 0.5 wt %, ReG, CoI, and AdA showed significantly higher microhardness compared to their respective control groups (p < 0.05). In the 1–10 wt % groups, the microhardness of ReG, CoI, and AdA demonstrated a gradual, significant decrease compared to the 0.7 wt % groups. Whereas in the 0.5–10 wt % groups, the microhardness of OpA showed a significant gradual decrease compared to the 0.3 wt % group. In summary, the optimal GO concentration could improve the surface hardness of ReG, CoI, AdA, and OpA. Full article

Objectives: Trauma to maxillary incisors is frequent, and requires timely, conservative management for optimal prognosis. This in vitro study evaluated the fracture resistance (FR) and orthodontic bracket bond strength (BS) of incisors following incisal fragment reattachment using various restorative techniques. Materials and Methods: Two independent tests—FR testing (Newtons) and BS testing (megapascals)—were conducted. Eighty intact human maxillary central incisors (n = 40/test), standardized in size and shape using a digital caliper (Mitutoyo, ±0.01 mm), were embedded in acrylic resin and numbered. An uncomplicated crown fracture was induced in 64 teeth (n = 32/test), and the teeth were randomly assigned (simple randomization using Excel’s RAND function) to five groups (n = 8/group/test): (1) intact teeth (negative control, NC); (2) nanohybrid composite buildup using Filtek Z250 and Single Bond 2 (positive control, CB); (3) fragment reattachment using flowable composite (Filtek Supreme, FL); (4) reattachment with a palatal veneer using a nanohybrid composite (PV); and (5) reattachment reinforced with a polyethylene fiber band (Ribbond Inc., RB). In BS testing groups, stainless steel orthodontic brackets (PINNACLE) were bonded using Transbond XT, centered over the fracture line. Light curing was performed using an LED unit (Mini LED Standard, Acteon, 1250 mW/cm², 20 s/bond, 40 s/composite, 2 mm curing tip distance). Specimens were stored in distilled water at room temperature for 24 h before reattachment. FR and BS were evaluated using a universal testing machine (Instron) until failure. Failure modes were analyzed, and data were statistically evaluated using one-way ANOVA, Tukey’s post hoc test, and Pearson’s correlation analysis. Results: Significant differences were observed among groups for both FR and BS (p < 0.05). The NC group exhibited the highest FR (514.4 N) and BS (17.6 MPa). The RB group recorded the second-highest FR (324.6), followed by the PV (234.6), CB (224.9), and FL (203.7) groups. The CB group demonstrated the second-best BS (16.6), followed by the RB (15.2), FL (13.4), and PV (6.5) groups. FR and BS were negatively correlated. Mixed failures predominated in the reattachment groups, except for the PV group, which showed mainly adhesive failures. In BS testing, mixed failures dominated in the NC and CB groups, while adhesive failures predominated in the PV and FL groups. Conclusions: Ribbond reinforcement improves the mechanical performance of reattached incisal fragments, and composite buildup may provide more reliable bracket bonding than fragment reattachment. Clinical Relevance: In cases where biomimetic, minimally invasive reattachment is indicated, Ribbond fiber reinforcement appears to offer a reliable restorative solution. Full article

Acid-etched zirconia has emerged as a high-strength alternative to traditional glass ceramics for laminate veneers in aesthetic dentistry. This randomized, double-blind controlled clinical trial aimed to evaluate the one-year clinical performance of zirconia veneers etched with a hydrofluoric-nitric acid mixture and bonded using a 10-methacryloyloxydecyl dihydrogen phosphate (MDP) containing polymeric adhesive system, compared to lithium disilicate veneers. Fifty-two patients were treated with either translucent zirconia or lithium disilicate veneers, and restorations were bonded using light-cured resin-based adhesives. Clinical parameters, including veneer survival, esthetics, marginal adaptation, postoperative sensitivity, and periodontal health, were assessed using modified United States Public Health Service (USPHS) criteria and periodontal indexes at 2 weeks, 6 months, and 12 months. Both materials showed high survival rates with no statistically significant differences in clinical outcomes. One zirconia veneer debonded early but was successfully rebonded without fracture, while one lithium disilicate veneer fractured upon debonding. The findings support the viability of acid-etched zirconia veneers bonded with polymer-based adhesives as a durable and esthetic restorative option. The study highlights the clinical relevance of polymeric bonding systems in enhancing zirconia veneer performance and reinforces their role in modern adhesive dentistry. Full article

The first seconds of light curing are crucial for the development of most properties of dental composites, especially for the 3s high-irradiance curing. This study investigated the influence of rapid high-irradiance curing on temporal development of temperature, transmittance and conversion of bulk-fill composites. Four materials were tested: Filtek One (FO), Tetric PowerFill (PFill), Tetric PowerFlow (PFlow) and SDR flow+ (SDR+) and cured with three curing units (LCU): Valo Cordles, Bluephase PowerCure and Translux Wave in 3s (3 W/cm²), 10s (1 W/cm²) and 20s (1 W/cm²) curing protocols. Light transmittance was measured at 2 and 4 mm, while temperature rise and polymerisation kinetics were evaluated at 4 mm depth during 5 min. Both light transmittance and temperature rise were greatest for SDR+ > PFlow > PFill > FO. The 20s curing protocol resulted in the highest degree of conversion (DC) for all materials and LCUs, but also contributed to the greatest temperature rise. Rapid curing with the 3s protocol caused the lowest temperature rise and the shortest time to reach maximum temperature. The polymerisation and temperature kinetics were strongly dependent on the material. The DC of PFill was statistically similar for 3s, 10s or 20s curing with BPC. Rapid curing is only recommended for materials developed for this purpose. Full article

The aim of this in vitro study is to evaluate the effect of resin type and placement technique on the hardness of resin-based composites (RBCs). A total of 300 samples consisting of five RBCs (Filtek Z250 microhybrid, Filtek P60 packable, Tetric Ceram hybrid, Admira ORMOCER, and Tetric Flow flowable RBCs) were prepared. Each RBC was placed into Teflon molds with a 4 mm diameter and 2 or 8 mm depths with standard, bulk and incremental techniques and was polymerized by second-generation LED (Hilux Ledmax 1055, 229.153 mW/cm²) and UV (ELC-410, 26.106 mW/cm²) light-curing units (LCUs) in standard mode (n = 10). The Vickers hardness number (VHN) was measured from the top and bottom surfaces of the RBCs. Data were statistically analyzed with a one-way ANOVA. Multiple comparisons were made using the Tukey, Scheffe, and t-tests (p < 0.05). The VHN of the RBCs polymerized with LED and UV LCUs varied between 110.33 and 25.16 and between 104.86 and 34.20, respectively. The Tetric Flow RBC did not polymerize with the LCUs on either surface. The RBCs placed using the bulk technique could not polymerize with the UV LCU on the top surface, except for the Filtek P60 RBC, but showed a higher VHN on the bottom surface. These significant findings highlight that the hardness is specific to the RBC material and placement technique. Full article

A novel monomer, 9-bis[4-(2-hydroxyethoxy)phenyl]fluorene di(mercaptopropionate), with a highly refractive index, purity, and excellent UV-curable properties, is synthesized through an optimized Fischer esterification process, reacting 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene with 3-mercaptopropionic acid. The structural characterization of this monomer is performed using Fourier-transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, high-performance liquid chromatography, and liquid chromatography-mass spectrometry. The synthesis conditions are optimized using a design-of-experiments approach. UV-curable resins are obtained by incorporating the synthesized monomer as the thiol component. The effects of thiol content on the UV-curing behavior, refractive index, shrinkage, adhesion to the polyethylene terephthalate (PET) foil, and viscoelastic recovery are examined. The thermal properties are assessed using differential scanning calorimetry and thermogravimetric analysis. Field-emission scanning electron microscopy confirms the successful replication of the prism film. In edge-lit light-emitting diode (LED) backlight units, the prism film showed increased luminance with higher thiol monomer content in the UV-curable resin while maintaining stable color coordinates. This novel highly refractive index monomer can be utilized in luminance-enhancing prism films, thereby contributing to future innovations in the display film industry. Full article

This study aimed to evaluate the depth of cure (DoC) of bulk-fill composite resins, measured by the bottom-to-top Vickers microhardness ratio, using different light-curing units (LCUs): single-wave LED, polywave LED, and halogen. Six bulk-fill composites—Tetric EvoCeram Bulk Fill, X-tra base, SonicFill, Venus Bulk Fill, SDR, and Filtek Bulk Fill—were tested. Four LCUs, including one halogen (Elipar Trilight) and three LEDs (Demi Ultra, Valo, and Bluephase style), were employed for polymerization. Vickers hardness measurements were taken at depths of 1 mm to 5 mm. One- and two-way ANOVA (α = 0.05) were used for data analysis. The results revealed significant differences in microhardness and microhardness ratios among the composites at depths of 4 mm and beyond, depending on the LCU used. It was observed that most bulk-fill composites showed an adequate DoC up to 4 mm, but the effectiveness varied with different LCUs. Importantly, polywave LED LCUs did not exhibit a superior advantage in achieving depth of cure compared to monowave LED LCUs for composites containing multiple photoinitiators. These findings suggest that while several factors affect the DoC, the type of LCU plays a crucial role, and polywave LEDs may not offer additional benefits over monowave LEDs. Full article

The degree of conversion (DC) is crucial in determining the mechanical and clinical performance of resin-based composites (RBCs). This in vitro study aimed to evaluate the effect of the resin type and placement technique on the DC of RBCs (micro-hybrid, packable, hybrid, ormocer-based and flowable) polymerized with a second-generation LED light-curing unit (LCU). A total of 75 RBC samples were divided into three groups. Each RBC was placed into 4 mm diameter and 2 and 8 mm heigh Teflon molds with conventional standard, bulk, and incremental techniques (n = 5) and polymerized by LED LCU (229.153 mW/cm²) using the standard mode. After 24 h, DC was determined by FTIR spectrophotometry. The data were analyzed with two-way ANOVA and Tukey’s HSD test (p < 0.05). The DC of the RBCs varied between 62.8 and 29.2%. While the same DC was obtained for 2 mm samples at the top and the bottom surfaces, the DC of the 8 mm samples gradually diminished from the top surface to the bottom surface. Significant differences were observed in the DC of the RBCs. An optimal DC was obtained for packable, micro-hybrid and ormocer-based RBCs polymerized by LED LCU with the recommended curing times. Considering that the polymerization process is versatile, further in vitro studies are needed. Full article

Background: This study aimed to evaluate the color stability of bulk-fill flowable resin composites with 2 difference shades at baseline and after artificial aging. Methods: Disk-shaped specimens (Ø10 × 4 mm) were fabricated from three bulk-fill flowable resin resin composites (Filtek Bulk-Fill Flow, Venus Bulk-Fill Flow, and Estelite Bulk-Fill Flow). The specimens in each bulk-fill resin composite group were divided into two subgroups (n = 10 per subgroup) with two different shades, A1 (N = 30) and A3 (N = 30), and were polymerized with light curing (800 mW/cm²/Valo LED Unit, Ultradent) and polished. The color difference between bulk-fill resin composites was evaluated at baseline and after artificial aging using a spectrophotometer (CM-700d, Konica Minolta, Tokyo, Japan) under D65 illumination. Color coordinates were measured with CIEDE2000, and color differences (∆E₀₀) and relative translucency parameter (RTP) values were calculated. Subsequently, the comparison of color changes (∆E₀₀) before and after thermocycling was performed using the t-test for paired samples. Results: The bulk-fill flow resin composites evaluated in the present study were capable of mimicking important optical properties such as light transmission. All the resin composites provided acceptable color stability at baseline and after thermocycling when the color A1 was used. On the other hand, whenever the shade A3 was used, the Venus Bulk-Fill Flow demonstrated the best optical properties. There was no statistically significant difference when comparing baseline and after thermocycling in bulk-fill flowable resin composites (p > 0.05). After thermocycling, A1 bulk-fill flowable resin composites provided acceptable color stability, and all A3 bulk-fill flowable resin composites provided visible color change, except for the Venus Bulk-Fill Flow (∆E₀₀ = 2.35). Conclusions: Estelite Bulk-Fill Flow displayed the best color stability (∆E₀₀ = 2.22) between all the combinations evaluated. Full article

Acacia gum (AG), a polysaccharide biopolymer, has been adopted to improve the strength of three cohesive soils by subjecting them to diverse environmental aging conditions. Being a polysaccharide and a potentially sustainable construction material, the AG yielded flexible film-like threads after 48 h upon hydration, and its pH value of 4.9 varied marginally with the aging of the stabilized soils. The soil samples for the geotechnical evaluation were subjected to wet mixing and were tested under their Optimum Moisture Content (OMC), as determined by the light compaction method. The addition of AG modified the consistency indices of the soils due to the presence of hydroxyl groups in AG, which also led to a rise in OMC and reduction in Maximum Dry Unit weight (MDU). The Unconfined Compressive Strength (UCS) and California Bearing Ratio (CBR) were determined under thermal curing at 333 K as well as on the same day of sample preparation. The least performing condition of the soil’s CBR was evaluated under submerged conditions after allowing the AG-stabilized specimens to air-cure for a period of 1 week. The UCS specimens tested after 7 days were subjected to the initial 7 days of thermal curing at 333 K. A dosage of 1.5% of AG yielded the UCS of 2530 kN/m² and CBR of 98.3%, respectively, for the low compressible clay (LCC) after subjecting the sample to 333 K temperature for 1 week. The viscosity of the AG was found to be 214.7 cP at 2% dosage. Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), and average particle size determination revealed the filling of pores by AG gel solution, adsorption, and hydrogen bonding, which led to improvements in macroproperties. Full article