Light Curing Research Articles

3D printing of cyanate ester resins with interpenetration networks for enhanced thermal and mechanical properties

AbstractCyanate ester (PT‐30) resin possesses exceptional thermal and mechanical properties, including high heat distortion temperature, high glass transition temperature (Tg), and outstanding mechanical characteristics. Conversely, the Tg of the homopolymer of tris(2‐hydroxyethyl)isocyanurate triacrylate (T‐acrylate) surpasses that of other acrylates. The combination of PT‐30 and T‐acrylate results in the formation of an interpenetrating polymer network (IPN) through a dual curing mechanism. Furthermore, the combination of these two polymers enables the tuning of rheology for shear thinning behavior for Ink Extrusion 3D printing technology by adjusting the amount of photoinitiator and rheological modifier. Here, 3D printable ink was formulated using PT‐30, T‐acrylate with a higher Tg, a photoinitiator, and a powdered rheological additive. The printed structures underwent a dual‐curing process involving exposure to UV light and thermal curing. Thermomechanical properties of the printed samples were characterized using dynamic mechanical analysis, thermogravimetric analysis, and tensile testing. The successful formation of an IPN structure through the polymerization of T‐acrylate and PT‐30 was observed, resulting in improved mechanical properties and an elevated Tg. The Fourier transform infrared spectroscopy analysis verified the formation of cross‐linked samples. Overall, this study demonstrates the feasibility of Ink Extrusion 3D printing, using a cyanate ester resin and tris(2‐hydroxyethyl)isocyanurate triacrylate with a dual‐curing mechanism. The enhanced mechanical properties at elevated temperatures (~80% retention of room temperature tensile strength at 200°C for sample with 70/30 wt%) and high Tg of 349 ± 3°C for printed structures shown in this study make them suitable for high‐performance structural applications in industries such as aerospace, defense, and microelectronics.

Comparison of Three Different Orthodontic Adhesives Bonded to Metallic and Ceramic Brackets: SEM and SEM/EDX Analysis (In Vitro Study).

To compare three different orthodontic adhesives (Transbond XT Light Cure Adhesive, Heliosit Orthodontic, Fuji Ortho LC) bonded to two types of orthodontic brackets: ceramic brackets (Fascination Roth 0.22) and metallic brackets (Topic Roth 0.22, Dentaurum). The study was performed on 18 human teeth (6 for each adhesive). The prepared teeth were divided into three groups according to the examination time. Subsequently, they were observed after 1, 2 and 3 weeks following bonding. After the experimental procedure, the teeth samples were cut in half along the longitudinal axis in the vestibulo-oral direction, fixed with conductive carbon cement, placed in a high-vacuum evaporator and then coated with carbon. One half of each sample was observed under a Field-emission gun scanning electron microscope (FEG-SEM Hitachi SU 8030, Japan), while on the second half of the samples qualitative (X-ray line-scans) and semi-quantitative point X-ray energy dispersive analyses (EDX) were performed with Thermo Noran (USA) NSS System 7, equipped with Ultra Dry detector (30 mm2 window). Transbond XT had an ideal bond with the enamel and the bracket base, with rare presence of microgaps and cracks in the enamel. Heliosit Orthodontic demonstrated a better bond relationship with the bracket base than the enamel, whereas in the latter the presence of microgaps in the bond was observed. The microphotographs of Fuji Ortho LC demonstrated many cracks inside the adhesive, and some of them continued to move forward into the enamel surface. Therefore, an impression of a very solid bond relationship with the enamel exists, with cracks being present in the enamel surface and never at the enamel-adhesive interface. Microgaps also appeared at the bracket-adhesive interface. Transbond XT is a highly filled composite resin and is an ideal orthodontic adhesive in each aspect examined, with an ideal enamel-adhesive and bracket-adhesive interface. Heliosit Orthodontic provides better bracket-adhesive interface compared to the enamel. Fuji Ortho LC as a solid resin-modified GIC provides a better enamel-adhesive interface, compared to the bracket base.

Polymerizable rotaxane of cucurbituril protecting dopamine based adhesive hydrogels

The catechol moiety found within mussel proteins plays a pivotal role in enhancing their adhesive properties. Nonetheless, catechol compounds, such as dopamine (DOP) derivatives, are susceptible to oxidation, leading to the formation of quinone. This oxidation process poses a significant challenge in the development of DOP-based hydrogels, hampering their adhesion capabilities and hindering polymerization. To protect DOP moieties from oxidation, DOP and N-(3-aminopropyl)methacrylamide (AMA) moieties were grafted onto the side groups of biocompatible poly(glutamic acid) (PGA). Subsequently, the DOP unit, serving as a second guest, would be captured by a polymerizable rotaxane of cucurbituril (CB[n]), in which the host molecule CB[8] complexed with the first guest, polymerizable methyl viologen (MV), forming a protective function and dynamic cross-linking. Upon exposure to light curing, a composite network emerged through the synergy of covalent cross-linking and supramolecular host-guest complexation of DOP with CB[8]. The generated complexation between DOP and CB[8] could protect the DOP moieties, resulting in photocured hydrogels with exceptional adhesive strength and remarkable tensile capabilities. Moreover, 3D printing technology was used to create various models with these DOP-based hydrogels, demonstrating their promising applications in future.

3-year randomized clinical trial to evaluate the performance of posterior composite restorations lined with ion-releasing materials

To evaluate the impact of using ion-releasing liners on the 3-year clinical performance of posterior resin composite restorations after selective caries excavation with polymer burs. 20 patients were enrolled in this trial. Each patient had two deep carious lesions, one on each side of the mouth. After selective caries removal using polymer bur (PolyBur P1, Komet, Brasseler GmbH Co. KG, Lemgo, Germany), cavities were lined with bioactive ionic resin composite (Activa Bioactive Base/Liner, Pulpdent, Watertown, MA, USA) or resin-modified glass ionomer liner (Riva Light Cure, SDI, Bayswater, Victoria, Australia). All cavities were then restored with nanofilled resin composite (Filtek Z350XT, 3M Oral Care, St. Paul, MN, USA). All the tested materials were placed according to the manufacturers’ instructions. Clinical evaluation was accomplished using World Dental Federation (FDI) criteria at baseline and after 6 months, 1, 2, and 3 years. Data were analyzed using Mann–whitney U and Friedman tests (p < 0.05). The success rates were 100% for all resin composite restorations either lined with ion-releasing resin composite or resin-modified glass ionomer liner. Mann–whitney U test revealed that there were no statistically significant differences between both ion-releasing lining material groups for all criteria during the follow-up periods (p > 0.05). Resin composite restorations showed acceptable clinical performance over 3 years either lined with bioactive ionic or resin-modified glass ionomer liners after selective caries excavation preserving pulp vitality. After the 3-year follow-up period, Activa Bioactive and Riva Light Cure liners were clinically effective and they exhibited with the overlying composite restorations successful clinical performance.Trial registration number: NCT05470959. Date of registration: 22/7/2022. Retrospectively registered.

Assessment of Degree of Conversion and Volumetric Shrinkage of Novel Self-Adhesive Cement.

The degree of monomer conversion and polymerization shrinkage are two of the main reasons for potential adhesion failure between the tooth structure and the restoration substrate. To evaluate the degree of conversion and polymerization shrinkage of a newly developed self-adhesive resin cement, the degree of conversion (DC) was measured using FTIR under different activation modes, temperatures, and times. Volumetric shrinkage was tested using the AcuVol video imaging method. The experimental cement showed a higher DC than other cements under self-curing. The DC of the experimental cement was higher than that of other cements, except SpeedCem Plus under light curing. The experimental cement had a higher DC than other cements, except SpeedCem Plus in some conditions under dual curing. All self-adhesive cements had a higher DC at 37 °C than at 23 °C under self-curing, and there was no statistical difference between 23 °C and 37 °C under light curing. All self-adhesive cements showed a significantly higher DC at 10 min than at 5 min under self-curing. There was no statistical difference between 5 min and 10 min for most cements under dual curing. All self-adhesive cements statistically had the same volumetric shrinkage under light curing and self-curing. The newly developed self-adhesive resin cement exhibited a higher degree of conversion and similar volumetric shrinkage compared to these commercial self-adhesive resin cements.

Comparative Evaluation of Bond Strengths Between Dual Cure Resin Cement and Light Cure Resin Cement in Root Surface Indirect Restorations: An In Vitro Analysis Study.

Aim The aim of this study was to evaluate the shear bond strength betweendual cure and light cure resin cements in root surface indirect restorations. Materials and methods Ten recently extracted human teeth were selected. Cylindrical blocks of resin were prepared and bonded nearthe Cemento-Enamel Junction (CEJ) of the prepared teeth to mimic the restoration at the root surface.The samples were randomly luted to the root surface using the light cure (Calibra Veneer, Dentsply Sirona, India) and dual cure (Fusion Ultra D/C, DenPro, USA) formingtwo groups. The bond strength was checked using the INSTRON 3000 device (INSTRON, MA, USA). The point of fracture of the prepared sample from the tooth surface was noted. All readings were tabulated and further statistically analyzed. Results On comparing the two groups, it was found that the light cured resin had a greater mean shear bond strength (57 N) than the dual cure resin cement (41 N).The difference in the mean value of the shear bond strength between two resin cements was found to be statistically not significant according to independent T-test analysis using Levene's Test (P>0.05). Conclusion From the results obtained and within the limits of the study conducted, we can infer that Calibra Veneer is a more viable option for luting to the root surface area. On the other hand, Fusion Ultra Dual cure resin cement seems to have similar results but has a lower bond strength than the other.

Preparation and wear resistance of water-based UV curable ink

ABSTRACT UV water-based inks have disadvantages such as slow curing speed and low degree of crosslinking. In this paper, the copolymer P(MMA-r-HEMA) was prepared by traditional free radical polymerization using methyl methacrylate (MMA) and hydroxyethyl methacrylate (HEMA) as monomers, and the copolymer P(MMA-r-HEMA) was modified by acrylic acid (AA) to synthesis completely water-soluble acrylic prepolymer P(MMA-r-HEMA)-g-AA. Triethylenetetramine reacted with glycidyl methacrylate (GMA) to yield a multifunctional reactive diluent TGMA. Secondly, acrylic prepolymer P(MMA-r-HEMA)-g-AA, multifunctional reactive diluent TGMA and photoinitiator were used to prepare water-based UV curable ink. The influence of the type and quality of photoinitiator, the relative molecular weight and mass fraction of P(MMA-r-HEMA)-g-AA, the number of functional groups and mass fraction of TGMA on the UV ink curing speed and the wear resistance of the ink film were discussed. When the mass fraction of the photoinitiator TPO was 1%, the number-average relative molecular mass of the prepolymer was 1.67 × 104 g/mol and the mass fraction was 60%, the number of functional groups of the reactive diluent was 6 and the mass fraction was 40%, the light curing of UV water-based ink was completed in 0.1 s, and the mass loss after 50 times abrasion was 0.2–0.4%.

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.

Bond Strength of Two Resin Cements with Leucite-reinforced Ceramic Using Different Bonding Agents.

To compare the bond strength of two resin cements to leucite-reinforced ceramics using three different boding agents and evaluate the compatibility of bonding agents. Twenty extracted sound human molars were sectioned horizontally 2-3 mm above the cementoenamel junction (CEJ). CAD/CAM ceramic blocks for inLab were also sectioned to create 4 mm thick and bonded to the dentin. The adhesive groups assigned were divided into four adhesive groups: Group I: Variolink II dual-cure resin cement and Scotchbond Multi-Purpose Plus adhesive, group II: Multilink Automix dual-cure resin cement and Multilink primers, group III: Multilink Automix and Clearfil SE bond 2 (CSE2) adhesive, group IV: Multilink Automix and CSE2 with light curing after adhesive application. Five specimens of each group were sectioned perpendicular to obtain six microsticks of 1 × 1 mm width from each sample. Microtensile bond strength data were expressed in MPa. Fracture modes (FrMs) analyzed for the surfaces were divided into six patterns. Microtensile bond strength data were statistically analyzed with one-way ANOVA and Tukey post hoc tests (α = 0.05). T-test was performed at the 5% significance level to analyze groups III and IV with and without light curing. Group I showed the highest μTBS average of 13.67 MPa, group IV showed 12.26 MPa, group III showed 12.15 MPa, and group II showed the lowest average of 10.84 MPa. No significant differences were found between the bonding agents. However, the six types of failure modes, although all observed, were characterized by the adhesive system: Type I: adhesive failure of laminated dentin and ceramic; type II: adhesive failure of laminated ceramic; type III: adhesive failure of laminated dentin; type IV: cohesive failure of luting agent; type V: cohesive failure of dentin, and type VI: mixed failure of adhesion and cohesion. As a result, the FrM most commonly observed was the adhesive failure at the luting cement-ceramic block interface. The combination of resin cements and bonding agents did not significantly affect the bond strength of CAD/CAM ceramic restorations and dentin. Several universal bonding agents are currently available for direct and indirect bonding, and using the same bonding agent for direct and indirect restorations could simplify inventory and benefit routine clinical practice. How to cite this article: Aida N, Koi K, Amaya-Pajares SP, et al. Bond Strength of Two Resin Cements with Leucite-reinforced Ceramic Using Different Bonding Agents. J Contemp Dent Pract 2023;24(11):859-863.

Advancement in orthodontic bonding: comparing 1-second and 5-second light emitting diode (LED) curing lights

&lt;p&gt;Recent advancements in dentistry have introduced new light-curing units such as 1-second and 5-second LED curing lights to orthodontics. We aimed to evaluate the shear bond strength and Adhesive Remnant Index (ARI) of stainless-steel orthodontic brackets cured with 1-second, and 5-second LED curing lights. Ninety human extracted upper premolars were selected based on the inclusion and exclusion criteria. The selected teeth were randomly divided into 2 groups - Group I and Group II. In Group I, the teeth were bonded with Standard pre-adjusted edgewise upper premolar brackets (Orthox, JJ Orthodontics) using Transbond XT and cured with Woodpecker iLED 1-second curing light. In Group II, the same brackets and composite were used to bond and light-cure with 5-seconds Woodpecker LED-D unit. The shear bond strength and the Adhesive Remnant Index (ARI) of brackets in both groups were evaluated. Student t-test was used for the statistical analysis of the data. In Group-I (1-second LED curing light), the shear bond strength was 6.62 MPa, whereas it was 10.32 MPa in group II (5-second LED curing light). A highly significant difference was observed in the shear bond strength between the groups. The ARI scores further revealed that the 5-second curing light resulted in a safer failure mode, with adhesive remaining mostly on the bracket. We found that the 5-second Woodpecker LED-D curing light demonstrated higher shear bond strength compared to the 1-second iLED curing light, although both sets of bond strength values are clinically acceptable.&lt;/p&gt;

The effect of post-ultraviolet light curing on the accuracy of direct-printed aligners: an in vitro study

Abstract Background/Objectives Direct-printed aligners have proven to be more cost effective and accurate. However, the post-curing process might affect their dimensional accuracy, leading to unwanted tooth movement. The present study aimed to investigate the effect of different post-curing durations on the location specific accuracy of direct-printed aligners. Method A stereolithography printer was used to produce 30 aligners using Dental LT V2 resin. The aligners were randomly assigned into 3 groups (n = 10 each) according to different post-ultraviolet light-curing durations: 0 min (No cure); 40 min or 60 min. The aligners in each group were then scanned and superimposed on certain landmarks to check for location specific deviations using a best fit algorithm. Discrepancies were assessed at 10 different points by one examiner at two different time intervals (0.25 mm was the clinically acceptable threshold limit). One way ANOVA and repeated measures ANOVA were applied for statistical analysis. Results Deviations were maximum in the ‘No cure’ group but were statistically insignificant (p-value &gt; 0.05). The deviation values in the ‘40 and 60 min cure’ groups were comparable and statistically significant (p-value &lt; 0.05), with maximum deviation noted in the anterior region. All values in the ‘40 and 60 min cure’ groups were within the clinically acceptable range. Conclusion Post-print ultraviolet light curing is a crucial step to ensure the rigidity of the direct-printed aligner. However, increasing the duration of light curing has little effect on aligner accuracy.

Effect of duration and infection control barriers of light curing unit on hardness of Bulk Fill composite resin.

This study aimed to investigate the impact of the duration of light curing unit (LCU) usage and the use of infection control barriers on the hardness of Bulk Fill composite resin after curing. The hypotheses were that extended usage of the LCU would not reduces its output power and resin hardness, and that the presence of polyethylene film barriers exacerbates the reduction in resin hardness. Based on the absence or presence of polyethylene film (PE) and the number of layers used, a 3M LED curing light (EliparTM DeepCure-S; 3M ESPE, St Paul, MN, USA) was divided into three groups: PE0, PE1, and PE3. The curing light was used 30 times daily for 20 s per exposure, at frequencies of 0, 6, and 12 months. Maximum output power tests were conducted for each group of curing lights. Custom-made plastic modules were used to stack Bulk Fill composite resin (Filtek Bulk Fill Posterior Restorative; 3M ESPE) to a thickness of 4 mm. Each group of curing lights was used to cure the modules in a direct contact manner for 20 s. Vickers hardness measurements were taken at the top and bottom surfaces of the resin specimens using a digital microhardness tester. A one-way or two-way ANOVA analyzed the power of LCUs, Vickers hardness of Bulk Fill composite resin, and hardness decrease percentage across groups. Pairwise comparisons used the Tukey test (α = 0.05). As the duration of usage increased, both the power of the curing light and the hardness of the resin significantly decreased. Significant differences were observed in power and resin hardness among the PE0, PE1, and PE3 groups. When the duration of usage was 6 months or less, only multi-layered PE films led to a significant increase in the percentage decrease of hardness of cured resin from top to bottom. However, at 12 months, both single-layer and multi-layered PE films resulted in a significant increase in the percentage decrease of hardness of cured resin from top to bottom. The output power of the light curing unit decreases with prolonged usage, thereby failing to meet the curing requirements of Bulk Fill composite resin. The use of single-layer PE as an infection control barrier is recommended.

Pulpal Temperature Variances During Step-by-step Adhesive Restorative Procedure Using Three Different High-irradiance Light-curing Units.

The rise in temperature in pulp tissues is related not only to heat transfer by high-irradiance light-curing units (LCUs), but also to restorative procedures. This research aimed to compare the rise in pulp temperature (PT) induced by three LCUs at each restorative step while considering the influence of resin composite shade and thickness. To accomplish this, the investigators used a proposed experimental model replicating pulp fluid circulation with a controlled, simulated intraoral temperature in bovine incisors. The recorded external and internal PT ranged from 36.7°C to 37.1°C and 32.7°C to 33.0°C, respectively. A significant decrease of internal temperature was recorded during class V preparation, followed by a progressive and representative rise of temperature in the subsequent restorative steps. The temperature was significantly higher during light curing of the adhesive system using Valo compared to light curing using Elipar and Radii Cal. However, none of the analyzed devices produced a temperature that exceeded the pulp tolerance limit (a temperature increase over 5.5°C). The paired test showed no significant difference in pulp temperature associated with the thickness of the increment of resin composite. However, shade was found to have more influence on the amount of energy absorbed by pulp tissue-A1 samples showed significantly higher temperature variation compared to samples using the A4 shade of resin composite. To conclude, the microcirculation and the performance of procedures under constant air-water flux dissipate the heat absorbed by the pulp. Additionally, the data suggest that all three LCUs analyzed can be safely used in clinical procedures, and that the resin composite shade may influence the amount of irradiance delivered to the tooth surface and represents a significant factor in pulp temperature variance.

Multi-peak Light-emitting Diode Curing Units and Polymerization of 3D-printed Crown and Bridge Resin.

This study aimed to evaluate the substitutive and additive efficacy of multi-peak light-emitting diode (LED) curing units for post-curing of a three-dimensional- (3D-) printed crown and bridge resin. A total of 792 disc- and 180 bar-shaped specimens were printed with a crown and bridge resin (NextDent C&B MFH) and post-cured using two LED curing units (VALO Cordless and Bluephase N G4) in fast and standard modes. Conventional post-curing (LC-3D Print Box, Group PC) was compared with LED-only curing (Groups V1, V2, B1, and B2) and LED-combined curing (Groups PV1, PV2, PB1, and PB2) in terms of microhardness, flexural strength, degree of conversion (DC), and CIE L*a*b* color and translucency parameters. Cytotoxicity of the resin eluates was evaluated using the WST-1 assay. Temperature increases on the resin surface were measured with infrared thermography. Data were statistically analyzed using ANOVA and Kruskal-Wallis tests (α=0.05). The microhardness and flexural strength in Groups V1, V2, B1, and DC in all LED-only groups were lower than in other groups (p<0.05). Larger color disparities existed between Group PC and all LED-only groups than between Group PC and the others (p<0.05). There was no significant difference in cytotoxicity among the groups. The temperature increase was lowest in Groups V1 and PV1 during light curing (p<0.05). Post-curing by multi-peak LED curing units was not as effective as the conventional post-curing device. Additional post-curing by LED curing units did not improve the material properties.

The role of protective liners and glass ionomer in managing pulp temperature during light curing.

To evaluate the thermal insulation of protective liners and glass ionomer cement during light-curing procedures. Human third molars underwent Class I preparations with dimensions 5 mm long × 4 mm wide × 4 mm deep in a standardized manner ensured a consistent ±0.5 mm dentin thickness at the pulpal floor. The teeth were attached to a customized oral cavity chamber simulator with a circulating bath at a standardized temperature of 34.2 ± 1oC. The temperature variations at the pulpal floor were captured in real-time by video using an infrared thermal camera (FLIR ONE Pro, FLIR Systems). The materials evaluated were: Dycal (Dentsply), TheraCal LC (Bisco), Activa (Pulpdent), and Fuji II LC (GC). All light-activation procedures were performed with the same light-curing unit (Valo Grand, Ultradent) in standard mode, 1000 mW/cm2, and time of exposure following manufacturer instructions. A power analysis was conducted to determine the sample size considering a minimal power of 0.8, with α=0.05. Statistical analyses were performed using ANOVA and Tukey's test for multiple comparisons. The temperature at the pulpal floor increased above the 5.5 ºC safety threshold difference for clinical scenarios tested. None of the materials provided proper thermal insulation for light-curing procedures (p = 0.25). The higher the number of light-cured steps, the longer the pulp remained above the 5.5 ºC temperature threshold. The materials tested provided improper thermal insulation (Δ > 5.5 ºC). Thus, prolonged or multiple light-curing exposures can be harmful to the pulp tissues. Therefore, for indirect pulpal capping procedures, self-cured materials or a reduced number of steps requiring light curing must be adopted to reduce the amount of time the pulp remains above the 5.5 ºC safety temperature threshold. Key words:Dental Pulp Capping, Calcium hydroxide, Bioactive, Thermal Damage.

Restoration-repair potential of resin-modified glass ionomer cement.

This in vitro study aimed to evaluate the repair bond strength of resin-modified glass ionomer cement using either the same material or a universal adhesive in the etch-and-rinse and self-etch modes plus resin composite. Twenty-four resin-modified glass ionomer cement blocks were stored in distilled water for 14 d and thermocycled. Sandpaper ground specimens were randomly assigned to three experimental groups according to the repair protocol: resin-modified glass ionomer cement (Riva Light Cure, SDI) and universal adhesive (Scotchbond Universal Adhesive, 3M Oral Care) in etch-and-rinse or self-etch modes and nanohybrid resin composite (Z350 XT, 3M Oral Care). After 24 h of water storage, the blocks were sectioned, and bonded sticks were subjected to the microtensile bond strength (μTBS) test. One-way ANOVA and Tukey's test were used to analyze the data. The failure mode was descriptively analyzed. The highest μTBS values were obtained when the resin-modified glass ionomer cement was repaired using the same material (p < 0.01). In addition, the mode of application of the universal adhesive system did not influence the repair bond strength of the resin-modified glass ionomer cement. Adhesive/mixed failures prevailed in all groups. Repair of resin-modified glass ionomers with the same material appears to be the preferred option to improve bond strength.

Comparative study of physical-chemical properties of bioactive glass ionomer cement.

This study analyzed the physical-chemical properties of bioactive ionomer materials. Cention N bioactive materials were evaluated chemically activated (CN) and light-cured (CN-LC), Equia Forte Fill (EQUI); conventional resin composite Filtek Z350 XT (Z350); resin glass ionomer cement Riva light Cure (RIVA) and flowable resin composite Filtek Bulk Fill Flow (BULK-F) were evaluated. Sixty specimens (n=10) were prepared for sorption (SR), solubility (SL), flexural strength (FS), shrinkage stress (SS), conversion degree (CD), microhardness (MI), and surface roughness (SR) tests. Non-cured and light-cured materials were assessed on FTIR. 30 human molar teeth were used in the bond strength test (BS). Data were subjected to ANOVA and post-hoc Tukey's test (5% of significance). EQUI showed more sorption in SR and no statistical difference from RIVA and CN-LC. CN group showed more solubility and EQUI presented less (p<0.05). BULK-F showed higher FS (MPa), without differences from CN and Z350, whereas EQUI presented the lowest FS not differing from RIVA. BULK-F and CN-LC showed more shrinkage stress differing from EQUI. CN-LC and CN showed higher CD differing from the other which showed no differences (p>0.05) between them. EQUI showed the highest hardness (p<0.05) in MI. There were no differences (p>0.05) in SR (µm). Z350 and BULK-F presented higher BS, whereas CN-LC showed the lowest, although not differing from EQUI and RIVA. Equia Forte's solubility and microhardness make it a good alternative as a restorative material. Cention N degree of conversion and flexural strength making it an esthetic option to amalgam.

Effect of Shade and Light Curing Mode on the Degree of Conversion of Silorane-Based and Methacrylate-Based Resin Composites

Effect of Shade and Light Curing Mode on the Degree of Conversion of Silorane-Based and Methacrylate-Based Resin Composites

Evaluation of Radiant Power of the Light Curing Units Used in Clinics at Governmental and Privates Dental Faculties.

To evaluate the radiant power of the light cure units (LCUs) in relation to their type, radiant exitance, number of years in clinical use, and condition of LCUs tips in governmental and public clinics in Dental Faculties in Sana'a City. LCUs were collected from different colleges at Sanaa City, Yemen, then LCU data as type, clinical age (<1 year, between 1-5 and ˃ 5-years), tip condition was visually inspected for damage and adhering debris, and the radiant exitance values of the tested LCUs. Radiant exitance values were subcategorized into three groups: <400, 400-850, and >850 mW/cm², labeled as inadequate, marginal, and adequate radiant exitances, respectively. A Woodpecker radiometer was used with a mode lasting of 20 seconds was used with each LCU. Descriptive statistics of the different parameters were evaluated with SPSS version 25. One-way ANOVA and Mann-Whitney tests were performed to determine the mean difference between the groups with a significance value of ˂ 0.05 was considered. Two hundred twenty-three LCUs were surveyed, and the majority were Light-emitting diode (LED). Forty-nine (21.9%), 117 (52.4%), 57 (25.6%) recorded lesser than, 400-850, and more than 850 mW/cm², respectively. Radiant exitances of < year-old units were found to be higher than those of units used for ˃ 5 years with significant differences (p=0.001). The ANOVA test showed significant differences between the radiant exitance with clinical age and LCU tip conditions and a strong correlation p ˃ 0.050. LED curing lights were the most used in the tested Dental Faculties. More than half of the used LCU offered sufficient radiant exitance. Clinical age, the presence or absence of composite buildups, and damage to curing tips showed significantly affect radiant exitance values.

Light transmittance through resin-matrix composite onlays adhered to resin-matrix cements or flowable composites

ObjectiveThe aim of this study was to evaluate the influence of the thickness of resin-matrix composite blocks manufactured by CAD-CAM on the light transmittance towards different resin-matrix cements or flowable composites. MethodsSixty specimens of resin-matrix composite CAD-CAM blocks reinforced with 89 wt% inorganic fillers were cross-sectioned with 2 or 3 mm thicknesses. The specimens were conditioned with adhesive system and divided in groups according to the luting material, namely: two dual-cured resin-matrix cements, two traditional flowable resin-matrix composites, and one thermal-induced flowable resin-matrix composite. Specimens were light-cured at 900 mW/cm2 for 40s. Light transmittance assays were preformed using a spectrophotometer with an integrated monochromator before and after light-curing. Microstructural analysis was performed by optical and scanning electron microscopy (SEM). Nanoindentation tests were performed to evaluate mechanical properties for indirect evaluation of degree of monomers conversion. ResultsOptical and SEM images revealed low thickness values for the cementation interfaces for the traditional flowable resin-matrix composite. The cement thickness increased with the size and content of inorganic fillers. The highest light transmittance was recorded for the onlay blocks cemented with the traditional flowable resin-matrix composites while a group cemented with the dual-cured resin-matrix cement revealed the lowest light transmittance. The elastic modulus and hardness increased for specimens with high content of inorganic fillers as well as it increased in function of the light transmittance. ConclusionsThe light transmittance of flowable resin-matrix composites was higher than that for resin-matrix cement after cementation to resin-matrix composites blocks. The type, size, and content of inorganic fillers of the luting material affected the thickness of the cement layer and light transmittance through the materials. Clinical relevanceOn chair-side light curing, the transmission of visible light can be interfered by the chemical composition and viscosity of the luting materials. The increase in size and content of inorganic fillers of resin-matrix composites and luting materials can decrease the light transmittance leading to inefficient polymerization.