Light-curing Units Research Articles

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

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. 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. 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). 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. 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 Mono- and Multiwave Light-curing Units on the Microhardness and Degree of Conversion of Light-cured Resin Cements.

This study evaluated the Knoop hardness (KH, N/mm2) and degree of conversion (DC, %) on the margins of light-cured resin cements with different photoinitiators using a single light-curing unit (LCU) with two heads (mono- and multiwave). Three types of resin cements were used with different photoinitiators: Megalink Esthetic (Odontomega, São Paulo, Brazil) with a camphorquinone photoinitiator; Allcem Veneer (FGM, Joinville, Brazil) with the Advanced Polymerization system (APS), and Variolink Esthetic LC (Ivoclar Vivadent, Schaan, Liechtenstein). Thirty samples were collected and divided into six groups (n=5 each). The resin cement samples were made into the shape of a maxillary right central incisor and photoactivated under a 0.5-mm-thick ceramic sheet. A single LCU (Radii Xpert, SDI) with two heads (mono- and multiwave) was used. The tip of the LCU was positioned at the center of the sample in a standardized manner. Raman spectroscopy was performed to evaluate the DC, and KH was evaluated through the Knoop microhardness test. Five regions were evaluated: cervical, mesial, buccal (center), distal, and incisal. There was a significant difference in the DC only for the type of cement (p<0.001), indicating that the cement with the APS photoinitiator presented excellent results. There were significant differences in the type of cement (p<0.001), type of light (p<0.001), region (p<0.001), and the interaction between the type of cement and type of light (p<0.001). The resin cement with the APS photoinitiator cured with monowave light showed the highest KH values. The beam profiles of all groups, with and without the interposition of ceramic and resin cement, were examined by light transmission. The cement with the APS photoinitiator presented the best results with respect to the DC and KH. In comparison with mono- and multiwaves, the LCU may not be a determining factor for the properties of light-cured resin cements. The buccal region showed the best results for DC and KH, indicating the need for a greater amount of light-curing at the cementation margins.

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

ObjectivesTo 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. MethodsCentral 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). ResultsThe 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. SignificanceThe light tip must cover the entire restoration to photocure the RBC beneath the light tip.

Effect of surface treatments on optical, topographical and mechanical properties of CAD/CAM reinforced lithium silicate glass ceramics.

To investigate the effect of different surface treatments on optical, topographical and mechanical properties of CAD/CAM lithium silicate-based glass ceramics (LSC's) and their combined effect on the output of a light curing unit (LCU). Four CAD/CAM LSC's were investigated: Lithium Disilicate (Emax CAD; EC), Zirconia-reinforced silicates (Vita Suprinity; VS and Celtra Duo;CD) and Lithium Aluminum Disilicate (CEREC Tessera; CT). Ceramic specimens (n=240) were divided into six subgroups according to their surface treatment: (a) Control, (b) Hydrofluoric acid (HF) 5%, (c) HF 5% +Neutralizing agent (N), (d) HF 9%, (e) HF 9% +N and (f) Self-etching ceramic primer (SEP). Irradiance, power and radiant exposure of a LCU were measured with MARC-LC following ceramic specimen interposition. Direct light transmission (T%) and absorbance (Abs%) of the specimens were measured with UV-Vis spectrophotometry. Roughness (Sa, Sq) and wettability (θ°) were measured with optical profilometry and sessile drop profile analysis, respectively. Biaxial flexural strength (σ) of the ceramic specimens was measured by the ball-on-three-balls method and ceramic specimens were examined microscopically. Statistical analyses was performed by two-way ANOVA followed by post hoc multiple comparisons (α=0.05). Acid neutralization decreased T% and increased Abs% in all LSC's and highest T% was exhibited with VS. Neutralized EC, VS and CD displayed higher Sa in HF9, while neutralized CT displayed higher Sa in HF5. Self-etch primer significantly reduced θ° (p<0.001). σ was observed in the followed ascending order: HF9+N<HF9<HF5+N<HF5<SEP <Control for all LSC's. Optical, topographical and mechanical properties of the CAD/CAM ceramic blocks were strongly dependent on the type of surface treatment. Results of neutralization post-etching indicate promising potential for future investigations.

Comparison of the Degree of Conversion of Orthodontic Adhesive when Cured with Different Curing Lights

Abstract Introduction: The final physical and mechanical properties of composites are determined by the degree of conversion (DC%) of monomer in the composite, which in turn determines the quality of bonding. Incomplete conversion of monomer might lead to the leach of various chemical compounds from the uncured resin. Aims and Objectives: This study assessed the DC% of Transbond XT composite resin when cured with three different light-curing units using Fourier transform infrared (FTIR) spectroscopy. Materials and Methods: A total of 60 metallic brackets were used. The bonding system was Transbond XT Primer, followed by Transbond XT composite resin that cured for 10 s, 3 s with Elipar DeepCure-L 3M and Woodpecker iLED, respectively, as recommended by the manufacturers and 20 s by BeeCool light-emitting diode-corded (taken as control) on extracted natural teeth which were mounted on the plaster of Paris base. One millimetre was used to standardise the distance between the light source and each specimen. Immediately after polymerisation, the debonded cured composites were tested using FTIR spectroscopy to assess DC%. Non-cured resin specimens were also subjected to FTIR spectroscopy, to serve as non-cured references. Results: With 3M, Woodpecker and BeeCool, the DC% of monomer was 58.83%, 58.53% and 21.55%, respectively. No statistically significant difference was found between 3M and Woodpecker lights. BeeCool showed significantly lower DC%. Conclusion: It is essential for clinicians to have prior knowledge of light-curing units before committing to purchase one as the reduction in exposure time is beneficial for both the patient and the orthodontist.

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

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

Color Stability Assessment of Three Different Resin Composites After Polymerization with Two Different Light-Curing Units

Purpose: Despite improvements in resin composite structures, color stability remains a challenge, and esthetic problems are the most common factors in renewing restorations. This study aimed to evaluate the effects of two light-curing units on the color stability of three different resin composite materials during a six-month period.&#x0D; Materials &amp; Methods: Three different resin composites (Filtek Z550, Filtek Ultimate Flowable, Filtek Bulk Fill Restorative) with an A2 color shade were prepared for each combination of resin composite-curing unit (5x2mm) for a total of 30 specimens. Specimens were cured with either QTH Hilux Ultraplus (700mW/cm2) for 40 seconds or Radii Plus LED Curing Light (1400mW/cm2) for 20 seconds. For standardization of the amount of transmitted energy to the composite, all specimens received 28J/cm2. Color parameters were measured with a colorimeter (Minolta CR-321, Konica Minolta Sensing Pte Ltd, Singapore) after polymerization and at 24 hours, first week, first month, third month, and sixth month. Color changes(∆E) were calculated for the different storage periods. One-factor repeated three-way analysis of variance (ANOVA) was used to examine the changes in ΔE measurements over time for different fillers and devices.&#x0D; Results: Significant differences between composites and periods were observed in the color stability with polymerization either QTH or LED. Independently of the composites, there was no significant difference at the end of six months between QTH and LED units with a fixed energy density. The Filtek Z550 material showed the smallest and the Filtek Ultimate Flowable material showed the highest ∆E values at the end of the six months among the materials used.&#x0D; Conclusion: Clinically acceptable color changes were observed for all the materials at the end of six months.

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

Background/PurposeIn 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 methods3D 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). ResultsMicrohardness 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. ConclusionThe 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.

An In vitro Comparative Evaluation of the Fracture Resistance of Teeth with Mesio-Occluso-Distal Preparations Restored with Different Esthetic Materials by Bulk-Fill and Incremental Methods

Introduction: One of the most popular restorative materials today is resin-based composite. Volumetric shrinkage is brought on by polymerization, which can cause contraction stress, microleakage, and adhesion failure. Adhesive restorations have several benefits, including the ability to preserve more healthy tissue and “reinforce” the remaining tooth structure. These benefits go beyond just being attractive. Materials and Methods: Eighty extracted human maxillary premolars were entrenched in a self-cured acrylic resin in a rubber mold cylinder (2.5 cm width-3 cm height). These were arbitrarily divided into 5 groups: 2 control groups (positive control group and negative control group) (n = 10) and 3 experimental (n = 20) groups (microhybrid composite, nanocomposite, and Giomer). The mesio-occluso-distal (MOD) cavities were prepared in 70 samples. After MOD cavities preparation, groups were further subdivided into two subgroups for bulk-fill and incremental methods. Universal Tofflemire Retainer and band were placed on the prepared cavities. The self-etch adhesive was applied on all aspects of the preparations and then it was light-cured using a light-curing unit for 15 s. Now, cavities were restored with different esthetic materials and methods. In the bulk-fill method, the MOD cavity was restored with a solitary increase of restorative material and light cured from all directions of tooth for 20 s each. In the incremental technique, the proximal box on both sides was reconstructed first in a gradual manner, in which two oblique increments and one horizontal increment were restored and treated for 20 s. Then, two oblique increments of material were used to reestablish the occlusal component, and it was once more light-cured for 20 s. Fracture resistance was checked using a steel bar with a diameter of 4.5 mm that was positioned in the middle of the occlusal surface and a crosshead speed of 3 mm/min, all of the samples were compressed axially loaded. Results: The fracture resistance of microhybrid composite resins in bulk technique was significantly higher than that of nanocomposites and Giomer. However, the fracture resistance of nanocomposite in the incremental method was significantly higher than the other two restorative materials. Conclusion: The quality of restoration depends both on the material and method used during the restoration procedure. Both factors are dependent on each other. Superior fracture resistance was shown by microhybrid composites when restored with the bulk-fill technique and nanohybrid composites when restored with the incremental technique.

Impact of a High-Power Light-Emitting Diode Unit With Reduced Curing Times on the Shear Bond Strength of Orthodontic Brackets and Their Adhesive Remnant Index Scores.

This study aims to evaluate the curing time minimally required for bonding stainless-steel (SS) brackets using a high-power light-emitting diode (LED) light curing unit (LCU) and examine the debonded enamel surface for adhesive remnant. Based on the LED LCU and curing time employed, 80 human maxillary first premolar teeth were equally segregated into four groups. Three groups were cured using a high-power LED unit (Guilin Woodpecker Medical Instrument Co., Ltd., Guilin, Guangxi, China) for one, two, and three seconds. The fourth group served as a control and was bonded with another intensive LED unit (Elipar™ S10 LED Curing Light; 3M, Saint Paul, Minnesota, United States) for 20 seconds. Transbond™ XT Light Cure Adhesive (3M, United States) adhesive was used for bonding the SS brackets. All the samples were exposed to shear bond strength (SBS) testing after a 24-hour immersion period in distilled water at 37°C. A stereomicroscope was used to examine and score the adhesive remnant on the debonded surface using a modified adhesive remnant index (ARI). Kruskal-Wallis-ANOVA and post-hoc Mann-Whitney U tests for multiple pairwise comparisons were performed to analyze the data. Time and intensity significantly affected the SBS (P<0.001). A higher SBS value (16.04 megapascals (MPa)) was obtained in the six-second group when compared to the three-second (11.58 MPa), one-second (10.69 MPa), and 20-second control (13 MPa) groups. The ARI was significantly affected by the curing method. Higher SBSs were recorded for the six-second group using the high-power LED. A greater ARI score is associated with a reduced curing duration and vice versa.

Shear bond strength of dual-cured resin cements on zirconia: The light-blocking effect of a zirconia crown

The presence of restorative material between resin cement and the light-curing unit can reduce light transmission. This study aimed to evaluate the effect of the light-blocking effect of zirconia crown on shear bond strength (SBS) between three dual-cured resin cements and the zirconia surface. Sixty zirconia specimens were prepared and divided into three groups according to the type of resin cement [RXU (RelyX Ultimate); SC2 (SmartCem2); MEC (Maxcem Elite Chroma)]. Each group was further divided into two subgroups, with or without a 1-mm-thick zirconia crown (n=10). The specimens were light-cured from five different directions for 20s each. All specimens were thermocycled 5000 times and subjected to SBS testing, followed by scanning electron microscope examination. The presence of a 1-mm-thick zirconia crown had no significant effect on the SBS in all resin cements. However, the SBS was significantly affected by type of resin cement. RXU showed the highest SBS (8.35MPa with crown; 8.57MPa without crown), followed by SC2 (5.48MPa with crown; 5.57 without crown) and then MEC (3.37MPa with crown; 4.04MPa without crown. Fractured surfaces exhibited varying degrees of mixed failure patterns. A 1-mm-thick zirconia crown material between the light source and the dual-cured resin cement did not significantly influence the SBS of the resin cements on the zirconia substrates. RXU exhibited the highest SBS regardless of zirconia crown coverage. With sufficient light-curing, dual-cured resin cements can be a good choice for zirconia crown cementation.

Correlation of Shear Bond Strength and Degree of Conversion in Conventional and Self-Adhesive Systems Used in Orthodontic Bonding Procedures.

(1) Background: Self-adhesive systems have been proposed for the orthodontic bonding with the intention to reduce the traditional three-component system. (2) Methods: The sample consisted of 32 extracted intact permanent premolars randomly divided into two groups (n = 16). In Group I the metal brackets were bonded with Transbond XT Primer and Transbond XT Paste. In Group II the metal brackets were bonded with GC Ortho connect. The resin was polymerized for 20 s from two directions (mesial and occlusal) using a Bluephase light-curing unit. The shear bond strength (SBS) was measured using a universal testing machine. Immediately after SBS testing, Raman microspectrometry was performed for each sample to calculate the degree of conversion (DC). (3) Results: There was no statistically significant difference in the SBS between the two groups. A significantly higher DC (p < 0.001) value was recorded in Group II, in which the brackets were bonded with GC. Very weak or no correlation (0.01) was recorded between SBS and DC in Group I and moderate positive correlation was recorded in Group II (0.33). (4) Conclusions: No difference was found in SBS between the conventional and two-step systems used in orthodontics. The two-step system demonstrated higher DC compared to the conventional system. There is a very weak or moderate correlation between DC and SBS.

Can different polymerization times affect the surface microhardness, water sorption, and water solubility of flowable composite resins?

This in vitro study evaluated and compared the effects of different polymerization times on the surface microhardness, water sorption, and water solubility of flowable composite resins. Three flowable composite resins [Es Flow (ESF), IGOS Flow (IGF), Estelite Flow Quick (EFQ)] were tested in this study. Each flowable composite resin (n = 7) was polymerized in a disc-shaped mould (1x10 mm) with an LED light-curing unit (D Light Pro) for two different times (20 and 40 sec.). The top surfaces of all specimens were polished (Sof-Lex). The surface microhardnesses of the flowable composite resins were measured with a Vickers HMV microhardness tester. Water sorption and water solubility were calculated according to the ISO 4049 standard. One-way ANOVA and post hoc Tamhane, Dunnett, and Tukey tests were used in the statistical analyses. Pearson’s and Spearman’s rho correlation tests were used to assess possible correlations between the different variables. The results were evaluated with a significance of p&lt;0.05. In terms of microhardness, a significant difference was found between materials at the same polymerization times (p&lt;0.05). All materials showed water sorption of less than 40 µg/mm3 and water solubility of less than 7.5 µg/mm3 by following ISO 4049. The correlations among surface microhardness, water sorption, and water solubility showed that the differences were determined by the materials and the polymerization times. The physical properties of all flowable composite resin materials were enhanced after polymerization for twice the time recommended by the manufacturers.

Toward Optimum Light Curing of Resin Composite Restorations: A survey on Current Awareness and Practice among General Dentists in Saudi Arabia

Introduction: This study aimed to assess the current awareness and practices of resin composite light curing of general dental practitioners (GDPs) in Saudi Arabia and to set several evidence-based recommendations to improve the quality of the outcome of concern. Methods: An online questionnaire was created. Two hundred and fifty email invitations were sent to GDPs appointed in general governmental hospitals in five main cities in Saudi Arabia to join the survey voluntarily and anonymously. The survey consisted of 24 questions classified into the following domains: 1-Demographic criteria 2- frequency and technical aspects of resin composites application 3- criteria of the currently used light curing units and curing light. Descriptive statistics and chi-square test were used to analyse the obtained responses. Results: One hundred and fifty-six responses were received. A significant number of GDPs are significantly satisfied with the quality of their light curing, not aware of the thermal hazards of light curing, and do not check power output of their LCUs (light curing units) (P&lt;0.05). An insignificant number of respondents use eye shields for eye protection during light curing. Conclusion: There was no uniform light curing protocol followed by respondent GDPs. GDPs in Saudi Arabia should improve their knowledge and clinical skills of light-curing resin composite.

Effects of Infection Control Barriers on Light Output from a Dental Light-Curing Unit Used in Various Positions

Light-curing units (LCUs) are often subject to clinician-determined factors such as infection control barriers (ICBs) and different positionings of the light tip that may reduce their radiant exposure. The objective of this study was to investigate the individual and cumulative effects of ICBs and LCU positioning on light output. One LCU was used, in combination with five different ICBs and five different distances and angles. ICBs were also tested when placed correctly to manufacturers’ guidelines, and with creases or seams obstructing the light tip. All variables were tested in isolation and in combination with other variables. Measurements were taken from a laboratory-grade spectrometer, giving values of radiant exposure, irradiance and spectral emission. All ICBs, angles and distances showed significant reductions in light output compared to the control (p &lt; 0.001). With increasing angle and distance, the light output was decreased further, with the greatest reduction of 80.6% from the control seen at 40° and 8 mm with an incorrectly placed ICB. When used with an ICB, an increasing angle also showed a protective relationship on the light output. When ICBs are used or when an increase in distance/angle is unavoidable, clinicians should consider compensating for the loss in radiant exposure by increasing curing times.

Effect of resin photopolymerization on primary teeth pulpal temperature change.

Purpose: The polymerization of restorative materials has the potential to increase pulpal temperature and may result in damage to the health of pulpal tissue. The aim of this study is to investigate the pulpal temperature change of primary teeth with two LED light-curing units (Valo Cordless®, EliparTM DeepCure-S) and three restorative groups (Filtek™ Bulk Fill Flowable, Filtek™ Z250 Universal Restorative and empty cavity) by using a microcirculation model.&#x0D; Material and Methods: Ten sound human maxillary second primary molars were used. Standardized Class V cavity preparations were performed with a dentin thickness of 1 mm and restorative groups were cured with LED light-curing units. The highest temperature point in the pulp chamber was recorded. A repeated measures ANOVA and paired samples t-test were used for analysis of the data (𝑝

3D-2D microleakage assessment of preheated bulk-fill composite resin applied with different parameters: a micro-CT analysis.

This study evaluated microleakage from class II cavities filled with bulk-fill composite preheated to different temperatures, applied at different thicknesses, and with different polymerization modes. A total of 60 mesio-occlusal cavity were drilled into the extracted human third molars at 2mm and 4mm thickness. Preheated bulk-fill composite resin (Viscalor; VOCO, Germany) was applied to the cavities at 68°C and 37°C after the adhesive resin was applied, and cured using standard and high-power light-curing modes of a VALO light-curing unit. An incrementally applied microhybrid composite was used as the control. The teeth were subjected to 2000 cycles of heating to 55°C and cooling to 5°C with a 30-s hold time. Then, they were immersed in a 50% silver nitrate solution for 24h and scanned with micro-computed tomography. Scanned data were processed using the CTAn software. Two (2D) and three (3D) dimensional analyses of leached silver nitrate were performed. The data's normality was assessed using the Shapiro-Wilk test before comparisons using a three-way analysis of variance. In both 2D and 3D analysis, bulk-fill composite resin preheated to 68°C and applied at 2mm thickness showed less microleakage. In the 3D analysis, restorations applied at 37°C and 4mm thickness in high-power mode showed significantly higher values (p < 0.001). Preheated bulk-fill composite resin can be applied at 68°C and effectively cured at both 2mm and 4mm thickness.

Comparison of two surface sealants on surface roughness and color stability of a commercially available denture base material – An in vitro study

Comparison of two surface sealants on surface roughness and color stability of a commercially available denture base material. Metallic discs were invested in a denture flask using dental stone to prepare a mold space. The denture base polymer and monomer were mixed in a ratio of 3:1 by volume and processed to form disc disc-shaped specimen. All the samples were finished, polished and checked for surface roughness. Sealants were applied on denture base material and cured using light-curing unit. All the 120 samples were divided into Group I(n=60) – Lucitone 199 and Optiglaze, and Group II(n=60) – Lucitone 199 and Easy Glaze. All the specimens were further subdivided into three groups based on the solution they were immersed i.e, coffee (n=20), tea (n=20), and distilled water (n=20). The specimens were checked for surface roughness and color stability for one week, one month, two months, three months, and four months. Samples were checked for surface roughness using optical profilometer and colour change using a spectrophotometer. The surface roughness of all the samples was within the normal range and tea-stained higher compared to coffee samples for color stability. The study concluded that Optiglaze is a better sealant compared to Easy Glaze with better properties like less surface roughness and good color stability of commercially available denture base materials. All groups had surface roughness less than the plaque accumulation threshold (0.20 µm). Beverages affected color stability of commercially available denture base materials after the application of two different surface sealants.

Effect of Using Manufacturer-recommended Exposure Times to Photo-activate Bulk-fill and Conventional Resin-based Composites.

To analyze the effect of using the resin-based composite manufacturer's recommended exposure time on the degree of conversion (DC), Knoop hardness (KH), and elastic modulus (E) of conventional and bulk-fill resin-based composites (RBCs). Three resin-based composites (RBCs) were tested: Tetric EvoCeram Bulk Fill (TET), Opus Bulk Fill APS (OPU), and RBC Vittra APS (VIT). They were photo-activated in 2 mm deep, 6 mm diameter molds for their recommended exposure times of 10 seconds, 20 seconds, or 40 seconds from four light-curing units (LCUs). Two delivered a single emission peak in the blue light region (Optilight Max and Radii-Cal) and two delivered multiple emission peaks in the violet and blue region (VALO Cordless and Bluephase G2). After 24 hours of dry storage at 37°C in the dark, the KH (Kgf/mm2), E (MPa) and DC (%) at the top and bottom surfaces of specimens (n=5) were measured and the results analyzed by 2-way analysis of variance (ANOVA) followed by a Tukey test (α=0.05). The irradiance (mW/cm2) and spectral irradiance (mW/cm2/nm) from the LCUs were reduced significantly (8-35%) after passing through 2.0 mm of RBC (p<0.001). The DC at the bottom of VIT and TET was less than at the top surface (p<0.001). OPU had the same DC at the top and bottom surface (p=0.341). The KH and E values at the top surface of VIT and TET were substantially higher than at the bottom (p<0.001). OPU exposed for 40 seconds achieved higher mechanical properties than TET that was photo-activated for 10 seconds (p<0.001). The opacity of different bulk-fill RBCs changed differently during the polymerization; OPU became more opaque, whereas TET became more transparent. When exposed for their recommended times, the 2 mm thick RBCs that used Ivocerin or the APS photoinitiator system were adequately photo-activated using either the single or multiple emission peak LCUs (p=0.341). After 24 hours' storage, all the 2 mm thick RBCs photo-cured in 6 mm diameter molds achieved a bottom-to-top hardness ratio of at least 80% when their recommended exposure times were used. TET, when photo-activated for 10 seconds, achieved lower mechanical properties than OPU that had been photo-activated for 40 seconds. The change in opacity of the RBCs was different during photo-activation.

Light-curing dental resin-based composites: How it works and how you can make it work

AimClinicians may become quite familiar with the rapid transformation of composite pastes to rigid solids as a routine phenomenon in operative dentistry. But they may still lack scientific understanding of how and why this happens. Efforts to learn scientifically about the interaction between light beams and resin-composites can significantly promote effective clinical placement of restorations. Neglect of such study can result in practical procedures of light curing that are inadequate or even seriously defective.MethodThis review addresses the underlying science and technology to elucidate how light curing works for dental resin-based composites, including—but not limited to—bulk fill types. This involves questions concerning: (a) the particle-wave understanding of light; (b) how photons can penetrate sufficiently deeply into bulk fill composites; (c) the necessary technology of LED light-curing units (LCUs); (d) the criteria for absorption of photons by photoinitiators to initiate free-radical addition polymerisation.ConclusionsThe implications for clinical practice are surveyed. These include design variables and selection criteria for LED-LCUs and guidelines on their use. This is to guide practitioners towards safe and effective light-curing procedures so that they can achieve optimal result for their patients.