Effect of High Irradiance on Depth of Cure of a Conventional and a Bulk Fill Resin-based Composite

Effect of Indenter Load on Vickers Microhardness and Indentation Depth of One Resin Composite

The load and size of the indentation may affect the hardness value. This study investigated the effect of the indentation size on the microhardness of one resin-based composite (RBC). Metal molds 4 mm deep and 12 mm in diameter were filled with Tetric EvoCeram Bulk Fill (Ivoclar) and light-cured for 10 s using a broad-spectrum LED curing light. The Vickers microhardness and the degree of conversion (DC) at the top and bottom surfaces were measured 24 h later before and after polishing the RBC. The microhardness measurements were made using 50, 100, 300 and 1000-gf loads with the same 8 s dwell time. The DC was measured in the same region using mid FT-IR spectroscopy. Repeated measures analysis of variance tests were used to determine if the surface (top vs. bottom) or the indenter loads had a significant effect on the VH, or if polishing affected the VH and the DC (alpha = 0.05). It was found that the indenter load did not affect the Vickers hardness of the unpolished top surface (p = 0.759), the polished top surface (p = 0.374), or the polished bottom surface (p = 0.083) of the Tetric EvoCeram Bulk Fill. Increasing the indenter load did increase the VH of the unpolished surface at the bottom (p < 0.0001). Polishing increased the DC by 13.5% at the top and by 46.7% at the bottom surface.

Efficiency of bulk-fill versus conventional resin-based composite in class II restorations: A dental student perspective

Purpose/objectives

The aim of the study was to evaluate the effect of two distinct light-polymerization protocols, used by dental students, on the placement time and polymerization efficiency of bulk-fill (BF) and conventional (CRC) resin-based composites (RBCs).

Methods

Thirty dental students participated in this study. Each student was asked to complete four Class II RBC restorations using two different types of RBCs (BF and CRC) paired with two distinct light-polymerization protocols: one using 1200 mW/cm2 irradiance (P1200) and one using 800 mW/cm2 irradiance (P800). Manufacturer instructions for curing times relative to these irradiance levels were adhered to. The restorations were retrieved, sectioned and Vickers microhardness (VMH) was measured at specific reading points. The placement time was recorded for each procedure. Multivariate analysis of variance and Bonferroni post hoc test were used for data analysis.

Results

Bulk-fill RBCs were associated with significantly shortened placement times (P < 0.001). VMH values of CRC-P800 were significantly higher compared to all other groups (P < 0.02). Across all groups tested, the VMH values at the deepest reading points exceeded those at the occlusal surfaces by over 80 %.

Conclusions

The use of BF RBCs with a P1200 light-polymerization protocol reduced students' procedural times while maintaining effective polymerization of the restorations.

Comparison of Blue and Infrared Light Transmission Through Dental Tissues and Restorative Materials

OBJECTIVES

The depth of cure using blue-light photocuring units (BL) is limited by tooth structure and qualities of the restorative material through which the activating wavelength must pass. Recent developments incorporate an infrared (IR) activated upconversion (UC) fluorescence of a lining agent filled with nanocrystals of NaYF4 and doped with YB+3 and Tm+3 that emit both blue and violet light locally at the interface of the liner and restorative resin. The purpose of this study was to evaluate the BL and 975 nm infrared (IR) light power transmission through dental tissues and restorative materials.

METHODS AND MATERIALS

Power transmissions of the IR laser (975 nm) and a monowave blue-only light-curing unit (Bluephase 16i) through dental tissues (enamel, dentin, and enamel/dentin junction, or DEJ), eight (8) various dental resin composites, and eight (8) dental ceramics, each at four thicknesses (1, 2, 3 and 4 mm) were evaluated (n=5) using a thermopile sensor (PM10, Coherent Inc) connected to a laser power meter (Fieldmate, Coherent Inc). Power transmission values of each light source and restorative material were subjected to analysis of variance and Tukey test at a pre-set alpha of 0.05.

RESULTS

A linear correlation (r=0.9884) between the supplied current and emitted IR power of the laser diode was found, showing no statistical power reduction with increased distances (collimated beam). For tooth tissues, the highest power transmissions for both light sources were observed using 1.0 mm enamel while the lowest values were found for 2.0 mm dentin and an association of 2.0 mm DEJ and 1.0 mm dentin. The only group where IR demonstrated significantly higher transmission when compared to BL was 1.0 mm enamel. For all resin composites and dental ceramics, increased thickness resulted in a reduction of IR power transmission (except for EverX Posterior fiber-reinforced composite and e.max HT ceramic). IR resulted in higher transmission through all resin composites, except for Tetric EvoCeram White. The highest BL transmission was observed for SDR Flow, at all thicknesses. Higher IR/BL ratios were observed for EverX Posterior, Herculite Ultra, and Lava Ultimate, while the lowest ratio was observed for Tetric EvoCeram White. Reduced translucency shades within the same material resulted in lower power ratio values, especially for BL transmission. Higher IR/BL ratios were observed for e.Max LT, VitaVM7 Base Dentin, and e.max CAD HT, while the lowest values were found for VitaVM7 Enamel and Paradigm C.

CONCLUSION

IR power transmission through enamel was higher when compared to blue light, while no difference was observed for dentin. The power transmission of IR was higher than BL for resin composites, except for a high value and low chroma shade. Fiber-reinforced resin composite demonstrated the highest IR/BL power transmission ratio. A greater IR/BL ratio was observed for lower translucency ceramics when compared to high translucency.

The Depth of Cure, Sorption and Solubility of Dual-Cured Bulk-Fill Restorative Materials

This study aimed to examine depth of cure (DoC), mass change, water sorption and solubility of dual-cured bulk-fill restorative materials (Surfil One and Activa) in comparison with a light-cured bulk-fill composite (Filtek One Bulk-Fill) and a resin-modified glass ionomer (Fuji II LC). Twenty specimens were prepared of each material using stainless steel molds designed with a slot (8 × 4 × 2 mm) and irradiated for either 20 or 40 s. The Vickers hardness (VHN) was measured at every 0.5 mm to assess the DoC after 24 h of storage at 37 °C. The depth of cure was reported as the depth corresponding to 80% of the maximum Vickers hardness. Disc-shaped specimens were prepared of each material (n = 5) to investigate mass change, sorption and solubility after 4 months of water storage. The data were analyzed using a two-way and one-way analysis of variance (ANOVA) followed by the Tukey post hoc test (p ≤ 0.05). Fuji II LC had the greatest DoC while Activa had the lowest. The two different irradiation times did not demonstrate a significant difference in DoC for all dual-cured materials (p > 0.05). Fuji II LC had the highest sorption while Filtek One showed the lowest. Surefil One and Fuji II LC had a negative solubility. This study concluded that dual-cured materials showed different depth of cure values despite having the same setting reaction. Both materials exhibited a high water sorption, which might jeopardize their dimensional stability and effect their clinical performance.

Effect of Type of Resin Composite Material on Porosity, Interfacial Gaps and Microhardness of Small Class I Restorations

AIM

This study aimed to compare the best restorative approach for the conservative class I cavity by comparing flowable and nanohybrid composites versus the placement technique regarding surface microhardness, porosity, and presence of interface gaps.

MATERIALS AND METHODS

Forty human molars were divided into four groups (n = 10). Standardized class I cavities were prepared and restored using one of the following materials: Group I - Flowable composite placed by incremental technique; group II - Flowable composite placed in one increment; group III - Nanohybrid composite placed by incremental technique; and group IV - Nano-hybrid composite placed in one increment. After finishing and polishing, specimens were sectioned into two halves. One section was chosen randomly for the Vickers microhardness (HV) evaluation and the other section was used for the assessment of porosities and interfacial adaptation (IA).

RESULTS

The surface microhardness range was 28.5-76.2 (p < 0.05), mean pulpal microhardness range was 27.6-74.4 (p < 0.05). Flowable composites had lower HV than conventional counterparts. The mean pulpal HV of all materials exceeded 80% of occlusal HV. Restorative approaches did not statistically differ in porosities. However, IA percentages were higher in flowable materials compared to nanocomposites.

CONCLUSION

Flowable resin composite materials have lower microhardness than Nanohybrid composites. In small class I cavities, the number of porosities was similar between the different placement techniques and the interfacial gaps were highest in the flowable composites.

CLINICAL SIGNIFICANCE

The use of nanohybrid resin composite to restore class I cavities will result in better hardness and less interfacial gaps compared to flowable composites.

The effect of filling technique on the cuspal strain, polymerization shrinkage stress, enamel crack formation and depth of cure of restored molars

OBJECTIVE

Evaluate the effect of different restorative filling techniques on the residual shrinkage stress (ShrS), cuspal strain (CS), depth of cure (DC), and enamel crack formation (Ec) in molars with MOD restorations.

METHODS

Post-gel shrinkage, elastic modulus, compressive and diametral tensile strength of the Filtek One Bulk Fill composite were calculated. Sixty molars with MOD preparations were restored using four filling techniques: Bulk; Horizontal; Oblique; Natural enamel and dentin substitution (NEDS) technique. CS was measured using a strain gauge (n = 10). The DC (n = 5) was measured using Knoop hardness. Shrinkage stress/strain was analyzed using 3D finite element analysis. The Ec analysis was carried out by transillumination. Two-way ANOVA with repeated measures and Tukey's HSD test (α = 0.05) was performed for the CS data. Two-Way ANOVA and Tukey's HSD test was performed for the DC data (α = 0.05).

RESULTS

CS was higher at the lingual cusp for the horizontal and NEDS technique. No statistical difference was found between the buccal and lingual CS values for the Bulk (p = 0.367) or Oblique techniques (p = 0.192). CS values were lower for the Bulk. More enamel cracks were found for the Bulk. DC was lower at 4 mm regardless the filling technique. The Horizontal showed the highest ShrS values. The Bulk generated the lower ShrS values.

SIGNIFICANCE

A Bulk technique caused the lowest shrinkage stress/strain. An Oblique technique yielded the best balance between stress, strain and crack formation. NEDS technique is a good alternative to decrease the number of increments while maintaining the stress levels nearby the Oblique technique.

[Light-curing effectiveness using led lamps: a review]

Introduction

LED lamps have a new light-curing technology which can be monowave or polywave, which allows it to reach more initiators such as camphorquinone, Lucirin TPO and Propanodione, which have a wide variety of advantages and disadvantages. These lamps have evolved over time, as have different ergonomics, longevity, systems and quality standards.

Objective

The objective of this literature review is to improve the clinician on the proper use of different LED lamps and how they influence the efficiency of resin photopolymerization.

Material and methods

Extensive research has been carried out in the existing literature on this topic. From the beginning of this information until April 18, 2022, the bibliographic search carried out includes 86 articles published in the Medline database through PubMed, LILACS, Science Direct and SciELO, and there is no language restriction.

Results

The photopolymerization effects of Polywave and Monowave LED lamps present significant differences between the compressive strength of the light-cured resin, with single-wave and polyvalent LED lamps where the types of light and lamp directly influence the compressive strength of the resin. composite resins.

Conclusion

The type of light and lamp directly affects the efficiency of the photopolymerization of the composite resin, so it is concluded that LED lamps with single wave technology (Monowave) produce a greater depth of photopolymerization than those with multiple wave technology (Polywave).

Evaluation of irradiance and radiant exposure on the polymerization and mechanical properties of a resin composite

The objective of the present study was to evaluate the effect of irradiance and radiant exposure on the chemical-mechanical properties of a resin composite. A micro-hybrid resin composite (Clearfil AP-X, Kuraray) was investigated under two different irradiances: low (300 mW/cm2) and high (800 mW/cm2) and radiant exposures: 8 and 16 J/cm2. Four groups, named Low 8 J/cm2, High 8 J/cm2, Low 16 J/cm2, and High 16 J/cm2 were tested, and their flexural strengths, elastic moduli, depths of cure, and degrees of conversion were evaluated. Data were analyzed using two-way ANOVA and Tukey's test. A multiple linear regression model was used to correlate the irradiance and radiant exposure with dependent variables (α = 0.05). Irradiance and radiant exposure were found statistically significant for all dependent variables. The interaction between the factors was statistically significant only for the degree of conversion and elastic modulus. Group Low 16 J/cm2 exhibited a significantly superior performance in all the evaluated properties. Barring the degree of conversion, no significant differences were observed among the properties evaluated between the Low 8 J/cm2 and High 8 J/cm2 groups. The adjusted R2 values were high for the depth of cure and degree of conversion (0.58 and 0.96, respectively). Both irradiance and radiant exposure parameters play an important role in establishing the final properties of a micro-hybrid resin composite. Irradiance has a greater influence under higher radiant exposures.

Influence of Matrix Type on Marginal Gap Formation of Deep Class II Bulk-Fill Composite Restorations

Background: To test the hypothesis that transparent matrices result in more continuous margins of bulk-fill composite (BFC) restorations than metal matrices. Methods: Forty standardized MOD cavities in human molars with cervical margins in enamel and dentin were created and randomly assigned to four restorative treatment protocols: conventional nanohybrid composite (NANO) restoration (Tetric EvoCeram, Ivoclar Vivadent, Schaan, Liechtenstein) with a metal matrix (NANO-METAL) versus transparent matrix (NANO-TRANS), and bulk-fill composite restoration (Tetric EvoCeram Bulk Fill, Ivoclar Vivadent, Schaan, Liechtenstein) with a metal matrix (BFC-METAL) versus transparent matrix (BFC-TRANS). After artificial aging (2500 thermal cycles), marginal quality was evaluated by scanning electron microscopy using the replica technique. Statistical analyses were performed using the Mann−Whitney U-test and Wilcoxon test. The level of significance was p < 0.05. Results: Metal matrices yielded significantly (p = 0.0011) more continuous margins (46.211%) than transparent matrices (27.073%). Differences in continuous margins between NANO (34.482%) and BFC (38.802%) were not significant (p = 0.56). Matrix type did not influence marginal gap formation in BFC (p = 0.27) but did in NANO restorations (p = 0.001). Conclusion: Metal matrices positively influence the marginal quality of class II composite restorations, especially in deep cavity areas. The bulk-fill composite seems to be less sensitive to the influence of factors such as light polymerization and matrix type.

Microleakage in class II restorations of two bulk fill resin composites and a conventional nanohybrid resin composite: an in vitro study at 10,000 thermocycles

Background

The contraction presented by resin composites causes an increase in stress at the tooth-resin interface, causing micro-gaps that allow microleakage. This study aims to evaluate the degree of in vitro marginal microleakage in class II restorations with two bulk fill resin composites compared to a conventional nanohybrid resin composite.

Methods

The present study was an in vitro experimental design. A total of 30 standardized class II cavities were prepared in 15 human molars (mesially and distally). These cavities were later distributed in 3 groups according to the type of resin. Groups A and B were restored with bulk fill resin composites (Filtek—3 M/ESPE and Tetric N-Ceram—Ivoclar/Vivadent respectively) in a single increment of 4 mm. Group C was restored with the Filtek Z350 XT – 3 M/ESPE resin composite and two increments of 2 mm. Later, the restorations were subjected to 10,000 thermocycles between 5 °C to 55 °C and immersed in a silver nitrate solution (1 M for 24 h). The crowns were then sectioned mesiodistally and observed under the stereomicroscope to determine the degree of marginal microleakage at the occlusal and cervical areas. The results were analyzed with the Kruskal–Wallis and the Mann–Whitney U statistical tests.

Results

There were no statistically significant differences regarding the degree of microleakage between the three types of resin composites in the occlusal and cervical areas (p > 0.05). Similarly, there were no significant differences after comparing each resin type in its occlusal and cervical area (p > 0.05).

Conclusion

Filtek Bulk Fill and Tetric N-Ceram Bulk Fill resin composites showed no statistically significant differences with the conventional nanohybrid resin composite Filtek Z350XT at both occlusal and cervical areas.

Effect of extended light activation and increment thickness on physical properties of conventional and bulk-filled resin-based composites

OBJECTIVES

To evaluate the biaxial flexural strength (BFS), flexural modulus (BFM), and Knoop microhardness (KHN) of incremental and bulk-filled resin-based composites (RBCs) using extended curing exposure times.

MATERIALS AND METHODS

Disc specimens (n = 8; 6-mm diameter) were fabricated using three stacked molds (0.5-mm thick for the top and bottom molds, and a 1-mm-thick center mold for the conventional and 3-mm thick for the bulk-fill RBCs). Conventional (Tetric EvoCeram/TCE and Filtek Z250/FIZ) and bulk-fill RBCs (Tetric EvoCeram Bulk Fill/TBF and Filtek One Bulk Fill Restorative/FOB) were evaluated. The stacked RBC-filled molds were light-cured for (1) the manufacturer-recommended exposure (MRE) duration; (2) 50%, and (3) 100% extension of the MRE. The BFS, BFM, and KHN of the top and bottom discs were measured. BFS and BFM were analyzed by three-way ANOVA (material*curing time*depth) and Tukey's post hoc (α = 0.05). KHN was analyzed by two-way ANOVA (curing time*depth) and Tukey's post hoc (α = 0.05).

RESULTS

Extending the exposure duration did not change the BFS and BFM on the top of the RBCs, but the BFS and KHN increased at the bottom of bulk-fill RBCs. For the conventional RBCs, TCE showed the highest increase on BFS at the bottom, going from 53.6 MPa at T1 to 69.9 at T3. Among the bulk-fill RBCs, FOB presented the highest increase on the bottom BFS (T1: 101.0 ± 19.9 MPa, T3: 147.6 ± 12.9 MPa). For all RBCs and exposure times, BFS and KHN were lower at the bottom. Only FIZ and FOB reached a bottom-to-top hardness ratio of 80%, at T3 and T2.

CONCLUSION

A significant increase on the BFS and KHN on the bottom of bulk-fill RBCs can be observed when the time of exposure to the curing light is double the MRE. However, extended exposure does not eliminate differences on the BFS and KHN between the shallow and deep regions of RBCs. TCE and TBF failed to reach an acceptable B/T hardness ratio at all evaluated exposure times.

CLINICAL RELEVANCE

Mechanical properties of RBCs can be affected by insufficient polymerization, specially at deeper regions of the increment. Therefore, clinicians should consider applying twice the MRE to curing-light to polymerize the maximal increment thickness of bulk-fill RBCs.

Comparative evaluation of the degree of conversion of four different composites polymerized using ultrafast photopolymerization technique: An in vitro study

Context

Lower degree of conversion (DC%) of monomer to polymer in a resin composite restoration could be a health hazard for the patient as well as it could affect the longevity of the restoration.

Aims

This study is aimed to compare and evaluate the DC% of four different composites polymerized using ultrafast photopolymerization.

Settings and Design

In-vitro study.

Materials and Methods

A total of 40 disc-shaped composite samples were used in the study. Twenty samples were prepared for each group using 2 mm height and 6 mm diameter Tygon tube as a matrix. All of the composites were cured using the Woodpecker i Led light-curing unit with an intensity of 2300-2500 mW/cm² (TURBO mode). Samples in Group 1 were cured for 1 s and samples in Group 2 were cured for 3 s. Each group had 4 subgroups of five samples of the 4 resin composites tested. After photo-activation, the specimens were stored under dark dry conditions at room temperature for 24 h before testing. The DC% was measured using Fourier-transform infrared spectroscopy.

Statistical Analysis Used

The DC% were analyzed using ANOVA, and Tukey HSD post hoc test using IBM SPSS 21 software.

Results

Among the experimental groups, Group 2 showed a higher DC% which ranges from 93.7% to 95.4% than Group 1 which ranges from 58.5% to 65.5%. There was a statistically significant difference in the DC% among the materials tested (P < 0.05).

Conclusions

Within the limitations of the study, it was concluded that composites cured for 3 s showed a higher DC% which ranges from 93.7% to 95.4% than those cured for 1 s. The DC% also varied among the four different composites tested.

Effect of Operator Experience on Ability to Place Sequential, 2-mm-thick Increments of Composite

Because an operator has only about one chance out of three to place a composite increment within this clinically acceptable range, clinicians are advised to use an instrument (e.g., a periodontal probe with a 2-mm mark) to estimate the thickness of each increment of composite they place.

SUMMARY

Objective: To measure and compare the effect of operator experience in their ability to place composite in increments that are 2 mm thick.Methods and Materials: Fifteen volunteers from each class of freshmen, sophomores, juniors, and senior dental students and 15 clinical faculty (total number of volunteers = 75) were asked to restore a Class I preparation that was 5 mm in diameter and 8 mm deep from the cusp tips using three increments of composite that were each to be 2 mm thick. Once completed, the models were sectioned, and the thickness of each increment was measured. A repeated-measures analysis of variance (pre-set α=0.05) was used to compare the mean increment thickness with respect to operator experience level and increment sequence number. In addition, the proportion of operators placing clinically acceptable increments (between 1.75 and 2.25 mm thick), as well as the proportions from each group who placed increments that either were thinner or thicker than this range, was determined using nonparametric analyses.Results: Overall, there was an increasing trend for groups with a higher experience level to provide mean incremental thickness values close to 2 mm. However, the likelihood of placing an increment that was thicker or thinner than the manufacturer-recommended thickness was not significantly different. Regardless of the increment value, only about one-third of the increments placed fell within the desired range of 1.75 to 2.25 mm.Conclusions: Operator experience had no overwhelming significant influence on the ability to place increments of composite that were between 1.75 and 2.25 mm thick. An operator has only about one chance out of three to place a composite increment within this clinically acceptable range when using no external measurement system.

Light Transmittance and Depth of Cure of a Bulk Fill Composite Based on the Exposure Reciprocity Law

The objective of this study was to evaluate the effect of the exposure reciprocity law of a multi-wave light-emitting diode (LED) on the light transmittance (LT), depth of cure (DOC) and degree of conversion in-depth (DC) of a bulk fill composite. A bulk fill composite (EvoCeram® bulk fill, Ivoclar Vivadent) was photoactivated using the multi-wave LED (VALO™ Cordless, Ultradent). The LED was previously characterized using a spectrophotometer to standardize the time of exposure when using the Standard or Xtra-Power modes with the same radiant exposure of 20J/cm2. LT was evaluated through samples of the bulk fill composite every millimeter till 4 mm in-depth. DOC was evaluated according to the ISO 4049. DC of the central longitudinal cross-section from each sample of the DOC test was mapped using FT-NIR microscopy. Data were statistically analyzed according to the experimental design (α=0.05; ß=0.2). The radiant exposure in the violet wavelength range for Standard and Xtra-Power was 4.5 and 5.0 J/cm2, respectively; for the blue wavelength range the radiant exposure for Standard and Xtra-Power was 15.5 and 15.0 J/cm2, respectively. There was no statistical difference in the DOC using Standard or Xtra-Power light-curing modes, but the DOC was lower than the claimed by the manufacturer (4 mm). The DC was not significantly affected by the light-curing mode up to 4 mm in depth (p>0.05). According to exposure reciprocity law, the reduction in exposure time using the same radiant exposure did not affect the depth of cure of the bulk fill composite.

Awareness and Utilization of Bulk-Fill Composites among Dental Practitioners in Saudi Arabia

Objective:

The aim of this study was to assess the knowledge and utilization of Bulk-Fill (BF) resin composites among dental practitioners in Saudi Arabia.

Materials and Methods:

An online survey was distributed through Twitter, Instagram and WhatsApp applications among dentists in Saudi Arabia. A 31-item questionnaire covering personal data, general knowledge and utilization of BF composites was used. Responses were collected and analyzed for trends. A knowledge scale was developed based on answers with specific weight for each correct answer provided by the participants. A score of ≥ 50% was considered as a satisfactory knowledge level for participants. Statistical analysis was conducted using One-sample Z- and Chi-square tests followed by Bonferroni correction at 0.05 significance level.

Results:

The total number of participants of the survey was 183, of which 41.5% had some knowledge and utilized BF composites in their practice. Only 9.84% of the participants score ≥ 50% on the knowledge scale. A significantly low proportion recognized accurately the compositional difference between BF and conventional resin composite as well as the minimum irradiance values needed for proper polymerization of BF. There was no effect for gender or years of experience on the knowledge or utilization of BF materials (p-value = 0.172).

Conclusion:

The proportions of practitioners with adequate knowledge and utilization of BF materials were very low. Additional focus must be provided in order to expose graduating dentists to advances in resin composite formulations.

Flexural strength and microhardness of bulk-fill restorative materials

BACKGROUND

Bulk-fill materials can facilitate the restorative procedure mainly for deep and wide posterior cavities. The purpose of this study was to evaluate flexural strength (biaxial flexural strength [BFS]) and microhardness (Knoop microhardness [KHN]) at different depths of bulk-fill materials.

METHODS

Five bulk-fill materials were tested: two light-curable composite resins, one dual-cure composite, one bioactive restorative, and a high-viscosity glass ionomer. A conventional composite was used as control. BFS and KHN were tested at different depths. Data was analyzed by two- and one-way ANOVAs, respectively and Tukey's post-hoc (α=0.05).

RESULTS

The high-viscosity glass ionomer material presented the lowest BFS at all depths. KHN for the two light-curable and the dual-cure bulk-fill resin composites was reduced following an increase in restoration depth, while the conventional composite, the bioactive material, and the high-viscosity glass ionomer were not affected.

CONCLUSION

There are differences in the properties of the tested materials at 4 mm depth, showing that the studied properties of some materials vary according to the cavity depth, although the results are material dependent.

CLINICAL SIGNIFICANCE

Mechanical properties of light-cured, bulk-fill materials may be affected by inadequate polymerization. Clinicians should consider complementary strategies to achieve adequate polymerization at high-increment depths.

Vickers Hardness and Shrinkage Stress Evaluation of Low and High Viscosity Bulk-Fill Resin Composite

The aim of this in vitro study was to evaluate the hardness and shrinkage stress (SS) of six bulk-fill resin composites. To evaluate microhardness (MH), ten 6 mm specimens were prepared using a metal mold for each selected bulk-fill resin composite and irradiated from the top side for 40 s using an LED light. After 24 h of storage, Vickers MH was evaluated on the upper, lower and lateral sides of the specimens. SS evaluation was then performed with a universal machine, which evaluated the contraction force generated by a bulk-fill composite specimen placed between two metal cylinders during and after light curing. The results were evaluated with a one-way ANOVA test with a post-hoc Bonferroni test and linear regression analysis (p < 0.05). All materials showed a significant MH decrease between the top and bottom surfaces. However, the bulk-fill materials tested performed differently when considering lateral depth progression. ANOVA tests for SS evaluation showed that both SDR and Venus Bulk Fill had significantly lower stress during irradiation than other tested materials. Further, MH decrease became significantly lower from the top surface at different depths in each tested group. Among the different resins, Venus Bulk Fill and SDR showed not only inferior hardness, but also a significant reduction in SS.

The effect of rapid high-intensity light-curing on micromechanical properties of bulk-fill and conventional resin composites

Rapid high-intensity light-curing of dental resin composites is attractive from a clinical standpoint due to the prospect of time-savings. This study compared the effect of high-intensity (3 s with 3,440 mW/cm²) and conventional (10 s with 1,340 mW/cm²) light-curing on micromechanical properties of conventional and bulk-fill resin composites, including two composites specifically designed for high-intensity curing. Composite specimens were prepared in clinically realistic layer thicknesses. Microhardness (MH) was measured on the top and bottom surfaces of composite specimens 24 h after light-curing (initial MH), and after subsequent immersion for 24 h in absolute ethanol (ethanol MH). Bottom/top ratio for initial MH was calculated as a measure of depth-dependent curing effectiveness, whereas ethanol/initial MH ratio was calculated as a measure of crosslinking density. High-intensity light-curing showed a complex material-dependent effect on micromechanical properties. Most of the sculptable composites showed no effect of the curing protocol on initial MH, whereas flowable composites showed 11–48% lower initial MH for high-intensity curing. Ethanol/initial MH ratios were improved by high-intensity curing in flowable composites (up to 30%) but diminished in sculptable composites (up to 15%). Due to its mixed effect on MH and crosslinking density in flowable composites, high-intensity curing should be used with caution in clinical work.

Color Stability and Micro-Hardness of Bulk-Fill Composite Materials after Exposure to Common Beverages

Objectives: To assess the color stability and surface microhardness of Bulk-Fill composite materials available in the Saudi Arabia market. Methods: Five composite materials (Filtek Z350, Filtek Bulk-Fill, Tetric N-Ceram Bulk-Fill, Sonic Fill 2, and SDR) were investigated. Samples (n = 20; 10 mm in diameter and 2 mm in thickness) were fabricated using a stainless-steel mold and were immersed in tea, coffee, berry juice, and distilled water (control). Baseline (T₀) shades of specimens were recorded using a spectrophotometer and after 10 (T₁), 30 (T₂), 60 (T₃), and 90 days (T₄) of immersion. Measurements were obtained against a black background and CIE L*a*b* data was used to calculate ΔE for each group. Vickers microhardness values were obtained at T₀ and T₄. Data was analyzed using mixed model repeated measure ANOVA at 0.05 significance level. Results: Time, material, and solution effects have statistically significant effect on ΔE. Tea was the most staining solution. Z350 was associated with the highest ΔE values while SDR showed the lowest values. No other materials showed significant difference between each other. Solutions were statistically different from each other. All materials were different from each other regarding microhardness. Conclusion: Bulk-Fill materials showed more color stability but lower microhardness values compared to universal resin control.

Comparisons of ISO depth of cure for a resin composite in stainless-steel and natural-tooth molds

The purpose of this study was to compare the depth of cure (DOC) of a resin-based composite (RBC) using the ISO DOC protocol with stainless-steel and molar-tooth molds (4 mm cylindrical cavity). The tooth mold included testing with and without the occlusal surface being covered with black tape around the cavity opening. The RBC was cured with either halogen (HAL) or light-emitting diode (LED) light. The results showed that specimens made in the non-taped tooth mold had DOCs that were significantly greater (28%-35%) than those in the stainless-steel mold. The taped tooth mold also produced significantly greater DOCs, but only by 6%-8%. Knoop hardness (KNH) measurements along the central axis of the RBC specimens showed that depths for 80% of maximum hardness were substantially greater than those determined by the ISO DOC protocol but were limited to the center and quickly dropped below 80% in a lateral direction. The KHN mapping for each of the three molds found that the ISO DOCs could validate a KHN of ≥80% across the RBC to the periphery, only for the non-taped tooth mold. This was due to light incident on the tooth surrounding the RBC being scattered into the RBC.

Depth of cure of high-viscosity bulk-fill and conventional resin composites using varying irradiance exposures with a light-emitting diode curing unit

The purpose of this study was to determine the depth of cure (DOC) of three resin-based composites (RBCs) using varying irradiance exposures with a corded light-emitting diode curing unit. DOCs for Filtek Z250, TPH Spectra, and Tetric EvoCeram Bulk Fill were determined using the International Organization for Standardization (ISO) Standard 4049. The RBCs were light-polymerized using three different power modes and manufacturer-recommended curing times. Irradiance was determined using a spectrometer sensor and the total energy density was calculated for each power mode and concomitant polymerization time. The DOC data were analyzed with a two-way analysis of variance and Tukey's post hoc test. Tetric EvoCeram Bulk Fill produced significantly greater DOCs than TPH and Z250 (P < 0.05) for all three power mode settings. Overall, the DOC of Tetric EvoCeram Bulk Fill was greater than those of TPH and Z250 at all power settings, but the individual RBCs did not show a significant DOC difference among the three power settings (P > 0.05).

Effects of Light Attenuation through Dental Tissues on Cure Depth of Composite Resins

Objective

Polymerization of light-cured resin-based materials is well documented; however, the intensity of the activating light can be reduced by passage through air, dental structure, or restoration compromising the physical properties of the restoration. The aim of this study was to evaluate the depth of cure of different light cured composite resins polymerized directly or transdental, through enamel and enamel/dentin tissues.

Material and methods

Five composite resins were selected for this experiment: SureFil SDR, Dentsply (SDR), Filtek Supreme Plus, 3M ESPE (FSP), Aelite LS, Bisco (ALS), Filtek LS, 3M ESPE (FLS), and TPH, Dentsply (TPH). Thirty specimens of each material were prepared with 2- or 4-mm thickness. The specimens were light-cured (Elipar 2500, 3M ESPE) for 40 sec using three different protocols: direct or transdental, through a disc of enamel with 1 mm of thickness, and a disc of enamel and dentin with 2 mm of thickness. Eight Vickers microhardness (VH) measurements were taken from each specimen, four on top and four on bottom surface (Micromet, Buehler, 100 g per 15 sec). Data was analyzed with ANOVA three-way, Tukey HSD post-hoc (α = .05).

Results

Bottom surfaces of specimens exhibited statistically significant lower Vickers microhardness than the top surfaces for all composite resin evaluated, regardless of the curing conditions, except for the SDR when direct light-cured. Transdental light curing through enamel/dentin layer, significantly decreased VH (P<0.05) on the bottom surface of all composite groups.

Conclusion

The results of this study showed that light-curing attenuation of dental structures negatively affect the micro-hardness of composite resins.

The Combination of CQ-amine and TPO Increases the Polymerization Shrinkage Stress and Does Not Improve the Depth of Cure of Bulk-fill Composites

OBJECTIVES

To evaluate the effect of combining camphorquinone (CQ) and diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO) on the depth of cure and polymerization shrinkage stress of bulk-fill composites.

METHODS AND MATERIALS

Experimental bulk-fill composites were produced containing equal molar concentrations of either CQ-amine or CQ-amine/TPO. The degree of in-depth conversion through each millimeter of a 4-mm-thick bulk-fill increment was evaluated by Fourier transform near-infrared microspectroscopy using a central longitudinal cross section of the increment of each bulk-fill composite (n=3). Light-transmittance of the multi-wave light-emitting diode (LED) emittance used for photoactivation (Bluephase G2, Ivoclar Vivadent) was recorded through every millimeter of each bulk-fill composite using spectrophotometry. The volumetric shrinkage and polymerization shrinkage stress were assessed using a mercury dilatometer and the Bioman, respectively. The flexural modulus was also assessed by a three-point bend test as a complementary test. Data were analyzed according to the different experimental designs (α=0.05 and β=0.2).

RESULTS

Up to 1 mm in depth, adding TPO to CQ-based bulk-fill composites increased the degree of conversion, but beyond 1 mm no differences were found. The light-transmittance of either wavelengths emitted from the multi-wave LED (blue or violet) through the bulk-fill composites were only different up to 1 mm in depth, regardless of the photoinitiator system. Adding TPO to CQ-based bulk-fill composites did not affect volumetric shrinkage but did increase the flexural modulus and polymerization shrinkage stress.

CONCLUSION

Adding TPO to CQ-based bulk-fill composites did not increase the depth of cure. However, it did increase the degree of conversion on the top of the restoration, increasing the polymerization shrinkage stress.

Physical and photoelastic properties of bulk-fill and conventional composites

Purpose

This study evaluated the influence of thickness increment on degree of conversion (DC), Knoop microhardness (KHN), and polymerization-shrinkage stress (PSS) by photoelasticity of three dental composites.

Methods

For DC and KHN, 45 samples were prepared and divided into nine groups (n=5), according to composite (microhybrid [Filtek Z250 - Z250], bulk-fill flowable [SureFil SDR Flow - SDR], and nanohybrid composite [N’Durance - NDU]) and increment thickness (1, 1.5, and 3 mm). PSS was measured by photoelastic analysis. Composites were placed into a photo-elastic model cavity and light-cured. DC and KHN data were subjected to two-way ANOVA and Bonferroni post hoc test. PSS results were qualitatively evaluated through Kruskal–Wallis test.

Results

SDR showed the highest DC values. At top and bottom surfaces, the highest KHN was obtained by Z250. Z250 showed higher PSS than SDR in 1.5 mm increments. NDU showed higher PSS than SDR in 3 mm increments.

Conclusion

The bulk-fill composite demonstrated better DC and similar KHN and PSS in deeper layers compared to conventional composites. Bulk-fill composites may perform as well as conventional nanohybrid and microhybrid composites.

Infection Control Barrier and Curing Time as Factors Affecting the Irradiance of Light-Cure Units

Objective

The objective of the study is to investigate the effect of infection control barrier (ICB) and curing time on irradiance of light cure units (LCUs).

Methods

Irradiance (mW/cm²) of the LCUs at a government dental school were recorded with and without ICB at 0 (T₀), 10 (T₁₀), and 20 (T₂₀) seconds using a digital radiometer. Data were analyzed using IBM^® SPSS^® Statistics Version 17 for Windows software for the analysis of variance and Bonferroni methods at 0.05 significance level.

Results

Using ICB resulted in a statistically significant effect on the irradiance mean (P < 0.01). A significant difference existed between the four different brands of LCUs at different time intervals, irrespective of the use of ICB. At T₀ and T₁₀, the mean output of Acteon mini-light-emitting diode (LED) was significantly higher than that of either the Kerr Demi Ultra or the Kavo Polylux II. At T₂₀, E-Morlit's mean irradiance was significantly higher than that of Kerr Demi Ultra, which in turn was significantly higher than that of the Kavo PolyLux II. The mean irradiance of the LEDs was significantly higher than that of the halogens irrespective of barrier placement and at all-time points.

Conclusion

The ICB used in this study resulted in a statistically significant reduction in the irradiance output. No significant difference in the irradiance was found at different curing time intervals for the tested units regardless of ICB usage.

Stability of the Light Output, Oral Cavity Tip Accessibility in Posterior Region and Emission Spectrum of Light-Curing Units

Objectives: 

This study evaluated the light output from six light-emitting diode dental curing lights after 25 consecutive light exposures without recharging the battery, tip accessibility in the posterior region, and light beam spread from light-curing units.

Methods: 

Irradiance, spectral peak, and radiant exposure were measured with the battery fully charged (Bluephase Style, ESPE Cordless, Elipar S10, Demi Ultra, Valo Cordless, and Radii-Cal) and monitored for 25 light exposures (each lasting 10 seconds). The tip diameter was measured to identify the beam size and the ability of the six light-curing units to irradiate all areas of the lower second molar in the standard output setting.

Results: 

Four curing lights delivered a single peak wavelength from 454 to 462 nm, and two (Bluephase Style and Valo Cordless) delivered multiple emission peaks (at 410 and 458 nm and 400, 450, and 460 nm, respectively). The irradiance and radiant exposure always decreased after 25 exposures by 2% to 8%, depending on the light unit; however, only ESPE Cordless, Valo Cordless, and Radii-Cal presented a statistical difference between the first and the last exposure. The tip diameter ranged from 6.77 mm to 9.40 mm. The Radii-Cal delivered the lowest radiant exposure and irradiance. This light was also unable to access all the teeth with the tip parallel to the occlusal surface of the tooth.

Conclusion: 

Not all of the blue-emitting lights deliver the same emission spectra, and some curing lights delivered a lower irradiance (as much as 8% lower) after the 25th exposure.

Structural and mechanical properties of a giomer-based bulk fill restorative in different curing conditions

Objective

The main goal of this study was to compare the polymerization degree of bulk-fill giomer resin cured with three different light-curing units (LCUs): a polywave third-generation (Valo); a monowave (DemiUltra: DU); and a second-generation LED (Optima 10: Opt) LCUs by using structural and mechanical properties.

Material and methods

Giomer samples of 2 and 4 mm cured with three LCUs were employed in vitro analysis. The degree of curing (DC%) was determined with Fourier-Transform Infrared Spectroscopy (FTIR). Microstructural features were observed with scanning electron microscopy (SEM). Flexural strength (FS), compression strength (CS), elastic modulus and fracturing strain were determined for mechanical properties. Surface microhardness (SMH) values were also measured. Oneway ANOVA, two-way analysis of variance and Tukey multiple comparison tests were used for statistically analyzing the FS and SMH.

Results

DC% values were 58.2, 47.6, and 39.7 for the 2 mm samples cured with DU, Opt., and Valo LCUs, respectively. DC% values of the 4 mm samples were 50.4, 44.6, and 38.2 for DU, Opt, and Valo, respectively. SMH values were Valo, Opt<DU at top of the samples; Valo<DU, Opt at 2 mm, and DU, Valo<Opt at 4 mm depth. Giomer samples cured with Opt and DU exhibited higher FS values than Valo. CS values were similar but compressive modulus and fracturing strain (%) varied depending on the curing protocol.

Conclusions

Based on the results, it can be concluded that curing device and protocol strongly affect crosslinking reactions and thus DC%, SMH, compressive modulus and strain at break values. Consequently, it can be deduced that curing protocol is possibly the most important parameter for microstructure formation of highly-filled composite restoratives because it may bring some structural defects and physical frailties on restorations due to lower degree of polymerization.

Influence of Emission Spectrum and Irradiance on Light Curing of Resin-Based Composites

PURPOSE

This study examined the influence of different emission spectra (single-peak and broad-spectrum) light-curing units (LCUs) delivering the same radiant exposures at irradiance values of 1200 or 3600 mW/cm² on the polymerization and light transmission of four resin-based composites (RBCs).

METHODS AND MATERIALS

Two prototype LCUs that used the same light tip, but were either a single-peak blue or a broad-spectrum LED, were used to deliver the same radiant exposures to the top surfaces of the RBCs using either standard (1200 mW/cm²) or high irradiance (3600 mW/cm²) settings. The emission spectrum and radiant power from the LCUs were measured with a laboratory-grade integrating sphere coupled to a spectrometer, and the light beam was assessed with a beam profiler camera. Four RBCs (Filtek Supreme Ultra A2, Tetric EvoCeram A2, Tetric EvoCeram T, and TPH Spectra High Viscosity A2) were photoactivated using four different light conditions: single-peak blue/standard irradiance, single-peak blue/high irradiance, broad-spectrum/standard irradiance, and broad-spectrum/high irradiance. The degree of conversion (N=5) and microhardness at the top and bottom of 2.3-mm-diameter by 2.5-mm-thick specimens (N=5) were analyzed with analysis of variance and Tukey tests. The real-time light transmission through the RBCs was also measured.

RESULTS

For all light conditions, the 2.3-mm-diameter specimens received a homogeneous irradiance and spectral distribution. Although similar radiant exposures were delivered to the top surfaces of the RBCs, the amount of light energy emitted from the bottom surfaces was different among the four RBCs, and was also greater for the single-peak lights. Very little violet light (wavelengths below 420 nm) reached the bottom of the 2.5-mm-thick specimens. The degree of conversion and microhardness results varied according to the RBC (p<0.05). The RBCs that included alternative photoinitiators had greater microhardness values at the top when cured with broad-spectrum lights, while at the bottom, where little violet light was observed, the results were equal or higher when they were photoactivated with single-peak blue lights. With the exception of the microhardness at the top of TPH, equivalent or higher microhardness and degree-of-conversion values were achieved at the bottom surface when the standard (1200 mW/cm²) irradiance levels were used compared to when high irradiance levels were used.

CONCLUSIONS

Considering the different behaviors of the tested RBCs, the emission spectrum and irradiance level influenced the polymerization of some RBCs. The RBCs that included alternative photoinitiators produced greater values at the top when cured with broad-spectrum lights, while at the bottom, results were equal or higher for the RBCs photoactivated with single-peak blue lights.

Factors affecting polymerization of resin-based composites: A literature review

AIM

The aim of this review was to help clinicians improve their understanding of the polymerization process for resin-based composites (RBC), the effects of different factors on the process and the way in which, when controlled, the process leads to adequately cured RBC restorations.

METHODS

Ten factors and their possible effects on RBC polymerization are reviewed and discussed, with some recommendations to improve that process. These factors include RBC shades, their light curing duration, increment thickness, light unit system used, cavity diameter, cavity location, light curing tip distance from the curing RBC surface, substrate through which the light is cured, filler type, and resin/oral cavity temperature.

CONCLUSION

The results of the review will guide clinicians toward the best means of providing their patients with successfully cured RBC restorations.