Light transmittance and micro-mechanical properties of bulk fill vs. conventional resin based composites

Effect of composite type and placement technique on cuspal strain

OBJECTIVE

To compare the cuspal strain in Class II restorations made with bulk-fill and conventional composite resins.

MATERIALS AND METHODS

Fifty extracted maxillary premolars were mounted into phenolic rings and divided into five groups (n = 10). Specimens received standardized MOD preparations. A two-step self-etch adhesive was applied and the preparations were restored using a custom matrix as follows: Filtek Supreme Ultra in eight 2-mm increments (FSUI); Filtek Supreme Ultra in bulk (FSUB); SonicFill in bulk (SF); SureFil SDR flow in bulk, covered with a 2-mm occlusal layer of Filtek Supreme Ultra (SDR/FSU); Tetric EvoCeram Bulk Fill in bulk (TEBF). Strain gages bonded to the buccal and lingual cusps recorded cuspal strain during restorations. End strain values were determined and data were subjected to Kruskal-Wallis testing, followed by one-way ANOVA and Tukey´s post hoc test.

RESULTS

Combined strain values and standard deviations (in µɛ) were: FSUI: 723 ± 102.8, FSUB: 929.2 ± 571.9, SF: 519.1 ± 80.2, SDR-FSU: 497.4 ± 67.6 and TEBF: 604.5 ± 127.1. A significant difference was found between group FSUI and groups SF, SDR-FSU, and TEBF. Group FSUB showed significantly higher mean strain and greater standard deviation than all other groups due to cuspal fractures, and was thus excluded from the statistical analysis.

CONCLUSIONS

The tested bulk-fill composite resins exerted less strain onto tooth structure than the incrementally placed conventional composite resin, although the magnitude of generated strain was product-dependent. Bulk-filling with conventional composite resins is contraindicated.

CLINICAL SIGNIFICANCE

Bulk-fill composite resins exerted less strain onto adjacent tooth structure than a traditional composite, even when that composite is was placed incrementally. Bulk-filling with traditional composite resins is unpredictable and contraindicated.

Influence of increment thickness on radiant energy and microhardness of bulk-fill resin composites

Determining the energy transferred at the bottom of eleven bulk-fill resin composites, comparing top and bottom microhardness's and evaluating the correlation between microhardness and radiant energy were aimed. Samples were placed over the bottom sensor of a visible light transmission spectrophotometer and polymerized for 20 s. The bottom and top Knoop microhardness were measured. Paired t-test and correlation analysis were used for statistics (p≤0.05). In all groups, the bottom radiant energy decreased significantly with increasing thickness. For groups of Aura 2 mm, X-tra Fil 2 and 4 mm, SDR 2 and 4 mm, X-tra Base 2 mm no significant difference was found between top and bottom microhardness. For the bottom levels of Aura, X-tra Fil, Filtek Bulk-Fill Posterior, SDR, X-tra Base groups no significant difference was found between the microhardness's of 2 and 4 mm thicknesses. For X-tra Fil, Tetric Evo Ceram Bulk-Fill, Filtek Bulk-Fill Flowable and Z100 groups radiant energy affected positively the microhardness.

The Effects of Cavity Preparation and Composite Resin on Bond Strength and Stress Distribution Using the Microtensile Bond Test

OBJECTIVES

To evaluate the effect of flowable bulk-fill or conventional composite resin on bond strength and stress distribution in flat or mesio-occlusal-distal (MOD) cavity preparations using the microtensile bond strength (μTBS) test.

METHODS

Forty human molars were divided into two groups and received either standardized MOD or flat cavity preparations. Restorations were made using the conventional composite resin Z350 (Filtek Z350XT, 3M-ESPE, St Paul, MN, USA) or flowable bulk-fill (FBF) composite resin (Filtek Bulk Fill Flowable, 3M-ESPE). Postgel shrinkage was measured using the strain gauge technique (n=10). The Z350 buildup was made in two increments of 2.0 mm, and the FBF was made in a single increment of 4.0 mm. Six rectangular sticks were obtained for each tooth, and each section was used for μTBS testing at 1.0 mm/min. Polymerization shrinkage was modeled using postgel shrinkage data. The μTBS data were analyzed statistically using a two-way analysis of variance (ANOVA), and the postgel shrinkage data were analyzed using a one-way ANOVA with Tukey post hoc test. The failure modes were analyzed using a chi-square test (α=0.05).

RESULTS

Our results show that both the type of cavity preparation and the composite resin used affect the bond strength and stress distribution. The Z350 composite resin had a higher postgel shrinkage than the FBF composite resin. The μTBS of the MOD preparation was influenced by the type of composite resin used. Irrespective of composite resin, flat cavity preparations resulted in higher μTBS than MOD preparations ( p<0.001). Specifically, in flat-prepared cavities, FBF composite resin had a similar μTBS relative to Z350 composite resin. However, in MOD-prepared cavities, those with FBF composite resin had higher μTBS values than those with Z350 composite resin. Adhesive failure was prevalent for all tested groups. The MOD preparation resulted in higher shrinkage stress than the flat preparation, irrespective of composite resin. For MOD-prepared cavities, FBF composite resin resulted in lower stress than Z350 composite resin. However, no differences were found for flat-prepared cavities.

CONCLUSIONS

FBF composite resin had lower shrinkage stress than Z350 conventional composite resin. The μTBS of the MOD preparation was influenced by the composite resin type. Flat cavity preparations had no influence on stress and μTBS. However, for MOD preparation, composite resin with higher shrinkage stress resulted in lower μTBS values.

Bulk-Fill Composites: Effectiveness of Cure With Poly- and Monowave Curing Lights and Modes

This study compared the effectiveness of cure of bulk-fill composites using polywave light-emitting diode (LED; with various curing modes), monowave LED, and conventional halogen curing lights. The bulk-fill composites evaluated were Tetric N-Ceram bulk-fill (TNC), which contained a novel germanium photoinitiator (Ivocerin), and Smart Dentin Replacement (SDR). The composites were placed into black polyvinyl molds with cylindrical recesses of 4-mm height and 3-mm diameter and photopolymerized as follows: Bluephase N Polywave High (NH), 1200 mW/cm² (10 seconds); Bluephase N Polywave Low (NL), 650 mW/cm² (18.5 seconds); Bluephase N Polywave soft-start (NS), 0-650 mW/cm² (5 seconds) → 1200 mW/cm² (10 seconds); Bluephase N Monowave (NM), 800 mW/cm² (15 seconds); QHL75 (QH), 550 mW/cm² (21.8 seconds). Total energy output was fixed at 12,000 mJ/cm² for all lights/modes, with the exception of NS. The cured specimens were stored in a light-proof container at 37°C for 24 hours, and hardness (Knoop Hardness Number) of the top and bottom surfaces of the specimens was determined using a Knoop microhardness tester (n=6). Hardness data and bottom-to-top hardness ratios were subjected to statistical analysis using one-way analysis of variance/Scheffe's post hoc test at a significance level of 0.05. Hardness ratios ranged from 38.43% ± 5.19% to 49.25% ± 6.38% for TNC and 50.67% ± 1.54% to 67.62% ± 6.96% for SDR. For both bulk-fill composites, the highest hardness ratios were obtained with NM and lowest hardness ratios with NL. While no significant difference in hardness ratios was observed between curing lights/modes for TNC, the hardness ratio obtained with NM was significantly higher than the hardness ratio obtained for NL for SDR.

Water sorption and solubility of bulk-fill composites polymerized with a third generation LED LCU

The aim of this study was to compare the degree of water sorption and solubility in bulk-fills after curing with a polywave light source. A total of 120 disc-shaped specimens (8 mm diameter; 4 mm depth) were prepared from three regular bulk-fill materials (X-tra Fil, Tetric N-Ceram Bulk Fill, SonicFill), and a control material (Filtek Z250), cured in 3 different modes (standard: 1000 mW/cm2-20 s; high power: 1400 mW/cm2-12 s; xtra power: 3200 mW/cm2-6 s) using a third generation light-emitting diode light curing unit. Water sorption and solubility levels of the specimens were measured according to the ISO 4049:2009 specification after storing in distilled water for 30 days. Data were analyzed using two-way ANOVA and Tukey's post-hoc test (p < 0.05). The Z250 sample exposed to high power presented a higher sorption compared to the X-tra Fil and SonicFill samples. In xtra power mode, the values of Z250 and SonicFill were similar to each other and higher compared to those of X-tra Fil. Only SonicFill exhibited significantly different sorption values depending on the curing mode, the highest of which was achieved when using the xtra power mode. The highest solubility values were obtained for SonicFill. No statistically significant differences were found among other groups. No significant correlation was detected between water sorption and solubility. The traditional composite group exhibited a higher water sorption values than the bulk-fills. The reduction in polymerization time significantly increased the sorption of SonicFill. SonicFill showed the highest water solubility value among the composites tested.

Microtensile Bond Strength and Microhardness of Composite Resin Restorations Using a Sonic-Resin Placement System

The aim of this study was to evaluate the efficacy of applying sonic energy on microtensile bond strength and microhardness after the restoration process. A total of 40 human third molars were extracted. Class II cavities were prepared and restored with composite SonicFill or Filtek Z350 XT with and without the application of sonic energy. After the teeth were stored in water for 24 h, the teeth were sectioned into sticks (1.0 mm2) and subjected to tensile testing. For a depth Knoop hardness test, the samples were cut and indentations were made sequentially from the surface of the samples to the bottom of the samples in three intervals of 1 mm each. The samples were then subjected to a load of 50 g for 10 s. The results from the tensile (factors: placement system and composite) and hardness (factors: placement system, composite and depth) tests were subjected to the Kolmogorov-Smirnov normality test, followed by analysis of variance and Tukey's test (5% significance). For the placement system factor, higher bond strength was observed for the cavities that were restored with sonic energy (p < 0.001). For depth Knoop hardness, the hardness at 1 mm depth was significantly greater than that at 3 mm depth just for the restorations with Filtek Z350 XT composite without the application of sonic energy. Therefore, the use of sonic energy during the restorative process improved bonding, yet it did not markedly affect the depth hardness for both composites.

Efficiency of polymerization of bulk-fill composite resins: a systematic review

This systematic review assessed the literature to evaluate the efficiency of polymerization of bulk-fill composite resins at 4 mm restoration depth. PubMed, Cochrane, Scopus and Web of Science databases were searched with no restrictions on year, publication status, or article's language. Selection criteria included studies that evaluated bulk-fill composite resin when inserted in a minimum thickness of 4 mm, followed by curing according to the manufacturers' instructions; presented sound statistical data; and comparison with a control group and/or a reference measurement of quality of polymerization. The evidence level was evaluated by qualitative scoring system and classified as high-, moderate- and low- evidence level. A total of 534 articles were retrieved in the initial search. After the review process, only 10 full-text articles met the inclusion criteria. Most articles included (80%) were classified as high evidence level. Among several techniques, microhardness was the most frequently method performed by the studies included in this systematic review. Irrespective to the "in vitro" method performed, bulk fill RBCs were partially likely to fulfill the important requirement regarding properly curing in 4 mm of cavity depth measured by depth of cure and / or degree of conversion. In general, low viscosities BFCs performed better regarding polymerization efficiency compared to the high viscosities BFCs.

Depth of cure of contemporary bulk-fill resin-based composites

This study evaluated the depth of cure (DOC) of packable and flowable bulk-fill resin-based composites (RBCs) including PRG (prereacted glass ionomer) and short-fiber materials. The materials were placed in a black split-mold with a 7 mm deep recess and cured at 700 mW/cm(2) for 20 s using a LED curing light. DOC was assessed using the ISO scraping and Knoops hardness tests. Data (n=5) were computed and analyzed using one-way ANOVA/Scheffe's post hoc test (p<0.05). ISO DOC ranged from 3.66 to 2.54 mm while DOC based on hardness testing ranged from 3 to 1.5 mm. For all materials, a decrease in hardness was observed with increasing depths. The DOC of bulk-fill RBCs was product dependent and greater than standard composites. At 4 mm depth, none of the bulk-fill RBCs had a depth: top hardness ratio of 0.8 and above.

Full in-vitro analyses of new-generation bulk fill dental composites cured by halogen light

The objective of this study was to investigate the full in-vitro analyses of new-generation bulk-fill dental composites cured by halogen light (HLG). Two types' four composites were studied: Surefill SDR (SDR) and Xtra Base (XB) as bulk-fill flowable materials; QuixFill (QF) and XtraFill (XF) as packable bulk-fill materials. Samples were prepared for each analysis and test by applying the same procedure, but with different diameters and thicknesses appropriate to the analysis and test requirements. Thermal properties were determined by thermogravimetric analysis (TG/DTG) and differential scanning calorimetry (DSC) analysis; the Vickers microhardness (VHN) was measured after 1, 7, 15 and 30days of storage in water. The degree of conversion values for the materials (DC, %) were immediately measured using near-infrared spectroscopy (FT-IR). The surface morphology of the composites was investigated by scanning electron microscopes (SEM) and atomic-force microscopy (AFM) analyses. The sorption and solubility measurements were also performed after 1, 7, 15 and 30days of storage in water. In addition to his, the data were statistically analyzed using one-way analysis of variance, and both the Newman Keuls and Tukey multiple comparison tests. The statistical significance level was established at p<0.05. According to the ISO 4049 standards, all the tested materials showed acceptable water sorption and solubility, and a halogen light source was an option to polymerize bulk-fill, resin-based dental composites.

Comparison of Polymerization Shrinkage, Physical Properties, and Marginal Adaptation of Flowable and Restorative Bulk Fill Resin-Based Composites

Purpose: The purpose of this study was to compare the marginal adaptation of two flowable bulk fill resin-based composites (FB-RBCs), two restorative bulk fill resin-based composites (RB-RBCs), and one regular incremental-fill RBC in MOD cavities in vitro. Additionally, the influence of linear polymerization shrinkage, shrinkage force, flexural modulus, and bottom/top surface hardness ratio on the marginal adaptation was evaluated. Methods: A Class II MOD cavity was prepared in 40 extracted sound lower molars. In group 1 (control group), the preparation was filled with Filtek Z350 (Z3, 3M ESPE, St Paul, MN, USA) using the incremental filling technique. The FB-RBCs, SDR (SD, group 2) (Dentsply Caulk, Milford, DE, USA) and Venus Bulk Fill (VB, group 3) (Heraeus Kulzer, Dormagen, Germany), were placed in the core portion of the cavity first, and Z350 was filled in the remaining cavity. The RB-RBCs, Tetric N-Ceram Bulkfill (TB, group 4) (Ivoclar Vivadent, Schaan, Liechtenstein) and SonicFill (SF, Group 5) (Kerr, West Collins, Orange, CA, USA), were bulk filled into the preparation. Images of the magnified marginal area were captured under 100× magnification before and after thermomechanical loading, and the percentage ratio of the imperfect margin (%IMwhole) was calculated. Gaps, cracks in the enamel layer, and chipping of composite, enamel, or dentin were all considered to be imperfect margins. Linear polymerization shrinkage, polymerization shrinkage force, flexural strength, flexural modulus, and bottom/top surface hardness ratio of were measured. Eight specimens were allocated for each material for each test. One-way analysis of variance with the Scheffé test was used to compare the groups at a 95% confidence level. Results: Before thermomechanical loading, %IMwhole was in the order of group 3 ≤ groups 2 and 5 ≤ groups 1 and 4 (p=0.011), whereas after loading, it was in the order of group 4 ≤ group 5 ≤ group 1 ≤ groups 2 and 3 (p&lt;0.001). The order of materials were Z3 &lt; TB and SF &lt; SD and VB (p&lt;0.001) in polymerization shrinkage; SF ≤ TB ≤ Z3 &lt; SD &lt; VB (p&lt;0.001) in polymerization shrinkage force; VB &lt; SD &lt; TB ≤ Z3 ≤ SF (p&lt;0.001) in flexural modulus; SD, VB, and TB &lt; Z3 and SF (p&lt;0.001) in flexural strtength; and SF&lt; Z3 &lt; TB &lt; VB and SD (p&lt;0.001) in bottom/top surface hardness ratio. The Pearson correlation constant between %IMwhole and polymerization shrinkage, shrinkage force, elastic modulus, and bottom/top surface hardness ratio was 0.697, 0.708, −0.373, and 0.353, respectively, after thermomechanical loading. Conclusion: Within the limitations of this study, RB-RBCs showed better marginal adaptation than FB- RBCs. The lower level of polymerization shrinkage and polymerization shrinkage stress in RB-RBCs seems to contribute to this finding because it would induce less polymerization shrinkage force at the margin. FB-RBCs with lower flexural modulus may not provide an effective buffer to occlusal stress when they are capped with regular RBCs.

Thirty-Six-Month Clinical Comparison of Bulk Fill and Nanofill Composite Restorations

OBJECTIVES

The aim of this study was to evaluate the clinical performance of a nanofill and a bulk fill resin composite in class II restorations.

METHODS AND MATERIALS

In accordance with a split-mouth design, 50 patients received at least one pair of restorations, restored with a nanofill resin composite (Filtek Ultimate [FU]) and with a bulk fill resin composite (Tetric EvoCeram Bulk Fill [TB]). Each restorative resin was used with its respective adhesive system according to the manufacturers' instructions. A total of 104 class II restorations were placed by two operators. The restorations were blindly evaluated by two examiners at baseline and at six, 12, 18, 24, and 36 months using modified US Public Health Service Ryge criteria. The comparison of the two restorative materials for each category was performed with the chi-square test (α=0.05). The baseline scores were compared with those at the recall visits using the Cochran Q-test.

RESULTS

At six, 12, 18, and 24 months, the recall rate was 100%, 98%, 94%, and 82%, respectively, with a retention rate of 100%. At 36 months, 81 restorations were evaluated in 39 patients with a recall rate of 78%. For marginal adaptation, four restorations from the TB group and 10 from the FU group rated as Bravo. Two restorations from the TB and eight restorations from the FU group showed marginal discoloration. There were statistically significant differences between the two restorative resins in terms of marginal adaptation and marginal discoloration (p<0.05). No differences were observed between the restorative resins in terms of retention (p>0.05). One restored tooth from the FU group was crowned. The retention rates for the TB and the FU groups were 100%. In the FU group, two restorations showed slightly rough surfaces, and two showed a slight mismatch in color. None of the restorations showed postoperative sensitivity, secondary caries, or loss of anatomic form.

CONCLUSIONS

The tested bulk fill restorative resin demonstrated better clinical performance in terms of marginal discoloration and marginal adaptation.

Genotoxic potential of dental bulk-fill resin composites

OBJECTIVE

To investigate both genotoxicity and hardening of bulk-fill composite materials applied in 4-mm layer thickness and photo-activated for different exposure times.

METHODS

Three flowable bulk-fill materials and one conventional flowable composite were filled in molds (height: 4mm) and irradiated for 20 or 30s. The top (0mm) and bottom (4mm) specimen surface were mechanically scraped, and eluates (0.01g composite in 1.5ml RPMI 1640 cell culture media) prepared for each material, surface level and irradiation time. Genotoxicity was assessed in human leukocytes using both the alkaline comet assay and cytokinesis-blocked micronucleus assay, and Knoop hardness (KHN) was measured at the top and bottom specimen surface (n=8).

RESULTS

At both irradiation times, none of the bulk-fill composites significantly affected comet assay parameters used in primary DNA damage assessment or induced significant formation of any of the scored chromatin abnormalities (number of micronuclei, nuclear buds, nucleoplasmic bridges), whether eluates were obtained from the top or bottom surface. Furthermore, no decrease in KHN from the top to the bottom surface of the bulk-fill materials was observed. On the other hand, the conventional composite irradiated for 20s showed at 4-mm depth a significant increase in the percentage of DNA that migrated in the tail and a significant increase in the number of nuclear buds, as well as a significant decrease in KHN relative to the top surface.

SIGNIFICANCE

Bulk-fill resin composites, in contrast to conventional composite, applied in 4-mm thickness and photo-activated for at least 20s do not induce relevant genotoxic effects or mechanical instability.

Characterization of Inorganic Filler Content, Mechanical Properties, and Light Transmission of Bulk-fill Resin Composites

OBJECTIVES

The aims of this study were to characterize inorganic content (IC), light transmission (LT), biaxial flexural strength (BFS), and flexural modulus (FM) of one conventional (layered) and four bulk-fill composites at different depths.

METHODS

Bulk-fill composites tested were Surefil SDR flow (SDR), Filtek Bulk Fill (FBF), Tetric EvoCeram Bulk Fill (TEC), and EverX Posterior (EXP). Herculite Classic (HER) was used as a control. Energy dispersive x-ray analysis and scanning electron microscopy were used to characterize filler particle composition and morphology. The LT through different composite thicknesses (1, 2, 3, and 4 mm) was measured using a laboratory-grade spectral radiometer system (n=5). For the BFS and FM tests, sets of eight stacked composite discs (0.5-mm thick) were prepared simulating bulk filling of a 4-mm-thick increment (n=8).

RESULTS

SDR demonstrated larger, irregular particles than those observed in TEC or HER. Filler particles in FBF were spherical, while those in EXP were composed of fiberglass strands. The LT decreased with increased composite thickness for all materials. Bulk-fill composites allowed higher LT than the HER. Furthermore, HER proved to be the unique material, having lower BFS values at deeper regions. SDR, FBF, and TEC bulk-fill composites presented reduced FM with increasing composite depth.

CONCLUSIONS

The bulk-fill composites investigated exhibited higher LT, independent of different filler content and characteristics. Although an increase in composite thickness reduced LT, the BFS of bulk-fill composites at deeper layers was not compromised.

Resistência de união de compósitos do tipo Bulk Fill: análise in vitro

Resumo Introdução A classe dos compósitos Bulk-Fill tem obtido popularidade com a promessa de ser fotopolimerizado efetivamente em camadas de até quatro milímetros, fato que contrasta com os dois milímetros requisitados para os compósitos convencionais para manutenção da adesividade da restauração. Objetivo O objetivo deste estudo foi analisar a resistência de união à dentina de restaurações confeccionadas com compósitos do tipo Bulk-Fill. Material e método Foram utilizados 15 terceiros molares humanos, cuja superfície oclusal foi cortada e a dentina foi exposta. Esses elementos dentários foram divididos em três grupos conforme o material restaurador utilizado. O sistema adesivo usado foi o mesmo para todos os grupos. Posteriormente, os dentes restaurados foram cortados para originar palitos de aproximadamente 1 mm de largura, 1 mm de profundidade e 8 mm de altura, que foram fixados às garras do dispositivo de microtração. Foram utilizados dez palitos de cada dente, totalizando 50 palitos por grupo. Os dados de resistência de união à microtração foram expressos em megapascal (MPa). As fraturas foram analisadas em microscópio óptico. Os dados foram analisados através dos testes ANOVA e Tukey (p<0,05). Resultado Os três compósitos estudados diferiram estatisticamente entre si (p<0,000). Os compósitos Bulk-Fill apresentaram resistências de união semelhantes e superiores ao convencional (p<0,000). A fratura mais encontrada foi a mista, em todos os grupos. Conclusão Os compósitos Bulk-Fill apresentaram maiores valores de resistência de união com a técnica restauradora utilizada.

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.

The effect of curing intensity on mechanical properties of different bulk-fill composite resins

OBJECTIVE

The purpose of this study was to investigate the effects of two curing light intensities on the mechanical properties (Vickers microhardness, compressive strength, and diametral tensile strength) of bulk-fill resin-based composites (RBCs).

MATERIALS AND METHODS

Four commercially available bulk-fill RBCs (Tetric^® N-Ceram, SonicFill™, Smart Dentin Replacement (SDR™) Posterior Flowable Material, and Filtek™ Posterior Restorative) were used in this study. A total of 72 cylindrical specimens of each RBC (n=288) were prepared and subjected to Vickers microhardness, compressive strength, and diametral tensile strength tests at high (1200 mW/cm²) and low (650 mW/cm²) curing light intensities (each n=12). Results were evaluated using independent and paired sample t-tests, one-way analysis of variance, and Tukey's post hoc test. All tests were performed at a significance level of P<0.05.

RESULTS

The highest mean microhardness was observed for SonicFill (58.3 Vickers hardness number [VHN]) cured using high-intensity light. Although having the least mean microhardness values, a significant difference was observed between SDR cured using high-intensity light and that cured using low-intensity light (P<0.05). In the total sample, the highest mean compressive strength was obtained for SonicFill (262.6 MPa), followed by SDR (253.2 MPa), both cured using high-intensity light, and the least was measured for Tetric N-Ceram cured using low-intensity light (214.3 MPa). At high and low curing light intensities, diametral tensile strength for all RBCs except SonicFill was significant (P<0.001).

CONCLUSION

A higher curing light intensity (1200 mW/cm²) had a positive influence on the compressive and tensile strength of the four bulk-fill RBCs and microhardness of two materials tested compared with lower curing light intensity (650 mW/cm²). SonicFill showed the greatest microhardness and compressive strength significantly for both curing light intensities and greater diametral tensile strength with high-intensity light, although not significant. SDR cured with high-intensity light showed the greatest diametral tensile strength among the four materials.

Marginal adaptation and microleakage of a bulk-fill composite resin photopolymerized with different techniques

The purpose of this study was to investigate the marginal adaptation and microleakage of SonicFill composite with different photopolymerization techniques. Class II cavities were prepared in 40 premolars and divided into groups according to the photopolymerization technique (n = 10): G1:1200 mW/cm² for 20 s; G2:1200 mW/cm² for 40 s; G3:Soft-start with 650 mW/cm² for 5 s and 1200 mW/cm² for 15 s; G4:Soft-start with 650 mW/cm² for 10 s and 1200 mW/cm² for 30 s. The cavities were restored with OptiBond FL adhesive and SonicFill. Epoxy resin replicas were obtained before and after thermocycling. The occlusal and cervical margins were analyzed with scanning electron microcopy and expressed as the percentage of continuous margins (%CM). The specimens were submitted to microleakage with silver nitrate. ANOVA and Tukey's test revealed that the %CM at the linguo-occlusal margin for group 1 (83.19%) was significantly different from groups 2, 3 and 4, which had values over 95%. At the cervical margin, there was no statistically significant difference between the groups. After thermocycling, there was a significant decrease in %CM. The predominant score of microleakage was 1 in enamel and 3 in dentin. The SonicFill composite led to gap formation and microleakage, especially in the dentin at the cervical margin, regardless of the photopolymerization technique employed.

Long Term Degree of Conversion of two Bulk-Fill Composites

OBJECTIVES

To investigate the long-term development of the post-cure degree of conversion (DC) for two flowable bulk-fill composites.

MATERIALS AND METHODS

Tetric EvoFlow Bulk Fill (TEFBF) and SDR were chosen due to their distinct compositional modifications that enable the decrease of translucency during polymerization and lower polymerization rate, respectively. DC was assessed using FT-Raman spectroscopy at the post-cure times of 0 h, 24 h, 7 d and 30 d. The post-cure behavior was analyzed by a mixed model ANOVA and partial eta-squared statistics.

RESULTS

DC ranged from 61.3-81.1% for TEFBF and 58.9-81.6% for SDR. The initial (0 h) DC was significantly lower at a depth of 4 mm than at a depth of 1 mm (4.9% for SDR and 11.1% for TEFBF). Both materials presented a significant post-cure DC increase, up to 16.4% for TEFBF and 20.6% for SDR. The post-cure DC development was depth-dependent for TEFBF, but not for SDR. The post-cure DC increase was observed during 24 h for TEFBF and 7 d for SDR.

CONCLUSIONS

Some of the bulk-fill composites may need longer times than the commonly accepted 24 h to reach the final conversion. This may be attributed to their compositional modifications that are mostly undisclosed by manufacturers. Our findings imply that investigations commonly performed 24 h post-cure may underestimate some of the bulk-fill composite properties, if these are affected by the slowly-developing DC. Reactive species may also be available for leaching out of the restoration during an extended time period, with possible implications on biocompatibility.

Influence of Adhesive Type and Placement Technique on Postoperative Sensitivity in Posterior Composite Restorations

PURPOSE

This double blind, randomized clinical trial compared the postoperative sensitivity of the placement technique (incremental and bulk fill) in posterior composite resin restorations bonded with two different adhesive strategies (self-etch and etch-and-rinse).

METHODS

Posterior dental cavities of 72 participants (n=236), with a cavity depth of at least 3 mm, were randomly divided into four groups. The restorations were bonded using either the etch-and-rinse Tetric N-Bond (Ivoclar Vivadent) or the self-etch Tetric N-Bond SE (Ivoclar Vivadent). The composite resin Tetric N-Ceram Bulk Fill (Ivoclar Vivadent) was placed either incrementally or using the bulk-fill technique. Two experienced and calibrated examiners evaluated the restorations using World Dental Federation criteria after one week of clinical service. Spontaneous postoperative sensitivity was assessed using a 0-4 numerical rating scale and a 0-10 and 0-100 visual analog scale up to 48 h after the restorative procedure and after one week.

RESULTS

The risk (p>0.49) and intensity of spontaneous postoperative sensitivity (p>0.38) was not affected by the adhesive strategy or the filling technique. The overall risk of postoperative sensitivity was 20.3% (95% confidence interval 15.7-25.9) and typically occurred within 48 hours after the restorative procedure.

CONCLUSIONS

The overall risk of immediate postoperative sensitivity was 20.3% and was not affected by either the adhesive strategy (etch-and-rinse/self-etch) or the filling technique (incremental/ bulk).

Class II composite resin restorations: faster, easier, predictable

Composite resin continues to displace amalgam as the preferred direct restorative material in developed countries. Even though composite materials have evolved to include nanoparticles with high physical properties and low shrinkage stress, dentists have been challenged to efficiently create quality, long lasting, predictable restorations. Unlike amalgam, composite resin cannot be condensed making the establishment of a predictable, proper contact more difficult. In addition, composite requires an understanding of adhesives and an appreciation for their exacting application. These facts combined with the precise adaptation and light-curing of multiple layers makes placement of quality Class II composite restorations tedious and time-consuming. For private practicing dentists, it can also have an effect on economic productivity. Clinicians have always wanted an easier, efficient placement technique for posterior composite restorations that rivals that for amalgam. It appears that advances in instrumentation, materials and technology have finally delivered it.

Three-year clinical evaluation of class II posterior composite restorations placed with different techniques and flowable composite linings in endodontically treated teeth

OBJECTIVE

The objective of this study is to evaluate the clinical performance of direct resin composite restorations placed with different techniques (incremental or bulk) and different flowable linings (conventional or bulk-fill) in endodontically treated teeth.

MATERIALS AND METHODS

Forty-seven pair class II (mesio-occlusal or disto-occlusal) composite restorations were placed in 37 patients. In all cavities, Adper Single Bond 2 was used. In one of the cavities of each pair, a conventional flowable composite, Aelite Flo, was applied in approximately 2 mm thick, and the remaining cavity was restored incrementally with GrandioSO. In the second cavity, a bulk-fill flowable composite, x-tra base, was applied in approximately 4 mm thick in bulk increments and the remaining 2-mm occlusal part of the cavity was restored with GrandioSO. All cavities were restored with open-sandwich technique by the same operator. At baseline and after 6-month, 1-, 2-, and 3-year follow-up visits, restorations were evaluated by modified USPHS criteria.

RESULTS

At 3-year recall, 33 restorations with Aelite Flo lining and 33 with x-tra base lining were available. Two restorations from each group (6.0 %) were scored as Bravo in terms of surface texture. One restoration's color match from x-tra base group scored as Bravo (3.0 %). All other evaluated criteria were scored as Alfa (100 %) for all restorations. No statistically significant difference between the two groups was found in all evaluated criteria during 3-year period (p > 0.05).

CONCLUSION

Bulk-filling technique showed clinically acceptable performance comparable to the incremental technique.

CLINICAL RELEVANCE

Restorations placed with bulk-filling technique with x-tra base lining and incremental technique with a conventional flowable lining showed highly clinical performance over 3-year period.

Color Stability of the Bulk-Fill Composite Resins with Different Thickness in Response to Coffee/Water Immersion

We aimed to evaluate the color stability of bulk-fill and conventional composite resin with respect to thickness and storage media. Twenty specimens of a conventional composite resin (6 mm diameter and 2 mm thick) and 40 specimens of the bulk-fill Tetric EvoCeram composite resin at two different thicknesses (6 mm diameter and 2 mm thick or 4 mm thick, n = 20) were prepared. The specimens were stored in distilled water during the study period (28 d). Half of the specimens were remained in distilled water and the other half were immersed in coffee solution 20 min/d and kept in distilled water between the cycles. Color changes (ΔE) were measured using the CIE L^⁎a^⁎b^⁎ color space and a digital imaging system at 1, 7, 14, and 28 days of storage. Data were analyzed using Two-way ANOVA and Tukey's HSD post hoc test (P < 0.05). Composite resins showed significant increase in color changes by time (bulk-fill > conventional; P < 0.001). Coffee exhibited significantly more staining susceptibility than that of distilled water (P < 0.001). There was greater color changes with increasing the increment thickness, which was significant at 14 (P < 0.001) and 28 d (P < 0.01). Color change of bulk-fill composite resin was greater than that of the conventional one after coffee staining and is also a function of increment thicknesses.

Curing characteristics of flowable and sculptable bulk-fill composites

OBJECTIVES

The aim of this study was to determine and correlate the degree of conversion (DC) with Vickers hardness (VH) and translucency parameter (TP) with the depth of cure (DoC) of five bulk-fill composites.

MATERIALS AND METHODS

Six specimens per group, consisting of Tetric EvoCeram Bulk Fill ("TEC Bulk," Ivoclar Vivadent), SonicFill (Kerr), SDR Smart Dentin Replacement ("SDR," Dentsply), Xenius base ("Xenius," StickTech; commercialized as EverX Posterior, GC), Filtek Bulk Fill flowable ("Filtek Bulk," 3M ESPE), and Tetric EvoCeram ("TEC," control), were prepared for DC and VH: two 2-mm-thick layers, each light-cured for 10 s; one 4-mm bulk-fill, light-cured for 10 or 20 s; and one 6-mm bulk-fill, cured for 20 s. DC was measured using a Fourier-transform infrared spectrometer, VH using a Vickers hardness tester. DoC and TP were measured using an acetone-shaking test and a spectrophotometer, respectively. Data were analyzed using ANOVA and Pearson's correlation (α = 0.05).

RESULTS

DC and VH ranged between 40-70 % and 30-80 VHN, respectively. TEC Bulk, Xenius, and SonicFill, bulk-filled as 4-mm-thick specimens, showed bottom-to-top hardness ratios above 80 % after 20 s curing. A positive linear correlation was found for bottom DC and VH. An average DC ratio of 0.9 corresponded to a bottom-to-top VH ratio of 0.8.

CONCLUSIONS

Sculptable bulk-fills require 20 s, whereas 10 s curing time was sufficient for flowable bulk-fills using a high-intensity LED unit.

CLINICAL RELEVANCE

Clinicians should be aware that longer curing times may be required for sculptable than flowable bulk-fill composites in order to achieve optimal curing characteristics.

The Influence of Irradiation Time and Layer Thickness on Elution of Triethylene Glycol Dimethacrylate from SDR® Bulk-Fill Composite

Objective. This study aimed to evaluate triethylene glycol dimethacrylate (TEGDMA) elution from SDR bulk-fill composite. Methods. Three groups of samples were prepared, including samples polymerized in a 4 mm layer for 20 s, in a 4 mm layer for 40 s, and in a 2 mm layer for 20 s. Elution of TEGDMA into 100% ethanol, a 75% ethanol/water solution, and distilled water was studied. The TEGDMA concentration was measured using HPLC. Results. The TEGDMA concentration decreased in the following order: 100% ethanol > 75% ethanol > distilled water. Doubling the energy delivered to the 4 mm thick sample caused decrease (p < 0.05) in TEGDMA elution to distilled water. In ethanol solutions, the energy increase had no influence on TEGDMA elution. Decreasing the sample thickness resulted in decrease (p < 0.05) in TEGDMA elution for all the solutions. Conclusions. The concentration of eluted TEGDMA and the elution time were both strongly affected by the hydrophobicity of the solvent. Doubling the energy delivered to the 4 mm thick sample did not decrease the elution of TEGDMA but did decrease the amount of the monomer available to less aggressive solvents. Elution of TEGDMA was also correlated with the exposed sample surface area. Clinical Relevance. Decreasing the SDR layer thickness decreases TEGDMA elution.

Transmission of violet and blue light through conventional (layered) and bulk cured resin-based composites

OBJECTIVES

This study measured the transmission of light in the 'violet' (350≤λ≤425nm) and 'blue' (425<λ≤550nm) spectral ranges from a polywave(®) LED curing light through different thicknesses of four commercial, resin-based composites (RBCs).

MATERIAL AND METHODS

Samples of conventional layered RBCs (Tetric EvoCeram A2, Filtek Supreme Ultra A2B), and bulk-curing resins (Tetric EvoCeram Bulk Fill IVA, and SureFil SDR Flow U) were prepared. Three samples of each RBC were made at thicknesses of 0.1, 0.7, 1, 2, and 4-mm. The uncured RBC specimens were affixed at the entrance aperture of a 6-inch integrating sphere and light-cured once for 20s using a polywave(®) LED curing light (Bluephase G2) on its high power setting. The spectral radiant power transmitted through each RBC in the 'violet' and 'blue' regions was measured using a fiberoptic spectrometer.

RESULTS

As RBC thickness increased, an exponential attenuation of transmitted light was measured (R(2)>0.98). Attenuation was greater for the 'violet' than for the 'blue' spectral regions. At the light tip, the violet light component represented 15.4% of the light output. After passing through 4-mm of RBC, the violet light represented only between 1.2-3.1% of the transmitted light depending on the RBC. Depending on RBC, approximately 100mW from the Bluephase G2 was transmitted through 0.1-mm of RBC in the 'violet' range, falling at most to 11mW after passing through 2-mm of RBC, and to only 2mW at 4-mm depth.

CONCLUSIONS

Increasing RBC thickness results in an exponential decrease in light transmission. This attenuation is RBC-dependent with shorter wavelengths (violet) attenuated to a greater extent than longer wavelengths (blue).

CLINICAL RELEVANCE

Despite the increased translucency of bulk curing RBCs, spectral radiant power shorter than 425nm from a curing light is unlikely to be effective at a depth of 4-mm or more.

Posterior bulk-filled resin composite restorations: A 5-year randomized controlled clinical study

OBJECTIVE

To evaluate in a randomized controlled study the 5-year clinical durability of a flowable resin composite bulk-fill technique in Class I and Class II restorations.

MATERIAL AND METHODS

38 pairs Class I and 62 pairs Class II restorations were placed in 44 male and 42 female (mean age 52.4 years). Each patient received at least two, as similar as possible, extended Class I or Class II restorations. In all cavities, a 1-step self-etch adhesive (Xeno V+) was applied. Randomized, one of the cavities of each pair received the flowable bulk-filled resin composite (SDR), in increments up to 4mm as needed to fill the cavity 2mm short of the occlusal cavosurface. The occlusal part was completed with the nano-hybrid resin composite (Ceram X mono+). In the other cavity, the resin composite-only (Ceram X mono+) was placed in 2mm increments. The restorations were evaluated using slightly modified USPHS criteria at baseline and then yearly during 5 years. Caries risk and bruxing habits of the participants were estimated.

RESULTS

No post-operative sensitivity was reported. At 5-year 183, 68 Class I and 115 Class II, restorations were evaluated. Ten restorations failed (5.5%), all Class II, 4 SDR-CeramX mono+ and 6 CeramX mono+-only restorations. The main reasons for failure were tooth fracture (6) and secondary caries (4). The annual failure rate (AFR) for all restorations (Class I and II) was for the bulk-filled-1.1% and for the resin composite-only restorations 1.3% (p=0.12). For the Class II restorations, the AFR was 1.4% and 2.1%, respectively.

CONCLUSION

The stress decreasing flowable bulk-fill resin composite technique showed good durability during the 5-year follow-up.

CLINICAL SIGNIFICANCE

The use of a 4mm incremental technique with the flowable bulk-fill resin composite showed during the 5-year follow up slightly better, but not statistical significant, durability compared to the conventional 2mm layering technique in posterior resin composite restorations.

Degree of Conversion and BisGMA, TEGDMA, UDMA Elution from Flowable Bulk Fill Composites

The degree of conversion (DC) and the released bisphenol A diglycidyl ether dimethacrylate (BisGMA), triethylene glycol dimethacrylate (TEGDMA) and urethane dimethacrylate (UDMA) monomers of bulk-fill composites compared to that of conventional flowable ones were assessed using micro-Raman spectroscopy and high performance liquid chromatography (HPLC). Four millimeter-thick samples were prepared from SureFil SDR Flow (SDR), X-tra Base (XB), Filtek Bulk Fill (FBF) and two and four millimeter samples from Filtek Ultimate Flow (FUF). They were measured with micro-Raman spectroscopy to determine the DC% of the top and the bottom surfaces. The amount of released monomers in 75% ethanol extraction media was measured with HPLC. The differences between the top and bottom DC% were significant for each material. The mean DC values were in the following order for the bottom surfaces: SDR_4mm_20s > FUF_2mm_20s > XB_4mm_20s > FBF_4mm_20s > XB_4mm_10s > FBF_4mm_10s > FUF_4mm_20s. The highest rate in the amount of released BisGMA and TEGDMA was found from the 4 mm-thick conventional flowable FUF. Among bulk-fills, FBF showed a twenty times higher amount of eluted UDMA and twice more BisGMA; meanwhile, SDR released a significantly higher amount of TEGDMA. SDR bulk-fill showed significantly higher DC%; meanwhile XB, FBF did not reach the same level DC, as that of the 2 mm-thick conventional composite at the bottom surface. Conventional flowable composites showed a higher rate of monomer elution compared to the bulk-fills, except FBF, which showed a high amount of UDMA release.

Effect of resin thickness, and curing time on the micro-hardness of bulk-fill resin composites

Background

Bulk-fill resin composite has been introduced, their manufacturers claimed that they can be applied in bulks of 4mm, without necessitating a prolonged curing time, or a light curing unit with increased irradiance. Thus this study was conducted to evaluate the effect of resin thickness, and curing time on the micro-hardness of two bulk -fill resin composites; Tetric Evo-Ceram [TE], and X-trafil [XF].

Material and Methods

120 cylindrical specimens were prepared, and divided into 24 groups (n=5/group), representing the two bulk-fill resin composites, three different material thicknesses (2, 3 and 4 mm) and the four curing times used in the study (10, 20, 40, and 60 seconds). The specimens were light-cured from the top surface only. Specimens were stored in light proof containers in complete darkness at 37°C for 24 hours. Micro-hardness test was conducted on both top and bottom surfaces using Vickers micro-hardness tester with 500 g load and a dwell time of 15 seconds. Data were statistically analyzed by Four-way ANOVA of Variance. The significance level was set at P ≤ 0.05. Pearson Correlation used to determine significant correlations between mean micro-hardness (top) and (bottom) surfaces.

Results

Four way-ANOVA shows that different tested materials produce a statistically significant effect on mean micro-hardness (VHN) at p≤0.001, while thickness, curing time, and surface revealed statistically non significant effect on mean micro-hardness (VHN) at p≥0.05. [XF] (92.01±3.15 VHN) showed statistically significant higher mean micro-hardness than [TE] (54.13±4.96 VHN). Pearson Correlation revealed that there was a significant direct correlation between micro-hardness (bottom) and mean micro-hardness (top) (mm), r = 0.985, p (2-tailed) ≤0.001.

Conclusions

Within the limitations of this study, the bulk-fill resin composites used in this study can be placed and cured properly in the 4 mm bulk.

Key words:Bulk-fill resin composite, micro-hardness, thickness, curing time.

Effect of Tooth-structure Thickness on Light Attenuation and Depth of Cure

Newer bulk-fill composites claim a greater depth of cure than conventional resin-based composites. To facilitate complete curing, the manufacturer of SonicFill (Kerr) recommends curing from the occlusal, as well as the buccal and lingual, surfaces of the tooth. The purpose of this study was to quantify the degree of curing light attenuation as it passes through natural tooth structure, and how this attenuation affects the depth of cure of different posterior resin composites. Ten noncarious extracted mandibular third molars were sectioned to produce 5-mm-thick pieces of buccal tooth structure. Sanding 0.5-mm increments from the flattened surface produced 4.5-, 4.0-, 3.5-, 3.0-, 2.5-, 2.0-, and finally 1.5-mm-thick sections. A Bluephase G2 (Ivoclar) curing light with an 8-mm-diameter light guide set on high for 20 seconds was used for measurement of irradiance as it passed through different thicknesses of tooth structure and air. The average irradiance (mW/cm(2)) was measured with a MARC-RC Resin Calibrator with a 4-mm-diameter sensor (BlueLight Analytics). To measure depth of cure of a conventional hybrid composite (Herculite Ultra; Kerr) vs a bulk-fill hybrid composite (SonicFill) through varying thicknesses of tooth structure, composites were cured in a 4-mm-diameter × 10.25-mm-long split mold according to International Organization for Standardization 4049. A mean and standard deviation was determined per group. Data were analyzed with a one-way analysis of variance (ANOVA)/Tukey test and two-way ANOVA/Tukey test (α=0.05). One-way ANOVA/Tukey found a significant decrease in irradiance based on thickness of tooth structure or distance through air (p<0.001). Two-way ANOVA/Tukey found a significant decrease in depth of cure based on thickness of tooth structure (p<0.001) and on composite type (p<0.001) with no significant interaction (p=0.623). SonicFill had a significantly greater depth of cure than Herculite Ultra.

Push-Out Bond Strength of Restorations with Bulk-Fill, Flow, and Conventional Resin Composites

The aim of this study was to evaluate the bond strengths of composite restorations made with different filler amounts and resin composites that were photoactivated using a light-emitting diode (LED). Thirty bovine incisors were selected, and a conical cavity was prepared in the facial surface of each tooth. All preparations were etched with Scotchbond Etching Gel, the Adper Scotchbond Multipurpose Plus adhesive system was applied followed by photoactivation, and the cavities were filled with a single increment of Filtek Z350 XT, Filtek Z350 XT Flow, or bulk-fill X-tra fil resin composite (n = 10) followed by photoactivation. A push-out test to determine bond strength was conducted using a universal testing machine. Data (MPa) were submitted to Student's t-test at a 5% significance level. After the test, the fractured specimens were examined using an optical microscope under magnification (10x). Although all three composites demonstrated a high prevalence of adhesive failures, the bond strength values of the different resin composites photoactivated by LED showed that the X-tra fil resin composite had a lower bond strength than the Filtek Z350 XT and Filtek Z350 XT Flow resin composites.

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

OBJECTIVES

This study evaluated the effect of using three commercial light curing units (LCUs) delivering a range of irradiance values, but delivering similar radiant exposures on the depth of cure of two different resin-based composites (RBCs).

METHODS

A conventional hybrid RBC (Z100 shade A2, 3M ESPE) or a bulk fill RBC (Tetric EvoCeram Bulk Fill shade IVA, Ivoclar Vivadent) was packed into a 10-mm deep semicircular metal mold with a 2-mm internal radius. The RBC was exposed to light from a plasma-arc-curing (PAC) light (Sapphire Plus, DenMat) for five seconds, a quartz-tungsten-halogen (QTH) light (Optilux 501, Kerr) for 40 seconds, or a light-emitting-diode (LED) light (S10, 3M ESPE) for 20 seconds and 40 seconds (control). The Knoop microhardness was then measured as soon as possible at the top surface and at three points every 0.5 mm down from the surface. For each RBC, a repeated measures analysis of variance (ANOVA) model was used to predict the Knoop hardness in a manner analogous to a standard regression model. This predicted value was used to determine at what depth the RBC reached 80% of the mean hardness achieved at the top surface with any light.

RESULTS

The PAC light delivered an irradiance and radiant exposure of 7328 mW/cm(2) and 36.6 J/cm(2), respectively, to the RBCs; the QTH light delivered 936 mW/cm(2) and 37.4 J/cm(2) and in 20 seconds the LED light delivered 1825 mW/cm(2) and 36.5 J/cm(2). In 40 seconds, the control LED light delivered a radiant exposure of 73.0 J/cm(2). For Z100, using 80% of the maximum hardness at the top surface as the criteria for adequate curing, all light exposure conditions achieved the 2.0-mm depth of cure claimed by the manufacturer. The LED light used for 40 seconds achieved the greatest depth of cure (5.0 mm), and the PAC light used for five seconds, the least (2.5 mm). Tetric EvoCeram Bulk Fill achieved a 3.5-mm depth of cure when the broad-spectrum QTH light was used for 40 seconds delivering 37.4 J/cm(2). It required a 40-second exposure time with the narrow-spectrum LED, delivering approximately 73 J/cm(2) to reach a depth of cure of 4 mm.

CONCLUSIONS

When delivering a similar radiant exposure of 37 J/cm(2), the QTH (40 seconds) and LED (20 seconds) units achieved a greater depth of cure than the PAC (five seconds) light. For both resins, the greatest depth of cure was achieved when the LED light was used for 40 seconds delivering 73 J/cm(2) (p<0.05).

Monomer conversion and shrinkage force kinetics of low-viscosity bulk-fill resin composites

OBJECTIVE

To investigate the subsurface degree of conversion (DC) and shrinkage force formation of low-viscosity (flowable) bulk-fill composite materials.

MATERIALS AND METHODS

Three flowable bulk-fill resin composites [SureFil SDR flow (SDR; Dentsply DeTrey), Venus Bulk Fill (VB; Heraeus Kulzer) and x-tra base (XB; VOCO)] and one conventional flowable control composite material [EsthetX flow (EX; Dentsply DeTrey)] were tested. The materials were photoactivated for 20 s at an irradiance of 1170 mW/cm2 and the DC (n=5) was recorded at 0.1-, 1.5- and 4-mm depth using Fourier transform infrared spectroscopy. Shrinkage forces (n=5) of 1.5-mm-thick specimens were continuously recorded for 15 min using a custom-made stress analyzer. Data were statistically analyzed by ANOVA, Tukey's HSD and Bonferroni's post-hoc tests (α=0.05).

RESULTS

SDR generated the significantly lowest shrinkage forces (22.9±1.4 N), but also attained the significantly lowest DC at 1.5-mm depth (67.5±0.8%). The conventional flowable composite EX generated the significantly highest shrinkage forces (40.7±0.7 N) and reached a significantly higher DC (74.4±1.3%) compared to SDR and XB at 1.5-mm depth. The shrinkage force values of VB (29.4±1.1 N) and XB (28.3±0.6 N) were similar (p>0.05). All materials attained significantly higher DC at 4-mm depth than at the near-surface.

CONCLUSION

The tested low-viscosity bulk-fill materials show lower shrinkage force formation than a conventional flowable resin composite at high levels of degree of conversion up to 4-mm incremental thickness.

Pre-heating of high-viscosity bulk-fill resin composites: effects on shrinkage force and monomer conversion

OBJECTIVES

To investigate the influence of pre-heating of high-viscosity bulk-fill composite materials on their degree of conversion and shrinkage force formation.

METHODS

Four bulk-fill composite materials (Tetric EvoCeram Bulk Fill-TECBF, x-tra fil-XF, QuixFil-QF, SonicFill-SF) and one conventional nano-hybrid resin composite (Tetric EvoCeram-TEC) were used. The test materials were either kept at room temperature or pre-heated to 68°C by means of a commercial heating device, before being photoactivated with a LED curing unit for 20s at 1170mW/cm(2). Shrinkage forces (n=5) of 1.5-mm-thick specimens were recorded in real-time for 15min inside a temperature-controlled chamber at 25°C (simulating intraoral temperature after rubber dam application) with a custom-made stress analyzer. Degree of conversion (n=5) was determined at the bottom of equally thick (1.5mm) specimens using Fourier transform infrared spectroscopy. Data were analyzed with Student's t-test, ANOVA and Tukey's HSD post-hoc test (α=0.05).

RESULTS

Composite pre-heating significantly increased the degree of conversion of TECBF, but had no effect on monomer conversion of the other materials investigated. For each of the test materials, pre-heated composite generated significantly lower shrinkage forces than room-temperature composite. At both temperature levels, TECBF created the significantly highest shrinkage forces, and QF caused significantly higher shrinkage forces than both XF and TEC.

CONCLUSIONS

Both the composite material and the pre-cure temperature affect shrinkage force formation. Pre-heating of bulk-fill and conventional restorative composites prior to photoactivation decreases polymerization-induced shrinkage forces without compromising the degree of conversion.

CLINICAL SIGNIFICANCE

Composite pre-heating significantly reduces shrinkage force formation of high-viscosity bulk-fill and conventional resin composites, while maintaining or increasing the degree of monomer conversion, dependent upon the specific composite material used.