Spectroscopic and Mechanical Properties of a New Generation of Bulk Fill Composites

Contemporary flowable bulk-fill resin-based composites: a systematic review

Flowable bulk-fill resin-based composites (BF-RBCs) represent a new and interesting alternative for the bulk-fill restorative techniques in the posterior region. However, they comprise a heterogeneous group of materials, with important differences in composition and design. Therefore, the aim of the present systematic review was to compare the main properties of flowable BF-RBCs, including their composition, degree of monomer conversion (DC), polymerization shrinkage and shrinkage stress, as well as flexural strength. The search was conducted following PRISMA guidelines in the Medline (PubMed), Scopus and Web of Science databases. In vitro articles reporting on the DC, polymerization shrinkage/shrinkage stress, and flexural strength of flowable BF-RBCs strength were included. The QUIN risk-of-bias (RoB) tool was used for assessing the study quality. From initially 684 found articles, 53 were included. Values for DC ranged between 19.41 and 93.71%, whereas polymerization shrinkage varied between 1.26 and 10.45%. Polymerization shrinkage stresses reported by most studies ranged between 2 and 3 MPa. Flexural strength was above 80 MPa for most materials. A moderate RoB was observed in most studies. Flowable BF-RBCs meet the requirements to be indicated for bulk fill restoration technique in the posterior region. However, important variations among composition and properties hinder extrapolation of the results to materials different from those reported here. Clinical studies are urgently required to assess their performance under a real working scenario.

Effect of Low pH Dietary Supplements on Discoloration of Resin Composites

AIM

This study aimed to evaluate the impact of the consumption of low pH dietary supplements on the color stability of different resin composites.

MATERIALS AND METHODS

Three different restorative materials were used for this in vitro study: Filtek One Bulk-Fill (FOB), Filtek Z550 (Z550), and Fill-Up (FUP). Samples fabricated from each composite group were divided into four subgroups, and color measurements were performed at baseline. The control subgroup was stored in distilled water, and the other three subgroups were immersed in acidic dietary supplement solutions (Redoxon, Supradyn, and Voonka Collagen Shake) for 2 minutes daily for 28 days. Color measurements were obtained using a digital spectrophotometer. Color change values (ΔE1) were calculated after each color measurement. Next, all samples were immersed in a coffee solution for 7 days and repeat color measurements were taken to determine ΔE2 values. The study groups were compared using the Kruskal-Wallis test (α =0.05).

RESULTS

ΔE1 values were significantly different among the groups (P < 0.05). While Voonka Collagen Shake produced the greatest discoloration in FOB (1.67 ± 1.08) and Filtek Z550 (3.59 ± 1.90) materials, Fill-Up showed the highest discoloration (3.14 ± 0.37) with Supradyn. Analysis of ΔE2 values demonstrated a significant difference only for the Filtek Z550-Redoxon group versus the control group (P < 0.05).

CONCLUSION

Acidic dietary supplements not only produce color alterations in resin composites but also reduce the staining resistance of the composite further, depending on the type of composite and dietary supplement. Consumption of staining food after taking Redoxon effervescent tablets produces greater discoloration in Filtek Z550 restorations compared with other restorative materials.

Effect of polymerization mode on shrinkage kinetics and degree of conversion of dual-curing bulk-fill resin composites

OBJECTIVES

To assess the behavior of dual-cure and conventional bulk-fill composite materials on real-time linear shrinkage, shrinkage stress, and degree of conversion.

MATERIALS AND METHODS

Two dual-cure bulk-fill materials (Cention, Ivoclar Vivadent (with ion-releasing properties) and Fill-Up!, Coltene) and two conventional bulk-fill composites (Tetric PowerFill, Ivoclar Vivadent; SDR flow + , Dentsply Sirona) were compared to conventional reference materials (Ceram.x Spectra ST (HV), Dentsply Sirona; X-flow; Dentsply Sirona). Light curing was performed for 20 s, or specimens were left to self-cure only. Linear shrinkage, shrinkage stress, and degree of conversion were measured in real time for 4 h (n = 8 per group), and kinetic parameters were determined for shrinkage stress and degree of conversion. Data were statistically analyzed by ANOVA followed by post hoc tests (α = 0.05). Pearson's analysis was used for correlating linear shrinkage and shrinkage force.

RESULTS

Significantly higher linear shrinkage and shrinkage stress were found for the low-viscosity materials compared to the high-viscosity materials. No significant difference in degree of conversion was revealed between the polymerization modes of the dual-cure bulk-fill composite Fill-Up!, but the time to achieve maximum polymerization rate was significantly longer for the self-cure mode. Significant differences in degree of conversion were however found between the polymerization modes of the ion-releasing bulk-fill material Cention, which also exhibited the significantly slowest polymerization rate of all materials when chemically cured.

CONCLUSIONS

While some of the parameters tested were found to be consistent across all materials studied, heterogeneity increased for others.

CLINICAL RELEVANCE

With the introduction of new classes of composite materials, predicting the effects of individual parameters on final clinically relevant properties becomes more difficult.

Investigating the Cytotoxicity of Dual-Cure Bulk-Fill Resin Materials on L929 Cells

The aim of this in vitro study was to investigate cytotoxic effects of dual-cure bulk-fill resin materials polymerized with a third-generation LED light-curing unit (LCU) on L929 fibroblast cells in terms of morphology and viability. Three novel dual-cure, flowable bulk-fill materials (Fill-Up!™), a bioactive material (ACTIVA™ BioACTIVE-RESTORATIVE™), and a dual-cure bulk-fill composite material (HyperFIL® HAp) polymerized by LED LCU (VALO™ Cordless) were tested. Each material was placed in plastic rings (4 mm × 5 mm) in a single layer. Unpolymerized rings filled with each material were placed in direct contact with cells and then polymerized. After polymerization, the removed medium was readded to wells. In this study, four control groups were performed: the medium-free control group, medium control group, physical control group, and light applied control group. Three samples were prepared from each group. After 24 h, the morphology of cells was examined and a WST-1 test was performed. The percentage of cell viability (PCV) of each group was calculated. The experiment was repeated three times. Data were analyzed by a Kruskal–Wallis Test and a Mann–Whitney U test. p < 0.05 was considered significant. The PCV of all groups were found to be significantly lower than the medium control group (p < 0.05). The lowest PCV was obtained in HyperFIL® Hap, while highest was in the Fill-Up!™. In the morphology of cells related to the experimental groups, it was observed that the spindle structures of cells were disrupted due to cytotoxicity; cells became rounded and intercellular space increased. There were no significant differences between the control groups (p > 0.05). All control groups showed acceptable PCV (>70%) and cells were spindle-like, similar to the original fibroblast cells. It can be suggested that clinicians should pay attention when applying dual-cure bulk-fill materials in deep cavities, or they should use a liner material under these materials.

Evaluation of the Surface Roughness of Bulk-Fill Composite Resins after Submission to Acidic and Abrasive Aggressions

This in vitro study aimed to assess the erosive effect of hydrochloric acid in association with toothbrushing procedure on the surface condition of three bulk-fill composite resins used for direct restoration. A total of 480 samples (160 from each composite resin): X-tra Fil (VOCO, Germany)—group A, Filtek Bulk-fill Posterior (3M-ESPE, St. Paul, MN, USA)—group B, G-aenial Posterior (GC Japan)—group C were prepared, submitted to chemical attack for 60 min with hydrochloric acid 30% and, subsequently, submitted to the abrasive effect of toothbrushing using 10,000 cycles with medium and hard bristles, at three different times (immediately and after 30 min after acid attack or without any chemical attack). The surface roughness of the samples was measured using a noncontact profilometer (Dektak XT, Bruker, Billerica, MA, USA). The values were analyzed using ANOVA and post hoc Bonferroni tests, with a p < 0.05. Chemical attack for 60 min associated with one year of toothbrushing with toothbrushes having medium or hard bristles increase the surface roughness of tested bulk-fill composite resins. No differences were recorded between toothbrushing with medium or firm bristles immediately or 30 min after acidic challenge for each of the three bulk-fill composite resins. Exposure to hydrochloric acid determines no effect on surface roughness of bulk-fill composite resins.

Aging-Dependent Changes in Mechanical Properties of the New Generation of Bulk-Fill Composites

This study evaluated the behavior of a new generation of bulk-fill resin composites after prolonged exposure to an aqueous environment and accelerated aging in ethanol. Six bulk-fill materials were tested (Tetric PowerFill, Filtek One Bulk Fill Restorative, Tetric EvoCeram Bulk Fill, Fill-Up!, Tetric PowerFlow, SDR Plus Bulk Fill Flowable) and compared to two conventional reference materials (Tetric EvoCeram and Tetric EvoFlow). Flexural strength, modulus, and Weibull parameters were examined at three time points: 1 day, 30 days, and 30 days followed by ethanol immersion. Degree of conversion after 30 days, water sorption, and solubility up to 90 days were also investigated. Filtek One Bulk Fill had the highest flexural strength and modulus among the tested materials, followed by Tetric PowerFill and SDR plus. Flexural strength and modulus of high-viscosity bulk-fill materials showed higher stability after accelerated aging in ethanol compared to their low-viscosity counterparts and reference materials. After 30 days, the degree of conversion was above 80% for all tested materials. Dual-cure material Fill-Up! was the best-cured material. The water sorption was highest for Fill-Up!, Filtek One Bulk Fill Restorative, and Tetric EvoFlow, while solubility was highest for Tetric EvoCeram. After aging in water and ethanol, new generation high-viscosity bulk-fill materials showed better mechanical properties than low-viscosity bulk-fill and conventional composites under extended light curing conditions.

Vibrational Imaging Techniques for the Characterization of Hard Dental Tissues: From Bench-Top to Chair-Side

Currently, various analytical techniques, including scanning electron microscopy, X-Ray diffraction, microcomputed tomography, and energy dispersive X-ray spectroscopy, are available to study the structural or elemental features of hard dental tissues. In contrast to these approaches, Raman Microspectroscopy (RMS) has the great advantage of simultaneously providing, at the same time and on the same sample, a morpho-chemical correlation between the microscopic information from the visual analysis of the sample and its chemical and macromolecular composition. Hence, RMS represents an innovative and non-invasive technique to study both inorganic and organic teeth components in vitro. The aim of this narrative review is to shed new light on the applicative potential of Raman Microspectroscopy in the dental field. Specific Raman markers representative of sound and pathological hard dental tissues will be discussed, and the future diagnostic application of this technique will be outlined. The objective and detailed information provided by this technique in terms of the structure and chemical/macromolecular components of sound and pathological hard dental tissues could be useful for improving knowledge of several dental pathologies. Scientific articles regarding RMS studies of human hard dental tissues were retrieved from the principal databases by following specific inclusion and exclusion criteria.

Comparison of three different bulk-filling techniques for restoring class II cavities: μCT, SEM-EDS combined analyses for margins and internal fit assessments

OBJECTIVE

Evaluation of the behavior of three different bulk-filling techniques in terms of internal adaptation and external marginal sealing for restoring class II cavities.

METHODS

Fifteen extracted sound molar teeth were used. Two standardized class II mesio/disto-occlusal (MO/DO) slot cavities, 4 mm long, 4 mm wide and 3 mm deep were prepared in each tooth, obtaining n=30 cavity preparations. The cavities were randomly assigned into three groups (n=10 per group) according to three bulk filling techniques: Bulk Traditional (BT), Bulk&Go (BG) and Bulk&Flow (BF). The teeth were analyzed by scanning electron microscopy (SEM) to investigate the external marginal seal. Thereafter, the chemical composition of tooth-restoration interface was analyzed by energy-dispersive X-ray spectroscopy (EDS). Complementary information to the SEM and EDS were obtained by micro-computed tomography (μCT) to assess the internal fit.

RESULTS

SEM analysis showed a proper external marginal seal for all groups tested as confirmed by the EDS investigation, highlighting the presence of adhesive layer at the tooth-restoration interface. The internal marginal adaptation by means of μCT analysis revealed gaps formation at the tooth-restoration interface only for BT group, while an intimate contact free of gaps were found in the other two groups. Moreover, in BT and BF groups voids were present within the restoration.

SIGNIFICANCE

BG and BF techniques can be considered as reliable alternatives to BT technique, as they simplify the class II restoration without transforming it into class I, thus ensuring a successful result.

Influence of the ceramic translucency on the relative degree of conversion of a direct composite and dual-curing resin cement through lithium disilicate onlays and endocrowns

INTRODUCTION

The goal of this study was to investigate the influence of the ceramic translucency, restoration type and polymerization time on the relative degree of conversion of a dual-curing resin cement and a conventional microhybrid resin composite using a high-power light-curing device.

METHODS AND MATERIALS

Two 4.0 mm thick onlay (O) and two 7.5 mm thick endocrown (E) lithium disilicate restorations in high and low translucency (HT/LT) were fabricated on a decapitated molar. The pulp chamber was prepared to accommodate a 2 mm layer of a microhybrid resin composite (MHC) or dual-curing resin cement (DCC). Composite specimens were light-cured (n = 15; 1200 mW/cm²) without or through an onlay or endocrown restoration. Fourier-transform infrared spectroscopy (FTIR) absorbance curves were collected for the same composite specimen after 3 × 20, 3 × 40, 3 × 60 and 3 × 90 s of light-curing. The relative degree of conversion (DC%) was calculated and results analyzed using Kruskal-Wallis test and Friedman's ANOVA. Alpha was set at 0.05.

RESULTS

After 3 × 60 s, the DC of MHC was significantly lower (p = 0.03; r = 0.61) under LT/EC restorations (Mdn: 77.8%) than HT/EC restorations (Mdn: 95.2%). DC of the DCC was not significantly affected by the ceramic translucency or restoration type. MHC had a significant higher DC than DCC under the HT/O, LT/O and HT/E restorations. There were no significant differences between MHC and DCC cured through LT/E restorations.

CONCLUSION

DC for DCC was not significantly affected by the ceramic translucency or restoration type. DC for MHC was significantly lower for LT/EC than HT/EC restorations after 3 × 60s polymerization, but not different for the high translucent restorations and low translucent onlays.

CLINICAL RELEVANCE

the use of light-curing microhybrid composite for bonding high translucent onlays and endocrowns and low translucent onlays seems feasible.

Dental Bulk-Fill Resin Composites Polymerization Efficiency: A Systematic Review and Meta-Analysis

Dental Bulk-Fill Composites (BFCs) and Bulk-Fill Flowables (BFFs) were introduced in the market to facilitate efficient bulk filling of cavities up to 5 mm. The aim of this study was to synthesize the literature investigating their polymerization efficiency. A comprehensive search of PubMed and the Cochrane Library from 2010 to January 2019 was performed using the medical subject headings. Screening of the titles, abstracts and full text was performed. Data extraction for relevant information was done on the included studies. Clinically relevant parameters were selected to present the study estimates (meta-analysis) using a random effects model for polymerization efficiency (Degree of Conversion (DC) and Depth of Cure (DoC)). Twenty one studies fulfilled the inclusion criteria and were included in the analysis reporting seven BFCs and nine BFFs. Ten materials reported acceptable DC values of above 55% and ten materials reported adequate DoC values. Most of the stated materials reported adequate DC and DoC values in at least one investigation with BFFs showing higher and more acceptable values compared to packable BFCs. It is suggested that future studies be carried out using a standard methodology following the ISO 4049 standard and manufacturer’s instructions to compare results.

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.

Microleakage Analysis of Different Bulk-Filling Techniques for Class II Restorations: µ-CT, SEM and EDS Evaluations

This study aimed to compare two different bulk-filling techniques, evaluating the internal and external adaptation of class II resin-composite restorations, by analysing the gap formation using microcomputed tomography (µ-CT) and scanning electronic microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS). Two standardized mesio/disto-occlusal (MO/DO) cavities were prepared in eight extracted human third molars that were divided, according to the filling technique used, in the following two groups (n = 4): BG (Bulk&Go group) and BT (Bulk Traditional group). After universal bonding application, followed by the light curing, all teeth were restored using a bulk-fill composite. Specimens were scanned with µ-CT to evaluate 3D interfacial gaps. Acquired µ-CT data were analysed to quantify the gap formation. Complementary information to the µ-CT analysis were obtained by SEM. Thereafter, the chemical composition of tooth-restoration interface was analysed using EDS. The µ-CT analysis revealed gaps formation at the tooth-restoration interface for both the BG and BT groups, while within the restoration, only in the BT group there was evidence of microleakage formation. The scanning electron micrographs of both groups showed that the external marginal integrity of the restoration was preserved, while EDS showed the three different structures (tooth surface, adhesive layer and resin composite) of the tooth-restoration interface, highlighting the absence of gap formation. In both BG and BT, the two filling techniques did not show significant differences regarding the internal and external marginal adaptation of the restoration. To achieve a successful restoration, the clinician could be advised to restore a class II cavity using a single increment bulk-filling technique (BG), thus treating it as a class I cavity.

The Effect of Shade and Thickness on the Depth of Cure of Bulk-Fill Composites with Different Viscosities

STATEMENT OF THE PROBLEM

In an attempt to enhance and simplify the restoration process, a new class of composite resins, called the bulk fill composite resins have been introduced. It is claimed that a depth of cure (DOC) of 4 mm can be achieved without affecting the properties of this material.

PURPOSE

The purpose of this study was to investigate the effect of different shades, thicknesses, and viscosities on the DOC of bulk-fill composites.

MATERIALS AND METHOD

In this experimental study, four bulk-fill composites [Filtek™ Bulk Fill Flowable (FBF), Filtek™ Bulk Fill posterior (FBP), Tetric® N-Flow Bulk Fill (TNF), Tetric® N-Ceram Bulk Fill (TNC)] and a conventional composite, Filtek™ Z250 XT Universal (FZ) were evaluated. The samples (n=5) were made using two different shades (light and dark), thicknesses (2 and 4mm), and viscosities (flowable and sculptable). Microhardness test was conducted on top and bottom surface using Vickers microhardness tester and DOC was calculated as the bottom/top ratio of yielded scores. Statistical analysis was done using a Mann Whitney test at p< 0.05.

RESULTS

DOC ranged between 52-95%. FBF composite exhibited the lowest overall hardness numbers. At 2-mm thickness, all the samples achieved an appropriate DOC. However, at 4mm thickness, only the light shades for FBF and TNF samples achieved a DOC very close to 0.8. At 4-mm thickness, the light shades for FBF, TNF and FZ samples exhibited significantly higher DOC compared to dark shades. For 4-mm-thick samples, the DOC of Filtek™ Bulk Fill (dark and light shades (and the DOC of Tetric® Bulk Fill (light shade (were different in flowable type from the sculptable type.

CONCLUSION

The shade and the viscosity of bulk-fill composites influence their DOC at 4-mm depths. Moreover, 20 seconds of light curing appears insufficient for 4mm thickness of bulk-fill composite.

Comparison of two curing protocols during adhesive cementation: can the step luting technique supersede the traditional one?

This study aims to compare the degree of conversion of two different curing protocols used during adhesive cementation. The following resin luting agents were tested: Hri Flow (MF) and pre-heated Hri Micerium (MH); light-cure Nexus Third Generation (NX3L) and dual-cure Nexus Third Generation (NX3D); dual cured RelyX Ultimate (RXU) and light-cure RelyX Veneers (RXL). For each tested material, ten samples were prepared and divided into two groups which had different curing protocols (P1 and P2): in P1, samples were cured for 40 s; in P2, samples were cured for 5 s, and then, after 20 s, cured again for additional 40 s. The degree of conversion (DC) was evaluated both during the first 5 min of the curing phase and after 1, 2, 7, 14 and 28 days (p = 0.05). Different trends were observed in DC values after 5 min by comparing P1 and P2. In both P1 and P2, DC decreased as follows, MH > MF > NX3L > RXL > RXU > NX3D. There were significant differences of DC values among all resin luting agents (p < 0.05) in P1, while no significant differences existed between MH and MF, and NX3L and RXL in P2. At 1, 2, 7, 14 and 28 days the light curing luting agents had a higher DC than the dual luting agents (p < 0.05). P1 and P2 were not statistically different at each time point (p > 0.05). Both P1 and P2 protocols let achieve an acceptable DC after 28 days. The tested P2 can be safely used to lute indirect restorations, simplifying the removal of cement excesses.

Comparison of objective indicators of various properties of photocomposite materials with the subjective assessment of dentists

Relevance. Composite materials of light curing have a large number of indications for use and are actively used by dentists in clinical practice. The properties of these materials differ from their composition and the size of the filler. We conducted a survey of dentists of general practitioners of public and private dental clinics in Omsk to determine compliance, objective indicators of physico-chemical parameters of the studied composite materials and their subjective assessment by doctors using these materials in their work.

Purpose. Comparison of objective indicators of various properties of photocomposite materials with the subjective assessment of dentists.

Materials and methods. The study of the physicochemical properties of light-cured composite materials most commonly used in the practice of Omsk dentists in public and private clinics. A research design was developed and a survey of 148 dentists in Omsk was conducted to determine the subjective assessment of these materials.

Results. A comparative analysis of the objective and subjective indicators of composite materials.

Conclusions. The physicochemical parameters of the photocomposite materials are fully consistent with the subjective assessment of dentists in Omsk.

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.

How Can Different Polishing Timing Influence Methacrylate and Dimethacrylate Bulk Fill Composites? Evaluation of Chemical and Physical Properties

The polishing procedure is commonly performed after direct composite restorations, and little information exists regarding the right timing during which it should be performed on bulk fill composites. This study investigated the effect of polishing timing on the degree of conversion (DC), Vickers microhardness (VMH), and surface morphology of a methacrylate- (MET-) and dimethacrylate- (DMET-) based bulk fill composite, by using FT-NIR, microhardness tester, and SEM. Composite samples were divided as follows: in Group I (immediate), samples were polished immediately after curing (t₀); in Group D (delayed), samples were polished after 24 h from curing (t₂₄), whereas the unpolished samples were considered as controls (Group C). The DC and VMH values were evaluated before and after polishing, at t₀ and t₂₄. Statistical analysis was performed with a significance level set at p < 0.05. At t₀, DC increased after polishing in both tested composites (p < 0.05), while at t₂₄, Group I and Group D were not different. By considering VMH, in the case of MET, all groups were not different both at t₀ and t₂₄. On the other hand, at t₀, VMH values of DMET increased after polishing. At t₂₄, DMET Group I and DMET Group D were not different. Qualitative evaluations of scanning electron micrographs showed that the surface morphology of MET presented a more irregular aspect than the DMET one. In summary, since the immediate polishing of MET can improve the DC, without negatively affecting VMH, but showing an irregular surface, it is suggested to wait 24 hours before proceeding with polishing. Otherwise, for DMET, the immediate polishing could definitively be recommended, since it improves both DC and VMH, also producing a regular surface. Therefore, clinicians may always safely polish a restoration performed using DMET-based bulk fill composites in one-chair appointment, avoiding a second appointment.

Curing Depth and Degree of Conversion of Five Bulk-Fill Composite Resins Compared to a Conventional Composite

Background:

Limited curing depth and its effect on the degree of conversion are among the challenges of working with light-cure composite resins. The use of bulk-fill composites is one strategy to overcome these limitations.

Methods:

Ever X Posterior (EXP), Filtek Bulk-Fill Posterior (FBP), Sonic Fill 2 (SF2), Tetric N-Ceram Bulk-Fill (TNB), and X-tra Fil (XF) bulk-fill and Filtek Z250 conventional composite were evaluated in this in vitro experimental study. Six samples for the assessment of microhardness and three samples for the evaluation of DC were fabricated of each composite. After light curing and polishing, the samples were incubated at 37°C for 24 hours. Microhardness was measured by a Vickers hardness tester three times and the mean value was calculated. DC of the top and bottom surfaces was determined using Fourier-Transform Infrared Spectroscopy (FTIR). Data were analyzed using one-way ANOVA and Tukey’s test.

Results:

Microhardness and DC were significantly different among the groups (P<0.001). XF and Z250 equally showed the highest bottom-to-top surface microhardness ratio (0.97 ± 0.01) and significantly higher DC in the top (P<0.001) and bottom (P<0.005) surfaces compared to other groups. TNB showed the lowest microhardness ratio (0.88 ± 0.04) and DC (68.66 ± 1.52 and 61.00 ± 2.00); the difference in DC of the bottom surface was statistically significant (P<0.003).

Conclusion:

It appears that bulk-fill composites evaluated in this study are adequately polymerized at 4 mm depth. Their DC was optimal and within the range of conventional composites.

Modern Trends in Dental Medicine: An Update for Internists

Traumatic injuries, genetic diseases, and external harmful agents such as bacteria and acids often compromise tooth integrity. There is an unmet medical need to develop alternative, innovative dental treatments that complement traditional restorative and surgery techniques. Stem cells have transformed the medical field in recent years. The combination of stem cells with bioactive scaffolds and nanostructured materials turns out to be increasingly beneficial in regenerative dental medicine. Stem cell-based regenerative approaches for the formation of dental tissues will significantly improve treatments and will have a major impact in dental practice. To date there is no established and reliable stem cell-based treatment translated into the dental clinics, however, the advances and improved technological knowledge are promising for successful dental therapies in the near future. Here, we review some of the contemporary challenges in dental medicine and describe the benefits and future possibilities of certain novel approaches in the emerging field of regenerative dentistry.

Depth of cure of bulk fill resin composites: A systematic review

OBJECTIVE

To evaluate scientific evidence regarding depth of cure of bulk-fill resin composites (BFRCs) and related factors.

MATERIAL AND METHODS

PubMed/Medline, Embase, Scopus, and ISI Web of Science databases were accessed from October 2016 to May 2017. Investigations published in English language, assessing depth of cure of BFRCs by microhardness test and/or degree of conversion (DC) were included. Studies using exclusively ISO 4049, employing specimens deepness less than 4 mm, as well as those not reporting exposure time and/or irradiance from light curing units (LCUs) were excluded.

RESULTS

In total, 742 studies were found from which 33 were included. From 21 studies evaluating BFRCs microhardness, 10 showed acceptable bottom/top ratios (≥0.8) for all tested materials. However, material-dependent results and non-satisfactory bottom/top microhardness ratios (<0.8) were reported in 9 and 2 investigations, respectively. From 19 studies that assessed DC, 11 showed acceptable results (≥50%) for all tested BFRCs, while 8 studies reported material-dependent outcomes. Overall, irradiance from LCUs ranged from 650 to 1330 mW/cm² and exposure time from 5 to 60 seconds. Favorable depth of cure results were observed with the use of LCUs emitting irradiance ≥1000 mW/cm² and exposure times ≥20 seconds.

CONCLUSIONS

High depth of cure rates by BFRCs, depends on some factors as material, irradiance and exposure time. Polywave LCUs were useful but not essential on polymerizing alternative photoinitiator-containing BFRC.

CLINICAL SIGNIFICANCE

LED curing devices (polywave or monowave) displaying an irradiance ≥1000 mW/cm² and 20 seconds of exposure time are imperative to accomplish successful polymerization of most BFRCs.

Novel Biological and Technological Platforms for Dental Clinical Use

Human teeth have a limited capacity to regenerate and thus biological reconstruction of damaged or lost dental tissues remains a significant challange in modern dentistry. Recent efforts focus on alternative therapeutic approaches for partial or whole tooth regeneration that complement traditional dental treatments using sophisticated materials and dental implants. These multidisciplinary approaches are based on the combination of stem cells with advanced tissue engineer products and computing technology, and they hold great promise for future applications in dentistry. The administration to patients of dynamic biological agents composed by stem cells and scaffolds will certainly increase the regenerative capacity of dental pathological tissues. The design of innovative materials for tissue restoration, diagnostics, imaging, and targeted pharmaceutical treatment will significantly improve the quality of dental care and will have a major societal impact. This review depicts the current challenges in dentistry and describes the possibilities for novel and succesful therapeutic applications in the near future.

Clinical performance of bulk-fill and conventional resin composite restorations in posterior teeth: a systematic review and meta-analysis

OBJECTIVES

The purpose of this systematic review was to compare the clinical performance of bulk-fill resin composites with conventional resin composites used for direct restorations of posterior teeth.

METHODS

This review followed the PRISMA statement. This review was registered at PROSPERO (registration number CRD42016053436). A search of the scientific literature was performed by two independent reviewers using the PubMed/MEDLINE, Embase, The Cochrane Library, and Web of Science databases from commencement until January 2018. The research question was "Do bulk-fill resin composites have a clinical performance comparable to conventional resin composites in posterior restorations?" Only studies evaluating class I and II direct restorations in permanent teeth with a follow-up period of at least 1 year were included. The RevMan 5 program was used for meta-analysis, calculating the relative risk (RR) and 95% confidence interval (CI) of the dichotomous outcome (restoration failure or success).

RESULTS

Ten articles were selected, comprising 941 analyzed restorations. The mean follow-up period was 33.6 months (12-72 months). No statistically significant differences in the failure rate were observed between conventional and base/flowable bulk-fill resin composites (p = 0.31; RR 1.49; 95% CI 0.69-3.25) or full-body/sculptable bulk-fill resin composites (p = 0.12; RR 1.89; 95% CI 0.84-4.24).

CONCLUSIONS

The present systematic review and meta-analysis indicate similar clinical performances of bulk-fill and conventional resin composites over a follow-up period of 12 to 72 months.

CLINICAL SIGNIFICANCE

Based on the results of this study, the bulk-fill resin composites could be an alternative for direct restorations in posterior teeth. However, clinical trials of longer duration are required.