Hardness investigation of conventional, bulk fill and flowable dental composites

Purpose: of the present paper is to investigate the micro-hardness of three types of resin-based composites – conventional, bulk fill and flowable. Design/methodology/approach: Cylindrical specimens with a diameter of 5 mm and thicknesses of 2, 3 and 4 mm were made from each composite. They were light cured for 20, 40 and 60 s with light intensity of 600, 1000 or 1500 mW/cm2. The Vickers micro-hardness was measured on the top and bottom surface of the specimens. Findings: The highest micro-hardness was measured in bulk fill composite, followed by conventional and the lowest was measured in the flowable one. Increasing the light intensity leads to increase of the micro-hardness on both surfaces of the three composites. The increase of the irradiation time results in increase of the micro-hardness mainly on the bottom surface of the composites. The change of the layer thickness influences the conventional and the flowable composites and almost does not affect the hardness of the bulk fill composite. Research limitations/implications: The limitations of this study concerns to the values of the light intensity, which are defined by the light curing unit (LCU) used. There are many LCUs on the market; consequently, constant investigations of dental composites micro-hardness are needed. Practical implications: The investigation of the micro-hardness of the three types of composites in different modes would be very helpful for clinicians to obtain successful polymerization of composite restorations in their everyday practice. Originality/value: The micro-hardness of three types resin-based dental composites – conventional, bulk fill and flowable is investigated and compared in varying of three mode parameters – light intensity, curing time and layer thickness.

Bond Strength of Self-Adhesive Flowable Composites and Glass Ionomer Cements to Primary Teeth: A Systematic Review and Meta-Analysis of In Vitro Studies

Background: Conventional composites are largely used in pediatric restorative dentistry and demonstrate successful clinical outcomes. However, the need for simplification of operative steps in young or uncooperative children demands reliable alternatives. Therefore, the aim of the present systematic review and meta-analysis was to evaluate the in vitro bond strength of glass ionomer cements (GICs) and self-adhesive flowable composites (SFCs) on deciduous teeth. Methods: A comprehensive literature search according to the PRISMA checklist was manually and electronically performed by two independent reviewers through the following databases: MEDLINE/PubMed, Google Scholar, Scopus, and Embase, to include in vitro studies comparing GICs and SFCs bond strength values of restorations on primary teeth. In addition, three groups of meta-analyses were conducted using random-effects models. Results: Three articles meeting the inclusion criteria were selected and subjected to both qualitative and quantitative assessment. No statistically significant difference was found between SFC versus GIC; however, both groups significantly differed with conventional flowable composites (CFs). Conclusions: Despite the absence of significant difference in bond strength values, SFCs may be considered a valid alternative to GICs in the restoration of deciduous teeth, although CFs proved better in vitro performances.

Relationships between Flexural and Bonding Properties, Marginal Adaptation, and Polymerization Shrinkage in Flowable Composite Restorations for Dental Application

To evaluate the flexural and bonding properties, marginal adaptation, and polymerization shrinkage in flowable composite restorations and their relationships, four new generation flowable composites, one conventional, and one bulk-fill flowable composite were used in this study. Flexural properties of the composites and shear bond strength to enamel and dentin for flowable restorations were measured immediately and 24 h after polymerization. Marginal adaptation, polymerization shrinkage, and stress were also investigated immediately after polymerization. The flexural properties, and bond strength of the flowable composites to enamel and dentin were much lower immediately after polymerization than at 24 h, regardless of the type of the composite. Polymerization shrinkage and stress varied depending on the material, and bulk-fill flowable composite showed much lower values than the others. The marginal adaptation and polymerization shrinkage of the composites appeared to have a much stronger correlation with a shear bond strength to dentin than to enamel. The weak mechanical properties and bond strengths of flowable composites in the early stage after polymerization must be taken into account when using them in the clinic. In addition, clinicians should be aware that polymerization shrinkage of flowable composites can still lead to the formation of gaps and failure of adaptation to the cavity regardless of the type of composite.

The results of self-etching self-adhesive flowable composite application for primary molars fissure sealing in children

Relevance. The use of light-cure sealants and flowable composites for fissure sealing in children is difficult due to the complexity of the procedure. The research aimed to study the efficiency of self-etching self-adhesive flowable composite for fissure sealing in primary molars in children.Materials and methods. The Local Ethical Committee permission and written informed voluntary consents from the parents were obtained before the study. Non-invasive fissure sealing with self-etching self-adhesive flowable composite (Constic, DMG, Germany) was performed in 48 primary molars in 48 children aged 2-5 years (mean 41.2 ± 1.3 months). After 6, 12, 18 and 24 months, the sealant’s retention (%) and frequency (%) of occlusal caries development, and 95% confidence intervals (CI) were calculated. The significance of the difference was assessed by the Student’s t-test.Results. After 6 and 12 months, complete sealant’s retention was revealed in 75.0% (CI 61.2-85.1%) and 60.4% (CI 46.3-73.0%) molars, p > 0.05; it decreased to 27.1% (CI 16.6-41.0%) and 18.7% (CI 10.2-31.9%), p > 0.05, after 18 and 24 months. Complete loss of the sealant was noted in 8.3-18.7% cases. The first caries lesion (2.1%, CI 0.4-10.9%) on the surface with the lost sealant was revealed after 12 months, after 24 months – 4.2% (CI 1.1-14.0%).Conclusions. In primary molars after non-invasive fissure sealing with self-etching self-adhesive flowable composite, complete loss of the sealant was from 8.3% to 18.7% after 6-24 months post-op, partial loss was from 8.3% to 31.3%. Occlusal caries was revealed in 6.3% cases after the sealant loss.

Mechanical and Rheological Properties of Flowable Resin Composites Modified with Low Addition of Hydrophilic and Hydrophobic TiO2 Nanoparticles

The aim of this work was to find the influence of the addition of low amount of hydrophilic and hydrophobic TiO2 nanoparticles on compressive strength, microhardness and rheological properties of flowable dental composite material. Specimens were prepared by adding 0.05; 0.2 and 1 wt. % of hydrophilic and hydrophobic 20 nm TiO2 nanoparticles. These specimens were compared to non-modified control specimens in compressive strength and microhardness. Furthermore, their rheological properties were determined. The optimal nanoparticle loading was 0.2 % hydrophobic TiO2, resulting in significantly higher compressive strength and microhardness than those of the control specimen group. Mechanical properties of flowable composites reinforced with hydrophilic and hydrophobic TiO2 at higher loadings are lower than those of control specimens, which is the result of nanoparticle agglomeration. TiO2 nanoparticles addition resulted in the decrease in viscosity in all specimens except for the specimewn with 1% hydrophilic TiO2 nanoparticles. In accordance to the obtained results, hydrophobic nanoparticle addition results in a more resistant and durable material, combined with an increased flowability compared to a non-modified composite.

Comparative evaluation of bond strength of three self-adhering flowable composites to sound and demineralized enamel – An in vitro study

Objectives: The purpose of this study was to determine bond strength of three self-adhering flowable composites. Materials and Methods: Mean tensile bond strength was measured in three groups – Group A – Constic, Group B – Dyad Flow, and Group C – Fusio Liquid Dentin on sound and demineralized primary teeth. Fracture pattern was studied using a stereomicroscope for each sample and in classified as adhesive, cohesive, or mixed fracture. Results: Mean tensile bond strength in sound enamel of Group A (Constic) was found to be 10.79 + 4.24, Group B (Dyad Flow) was 10.30 + 4.63, and of Group C (Fusio Liquid Dentine) was 11.87 + 4.45. No significant difference was found between the three groups (f = 0.327 and P = 0.724). However, a significant difference was found with demineralized enamel in three groups. Constic and Dyad Flow exhibited adhesive fracture pattern in majority of samples on sound enamel, whereas Fusio Liquid Dentin had mixed fracture pattern. On demineralized enamel, Constic exhibited adhesive fracture pattern majorly, whereas Dyad flow demonstrated mixed pattern and Fusio Liquid Dentin had more of cohesive fractures. Conclusion: Constic, Dyad Flow, and Fusio Liquid Dentin can be used instead of conventional pit and fissure sealants or in small occlusal cavities in primary teeth as a single step material.

Effect of Ultrasonic Vibration on Structural and Physical Properties of Resin-Based Dental Composites

This study aimed to investigate the influence of ultrasonic heat before photo-polymerization on the structural and physical properties of dental composites. Commercially available bulk-fill, nano-hybrid, micro-hybrid, and flowable composites were used. The samples were divided into three groups i.e., (i) without ultrasonic activation, (ii) ultrasonic activation at 15 Hz for 30 s, and (iii) ultrasonic activation at 15 Hz for 60 s. The degree of conversion percentage (DC%) and structural changes were evaluated with Fourier transform infrared spectroscopy. The presence of voids in restored tooth cavities were investigated with micro-computed tomography. The statistical analysis was performed using a one-way analysis of variance (ANOVA) post hoc Tukey’s test. The DC% was significantly increased with ultrasonic application in all groups except for flowable composites, whereby flowable composite showed a significant increase with 30 s ultrasonic activation only. The highest DC% was observed in 60 s ultrasonically activated nano-hybrid and micro-hybrid composites. The voids were reduced linearly with ultrasonic application in flowable and bulk-fill composites; however, non-linear behavior was observed with micro-hybrid and nano-hybrid composites, whereby the difference was significant within the groups. The frequency and time of the ultrasonic application is an important factor to consider and can be used to preheat composites before clinical application.

Effects of flowable liners on the shrinkage vectors of bulk-fill composites

Objectives This investigation evaluated the effect of flowable liners beneath a composite restoration applied via different methods on the pattern of shrinkage vectors. Methods Forty molars were divided into five groups (n = 8), and cylindrical cavities were prepared and bonded with a self-etch adhesive (AdheSe). Tetric EvoCeram Bulk Fill (TBF) was used as the filling material in all cavities. The flowable liners Tetric EvoFlow Bulk Fill (TEF) and SDR were used to line the cavity floor. In gp1-TBF, the flowable composite was not used. TEF was applied in a thin layer in gp2-fl/TEF + TBF and gp3-fl/TEF + TBFincremental. Two flowable composites with a layer thickness of 2 mm were compared in gp4-fl/TEF + TBF and gp5-fl/SDR + TBF. TEF and SDR were mixed with radiolucent glass beads, while air bubbles inherently present in TBF served as markers. Each material application was scanned twice by micro-computed tomography before and after light curing. Scans were subjected to image segmentation for calculation of the shrinkage vectors. Results The absence of a flowable liner resulted in the greatest shrinkage vectors. A thin flowable liner (gp2-fl/TEF + TBFbulk) resulted in larger overall shrinkage vectors for the whole restoration than a thick flowable liner (gp4-fl/TEF + TBF). A thin flowable liner and incremental application (gp3-fl/TEF + TBFincremental) yielded the smallest shrinkage vectors. SDR yielded slightly smaller shrinkage vectors for the whole restoration than that observed in gp4-fl/TEF + TBF. Conclusions Thick flowable liner layers had a more pronounced stress-relieving effect than thin layers regardless of the flowable liner type. Clinical relevance It is recommended to apply a flowable liner (thin or thick) beneath bulk-fill composites, preferably incrementally.