Polymerization shrinkage and shrinkage stress of bulk-fill and non-bulk-fill resin-based composites

Clinical comparison of high-viscosity glass-hybrid systems with a sculptable bulk-fill composite resin in different cavity types

OBJECTIVE

This randomized, double-blind clinical investigation assessed the performance of two high-viscosity glass-ionomer systems and a bulk-fill composite in different cavity types.

MATERIALS AND METHODS

In 146 participants, 360 (class I, II, and V) cavities were restored using three different materials (Equia Forte HT, Chemfill Rock, and SonicFill 2) with equal allocation. Using modified World Dental Federation criteria, restorations were assessed after 1 week, 6 months, and 18 months by an experienced examiner. Statistical analysis was conducted using Fisher's exact and Wilcoxon signed rank tests (α = 0.05).

RESULTS

After 18 months, 267 restorations were assessed in 116 participants. After 18 months, 5 Equia Forte HT restorations failed due to debonding and fracture. Only one loss was observed in the Chemfill Rock restorations. Equia Forte HT exhibited significantly lower retention than SonicFill 2 after 18 months (p = 0.019), irrespective of cavity type. At 1 week, 3 Class I restorations with SF showed postoperative sensitivity. The type of cavity did not affect the performance of the restorative materials used (p > 0.05).

CONCLUSION

Equia Forte HT and Chemfill Rock presented similar clinical performance regardless of color match. Equia Forte HT showed a lower performance compared to SonicFill 2.

CLINICAL SIGNIFICANCE

Glass-hybrid materials presented a lower performance in terms of color match or retention when compared to a sculptable bulk-fill composite resin.

Performance of low shrinkage Bis-EFMA based bulk-fill dental resin composites

OBJECTIVES

The purpose of this study was evaluating the performance of new Bis-EFMA based bulk-fill composites with common methacrylate based composites and commercial dental composites.

METHODS

The Bis-EFMA monomer was synthesized and the novel Bis-EFMA based bulk-fill composites were prepared. The resin composite samples were co-cultured with human gingival epithelial cells and human dental pulp stem cells to test the biocompatibility. The edge adaptation was observed under a combination of stereoscope and scanning electron microscope. The internal hardness was measured using a Vickers microhardness tester after one-time filling of cavities prepared in extracted teeth. After friction and wear test on the surface of the resin composites, the surface morphology and volume wear of each group were measured by the optical profilometer. The color stability was measured by a colorimeter.

RESULTS

Direct contact with human gingival epithelial cells and human dental pulp stem cells did not cause significant changes in their growth density and morphology, indicating good biocompatibility of Bis-EFMA group (p > 0.05). The continuous margin proportion of the Bis-EFMA group was as good as commercial bulk-fill composites (p > 0.05). The sectional microhardness results showed that the Bis-EFMA group had the highest microhardness. After the friction and wear test, the volume wear of the Bis-EFMA group was minimal, indicating its good wear resistance and mechanical strength. Color changes in all resin groups after 28 days of immersion were within the clinically acceptable range.

SIGNIFICANCE

The addition of Bis-EFMA demonstrated excellent biocompatibility, edge adaptation and color stability comparable to commonly used clinical bulk-fill composites, along with preferable mechanical strength, friction and wear resistance. Bis-EFMA based bulk-fill composites have the potential to be employed as a bulk filling material in commercial dental composite applications.

Multi-acrylamides improve bond stability through collagen reinforcement under physiological conditions

OBJECTIVES

Acrylamides were shown to significantly improve bonding stability in adhesive restorations, but the reinforcement mechanism has not been fully elucidated. We tested the hypothesis that hydrogen bonding reinforcement of the collagen network (with secondary or tertiary acrylamides), as well as degree of crosslinking of the polymer network (with di- or tri-functional acrylamides), can be two of the factors at play.

METHODS

Two-step total etch adhesives comprising UDMA (60 wt%) and 40 wt% of: TAAEA, TMAAEA (secondary, tertiary tri-acrylamides), BAAP, DEBAAP (secondary, tertiary di-acrylamides) or HEMA (mono-methacrylate - control) were formulated. Simulated composite restorations (n = 5) were tested after cyclic mechanical and biological (S. mutans biofilm) challenges. Gap formation before and after aging was assessed with SEM imaging. Micro-tensile bond strength (μTBS, n = 6) was assessed after seven-day incubation in water or S. mutans-containing culture medium. Collagen reinforcement was assessed with hydroxyproline assay (n = 10) and rheology (n = 3). Data were analyzed with one-way/two-way ANOVA/Tukey's test (alpha=5%).

RESULTS

Gap formation increased and bond strength decreased for all monomers after biofilm incubation (p < 0.001). Except for DEBAAP, secondary and tertiary di/tri-acrylamides showed lower occlusal gap width values, but no significant differences overall gap length compared to HEMA. μTBS increased for tri-acrylamides compared with HEMA. Samples treated with multi-acrylamides had lower concentration of hydroxyproline (by-product of collagen degradation) (p < 0.001), except for DEBAAP, which showed values close to HEMA (p > 0.05). Dentin shear modulus increased for all acrylamides after 72 h, especially TMAAEA.

SIGNIFICANCE

In general, multi-acrylamides promote collagen reinforcement, leading to reduced gap formation, and stabilize the bond strength under physiological conditions.

Polymerization shrinkage of contemporary dental resin composites: Comparison of three measurement methods with correlation analysis

The aim of this study was to evaluate a novel approach for measuring the polymerization shrinkage of dental resin composites - measurement of sample depth variation. This new method was compared with two testing methodologies used for assessing the polymerization shrinkage (buoyancy and strain gauge methods). Eleven commercial resin composites were investigated (EverX Posterior; EverX Flow Bulk & Dentin; G-aenial Anterior, Posterior, A'chord & Universal Injectable; Filtek One Bulk Fill & Universal Restorative; SDR + Flow and Aura Bulk Fill). In addition, filler content (wt. %), flexural modulus, and the degree of conversion were evaluated. Shrinkage values, obtained by the buoyancy method, are greater than shrinkage evaluated by the strain gauge. There are significant differences in polymerization shrinkage among the tested resin composite materials. There is a strong correlation between the newly proposed method of shrinkage measurement and the buoyancy method (r2 = 0.8; p < 0.01). There is no correlation between volumetric shrinkage measurement (depth changes and buoyancy method) and linear strain measurement. Volumetric filler amount correlates with shrinkage values evaluated by all three methods. The degree of conversion for the tested resin composites ranges from 36 % to 52 %. There are some differences (around 10 %) between the filler content (wt. %) measured by the ashing-in-air method and the data given by the manufacturers. The highest flexural modulus is 14.8 GPa and the lowest 6.6 GPa. New formulations may introduce unknown relationships between the fundamental properties of dental resin composites.

Bonding performance and interfacial adaptation of modern bulk-fill restorative composites after aging in artificial saliva: an in vitro study

OBJECTIVES

This study aimed at comparing the microtensile bond strength (MTBS) and interfacial adaptation of a modern self-curing and a light-curing restorative bulk-fill composite to a conventional composite applied with the layering technique.

METHODS

Forty-eight occlusal cavities were divided in three main groups (16/group) based on tested materials: (i) STELA, bulk-fill self-curing restorative (STELA, SDI Ltd.); (ii) 3 M-BULK, bulk-fill composite (Filtek One Bulk-Fill, 3 M Oral Care); and (iii) 3 M-CTR, a conventional composite (Filtek Supreme XTE, 3 M Oral Care). These were used in combination with their adhesives in self-etch (SE) or etch-and-rinse (ER) mode. Specimens stored in artificial saliva (24 h or 12 months) were evaluated for MTBS and fractography. The interfacial analysis was performed through confocal microscopy. ANOVA and Fisher's LSD post hoc tests were performed with a level of significance of 5%.

RESULTS

All the tested materials applied in ER mode presented (24 h) greater bond strength than in SE mode. Although all materials showed a significant drop in the bond strength after prolonged storage, STELA showed the highest bonding performance and interfaces with few gaps. 3 M-BULK had the lowest bond strength and an interface with several voids and gaps.

CONCLUSIONS

All materials were affected by interface degradation and bonding reduction over prolonged aging. However, their use in combination with adhesives applied in ER mode may offer greater immediate bonding performance.

CLINICAL RELEVANCE

The use of restorative light-curing bulk-fill composites may generate gaps at the bonding interface and voids. STELA may represent a suitable alternative to avoid such issues.

Physical Properties and Clinical Performance of Short Fiber Reinforced Resin-based Composite in Posterior Dentition: Systematic Review and Meta-analysis

OBJECTIVE

This study compares the physical properties and clinical performance of short fiber reinforced composites (SFRC) to those of particulate-filled resin-based composites (PFRC) for class I and II direct restorations in permanent dentition.

METHODS

Systematic review and meta-analysis was conducted using PubMed, Embase (Elsevier), and Dentistry and Oral Sciences Source (EBSCO) databases. The outcomes evaluated were physical properties including flexural strength, flexural modulus, elastic modulus, microhardness, shrinkage, fracture toughness, degree of conversion, and depth of cure. Clinical performance was evaluated with a systematic review.

RESULTS

The meta-analyses favored SFRC for flexural strength and fracture toughness compared to every PFRC subgroup, with a high quality of evidence. For all other properties, the meta-analyses favored SFRC to overall PFRC, with some non-significant differences with certain PFRC subgroups. The most recent clinical trial showed SFRC performed similarly to PFRC, however older studies suggest inferior surface texture and discoloration of SFRC compared to PFRC.

CONCLUSION

This study can aid dental professionals in clinical decision making, supporting that SFRC offers improved physical properties, especially fracture resistance and flexural strength, compared to PFRC.

Bulk-Fill Resins versus Conventional Resins: An Umbrella Review

Currently, composite resins have become the material of choice for the restoration of posterior teeth. Although bulk-fill resins represent a tempting alternative due to their lower complexity and faster use, some dentists are reluctant to use this material. The objective is to compare the performance of bulk-fill resins and conventional resins in direct restorations of posterior teeth based on the literature. The databases that were used to carry out the research were PubMed/MEDLINE, Embase, the Cochrane Library and the WOS. This umbrella literature review complies with PRISMA standards and assesses the quality of studies using the AMSTAR 2 tool. With the application of the criteria of the AMSTAR 2 tool, the reviews were considered low to moderate. The overall meta-analysis, although without statistical significance, favours mostly the use of conventional resin, as it is about five times more likely to obtain a favourable result than bulk-fill resin. Bulk-fill resins result in a simplification of the clinical process of posterior direct restorations, which is an advantage. The performance in terms of several properties of bulk-fill resins and conventional resins showed that they present similar behaviour.

Latest Advances in Highly Efficient Dye-Based Photoinitiating Systems for Radical Polymerization

Light-activated polymerization is one of the most important and powerful strategies for fabrication of various types of advanced polymer materials. Because of many advantages, such as economy, efficiency, energy saving and being environmentally friendly, etc., photopolymerization is commonly used in different fields of science and technology. Generally, the initiation of polymerization reactions requires not only light energy but also the presence of a suitable photoinitiator (PI) in the photocurable composition. In recent years, dye-based photoinitiating systems have revolutionized and conquered the global market of innovative PIs. Since then, numerous photoinitiators for radical polymerization containing different organic dyes as light absorbers have been proposed. However, despite the large number of initiators designed, this topic is still relevant today. The interest towards dye-based photoinitiating systems continues to gain in importance, which is related to the need for new initiators capable of effectively initiating chain reactions under mild conditions. In this paper we present the most important information about photoinitiated radical polymerization. We describe the main directions for the application of this technique in various areas. Attention is mainly focused on the review of high-performance radical photoinitiators containing different sensitizers. Moreover, we present our latest achievements in the field of modern dye-based photoinitiating systems for the radical polymerization of acrylates.