Durability of self-healing dental composites: A comparison of performance under monotonic and cyclic loading

Fatigue behaviour of a self-healing dental composite

OBJECTIVE

Novel self-healing resin-based composites containing microcapsules have been developed to improve the mechanical performance of dental restorations. However, the long-term fatigue behaviour of these self-healing composites has still been hardly investigated. Therefore, this manuscript studied the fatigue behaviour of self-healing composites containing microcapsules by subjecting the specimens to traditional staircase tests and ageing in a custom-designed chewing simulator (Rub&Roll) to simulate oral ageing physiologically relevant conditions.

METHODS

To prepare self-healing composite, poly(urea-formaldehyde) microcapsules containing acrylic self-healing liquids were synthesized. Subsequently, these microcapsules (10 wt%) and initiator (benzoyl peroxide, BPO, 2 wt%) were incorporated into a commercial flowable resin-based composite. Microcapsule-free resin-based composites with and without BPO were also prepared as control specimens. A three-point flexural test was used to measure the initial flexural strength (Sinitial). Subsequently, half of the specimens were used for fatigue testing using a common staircase approach to measure the fatigue strengths (FS). In addition, the other specimens were aged in the Rub&Roll machine for four weeks where after the final flexural strength (Sfinal) was measured.

RESULTS

Compared to Sinitial, FS of all tested specimens significantly decreased as measured through staircase testing. After 4 weeks of ageing in the Rub&Roll machine, Sfinal was significantly reduced compared to Sinitial for microcapsule-free resin-based composites, but not for the self-healing composites (p = 0.3658). However, the self-healing composites are still in the experimental phase characterized by a low mechanical strength, which still impedes further clinical translation.

SIGNIFICANCE

Self-healing composites containing microcapsules exhibit improved fatigue resistance compared to microcapsule-free non-self-healing composites.

Fracture toughness of 3D printed denture teeth

BACKGROUND

Advances in digital dentistry lead to use of three-dimensional (3D) printed resin denture teeth. Fracture toughness of these teeth must be assessed.

OBJECTIVE

This study aimed to compare the chipping and indirect tensile fracture resistance of denture teeth fabricated by 3D printing technique with traditionally fabricated resin denture teeth.

METHOD

Four groups (Gr) were made (n= 50/group): Gr-1 3D printed denture teeth (denture teeth; Formlabs Inc., Somerville, MA, USA), Gr-2 SR-Orthosit-PE (Ivoclar Vivadent AG), Gr-3 Portrait IPN (Dentsply Sirona), Gr-4 Pala Premium 8 (Heraeus Kulzer GmbH). Stereolithography 3D printing was used to create the methacrylate-based photopolymerized resin teeth models and remaining group teeth were collected commercially. A 1 mm/min chipping and indirect tensile fracture speed tests were carried out till fracture occurred. The data so obtained were statistically analysed using one-way analysis of variance with Tukey's honestly significant difference multiple comparisons test (p< 0.05). At the end of the test, the fractured areas of the specimens were evaluated by the chief researcher to assess the fracture pattern of the teeth.

RESULTS

The indirect tensile fracture values of the 3D printed teeth were more than that of Pala Premium-8 and SR-Orthosit-PE but it was lower than that of Portrait IPN teeth. In chipping test, buccal chipping of the loaded cusp was seen in 3D printed resin without distortion and in indirect tensile test in 3D printed resin teeth, line of fracture emerges near the loading point propagates from the inner incline of both cusps and extends cervically, unlike in other groups where first deformation occurs then fracture.

CONCLUSION

Prosthetic teeth fabricated by the 3D printing technique using printable resin material provide adequate fracture resistance as denture teeth.

Development of functional fillers as a self-healing system for dental resin composite

OBJECTIVES

To evaluate the incorporation of repairing capsules containing different monomers and polymerization modulators on the self-healing efficiency of an experimental photopolymerizable resin-based composite.

METHODS

Self-healing capsules containing different monomers and polymerization modulators were prepared by emulsion polymerization: TC_DHEPT (TEGDMA and DHEPT), BTC_DHEPT (Bis-GMA, TEGDMA, and DHEPT), and BTC_BPO (Bis-GMA, TEGDMA, and BPO). The capsules were analyzed through Fourier transform infrared spectroscopy and scanning electron microscopy. The capsules were added into experimental photopolymerizable resin composites establishing the following groups: ER (Control without capsules), ER+BPO, ER+BPO+TC_DHEPT, and ER+BTC_BPO+BTC_DHEPT. Filtek Z350 resin composite (3 M ESPE) was used as a commercial reference. The materials were tested for degree of conversion (DC), flexural strength (σf), elastic modulus (Ef), fracture toughness (virgin K_IC), self-healing efficiency (healed K_IC), and roughness. For statistical analysis, the significance value was established at an a = 0.05 level.

RESULTS

When compared to the control material, the incorporation of repairing capsules did not affect DC, σf, and Ef. Fracture toughness was statistically similar between the experimental groups (p ≤ 0.05). Healed K_IC was statistically different between the groups ER+TC_DHEP and ER+BTC_BPO+BTC_DHEPT; the self-healing efficiency was higher for ER+TC_DHEPT. Surface roughness was statistically similar among all groups.

CONCLUSIONS

The use of self-healing capsules promoted repair of the material. Studies with material aging after the self-healing process are necessary to better demonstrate the effectiveness of this system.

CLINICAL SIGNIFICANCE

The self-healing system seemed to be a promising technology to be used in self-repaired restorative materials, which may prevent restoration fractures.

Resin-Based Composites for Direct and Indirect Restorations: Clinical Applications, Recent Advances, and Future Trends

Continuous advancements in resin-based composites can make selection of the appropriate system a daunting task for the clinician. This review aims to simplify this process and clarify some new or controversial topics. Various types of composites for direct and indirect applications are discussed, including microfilled and microhybrid composites, nanocomposites, single shade, bulk fill, fiber-reinforced, high temperature/high pressure processed, CAD/CAM, and three-dimensional printable composites. Recent material advancements that lead to improved seal and toughness, degradation resistance, antimicrobial and self-healing capabilities are presented. Future directions are highlighted, such as the development of "smart" materials that are able to interact with the host environment.

An Overview of Self-Healable Polymers and Recent Advances in the Field

The search for materials with better performance, longer service life, lower environmental impact, and lower overall cost is at the forefront of polymer science and material engineering. This has led to the development of self-healing polymers with a range of healing mechanisms including capsular-based, vascular, and intrinsic self-healing polymers. The development of self-healable systems has been inspired by the healing of biological systems such as skin wound healing and broken bone reconstruction. The goal of using self-healing polymers in various applications is to extend the service life of polymers without the need for replacement or human intervention especially in restricted access areas such as underwater/underground piping where inspection, intervention, and maintenance are very difficult. Through an industrial and scholarly lens, this paper provides (a) an overview of self-healing polymers, (b) classification of different self-healing polymers and polymer-based composites, (c) mechanical, thermal, and electrical analysis characterization, (d) applications in coating, composites, and electronics, (e) modeling and simulation, and (f) recent development in the past 20 years . This review highlights the importance of healable polymers for an economically and environmentally sustainable future, the most recent advances in the field, and current limitations in fabrication, manufacturing, and performance. This article is protected by copyright. All rights reserved.

Strategies to design extrinsic stimuli-responsive dental polymers capable of autorepairing

Objectives

For many years, the requirements for dental polymers were limited to inertially filling the cavity and restoring form, function, and esthetics. Inorganic filler systems were widely enhanced to maximize the mechanical properties and optimize finishing and polishing procedures. The development of alternative photoinitiator systems also improved the carbon-carbon double bond conversion, increasing biocompatibility, wear, and stain resistance. However, despite laudable progress, the clinical life span of dental restorations is still limited, and their replacement is the most common procedure in dental offices worldwide. In the last few years, the development of materials with the potential to adapt to physiological stimuli has emerged as a key step to elevating dental polymers to a higher excellence level. In this context, using polymeric networks with self-healing properties that allow for the control of the propagation of microcracks is an appealing strategy to boost the lifetime of dental restorations. This review aims to report the current state-of-the-art of extrinsic self-healing dental polymers and provide insights to open new avenues for further developments. General classification of the self-healing polymeric systems focusing on the current extrinsic strategies used to inhibit microcracks propagation in dental polymers and recover their structural integrity and toughness are presented.

Search Strategy

An electronic search was perfomed using PubMed, Google Scholar, and Scopus databases. Only studies published in English on extrinsic self-healing polymeric systems were included.

Overall Conclusions

Self-healing materials are still in their infancy in dentistry, and the future possibilities are almost limitless. Although the mouth is a unique environment and the restorative materials have to survive chemical, physical, and mechanical challenges, which limits the use of some strategies that might compromise their physicochemical performance, there are countless untapped opportunities to overcome the challenges of the current systems and advance the field.

The Development of Filler Morphology in Dental Resin Composites: A Review

Dental resin composites (DRCs) with diverse fillers added are widely-used restorative materials to repair tooth defects. The addition of fillers brings an improvement in the mechanical properties of DRCs. In the past decade, diverse fillers have emerged. However, the change of emerging fillers mainly focuses on the chemical composition, while the morphologic characteristics changes are often ignored. The fillers with new morphologies not only have the advantages of traditional fillers (particles, fibrous filler, etc.), but also endow some additional functional characteristics (stronger bonding ability to resin matrix, polymerization resistance, and wear resistance, drug release control ability, etc.). Moreover, some new morphologies are closely related to the improvement of traditional fillers, porous filler vs. glass particles, core-sheath fibrous vs. fibrous, etc. Some other new morphology fillers are combinations of traditional fillers, UHA vs. HA particles and fibrous, tetrapod-like whisker vs. whisker and fibrous filler, mesoporous silica vs. porous and silica particles. In this review, we give an overall description and a preliminary summary of the fillers, as well as our perspectives on the future direction of the development of novel fillers for next-generation DRCs.

A Review on Current Trends of Polymers in Orthodontics: BPA-Free and Smart Materials

Polymeric materials have always established an edge over other classes of materials due to their potential applications in various fields of biomedical engineering. Orthodontics is an emerging field in which polymers have attracted the enormous attention of researchers. In particular, thermoplastic materials have a great future utility in orthodontics, both as aligners and as retainer appliances. In recent years, the use of polycarbonate brackets and base monomers bisphenol A glycerolate dimethacrylate (bis-GMA) has been associated with the potential release of bisphenol A (BPA) in the oral environment. BPA is a toxic compound that acts as an endocrine disruptor that can affect human health. Therefore, there is a continuous search for non-BPA materials with satisfactory mechanical properties and an esthetic appearance as an alternative to polycarbonate brackets and conventional bis-GMA compounds. This study aims to review the recent developments of BPA-free monomers in the application of resin dental composites and adhesives. The most promising polymeric smart materials are also discussed for their relevance to future orthodontic applications.

[Application and potential future directions of self-healing polymers in dentistry]

Self-healing materials have rapidly developed in recent years to overcome the micro-cracks occurring in the polymer matrix. Self-healing ability offers autonomous crack repairs to prolong the service lives of polymers or polymer composites. As a main approach, extrinsic self-healing materials based on microcapsules have been applied in dentistry recently. This paper comprehensively presented and reviewed the definition and classification of self-healing materials, the synthesis of microcapsules, the calculation of self-healing efficiency, and the application of self-healing materials in dentistry. The future directions of self-healing polymers are also discussed.

Resin based restorative dental materials: characteristics and future perspectives

This review article compiles the characteristics of resin based dental composites and an effort is made to point out their future perspectives. Recent research studies along with few earlier articles were studied to compile the synthesis schemes of commonly used monomers, their characteristics in terms of their physical, mechanical and polymerization process with selectivity towards the input parameters of polymerization process. This review covers surface modification processes of various filler particles using silanes, wear behaviour, antimicrobial behaviour along with its testing procedures to develop the fundamental knowledge of various characteristics of resin based composites. In the end of this review, possible areas of further interests are pointed out on the basis of literature review on resin based dental materials.

3D Printing of Resin Material for Denture Artificial Teeth: Chipping and Indirect Tensile Fracture Resistance

3D printing of denture artificial teeth with resin materials is worthy of study in a novel way. This study evaluated chipping and indirect tensile fracture resistance of 3D printing resin material (Dentca 3D printing denture teeth resin) compared with conventionally prefabricated resin denture teeth (Premium-8, Surpass, SR-Orthosit-PE, and Preference). One hundred tooth specimens were prepared for testing. The 3D printed tooth specimens were printed at a 50 µm layer thickness with methacrylate-based photopolymerized resin by stereolithography 3D printing. Chipping and indirect tensile fracture tests were conducted at a speed of 1 mm/min until fracture. The indirect tensile fracture loads of the 3D printed resin teeth were higher than those of Premium-8, Surpass, and SR-Orthosit-PE, and lower than those of Preference teeth. Regarding chipping resistance, the 3D printed resin teeth were not different from Surpass and SR-Orthosit-PE, and were lower than Premium-8 and Preference teeth. The 3D printed resin teeth exhibited vertical fracture of the loaded cusp without deformation in chipping. The 3D printed resin teeth showed simultaneous fracture of two cusps in indirect tensile fracture, unlike other teeth. The results of this study suggest that 3D printing technology using resin materials provides adequate fracture resistance for denture artificial tooth use.