Effects of water-aging on self-healing dental composite containing microcapsules

A Review on the Current State of Microcapsule-Based Self-Healing Dental Composites

Resin-based dental composites, commonly used in dentistry, offer several advantages including minimally invasive application, esthetically pleasing appearance, and good physical and mechanical properties. However, these dental composites can be susceptible to microcracks due to various factors in the complex oral environment. These microcracks can potentially lead to clinical restoration failure. Conventional materials and methods are inadequate for detecting and repairing these microcracks in situ. Consequently, incorporating self-healing properties into dental composites has become a necessity. Recent years have witnessed rapid advancements in self-healing polymer materials, drawing inspiration from biological bionics. Microcapsule-based self-healing dental composites (SHDCs) represent some of the most prevalent types of self-healing materials utilized in this domain. In this article, we undertake a comprehensive review of the most recent literature, highlighting key insights and findings related to microcapsule-based SHDCs. Our discussion centers particularly on the preparation techniques, application methods, and the promising future of self-healing microcapsules in the field of dentistry.

Effects of chitosan and TiO2 nanoparticles on the antibacterial property and ability to self-healing of cracks and retrieve mechanical characteristics of dental composites

The aim of this study was to improve the self-healing properties of dental nanocomposite using nanoparticles of TiO2 and chitosan. We evaluated flexural and compressive strength, crack-healing, and self-healing lifespan after 3 months of water aging. The effect of the developed composite on cell viability and toxicity was assessed by an MTT assay on human alveolar basal epithelial cells (A549 cell line). The nanocomposite included 7.5 wt% polyurea-formaldehyde (PUF) and 0, 0.5, and 1 wt% n-TiO2 and chitosan. After the fracture, the samples were put in a mold for 1-90 days to enable healing. Then, the fracture toughness of the healed nanocomposites and the healing yield were measured. The flexural strength of the nanocomposite improved by adding 0.5 wt% n-TiO2, while the compressive strength increased after adding 0.5 wt% chitosan (p > 0.1). When these two materials were used simultaneously, the flexural strength was improved by around 2%; however, the compressive strength was unaffected. Compared to the other sample, the nanocomposite with 0.5 wt% n-TiO2 and chitosan had higher KIC-healing and self-healing efficiency. Self-healing efficacy had no significant effect of water aging over 90 days compared to one day (p > 0.1), demonstrating that the PUF nanocapsules were not damaged.

Effect of silanization of poly (urea-formaldehyde) microcapsules on the flexural strength and self-healing efficiency of an experimental self-healing dental resin composite (An in-vitro study)

OBJECTIVES

This study investigated the impact of using γ-methacryloxypropyl trimethoxy silane (MPS) for surface silanization of poly (urea-formaldehyde) (PUF) microcapsules which enclose a healing liquid of "triethylene glycol dimethacrylate (TEGDMA) and N,N dihydroxyethyl-p-toluidine (DHEPT)" on some mechanical properties of an experimental dental composite as well as its self-healing efficiency.

METHODS

Synthesis of PUF microcapsules was done via in situ polymerization, followed by silanization with MPS silane. Silanized and non-silanized microcapsules were incorporated into a composite containing 30% polymer matrix and 70% fillers at different weight percentages (0%, 5%, 7.5% and 10%). The composite strength and elastic modulus were evaluated by Flexural testing. Fracture toughness KIc and self-healing efficiency were assessed by utilizing the "single edge notched beam" method.

RESULTS

Flexural strength of all groups containing silanized microcapsules was non-significantly different from control group without microcapsules. However, in contrast to control group, all groups containing non-silanized microcapsules displayed considerably decreased flexural strength. Adding silanized and non-silanized microcapsules didn't show a significant change in the KIc-virgin. The silanized microcapsules' groups achieved a self-healing efficiency of about 49-77% recovery in KIc-virgin compared to 38-69% for their non-silanized counterparts.

SIGNIFICANCE

In order to increase the interfacial adhesion with the polymer matrix, improve the mechanical properties, and increase the efficiency of self-healing of dental resin composite, PUF microcapsules were silanized for the first time in the dental field using MPS silane. This innovative silanized microcapsule-containing self-healing composite may hold promise for repairing the damage caused by restorative cracks and extending their service life.

Synthesis and characterisation of microcapsules for self-healing dental resin composites

AIM

The purpose of this study was to i) synthesise TEGDMA-DHEPT microcapsules in a laboratory setting; ii) characterise the resultant microcapsules for quality measures.

MATERIALS & METHODS

Microcapsules were prepared by in situ polymerization of PUF shells. Microcapsules characterisation include size analysis, optical and SEM microscopy to measure the diameter and analyse the morphology of PUF microcapsules. FT-IR spectrometer evaluated microcapsules and benzyl peroxide catalyst polymerization independently.

RESULT

Average diameter of TEGDMA-DHEPT microcapsules was 120 ± 45 μm (n: 100). SEM imaging of the capsular shell revealed a smooth outer surface with deposits of PUF nanoparticles that facilitate resin matrix retention to the microcapsules upon composite fracture. FT-IR spectra showed that microcapsules crushed with BPO catalyst had degree of conversion reached to 60.3%.

CONCLUSION

TEGDMA-DHEPT microcapsules were synthesised according to the selected parameters. The synthesised microcapsules have a self-healing potential when embedded into dental resin composite as will be demonstrated in our future work.

Novel low-shrinkage dental resin containing microcapsules with antibacterial and self-healing properties

Dental resin restorations commonly fail because of fractures and secondary caries. The aim of this research was to synthesize a novel low-shrinkage dental resin with antibacterial and self-healing properties. The low-shrinkage dental resin was obtained by incorporating a 20 wt% anti-shrinkage mixture of an expanding monomer 3,9-diethyl-3,9-dimethylol -1,5,7,11-tetraoxaspiro[5,5] undecane and an epoxy resin monomer diallyl bisphenol A diglycidyl ether (1:1, referred as "UE") and different mass fractions of self-healing antibacterial microcapsules (0%, 2.5%, 5%, 7.5%, and 10%) were incorporated into the matrix to prepare multifunctional dental resin. Polymerization shrinkage, mechanical properties, antibacterial activity, self-healing ability, and cytotoxicity of this dental resin were evaluated. The polymerization volumetric shrinkage of resin containing 20 wt% UE and 7.5 wt% microcapsules was reduced by 30.12% (4.13% ± 0.42%) compared with control. Furthermore, it exhibited high antibacterial activity and a good self-healing efficiency of 71% without adversely affecting the mechanical property and cell viability. This novel multifunctional dental resin with low polymerization shrinkage and excellent antibacterial activity and self-healing capability has potential application as a dental resin material to decrease the incidence of fractures and secondary caries.

Novel antimicrobial and self-healing dental resin to combat secondary caries and restoration fracture

OBJECTIVE

Dental resin composites have been the most popular materials for repairing tooth decay in recent years. However, secondary caries and bulk fracture are the major hurdles that affect the lifetime of dental resin composites. This current study synthesized a novel antimicrobial and self-healing dental resin containing nanoparticle-modified self-healing microcapsules to combat secondary caries and restoration fracture.

METHODS

Multifunctional dental resins containing 0-20% nanoparticle-modified self-healing microcapsules were prepared. The water contact angle, antimicrobial properties, mechanical properties, cell toxicity, and self-healing capability of the dental resins were tested.

RESULTS

A novel multifunctional dental resin was synthesized. When the microcapsule mass fraction was 10%, the resin presented a strong bacteriostasis rate (80.3%) and excellent self-healing efficiency (66.1%), while the hydrophilicity, mechanical properties, and cell toxicity were not affected.

SIGNIFICANCE

The novel antimicrobial self-healing dental resin is a promising candidate for use in clinical practice, which provides a simple and highly efficient strategy to combat secondary caries and restoration fracture. This novel dental resin also gives the inspiration to prolong the service life of dental restorations.

Explore the most recent advancements in the domain of self-healing intelligent composites specifically designed for use in dentistry

Dental composites are commonly utilized in dental treatments because they have the ability to preserve the natural appearance of teeth, are minimally invasive and conservative, and enhance the overall physical and mechanical attributes. Dental composites can experience damage, like small cracks, due to factors like temperature changes and physical strain, which can reduce their effectiveness. Detecting these tiny cracks in dental composites can be quite challenging, and in certain situations, it may even be impossible. In addition, it is not possible to repair these damages in situ by using conventional materials and methods. Therefore, the self-healing ability in dental composites is necessary. In recent years, the spontaneous repair of damages such as micro-cracking in dental composite materials has been developed without any type of human intervention and the replacement of new components. The most widely used approach to create self-healing dental composites involves encapsulating a healing agent within polymer shells and dispersing these microcapsules within the acrylate matrix of the dental composite. To assess the self-healing abilities of these composites, researchers can examine changes in their fracture toughness before and after the healing process using a test called the Single Edge V-notch beam test. In the present article we reviewed the latest findings in the field of self-healing intelligent composites for application in dentistry, and also in the present study, the studies on self-healing smart dental composites will be reviewed.

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.

Innovations in the Design and Application of Stimuli-Responsive Restorative Dental Polymers

The field of dental materials is undergoing rapid advancements in the pursuit of an innovative generation of dental polymeric restorative materials. There is a growing interest in the development of a distinct category of dental polymers that transcend the conventional role of inertly filling prepared cavities. Instead, these materials possess the capacity to actively detect and respond to alterations within the host environment by undergoing dynamic and controlled molecular changes. Despite the well-established status of stimuli-responsive polymeric systems in other fields, their implementation in dentistry is still in its nascent stages, presenting a multitude of promising opportunities for advancement. These systems revolve around the fundamental concept of harnessing distinctive stimuli inherent in the oral environment to trigger precise, targeted, predictable, and demand-driven responses through molecular modifications within the polymeric network. This review aims to provide a comprehensive overview of the diverse categories of stimuli-responsive polymers, accentuating the critical aspects that must be considered during their design and development phases. Furthermore, it evaluates their current application in the dental field while exploring potential alternatives for future advancements.

Impact assessment of synthesis parameter stirring speed in final physicochemical properties of PU microcapsules incorporated into epoxy matrixes

A considerable number of papers have been published to assess self-healing capacity of several materials, as well as several applications in different areas. However, the impact assessment of changing synthesis parameters of microcapsules, hollow fibers or microvascular systems in its final physicochemical properties are still an emerging research field. This current paper presents a synthesis process of PU microcapsules containing TDI as core agent and the characterization of microcapsules physicochemical properties. During the synthesis, the reaction parameter stirring speed was changed to assess the impact that this parameter has in the final microcapsules' physicochemical properties. Microcapsules were characterized by FT-IR, TGA and image analysis (OM and SEM). Additionally, microcapsules were incorporated to an epoxy matrix (5% weight/weight) to assess the impact in the final physicochemical and mechanical matrix properties. Epoxy-based test specimens were also obtained within aramid and silica, which are traditional reinforcing loads in rubber synthesis. Final mechanical properties of matrixes within aramid and silica were compared to the properties of matrixes within microcapsules to determine what kind of behavior the microcapsules have when incorporated to epoxy matrixes.

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.

Novel nanoparticle-modified multifunctional microcapsules with self-healing and antibacterial activities for dental applications

OBJECTIVE

Although microcapsules (MCs) have been used for dental resins to achieve self-healing capabilities, the fragile organic shell and single healing event functions during the service period limit their use. Herein, a novel nanoparticle-modified MC with a nano-antibacterial inorganic filler (NIF) containing a quaternary ammonium salt was synthesized to address these issues.

METHODS

MCs with 0 %-30 % NIFs were prepared via an in situ polymerization method and characterized their morphology, chemical composition, thermal stability, roughness, mechanical properties, and antibacterial effect. Subsequently, M-10 MCs were mixed into the resin matrix at a mass fraction of 7.5 %. The self-healing capability and cytotoxicity were evaluated.

RESULTS

The introduction of nanomaterials enhances the shell of the MCs and endows them with an antibacterial effect. With the addition of NIFs, the roughness, modulus, and hardness values of MCs all increased (p < 0.05). The presence of M-10 MCs reduced the CFU by 2-3 orders of magnitude compared to the control group. The dental resin containing 7.5 % M-10 MCs obtained almost 69 % self-healing efficiency, without significantly compromising cell viability (p < 0.05).

SIGNIFICANCE

Self-healing MCs with NIFs were prepared for the first time with strong antibacterial properties, a substantial self-healing capability, and low toxicity. This multifunctional MC is a promising candidate for use in dental resins to extend the service life and resolve the problem of bulk fracture and secondary caries.

Properties of A Model Self-Healing Microcapsule-Based Dental Composite Reinforced with Silica Nanoparticles

Aim: The purpose of this study was to evaluate the mechanical properties of an experimental self-healing dental composite model (SHDC) composed of SiO₂ nanoparticles with varying percentages of triethylene glycol dimethacrylate (TEGDMA) monomer and N,N-dihydroxyethyl-p-toluidine (DHEPT) amine microcapsules. Materials and methods: Microcapsules were prepared by in-situ polymerisation of PUF shells, as explained in our previous work. The model SHDC included bisphenol A glycidyl dimethacrylate (Bis-GMA:TEGDMA) (1:1), 1 wt% phenyl bis(2,4,6-trimethylbenzoyl) phosphine oxide (BAPO), 0.5 wt% benzoyl peroxide (BPO) catalyst, 20 wt% silanised silica dioxide (SiO₂) (15 nm) and (0, 2.5, 5, 7.5, 10 wt%) of microcapsules (120 ± 45 μm). Light transmission, hardness, degree of conversion (DC), flexural strength and elastic modulus of the SHDC model were measured. Results: The degree of conversion of the SHDC ranged from 73 to 76% 24 h after polymerisation. Hardness measurements ranged from 22 to 26 VHN (p > 0.05); however, the flexural strength was adversely affected from 80 to 55 MPa with increasing microcapsules of up to 10 wt% in the composites (p < 0.05). Conclusion: Only flexural strength decreased drastically ~30% with increasing microcapsules (>10 wt%) in the composites. All other measured properties were not significantly affected. Accordingly, we recommend a stronger composite material that could be created by increasing the filler content distribution in order to achieve a hybrid self-healing composite with enhanced mechanical properties.

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.

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.

Strategic conceptualization and potential of self-healing polymers in biomedical field

Smart polymeric materials and hydrogels derived from acrylate, epoxy resins, etc. mimic the healing ability of natural organisms and biological cells by showing shape memory and tissue regenerative properties wherein, the healing ability in some of the materials is triggered by external stimuli like temperature, pH and light. This article provides an overview of various conceptual strategies and chemical and mechanical interactions involved in the different types of biomimetic self-healing materials to regain the deformed structure by repairing the cracked shape which play important role in contributing to the structural properties and functional recovery. Also, different chemical bonding like π-π interaction, ligand-metal, hydrogen bonding, etc. takes place at the molecular level for replenishing the damaged structure with greater bond strength. The regeneration ability of artificial self-healing polymeric materials not only shows use in material sciences, engineering but also exhibits a wide range of applications in site-specific drug delivery, skin grafting, implantation, dentistry and bone and tissue regeneration to restore injured surfaces with better biocompatibility, healing efficiency and higher tensile strength to serve as a next-generation material for amplifying the use in biomedical field.

Influence of microcapsule parameters and initiator concentration on the self-healing capacity of resin-based dental composites

OBJECTIVE

Fracture is one of the main causes for failure of resin-based composite restorations. To overcome this drawback, self-healing resin-based composites have been designed by incorporation of microcapsules. However, the relationship between their self-healing capacity and microcapsule and resin parameters is still poorly understood. Therefore, the objective of this study was to systematically investigate the effect of initiator concentration (in the resin) and microcapsule size and concentration on the self-healing performance of commercially available flowable resin-based composites.

METHODS

Poly(urea-formaldehyde) (PUF) microcapsules containing acrylic healing liquid were synthesized in small (33±8μm), medium (68±21μm) and large sizes (198±43μm) and characterized. Subsequently, these microcapsules were incorporated into a conventional flowable resin-based composite (Majesty Flow ES2, Kuraray) at different contents (5-15wt%) and benzoyl peroxide (BPO) initiator concentrations (0.5-2.0wt%). Fracture toughness (K_IC) of test specimens was tested using a single edge V-notched beam method. Immediately after complete fracture (K_IC-initial), the two fractured parts were held together for 72h to allow for healing. Subsequently, fracture toughness of the healed resin-based composites (K_IC-healed) was tested as well.

RESULTS

The fracture toughness of healed dental composites significantly increased with increasing microcapsule size and concentration (2wt% BPO, p<0.05). The highest self-healing efficiencies (up to 76%) were obtained with microcapsules sized 198±43 um.

SIGNIFICANCE

commercially available resin-based composites can be rendered self-healing most efficiently by incorporation of large microcapsules (198±43μm). However, long-term tests on fatigue and wear behavior are needed to confirm the clinical efficacy.

[Development of novel self-adhesive resin cement with antibacterial and self-healing properties]

OBJECTIVE

This study aimed to develop novel self-adhesive resin cement with antibacterial and self-healing properties. Furthermore, the dentin bonding strength, mechanical properties, self-healing efficiency, and antibacterial property of the developed cement were measured.

METHODS

Novel nano-antibacterial inorganic fillers that contain quaternary ammonium salts with long-chain alkyls were synthesized. These fillers were added into self-adhesive resin cement containing self-healing microcapsules at mass fractions of 0, 2.5%, 5.0%, 7.5%, or 10.0%. The dentin shear bonding test was used to test the bonding strength, whereas the flexural test was used to measure the flexural strength and elastic modulus of the cement. The single-edge V-notched beam method was used to measure self-healing efficiency, and human dental plaque microcosm biofilms were chosen to calculate the antibacterial property.

RESULTS

The dentin shear bond strength significantly decreased when the mass fraction of the nano-antibacterial inorganic fillers in the novel cement reached 7.5% (P<0.05). The incorporation of 0, 2.5%, 5.0%, 7.5%, or 10.0% mass fraction of nano-antibacterial inorganic fillers did not adversely affect the flexural strength, elastic modulus, fracture toughness, and self-healing efficiency of the cement (P>0.1). Resin cement containing 2.5% mass fraction or more nano-antibacterial inorganic fillers significantly inhibited the metabolic activity of dental plaque microcosm biofilms, indicating strong antibacterial potency (P<0.05).

CONCLUSIONS

The novel self-adhesive resin cement exhibited promising antibacterial and self-healing properties, which enable the cement to be used for dental 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.

Development of an Innovative Urease-Aided Self-Healing Dental Composite

Dental restorative materials suffer from major drawbacks, namely fracture and shrinkage, which result in failure and require restoration and replacement. There are different methods to address these issues, such as increasing the filler load or changing the resin matrix of the composite. In the present work, we introduce a new viable process to heal the generated cracks with the aid of urease enzyme. In this system, urease breaks down the salivary urea which later binds with calcium to form calcium carbonate (CaCO3). The formation of insoluble CaCO3 fills any resultant fracture or shrinkage from the dental composure hardening step. The healing process and the formation of CaCO3 within dental composites were successfully confirmed by optical microscope, scanning electron microscopy (SEM), and energy-dispersive X-ray (EDS) methods. This research demonstrates a new protocol to increase the service life of dental restoration composites in the near future.

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.

Dental Composite Formulation Design with Bioactivity on Protein Adsorption Combined with Crack-Healing Capability

Short Title

Protein-repellent dental composite with crack-healing ability

Abstract

Fracture and secondary caries are the primary reasons for the failure of dental restorations. To face this omnipresent problem, we report the formulation design and synthesis of a protein-resistant dental composite composed of 2-methacryloyloxyethyl phosphorylcholine (MPC) that also can self-repair damage and recover the load-bearing capability via microencapsulated triethylene glycol dimethacrylate (TEGDMA) and N,N-dihydroxy ethyl-p-toluidine (DHEPT). The bioactivity of the resulting MPC-microencapsulated TEGDMA-DHEPT was evaluated on protein adsorption through early bacterial attachment. Its mechanical properties were also investigated, including self-healing assessment. Microcapsules of poly (urea-formaldehyde) (PUF) were synthesized by incorporating a TEGDMA-DHEPT healing liquid. A set of composites that contained 7.5% of MPC, 10% of microcapsules, and without MPC/microcapsules were also prepared as controls. The two distinct characteristics of strong protein repellency and load-bearing recovery were achieved by the combined strategies. The novel dual composite with a combination of protein-repellent MPC and PUF microcapsules for restoring microcracks is a promising strategy for dental restorations to address the two main challenges of fracture and secondary caries. The new dual composite formulation design has the potential to improve the longevity of dental restorations significantly.

Trends in restorative composites research: what is in the future?

Clinical trials have identified secondary caries and bulk fracture as the main causes for composite restoration failure. As a measure to avoid frequent reinterventions for restoration replacement, composites with some sort of defense mechanism against biofilm formation and demineralization, as well as materials with lower susceptibility to crack propagation are necessary. Also, the restorative procedure with composites are very time-consuming and technically demanding, particularly concerning the application of the adhesive system. Therefore, together with bulk-fill composites, self-adhesive restorative composites could reduce operator error and chairside time. This literature review describes the current stage of development of remineralizing, antibacterial and self-healing composites. Also, an overview of the research on fiber-reinforced composites and self-adhesive composites, both introduced for clinical use in recent years, is presented.

New Resins for Dental Composites

Restorative composites have evolved significantly since they were first introduced in the early 1960s, with most of the development concentrating on the filler technology. This has led to improved mechanical properties, notably wear resistance, and has expanded the use of composites to larger posterior restorations. On the organic matrix side, concerns over the polymerization stress and the potential damage to the bonded interface have dominated research in the past 20 y, with many "low-shrinkage" composites being launched commercially. The lack of clinical correlation between the use of these materials and improved restoration outcomes has shifted the focus more recently to improving materials' resistance to degradation in the oral environment, caused by aqueous solvents and salivary enzymes, as well as biofilm development. Antimicrobial and ester-free monomers have been developed in the recent past, and evidence is mounting for their potential benefit. This article reviews literature on the newest materials currently on the market and provides an outlook for the future developments needed to improve restoration longevity past the average 10 y.