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

Durability is an important quality of dental restorative materials, and the ability to autonomously heal damage incurred during their oral function is highly desirable. OBJECTIVE: The objective was to evaluate the improvement in durability of self-healing dental composites (SHDCs) in terms of their resistance to fracture and capacity for healing of damage under monotonic and cyclic loading. METHODS: SHDCs were prepared by incorporating dental resin composites with microcapsules containing healing liquid. Control specimens with the same mass fraction (5% and 25%) of microcapsules filled with water were also evaluated. Two sets of SHDCs were distinguished by the silane coupling agents that functionalized and bonded the microcapsules to resin network. One set used a methacrylate silane (MA-silane) that connected resin network through covalent bonds, and the other used a H-bonding forming hydroxyl silane (OH-silane). The fatigue crack growth resistance was assessed in terms of the threshold stress intensity range and the conventional Paris Law parameters. Cyclic loading was conducted at 5 Hz with maximum cyclic load ranged between approximately 1 N and 5 N. The efficiency of the autonomous healing was determined per the recovering of the fracture toughness and the extension of fatigue life. RESULTS: The SHDCs with 5 wt% of healing microcapsules exhibited a larger fracture toughness than those with 25 wt% microcapsules. MA-silane SHDCs had approximately five times more responsive microcapsules triggered by fracturing of the composites. Consequently, the MA-silane SHDCs with 5 wt% of microcapsules achieved the best performance in terms of fracture toughness and healing efficiency. In regards to the fatigue crack growth behavior, there was a significant increase in the resistance to fatigue crack growth and 580 ±â€¯15% improvement in the fatigue life. SIGNIFICANCE: Strong silanization is vital in SHDCs to simultaneously achieve clinically applicable mechanical performance and substantial healing capability. Moreover, the evaluation of self-healing under cyclic loading is a promising tool in quantifying the degree of fracture-induced healing.

High performance dental resin composites with hydrolytically stable monomers.

OBJECTIVE: The objectives of this project were to: 1) develop strong and durable dental resin composites by employing new monomers that are hydrolytically stable, and 2) demonstrate that resin composites based on these monomers perform superiorly to the traditional bisphenol A glycidyl dimethacrylate/triethylene glycol dimethacrylate (Bis-GMA/TEGDMA) composites under testing conditions relevant to clinical applications. METHODS: New resins comprising hydrolytically stable, ether-based monomer, i.e., triethylene glycol divinylbenzyl ether (TEG-DVBE), and urethane dimethacrylate (UDMA) were produced via composition-controlled photo-polymerization. Their composites contained 67.5wt% of micro and 7.5wt% of nano-sized filler. The performances of both copolymers and composites were evaluated by a battery of clinically-relevant assessments: degree of vinyl conversion (DC: FTIR and NIR spectroscopy); refractive index (n: optical microscopy); elastic modulus (E), flexural strength (F) and fracture toughness (KIC) (universal mechanical testing); Knoop hardness (HK; indentation); water sorption (Wsp) and solubility (Wsu) (gravimetry); polymerization shrinkage (Sv; mercury dilatometry) and polymerization stress (tensometer). The experimental UDMA/TEG-DVBE composites were compared with the Bis-GMA/TEGDMA composites containing the identical filler contents, and with the commercial micro hybrid flowable composite. RESULTS: UDMA/TEG-DBVE composites exhibited n, E, Wsp, Wsu and Sv equivalent to the controls. They outperformed the controls with respect to F (up to 26.8% increase), KIC (up to 27.7% increase), modulus recovery upon water sorption (full recovery vs. 91.9% recovery), and stress formation (up to 52.7% reduction). In addition, new composites showed up to 27.7% increase in attainable DC compared to the traditional composites. Bis-GMA/TEGDMA controls exceeded the experimental composites with respect to only one property, the composite hardness. Significantly, up to 18.1% lower HK values in the experimental series (0.458GPa) were still above the clinically required threshold of approx. 0.4GPa. SIGNIFICANCE: Hydrolytic stability, composition-controlled polymerization and the overall enhancement in clinically-relevant properties of the new resin composites make them viable candidates to replace traditional resin composites as a new generation of strong and durable dental restoratives.

Design and development of self-healing dental composites.

The purpose of this project is to design and develop a clinically applicable self-healing dental composite (SHDC). The value of resin-based dental restorations could be improved by increasing their service lives. One way to improve longevity is to obturate micro-cracks that form during or after the composite hardens in the dental cavity. Toward this end, we introduce here a new type of SHDC made with contemporary dental components plus two additional ingredients: a healing powder (HP, strongtium fluoroaluminosilicate particles) and a healing liquid (HL, aqueous solutions of polyacrylic acids) that is enclosed within silica microcapsules. As micro-cracks develop, they will break the microcapsules in their propagation path, thereby releasing HL. This liquid will then react with particles of HP exposed by the crack formation, forming an insoluble reaction product that fills and seals the cracks. The key factors to achieve this self-healing of cracks are discussed. The elastic modulus of a SHDC appeared to be satisfactory. The healing process was confirmed by means of mechanical, morphological, and chemical methods. The SHDC restored micro-cracks without external intervention, thereby showing potential for increasing the service lives of dental restorations. Importantly, this SHDC contains only clinically-tested, biocompatible materials, making it readily applicable.

Preparation of Dental Resins Resistant to Enzymatic and Hydrolytic Degradation in Oral Environments.

The short average service life of traditional dental composite restorative materials and increasing occurrence of secondary caries adjacent to composite restorations and sealants are necessitating the development of new, longer lasting compositions. Novel monomers and their polymers, reinforcing fillers, and adhesive components are needed. The goal of this research is to develop resin systems for use in restorations, sealants, and other dental services that are superior in properties and endurance to currently used bisphenol A glycidyl dimethacrylate/triethylene glycol dimethacrylate (Bis-GMA/TEGDMA) and urethane-dimethacrylate products. Ether-based monomers and their polymers that were not susceptible to enzymatic or hydrolytic degradation were prepared and characterized. They showed no degradation under hydrolytic and enzymatic challenges, whereas the hydrolysis of ester links weakened contemporary resins within 16 days under these challenges. The success of the ether-based materials is promising in making durable systems that are subjected to long-term biochemical and hydrolytic challenges in oral environments.

Percolation Diffusion into Self-Assembled Mesoporous Silica Microfibres.

Percolation diffusion into long (11.5 cm) self-assembled, ordered mesoporous microfibres is studied using optical transmission and laser ablation inductive coupled mass spectrometry (LA-ICP-MS). Optical transmission based diffusion studies reveal rapid penetration (<5 s, D > 80 µm²âˆ™s-¹) of Rhodamine B with very little percolation of larger molecules such as zinc tetraphenylporphyrin (ZnTPP) observed under similar loading conditions. The failure of ZnTPP to enter the microfibre was confirmed, in higher resolution, using LA-ICP-MS. In the latter case, LA-ICP-MS was used to determine the diffusion of zinc acetate dihydrate, D~3 × 10-4 nm²âˆ™s-1. The large differences between the molecules are accounted for by proposing ordered solvent and structure assisted accelerated diffusion of the Rhodamine B based on its hydrophilicity relative to the zinc compounds. The broader implications and applications for filtration, molecular sieves and a range of devices and uses are described.

Fabricating Nanoporous Silica Structure on D-Fibres through Room Temperature Self-Assembly.

The room temperature deposition of self-assembling silica nanoparticles onto D-shaped optical fibres ("D-fibre"), drawn from milled preforms fabricated by modified chemical vapour deposition (MCVD), is studied. Vertical dip-and-withdraw produces tapered layers, with one end thicker (surface coverage >0.85) than the other, whilst horizontal dip-and-withdraw produces much more uniform layers over the core region. The propagation of induced fracturing over the core region during drying is overcome using a simple protrusion of the inner cladding. Thick coatings are discernible through thin film interference colouring, but thinner coatings require scanning electron microscopy (SEM) imaging. Here, we show that fluorescence imaging, using Rhodamine B, in this example, can provide some qualitative and speedy assessment of coverage.

Magnetic induction-induced resistive heating of optical fibers and gratings.

Magnetic induction heating of optical fibers packaged with a steel plate is studied using a fiber Bragg grating. The dependence on the induced wavelength shift with magnetic field is obtained for a commercially available induction heater. More than a 300°C temperature rise is observed within seconds. The potential of magnetic induction as an efficient and rapid means of modulating devices and as a novel approach to potential optical based magnetic field and current sensing is proposed and discussed. The extension of the ideas into micro and nanophotonics is described.

Porphyrin-doped solgel-lined structured optical fibers for local and remote sensing.

We constructed a type of sensor by depositing a solgel layer within the interior holes of a silica-structured fiber and, subsequently, coating this with an acid-responsive porphyrin. Protonation of the porphyrin by an acidic gas (HCl in this case), is detected by a large change in the visible spectrum. Compared to previous work on a liquid-core sensor in a structured optical fiber, the signal-to-noise ratio of this gas sensor shows a reduced signal strength, but the detection rate is increased about fortyfold.

Evaluation of optical fiber microcell reactor for use in remote acid sensing.

An optical fiber acid-sensor based on protonation of a porphyrin solution within a single-hole structured optical fiber is proposed and demonstrated. The liquid-core fiber acts as a microcell reactor, and changes in the spectral signature with acidification are detected. Challenges and limitations in the practical deployment of such sensors are evaluated. An effective chemical sensor is demonstrated, but issues such as diffusion limit its full utilization. Some solutions are discussed.

Focused ion beam processing and engineering of devices in self-assembled supramolecular structures.

Self-assembled supramolecular structures such as optical wires, films and 2D slabs offer a new generation of electronic and optical devices. In particular, self-assembled porphyrin devices, including those integrated onto silica and silicon platforms, open new opportunities in photonic applications spanning molecular biosensing, photovoltaics and telecommunications. All reports to date, however, largely highlight the potential but have not established a clear pathway to the actual implementation of more complex device prototypes. In this paper, we propose and demonstrate the use of a focused ion beam (FIB) to process and fabricate devices in porphyrin-based supramolecular structures. These self-assembled structures have an initial root mean squared (rms) values for surface roughness of < 0.5 nm as measured by atomic force microscopy. Under appropriate FIB processing and cutting conditions, the rms value for surface roughness falls to < 0.4 nm, comparable with some of the best optical flatnesses obtained within, for example, structured optical fibres and integrated optical waveguides. The milling rate of the porphyrin structures was estimated to be approximately 70% of that of silica. The versatility of a FIB as a tool for rapid processing and fabricating 1D and 2D photonic waveguide structures within supramolecular self-assembled platforms is demonstrated by fabricating a 2D coupler, setting the groundwork for true optical device engineering and integration using these new organic systems.