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Introduction to electrospinning in dental applications

The field of dentistry is very wide including specializations such as endodontics, periodontics and orthodontics. Electrospinning, due to its flexibility in material selection and its ability to produce fibers in the submicron to nanometer dimension, is ideally suited in producing materials for dental applications. Materials used for dental applications are typically found in small volume and size due to the size constrain of the oral cavity. Electrospun materials are been investigated for various dental applications.


Composite

Dental composites are typically filled resins for use as fillers or for bonding purpose. The strong mastication force encountered by the composite requires it to be strong with good fracture properties. Various electrospun fibers have been tested as fillers in dental composites to improve its mechanical properties. Generally, only a small amount of nanofibers is needed to substantially improve the mechanical properties although beyond an optimal amount, the performance starts to deteriorate. Dodiuk-Kenig et al (2008) used electrospun polyvinyl alcohol, poly-L-lactide and nylon 6 as reinforcement to improve the mechanical property of hyperbranched polymer modified (Hybrane, 0.3 wt.% DSM) dental formulations. Their test showed that the mechanical property is influenced by the fiber diameter, type and concentration. For fiber diameters of 250 nm and 125 nm, there is no apparent trend in its effect on the compressive strength, flexural strength and tensile strength [Dodiuk-Kenig et al 2008]. Tian et al (2007) investigated the reinforcing effect of nylon 6 nanocomposite nanofibers containing highly aligned fibrillary silicate single crystals when blended into 2,2'-bis-[4-(methacryloxypropoxy)-phenyl]-propane (Bis-GMA) / tri- (ethylene glycol) dimethacrylate (TEGDMA) dental composites. With 2% mass fraction of nanofibers impregnated, the composite flexural strength, elastic modulus and work-of-fracture improves by 23%, 25% and 98% respectively. However, when higher mass fraction of nanofibers is impregnated, the mechanical properties dropped. This may be due to inadequate wetting, presence of voids/defects and weakness in the nanofiber filler.

Glass fibers are commonly used as fillers in polymer matrix composite. Electrospinning has been used to produce fibers out of glass precursors and subsequently pyrolyzed to form nano-scaled glass fibers. Gao et al (2008) tested the mechanical properties of Bis-GMA/TEGDMA with 70% fillers comprising of a mixture of electrospun-derived glass fiber and Esstech glass powder. Having a composition of electrospun-derived glass fiber reinforcement at 7.5% such that the total mass fraction of filler remains at 70%, the flexural strength, elastic modulus and work-of-fracture of Bis-GMA/TEGDMA with 70% Esstech glass powder fillers was improved by 44%, 29% and 66% respectively. Other types of electrospun inorganic fibers have also been fabricated with the potential use as fillers in composite. Shah et al (2012) has shown that it is possible to fabricate two dimensional nanofibrous membrane and three dimensional wool-like nanofibrous structures by increasing the ratio of polyethylene oxide (PEO) to silica colloidal solution (30% solid loading) from 80:20 to 50:50 with the former generating two dimensional membrane and the latter, three-dimensional structure. Pyrolysis is used to remove PEO to give pure silica fibers. Proper preparation such as ensuring complete wetting of the nanofiber mesh and removal of air inclusion may be more challenging in a three-dimensional nanofibrous form due to its greater bulk. Poor impregnation of the nanofiber filler in the matrix will result in a composite that is weaker than unfilled resin [Boyd et al 2012].

Composition Fexural Strength Elastic modulus Work-of-fracture Reference
Bis-GMA/TEGDMA 95 MPa 2 GPa 4.3 kJ/m2 Tian et al 2007
Bis-GMA/TEGDMA with 2.0% (mass fraction) neat nylon 6 nanofiber 106 MPa 2.4 GPa 6.7 kJ/m2 Tian et al 2007
Bis-GMA/TEGDMA with 2.0% (mass fraction) neat nylon 6/ fibrillar silicate nanocomposite nanofiber nanofiber 117 MPa 2.5 GPa 8.5 kJ/m2 Tian et al 2007
Bis-GMA/TEGDMA with 70% Esstech glass powder 88 MPa 4.9 GPa 6.1 kJ/m2 Gao et al 2008
Bis-GMA/TEGDMA with 7.5% silanized electrospun glass fiber and 62.5% Esstech glass powder 127 MPa 6.3 GPa 10.1 kJ/m2 Gao et al 2008
Bis-GMA/TEGDMA with 0.3% wt hyperbranch polyesteramide and 0.05 wt% polyvinyl alcohol nanofibers 357 MPa Not tested Not tested Dodiuk-Kenig et al 2008
Bis-GMA/TEGDMA with 0.3% wt hyperbranch polyesteramide and 0.3 wt% poly-L-lactide nanofibers 357.3 MPa Not tested Not tested Dodiuk-Kenig et al 2008
Bis-GMA/TEGDMA with 0.3% wt hyperbranch polyesteramide and 0.01 wt% polyamide-6 nanofibers 257.5 MPa Not tested Not tested Dodiuk-Kenig et al 2008

Tissue regeneration

Electrospun nanofiber scaffold with its resemblance to natural extracellular matrix (ECM) is known to facilitate cell adhesion and proliferation. This has prompted research into its use as a scaffold for dental tissue engineering. Of particular interest is the response and biocompatibility of dental pulp stem cells on electrospun scaffold. Dental pulp stem cells have the ability to differentiate and may form dentine-pulp complex which is vital for tooth regeneration. Several studies have shown that dental pulp stem cells is able to adhere and proliferated well on electrospun scaffolds [Deng et al 2007, Yang et al 2010]. Yang et al (2010) showed that electrospun composite scaffolds made of polycaprolactone (PCL)/ gelatin/nano-hydroxyapatite (nHA) and PCL/gelatin was able to support dental pulp stem adhesion, proliferation and odontogenic differenation. In particular the presence of nHA significantly increases odontogenic differenation both in vitro and in vivo.

Eap et al (2014) brought a step closer to tooth regeneration when they successfully reinnervate a bioengineered tooth on electrospun polycaprolactone membrane loaded with neural growth factor. ED14 tooth germs were cultured on electrospun PCL membrane for six days before implanting behind the ears of mice for 2 weeks. Following 2 weeks of implantation, correct development of tooth crown can be seen with secretion of predentin/dentin. Their study showed that without neural growth factor, there is no innervation. In contrast, the presence of growth factor encourages axon growth and innervation of the dental pulp.


Enamel Regeneration

Electrospinning can be used to form fiber carrier for various organic and inorganic materials. Fletcher et al (2011) used this advantage of electrospinning to create a mat of amorphous calcium phosphate (ACP)/poly(vinylpyrrolidone)(PVP) nanofibers for remineralization of enamel. In the presence of fluoride, it was shown that ACP phase at the surface of the enamel formed a contiguous overlayer of crystalline fluoridated hydroxyapatite. This is potentially useful for regeneration of enamel and for the alleviation of dentine hypersensitivity amongst others.


Dental implant surface modification

Dental implant is often used as a more permanent fix to replace lost tooth. However, the clinical success of the dental implant is dependent on its osseointegration which is the ability of host tissues to form new bone around the implant. Failure of the implant is often attributed to the formation of fibrous tissues around the implant instead of direct bone contact to the implant surface. As the fibrous tissue is mechanically weak, it is unable to provide long term support for the implant after the healing process is completed. To ensure direct bone contact to the implant surface, one method is to encourage mineral deposition on the implant surface by osteoblast or mesenchymal stem cells. Ravichandran (2009) showed that adhesion of mesenchymal stem cells (MSC) on titanium plate and alloy is significantly enhanced with nanofiber coating even with man-made polymer such as poly(lactic acid)-co-poly(glycolic acid) (PLGA). Incorporation of the PLGA nanofiber with collagen and hydroxyapatite (HA) further increases the adhesion of MSCs on the implant surface. Titanium alloy coated with PLGA/collagen and HA nanofibers showed better proliferation and exhibited significantly greater alkaline phosphatase activity and mineral secretion than untreated titanium alloy.

SEM image of the fractured surface of 3D nanofibres filled epoxy resin clearly showing how some fibres have not been infiltrated by the resin resulting in poor performance [Boyd et al. J. Cellulose Nanofibre Mesh for Use in Dental Materials. Coatings 2012; 2: 120. CC By 4.0].


Dental Pulp Capping

Pulp capping is a technique used to protect dental pulp after it has being exposed during cavity preparation. A favourable outcome is quick formation of dentin bridge over the cavity so that further restorative work can be carried out. Mineral trioxide aggregate (MTA) is commonly used for direct pulp capping. Lee et al (2015) tested the clinical performance of MTA alone and electrospun poly(ε-caprolactone) (PCL) fiber mesh as a barrier for MTA. After 3 months, teeth treated with PCL and MTA formed approximately 3-fold thicker dentin bridge than MTA direct pulp capping. Dentin bridge formation with PCL and MTA was also significantly faster.


Antibiotic film

Ease of incorporating drugs and other additives into electrospun fibers have led to the development electrospun anti-microbial nanofibers for various applications. Large surface area of nanofibers increases the chance of contact and exposure by microbes to the anti-microbial additives. Albuquerque et al (2015) tested the potential use of electrospun scaffold embedded with Ciprofloxacin to reduce infection of the root canal system before regenerative procedures. The efficacy of the drug loaded polydioxanone nanofibers was tested on dentin specimens infected with E. faecalis biofilm. Polydioxanone nanofibers with 25 wt% drug loaded showed no microbial growth after two days while nanofibers without drug showed very high bacterial count.


Published date: 11 August 2015
Last updated: 21 June 2016

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