Jojo KottoorTechnology - Biomimetic endodontics: barriers and strategies TECHNOLOGY BIOMIMETIC ENDODONTICS : BARRIERS AND STRATEGIES JOJO KOTTOOR Department of Conservative Dentistry and Endodontics, Mar Baselios Dental College, Kothamangalam, Kerala, India Correspondence to: [email protected] Abstract Biomaterials used in the medical field lack the ability to integrate with biological systems through a cellular pathway. Conversely, biomimetic materials transcend the regular biomaterial in utility and will suitably perform the functions of the biological molecule that needs to be replaced. However, certain practical obstacles are yet to be overcome before biomimetic approaches can be applied as evidencebased approach in clinics. The article highlights on the past achievements, current developments and future prospects of tissue engineering and regenerative therapy in the field of endodontics and bioengineered teeth. Introduction Biomimetics is defined as the study of the formation, structure, or function of biologically produced substances and materials and biological mechanisms and processes especially for the purpose of synthesizing similar products by artificial mechanisms which mimic natural ones. A material fabricated by biomimetic technique Health Sciences 2013;2(1):JS007 1 based on natural process found in biological systems is called a biomimetic material.1,2 Biomimicry or biomimetics (from bios, meaning life, and mimesis, meaning to imitate) involves studying nature’s most successful developments and then imitating these designs to create new materials. The main disadvantage with traditional biomaterials used in the medical field is that they lack the ability to integrate with An Open Access Peer Reviewed E-Journal 2(1):JS007 2 pulp stem cells (DPSCs). and viii) Endothelial progenitor cells (EPCs).Jojo Kottoor Technology . Embryonic and Adult stem cells their most important properties being their ability of self renewal and their ability to grow in-vitro. T i s s u e e n g i n e e r i n g t r i a d Stem cells are defined as cells that have the ability to continuously divide and produce progeny cells that develop into various other cells or tissues.Biomimetic endodontics: barriers and strategies biological systems through a cellular pathway which can lead to failure of the material. The key elements of tissue engineering are stem cells.5 There are two major types of stem cells.3 A biomimetic approach to restore tooth structure is based on regenerative endodontic procedures by application of tissue engineering which opens up a whole new arena for the practioner. a response of pulpdentin repair.4 F ig u r e 1 . iii) Stem cells from apical papillae (SCAP). vii) Stem cells from the dental follicle (DFSC). are presently being used in medical therapies and are readily accessible. eight types of human dental stem cells have been isolated and characterized: i) Dental Health Sciences 2013. which have the least amount of ethical concerns. v) Epithelium-originated dental stem cells (EpSC). morphogen. biomimetic materials transcend the regular biomaterial in utility and will suitably perform the functions of the biological molecule that needs to be replaced. Signaling molecules or morphogens are extracellular secreted signalling molecules that play a key role in signaling many of the events of repair and regeneration including tertiary dentinogenesis. ii) Stem cells from human exfoliated deciduous teeth (SHED). However. and a scaffold of extracellular matrix (Figure 1). To date. iv) Periodontal ligament stem cells (PDLSCs). vi) Mesenchymal stem cells (BMSC). These signalling networks can An Open Access Peer Reviewed E-Journal . including dental tissues. adult stem cells. Comparing the different stem cell types.6 Postnatal stem cells have been found in almost all body tissues. Biomimetic endodontics: barriers and strategies be generally classified into growth factors and inflammatory cytokines. Mineral based scaffolds usually are made of calcium phosphates in the form of hydroxyapatite or beta Tricalcium phosphate and by varying the content of calcium the rate of degradation of these scaffolds can be controlled. They lack the strength of natural scaffolds and are Health Sciences 2013. matrix synthesis and tissue differentiation. Hedgehog. the challenge lies in designing and fabricating biomimetic materials like enamel. Although current root canal treatment modalities offer high levels of success for many conditions.12 B io m i m e t i c regeneration approaches for The creation and delivery of new tissues to replace diseased.2(1):JS007 3 brittle making it susceptible to fracture 10 and hence were introduced the synthetic scaffolds.8 The scaffold or the extracellular matrix is a mixture of proteins including collagen.7 Growth factors are soluble proteins that act as signaling agents for cells. fibronectin. pulp. These include the porous ceramics.Jojo Kottoor Technology . The main disadvantage of natural scaffolds is that they often lack the desired structural integrity for its independent use in load bearing areas. dentin. infection and wound healing. but have the disadvantage of lacking osteoinductiveness and an inherent difficulty in obtaining high porosity and regular pore size. poly lactic acid (PLA). proteoglycans and laminins forming an elastic network surrounding most cells and tissue structures. five eminent families of growth factors appear to regualate the process of odontogenesis: Fibroblast growth factor. or traumatized pulp is referred to as regenerative endodontics. poly lactic-co-glycolic acid (PLGA) which are all polyester material that degrade within the human body. spongiosus collagen. Natural scaffolds like Collagen. and their copolymers. such as cell division. an ideal form of therapy might consist of regenerative approaches in which diseased or necrotic pulp tissues are removed and replaced with healthy pulp tissues to revitalize the teeth. They have the advantage of being able to function in load bearing. Bone morphogenic protein (BMP). Primarily. Wingless (WNT) and Transforming growth factor. lyophilized bone and coral are the most commonly used natural scaffold. fibrous titanium mesh. Inflammatory cytokines (Interleukin and Tumor necrosis factor) are molecules that regulate cellular behaviour of bone under inflammation. poly glycolic acid (PGA). and influence critical functions.9 Current scaffolds used in tissue engineering can be grouped into three main categories. polysaccharide hyaluronic acid. missing. However.11 This has led researchers to concentrate efforts to engineer scaffolds at the nanostructural level to modify cellular interactions with the scaffold. bone and periodontal ligament and focus should be toward regenerating the diseased and necrotic tissues rather than replacing them An Open Access Peer Reviewed E-Journal . cementum. Stem cell therapy The simplest method to administer cells of appropriate regenerative potential is to inject the postnatal stem cells into the disinfected root canal system. The use of SHED might bring advantages for tissue engineering over the use of stem cells from adult human teeth as follows: (a) An Open Access Peer Reviewed E-Journal .2(1):JS007 4 be observed. metronidazole. diagnosed with apical periodontitis. revascularization procedures lack standardization of treatment protocols with a myriad of reported techniques. An antimicrobial agent (either an antibiotic such as metronidazole. and the access cavity is sealed. root canal revascularization is a procedure to establish the vitality in a nonvital tooth to allow repair and regeneration of tissues. in the absence of symptoms. but the thin dentinal walls increase the risk of a subsequent fracture. Root canal revascularization Treatment of the young permanent tooth with a necrotic root canal system and an incompletely developed root is fraught with difficulty. The typical revascularization protocol advocates that the immature tooth. and then MTA is placed over the blood clot. This article reviews current biomimetic approaches for regeneration tooth and its associated structures. Stem cells from human exfoliated deciduous teeth (SHED). intracanal medicaments and irrigants.25% NaOCl and Peridex TM (Procter & Gamble. Among the eight different post natal dental stem cells Dental pulp stem cells (DPSCs).14 DPSCs are the stem cells isolated from human dental pulp.Jojo Kottoor Technology . Other than the procedure like maturogenesis or apexogenisis.13 However. a. the tissue is irritated until bleeding is started and a blood clot produced.15 Stem cells from human exfoliated deciduous teeth (SHED) have become an attractive alternative for dental tissue engineering. After an average of 3 weeks. and Stem cells from the apical papilla (SCAP) were more commonly used in the field of regenerative endodontics. OH). Autologous dental stem cells are the most accessible stem cells for this therapy. b. minocycline or Ca (OH)2 should be then applied into the root canal system. the tooth is reentered. Cincinnati.Biomimetic endodontics: barriers and strategies with some conventional replacement materials. and fibrous tissue containing blood vessels in an arrangement similar to the dentin-pulp complex found in normal human teeth. Within the next 2 years a gradual increase in root development can Health Sciences 2013. and the access is sealed. The most striking feature of DPSCs is their ability to regenerate a dentin-pulp-like complex that is composed of mineralized matrix with tubules lined with odontoblasts. Not only is the root canal system often difficult to fully debride. ciprofloxacin or ciprofloxacin. should be accessed and irrigated with either 5% NaOCl _ 3% H2O2 or 5. 20 An Open Access Peer Reviewed E-Journal . exfoliated deciduous teeth. Collagen served as the scaffold. and a recent review has described several potential endodontic applications. and painless stem cell collection with minimal invasion.Biomimetic endodontics: barriers and strategies SHED were reported to have higher proliferation rate compared with stem cells from permanent teeth. It is hypothesised that SCAP appear to be the source of primary odontoblast that are responsible for the formation of root dentine. a collagen scaffold. Rebecca et al had generated Dental pulp like tissue by using the tissue engineering triad. 17 Since these stem cells are in the apical papilla. ie. (b) SHED cells are retrieved from a tissue that is "disposable" and readily accessible in young patients. the cells may have low survival rates. and dentin matrix protein 1 (DMP1) was the growth factor. Pulp implantation Dental pulp tissue is vulnerable to infection. autogenous stem cells are relatively easy to harvest and to deliver by syringe.commonly known as root-canal therapy.2(1):JS007 5 are several disadvantages to a delivery method of injecting cells.16 A recent finding is the presence of a new population of a mesenchymal stem cells residing in the apical papilla of incompletely developed teeth. 19 Similarly pulp tissue has also been successfully regenerated in-vitro using the tissue engineering triad. a Collagen Scaffold. There are several advantages to an approach using postnatal stem cells. entire pulp amputation followed by pulp-space disinfection and filling with an artificial rubber-like material is employed to treat the infection . Currently. and Dentin Matrix protein 1 after subcutaneous transplantation in mice. replacement pulp tissue is produced by tissue engineering triad and is transplanted into cleaned and shaped root canal systems. possibly leading to aberrant patterns of mineralization. and the cells have the potential to induce new pulp regeneration. Second. which enables it to survive during the process of pulp necrosis. They are termed stem cells from the apical papilla (SCAP). including bone marrow replacement. Second. this approach is already used in regenerative medical applications. First. the cells might migrate to different locations within the body. In pulp implantation. which might lead to hard tissue formation. whereas DPSCs are likely the source of replacement odontoblast. and DMP1 can induce an organized matrix formation similar to that of pulpal tissue. which might facilitate the expansion of these cells in vitro before replantation. scaffold and morphogens. but by using a different stem cell. they are benefited by its collateral circulation. The result concluded that the triad of DPSCs. there Health Sciences 2013.Jojo Kottoor Technology . the Dental Pulp Stem Cells (DPSCs). First. c.18 However. It also has an added advantage of abundant cell supply. research is focusing on making them photopolymerizable to form rigid structures once they are implanted into the tissue site.23 This will allow tissue engineered pulp tissue to be administered in a soft three-dimensional scaffold matrix. with the addition of endothelial cells. 52 To make hydrogels more practical. When implanting pulp into the root canals that have blood supply only from the apical end. As a result.Jojo Kottoor Technology . In theory.21 Recent efforts in developing scaffold systems for tissue engineering have been focusing on creating a system that promotes angiogenesis for the formation of a vascular network. Three-dimensional cell printing One of the most promising approaches in tissue engineering is the application of 3D scaffolds. enhanced vascularization is needed in order to support its vitality. hydrogels at are at an early stage of research. novel technologies capable of producing 3D structures in accordance with predefined design are An Open Access Peer Reviewed E-Journal . Injectable scaffold delivery Rigid tissue engineered scaffold structures provide excellent support for cells used in bone and other body areas where the engineered tissue is required to provide physical support. and this type of delivery system. in root canal systems a tissue engineered pulp is not required to provide structural support of the tooth. although promising. microscale technologies that provide open channels or the ability to guide vascular ingress from the apex through the pulp may be of particular benefit.25 e. has yet to be proven to be functional in vivo.Biomimetic endodontics: barriers and strategies One of the potential problems associated with the implantation of cultured pulp tissue is that specialized procedures may be required to ensure that the cells properly adhere to root canal walls. but advances in formulation have dramatically improved their ability to support cell survival. In order to control cell migration and cellular interactions within the scaffold. Among the injectable biomaterials investigated so far. 24 Despite these advances. the hydrogel may promote pulp regeneration by providing a substrate for cell proliferation and differentiation into an organized tissue structure. d. Past problems with hydrogels included limited control over tissue formation and development. However. Hydrogels are injectable scaffolds that can be delivered by syringe and have the potential to be noninvasive and easy to deliver into root canal systems. The porosity of the scaffold and internal pore organization influence cell migration and play a major role in its biodegradation dynamics. which provide cell support and guidance in the initial tissue formation stage.22 These scaffolds are impregnated with growth factors such as VEGF (vascular endothelial growth factor) and/or platelet derived growth factor or further. nutrient diffusion and mechanical stability.2(1):JS007 6 in the field of tissue engineering. hydrogels are more and more attractive Health Sciences 2013. DPSCs were isolated. an ink-jet-like device is used to dispense layers of cells suspended in a hydrogel to recreate the structure of the tooth pulp tissue. In the in vivo approach. retroviral. The ex vivo approach involves genetic manipulation of cells in vitro. the disadvantage of using the threedimensional cell printing technique is that careful orientation of the pulp tissue construct according to its apical and coronal asymmetry would be required during placement into cleaned and shaped root canal systems. herpes simplex virus. lentivirus are being developed. or incorporating them into An Open Access Peer Reviewed E-Journal . differentiated into odontoblasts with recombinant BMPs or BMP genes. This indicates the potential of adding growth factors before pulp capping. This may involve positioning of odontoblasts around the periphery. In the field of conservative dentistry.30 Both in vivo and ex vivo approaches can be used for gene therapy. affordable. Widespread clinical application still awaits the development of vectors that are safe. BMPs or BMP genes are directly applied to the exposed pulp. peptides.27 The three-dimensional cell printing technique can be used to precisely position cells. efficient.2(1):JS007 7 gene guns. with fibroblasts in the core. and this method has the potential to create tissue constructs that mimic the natural tooth pulp tissue structure. f. and finally autogenously transplanted to regenerate dentin. electroporation. At present adenoviral. and sonoporation to address safety concerns such as immunogenicity and mutagenesis.26.29 Most of the risks of gene therapy may arise from the vector system rather than the gene expressed. adenoassociated virus. The major challenge involved is the precise orientation of cellular suspensions according to the apical and coronal asymmetry of pulp. Nonviral delivery systems uses plasmids.32 The main challenges for gene therapy in the next decade will be the requirements to demonstrate that gene therapy can provide cost-effective and safe long-term treatments for conditions that would otherwise lead to significant pulp necrosis. Gene Therapy Gene therapy is a method of delivering genes with the help of viral or non-viral vectors. Viral vectors are genetically altered to eliminate ability of causing disease.28 Theoretically. The gene delivery in endodontics would be to deliver mineralizing genes into pulp tissue to promote tissue mineralization. without losing infectious capacity to the cell.Biomimetic endodontics: barriers and strategies required. DNA-ligand complex. In conservative dentistry. simple for application. which are subsequently transplanted to the regeneration site. In theory. cationic liposomes. and that have ability to express the required level of transgene for the sufficient long term. the gene is delivered systemically into the blood stream or locally to target tissues by injection or inhalation. Health Sciences 2013.Jojo Kottoor Technology . Biomimetic endodontics: barriers and strategies restorative and endodontic materials to stimulate dentin and pulp regeneration. which was erupted and occluded. the bioengineered tooth was smaller than the other normal teeth. bone and cartilage. in a more recent study Oshima et al showed that the crown widths and the cusp numbers of bioengineered molar could be regulated by cell manipulation method. which is one of the ultimate goals of regenerative therapies. had the correct tooth structure. Research on whole tooth regeneration is also advancing using a strategy of transplanting artificial tooth germ and allowing it to develop in the adult aral environment. were implanted for 20-30 weeks into omentum. In addition. cementum and even the pulp tissue.36 Bioengineered tooth. dentine. Regeneration of the lost tooth structure rather than replacement during treatment will ensure better prognosis and higher rate of success.35 However. Hence the future of endodontics would involve the use of such biomimetic materials which could successfully replace lost enamel. C o n c l u s io n s The practice of endodontics has grown by leap and bounds in the past few decades. g.33 Research on the fabrication of teeth from dissociated cells was first performed using tooth germ cells. cusp position. the regenerated teeth were not identical to their naturally formed counterparts. and Health Sciences 2013. seeded with porcine third impacted tooth bud cells. Biomimicry: Innovation Inspired by Nature. Replacement of diseased or lost tooth structure with biocompatible restorative materials is currently the order of today but each of these procedures does have their own limitations and drawbacks. References 1.34 When explanted.2(1):JS007 8 tooth patterning including anterior/posterior and buccal/lingual structures. However.37 Tooth regeneration is an important stepping stone in the establishment of engineered organ transplantation. Benyus JM. New York: William Morro 1997. the authors couldn’t regulate the crown width. Bioengineered tooth The ultimate goal of regenerative therapy is to develop fully functioning bioengineered organs that can replace lost or damaged organs following disease. However. injury. or aging. hardness of mineralized tissues for mastication. Tissue engineering builds a tissue such as skin. An Open Access Peer Reviewed E-Journal .Jojo Kottoor Technology . 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