Biomimetic dentistry

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Review Article

Biomimetic dentistry Suchetana Goswami Department of Pedodontics and Preventive Dentistry, Dr. R. Ahmed Dental College and Hospital, Kolkata, West Bengal, India

Abstract

“Biomimetics” is the field of science that uses the natural system of synthesizing materials through biomimicry. This method can be widely used in dentistry for regeneration of dental structures and replacement of lost dental tissues. This is a review paper that states its scope, history, different fields of biomimetic dentistry, and its future conditions in India. Keywords: Biomimetic materials, regeneration, remineralization

Address for correspondence: Dr. Suchetana Goswami, Dr. R. Ahmed Dental College and Hospital, 114 AJC Bose Road, Kolkata ‑ 700 014, West Bengal, India. E‑mail: [email protected]

INTRODUCTION

HISTORY OF BIOMIMETIC MATERIALS

The term “bio” means life and “mimesis” in Greek means imitate. Biomimetics is the field of study that attempts to design system and synthesize materials through biomimicry.[1] Biomimetics can be defined as the study of the structure, formation, and function of biologically produced materials and also biological mechanisms and processes especially for the purpose of synthesizing similar products by artificial mechanisms which mimic natural ones.[2] A material thus formed by biomimetic technique based on the natural process is called a biomimetic material.[2,3] The main principle of biomimetic dentistry is to replace the lost dental tissues by materials to restore full function and bear with all functional stresses along with the maintenance of esthetic results. Biomimetics is an interdisciplinary field that gathers information from the study of biological structures and functions with chemistry, physics, mathematics, and engineering to develop principles that are important for the generation of novel synthetic materials and organs.[1‑4]

The history dates back to the 1950s when Ottoschmit coined the term biomimetics. The word “bionics” was first used by Jack Steele in 1960. Although the concept was very old, its real implementation is possible only recently due to the enormous research in the fields of biochemistry and molecular biology. It is believed that the attempts to replace body parts started at least 2500 years ago when artificial teeth were carved from the bones of oxen.

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Crude dental implants were attempted as early as in the first and second century AD in Roman population and in pre‑Columbian cultures of Central and South America. The use of dental amalgam to repair decayed teeth was recorded in the Chinese literature dates back to the year of 659 AD. The middle of 20th century was important in the history of biomimetic medicine due to the sophisticated inventions of the cardiac pacemaker, artificial heart valves, and knee

For reprints contact: [email protected] DOI: 10.4103/jorr.jorr_3_17

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How to cite this article: Goswami S. Biomimetic dentistry. J Oral Res Rev 2018;10:28-32.

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Goswami: Biomimetic dentistry

joint replacement. Accidental organ and tissue loss have been treated by surgical reconstruction and the use of mechanical devices such as kidney dialyzers and organ transplant from one individual to other increases in recent years.[3,4] OBJECTIVES

The main objectives of biomimetic dentistry are to return the tooth to its function, esthetics, and strength. In conventional approach, more tooth structures are removed; the diseased tooth structures are replaced with rigid materials. These techniques and materials have shortened the life span of restorations and weakened the tooth structures. Therefore, attempts are being made to develop materials which will regenerate dental structures and replacement of lost dental tissues by processes which mimic natural ones. BIOMATERIALS

The various bioactive materials that are used in dentistry are discussed. Synthetic polymer

Both biodegradable and nonbiodegradable polymers are used as restorative materials in dentistry. The biodeg radable polymers include polylactic acid and polyglycolic acid copolymers. These polymers are used primarily as suture materials but are now also being examined as bone, skin, and liver substitutes. Within the body, they are broken down hydrolytically to produce lactic acid and glycolic acid. Recently introduced materials in this field are polyanhydrites, polyphosphazenes, polymethyl methacrylate (PMMA), polytetrafluoroethylene (PTFE), and polyhydroxyethylmethacrylate. These are alloplastic synthetic nonbiodegradable polymers. PMMA is used primarily for dentures base materials and also as cement for many orthopedic prostheses. PTFE is used for bone augmentation and guided bone regeneration. Ceramics

Ceramics are commonly used for replacement of lost tooth str uctures (crown fabrication) and in bone tissue engineering. The common ceramics that are used in dentistry and hip prosthesis are alumina and hydroxyapatite. Alumina has a very good corrosion resistance, high strength, and wear resistance. Hydroxyapatite is a calcium phosphate‑based ceramic material and is the major component of bone and teeth. Calcium phosphate hydroxyapatite and various types of alumina are biocompatible in nature and are coated to the

implants that enhance osseointegration.[2‑4] Bioceramics are recent inclusion in this field. These materials are highly biocompatible and chemically stable in oral environment. BIOMIMETIC PRINCIPLES IN RESTORATIVE DENTISTRY

The main goal of biomimetics in restorative dentistry is to return the hard tissues (enamel and dentin) to attain full function by a hard tissue bond. This allows functional stresses to pass through the tooth making the entire crown into a unit that provides near normal function and biologic and esthetic result. Unfortunately, in dentistry, there is no such biomaterial that has the same mechanical, physical, and optical properties as that of tooth structures (i.e., enamel, dentin, and cementum). In biomimetic approach of restorative dentistry, the search is for materials that will have esthetic and functional properties closer to tooth structure. Although lacking in strength, composites have many favorable properties over amalgam. The newer techniques favor minimal preparation, decrease pulpal involvement, and reduce the chances of tooth fractures. Glass ionomer cements (GICs) are considered as biomimetic materials because it has properties similar to dentin, adhesiveness to tooth structures, and fluoride release.[5] GICs are useful in deep I and II cavities to fill up the base as lining material. They are also used as restorative materials in buccal class V cavities. GIC releases fluoride, which has bactericidal properties, and stimulates sclerotic dentin. However, its tensile strength is poor and is not advocated in areas of high occlusal stress and force concentration. Biodentine, a newly developed material, may replace GIC as a liner in deep fillings in the future, but further research is needed in this field. GIC is currently being the main material for minimum invasive dentistry. Nowadays, due to the development of improved adhesives, the use and indications for bases and lines have decreased. The indication for placing a liner under adhesive restoration is mainly for pulp protection in the form of partial lining using Ca(OH)2 cements.[6,7] Endodontically treated teeth are fragile and susceptible to fracture because of tooth structure removal and loss of cushioning effect due to the removal of pulp. In case of posterior teeth, total cuspal coverage with porcelain is

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Goswami: Biomimetic dentistry

recommended because it will significantly strengthen the crown and increase cusp stabilization.[4,8] BIOMIMETICS IN COSMETIC DENTISTRY

Biomimetic dentistry is based on the philosophy that the intact tooth in its ideal hues and shades are more important. Its intracoronal anatomy, mechanics and locations in the arch are also important to reconstruction and determines success.[9,10] BIOMIMETIC APPROACHES FOR REGENERATION

Different regenerative technologies are invented based on biomimetic approaches. Regeneration of dentin‑pulp complex

Recombinant human BMP2 and BMP4 can induce new dentin formation. When recombinant BMP is delivered in a scaffold of demineralized dentin matrix, it induces classic tubular dentin in amputated pulp. Whereas BMP when delivered using type I collagen matrix, it induces osteodentin formation. In nonhuman primates, the use of recombinant human BMP7 with an insoluble type I collagen matrix induces reparative dentin formation in freshly cut healthy pulp tissue. The size and shape of the inductive material is important as it controls the size and shape of the reparative dentin.[5,6] Stem cell therapy

Stem cell therapy is an upgraded procedure that can be used for the treatment of degenerated tissues. Stem cells are multipotent cells that can be differentiated into any other forms of cells. The easiest method of stem cell therapy is to administer cells of definite regenerative potential into the disinfected root canal system. The most commonly used stem cells in regenerative endodontics are stem cells from human exfoliated deciduous teeth (SHED), dental pulp stem cells (DPSCs), and stem cells from the apical papilla (SCAP). DPSCs are derived from human dental pulp. The characteristic feature of these cells is their ability to regenerate dentin‑pulp complex like natural human tooth. SHED are good alternative for dental tissue engineering. They are more efficacious than adult teeth stem cells due to higher proliferation rate and have the advantage of painless stem cell collection with minimal invasion and abundant viable cell supply. Nowadays, stem cells are also collected from mesenchymal stem cells present in the apical papilla of incompletely formed teeth. They are called SCAP.[10,11] 30

Pulp implantation

Generation of pulp tissue is possible in laboratory by tissue engineering process and then it is transplanted into cleaned and shaped root canal system. Rebeca et al. had developed dental pulp‑like tissue using the tissue engineering triad: DPSCs, dentin matrix protein I and a collagen scaffold following subcutaneous transplantation in mice. Collagen acts as scaffold and dentin matrix protein I was the growth factor. The investigators have shown that the tissue engineering triad of DPSCs, dentin matrix protein I, and a collagen scaffold can induce an organized matrix similar to pulp tissue which may lead to hard tissue formation.[12] Root canal revascularization

And Irrigation of root canal with sodium hypochlorite and chlorhexidine along with the placement of antibiotics (mixture of ciprofloxacin, metronidazole, and minocycline paste) for several weeks to disinfect the root canal system is the current practice. Our aim should be to increase chances of revascularization of avulsed necrotic tooth. The success of the revascularization process ensures the life of the tooth in the arch. In this technique, the chances of immune rejection and pathogen transmission are less as regeneration of the tissue takes place by patient’s own blood cells.[12] Injectable scaffold theory

In this procedure, pulp tissue is obtained by tissue engineering process and then it is administered in a soft three‑dimensional scaffold matrix. Among all the injectable biomaterials, hydrogels are more favorable in the field of tissue engineering. Hydrogels are injectable scaffolds that can be delivered by a syringe, are noninvasive in nature, and easy to deliver into the root canal systems. Theoretically, hydrogel promotes pulp regeneration by providing a substrate for cell proliferation and differentiates into an organized tissue structure.[12‑15] Gene therapy

It is a method of delivering genes with viral or nonviral vectors. Viral vectors are genetically altered to eliminate ability of causing disease without losing the capacity of infecting a cell. Viral vectors are adenovirus, retrovirus, lentivirus, and Herpes simplex virus. The nonviral delivery systems include plasmids, peptides, cationic liposomes, DNA‑ligand complex, gene guns, electroporation, and sonoporation. The gene delivery system in endodontics aims to deliver mineralizing genes into pulp tissue to induce mineralization.[11‑16] Bioengineered tooth

Whole‑tooth regeneration is an advancing field which uses a strategy of transplanting artificial tooth germ and allowing it to develop in the oral environment.[17] Journal of Oral Research and Review | Volume 10 | Issue 1 | January-June 2018

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Goswami: Biomimetic dentistry

Biomimetic mineralization

Biological mineral synthesis process manufactures materials of highly controlled size, habit, texture, composition, and structure. A recently introduced technique of guided for mation of enamel‑like fluoroapatite layer on a mineral substrate has the potential to enable remineralization of superficial enamel defects on exposed dentin.[18‑21] Biomimetic remineralization

Biomimetic remineralization of dentin is possible using some ion‑containing solutions or ion‑leaching silicon‑containing materials. Recent studies reported the use of bioactive “smart” composites containing reactive calcium silicate. Many researchers used “agarose” gel containing sodium hypophosphate that covered an acid‑etched dentin material.[19‑21] Development of artificial salivary gland

Patients with autoimmune diseases such as Sjogren’s syndrome or oral cancer patients who have undergone radiotherapy may have their salivary glandular tissues destroyed and the ultimate result would be dry mouth. Patients experience difficulty in chewing, swallowing, and speaking. In an attempt to regenerate salivary gland, adult embryonic stem cells are used to develop parenchymal cells and restoration of its secretory functions. Efforts have been made to create a rather simple device  –  blind‑end tube suitable for graft in the buccal mucosa in patients whose salivary glandular tissues have been destroyed. The lumen of this tube would be lined with compatible epithelial cells which are physiologically capable of unidirectional water movement.[2]

is needed in this field. Regeneration of the lost dental tissue rather than mild replacement with dental materials ensures better prognosis, excellent biocompatibility, and high success rate. The scope of biomimetic dentistry in India is enormous in the near future. Biomimetic dentistry would successfully replace lost dentin, enamel, cementum, and pulp and open a new era of dentistry. Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest. REFERENCES 1. 2. 3. 4. 5. 6. 7.

8. 9. 10.

BIOMIMETIC APPROACHES OF ORAL SURGERY

Attempts are made to utilize biomimetic techniques in oral and maxillofacial surgery for craniofacial reconstruction. Multipotent stem cells (MSCs) have been used in the tissue engineering of human‑shaped temporomandibular joints. Mandibular condyles are made up of cartilaginous and bone tissues. MSCs were differentiated into chondrogenic and osteogenic cells and these cells were subsequently encapsulated in a poly (ethylene glycol) diacrylate hydrogel which was then molded into an adult human mandibular condyle in stratified yet integrated layers of cartilage and bone.[20,21] CONCLUSION

Biomimetics in dentistry is a very useful concept and further and firmer multidisciplinary scientific and technical research

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tooth unit as a mature organ replacement regenerative therapy. PLoS One 2011;6:e21531. 18. Busch S, Schwarz U, Kniep R. Chemical and structural investigations of biomimetically grown fluroapatite‑gelatin composite aggregates. Adv Funct Mater 2003;13:189‑98. 19. Clark DJ. Biomimetic Endodontics: The Final Evolution? Dentistry today.com; July, 2007. Available from: http://www.dentistrytoday.com.

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