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 Table of Contents  
REVIEW ARTICLE
Year : 2017  |  Volume : 7  |  Issue : 1  |  Page : 29-33

Hydrogels in maxillofacial prosthesis


1 Department of Prosthodontics, KSR Institute of Dental Sciences, Tiruchengode, Tamil Nadu, India
2 Teja Institute of Dental Sciences, Tirupathi, Andhra Pradesh, India
3 Department of Prosthodontics and Crown and Bridge, Pearl's Dental Clinic, Chennai, Tamil Nadu, India
4 Department of Prosthodontics and Crown and Bridge, KSR Institute of Dental Sciences, Tiruchengode, Tamil Nadu, India

Date of Web Publication30-Jun-2017

Correspondence Address:
Muthuvignesh Jayaram
Department of Prosthodontics, KSR Institute of Dental Sciences and Research, Tiruchengode, Tamil Nadu
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ijmd.ijmd_63_16

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  Abstract 

Background: There is a growing need for prosthetic replacements in humans due to various reasons. Oro-facial deformities contribute more for these treatment modalities due to impairment in both function and esthetics. Biomaterials play an important role in replacing any form of defects. Selection of a good biomaterial is of prime importance as these materials determine the success of the treatment outcome. Acrylic resins and silicones are the most popular materials for replacing the lost tissues as far as the maxillofacial prosthesis is concerned. But these materials only help in covering the defect and give a very little therapeutic effect. Acrylic resins are very rigid materials and are less tolerated by the ailing patients. Silicones have very poor edge strength and colour retaining capacity.
Purpose of Study: Hydrogels are hydrophilic gels which can be manipulated using polymeric network, are considered suitable maxilla facial materials. Hydro gels in dentistry can readily replace silicones as they have good physical, chemical and biological properties. They can also act as drug delivering devices which aids in healing of the defect and carriers for growth factors by which they stimulate the bone and tissue growth and they can be modified for their rigidity to have a good edge strength more recently. All these factors facilitate the hydrogels to serve as a good maxillofacial prosthesis material.
Summary and Conclusion: Hydrogels are biocompatible materials which act as both therapeutic and replacement devices for the oro facial defects and can improve the patient's perception towards the positive outcome of the treatment.

Keywords: Biomaterials; hydrogels; maxillofacial defects


How to cite this article:
Jayaram M, Sumankumar N, Egammai S, Rajkumar S, Nivethitha N. Hydrogels in maxillofacial prosthesis. Indian J Multidiscip Dent 2017;7:29-33

How to cite this URL:
Jayaram M, Sumankumar N, Egammai S, Rajkumar S, Nivethitha N. Hydrogels in maxillofacial prosthesis. Indian J Multidiscip Dent [serial online] 2017 [cited 2022 Aug 13];7:29-33. Available from: https://www.ijmdent.com/text.asp?2017/7/1/29/209277


  Introduction Top


The oral and the maxillofacial area is subjected to various developmental and congenital defects, infections, trauma following road traffic accidents and others, osteomyelitis and defects due to carcinoma which make rehabilitation of this area difficult. Any form of defects from the above factors is complex because they mainly involve skull bones, calvaria, meninges, facial tissue, air sinuses, and salivary glands. These defects are characterized by bacterial contamination from the oral cavity and sinus cavity, food impaction and often leading to impaired healing and infection. Hence, the main aim of the treatment should restore health and comfort as well as function and aesthetics. The modalities of treatment for orofacial defects are widespread. Surgery is not always amenable for correction of these defects and seek of other modalities is needed. The maxillofacial prosthesis is considered to be an alternative treatment option when surgery is not possible or following surgery.

Biomaterials play an important role in replacing human body parts. Biomaterial is a nonviable material used in a medical device, intended to interact with biological systems or a systemically and pharmacologically inert substance designed for implantation or incorporation with living systems. Biomaterial is a biologic or synthetic substance which can be introduced into the body tissue as an implant or used to replace an organ, bodily function, etc. Sushruta Samhita, an Indian saint was the first person to use a biomaterial in the human body. He performed rhinoplasty and skin graft as early in 6th century BC and used cloth for suturing. He gave the technique of “NEW NOSE” which was followed by the western countries later.[1] Through the eras, infinite materials had been introduced in this field. Many materials for maxillofacial prosthesis are being used ranging from metals, polymethylmethacrylate, polyethylmethacrylate. The mechanical stress from this rigid maxillofacial prosthesis led to complications such as functional impairment, tissue abuse, and infection. Hence, the focus of research shifts to softer biomaterials such as silicones. The silicones had disadvantages such as poor esthetics, may become less elastic due to aging and contact with body fluids. Hence, the search continued for a more biodegradable or bioinert material which can help in tissue healing, regrowth and regeneration.

Considering various circumstances an ideal biomaterial for maxillofacial prosthesis should be flexible, dimensionally stable, should not have much weight, with optimal thermal conductivity, biocompatible, stable in living tissues, bioinert, with optimal mechanical properties and high esthetic values. However, not all the materials behave with all ideal and desirable characteristics. Hydrogels are the smart materials that can be used as a biomaterial in the oral and maxillofacial reconstruction as it is biodegradable, biocompatible, bioinert, and biomimicking. Hydrogels are defined as water swollen, and cross-linked polymeric network produced by simple reactions of one or more monomers. The advantages of these materials can be extracted and engineered for the prosthetic purpose as they show less mechanical stress to the living tissue compared to other materials as they are more hydrophilic. Their flexibility can be altered because of the water content and can be made to mimic the natural tissue. These novel polymeric materials maintain their three dimensional structure and they contain various amounts of water depending on nature and density. The extent of swelling or deswelling in response to changes in the external environment of hydrogel is called as volume collapse. These polymers can be specifically engineered with desirable properties such as biodegradation, mechanical strength, biological response which forms it as a novel material in the future.


  History Top


The history of hydrogels dates back to 1894.[2] The first material to be developed with typical properties of hydrogel was hydroxyl ethylmethacrylate.[3] In 1960, in vitro studies were done, Buwalda et al. classified the hydrogel according to history can be divided into three main blocks or three generations. The first generation mainly involves cross-linking, the second generation consists of materials capable of response to stimuli, the third generation mainly involves stereo complex material.[3] The biomedical applications of hydrogels were mainly described in the year 1974. The 21st century can be called the era of hydrogel as its applications in the human body have been elaborated, and research in this area is increasing. Hence, they are now called as the smart hydrogels.[2]


  Classification Top


Hydrogels are classified according to various ways such as sources, polymeric composition, configuration, type of crosslinking, physical appearance, and electrical charge.[4] Out of all these, the main one to be considered is based on the source. Natural and synthetic are two types mainly included under the classification. Natural hydrogels are mainly fibrin, collagen, hyaluronic acid, chitosan, alginate, gelatin, dextran and the synthetic hydrogels are prepared from hydroxyethyl methacrylate, polyethylene glycol acrylate/methacrylate, poly (acrylamide), polyethylene glycol diacrylate/dimethacrylate, poly (vinyl alcohol), vinyl acetate, acryolic acid, methacrylic acid, N-isopropyl acrylamide, N-Vinyl-2-pyrrolidine.[3],[5] Third type of hydrogels is called as the combined hydrogels.


  Properties Top


Swelling and solubility

Hydrogel is hydrophilic polymer which is dispersed in a liquid. The solute like particles are the polymers and the solvent like particles are liquid holding the polymers in the solvent and allowing free diffusion.[6] The hydrogel is divided into wet hydrogel and dry hydrogel, the dry hydrogel is first formed and contains primary bound water and the wet hydrogel is then formed and contains secondary bound water. The primary and secondary bound water is together called as total bound water.[3] The water is the prime constituent in the hydrogel. There is equilibrium in the water content and makes it light by weight. Hydrogels do not dissolve in water and water acts as a plasticizer. Hydrogels swell and depends on network, polymer type, and type of solvent. The solubility of the polymers depends on the functional groups in it namely OH, NH2, and COOH.[5]

Elastic modulus

The elastic modulus is important for the gel property and stiffness. This varies for the application. For prosthetic use, more stiffness is used, and the elastic modulus will differ accordingly. The elastic modulus depends on the crosslink and charge densities of the polymer network. Elastic modulus of hydrogels increased with polymer fraction and decreased with water fraction. Recently, the stiffness is increased by tough double network gels.[7]

Porosity

Multifactorial influence is present on the porosity and diffusion of the hydrogel.[3] It depends on the factors such as concentration of chemical crosslink, concentration of polymer strands, net charge and this will affect the qualitative aspects of hydrogel for prosthetic use.

Crosslinking

Crosslinking varies due to various factors such as ultraviolet radiation, heat, chemicals, magnetic field, electric field, pH, and temperature.[4],[8] The degree of crosslinking will alter the quantity and quality of hydrogel. Thiol-ene crosslinking shows good efficiency and is mainly increased by ultraviolet radiation. Polyethylene glycol is used as telechelic polymers.[6] Physical and chemical are two types of crosslinking in hydrogel. The units in the polymer are natural or synthetic, and it can be a single network or interpenetrating network. Cellulose-reinforced hydrogels are sustainable type of hydrogels.[7] Modifying the crosslinking will provide beneficial properties for prosthetic use. Newer developments in crosslinking are derived from various researches such as sliding crosslinking, double networks, and nanocomposite hydrogels. These newer crosslinking materials show superior mechanical properties.[9],[10]

Inhomogeneity of hydrogels

The hydrogels show a property called spatial gel inhomogeneity [11] which involves inhomogeneous crosslinking. However, this property affects the mechanical properties in an adverse way.

Degradation of hydrogels

Hydrogels degrade through three main mechanisms, namely, enzymatic, hydrolytic, exchange of ions. The degradation can be altered by altering the concentration of the polymeric content, the crosslinking type and the anatomy of the defect.

Surface properties

The surface of hydrogels can be rough, smooth, or stepped. The surfaces transduce the message and will create the response at the molecular level in the cells and alter the response of the immune system. This property is important for the biocompatibility of hydrogel.[5]

Newer development in hydrogels

Newer developments in crosslinking are derived from various researches such as sliding crosslinking, double networks, and nanocomposite hydrogels. These newer crosslinking materials show superior mechanical properties. Stimuli-sensitive hydrogels that undergo changes with electric fields magnetic field, light, temperature is a type of hydrogel, self-assembled hydrogels, hybrid systems, self-assembled hydrogels from genetically engineered block copolymers are other modifications of hydrogel system.[10]


  Applications Top


Hydrogels are used in the human body as drug delivery systems mainly in the intraocular lenses, wound dressing, surgical tissue sealant, anti-adhesive of tissue, hydrogel tissue expander, transdermal patches, and insulin delivery systems.[2] They gels are used in cell encapsulation, nanoparticle coatings, and in diagnostic microdevices such as microfluidics,[10],[12] antibiotic drug delivery, tissue engineering [13],[14] extracellular matrix, implantable devices, biosensors, separation systems, materials controlling the activity of enzymes, phospholipid bilayer destabilizing agents, materials controlling reversible cell attachment, smart micro fluids with responsive hydrogels and energy conversion systems. New designs are also available involving protein domains containing noncanonical amino acids, self-assembling peptide fibers, artificial glycoproteins for controlling cell responses, building materials for micro chemotaxis devices, DNA recognition motifs, tunable liquid lens that permits autonomous focusing.[10] They are used in growth factor delivery, carrier material for multiple tissue regeneration, injectable ceramic materials, composite for bone tissue regeneration, cell delivery for engineering complex tissues, injectable scaffold material.[14] Hydrogels are also used in defibrillation electrodes, electrosurgical grounding pads, skin cushion pads, and neonatal electrodes.


  Ydrogel as a Maxillofacial Material Top


Hydrogels are considered to a compatible alternative for the natural system as it can be modified and developed for specific uses in novel ways. The potential of hydrogel to be used as a tissue substitute is appreciable by the researches as they mimic the human tissue and cells.

Hydrogels are colorless, odorless material. Color can be artificially modified by pigments and coloring agents according to the hue.[15] They are nontoxic, nonirritant, nonallergic and hence can be well supported by the host living tissue. They are bioinert and hence do not disturb the nearby biologic tissues. They are stable in light and have optimal trans illuminance and hence can be used in areas which are exposed to sunlight like the maxillofacial area. It is light in weight, flexible, and these increases the potential of it to be used as a maxillofacial prosthesis as these areas are more prone to natural creases and wrinkles as the natural appearances of external soft tissues are more important for aesthetics. The patient acceptance of this material hence can be improved. The rigidity of hydrogels can be altered by modifying its properties for using it in different areas of the maxillofacial region accordingly. The shelf life of the hydrogel can be extended up to 3 years by altering its physical and chemical properties and can successfully be used as the definitive maxillofacial material. The diffusion of oxygen through the hydrogel is comparatively higher than other material and hence can be stable near living tissues. Shear moduli, compressive moduli, and crosslink densities increase with increase in polyethylene glycol concentration, and the mechanical properties can also be altered by interpenetrating polymer network. This advantage can be used to improve the mechanical properties of and successfully use it as a maxillofacial material. Nanocomposite gels are mainly altered hydrogels. These gels show superior mechanical properties such as increased compressive strength, tensile strength, yield stress, and this can be altered by changing or altering the crosslinking and also by reinforcing the carbon nanotubes.[16]

The hydrogels can be used along with other materials in various combinations according to their compatibility. These combinations may be used efficiently in the following.

Oral mucositis

Oral mucositis, the inflammation of the oral mucosa, is a very common adverse effect after radiotherapy and chemotherapy which are the main treatment options for malignancies. It appears 2 weeks after the start of the therapy and lasts till 2–6 months after the therapy. The hydrogels combined with keratinocyte growth factors and granulocyte-macrophage colony stimulating factors promotes healing, and this can be used as a treatment modality for mucositis.

Drug delivery

Tobramycin, a newer aminoglycoside has shown efficient results with hydrogels, and this can be used against microflora during initial stages of wound healing and suppress the spread of infection locally.[14] It has more efficacies against the streptococcus species. Hence, this can be used in the defect areas in the oral maxillofacial regions which has more potential to get infected by the oral microbiota. Sustained and targeted release are available as smart hydrogels.[3]

Bone regeneration and osteoradionecrosis

Poly(lactid-co-glycolide) (PLGA) microparticles are added within the injectable calcium phosphate, and this can be used for bone regeneration with controlled delivery mechanisms. Cross-linked biotinylated PLA-PEG microparticles using avidin in the presence of cells to create injectable cell-containing matrices with mechanical strength suitable to support bone regeneration in vivo.[14] Osteoradionecrosis is the damage which is occurring in the irradiated bone. The main factors associated with osteoradionecrosis are hyopovasularity, hypocellularity, and hypoxia. PLGA microspheres which are packed along with the fibroblast growth factor 2 have increased the vascularization. This can be made use in the osteoradionecrosis which shows hypovascularity. Polyethylene glycol combined with deproteinized bovine bone mineral can be used as a scaffold to maintain the bone graft volume and helps in bone regeneration.[17] Polyethylene glycol is also used in target specific injection of bone marrow stem cells in the defective areas and enhances the bone growth and regeneration.[18] Polyethylene glycol can be added with the arginine-glycine-aspartic acid sequence, and this can be used for extensive bone regeneration and also soft tissue integration.[19] High-density nano-hydroxyapatite with the polyvinyl alcohol hydrogel has increasing biocompatibility and biologic fixation and can replace both the cartilage and bone.[20]

Soft tissue expansion

Polyethylene glycol-based hydrogels are used as a soft tissue expander, and it shows high-efficiency soft tissue expander. Shortage of soft tissues due to resection of infected tissue may lead to poor healing. Soft tissue expansion leads to stretching of the existing skin, which stimulates and results in the formation of the new cells followed by the growth of new tissue.

Wound healing and hemostasis

Chitosan-based hydrogels are used as tissue adhesives and it adheres to wound site for desired period, shows good enzymatic crosslinking and anti-infective activity. This aids in wound healing and hemostasis and hence can be used postinjuries in the maxillofacial area. Few hydrogels can be altered with peptides and can be cross-linked along with thrombin and clotting factor cascade.[14] Hyaluronic acid and gelatin show better results in wound healing.[3]

Growth factors

The hydrogels can be combined with growth factors such as angiogenic growth factors, chondrogenic growth factors, and osteogenic growth factors.[14] These growth factors have shown improved effects on the tissue repair, regeneration, blood vessel formation, and bone regeneration. This use of growth factors combines with hydrogels can be used for prosthesis in the defective areas in the maxillofacial areas and the growth factors will promote the regeneration of soft tissues and bone tissues around the defect without impeding the growth of the individuals.

All of these combinations can be used either as an injectable material through minimally invasive methods or as a direct prosthesis in the maxillofacial area and are capable of decreasing the defect size,[21] promoting wound healing, assisting in repair and regeneration, combating infection, minimizing the suffering caused by neoplasia and/or other disease processes.


  Summary Top


To summarize more research and clinical trials are needed to engineer hydrogel as an ideal maxillofacial material. Silicones are technique sensitive, subject to physiologic ageing and their decreased edge strength and hence hydrogels are replacing them in various other fields and it can be successfully introduced as a maxillofacial material. The success of a biomaterial can be viewed from patient acceptance and human body acceptance; the smart hydrogels are compatible with the humans and the human body and hence can bring in new dimensions to maxillofacial rehabilitation which is economical and ecofriendly.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

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Introduction
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Ydrogel as a Max...
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