Scope of biomaterials in conservative dentistry and endodontics.
Abstract: Biomaterials and their applications in medicine and dentistry have been recognized in regular clinical practice. In recent years lot of research is being done on its application in the field of medicine and particularly in restorative dentistry. These materials found to be successful for restoration of teeth in esthetic, function and to maintain the integrity of masticatory muscles. Some of the dental materials, the biocompatibility and application has been discussed and reviewed.
Subject: Biological products (Usage)
Alloys (Usage)
Ceramic materials (Usage)
Ceramics (Usage)
Authors: Rao, C.V. Subba
Vanajasan, P. Pranau
Chandana, V.S.
Pub Date: 04/01/2011
Publication: Name: Trends in Biomaterials and Artificial Organs Publisher: Society for Biomaterials and Artificial Organs Audience: Academic Format: Magazine/Journal Subject: Health Copyright: COPYRIGHT 2011 Society for Biomaterials and Artificial Organs ISSN: 0971-1198
Issue: Date: April, 2011 Source Volume: 25 Source Issue: 2
Product: Product Code: 2831000 Biological Products; 3260100 Ceramic Materials; 3290000 Misc Nonmetallic Mineral Products; 3200000 Stone, Clay & Glass Products; 3200100 Nonmetal Mineral Products; 3200300 China, Glass & Ceramics NAICS Code: 325414 Biological Product (except Diagnostic) Manufacturing; 32711 Pottery, Ceramics, and Plumbing Fixture Manufacturing; 327999 All Other Miscellaneous Nonmetallic Mineral Product Manufacturing; 327 Nonmetallic Mineral Product Manufacturing
Accession Number: 308434333
Full Text: Introduction

Science of Biomaterials made giant strides for past few decades and has been recognized as a separate specialty in the field of Medicine and Dentistry. In conservative dentistry and endodontics various biologically accepted materials were used such as Gold alloys, Silver Amalgam, Ceramics, Glass Ionomer cements, Composites, Fiber Reinforced resins and nanocomposites.

Historical Background

The technique of restoration of teeth with gold bands and wires was introduced in 700 BC, In 1480 gold foil was used for filling the teeth. In 16th century attempt were made to study the effect of metals on human body by Paracelsus- to assess biocompatibility. John Greenwood developed dental drill and fabricated dentures in bone and ivory which was bioacceptable.

In 1840, Emergence Of Dental Journal reporting developments in material such as volcanite, porcelain has lead to clinical and scientific research for new improved materials such as--colloid crowns, Gutta Percha, Aluminum, barium and iridium found their place in dentistry [1].

The Biocompatibility of the materials used in dentistry depends on tissue response, histological & pathological findings. The ideal requisite of Biomaterials should be Noncarcinogenic, Bacteriostatic, Should not discolor tooth, Promote Cementogenesis, Osteogenesis & healing [2].

Biomaterials were classified as inert, resorbable and active. Their clinical application has been extended to the physically challenged individuals for knee prosthesis, hip prosthesis and maxillo- facial reconstruction. Application of this science and technology has gained popularity in restoration and replacement of teeth due to their biocompatibility.

Gold was used as a Restorative material in dentistry since the mid-1800s. It is chemically inert & highly biocompatible. It also takes up high polish and prevents physical irritation to the tissues and plaque retention. It has high compressive strengths and withstand masticatory forces hence it is added advantage as a posterior restorative materials. Due to its high feasibility it bonds to porcelain also serve as anterior restoration material. It is highly malleable and ductile hence it can be burnished to the tooth surface which prevents marginal leakage [3]. Where as gold foil was used as an ideal restorative material in incipient lesions. It is interesting to note from the literature that direct gold has been tried as a retrograde filling material and also successfully tried for the closure of oro-antral fistula when surgical procedures has failed. In cases of palatal erosion, palatal gold veneers have been tried, since it helps in minimal tooth removal. It has been claimed that manipulating gold foil restoration in an inexperienced hands may cause pulpal and periodontal damage, and sometimes while compacting gold foil damage to enamel margin may occur. So far allergic to gold has not been documented [4,5].

Dental amalgam has been accepted as an ideal posterior restorative material for more than 10 decades. Literature revealed that in the year 1861, John Tomes reported shrinkage of amalgam restoration. The marginal leakage around the filling was studied by Fletcher by using dyes. In the year 1987, Kriby used micrometer device to measure dimensional changes in Ag restorations. G.V. Black in 1895 established the uses of silver amalgam in clinical practise. Although silver amalgam has a few short comings such as chemical corrosion, electrochemical corrosion, and galvanic corrosion, this can be reduced considerably by giving a protective layer on the surface of the restoration like cavity varnish and bonding agents. The galvanic corrosion can be avoided by eliminating dissimilar metals on the opposing teeth. The resistance to corrosion has been increased with the introduction of high copper alloys [2, 12]

Introduction of BASE metal alloy and their clinical applications in preparation of crowns, bridges, inlays, onlays has been accepted for the past few decades. Due to its increased strength, durability, bonding with porcelain, it is used in metal ceramic restorations. It has retained its popularity in spite of potential toxicity of beryllium, and allergic potential of Nickel, addition of Chromium provide passivation and corrosion resistance [6].

It has been reported in the literature regarding allergic reactions to Nickel & Palladium. Further when the acidic condition increases in oral cavity the nickel ions are released from the restoration resulting in Clinical symptoms like gingivitis, inflammation of tongue & oral lichenoid reactions. The pathological findings confirmed nickel ions induce intracellular adhesion molecules in the endothelium which release, cytokines from monocytes & other cells [2, 11]

The allergenic effects of Nickel on dental patients and the potential toxic effects of Nickel & Beryllium on dental technicians continue to be concerned to dental profession, where as titanium alloys used for crown and bridge are biocompatible and corrosion resistance [13].

Various esthetic restorations have been in use in dental practice for the past few decades and more recently Resin Reinforced Glass Ionomer, Compomer and Nanocomposite are gaining popularity.

Porcelain has been in use in dental practice for more than 20 decades. Due to its brittle nature it has its limitation as post restorative material. Incorporation of alumina and zirconia has improved its strength. Due to its Physical, chemical, mechanical & biological Properties it considered as an biologically accepted ideal restorative material [2, 3]. It has low coefficient of thermal expansion similar to enamel and dentin hence marginal leakage is negligible. It has high modulus of elasticity, stronger in compression than tension and brittle with low fracture toughness. Due to its low chemical reactivity it is highly durable. Because of its low absorption and solubility there is no staining and discoloration and it is relatively inert with no tissue irritation [14].

In the year 1972, Wilson and Kent introduced glass ionomer cement an adhesive restorative material. The main advantage claimed with this cement is the powder particle is incorporated with fluoride ions. The Matrix of the set material releases fluoride ions. Compressive strength is comparatively less to be used as posterior restoration in permanent dentition [2, 3].

"Fluoride reservoir effect" which absorbs and stores after application of 2% sodium fluoride or APF gel. Fluoride ion concentrations is high enough to increase the fluoride content of enamel/dentin or cause death of bacterial cells which is responsible for dental caries.3 Large amounts of fluorides are released during the first few days after placement of this cement after which, it gradually declines during the first week and stabilizes after 2-3 months and continue for few years [8].

Evidence of initial irritation was observed in freshly prepared GIC. Its acidity decreases as setting occurs. There is no evidence of adverse histological reaction at the periapical tissue. Sealing ability of GIC was adversely affected with moisture contamination during placement. It is highly biocompatible, negligible effect on the pulp. It has an ability to bond chemically to tooth structure provides an excellent marginal seal. Polyacrylic acid is a weak acid with higher molecular weight limits diffusion through the dentinal tubules into the pulp [9]. Useful as a restoration material in rampant caries, and in deciduous molars due to its anticaries effect.

Introduction of metal modified GIC or otherwise known as Ceremets were found to be useful in core build up prior to restoration of full crown. In case were esthetic is prime importance especially in deep cavities, GI cement is used as bilayed or sandwich restoration [2, 3].

Light cure resin reinforced GIC was also successfully tried as a retrograde filling, it showed least microleakage due to less moisture sensitivity, less curing shrinkage, better adhesion than conventional GIC. Recent introduction of glass ionomer cements incorporated silver nanoparticles reported to have less leakage and showed acceptable tissue response [2, 3]

Giomers have been introduced in the year 1997, it is also known as PRG composite. It is the combination of Pre-reacted glass ionomers & resin composites, cured with visible light. The fluroaluminosilicate glass in these materials is reacted with polyalkenoic acid prior to its inclusion into composite resin. And it requires bonding agents for adhesion to tooth structure. Due to its biocompatibility it is accepted as a material of choice for restoration of root caries, non-carious cervical lesions, restoration of cervical caries in deciduous teeth [8, 9, 10]

The introduction of conventional composites has satisfied the need of esthetic restorations. It has inherent chemical toxicity and marginal leakage due to polymerization shrinkage. Further research to reduce the above properties has resulted in introduction of hybrid composites and nanocomposites. It has been assessed that very minimal to negligible amount of monomer may leach out, but rare allergic reaction has been reported. Still it is considered as an ideal tooth coloured restorative material [2, 3]

In the year 1998 smart composite has been introduced in the name of Ariston. The contents of the material are Barium, Aluminum, Flurosilicate glass filler (1mm) with Ytterium trifluoride, silicon dioxide and alkaline glass (1.6 mm) in dimethacrylate monomers. It releases functional ions such as fluoride, hydroxyl, and calcium ions as the pH drops in the area immediately adjacent to the restorative materials, as a result of active bacterial plaque. The release of fluoride is found to be lesser than glass ionomers and more than that of compomers. It has an ideal mechanical property, biocompatible and hence used as a posterior restorative material [22]

Introduction of Nanocomposites has resulted in reduction of 50% of polymerization shrinkage. It has improved physical, mechanical, esthetic and biological properties. Their properties have been improved by incorporation of nanoparticles, which are similar to liquid and they do not thicken the resin. It encompasses large variety of systems, made of organic--inorganic components and mixed at the nanometer scale. This material has a refractive index of 1.508 and claim to have reduced polymerization shrinkage when compared to conventional composites [27]. The Particle size is below absorption of visible light i.e (0.4-0.8 mm) and hence does not affect the esthetics of the restoration. It enhances the polishability of the resin. Further the filler loading helps in workable consistencies due to high surface area to volume ratio and its ability to fit between several polymer chains with better mechanical properties. It has increased hardness, wear resistance and improves the longevity of the restoration [27].

Depending upon the particle size they are divided into Nanomeric and nanocluster. Nanomeric is a monodisperse nonaggregated and nonagglomerated silica nanoparticles of 20 and 75 nm diameter. Whereas, nanoclusters are spheroidal agglomerated particles of 2 to 20 nm. Nano-optimised mouldable ceramic particles comprises of zirconia-silica particles of 2 to 20 nm and zirconyl salt from 75 nm [27].

Fiber reinforced composite has been successfully used in restoration of extensive destruction of tooth, and as post endodontic restoration in root canal treated teeth. Composites, when reinforced with fibers show an increase in flexural modulus, flexural strength and the elastic modulus made similar to that of dentin. It consists of fiber material held together by a resinous matrix [28].

Various types of FRC posts are available and they are made up of Polyethylene, Carbon and Glass Fiber. Among them, Glass-fibers are preferred for clinical purpose due to their ideal mechanical properties, aesthetic qualities and their ability to chemically bond to dental composite resin materials. FRC substructure materials retain a sticky, oxygen-inhibited surface layer that allows for direct chemical bonding with a veneer composite [28].

An ideal requisite of a Retrograde Filling is to prevent leakage and to provide hermetic seal, dimensional stability, adhere to walls of cavity, resistant to resorption, moisture resistance and should be insoluble [1]. Freshly mixed amalgam has free mercury with cytotoxicity rapidly decreases as the material hardens. GUTTA PERCHA is an inert material, it is porous there by reduces microleakage. Deposition of calcified tissues over Gutta Percha were also reported in literature Gold foil is found to be the least toxic but requires good isolation. Zinc oxide cements get encapsulated by tissue and showed significantly less inflammation [1, 2, 3].

Super EBA, has better physical properties, high compressive strength, tensile strength, neutral pH, and low solubility. It adheres to tooth structure even in moist conditions. A good healing response to super EBA with minimal chronic inflammation at the root apex with no leakage has been reported hence provides a better seal [1, 24].

Recently introduced retrofilling material, mineral trioxide aggregate was developed at Loma Linda University, CA, U.S.A in 1993. It contains tricalcium silicate, tricalcium aluminate, tricalcium oxide, silicate oxide and other mineral oxides forming a hydrophilic powder which sets in the presence of water. This mixture results in colloidal gel which solidifies within 4 hours. The initial pH is 10.2 which rises to 12.5 three hours after mixing. It is found to be more opaque than EBA and IRM. They provide superior seal when compared with Amalgam, IRM and Super EBA with better Marginal adaptation [1, 25].

As a root-end filling material, MTA showed evidence of healing of the surrounding tissues, forming connective tissue within the postoperative week. Osteoblasts have favorable response to MTA and longer term clinical study reported new cementum formation on the surface of the material [25, 26].

Latest material of introduction in dentistry is bioceramics. Materials that can be classified as bioceramics are Alumina, Zirconia, Calcium phosphate, Silica based glasses or glass ceramics and pyrolytic carbons. Bioceramics are available as Micro-spheres, thin layers or coatings on a metallic implant, Porous networks, Composites with a polymer component and as well as large well polished surfaces [15, 17, 18]. Bioceramics are biologically accepted there by subsequent soft tissue encapsulation and close interface between bone and implant is formed. They also has a property of bioadhesive and bioreactive hence it develops a chemically mediated interface with vital bond in addition to ionic exchange between implant and bone. Calcium phosphate ceramics are bioactive and have Osteoconductive potential & direct bone formation on implant [15, 16, 20].

Clinical applications of osteoinductive material include alveolar ridge augmentation and filling bony defects. It is also available in a block, granular and injectable forms there by provide a scaffold for new bone growth [19]. Recently introduced materials like silver nanoparticles are antibacterial, biocompatibility, and gaining more popularity [20, 27]. Further research may be required for their existence and usage in clinical practice.

Conclusion

Some clinicians often face problems due to ignorance of the precise nature of the materials which are manipulated and placed in the mouth. Hence adequate knowledge of the science of biomaterials is essential for their application in clinical practice particularly in restorative dentistry. To confirm biocompatibility of a material, animal experiments, tissue culture, clinical studies and Prospective and retrospective track record of usage reports are mandatory, for key of success.

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C.V. Subba Rao *, P. Pranau Vanajasan, V.S. Chandana

Department of Conservative Dentistry and Endodontics, College of Dental Surgery, Saveetha University, Chennai 600 077

* Corresponding author: Prof. C.V. Subba Rao, e-mail: ur_chandana@yahoo.co.in

Received 31 July 2010; Accepted 3 August 2010; Available online 4 May 2011
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