Log in Register

Login to your account

Username *
Password *
Remember Me

Create an account

Fields marked with an asterisk (*) are required.
Name *
Username *
Password *
Verify password *
Email *
Verify email *
Captcha *

Captcha Image Reload image challenge



Authors: Dr. Hemant Kumar, Dr. Bharatendu Kawatra

ABSTRACT

Biocompatibility of a material is the quality of not having toxic or injurious effects on biological systems (According toDorland's Medical Dictionary2008). A number of restorative materials have flooded the markets from time to time .Hence biocompatibility issues are a major concern in the selection of future restorative materials. Dentistry shares concerns about biocompatibility with the other fields of medicine such as orthopedics, cardiology and vascular biology.The biocompatibility of a material is not absolute; it must be measured with regard to the way the material is used. Measuring biocompatibility is a complex process that involves in vitro and in vivo tests. These tests contribute to understanding biologic responses to a material but cannot define the material’s biocompatibility with hundredpercent certainty. Dental Practitioners should understand enough about biocompatibilitytesting methods to critically judge advertising claims and ask relevant questions of manufacturers. Because there is no infallible way to assess biologic response to a material, decisions about the clinical use of material ultimately must weigh the biologic risks of a material against its potential benefits.

INTRODUCTION

According to Williams, 2008. It refers to the ability of a biomaterial to perform its desired function with respect to a medical therapy, without eliciting any undesirable local or systemic effects in the recipient or beneficiary of that therapy, but generating the most appropriate beneficial cellular or tissue response in that specific situation, and optimising the clinically relevant performance of that therapy.

According to Craig :2006 It is defined as the ability of the material to elicit an appropriate biological response in a given application in the body.

According to Glossary of Prosthodontic Terms 2005 It is the capability of a material to exist in harmony with the surrounding biological environment.

According to John .C.Wataha, Phillips:1987 Ability of a material to elicit an appropriate biological response in a given application in the body. It is now recognized as the fundamental requirement for any dental restorative material.(1)Although these technical issues of biocompatibility may seem beyond the scope of most practicing dentists, knowledge of these issues is fundamentally important to ensure the health of patients, dental staff and practitioners. Furthermore the legal liability of dentists is often linked to biocompatibility issues.(2)In the development of any biomaterial, one must consider the biocompatibility, the demand for appropriate biological responses are increasing as we require that materials perform more sophisticated functions in the body for longer time periods.(3)The considerations of biocompatibility are important to manufacturers, practitioners, scientists and patients. The field of biocompatibility is interdisciplinary and draws on knowledge from material science, bioengineering, biochemistry, molecularbiology and tissue engineering.(3) The biocompatibility of restorative materials have receivedadditional attention as a result of amalgam issue .It is important to realize that many dental materials contain known allergens,some of which have been shown to result in allergic reaction in the sensitized individual. Sensitization may also occur from the use of dental materials, members of the clinical team represents a high risk group in this respect.(3)In accordance with existing standards, all dental materials should pass primary tests(screening to indicate cellular response), secondary tests (evaluating tissue responses),and usage tests in animals before being evaluated clinically in humans.(4)The oral environment is especially hostile for dental restorative dental materials. Saliva has corrosive properties, and bacteria are ever present. This environment demands appropriate biological tests and standards for evaluating any material that is developed and intended to be used in the mouth.Until a few years ago, almost all national and international dental standards and testing programs focused entirely on physical and chemical properties. The physical and chemical requirements set forth in the specifications for dental materials have been based on published clinical studies and clinical use of the materials: that is, the specifications lag behind materials development. Today, however, dental materials standards require biological testing as well. The science of dental materials now encompasses a knowledge and appreciation of certain biological considerations associated with the selection and use of materials designed for use in the oral cavity (Phillips, 1991).(4)

BIOCOMPATIBILlTY:HISTORICAL BACKGROUND
  • 16thcentury - Biocompatibility of dental materials - Paracelsus
  • 19thcentury - Testing of dental materials.
  • 1926 - Guidelines for dental material-American Dental Association
  • 1933 - Uniform tests for all materials by Dixon&Rickert.
  • 1950 - Biological responses to dental material-Paffenbarger
  • 1954 - Technique towards standardization-Mitchell.
  • 1963 - Testing procedure for generalized use..
  • 1976 - The biological testing of all materials was given high priority.
  • 20th Century - Biological testing of material –updated –American Dental Association
  • 2000 - International standard for testing the BC-ISO 10993

Although the concept of the ethical treatment of patients extends back to the time of Hippocrates (460-377 B.C.), the idea that new dental materials must be tested for safety and efficacy before clinical use is much more recent. As late as the mid 1800s, dentists tried new materials for the first time by putting them into patients' mouths.(1) Many exotic formulations were used. For example, Fox developed a "fusible metal" that consisted of bismuth, lead, and tin, which he melted and poured into the cavity preparation at a temperature of approximately 1000 C. Even G.V. Black used patients to test many of his new ideas for restorative materials, such as early amalgams. The concept of protecting the patient as a research subject is only 30 to 40 years old, and many of the regulations and ethics in this area are still being challenged and defined today. In most cases, a committee of clinicians, basic scientists, and laypersons regu¬late and oversee the testing of new materials in humans. These committees are gen¬erally, but not always, university-based and are called IRBs (Institutional Review Boards). Regulations for IRBs are maintained by the Department of Health and Human Services, an agency of the U.S. federal government.(1)Public out¬cry against the use of nonconsenting humans as research subjects-for example, the use of nonconsentingU.S. citizens for radiation experiments by the Department of Energy (1931-1994) and the use of institutionalized mentally retarded children for Hepatitis research (1963-1966)-drove the development of regulations to protect humans in research. The oversight for this testing now rests largely with the Food and Drug Administration (FDA) but these activities also are regu¬lated by organizations such as the American National Standards Institute (ANSI), the American Dental Association (ADA) and the International Standards Organization (ISO).Today, the field of biocompatibility testing has reached a point where some prediction of biological properties is possible and the future will likely provide the ability to design materials that elicit customized biological responses.

Stanley and Pameijer 1984 found pulp abscess and hemorrhage when the remaining dentin thickness was less than 0.5mm .Ideally a base of calcium hydroxide under glass ionomers cement should be ideal and particularly when the remaining dentin thickness in 1mm or less.

Smith and Ruse 1986 compared initial acidity of glass ionomers with zinc polycarboxylates and zinc phosphate cements and formed a general risk of ph for all cements during first 15minutes .but the initial reaction of glass ionomer was slow leaving an acidic pH of 2.0 at 5minutes and 3.0 at 10 minutes time.

Parameswaran. A. 1990 stated that placement of dental materials in or on the material has to be assessed by the solubility disintegration, corrosion and others. Dental materials are frequently required to fulfill esthetic as well as functional, preventive or therapeutic purposes and consequently their characterization is very complex.

Bob Marshall 1994 stated the fears of concerned patients and dentists claiming that when mercury is combined with other metals as used in dental amalgam, its toxic properties are made harmless. However, ongoing scientific research spanning many authors and several countries clearly identifies the ability of mercury to slowly leach out of the tooth (even in its combined state with other metals) and end up in the body’s organs and glands. Tests with mercury vapor detectors placed inside the mouth show that mercury vapor does indeed routinely escape from dental fillings — and the mercury can end up into the sinus, brain, eyes, ears, heart, nervous system, and many other body organs and concluded that Most dental materials are selected based on how long they last in your mouth, how durable they are and/or how aesthetic they look, but often little thought goes into whether the body’s owner may be negatively reacting to the dental material Charles W.Wakefield,KellyR.Kofford2001stated that biocompatibility issue is becoming a strong consideration for resin based material components in bis-GMA,TEG-DMA and UDMA based resin material have been implicated in promoting estrogenicity in humans and in causing hypersensitivity reactions. Charles F.Cox,AbeerA.Hafez 2001concluded that after initial compliance and acceptance of ISO in vitro study results in vivo ISO connective tissue tests are then carried out by placement of single component into subcutaneous tissues of rabbit and then examined histologically and then used as restorative material.

J.D Eick, E.L Kostoryz et al 2002 studied the in vitro biocompatibility of dental composites with promising physical properties and reported that composites based on methacrylate chemistry shrinks about 2% to 3% by volume causing stresses that can cause pain, fracture of restoration, chipping of margins, debonding and microleakage.

Phillips 2003 has stated that the science of dental material now encompasses a knowledge and appreciation of certain biological considerations associated with the selection and use of material designed for use in the oral cavity.

John C.Watah,PetraE.Lockwood et al 2003 assessed and compared the in vitro cytotoxicities of commercially available core and flowable dental restorative materials and reported that core materials are uniformly and severely cytotoxic initially, but several materials improved somewhat with aging in artificial saliva, whereas flowable materials were uniformly and severely cytotoxic with no change with aging.

KEY CONCEPTS OF BIOCOMPATIBILITY

According to Craig following are the three key concepts of biocompatibility

Biomaterials are not biologically inert :

Clinician should understand that there are no “inert” materials. When a material is placed into living tissue, interactions with the complex biologic systems around it occur, and those interactions result in some sort of biologic response. The interactions depends on the material, the host, and the forces and conditions placed on the material (its function), the material affects the host and the host affects the material. Inertness of materials implies an absence of such interactions. Most scientists today agree that no material is truly inert in the body.(2)

Biocompatibility is a dynamic process :

Biocompatibility is a dynamic, ongoing process, not a static one. A dental implant that is osseointegrated today may or may not be osseointegrated in the future. The response of the body to a material is dynamic because the body may change through disease or aging, the material may change through corrosion or fatigue, or the loads placed on the material may change through changes in the occlusion or diet. Any of these changes may alter the conditions that initially promoted an appropriate and desired biologic response. The interactions among material, host, and function continue over time; therefore, the biologic response to a material is an ongoing process.(2)

Biocompatibility is a property of a material and its environment :

Biocompatibility is a property not only of a material, but also of a material interacting with its environment. In this sense, biocompatibility is like color. We often ascribe color to a material, but color is a property of both the material and the material’s interaction with light (its environment). Without the light interaction, there is no color. Ultimately, the color of the material depends on the light source, how the light interacts with the material, and the bias of the observer. Consider an example of this concept with dental implants. Under the proper conditions, a titanium alloy implant willosseointegrate with the bone over time. This means that the bone will approximate to within 100 of the implant with no intervening fibrous tissue. If a cobalt-chromium alloy is placed into the same situation – same host, same placement technique, same load no osseointegration will occur. Conversely, if a titanium alloy is used as the ball portion of a femoral hip joint, it will wear against the acetabulum into small particlesthat ultimately will cause the hip to fail. Yet the cobalt-chromium alloy which wears less, will do better. Because biocompatibility depends on the interaction of the material with its environment, it is inappropriate to label the titanium alloy a “biocompatible material” and the cobalt-chromium alloy an “incompatible material”. One cannot define the biocompatibility of a material without defining the location and function of the material.(2)

BIOCOMPATIBILITY AND ITS RELEVANCE TO DENTAL SURGEON

Dentists’ Potential concerns about biocompatibility can be organized into four areas(2)

  1. Safety of the patient
  2. Safety of the dental staff
  3. Regulatory compliance issues
  4. Legal liability.
Safety of the patient :

One of the primary concerns of any dental practitioner is to avoid harming the patient. Evidence has shown that, although adverse reactions to dental materials are not common, they can occur for many type of materials, including alloys, resins, and cements.One biocompatibility / patient safety issue that has been prominent in dentistry in recent years is the hypersensitivity of patients to dental biomaterials. Classically, this concern has focused on allergy to materials such as nickel or methacrylates. The incidence of nickel allergy in the general population ranges between 10% to 20% and is far more common in females than males. In patients sensitive to nickel, oral exposure to nickel may or may not elicit an allergic response, but these responses may be spectacular. There is also prime concern about the hypersensitivity of patients to resin-based materials and to latex. Although uncommon, patients can have severe or even fatal (anaphylactic) reactions to these materials. There have been recent reports of a growing incidence of contact sensitivity in children to a variety of substances, including dental materials. One report found that 49% of children were sensitive to some type of material or food.

2. Safety of the dental staff :

The classic example of this problem is :

  1. Dental amalgam because the release of mercury vapor from amalgam during placement orremoval is substantially higher than when it is undisturbed in the mouth.
  2. These types of issues also are relevant to casting alloys, resins, and other dental materials usedin prosthodontics.
  3. Risks for dental staff appear to result from chronic contact with latex and resin-based materials.
  4. Inhalation of fumes of Hydrochloric Acid during Pickling.
3. Regulatory compliance issues :

Biocompatibility issues are closely linked to regulations that affect dental practice. An example of this link is related to dental amalgam. Because of the biologic concerns about mercury, regulators have considered monitoring and restricting the amount of mercury in waste water from dental practices.

4. Legal liability :

Biocompatibility issues also influence liability issues that affect dental practitioners. Because dental materials can affect the well-being of patients and dental auxiliaries, practitioners assume a legal risk when using these materials. Litigation as a result of biomaterials causing harm to a patient is probably rare. Nevertheless, when these problems occur, they are (at best) emotionally and financially stressful to the practitioner.(2)

CONCLUSION

With the long history of use of many materials in dental surgery, biocompatibilityconcerns are not as great a concern as other issues, such as long-term degradation, mechanical strength problems, and prevention of secondary caries. It is important, however, not to forget that the potential exists for adverse tissue responses to synthetic materials used in repair, augmentation, and repair of natural tissue structures.

REFERENCES
  1. Philips’ science of Dental Materialseleventh edition .
  2. John C. WatahaBiocompatibility of dental materials .
  3. CraigsRestorative Dental Materials.
  4. Dental Amalgam: A Scientific Review and Recommended Public Health Service strategy for Research, Education and Regulation edited by James S. Benson

Add comment


Security code
Refresh