Bio-compatibility of Dental Materials

BIO-COMPATIBILITY OF DENTAL MATERIALS


Contents
INTRODUCTION
DEFINITION
HISTORICAL BACKGROUND
LOCAL AND SYSTEMIC EFFECTS
KEY PRINCIPLES THAT DETERMINE ADVERSE EFFECTS OF MATERIALS

MEASURING THE BIOCOMPATIBILITY OF MATERIALS.
    A.DEFINING THE USE OF MATERIAL
    B.TYPES OF TESTS
          
    C.HOW TESTS ARE USED TOGETHER
10. CURRENT BIOCOMPATIBILITY ISSUES IN DENTISTRY
A. LATEX
B.NICKEL
C. MERCURY AND AMALGAM
SUMMARY
CONCLUSION
INTRODUCTION
The biocompatibility of dental materials is a complex topic that draws on knowledge from biology, patient risk factors ,clinical experience and engineering.
Although ignored for many years, biocompatibility is now recognized as a fundamental requirement for any dental restorative material.
DEFINITION
Biocompatibility depends on the condition of the host, the properties of the material and the context in which the material is used.
Biocompatibility Interactions

HISTORICAL BACKGROUND
The concept of ethical treatment of patients dates back to the time of Hippocrates(460-370)
As late as mid 1800s dentists tried new materials for the first time by putting them into patient’s mouth
G.V.Black  used patients to test many of his new ideas for restorative materials ,such as early amalgams.
The concept of protecting the patients as research is only 30 to 40 years old.
The current philosophy about testing biological properties of dental materials in a systematic way evolved in the 1960s
ADVERSE EFFECTS FROM DENTAL MATERIALS
   The biological reactions to materials  have been separated into

§  toxic

§  inflammatory

§  allergic and

§  mutagenic reactions

Materials may be capable of releasing substances into patients body and the release of certain substances in adequate amounts can cause overt toxicity.
Example
Early dental materials containing lead posed a real risk to the patient because of the toxic properties of the lead that leached into the patients body.

Inflammation is  a fundamental type of biological response to a material.
The inflammatory response is complex but involves the activation of the hosts’ immune system to ward off some threat.
 Inflammation may result also from toxicity or from allergy, and often the inflammatory response proceeds toxicity.
Current biocompatibility research attempts to determine whether materials may cause or contribute to inflammation in the host even if no toxicity is evident.
An allergic reaction occurs when the body specifically recognizes a material, as foreign and reacts disproportionately to the amount of the material present.
A key difference between a non-allergic inflammatory response and an allergic response is the fact that in an allergic response, the individuals immune system recognizes a substance as foreign.
Thus not all individuals will react to that substance.
Mutagenic reactions result when the components of a material alter the base pair sequences of the DNA in cells.
 These alterations are termed mutations.
Mutations may be caused by direct interactions between a substance and DNA or indirectly by alterations in cellular processes that maintain DNA integrity.
LOCAL AND SYSTEMIC EFFECTS OF MATERIALS
Any material used in the body may have local or systemic biological effects.
These effects are modulated primarily by substances that are released from the material and the biological responses to those substances.
Systemic effects from dental materials are also a function of the distribution of substances released from materials.
These substances might gain access to the body via ingestion and absorption in the gut, inhaled vapour ,release at the tooth apex, or absorption through the oral mucosa.
Their distribution may occur by simple diffusion and absorption through the oral mucosa.
It may occur by simple diffusion or transport via the lymphatic or blood vessels.
The systemic biological response depends on:

o   The duration and concentration of the exposure

o   The excretion rate of the substance

o   The site of the exposure

Furthermore not all tissues react equally. systemic reactions may also be  influenced by organs such as the  liver that alter substances in an attempt to digest or excrete them.
KEY PRINCIPLES THAT DETERMINE ADVERSE EFFECTS FROM MATERIALS
There are two key factors that appear to be paramount in determining a materials biocompatibility .
The first factor involves the various types of metal corrosion .
Corrosion results in the release of substances from material into the host.
For example a metallic crown may release metal ions as result of electrochemical forces or it may release particles dislodged by mechanical forces such as occlusion or tooth brushing .
The key point is that the biocompatibility of the material depends to a large degree on the amount, composition and form of these products, as well as their location in tissues.
Corrosion may be visible or invisible to the naked eye, but is ongoing for very dental material at some level.
The second key factor that affects the biocompatibility of material is its surface characteristics .
Research has shown that for all materials the surface is quite different than the interior region of a material,
For example a dental casting alloy that has 70wt% gold on average may have nearly 95% gold at its surface.
The surface characteristics may affect the corrosion properties of a material, or they may influence biocompatibility in other ways.
TYPES OF TESTS 

ADVANTAGS AND DISADVANTAGES
There are three basic types of  tests used to measure the biocompatibility of dental materials,

1.    the in vitro test,

2.    the animal test,

3.    the usage test

(performed either in animals or in humans)
IN VITRO TESTS
 Are performed outside of an  organism.
Historically in vitro tests have been ensued as the first screening test to evaluate a new material.
These tests may be conducted in a  test tube, cell culture dish, flask, or other container but they are performed separately from an intact  organism .
In any case the material or an extract of a material is placed into contact with some biological system.
The biological system may consist of mammalian cells, cellular organelles, tissue bacteria  or some sort of enzyme.
The contact between the biological system and the material may be direct or indirect.
DIRECT CONTACT involves  the exposure of a material or an extract from  material directly with the biological system,
INDIRECT CONTACT occurs through a barrier of some sort, such as a agar ,a membrane filter, or dentin.
In vitro tests have several advantages  over animal or usage tests.
They are relatively fast, inexpensive and easily standardized.
Animal tests place a material into an intact organism of some type .
Common animals for this type of test are mice, rats, hamsters, ferrets or guinea pigs but many other types of animals have been used, including sheep, monkeys baboons, pigs, cats and dogs..
In ANIMAL  TESTS, an intact animal is used rather than cells or tissues form an animal.
Animal test are distinct from usage tests in that animal tests expose the animal to the material without regard to the materials final use.
Animal tests may also be subdivided into several types, including short term or long term systemic toxicity, exposure to intact or abraded membranes and immune sensitization or bone response.
There are also animal tests for mutagenicity, carcinogenicity and other specialized conditions.
Regardless of the type of test used, the advantage of an animal test is its ability to allow an intact biological  system to respond to a material.
The material may interact with the many complex biological systems within the animal and a more complete biological response is therefore measured.
 However animal tests are expensive and  difficult to control, and they may take many months even years to complete, depending on the species used.
These tests are also controversial because of ethical concerns about proper animal treatment.
Furthermore the relevance of an animal test is often questioned because of concerns about the ability of any animal species used to adequately represent the human species
Despite their disadvantages, animal tests provide an important bridge between the in vitro environment and the clinical use of the material, and these tests are likely to be used in some capacity for the foreseeable future.
USAGE TESTS are performed in animals or humans.
A usage test requires that the material be placed in an a environment clinically relevant to the use of the material in clinical practice.
If the test is performed in human, it is called a clinical trial rather than a usage test.
 The choice of animals for a usage test will be more limited than for an animal test because not all species can be used for all clinical situations often because of the size or anatomy of a given species.
Thus usage tests more likely to be performed on larger animals with anatomy that more closely resembles that of humans.
The relevance of usage test to clinical practice is potentially high by definition.
 However the ultimate relevance of a usage test depends directly on the quality with which the test mimics the clinical use of the material in terms of time, area, clinical environment and placement technique.
The human clinical trial is therefore the ‘gold standard’ of usage tests and is the standard by which in vitro and animal tests are judged.
Usage tests a also have a number of disadvantages.
These tests are extremely complex and difficult to perform in terms of experimental control and interpretation.
The tests are exceptionally expensive ,thousands of dollars may be needed for a single subject.
If humans are to be used, approval for clinical trial must be obtained, by law, from an institutional  review board.
The time required for these tests may stretch from months to years if data on the long term performance of a material are desired.
Finally, human usage tests may involve many legal liabilities and issues that are not factors for animal and in vitro tests.
CURRENT BIOCOMPATIBILITY ISSUES IN DENTISTRY
LATEX
Reactions to latex may vary from localized rash and swelling to more serious wheezing and anaphylaxis.
Dermatitis of hands  is  the most common adverse reaction.
 A history of eczema and  a familial history of allergies are predisposing factors, and repeated exposure and duration of exposure play a role in the degree of response.
 The most serious systemic allergic reactions occur when latex containing products, such as gloves and rubber dams, contact the mucous membranes.
Such exposures may result in angioneurotic edema, chest pain, and a rash on the neck and chest of severely allergic persons.
Asthmatic reactions and other respiratory reactions have also been reported to components of the latex that are released into the air and carried by the powder coating on many latex products.
NICKEL
Nickel is a common component of many dental alloys including those used for crown, fixed dentures, removable partial dentures and some orthodontic appliances .
Nickel is also used in many types of endodontic files, although the duration of exposure  through this route is faster and  shorter
 Nickel is the most allergenic metal known, with an incidence of some where between 0% to 20%,depending on the study .
MERCURY AND AMALGAM
The controversy over the biocompatibility of amalgam has waxed and waned several times in the 170 plus year history of its dental use in the United States.
Most of the controversy stems from the known toxicity of mercury and the debate over  whether  mercury from amalgams has toxic effects.
 Mercury occurs in three forms. As the metal or in a one of several organic forms, such as methyl or methyl mercury.
Metallic mercury gains access to the body via the skin or as a vapor through the lungs. Ingested metallic mercury is poorly absorbed from the gut (0.001%) ,so the primary portal into the body is inhalation of mercury vapor.
Numerous studies have shown that amalgams release sufficient vapor to cause between 1 and 3 µg of mercury absorption per day, depending on the number of amalgams present.
The inhaled mercury gains access to the blood stream via the alveoli of the lungs.
From the blood, mercury is distributed  in the body.
Methyl mercury is the most toxic form of mercury and is also very efficiently absorbed from the gut (90% to 95%).
the primary source of methyl mercury is in the diet, with fish contributing a significant portion.
Concerns about mercury stem from its toxicity and its relatively long half life in the body. The toxicity of mercury is well known and the symptoms depend some what on the form.