BIOCOMPATIBILITY OF DENTAL MATERIALS

Introduction

History

Requirement of dental materials

Biologic response in the dental environment

Enamel

Dentin

Pulp

Pediodntium

Gingival and mucosa

The oral immune system

Adverse Effects from dental materials

Toxicity

Inflammation

Allergy

Mutagenic radians.

Local and systemic effects of materials

Measuring the biocompatibility of materials

Types of Tests

In Vitro tests

Cytotoloxicity assays

Cell number and growth

Membrane permeability tests

Tests for cell metabolism or cell function

Tests that USC barriers.

Other Assays for cell functions

Mutagenesis assays

Animal tests

Usage tests

Dental implants in bone

Using in vitro, animal and usage tests together.

Standards that regulate the measurement of biocompatibility.

Biocompatibility of dental materials

Reaction of pulp

Microleakage

Amalgam

Direct filling gold

Dental casting alloys

Non metallic restorative materials

Bonding agents

Composite resins

Liners and varnishes

Ceramics

Conclusion

INTRODUCTION

When a biomaterial is placed in contact with the tessiues and fluids of the

human body, there is inivariable some form of interaction between the material and

biological environment this interaction is referred to as biocompatibility.

Biocompatibility is defined as the ability of a material to function in a specific

application in the presence of an appropriate host response.

Dentistry shares concerns about biocompatibility as with other fields of

medicine, such as orthopedics, cardiology and vascular biology among others. In the

development of any biomaterial, one must consider the strength, esthetics and

functional aspects of the material, as well as its biocompatibility furthermore,

demands for appropriate biological responses are increasing as we requires that

materials perform more sophisticated functions in the body for longer time periods

Thus, considerations of biocompatibility. sophisticated functions in the body for

longer time periods. Thus considerations of biocompatibility are important to

manufacturers practitioners, scientists and patients.

The field of biocompatibility, is interdisciplinary and draws on knowledge

from materials science, bioengineering biochemistry, molecular biology tissue

engineering and other fields.

Biocompatibility HISTORICAL BACKGROUND

Although the concept of ethical treatment of patients extends back to the line

of Hippocrates ( 460 – 377 B.C) the idea that new materials must be tested for safety

and efficacy before clinical use is more recent. As late as the mid 1800’s dentists tried

new materials for the first time by putting patients mouths.

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 30-40 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 regulate and oversee the testing of new materials in

humans.

Using humans as research subjects today without some previous testing or

knowledge of the biological proportions is unethical and illegal still over new material

must be inserted into a human for the first time at same point. Therefore many

alternative tests have been developed to try to minimize the risks to humans. The

current philosophy about testing the biological properties of dental materials in a

systematic way evolved in the 1960’s as the need to protect patients became

politically acute and the number of new materials increased.

The oversight for this testing in U.S now rests largerly with the Food and Drug

Administration ( FDA), but these activities are regulated by the American National

Standards Institute ( ANSI). American Dental Association ( ADA) Biological testing

of materials has significantly evolved over the past 40 years. Since initially being used

on animal models. Many studies between the 1950’s and the 1970’s involved the use

at premolar teeth that were scheduled for orthodontic extraction. As well as cell

solutions techniques and biological responses to material today the field of

biocompatibility 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. Some of the pioneering works are

Use of in vitro techniques to study the toxicity of various synthetic

materials began some 30 yrs. After tissue culture was first established as a

technique in 1926.

Various investigators began to apply organ and tissue culture techniques to

toxicological problems in 1950’s and 1960’s.

Kawahara;s lab began to use cell culture methods to investigate dental

materials in the 1950’s these investigators reported the cytotoxicity of pure

metals, dental cements and medicaments.

Leirskar and Helgeland (1972) did the first study of cell culture tests using

human epithelial cells on and around standard size disks of dental

materials, including silver amalgam and copper amalgam resins silicate

and gold alloy.

One of the earliest quantitative in vitro tests was a membrane permeability

assay for release using L- 929 cells by spangbeng in 1973.

Schmalz in 1982 was one of the first dental investigators to apply the agar

overlay techniques to test the cyloloxicity of dental materials.

REQUIREMENT OF DENTAL MATERIALS

Be nontoxic

Be non irritant to the oral or other tessiues

It should not produce allergic reactions.

It should not be mutagenic or Coriogenicity

Classification of materials

Matrials may be classified into following types from the perspective of

biological compatibility

a) those which contact the soft tissue within the mouth.

b) Those which could affect the health or vitality of the dental pulp/

c) Those which are used as used as root eanal filling materials.

d) Those which affect the hard tessuies of the mouth.

e) Those used in the dental laboratory, which though not used I the mouth,

are handled and may be accidentally engisted or inhaled.

Examples of hazards

a) some dental cement components are acidic and may cause irritation.

b) Polymer based filling materials may contain irritating chemicals such as

unreacted monomers.

c) Mercury is used in dental amalgam, and mercury vapour is toxic.

d) Dust from alginate impression materials may be inhaled,some products

contain lead compounds/

e) Some people show allergic reactions to alloy containing nickel.

f) Some dental porcelain powder contain uranium.

g) Laboratory materials have their hazards,such as cyanaids solution for

electroplating,vapoures from low fucing metal dies, silicious particles in

investment materials and fleeces containing fluorides.

Evaluation of the biocompatibilities-before adopting any methods for

biocompatibility fests the following aspects must be careful considred:

1. location of the material

2. nature of the tessiues-soft or meniralized hard tessuie

3. exposure of the materials to the oral situations,salvia blood

4. type of contacts, direct or indirect through a barriears like a epithelvies

5. chemical nature –compositions ,degradations.

6. physical condition –like stresses,fatigue resistancs.

ANATOMICAL AND PATHOLOGICAL ASPECTS OF ORAL TESSUIES

Oral anatomy influencing the biologic response

Several aspects of oral anatomy influence the biocompatibility of dental

restorative materials. The full effects of the oral anatomy on the biocompatibility of

materials are not known but these effect will be a major focus of anatomy of the tooth,

the periodontal attachment and to the peripical environment that have influences on

the biologic response to materials and all are sites of interface between materials and

tissue in dentistry.

ENAMEL

Mature human enamel is highly meneialyid enamel rods have a specific

orientation with each other,and the orientation provides maximal strength because of

its high mineral (hydroxylapatile) content, enamel is much more bittele than dentin

and is soluibied to a greater extent by acid solution this property is used to advantage

with bonding agents, when acids are used to etch the enamel to provide

micromechanical retention of resin composites. The differential etching that occurs is

a consequence of the different orientation of enamel rods. permeability of enamel to

most oral molecules is quite low, and it seals the tooth to outside agents.

However recent evidence indicates that enamel is not totally emperineable.

Peroxides in bleaching agents has been shown to penetrate intact enamel in just a few

seconds.

Dentin and pulp:

The dentin and pulp to be a single tissue the dentinial matrix (both ciassified

and unclassified forms the greatest bulk of the tooth collagen constitutes

approximately 85% of the organic portion of dentin and hydroxy apatite is the main

unorganic compound the dentenail matrix contains protein type 1 type 5 collagens,

osteoclasin and osteopontien, phosphoryjns dentinsealoprotien and dentin matrix

protein.

The dentin matrix surrounds dentenial tubles that are filled with odontoblastic

processes. The tubules traverse the region between the dentino enameljunction (DEJ)

and the pulp.

A serum like fluid fills the dentenial tubules this fluid has conteneity with the

extracellular of the pulp tissue. pulpal circulation maintains an intercellular hydraulic

pressure, which causes fluid flow into tubules to be directed from the pulp outward

towards the DEJ when enamel is removed.external hydrostatic and osmotic pressure

can also cause fluid movement toward or from the pulp. The positive or negative

displacement of this fluid through exposed denture tubules is capable of affecting

either odontoblasts or pulpal nerve endings. These effects are the basis of

hydrodynamic theory of hyperlagesisa (pulpal hypersensitivity).

Smear layer is formed by the action of the beer or hand instruments on the

classified dentin matrix. this occludes the dentinal tubules to some extent and it is

quite effective in reducing hydrostatin pressures but less effective in reducing

hydrosstative pressures but less effective in reducing diffusion.

The smear layer can be removed by acid etching. Which also deminiralyses

the openings of the tubules. The dentenial tubules establish continuity with the pulpal

fluid to facilitate the diffusion of molecules both natural or from materials into and

out of the pulp. The smear layer ,dentenial tubules and dentenial matrix are all

important in the application of dentenial bonding agents and the ability of components

of the bonding agents to reach and affects pulpal tessuies.

The pulp of the tooth is a connective tessuie containing normal elements such as

fibroblasts,collages,capillarises and nerve pulp supplies the cells, which replace any

odontoblasts desriyed during cavity preparation or material placement and allowes the

tooth to form secondary or separation dentin.

PERIODONICAL ATTACHMENT:

Junction between the outside of the body (oral cavity) and the inside of the

body. The dentin of the root of the tooth is covered by a thin layer of the root of the

tooth is covered by a thin layer of cementum that may seal the dentenial tubules

cementum attaches the collages fubers of the periodontal ligament the genguia

normally extends above the level of the cementum and forms a potential space against

the enamel called periodontal pochet.the gingivial epithelium is also attached to the

cementum of the tooth by a specialized junctional epithelium. The periodontial pocket

is the site of the development of periodontal pocket is the site of the development of

periodontal desease,which can destroy the junctional ipetheluim,periodontal ligament

and supporting aluolar bone.

Because many dental restorations are near or in the periodontal attachment area the

biocompatibility of these materials may influence the normal periodontal

architecture,the periodontal desease process or the body,s ability to defend against

bacteria that cause periodontal desease periodontal desease periodontal pocket is a

unique microenvironment that allow concentration of components from materials to

reach higher levels than are seen in the rest of the oral cavity the influence of dental

materials on the periodontal disease and the biting forces that strain the periodontal

ligament and supporting bone. It is often difficult to determine with certainty whether

inflammation in this area is caused by periodontal disease, occlusal trauma, the

material or some combination of these factors. the periodontal pocket has also been

used as a site to place materials that release therapeutic agents to combat periodontal

disease. It is likely that this approach will expand as better drug delivery materials are

developed.

PERIAPICAL AREA:

Another interface between materials and the inside of the body. The apex of the tooth

is the junction of the pulp of the tooth and the alueolar bone nerves and blood vessels

entire through the apical foramen. When the pulp of the tooth is destroyed by

infection or during restoration of a tooth, endodontic materials are placed in the

pulpal space and these materials interface with the body through the apex of the tooth.

If the endodontic procedure is not performed correctly the filling materials may

extruded from the apex into the periapical area and cause additional physical damage.

The ability of the root canal material toward the apex is also an important

consideration.

The use of the retrograde approach to seal the apical foramen, the filling materials

will be in direct contact with the perapical tessuies. Thus biological responces to these

materials must be critically examined. As with the periodontal attachment area, the

release of substances from root canal filling materials may cause adverse responses

around the apex or may alter the body’s reaction to bacterial products that have

contaminated the area.

The delineation between the bacterial and material threats are not clear , and the

ability of materials to influence the body’s immunological response in the perapical

area has only recently been studied.

SPECIAL BIOLOGICAL INTERFACE WITH DENTAL MATERIALS:

Dentin rein interface

Implant bone interface

Dentin resin interface:-when resin based restorations material bonds to dentin. The

composite nature of the denture allows the mineralized matrix to be dissolved away

by acids which preserving the collagen network. If the network doesnot collapse,

which may happen if the dentin is dessicated it may be embedded by a resin –

containing material thereby mechanically bonding the resin material to dentin.

If the resin material doesnot penetrate the collgenous network or debonds from it as

the resin shrinks during polymerization, a gap will form between the resin and the

dentin. this also occurs in enamel this few missions wide gap allows bacteria and oral

fluids to pucolate from the pulp outward or from the oral cavity onward. This leakage

is termed as microleakage.

The bio compatibility of a restoration is altered by the leakage process which

may cause a number of undesirable events:-

1. It may allow bacteria or bacterial products to reach the pulp and cause

infection.

2. It encourages the breakdown then exposes the margins of the restorations

making the tooth restoration complex aesthetically unacceptable.

If the resin penetrate the collagen network of the dentin but does not penetrate it

completely a much smaller gap will exist between the mineralized matrix of the

dentin and collagen resin hybrid layer. Nanoleakage.

Although nanoleakage probably doesnot allow bacteria or bacterial

products to penetrate the marginal gaps of the restoration and the pulp,fluid exchange

most likely occurs that can degrade the resin or the collagen network. That has been

uncompletely embedded with resin, thereby reducing the longevity of the dentin resin

bond this degradation process may also gradually increase the gap size until

microleakage begins to occur.

Osseointegration:

The use of endosseous dental implants has uncriased tremendulously over the past

decade. the success of these implants relieves on the ability of the material to promote

osseointegration and allow a close approximation of bone with the material..the

ability of a material to allow osseointegration is closely related to its biocompatibility

in dentistry, relatively few materials allow osseointegration

1.they are commercially purelitanum.

2. titanium-aluiminium-vanaduim alloy.

3.tantalum

4. several types of ceramics.

Materials that allow osseointegration have very low osseointegration have very low

degradation rates,and they tend to form surface oxides that promote bony

approximation some materials such as bioglass-ceramics, promote an integration

between the bone and material with no intervening space at all.when this integration

occurs,the material is said to biointegrate with the bone.biointegration appears to

require a degradation of the ceramic to promote bone formation .no known desirabily

of osseointegration over biointegration has been established.like all biocompatibility

phenomena osseointegration and biointegration are dynamic processes that may be

altered by changes in the host,fatigue of the materials or function of the implant.it is

also important to understand that neither osseointegration nor bio integration munic

the normal ligamentous connection between a tooth root and alerolar bone.

Oral immuno system:

It plays an important role in the biological response to any material.it appears to

behave some what differently in oral epitheluium and connection tessuie than in the

rest of the body and the biological responses to materials in the mouth may not always

parallel those seen in other locations the oral environment is not always equivalent in

structure or function to other areas of the body and that differences may alter the

biological response to materials

ADVERSE EFFECT FROM DENTAL MATERIALS

TOXICITY

Material release certain substances which in convert concentration can lead to the

toxicity. It in the first screening test used for all dental materials. This is a close-

related potential of a material resulting in cell or tissue death. Example-some

substances like mercury ,,nickel, berylluim released into the body, which can cause

overt bixicity above a certain amount.

INFLAMMATION

It is a second fundamental type of biological response to a material. it

involves the activation of the host immune system inflammation may result toward off

some threat. toxicity or from allergy and often the inflammatory response precedes

toxicity.the inflammation may be caused by toxic or allergic materials. And

sometimes may preceed toxicity. The pulpal and periodontal disease are largely

chronic inflammatory responses to long term infections.

HYPERSENSITIVELY AND ALLERGY

Hypersensitively is the abnormal reaction that occurs when the body is exposed to a

foreign material this materials sensitive the immune system, so that when the person

is repiately exposed to the same material the body responds with a hypersensitivity

reaction which is not dose dependent.

The allergic or hypersensitive reaction developes only in persons whose immune

system recognize the material as foreign the allergic reactions can manifest as

localized reaction in the tessuie which is directly in contact with the material allergy

can be a systemic manifestations in the form of itching skin

eruptions,sneezing,erythema,breathing difficulties.

According to gell and coomb’s classifications the allergic reaction or immune

responses can be-:

Type I-immedaite

TypeII-cyto-toxic hypersensitivity

TypeIII-immune complex hypersensitivity

Type 4 delayed, cell-medicated hypersensitivity

The allergic reaction are due to there individuals emmuine systems,recognizing a

substance as foreign and are initially dose dependent

Mutagenic Reactions

These are caused by the materials or its components,altering the base-pair

sequence of DNA in cell (mutation) some resin-based restoration,realants,cons of

metals (Ni,Be,Cu) are found to be mutagens.fortunately these may not be

(arcinogenic,as the immune system supplies lot of cellular energies and mechanics to

repair the mutated DNA.

Oestroginicity-

It is the ability to produce materials like xeno-istrogens,to act in the body as

estrogens.the resin,bisphenol A,the starting substance of BISGMA,composite

restoratibe materials and few other series are found to be esteogenic.

In most cases the surface characterstics such as composition,roughness and

corrosion degradation products affect the biocompatibility.

Osseo integration and bio integration

It is the dynamic interaction between the body and materials.it is the key

phenomena in the implantology.

Osseointegration-

Formation of living body tissues with in 10 mm space from the implant materials

surface without any fibrous connection tessuis

Eg: Tantalum ceramics.

Biointegration :

Certain materials like bioglasses which undergo biointegration with the bone directly

any intervening space.

Immunotoxicity:

it is due to the alteration in the cells of immune system by the matrials.this cause

either increase or decrease of cellular of functions.

Eg-mercury,palladium,HEMA

EVALUATION TEST OF BIOCOMPATIBILITY:

Historically new materials were simply tested in human to assess their

biocompatibility, this practice has not been acceptable for many years and current

materials must be extensively screened for biocompatibility before they are used in

humans. Several varieties of tests are currently used to unsure that new materials are

biologically acceptable.

These are classified as

a) in vitro test

b) animal test usage test

a) in vitro test: these tests are performed outside of an organism. These tests maybe

conducted in a test tube, cell culture dish, flash, or other contains but they are

performed separately from an intact organisms. The biological system may

consist of mammalian cells, cellular organelles, tessuies ,bacteria or some text of

enzyme. The contact involves the exposure of a material and biological system

are a)direct

b) indirect

direct contact involves the exposure of a material or an extract from a material

directly with the biological system where as indirect contact occurs through a barrier

of some sort such as agar, a membrane filter, or dentin.

In vitro test can be subdi

MEASURING THE BIOCOMPATABILITY OF MATERIALS

Measuring the biocompatibility of a material is not simple and the methods of

measurement are evolving rapidly as more is known about the interactions between

dental materials and oral tissues as technologies for testing improve. Historically new

materials were simply tested in humans to assess their biocompatibility. However this

practice has not been acceptable for many years and current materials must be

extensively screened for biocompatibility before they are used in humans several

varieties of tests are currently used to ensure that new materials are biologically

accepted.

Types of Tests

There are three basic types of tests : the in vitro test, the animal test, and the

usage test performed either in animals or in humans.

In vitro tests are performed outside f an organism historically, in vitro tests

have been used 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 containers, but they are

performedseperately from an intact organism, which is placed in contact. With some

biologic system the biologic system may consist of mammalian cells, cellular

organells 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 a material directly with the biological

system where as indirect contact occurs through a barrier of some sort. Such as agar a

membrane filter or death. In vitro tests can be subdivided into tests that measure cell

growth or death, those that determine cellular function of some type, and those that

evaluate the integrity of the genetic materials of the cell.

ADVANTAGES

Relatively fast

Less expensive

Can be standardized

Large scale screening

Good experiment control

Tightly controlled conditions for quality.

Disadvantages

Relevance to in vivo is questionable

Lack of complex co-ordination of systems that is present in an organism

such as immune, inflammatory and circulatory system.

IN VITRO TESTS

SYTOTOXICITY ASSAYS

By these tests the effect of the material or its leachable products are studied on

the metabolic functions of the test cell system. In general cytotoxicity tests measure

the effect of a material on

Cell number or growth

Integrity of cell membranes

Biosynthesis or enzyme activity or

The genetic material of the cell.

Advantages of cytotoxicity assays are

Testing for a specific function of cell metabolism in isolation from other

events.

Screening large number of samples quickly and inexpensively

Quantifying results

Having potential for standardization of test methods

Disadvantages include

Limitation of testing to only one cell type at a time

Dissimilarity of test cells to host cells

Lack of inflammatory and other tissue protective mechanism in tissue

culture.

The biological systems used in vitro cytotoxicity tests may be

Organ cultures

Cells in culture or

Cell organelles.

The most widely used biological systems for in vitro toxicity testing of dental

materials are cells in culture. Two types of cells can be used for in vitro assays.

Primary cells are those cells taken directly from an animal and cultured. These

cells will grow for only a limited time in culture but retain many of the characteristic

of cells in vivo.

Continuous cells or cell lines are primary cells that have been transformed

previously to allow them to grow more or less indefinitely in culture because of this

transformation. These cells do not retain all in vivo characteristic but they do

consistently exhibit any features that they do retain.

In all cytotoxicity tests the test system itself must be nontoxic, sterile and

reproducible so as not to interfere with the analysis of the material.

MEMBRANE PERMEABILITY TESTS

Membrane permeability is the ease with which a dye can pass through a cell

membrane. This test used on the basis that a loss in membrane permeability is

equivalent to or very nearly equivalent to cell death. The main advantage of

membrane permeability is

It identifies cells that are dead or alive under the microscope. This feature is

important because it is possible for cells to be physically present but dead (when

materials fix the cell.)

There are two basic types of dyes used, vital dyes are actively transported into

viable cells where they are retained unless cytotoxic efforts increase the permeability

of the membrane. It is important to establish that the dye itself does not exhibit

cytotoxicity during this frame of the test. Eg. Neutral red Na2 Cr o4

Non vital dyes are not actively transports and are only taken up if membrane

permeability has been compromised by cytotoxic. Eg. Trypan blue and propidium

iodine.

The main disadvantages of this test is the managing of radioactive isotopes (a

gamma radiation emitter.

CELL NUMBER AND GROWTH TESTS

These assess the cytotoxicity of a material by measuring cell number or

growth after exposure to a material cells are plated in a well of a cell culture dish

where they attach. The material is then placed in the test system if the material is not

cytotoxic, the cells will remain attached to the well and will proliferate with time. If

the material is cytotoxic, the cells may stop growing exhibit cytopathic features or

detach from the well. If the material is a solid, then the density of cells may be

assessed at different distances from the material and a zone of inhibited cell growth

may be described. The cell density can be assessed either quantitatively, semi

quantitatively or quantitatively substances such as Teflon can be used as negative

( non cytotoxic) controls where as materials such as plasticized polyvinyl chloride can

be used as positive cytotoxic controls.

TESTS FOR CELL METABOLISM OR CELL FUNCTION

Some in vitro tests for biocompatibility, use the biosynthetic or enzymatic

activity of cells to assess cytotoxic response. Tests that measure DNA or protein by

cells is usually analyzed by adding radio isotope labeled precursors to the medium

and quantifying the radioscope incorporated into DNA or protein. (eg. 3H –

thymidine)

A commonly used enzymatic test for cytotoxicity is the MTT test. This test

measures the activity of cellular dehydrogenases, which converts a chemical MTT,

via several cellular reducing agents, to a blue, insoluble formazan compound. If the

dehydrogenases are not active because of the cytotoxic effects, the formazan will not

form. Production of Formazan is quantified by dissolving if and measuring the optical

density of the resulting solution, they can also be localized around the test sample by

light or electron microscopy.

Recently developed indicator dyes such as alam blue have been formulated to

quantitatively measure cell proliferation using and oxidation reduction (redox)

indicator that yields a calorimelic change and fluorescent signal in response to

metabolic activity and permit continous monitoring of cells overtime.

TESTS THAT USE BARRIERS

Indirect tests researches have long recognized that in vivo direct contact does

not exist between cells and the materials separation of cells and materials may occur

from keratinized epithelium dentin or extracellular matrix. Thus several in vitro

barrier tests have been developed to mimic in vivo conditions.

One such test is the agar overlay method in which a monolayer of cultured

cells is established before adding 1% agar plus a vital stain such as neutral red to a

fresh culture media. The agar forms a barriers between the cells and the material

which is placed on top of the agar sold test sample or liquid samples adsorbed onto

filter paper can be tested with this assay upto 24 hrs.

However the agar may not adequately represent barriers that occur in vivo,

furthermore because of variability of the agar’s diffusion properties, it is difficult to

correlate the intensity of color or width of the zone around or material with the

concentration of leachable toxic products.

A second barriers assay is the Millipore filter assay. This technique establishes

a mondayer of cells on filters made of cellulose esters. The culture medium is then

replaced with medium containing 1% agar and this mixture is allowed to get over the

cells, finally the filter monolay get is detached and turned over so that the filter is on

top for placement of solid or soluble test samples for 2 or more hours. After exposure

to the test samples the filter is removed and an assay is used to determine the effect of

the sample on acellular metabolic activity toxicity in the Millipore filter test is

assessed by the width of the cytotoxic zone around each test sample.

It has the drawback of arbitrarily influencing the diffusion of leachable

products from the test materials.

Dentin barriers tests have shown improved correlation with the cytotoxicity of

dental materials in usage tests in teeth and are gradually being developed for

screening purpose. A number of studies have shown that dentin forms a barrier

through which toxic materials must diffuse to reach pulpal tissue.

The thickness of the dentin correlates directly with the protection offered to

the pulp thus assays have been developed that incorporate dentin disks between the

test sample and the cell assay system.

The use of dentin disks offers the added advantage of directional diffusion

between the restorative material and the culture medium.

OTHER ASSAYS FOR CELL FUNCTIONS

In vitro assays to measure immune functional or other tissue reaction have also

been used. These assays measure cytokine production by lymphocytes macrophages,

lymphocyte, proliferation, chemotaxis or T- cells. Other tests measure the ability of a

material to alter cell cycle or activate complement. Material that activate complement

may generate inflammation or thrombi and may propagate a chronic inflammatory

response whereas concerns about complement activation by dental materials are

fewer, it is possible that activation of complement by resins or metals or their

corrosion products may prolong inflammation in the gingival or pulp.

MUTAGENESIS ASSAYS

They assess the effect of materials on a cells genetic material. There is a wide

range of mechanisms by which materials can affect the genetic material of the cell.

Genotoxic mutagens directly alter the DNA of the cell through various types of

mutations. Each chemical may be associated with a specific type of DNA mutation

Genotoxic chemicals may be mutagens in their native states or may require activation

or biotransformation to be mutagens, in which case they are called promutagens

mutagens may or may not be carcinogens and carcinogens may or may not be

mutagens. Thus the qualification and relevance of tests that attempt to measure

mutagenesis and carcinogensis are extremely complex.

The Ames test is the most widely used short term mutagenesis test and the

only short term test that is considered thoroughly validated. It uses mutant stocks of

salmonella typhimurium that require exogenous histidine native stocks of bacteria do

not require expgenous histidine. Exclusion of histidine from the culture medium

allows a chemical to be tested for its ability to convert the mutant strain to a native

strain. Chemicals that significantly increase the frequency of reversion back to the

native state have a reportedly high probability of being carcinogenic in mammals

because they significantly alter genetic material performance of this test requires

experience in the field and special strains of salmonella to produce meaningful results.

A second test for mutagenesis is the styles cell transformation test. This test on

mammaion cells was developed to offer an alternative to bacterial tests ( Ames test)

which may not be relevant to mammation systems. This assay quantifies the ability of

potential carcinogens to transform standard cell lines so that they will grow in soft

agar untransformed fibroblasts normally will not grow within an agar get whereas

genetically transformed cells will grow below the gel surface. This characteristic that

correlate with the ability of cells to produce tumors in vivo. However there has been

some difficulty in reproducing these results.

ANIMAL TESTS

After screening by initial tests of the materials developed for a specific use

animal tests for biocompatibility are used in mammals such as mice rats hamsters or

guinea pigs. Animal tests are distinct from usage tests in that the material is not placed

in the animal with regard toxic use. The use of an animal allows many complex

interactions between the material and a functioning complete biological system to

occur. The biological responses in animal tests are more comprehensive and may be

more relevant than in vital tests.

Disadvantage include

They can be difficult to interpret and control

Expensive

Time consuming

Often involve significant ethical concerns and paperwork

Relevance of the test to the in vivo use of a material can be quite unclear,

especially in estimating the appropriateness of an animal species to

represent a human.

Mucous membrane Irritation test

This determines a material causes inflammation to mucous membrane or

abraded skin. This test is conducted by placing the test materials and positive and

negative controls into contact with hamster’s cheek pouch tissue or rabbit oral tissue.

After several weeks of contact the control and test sites are examined and the

gross tissue reaction in the living animals are recorded and photographed in color. The

animals are then sacrificed and biopsy, specimens are prepared for histological

evaluation of inflammatory, changes.

Skin sensitization Test ( Guinea pig maximization test)

Used in guinea pigs, the materials are injected intradermally to test for the

development of skin hypersensitivity reactions. This injection is followed by

secondary treatment with adhesive patches containing the test substance.

If hypersensitivity develops from the initial injector, the patch will elicit an

inflammatory response. The skin patch test can result in a spectrum from no reaction

to intense redness and swelling. The degree of reaction in the patch test and the

percentage of animals that show a reaction are the basis for estimating the

allergenicity of the material.

IMPLANTATION TESTS

These tests are used to evaluate materials that will contact subcutaneous tissue

or bone. The location of the implant site is determined by the use of the material and

may include connective tissue, bone or muscle. Although amalgams and alloys are

tested because the margins of the restorative materials contact the gingival most

subcutaneous tests are used for materials that will directly contact soft tissue during

implantation endodontic or periodontal treatment.

Short term implantation is studied by aseptically placing controls are placed at

separate sites and allowed to remain for 1 – 11 weeks. Alternatively an empty tube is

embedded first and the inflammatory reaction from surgery is allowed to subside. The

implant site is then reopened and the test material is placed into this healed site or is

packed into the tube and the test material is placed into this healed site or is packed

into the tube that was placed previously. At the appropriate time, the areas are excised

and prepared for microscopic examination and interpretation. The tissue response can

be evaluated by normal histological, histochemical, or immunohistochemical

method. Implantation tests of larger duration, for identification of either chronic

inflammation or tumor formation are performed in a manner similar to that of short

term tests except the materials remains in place for 1 to 2 years before examination.

Animal tests that measure the mutagenic and carcinogenic properties of

materials have been developed by toxicologists. Those tests are employed with a

strategy tests are applied in a specific order and testing is stopped when any indicates

mutagenic potential of the material or chemical. The validity of any of these tests may

be affected by tissue of species tissue gender and other factors. Tests are generally

divided into

Limited in vivo tests that measure altered lives function or increased tumor

induction when animals are exposed to the chemicals for a fraction of their

lifetimes.

Long term invivo tests are performed by keeping the chemical in contact

with the animals over the majority of its lifetime.

Fidelity, with which the test mimics

USAGE TESTS

These tests may be done in animals or human volunteers. They are distinct

from other animal tests because they require the material be placed in a situation

identical to its intended clinical use. The usefulness of a usage test for predicting

biocompatibility is directly proportional to the fidelity with which the test mimics the

clinical use of the material in every regard include time location environment and

placement techniques. For this reason usage tests in animals employ larger animals

that have similar oral environment to humans such as dogs or monkeys. If humans are

used, the usage test is dentical to the clinical trial.

In dentistry dental pulp periodontium and gingival or mucosal tissue are

generally the largest of usage tests.

These tests are gold standard in that they give the ultimate to whether or not a

material will be biocompatibility.

Advantage

Relevance to use of material is assured.

Disadvantage

Very expensive

Very time consuming

Major legal / ethical issues

Can be difficult to control

Difficult to interpret and quantify.

Dental pulp irritation tests

Materials to be tested on the dental pulp are placed in class V cavity

preparations in intra noncarious teeth of monkeys or other suitable animals. After

careful uniformly sized cavity preparations under sterile conditions the compounds

are placed in equal number of anterior and posterior teeth of the maxilla and mandible

to ensure uniform distribution in all types of teeth. The materials are left in place from

1 to 8 weeks. Zinc oxide eugenol and silicon cements have been used as negative and

positive control materials respectively.

At the conclusion of the study, the teeth are removed and sectioned for

microscopic examination. The tissue sections are evaluated by the investigation

without knowledge of the identity of the materials and necrotic and inflammatory

reaction are classified.

According to the intensity of the response the thickness of the remaining

dentin and reparative dentin for each histological specimen is measured with a

phalomicrometer and recorded. The response of the pulp is evaluated based on its

appearance after treatment. The severity of the lesion is based on disruption of the

structure and the number of inflammatory cells present.

Pulpal response is classified as either

Slight

Mild hyperemia, few inflammatory cells slight hemorrhage in the

odontoblastic zone.

Moderate

Definite increase in number of inflammatory cells hyperemia slight disruption

of odontoblastic zone.

Severe

Decided inflammatory infiltrate hyperemia total disruption of odontoblastic

lay and even localized abscesses

Efforts have been made to develop techniques that identify bacterial insults to

pulp. Usage tests that study teeth with induced pulpils allow evaluation of types and

amount of reparative dentin formed.

MUCOSA AND GINGIVAL USAGE TESTS

Since various dental materials contact gingival and mucosal tissues, the tissue

response to these materials must be measured. Materials are placed in cavity

preparation with subgingival extensions. The materials effects on gingival tissues are

observed at 7 days and again after 30 days. Responses categorized as

Slight characterized by a few mononuclear inflammatory cells (mainly

lymphocytes) in the epithelium and adjacent connective tissue.

Moderate characterized by numerous mononuclear cells in the connective

tissue and a few neutrophils in the epithelium.

Severe evokes a significant mononuclear and neutrophilic infiltrate and

thinned or absent epithelium

Difficulties include

Presence of some degree of preexisting inflammatory in gingival tissue.

Bacterial plaque

Secondary factors are the surface roughness of the restorative material open or

overhanging margins and over contouring or under contouring of the restoration.

DENTAL IMPLANTS IN BONE

The best estimations of the success and failure of implants are gained from

three tests.

1. Penetration of periodontal probe along the side of the implant.

2. Mobility of the implant

3. Radiographs indicating either osseous integration or radiolucency around

the implant.

Previously investigators argued that formation of a fibrous connective tissue

capsule around a subperiosteal implant or root cylinder was the natural reaction of the

body to a material. They argued that this was actually an attachment similar to the

periodontal ligament and should be considered a sign of an acceptable material.

However, in most cases it resembled the wall of a cyst, which is the body’s attempt to

isolate the implanted material as the material slowly degrades and leaches its

components into tissue.

Currently for implants in bone, implants should be completely encased in bone

the most differentiated slab of that tissue fibrous capsule formation is a sign of

irritation and chronic inflammation.

Using in vitro Animal and Usage Tests Together

Generally no single test is used to evaluate the biocompatibility of a new

material. The ways by which these tests are used together however are controversial

and have evolved over the years as knowledge has increased and new techniques

developed.

Early combination schemes proposed a pyramid testing protocol in which all

materials were tested at the bottom of the pyramid and materials were weekend out as

the testing continued towards the top of the pyramid. Tests at the bottom of the

pyramid were unspecific toxicity tests of any type with conditions that did not

necessarily reflect those of the material use. The next layer shows specific toxicity

that presumably death with conditions more relevant to the use of the material. The

final lie was a clinical trial of the material.

Number of tests Number of tests

Later another pyramid schemes was proposed that divided tests into initial

secondary and usage tests. The philosophy was similar to the first scheme except the

types of tests were broadened to encompass biological reactions other than toxicity

such as immunogenicity and mutagenicity. The concept of a usage test in an animal

was also added first only materials that passed the first lier of tests were graduates to

the second lier and only those that passed the second lier were graduated to the

clinical trials.

Two newer schemes have evolved in the recent past with regards to using

combinations of biocompatibility tests to evaluate materials.

Firstly all tests continue to be of value in assessing biocompatibility of a

material during its development and even in its clinical service.

Eg. Tests in animals for inflammatory response may be useful not only during

development of a material but also if a problem is noted with the material after it has

been on the marked for a time.

Secondly these new schemes recognize the inability of current test methods to

accurately and absolutely screen in or out a material.

They incorporate the philosophy that assessing the biocompatibility is an

ongoing process.

STANDARDS THAT REGULATE THE MEASUREMENT OF

BIOCOMPATABILITY

The first efforts of the ADA to establish guidelines for dental materials came

in 1926 when scientists at the national Bureau of standards development

specifications for dental amalgam. Since then standardization has been difficult and a

length, process made more difficult by disagreement on the appropriateness and

significance of particular tests. In 1972, the council on dental materials, instruments

and equipments of ANSI / ADA approved document no 41 for recommended standard

practices for biological evaluation of dental materials. The committee that developed

this documents recognized the need for standardized methods of testing and for

sequential testing of materials to reduce the number of compounds that would need to

be tested clinically.

ANSI / ADA DOCUMENT 41

The original ANSI/ ADA documents 41 for biological testing was updated in

1982 to include tests for mutagencity. This specification uses the linear paradigm for

materials screening and divides testing into initial secondary and usage tests.

The initial tests include in vitro assays for cytotoxicity red blood cell

membrane lysis mutagenesis and carcinogenesis as well as animal tests for

inflammatory or immune responses secondary tests include animal tests for

inflammatory or immune responses. Usage tests include tests for pulpal and bone

response.

The required tests for a given material are not listed specifically, rather it is up

to the manufacturer to select the tests and defined the selection to the ANSI /ADA and

later FDA when applying for approval of the materials.

ISO STANDARD 10993

The ISO 10993 document is the international standard for testing the

biocompatibility of materials unlike ANSI / ADA documents 41, it is not restricted to

dental materials. This document is periodically documents. In 2002 consisted of 16

parts each addressing a different area of biological testing.

Two types of tests for cytotoxicity, sensitization and systemic toxicity and

supplementary tests for chronic toxicity carcinogenicity and biodegradation. In

addition some specialized tests for devices are addressed such as the dentin barrier

test for restorative dental materials. In this standard usage tests are part of

supplementary tests. As the ANSI/ADA standard the selection of test is left to the

manufacturer who must defined the selection upon application for approval.

BIOCOMPATABILITY OF DENTAL MATERIALS

Reaction of pulp

Dentin protects the pulp and owes its validity and its sensitivity to

stimulation of the dental pulp. This intimate relationship has far reaching

clinical application.

The nature of pulp reaction that follows peripheral injury of the dentin

which depends on

The nature of the causative agent

It’s proximity to the pulp.

1 Attrition abrasion

Responses

Mild irritation

Reparative dentin

2. Progressive dental caries

Inflammation of pulp

3. Iatrogenic injuries

May result in inflammation of pulp

As pulp inflammation can also be iatrogenic in origin Do not Harm is the basic

principal should be followed by all members of the health profession.

Iatrogenic pulp injury can develop

During the preparation of a tooth for a restoration

During the insertion of the restorative material

It can be due to inherent irritational properties of the material either.

Clinical components of the material

Injurious products generated during setting of the material

Pulpal reactions can also be caused by Bacterio

Either residual bacteria left behind in the cavity.

Or by the bacteria that gain access to the cavity after restoration as a

result of microleakage.

Pulpal response to cast metal restoration, porcelains etc mainly

depends on the comenting agents, proximation of the pulp and

techniques of cementation.

MICROLEAKAGE

There is evidence that restorative materials may not bond to enamel or dentin

with sufficient strength to resist the forces of contraction during polymerization wear

or thermal cycling when debonding occurs, bacteria, food debris or saliva may be

drawn into the gap between the restoration and the tooth by capillary action. This

effect has been termed microleakage. The importance of microleakage in pulpal

irritation has been extensively studied early studies reported that various dental

restoration materials irritated pulp tissue in animal tests.

However, several recent studies hypothesized that it was often the products of

microleakage, not the restorative materials that caused pulpal irritation. Subsequently

numerous studies should that bacteria were present under restoration and in dentinal

labours which might be responsible for pulpal irritation.

Microleakage can lead to

Secondary caries

Stains or discoloration

Pulpal pathology

Post operative sensitivity

Restorative materials depending on their chemical nature can be grouped as

Metallic restorative materials Non- metal restorative materials

Amalgam Different restorative materials

Direct filling Gold Acrylic

Dental casting Alloys Composite

Techniques Alloys Gold Porcelain

Base metal alloys

AMALGAM

Dental amalgam has been used extensively for dental restoration

Biocompatability of amalgam is thought to be determined largely by the correction

products released while in service. Corrosion in turn depends on the type of amalgam

whether it contains the y2 phase and its composition In cell culture screening tests,

free or non leaded mercury from amalgam is toxic with the addition of copper

amalgams become toxic to cells in culture but low copper amalgam that has set for 24

hrs. does not inhabit cell growth. Implantation tests show that low copper amalgams

are well tolerated but the high copper amalgams can cause severe radiations when in

direct contact with tissue. In usage tests, the response of the pulp to amalgam in

shallow or in deeper but lined cavities is minimal and amalgam rarely causes invisible

damage to the pulp however, pain results from using amalgam is deep unlined cavity

preparations( 0.5 mm or less)

Firstly because of its thermal conductivity

Secondly margins of newly placed amalgam restorations show significant

microleakage marginal leakage of corrosion and microbial products is probably

enhanced by the natural daily thermal cycle in the oral cavity.

Lichenoid reaction representing a long term effect in the oral mucous

membrane adjacent to amalgam restoration is quite often Buccal mucosa and lateral

border of the longer being the areas affected.

For many years a controversy has raged over the biocompatibility at amalgam

restoration because of the presence of element hg. The symptoms of chronic Hg.

Poisoning ( elemental) are

Weakness

Fatigue

Anorxia

Weightloss

Insomnia

Irrilability

Tremois in extremities

Shyness

The signs and symptoms of meth Hg poisoning ( Sea food)

Alaxia (gait disturbances)

Paresthesia of extremities lips and tongue

Constriction of visual fields

Amalgams based on gallium rather than mercury have been developed to

provide direct restorative materials that are mercury free, but appeared to be more

cytotoxic than high copper amalgams chemically these materials show much higher

corrosion rates than standard amalgam leading to roughness and discolouration.

Accepted Hg levels

Patient with amalgam – over Hg level

Normal 0.7 mg/ml

DIRECT FILLING GOLD

The pulp responses from the insertion of cohesive and compacted gold are

associated with condensation, whether with hand instrument / with mechanical

pneumatic instrument.

The responses develop when the condensation occurs over freshly cut dentinal

lubules.( minimum of 2 mm sapiapulpal dentin thickness) but not when the dentinal

tubules are lined with pre-operatively formed reparative dentin induced from previous

episodes of disease / restorative procedures.

Apparently it was found that when compact properly into sound tooth

structure produce only minimal pulp response showing least marginal leakage.

Under extremely rare conditions patients have been reported with

Burning sensation

Lichenoid lesions of oral mucosa

Generalized systemic reactions.

DENTAL CASTING ALLOYS

We have to select alloys based on individual patients specific functional and

economics requirement – There is no one alloy suitable for all applications e.g certain

base metal alloys contain Be, Ni, Co, Cr. And the biocompatibility of each metal

varies to different degree of tissue tolerance.

1) Beryllium : To date there have been no documented cases of Be toxicity at

dental origin.

However, under controlled conditions, when inhalation of dust and fumes can

be anticipated, the presence of be constitutes recognized health hazard.

It may result in

Acute form

Response vary from contact dermatitis to severe chemical

Chronic form

Symptoms range from coughing, chest pain and general weakness

To pulmonary dysfunction

Chronic inflammatory condition - Berylliosis

Which result in lung cancer.

2) NICKEL : Epidermiologic studies on workers in non dental industries have

identified Ni. And Ni. Compound as carcinogenic. The major hazardous route

is aspiration. The use of nickel has been controversial for many years because

of the biological properties of nickel ions and compound.

There is no experimental evidence that Ni. Compounds are carcinogenic when

admixture by oral cutaneous route.

It causes dermatitis ( contact) because it is a potential sensitizing agent and in

sensitized patients intra orally.

Burning and tingling sensation during the first 24 hours and.

Later exhibited a slight erythematous reaction in the mucosa.

However there is no correlation found between the incidence of Ni

hypersensitivity and the presence of intra oral Ni alloy restoration.

Cobalt alloys have a potential for

Dermatologic

Systemic effect that may result from patient and personal exposure to

cobalt alloys.

Inhibition of cell metabolism is reversible in tissue culture by high levels of

serum proteins suggesting that protein binding or buffering in inflamed pulp tissue

may play an important role in detoxifying these materials in vivo. The initial

response after exposing pulp tissue to these highly alkaline pulp capping agents is

necrosis to a depth of 1 mm or more. The alkaline pH also helps to coagulate any

hemorrhagic exudates of the superficial pulp shortly after necrosis occur neutrophils

infiltrate into the subnecrotic zone. After 5-8 weeks only a slight inflammatory

response remains within weeks to months however the necrotic zone undergoes

dystrophic calcification which appears to be a stimulus for dentin bridge formation.

When resins are incorporated, the Ca(OH2) become less irritating and are able

to stimulate reparative dentin bridge formation mere quickly than Ca(OH)2 suspension

alone with no zone of necrosis and reparative dentin is laid down adjacent to the liner.

This indicates that replacement odontoblasts form the dentin bridge in contact with

the liner.

The liners such as copal vanishes and polystyrenes are not generally used

under resin based materials, because resin components dissolve the film of vanish.

Because liners are used in such thin layers, they do not provide thermal

insulation but do initially isolate the dentinal tubule contents from the

cavity preparation.

They may also reduce penetration of bacteria or chemical substances for a

time.

The vanish also prevent penetration of corrosion products of amalgams

into the dentinal tubules.

CERAMICS

Among the most biocompatible materials used for dental restorations are

ceramics and the use of dental constructions manufactured using ceramics has

increased during the past few decades, new ceramics materials have been used both as

high strength care materials and as veneers.

This biocompatibility of dental ceramics has been largely assumed on the

basis of studies of traditional feldspathic porcelains and the low corrosion rates of

feldspathic materials studies showed clearly that all ceramics materials are not

equivalent in their initial state of fabrication with aging after polishing procedure.

GROUP II

ZINC PHOSPHATE CEMENT

It has an irritational potential intermediate to Z no E and silicate cement

As a base it is not highly toxic

As a lulling agent on pressure causes a widespread three dimensional

lesion involving all the coronal pulp tissue as the phosphoric acid within

the mix of 2n phosphate cement is forced in the dentinal tubules.

A young tooth with wide open dentinal tubules is more susceptible to

such an intense inflammatory response compared to an older tooth which

has sclerotic / Reparative dentin that blocks dentinal tubules and prevent

the acid from reaching the pulp.

The P-11 of the cement 3 minute after mixing is 3.5 the P-11 rapidly

increases thereafter approaches neutrality in 24 hours. Thus damage to the

pulp occurs during the first few hours after insertion of the cement, this

can be prevented by using appropriate varnishes and dentin bonding

agents.

Tendency to form complexes with proteins would limit its diffusion

through the tissues

In this regard polycarboxylate cements are equivalent to ZOE cements.

Post operative sensitivity effects are negligible for cements.

GLASS IONOMER CEMENT

Glass ionomers have been used as both cement ( luting agent) and as a

restorative material light cured ionomer systems have been introduced these systems

use BISGMA or other oligomers as pendant chains on the polyacrylate main chain.

In screening tests freshly prepared ionomer is mildly cytotoxic but this

effect is reduced over time.

The fluoride release from these materials is of therapeutic value

The overall pulpal biocompatibility of glass ionomer cement has been

attributed to the weak nature of the polyacrylic acid. It is unable to diffuse

through dentin due to its high molecular weight.

Histological studies in usage tests show that any inflammatory intitrak

from ionomer is minimal or absent after a month.

GROUP III

SILICATE CEMENT

It has high irritational potential

It is an ideal material for the control in studies that evaluate pulp reactions

to restorative materials.

The ptt is below 3 at the time of insertion and the ptt remains below

neutrality even after 1 month calcium hydroxide base provides adequate

pulp protection from the cement.

RESINS

Those is no indication that commonly used acrylic resins produce systemic

effects in humans.

The amount of residual monomer in processed polymethyl is externally

low.

The oral mucosa and underlying tissues function as barriers that

significantly diminish the volume of monomer reaching the blood stream.

Residual monomer that reaches the blood stream is rapidly hydrolyzed to

methacrylic acid and excerted.

Clinical experience indicates that true allergic reactions to acrylic resins

seldom occurs in the oral cavity.

Theoretically, such reaction( toxic and allergic) could occur after contact

with polymer residual monomer benzyl peroxide hydroquinone.

Clinically most patients reported denture induced SORE MOUTH which

on evaluation indicates tissue irritation which is generally related to

unhygiene conditions / trauma caused by ill fitting prosthesis.

Repeated prolonged contact with monomer may result in contact

dermatitis.

Finally inhalation of monomer vapour may be detrimental therefore, the

use of monomers should be restricted to well ventilated areas.

COMPOSITE RESINS

The material whether conventional / microfilled auto polymerizing photo

activated (UV/VL) are found irritating to the pulp. In vitro, freshly set chemically

cured and light cured resins often cause moderate cytotoxic reaction in cultured cells

over 24 to 72 hrs. of exposure although several newer systems seem to have minimal

toxicity. The cytotoxicity is significantly reduced 24-48 hrs. after setting and by the

presence of a dentin barrier.

Cytotoxicity is thought to be medicated by resin compounds released from the

materials. It appears likely that reactive radicals generated during polymerization of

the resin are responsible for pulp injury.

Evidence indicates that the light cured resins are less cytotoxic than

chemically cured systems, but this effect is highly dependent on curing efficiency of

the light and the type of resin system used.

BONDING AGENTS

Numerous bonding agents have been developed and are applied to cut dentin

during restoration of the tooth. Many of these reagents are cytotoxic to cells if tested

alone, however when placed on dentin and rinsed with water between applications of

subsequent reagents as prescribed by the manufacturer the cytotoxicity is reduced.

Long term in vitro studies suggest that compounds of the bonding agent may

penetrate upto 0.5 mm of dentin and cause significant suppression of cellular

metabolism for upto 4 week after application suggesting that residual unbound

reagents may cause adverse effects.

Hydroxyethyl methacrylate (HEMA) a hydrophilic resin contained in several

bonding systems is at least 100 times less toxic in tissue culture than BIS GMA

studies using long term in vitro systems have shown, however that adverse effects of

resins occur at much lower concentrations when exposure times are increased to 4-6

weeks. Many cytotoxic effects of resin compounds are reduced significantly by the

presence of a dentin barrier studies have shown that combinations of HEMA and

other resins found in dentin bonding agents may ad synergistically to cause cytotoxic

effects in vitro.

LINERS AND VARNISHES

Calcium hydroxide cavity liner come in many forms, ranging from saline

suspensions with a very alkaline PH( above 12) to modified forms containing Zinc

oxide, titanium dioxide and resins.

The high PH of calcium hydroxide in suspensions leads to extreme

cytotoxicity in screening tests calcium hydroxide cements containing resins cause

mild to moderate cytotoxic effects in both cut and long term set conditions.

CONCLUSION

Biocompatibility of a dental material depends o its composition location and

interaction within the oral cavity. Diverse biological response to these materials

depends on whether they release their components and whether those components are

toxic immunogenic or mutagenic at the released concentrations. The location of a

material in the oral cavity. Partly determinesits biocompatibility finally the

interactions between the material and the body influence the biocompatibility of the

material. In the end, no material can be shown to be 100% safe or risk free, further

more the clinician must rely on clinical judgement, data available and analyze the risk

benefit ration before choosing a dental material.

Elements such as potassium and sodium appear to be the most liable from the

ceramics but these elements are not particularly hazardous. In cytotoxicity assays by

siogren et al in 2000, there was no evidence of cytotoxicity in dental ceramics

indicating good biocompatibility in vitro break down in products of dental ceramics

have not been reported to have known toxic effects and several of the ions in dental

ceramics are considered non toxic.