Jagadeesh .Kp.g studentDept. Of conservative dentistry & endodonticsg.d.c.h,vijayawada

Rule over the fish in the sea and the birds in the sky and over every living creature ... the birds of the heavens and over every living thing that moves on the earth. ... God blessed the humans by saying to them

CONTENTSDefinition

Defining the use of a material

Historical background

Methods of measuring biocompatibilty

Biocompatibilty of dental materials

Conclusion

Referencs

Biocompatibility

It is the ability of a material to elicit an appropriate biological response in a given application in the body. [Craig]

Biocompatibility is not a property of just a material, but rather a property of how a material reacts with its environment.

The ability of a biomaterial to perform its desired function with respect to a medical (or dental) 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 optimizing the clinically relevant performance of that therapy.

Williams 2008

DEFINING THE USE OF A MATERIALThere are several factors that must be

considered when trying to measure the biological response.

The most important factors include

Location of material

The duration of material in the body

Stresses placed on material

Location of materialThe location of a material is important to its

overall biological response.

In general materials that communicate through the epitheliuim 0r lie completely beneath it will need closer scrutiny when assessing the biological response than materials that do not penetrate the epithelium. Similarly, materials that penetrate tooth enamel will need more scrutiny than materials than do not.

The duration of material in the bodyThe duration of the material in the body is

important to the biological response.

The duration of the presence of a material is an important factor, because many interactive effects between the body and material take some time to develop.

In general, the most stringent tests to measure biocompatibility are required for materials that are present for the longest times..

Long durations give sufficient time for the material to affect the body and for the body to affect the material in many complex ways

Stresses placed on materialstresses placed on the material are important

to the biological response, These stresses may be physical, chemical, or thermal in nature.

Short-term, long-term, and fatigue stresses all need to be considered when assessing the effect of stress on the biological performance of material.

HISTORICAL BACKGROUNDAlthough the concept of the ethical treatment

of patients extends back to the time of Hippocrates (460-377 KC.), 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.

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 100" C.

Even G.V. Black used patients to test many of his new ideas for restorative materials, such as early amalgams.

The current philosophy about testing the biological properties of dental materials in a systematic way evolved in the 1960s as the need to protect patients became politically acute and as the number of new materials increase.

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 still being challenged and defined today.

Nazi human experimentationNazi human experimentations were a series of medical experiments on large numbers of prisoners, mainly Jews from across Europe

Doctors trial nuremberg code of ethics

Measuring the biocompatibility:

In vitro tests

Animal tests

Usage tests

In vitro testsTests are done in test tube, cell culture dish,

or other wise out side a living organism.

Direct tests: material contacts the cell system without barrier.

Direct tests can be further subdivided into Those in which the material is physically

present with the cells Extract from the material contact the cell

system

Indirect tests: when there is a barrier of some sort between the material and the cell system.

Agar overlay method Millipore filter assay Dentin barrier tests

Advantages:

1. Quick to perform

2. Least expensive

3. Can be standardized

4. Large scale screening

5. Good experimental control

6. Excellence for mechanism of

interaction

Disadvantages:

1. Relevance to the final in vivo use is questionable

2. Lack if inflammatory and other tissue protection mechanisms in the in vitro environment

3. Cannot predict the overall biocompatibility of a material

Cells used for in vitro tests

1. primary cells: taken directly from animals and cultured . A primary cell culture may be composed of

mixture of cell types. Retains many of the characteristics of cells in- vivo2. Continuous cells or cell lines: cell lines

have at least one passage. With each subsequent culture the cell population becomes more homogenous.

These cells do not retain all in vivo characteristics

Cyto toxicity testsIt can be assessed by the following formula = Cell death by material Cell number before the exposure

Cells are plated in a well of a cell culture dish where they attach. The material is then placed in the best system.

If the material is not cytotoxic cells will remain attached to the well and will proliferate over time

If the material is cytotoxic, 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

Negative control materials (non cyto toxic materials)- Teflon and cell culture treated poly styrene

Positive control materials (cytotoxic material)- Plasticized poly vinyl chloride

Membrane permeability tests

Measure cytotoxicity by the ease with which a dye can pass through a cell membrane, because membrane permeability

Is equialent to or very nearly equvalent to cell death

Change in the membrane permeability to the dye

1. Vital dyes: Neutral red & Na2CrO4

2.Nonvital dyes: Trypan blue & Propodium iodide

Tests for cell metabolism or cell function

Bio synthetic or enzymatic activity of cells are used to assess cyto toxicity of the test material

E g. Tests that measures DNA synthesis or protein synthesis

Synthesis is analyzed by adding radio isotope labeled precursors to the medium and quantifying the radioisotope [H-thymidine or H-leucine]incorporated into DNA or Protein

MTT test:[3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide]

Measures the activity of cellular dehydrogenase

MTT is a yellow, soluble molecule

Chemical MTT is used to know the enzymatic action of cell.

If the cell is able to reduce the MTT the resulting Formazen formed is proportional to the enzymatic activity

Formazen quantified by dissolving it and measuring the optical density of the resulting solution alternatively the formazen can be localized around the test sample by light or electron microscopy

Other formazen generating chemicals NBT, DXTT, WST, Alamar Blue.

Alaram blue tests quantitatively measure cell proliferation using a fluorescent indicator that allows the continuous monitoring of cells over time.

Tests that use barriers [Indirect tests]

Cyto toxicity tests measure the toxicity when material is indirect contact with the cell culture

Agar overlay methodMillipore filter assay Dentin barrier tests

Agar over lay method

Monolayer of cultured cells +neutral red +fresh culture medium

Agar layer

Sample

Agar forms a barrier between the cells and the material which is placed in the top of the agar

Nutrients, gas and soluble toxic substances can diffuse through the agar

Solid test samples or liquid samples absorbed on to filter paper can be tested with this assay for up to 24hrs

Millipore filter assay Establish monolayer of cells on the filter Culture medium placement and this mixture

is allowed to gel over the cells Filter- monolayer gel 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 the toxicity in the Millipore filter test is assessed by the width of the cytotoxic zone around each test sample

Dentin barrier tests

It shows the improved correlation with the cytotoxicity of dental materials in usage tests in teeth

Incorporation of dentin disks between the test samples and the cell assay system

Then the cytotoxicity is measured the testing material placed on one side of the dentin disk in the devised used to hold the dentin disk

Cells can also be grown in the collection side of the disks. Collection fluid is also in the other side.Immortalized pulpal fibroblats can be used as target cells.

Components of the material may diffuse through

the dentin and effect of medium on cell metabolism can be measured

To assess the rate of diffusion the collection fluid can e circulated into and out of the collection

Other assays for cell functionThese assays measures cytokine production

by lymphocytes and macrophages, lymphocyte proliferation, chemotaxis or T-cell rosetting to sheep red blood cells

Other tests measure the ability of a material to alter the cell cycle or activate complement

Mutagenesis assays These tests elicit the effect of dental material on

a cells genetic material

Ames test: most widely used short term mutagenesis test

Only short term one that is thoroughly validated

Genetically altered bacteria are used as test organisms. These bacteria cannot grow and form colonies on a special culture agar, which is histidine-deficient.

But as soon as they come into contact with a mutagenic substance, they begin to grow. The number of forming colonies is a criterion for the mutagenicity.

Styles cell transformation test :This test on Mammalian cells offers an

alternative to bacterial tests(ames test)

Untransformed fibroblasts normally will not grow with in a agar gel where as genitically altered cells can grow

In vitro test systems based on cells include the HPRT test, in which an alteration of the gene is detected that encodes for the enzyme HPRT.

in vitro micronucleus test, in which direct morphological alterations of the chromosomes are identified (formation of micronuclei)

HPRT- H ypoxanthin- G uanin- P hospho s ribosyl t ransferase

Animal tests Mice, Rat, Hamsters, Guinea pigs More relevant than In-vitro tests difficult to

interpret and control Expensive, Time consuming, Involves significant

ethical concern

1. Mucous membrane irritation test2. Skin sensitization test3. Implantation tests

Mucous membrane irritation test+ve control, test material, -ve controls are all

placed into contact with Hamster cheek pouch tissue or rabbit oral tissue

Several weeks after test sites are examined and the gross tissue reactions in the living animals are recorded and photographed in color

The animals are sacrificed and biopsy specimens are prepared for histological evaluation

Skin sensitization tests

Materials are injected intradermally to test for development of skin hypersensitivity reactions, followed by secondary treatment with adhesive patches containing the test substance.

Two test methods are recommended using guinea pigs:

The maximization test and The Buehler test

The Maximization testThe investigated substance is at first injected

intradermally into the experimental animal, together with Freud’s Complete Adjuvans (FCA).

Seven days later, the same substance is applied topically at the same site for 2 days.

It is intended to amplify the immunological effect by FCA and, thus, to increase the sensitivity of the test.

Fourteen days after this induction period, the test substance is applied on a different area of the skin

Subsequently, the skin reaction is assessed after an appropriate exposure time . It is important that the substances be applied at a concentration that does not evoke primarily toxic (irritating) skin reactions.

Buehler test

The Buehler test is similarly executed on guinea pigs but without the application of FCA. Therefore, the

Buehler test is considered to be more protective for the animals than the maximization test.

Usage TestsUsage tests may be done in animals or in human

study participants.

They are distinct from other animal tests because they require that the material be placed in a situation identical to its intended clinical use.

The usefulness for predicting biocompatibility is directly proportional to the fidelity with which the test mimics the clinical use of the material in every regard, including time, location, environment, and placement technique.

For this reason, usage tests in animals usually employ larger animals that have similar oral environments to humans, such as dogs, mini-swine or monkeys.

When humans are used, the usage test is termed a clinical trial.

Advantages

Relevance to use of material is assured

Disadvantages

Very expensive

Very time consuming

Major legal/ethical issues

Can be difficult to control

Difficult to interpret and quantify

Dental Pulp Irritation TestsPulp compatibility of a material is investigated on

teeth of experimental animals or on human teeth that have to be extracted for orthodontic reasons.

In both cases, class V cavities are prepared as atraumatically as possible and are then filled with the test material. This approach is equivalent to the future mode of application on patients.

After a period of days to several months, the teeth are

removed and histologically prepared, and the pulps are microscopically evaluated for signs of acute or chronic inflammation and odontoblast reaction (including dentin neogenesis)

In addition, the space between test material and the cavity wall is investigated for bacterial penetration.

These methods can be modified in such a way that the pulp is exposed or part of the pulp is removed before

the material is applied

Assessment: The most important causes of pulp damage resulting from a restorative procedure (in addition to cavity preparation) are the following:

• Toxic substances released from the material

• Bacteria and their toxins between the material and the cavity

The pulp can react to these irritations in the following ways:

InflammationTertiary dentin formation

Dentin sclerosis reduces the dentin’s permeability, but low-molecular substances may diffuse even through sclerotic dentin.

However, sound teeth, mostly without obliterated dentin, are used in pulp/dentin tests.

Thus, there may be a discrepancy between the

clinical situation (below a carious lesion with dentinal sclerosis) and the usage test with filling materials.

The diffusion of potentially damaging substances through sclerotic dentin toward the pulp may be reduced.

In addition, the target organ of the pulp/dentin test is the pulp of sound (test) teeth and not the “predamaged” pulp, as is frequently the case in patients.

A chronic inflammation in the patient’s tooth pulp may impair the defensive capacity of the pulp, rendering it more susceptible to toxic material components.

Periapical Tissue Damageand Endodontic Usage Test

The literature includes descriptions of animal models (e.g., primates, dogs) that allow the application of a given material into the root canal according to endodontic techniques after a usual root canal preparation.

Compatibility is assessed by histologic evaluation of the periapical tissues.

Assessment: The classic endodontic usage test is very elaborate and includes the same technical and ethical problems as the pulp/dentin test using large experimental animals.

Relatively few studies using this test method are available in the literature.

The presented findings, however, document a good correlation with clinical observations.

In particular, stimulating effects on special cells can be determined, such as the influence of calcium hydroxide compounds on periapical cementoblasts.

Otherwise, implantation tests, in which Teflon tubes are filled with the experimental material and subsequently implanted, may be used as alternatives

Such tests are especially useful when assessing the claimed bioactive effects of test materials.

Dental Implants in BoneMaterials used for dental implants are

inserted into the jaw of test animals (intraosseous implants).

For this, penetration of the epithelial barrier, equivalent to the treatment of patients, is simulated on experimental animals.

Appropriate animals are, among others, primates, dogs, miniature pigs, guinea pigs, and rats.

Tissue reaction is assessed histologically, with the tissue in contact with the implant being particular interest

A good correlation of these findings with patients’ situations can be expected.

Mucosa and Gingival Usage Tests

Tissue response to materials with direct contact of gingival and mucosal tissues is assessed by placement in cavity preparations with subgingival extensions.

The material’s effect on gingival tissues are observed and responses are categorized as slight, moderate, or severe, depending on the number of mononuclear inflammatory cells

A difficulty with this type of study is the frequent presence of some degree of pre existing inflammation in gingival tissue due to the presence of bacterial plaque, surface roughness of the restorative material, open or overhanging margins, and over- or under-contouring of the restoration.

Correlation Among In Vitro,Animal, and Usage Tests

In the field of biocompatibility, some scientists question the usefulness of in vitro and animal tests in light of the apparent lack of correlation with usage tests and the clinical history of materials.

However, lack of correlation is not surprising in light of differences among these tests.

in vitro and animal tests often measure aspects of biological response that are more subtle or less prominent than those observed during a material’s clinical use.

Furthermore, barriers between the material and tissues may exist in usage tests or clinical use, but may not exist in the in vitro or animal tests.

Thus it is important to remember that each type of test has been designed to measure different aspects of biological response to a material, and correlation is not always to be expected.

Using In Vitro, Animal, and Usage Tests TogetherPyramid testing protocol

Early strategy for the use of biocompatibility tests

The contemporary strategy used in most standards documents.

Two suggested future strategies for biocompatibility testing of materials

Allergic Responses to dental materials:Allergic contact dermatitis or stomatitis

This is most common adverse reaction to dental materials

The interval between exposure to the causative agent and the occurrence of clinical feature varies between 12-48 hrs.

It usually occurs where body surface makes direct contact with the allergens.

E.g.: - monomers of bonding agent, acrylic components of dental cements.

Industry workers who handle these materials are also affected.

Allergy to latex Products: -In 1991, FDA issued a bulletin in respond to

the increasing number of latex-related allergic reactions.

Malten & associates (1976) reported increasing incidence of hypersensitivity.

March (1998), suggested that the polyether in latex rubber gloves was causative agent

Dermatitis of the hands (eczema) in the most common adverse reaction.

Reactions vary from localized rashes and swelling to wheezing and anaphylaxis.

To avoid these reactions to latex products, vinyl gloves may be used.

Blink horn and Leggate (1984) and Axelsson et al (1987) reported adverse reaction to rubber dam involving respiratory distress, edema, and chest pains.

The definitive diagnostic test for these is patch test.

The suspected allergen is applied to skin with intent to produce reaction in around 48-96 hrs.

Mercury Controversy: -

Controversy has raged over biocompatibility of amalgam restorations because of the presence of elemental mercury.

Recognized symptoms of chronic mercury poisoning are weakness, fatigue, anorexia, weight loss, insomnia, etc.

The lowest level of total blood mercury at which non-specific symptom occur is 35 ng/mL.

Minimizing Dental Iatrogenesis:Iatrogenesis is defined as the creation of side

effect, problems, or complications resulting from treatment by a physician or dentist.

Cavity preparation:Stanley HR (1994) reported that low hand

piece speed (6000-20,000 rpm) with air water spray, a cavity preparation 2 mm from the pulp, elicits minimal pulp lesion.

If preparation is less than 1 mm of the pulp, intensity of response increases.

 

Histopathologically, thermal insult results in loss of cytoplasmic continuity of odontoblasts and displacement of odontoblast nuclei into the dentinal tubules due to dehydration.

 The generation of heat within the pulp is the most severe trauma that restorative procedures impart on the pulp.

If the insult is extensive and cell rich zone of pulp is damaged, reparative dentin formation may be impaired.

The pulp is a tissue of low compliance according to Goodies et al (1989) because “It is encased in hard dentinal walls, it consists of a large amount of connective tissue with a small blood supply and has no possibility of developing a collateral circulation. For these reasons, the pulp is vulnerable to thermal damage during and after extensive restorative procedures.

 Zach and Cohen (1965) reported 15% of

irreversible pulpal damage in monkeys for a temperature elevated to 5.60C, 60% for a temperature elevated to 110C and 100% for a temperature elevated to 16.60C

In a cavity preparation with a diamond bur, the entire surface of the bur is in contact with the tooth surface thus generating frictional heat but in the case of TC bur the flutes themselves may allow a slight cooling action with a greater cutting efficiency.

According to Cohen, ‘Blushing’ of teeth during or after cavity or crown preparation is attributed to frictional heat. Coronal dentin develops a pinkish hue very soon after dentin is cut. This represents vascular stasis and is reversible

Pulpal reaction to restorative materials

Pulp responses to specific agents:

Bleaching agentsThese are used in non-vital and vital teeth.

These agents contain peroxides

These agents may be in contact with teeth for several minutes to severe hours.

Peroxides can penetrate the intact enamel and reach the pulp.

Occurrence of tooth sensitivity is very common with the use of these agents.

Bleaching agents will also damage the gingiva, if not isolated properly.

Amalgam:

Swerdlow and Stanley (1962) reported that the pulp response to amalgam placement is due to condensation pressure.

Little pulpal response is elicited when cavity is prepared with high-speed air-water spray technique

However, when cavity is restored with amalgam the pressures of condensation will intensify the response

Boremark and associates (1968) showed that radioactive mercury reached the pulp in humans after 6 days if no cavity liner was used.

Implantations tests show that low copper amalgams are well tolerated, but high copper amalgam cause severe reaction.

Liners are suggested to avoid pulpal reaction.

Amalgam based on gallium rather than mercury have been developed that are free of mercury.

Pulp Reactions

The following pulp reactions may occur immediately after application/condensation of amalgam in deep cavities with a remaining dentin thickness (RDT) of less than 0.5 mm • Reduced number of odontoblasts • Odontoblast nuclei in dentin tubules • Dilated capillaries • Slight to severe inflammatory cell infiltration in

the odontoblast layer

Pulp reaction 1 month after application of an amalgamfilling. Dilated blood vessels close to the predentin; otherwise,no noteworthy alterations. Distance between pulp andcavity is 0.52 mm

Visible light-cure Resin composites: The level of the pulp response to resin

composite restorations is especially intensified in deep cavity preparations when an incomplete curing of resin permits a higher concentration of residual unpolymerized monomer to reach the pulp.

Visible light-cured systems were developed to provide greater depth of cure, shorter curing time, less porosity and more wear resistant composite restoration.

A more conservative cavity preparation with incremental placement of the resin composite is highly recommended to minimize the pulp response.

No pulp damage is to be expected if resin-based composites or adhesives are applied in shallow or medium cavities, even after prior acid-etching of the dentin (total etch/total bonding technique).

In these situations, adhesives may serve as sealants and thus as protection against potentially penetrating bacteria

In deep cavities, however, especially if microexposure of the pulp cannot be excluded, the use of a calcium hydroxide preparation applied on the deepest part of the cavity is still recommended.

If a calcium hydroxide suspension is used for this purpose, then it should be covered by suitable glass ionomer cement.

Zinc Phosphate CementIf zinc phosphate is used instead of ZOE to

cement a crown or inlay, the phosphate cement is forced into the dentinal tubules

After 3-4 days, it creates a wide spread three-dimensional inflammatory lesion involving all the coronal pulp tissue.

A young tooth with wide – open dentinal tubules is more susceptible to intense response than an older tooth, which has produced sclerotic and reparative dentin that block’s the tubules.

Zinc phosphate cements elicits strong to moderate cytotoxic reactions that decrease with time after setting Leaching of zinc ions and a low pH is cause of these effects

Initial pH on setting is 4.2 at 3 minutes

The best protection against phosphoric acid penetration is provided by coating the dentin with two coats of an appropriate varnish, a dentin-bonding agent, or a thin wash of calcium hydroxide.

Calcium hydroxide plugs the dentin tubules and neutralizes acids; hydrophilic resin primers infiltrate the collagen mesh produced by acid-etching of the dentin and seal the patent dentin tubules.

These procedures eliminate 90% of the severity of the adverse pulp responses, making them similar to those of polycarboxylate cement

Polycarboxylate cementsThey cause slight to moderate response after 3

days.They are recommended only in cavities with

intact dentin

Zinc Oxide Eugenol cements

ZOE is recommended as a nontoxic reference substance in respective

Cox CF et al 1987 stated that eugenol from ZOE fixes cells, depresses cell respiration and reduces nerve transmission with direct contact

ZOE may form a temporary seal against bacterial invasion

It inhibits the synthesis of prostaglandin and leukotriens (anti-inflammatory)

Interaction of eugenol with vallinoid receptors on nerve cells playing an important role in nociception

Glass Ionomer Cement

When GIC first introduced, the pulpal response were classified as bland, moderate, less irritating than silicate cement, zinc phosphate cement.

The blandness of GIC is attributed to absence of strong acids of toxic monomers.

Polyacrylic acid and polyacids are much weaker than phosphoric acid and possess higher molecular weight that limit their diffusion through dentinal tubules to the pulp.

Tobias and other (1978), found that glass ionomer cements were less irritating than zinc phosphate cement, equivalent in irritancy to polycarboxylate cement and more irritating than zinc oxide cement.

Smith and Rusa (1986) compared the initial activity of GIC with zinc polycarboxylate and zinc phosphate cements and found a general rise in pH for all cements during first 15 minutes. However, the initial reactions of GIC’s were slower.

It is recommended that if there is less than 0.5-mm residual dentin or a pulp exposure, an appropriate lining of calcium hydroxide should be placed prior to the placement of a glass ionomer

Resin – based composite cements (Dual-Cure)

These are low viscosity resin cements, proper restoration seating with less pressure reduces the possibility for luting voids beneath stress bearing where fracture are most likely to occur.

Pameijir and Stanley (1992) compared the pulp responses to dual-cured (light cured and chemically, self-cured) agents. Only when the dual-cure resin cement received no visible light energy did the average pulp response levels exceed the accepted level of biocompatibility.

Conditioning (etching) agents: -Before a resin composite or a GIC restorative

material is placed, surface contaminants must be removed to permit the micro mechanical attachment or the ionic

exchange of the dental material with the tooth structure.

Brannstrom and Nordenvall (1977) noted no significant difference between dentinal surface conditioned for 15 seconds and those conditioned for 2 seconds and thus recommended shorter conditioning times.

Brannstrom (1981), showed that conditioning of dentin and removal of smear layer allows the ingress of bacteria and the outward flow of dentinal fluid within the tooth – material inter facial region resulting in biofilm formation that interfaces with adhesion.

Some scientists recommend that smear layer showed remain but in modified form, where as some other propose that the smear layer be completely removed.

Bowen and colleagues (1982) introduced mordanting solution (acidified ferric oxalate), that appeared to dissolve the original smear layer and replace it with a more uniform ‘artificial’ (altered) smear layer.

With the use of less concentrated acids with higher molecular weights and shorter time intervals for conditioning, pulp response is minimized.

Bonding Agents Bonding agents do not appear to be toxic

To enhance bonding to composite, a fast setting visible light cured, low viscosity (unfilled) resin primer is applied that infiltrates the demineralized dentin surface and the exposed collagen mesh to form hybrid layer.

The plugging of the dentinal tubules prevents the penetration of toxic components to the pulp from composite restorations.

Influence of Patient Age on Pulp response

As permanent teeth endure the effects of abrasion, caries and restorative procedure, the pulp becomes reduced in size because of deposition of secondary dentin, pulp stones and clarifications.

At age 55 years, the volume of pulp tissue is one fifth that at age 25 years and contains only one fifth of its former blood supply (Stanley, 1990)

If an inflammation develops in pulp of an aging patient, that pulp has less defense in resolving a lesion and resisting infection.

Pulps Responses to Clinical Procedures:Some clinicians observed that postoperative

pulpits could be reduced if restorations are luted with temporary cement before final cementation thus waiting for formation of reparative dentin.

More practical approaches are (1) the application of cavity liner, coating or base. (2) Sealing the dentin by infiltrating the conditional dentin with a primer.

Micro Leakage

Incomplete bonding or resin penetration into the collagen mesh of acid-etched dentin can lead to fluid ingress along gaps wider than 1 μm, which is referred to as microleakage.

Although this gap is only a few microns wide, it is wide

enough to permit bacteria to penetrate this interfacial space, since the average size of a Streptococcus bacterium is only about 1 μm in diameter.

The bacteria that migrate to the pulp may initiate an infection of pulp tissue. The gap also promotes material breakdown along the unsupported margin.

If the resin penetrates the collagen network of dentin but does not penetrate it completely, then a much smaller gap (less than 0.1 μm in most cases) will exist between the mineralized matrix of dentin and the collagen–resin hybrid layer.

This much smaller gap has been claimed to allow nanoleakage, which probably does not allow bacteria or bacterial products to penetrate the marginal gaps of the restoration and the pulp.

However, fluid exchange most likely occurs, and this may degrade the resin or the collagen network that is incompletely embedded with the resin, thereby reducing the longevity of the dentin–resin bond.

 Dentin Hypersensitivity

When the nerve endings in the odontoblastic layer and predentin, are injured by a restorative procedure, the healing process induces an enormous out growth of dendrites contributing to hypersensitivity.

Approximately, 21 days are required for complete regeneration of the nerve ending.

If symptoms disappear over time (7-12 weeks), this may mean sufficient reparative dentin has formed to block the tubules and eliminate postoperative sensitivity.

If symptoms persists, it may be due to Degradation of micro mechanical bond

Shrinkage of resin during polymerization

Exposure of patent dentinal tubules etc.

If patient experiences prolonged sensitivity and the composite is replaced with other material, the symptoms may soon disappear. This may result due to sealing of involved tubules.

Powell and colleagues (1990, 91), using teeth from adolescents and a few adults, found that the most severe postoperative pain occurred in females.

Pulp Capping:

Calcium Hydroxide:

Calcium hydroxide has been mainly used in pulp capping, pulpotomy, root amputation, apexificaiton and apexogenesis.

The cement is alkaline in nature. The high pH is due to presence of free hydroxyl ions in the set cement. The pH ranges from 11-13.

The following zones of tissue reaction can be observed histologically after application of calcium hydroxide for direct pulp capping:

Zone of obliteration (early changes, caustic effect, area of superficial debris)

Zone of coagulation necrosisThe line of demarcationEarly stages of dentin bridge formationCalcification of the bridge

The calcium-hydroxide-triggered coagulation necrosis seems to be a stimulus that is sufficient to initiate healing in the subjacent vital pulp tissue.

This process will then initiate the differentiation of cells to odontoblast-like pulp cells (secondary odontoblasts), which will finally result in a bridging.

Tunnel defects may cause a problem. These defects, which are located in newly formed

dentin, create tunnels and thereby open communications between the calcium hydroxide and the pulp and may act as access for bacteria.

This problem underscores that a tight restoration and sealing of the cavity is decisive for the success of a direct pulp capping. Bacterial infection is the most important reason for failure of a direct pulp capping

ENDODONTIC MATERIALSGUTTA PERCHA

Only highly purified gutta-percha should be used in patients with a latex allergy. If necessary, synthetic gutta-percha points can be applied (e.g., Synthapoints).

It may be concluded from these data that thermomechanical compaction (condensation), specifically at a higher rotational speed (>10,000/min), may damage the periodontal tissues.

ZOE SEALERSPatients with an allergy to eugenol (or to

fragrances) should not be treated with materials containing eugenol, isoeugenol, or Peru balm.

Data show that ZOE sealers are characterized by a moderate local toxicity, which is significantly increased if paraformaldehyde is added.

A number of case reports document that paraformaldehyde-containing ZOE sealers may cause an aspergillosis of the maxillary sinus when the root canals of upper posterior teeth are overfilled and the sealers are pressed into the maxillary sinus

Epoxy-based sealers

Epoxy-based sealers are initially toxic, but toxicity considerably declines when the materials are set,and then no tissue reactions, or only slight ones, are observed.

Epoxy-based sealers are initially toxic, but toxicity considerably declines when the materials are set, and then no tissue reactions, or only slight ones, are observed.

Calcium-Hydroxide-Based Sealers

CH sealers are characterized by a low toxicity, which occurs only in the initial period after application.

There is clear indication that these materials may stimulate the formation of hard tissue.

However, an inferior marginal adaptation together with microleakage due to increased solubility is a potential risk to be considered for this group of materials.

MTA

Endodontotic proceduresAs a consequence of pathologic changes in the

dental pulp, the root canal system can harbor numerous irritants.

As irritants are released from the root canal system into the periradicular tissue, granulation tissue proliferates and replaces normal periradicular tissues.

Removal of irritants from the root canal system and its total obturation results in repair of the periradicular tissue to its normal architecture.

Grossman indicated that ideal root canal filling material should meet the following requirements-

It should seal the canal laterally as well as apically

It should not shrink after being insertedIt should be impervious to moistureIt should be bacteriostatic or at least not

encourage growth It should not irritate periradicular tissue.It should be neither mutagenic or

carcinogenic

The sealers form a fluid – tight seal at the apex by fillingThe minor interstices between solid material

and the canal wallThe patent accessory canals.

A minimal reaction was found when the canal was not overfilled with sealant.

When the teeth were overfilled with sealant, there was persistent chronic inflammatory response.

Gulati et al 1990 stated that cytotoxicity of zinc oxide eugenol might be attributed to the fact that eugenolate

formed hydroxide in contact with tissue fluids and released free eugenol which was responsible for toxicity

Oswald and Cohn reported systemic distribution of lead contained in N2 – filled root canals in liver, kidney, adrenal gland and spleen.

Mittal et al 1999 attributed the toxicity of Sealapex to polymeric resin and for Endoflas FS to presence of eugenol and para monochlorophenol

AH26 resin sealer cause moderate to severe toxicity. This toxicity is due to release of formaldehyde during the initial setting reaction between bisphenol A resin and hexamethylene tetramine. (Span Burg et al 1993).

 Sealer efficacyAlthough all root canal sealers leak to some

extent, there is a critical level of leakage that is unacceptable for healing and may result in endodontic failure.

Leakage may occur at the interface of dentin and sealer, at interface of solid core and sealer, through the sealer itself etc.

If the apical surface can be blocked principally by a solid core material success is improved over time.

In most studies when obturation was done without sealers the leakage results were enormously greater.

Without question, all the materials used to seal root canal irritate periradicular tissue if allowed to escape from the canal.

Apical filling with dentin chipsIn advertently, dentin chips may produce an

apical plug when the materials are compacted

Dentin chips produced by endodontic procedure may occlude apical foramen.

To condense dentin chips deliberately constitutes a biologic seal rather than a mechanical chemical seal.

Such plug can prevent overfilling and can restrict the irrigating solution and obturating material to the canal spaces.

M. Mittal, Satish Chandra and Shallen Chandra

Comparative tissue toxicity evaluation of four endodontic sealers.

Journal of Endodontics.Vol.21, No.12, 1995, 622-62.

They evaluated the response of the tissue histologically to four root canal sealers Zinc Eugenol, Tubliseal, Sealapex and Endoflas. By injecting them into the subcutaneous connective tissue of dorsal surface of rats

This study concluded all the sealers caused some inflammation that decreased with time. Overall, Sealapex showed least inflammatory reaction compared with other sealers.

Kuo-wei Tai, and Yu-Chao Chung.

Cytotoxicity evaluation of perforation repair materials on human periodontal ligament cells in vitro.

Journal of Endodontics: Vol. 26, No.7, 2000, 395-97

 

They evaluated the cytotoxicity of amalgam, light-cured composite resin and light cured glass ionomers using cultured human periodontal ligament cells.

This study concluded that both the type of the material and time of contact affected the cell viability and proliferation of the cultured cells.

Composite resin exhibited most cytotoxic effects followed by glass ionomer and amalgam during 14-day incubation period

T.R. Pittford“Tissue reactions to two root canal sealers

containing formaldehyde”.

Oral Surg Oral Med Oral Pathol Oral Radiol Endod : 60 : 1985 : 661-665.

He investigated tissue response to tooth roots filled with N2 or Endomethasone root canal sealents in the premolar teeth of dogs. Periapical inflammation was a common finding with all the materials. It was most severe with Tubliseal (control) and least severe with Endomethasone.

R.S. Tobias et al

“Pulpal response to two semihydrous glass ionomer luting cements”

International Endodontic Journal, 1991., 24 : 95-107

This study compared the pulpal responses to two semihydrous glass ionomer luting cement (STA and ZIN) with those previously obtained for a anhydrous glass ionomer luting cement Aquacem.

ZIN contained zinc oxide in the formulation, study was conducted in vivo in ferrets. ZIN was associated with minimal pulpal response whereas STA was similar to Aquacem.