Contents

Introduction Relevance to dentists Tests for evaluation of biocompatibility Craig’s classification of tests Advantages – disadvantages of tests Standards that regulate the measurement of

biocompatibility

Pulpal responses to specific agents and techniques. Reaction of oral soft tissues to restorative materials Reaction of bone and soft tissues to implant material Biocompatibility of metals

Biocompatibility is defined as “the ability of a material to elicit an appropriate biological response in a given application in the body”.

The term “Biocompatible” is defined in Dorland’s Medical Dictionary as “being harmonious with life and not having toxic or injurious effects on biologic function”.

In general, biocompatibility is measured on the basis of

– Toxicity [such as pulp and mucosal response], – Inflammation, – Allergic responses and – Mutagenic reactions.

Requirements of a biocompatible dental material

It should not be harmful to the pulp and soft tissues. not contain toxic diffusible substances that can be released and

absorbed into the circulatory system to cause a systemic toxic response.

be free of potentially sensitizing agents that are likely to cause an allergic response.

have no carcinogenic potential.

Whether a material is biocompatible or not is dependent on what physical function.

RELEVANCE TO DENTISTS

Dentists potential concerns about biocompatibility can be organized in to 4 areas:

1) Safety of the patient

Ex: Alloys, resins and cements.

2) Safety of Dental staff

Ex: Amalgam – Mercury vapour.

Chronic exposure to latex and resin based materials.

3) Regulatory compliance issues Biocompatibility issues are closely linked to regulations

that affect dental practice.

Ex: Dental amalgam. Because of the biologic concerns about mercury,

regulators have considered monitoring and restricting amount of mercury in waste water for dental practice.

4) Legal Liability Biocompatibility issues also influence liability issues that

affect dental practitioners. Because dental materials can affect the well-being of

patients and dental auxillaries, practitioners assume a legal risk when using these materials.

ELEMENTS INVOLVED AND INTERFACES

Tests for evaluation of Biocompatibility

The purpose of biocompatibility tests is to eliminate any potential product or component of a product that can cause harm or damage to oral and maxillofacial tissues.

Biocompatibility tests are classified on three levels, with the most rapid and economical occurring at primary level.

Group I : PRIMARY TESTS

Group II: SECONDARY TESTS

Group III: PRE-CLINICAL USAGE TESTS

Animal testsIn vitro tests Usage tests

Direct Indirect

Biocompatibility Tests

Tests for evaluation of Biocompatibility:Craig classification

Skin sensitization tests

Mucous membrane irritation tests

Cytotoxicity tests Tests for cell metabolism or cell function Tests that measure immune function Muagenesis assays

Group I : PRIMARY TESTS

The primary tests consist of cytotoxic evaluations either in direct or indirect methods.

Genotoxicity Test Mammalian or non mammalian cells, bacteria, yeasts or

fungi are used to determine whether gene mutations, changes in chromosomal structures or other deoxyribo nucleic acid or genetic changes are caused by the test materials, devices and extracts from materials.

Group II: SECONDARY TESTS

At this level the product is evaluated for its potential to create systemic toxicity, inhalation toxicity, skin irritation and sensitization and implantation responses.

In systemic toxicity tests such as oral median lethal dose test, test sample is administered daily to rats for 14 days either by oral gavage or by dietary inclusion. If 50% of animals survive, the product has passed the test.

The inhalation toxicity tests are performed in an exposure chamber with aerosol preparations by releasing the spray material around head and upper trunk of animals.

The animals are subjected to 30 seconds of continuous spray released at 30 minute interval. After 10 consecutive exposures, the animals are observed over a 14 days period. If any animal dies within 2-3 minutes, the agent is considered very toxic.

Implantation tests

The animal species is selected according to the size of the implant test specimen and the intended duration of the test in relation to the life span of animal.

Short term tests ( 12 weeks) Mice, rats, guinea pigs

Long term tests ( Weeks) dogs, rabbits, sheep, goats.

Group III : PRE – CLINICAL USAGE TESTS

Pulp and Dentin Usage test This test is designed to assess the biocompatibility of dental

materials placed in dentin adjacent to the dental pulp. Class V cavity preparations are done to leave 1mm or less of tubular dentin between the floor of cavity preparation and pulp.

The appropriate number of cavities are restored, and some are retained for control specimens.

The animals are sacrificed after 7 days, 28 3 days and 70 5 days.

After routine histopathologic processing, specimens are graded for degree of inflammatory response to prevalence of reparative dentin formation in pulp and the number of microorganisms (microleakage) entrapped in the surrounding cavity walls and cut dentinal tubules.

Pulp Capping and Pulpotomy Usage test

In this test procedure pulp is merely exposed for the pulp capping evaluation and is partially removed for pulpotomy assessment.

A Ca(OH)2 product is used as a negative control. The

animals are sacrificed after 7 2 days 70 5 days. Observations are made of dentinal bridge formation

adjacent to or sub adjacent to the applied material.

Pulpotomy

Pulp capping

Endodontic usage test

Root canals are replaced by obturating test material and control material. ZOE alone or ZOE combined with a sealer is used as control material.

The animals are sacrificed after 28 3 days and 13 Weeks. For a biocompatible material, one should observe minimal or

no response.

Standards that regulate the measurement of Biocompatibility

ADA established guidelines 1926. In 1972 the council on Dental materials, instruments, and

equipment of ANSI/ADA approved Document No. 41 for recommended standard practices for biological evaluation of Dental materials.

Three categories of tests are described in the 1982 ANSI /

ADA document: initial, secondary and usage tests.

Initial tests include invitro assays for cytotoxicity, red blood cell membrane lysis (hemolysis) mutagenesis and carcinogenesis at the cellular level.

Secondary tests (in-vivo) for inflammatory or immunogenic potential.

Finally, materials that pass secondary tests and still hold potential are subjected to one or more in vivo usage tests.

ISO 1993

It contains 12 parts, each dealing with a different aspect of biological testing.

This standard divides tests into “initial” and “supplementary” tests to assess the biological reaction to materials.

-Initial tests for cytotoxicity, sensitization, systemic toxicity.

-Supplementary tests are tests such as chronic toxicity, carcinogenicity and biodegradation.

Pulpal Responses to specific Agents and Techniques

I. AMALGAM While placing a conventional amalgam restoration,

pressure of condensation will intensify the initial minimal inflammatory response and it will subsequently increase the formation of reparative dentin.

II Chemically Cured Resin Composites

The addition of mineral fillers to the direct filling chemically cured resin composites did not reduce their potential for creating severe pulp responses.

If not lined properly, they cause chronic pulpitis that persists for an indefinite time.

III Visible light Cured Resin composites

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

Precautions:

1) Use twice the recommended time exposure

2) Cure in increments.

IV Zinc phosphate cement

As a base more toxic than as a luting agent. A young tooth with wide open dentinal tubules is more

susceptible. Coat the dentin with two coats of an appropriate varnish, dentin

bonding agent, liner, or a thin wash of calcium hydroxide.

V. Zinc oxide eugenol cement

In vitro, eugenol from ZOE, depresses cell respiration and reduces nerve transmission with direct contact.

The concentration of eugenol in cavity preparation just below ZOE is bactericidal, the concentration on the pulpal side of dentin may be less.

This lower concentration reportedly suppresses nerve transmission and inhibits synthesis of prosta glandins and leukotrienes. [anti inflammatory]

VI. Glass lonomer cement

Polyacrylic acid and related poly acid are much weaker than phosphoric acid, as polymers, they possess higher molecular weights that may limit their diffusion through the dentinal tubules to the pulp.

VII. Conditioning (etching) Agents

Conditioning procedures are used with both resin composite systems and GIC’s.

Conditioning techniques that are associated with weaker acids, shorter periods of application, and elimination of subbing and scrubbing procedures produce a minimal pulp response.

VIII. Bonding Agents Many of these reagents are cytotoxic to cells invitro if tested

alone. When placed on dentin and rinsed with tap water between

applications of subsequent reagents, cytotoxicity is decreased.

Long term in vitro studies suggest that components of many bonding agents permeate up to 0.5 mm of dentin to cause significant suppression of cellular metabolism for up to 4 weeks after their application.

IX. Liners, Varnishes and Non-resin Cements

Calcium hydroxide cavity liners 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.

Necrosis to a depth of 1mm

Neutrophil infiltration.

Coagulation of hemorrhagic exudates of superficial pulp.

after 5-8 weeks only slight inflammation remains.

Necrotic zone Dystrophic calcification

Stimulus for dentin bridge formation

The initial response of exposed pulpal tissue to highly alkaline aqueous pulp – capping agents.

X Bleaching Agents

These agents usually contain some form of peroxide (generally carbamide peroxide).

Invitro studies have shown that peroxides can rapidly traverse the dentin in sufficient concentrations to be cytotoxic.

Studies showed that peroxides rapidly even penetrate intact enamel and reach the pulp in a few minutes and occurrence of tooth sensitivity is very common.

Reaction of other Oral soft tissues to restorative materials

Released products of restorative materials also contribute either directly or indirectly to this inflammation, particularly in areas where the washing effects of saliva are less such as inter proximal areas, in deep gingival pockets or under removable appliances.

Cements – cytotoxicity - decreases substantially with time. The buffering and protein – binding effects of saliva.

Composites are initially very cytotoxic in invitro tests of direct contact with fibroblasts. This is primarily from unpolymerized components in the air – inhibited layer that leach out from the materials.

Amalgam restorations carried in to gingival crevice may cause inflammation of gingiva because of products of corrosion or bacterial plaque.

Denture base material

Denture base materials, especially methacrylates - immune hypersensitivity reactions of gingiva and mucosa.

The greatest potential for hypersensitization is for dental and laboratory personnel who are exposed repeatedly to a variety of unreacted components.

Soft denture liners

Plasticizers which are incorporated into some materials to make them soft and flexible, are released in vivo and in vitro.

In animal tests, several of these materials have caused significant epithelial changes, presumably from the released plasticizers.

Reaction of Bone and soft tissues to implant materials

There are four basic materials used in implant

fabrication : ceramics, carbon, metals and polymers

Reactions to Ceramic Implant Materials

Most ceramic implant materials have very low toxic

effects on tissues, either because they are in an oxidized

state or are corrosion resistant.

These are toxic and are non imunogenic and non

carcinogenic.

Reactions to pure Metals and Alloys

A variety of implant materials has been used, including

stainless steel, chromium cobalt – molybdenum and titanium and

its alloys.

Titanium is a pure metal which forms a thin film of

various titanium oxides, which is corrosion resistant and allows

bone to osseo-intregrate in the soft tissue.

Peri-implantitis is now a documented disease around

implants and involves many of same bacteria as periodontitis.

BIOCOMPATABILITY OF METALS

BERYLLIUM Although the beryllium concentration in dental alloys

rarely exceeds 2 wt % the amount of beryllium vapor released in to the breathing space during melting of Ni-Cr-Be alloys may be significant over an extended period.

The risk of beryllium vapor exposure is greatest for dental technicians during alloy melting especially in the absence of an adequate exhaust and filtration system.

High levels of beryllium have been measured during finishing and polishing when a local exhaust system was not used. They were reduced to levels considered safe when exhaust fan was used.

Exposure of beryllium may result in acute and chronic forms of beryllium disease – BERYLLIOSIS

Clinical features Symptoms range from coughing, chest pain and general

weakness to pulmonary dysfunction.– Contact dermatitis– Chemical pneumonitis

NICKEL

It is a great concern to dental patients with a known allergy to this element.

Dermatitis resulting from contact with nickel solutions was described as early as 1989.

Inhalation, ingestion and dermal contact of nickel or nickel containing alloys are common because nickel is found in environmental sources such as air, soil and food as well as in synthetic objects such as coins, kitchen utensils, and jewellery.

Nickel allergy was determined by a standard patch test consisting of 5% Nickel sulfate solution or 5% Nickel sulfate solution on a petrolatum base, in centre portion of a square band-aid.

This is applied on medial aspect of upper arm, which was cleaned with a alcohol swab. This is left in place for 48hr undisturbed. A plain band-aid acts a control.

It is read after 20 min.

0 no reaction.

+ erythema is seen.

++ erythema, papules are seen.

+++ erythema, papules, vesicles are seen.

++++ edema with vesicles is seen.