biocompatibility of dental materials dr.ramashanker associate professor deptt. of prosthodontic 3 rd...

BIOCOMPATIBILITY OF DENTAL MATERIALS

DR.RAMASHANKERDR.RAMASHANKER

Associate professorAssociate professor

Deptt. of prosthodonticDeptt. of prosthodontic

33rdrd nov2014 time-10-11am nov2014 time-10-11am

CONTENTS Introduction History Definition Requirements Tests for evaluation Allergic responses to dental

materials

Materials considered for biocompatibility

Physical factors affecting pulp health Summary References

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Introduction Biocompatibility :-

interaction between body & material

Body ↔ Material Placement of material

creates interface : dynamic Interface activity depends

on: - location of

material - its duration in

body - its properties - health of host

History Mid 1800’ s dentists tried

new materials for first time by directly putting them in patient’s mouth

eg. Fox : fusible metal-

bismuth, lead & tin-melted & poured in cavity preparation at appx.100o C

G.V. Black tried his new

ideas of restorative materials, like early amalgams in patients’ mouth

Concept of protecting patients- early 1960’s

Regulations & ethics introduced

Organisations like FDA,ANSI,ADA and ISO .

Definition

Being harmonious with life & not having toxic or injurious effects on biologic function.

(G.P.T. 8th edn.-2005)

Ability of the material to elicit an

appropriate biological response in a given application in the body (Kenneth J.A).

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Requirements for Dental Material Biocompatibility

Should not be harmful to pulp & soft tissues

Should not contain toxic diffusible substances

Should not produce allergic responses

Should not be carcinogenic

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Biomaterial

Any substance, other than a drug, that can be

used for any period as a part of a system that

treats, augments, or replaces any tissue,

organ or function of the body. (G.P.T. 8th edn.-

2005)

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Classification of Biomaterials from perspective of Biocompatibility

Those which contact soft tissues within the oral cavity

eg. Acrylic resin

Those which could affect health or vitality of pulp eg. Liner, bases

Those which are used as root canal filling materials

eg. Gutta percha

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Those which affect hard tissues of oral cavity

eg. Implants

Those used in dental laboratory eg. Nickel, chromium, cobalt

Classification of Biomaterials from perspective of Biocompatibility

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ADVERSE EFFECTS FROM DENTAL MATERIALS

• Classical biological reactions to materials are :

TOXICITY

INFLAMMATION

ALLERGY

MUTAGENICITY

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TOXICITY

Earliest response studied

Earlier material containing LEAD posed a risk to patient due to toxic property of lead

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INFLAMMATION

Involves activation of the host immune system

Histologically it is characterized by edema of the tissue with infiltration of acute & chronic inflammatory cells

ALLERGY Most common response that occurs when the body

recognizes a material as foreign

Reactions involves all dimensions of immune system

An allergic reaction results histologically in an inflammatory response that can be difficult to differentiate between non allergic inflammation or low grade toxicity .

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Allergy

Allergic Responses to Dental Materials

Allergic Contact Dermatitis

Allergic Contact Stomatitis

Allergy to Latex products

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Most common occupational disease

Susceptibility & prior sensitization necessary

Dose independent

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Usually occurs where body surface makes Usually occurs where body surface makes

direct contact with allergen.direct contact with allergen.

eg. Monomers of bonding agent-eg. Monomers of bonding agent-

distal part of fingers & palmer aspect distal part of fingers & palmer aspect

of fingertipsof fingertips

Acrylic component of dental cements, Acrylic component of dental cements,

nickel & resin monomers-allergic contact nickel & resin monomers-allergic contact

sensitizers.sensitizers.

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Patch Test Most definitive diagnostic test Suspected allergen applied to skin to produce small area

of allergic contact dermatitis After 48 to 96 hrs hyperemia, edema, vesicle formation & itching Positive reaction (Slavin and Ducomb,1989)

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Most common adverse reaction to Dental Materials

A) Local/contact type lesions

B) Systemic/distant lesions

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Common allergens :- chromium, cobalt, mercury, eugenol, components of resin based materials, & formaldehyde

Mouthwashes, dentifrices, lozenges, & cough drops cause burning, swelling & ulceration of oral tissues.

Lichenoid reactions :- Long-term effect in oral mucous membrane adjacent amalgam & composite resins.

(Bratel and Johntell,1994)


2323

Allergy to Latex Products

Polyether component-main causative agent

…March,1988

Dermatitis of hand (eczema) most common adverse reaction

Localized rashes & swelling to wheezing & anaphylaxis

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Repeated exposure & duration plays important role.

Most serious systemic reactions occur when gloves or rubber dam contact mucous membrane - generalized angioneurotic edema, chest pain, rash on neck or chest region and respiratory distress

…Blinkhorn and Leggate,1984

2525

Prevention: Use Vinyl gloves or gloves made of other synthetic polymer gloves:-

Polythene gloves. Powder free gloves. Nitrile gloves.

MUTAGENIC REACTIONS

• Mutagenicity results when the components of the material alter the base pair sequences of the DNA in cells

• Dental materials or components such as nickel,

copper, beryllium, some components of root canal sealers & resin based materials are mutagens

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KEY PRINCIPLES THAT DETERMINE ADVERSE EFFECTS

• Two key factors have paramount importance :

Metal Corrosion or Metal degradation Surface Characterstics

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CORROSION• Biocompatibility depends on degradation process• Biological response of corrosion products depends on:

Amount

Composition

Form

Location in tissues

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CORROSION • Biological environment in contact also

determines the corrosion property

for eg: salivary esterases accelerate breakdown of dental

resins Ingestion of acidic substances may alter corrosion

of alloys or ceramics

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SURAFCE CHARATERISTICS• Surface different from the Interior region • For eg: casting alloy

sealant• EFFECTS OF SURFACE :

Ti alloys promote osseointegration

Rough surface promotes corrosion

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Tests for Evaluation of Biocompatibility

Aim To eliminate any potential harm or damage to oral or

maxillofacial tissues from a product or any component of a product

To modify or control the use by manufacturer & operator to prevent cytotoxicity.

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Tests for Evaluation of Biocompatibility

Biocompatibility tests are classified on three levels (tiers) :-

1. Group I : Primary tests

2. Group II : Secondary tests

3. Group III : Usage tests

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Group I : Primary Tests

Advantages :- in vitro test, done in controlled experimental

condition Most rapid, economical & easily standardized Large scale screening

Disadvantages :- Lack of relevance to in vivo use of material Lack of immune, inflammatory & circulatory

system

Cytotoxicity Tests

Material in a fresh or cured state → placed directly on tissue culture cells or on membranes overlying them.

e.g.. Agar (Agar overlay technique)

Barriers like dentin disks

Genotoxicity Tests

Determines carcinogenic/mutagenic potential

Carried out on mammalian or non-mammalian cells, bacteria, yeasts, or fungi.

Evaluates gene mutations, changes in chromosomal structure & other DNA or genetic changes caused by dental materials.

Genotoxicity Tests

Ames Test :-

-Material is tested with mutant histidine dependant bacteria

-Agent is added to culture medium consisting salmonella typhimurium mutant gene which cannot produce histidine

-If carcinogenic :- salmonella species reversed to original state, i.e.... start producing histidine again

Group II : Secondary Tests Advantages :- Intact biologic system to respond to a material Provide important bridge between in vitro

environment & clinical use of material

Disadvantages :- More expensive & difficult to control Time consuming Ethical concerns

Group II : Secondary Tests

1. Systemic toxicity test :- Material administered to test animals e.g.. Rats-

orally or i.v.

If > 50% animals survive material is

safe


2. Skin irritation test :- Irritation is inflammation without intervention of

antibody or immune system.

Material held in contact with shaved skin of rats

for 24 to 90 days

Erythema & edema are examined & confirmed.


3. Skin Sensitization test :-

Sensitization is inflammatory response requiring

participation of an antibody system specific for

material allergen. Done similar to irritation tests


4. Inhalation toxicity test :- Performed on rats, rabbits or guinea pigs in

exposure chamber with aerosol preparations by releasing spray material around head & upper trunk of animals.

Death within 2 to 3 min. very toxic

No death safe for human application

Group II : Secondary Tests 5. Implantation test :- Only used for testing implants & endodontic

materials. Material placed subcutaneously,intramuscularly, or

as a bone implant at lateral cortex of femur or tibia or both

Histopathological examination has to be done Observation period may be upto 1 year.

IMPLANTATION TEST

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Group III : Usage Tests Advantage :- Material placed in an environment clinically relevant to

its use in clinical practice

Disadvantages :- Extremely complex & difficult to perform Exceptionally expensive & very time consuming Ethical concerns

In animals : usage tests In humans : clinical trials

Classical progression of biocompatibility tests

Newer schemes for progression of biocompatibility tests

VARIOUS DENTAL MATERIALS CONSIDERED FOR

BIOCOMPATIBILITY

Metals : Amalgam & mercury

Nickel

Beryllium

Gold

Resins : Acrylic Resins

Chemically cured composite resins

Light cured composite resins

Cements : Silicate cement

Zinc Phosphate cement

Glass ionomer cement

Zinc oxide Eugenol cement

Miscellaneous : Impression materials

Implant materials

Amalgam & Mercury Mercury itself has no effect on pulp

Pulp response related to condensation pressure

Rate of diffusion into enamel & dentin-inversely related to degree of mineralization.

Mercury Elemental mercury, Inorganic ion & Methyl mercury

Methyl mercury :-formed by biologic action of elemental mercury; Absorbed 100% in gut; Most toxic

Elemental mercury absorbed less than 0.01%

65% to 85% mercury vapor that is inhaled is retained in body

Mercury Levels in Blood

Subjects with amalgam restoration 0.7ng/mL Subjects without amalgam restoration 0.3ng/mL

Lowest level at which earliest 35ng/mL non-specific symptoms occur

Mercury Hazard to Dental Personnel

Via inhalation & skin contact (allergic contact dermatitis)

Accidental spillage Handling with bare fingers Improper storage Improper retrieval of spilled mercury or waste

amalgam Faulty equipment

Acute mercury poisoning :-

Rare; stomatitis & diarrhoea

Chronic mercury poisoning :-

Weakness, fatigue, anorexia, wt. loss, insomnia,

irritability, shyness, dizziness & tremors in extremities.

Methyl mercury poisoning :-

Paresthesia of extremities, lips & tongue; ataxia (gait disturbance), & concentric constriction of visual fields (Tunnel Vision)

Recommendations in Mercury Hygiene1. Store in unbreakable tightly sealed containers

2. Clean-up spilled mercury immediately

3. Do not handle with bare hands

4. Salvage all amalgam scrap & store it under water

5. Use water spray & suction while grinding

6. Do not use ultrasonic condensers

7. Periodic mercury vapor level determination in clinic

8. Alert health personnel about hazards of mercury

9. Use of rubber dam

10. Provide adequate ventilation

Nickel

Most common cause of allergic dermatitis

Female : Male :: 10 : 1 Intraorally : little chance

of allergy Nasal & sinus cancer

among nickel refinery workers due to nickel carbonyl

Beryllium

Component of base metal alloys

Highest risk to dental technicians during melting & trimming of alloy

Berylliosis : inflammatory lung disease due to inhalation of beryllium dust or fumes

Beryllium

Prevention :

• Confirm allergy by Patch test

• Avoid base metal restorations in patients with known allergy

• Good ventilation & exhaust

Gold

Pure gold is inert

Allergy to gold is very rare

(1 in 1 million)

Cements

Acrylic Resin

Cause allergic reactions (denture stomatitis) when used as denture base material or provisional fixed partial denture resin

Highest risk for dental professionals due to frequent exposure to unpolymerized monomer

Chemically Cured Resin Composites Require use of matrix pressure to enhance adaptation to

cavity walls : Potential pulp irritant

Chronic pulpitis : persists for indefinite period, after

2 to 3 weeks, develop massive pulp lesion

Thin coating of hard setting Ca(OH)2 cement recommended for deep cavities

Light-Cured Resin Composites Visible light cured systems : greater depth of cure, shorter

curing time, less porosity & more wear-resistant restorations than UV light cured systems less pulp response

Use twice the recommended time exposure to light

Conservative cavity preparation & incremental curing;

no need for matrices & pressure, to gain adaptation

less toxicity to pulp

Impression Materials Irreversible hydrocolloids :- Inhaling fine airborne

particles (dust) can cause silicosis & pulmonary hypersensitivity.

Dustless/Dustfree alginate is preferred

Elastomers :- Cellular toxicity levels

Polyether > Addition Silicone > Polysulphide

Implant Materials

Commercially pure Titanium & its alloys are the most biocompatible restorative materials

Bio-glass ceramics used as implant materials also exhibit good biocompatibility

Implant Materials

Osseointegration :- Materials have very low degradation rates, & tend to form surface oxides that promote bony approximation within 100Ao space

eg. Titanium, tantalum, several forms of ceramics

Biointegration :- Materials undergo degradation to promote bone formation without any intervening space

eg. Bio-glass ceramics

PHYSICAL FACTORS AFFECTING PULP HEALTH

Microleakage

Free penetration of fluids, micro-organisms & oral debris along interface between restoration & tooth, progressing down the walls of cavity preparation

It can result in :-

1. Secondary/Recurrent caries acute/chronic pulpitis, pulp abscess, etc.

2. Staining or discoloration 3. Sensitivity due to continuing Pulpal irritation

Nanoleakage vs Microleakage

Prevention:- 1. Use bonding/adhesive techniques for better adaptation

of restoration to tooth surface

2. Regular monitoring of restoration

3. Use cavity varnish below amalgam restoration

(leakage space filled by corrosion products thereby sealing cavity : but requires much time)

Thermal Changes Temperature fluctuations in oral cavity may crack

restorative material or produce undesirable dimensional changes Microleakage

Thermal conductivity & coefficient of thermal expansion

Metals are good conductors of heat, causing sensitivity with large metallic restorations

eg. Amalgam or gold inlays Provide suitable base

Galvanism Flow of current when two

dissimilar metallic restorations oppose each other in oral cavity

Due to different electromotive potentials of opposing metals

Saliva acts as electrolyte

Contact Short-circuit current flows through pulp Pain & Discomfort

Current falls off if fillings are maintained in contact due to polarization of cell

Pain perception depends on patient sensitivity rather than magnitude of current

Magnitude of current depends on composition & surface area of metals

eg. Alloy of stainless steel develop higher current density than

gold or cobalt-chromium alloys when in contact with amalgam

Galvanism

Galvanism

As size of cathode (eg. gold alloy) increase relative to anode (eg. Amalgam), current density increases

Larger cathode enhances corrosion of smaller anode Current density in non-gamma2 containing amalgam is

less than gamma2 containing amalgam

Prevention :- Placement of insulating base Applying varnish on cavity walls Proper planning of restoration

Estrogenicity

• Ability of a chemical to act in the body in a manner similar to that of an estrogen.

• Bisphenol A –xenoestrogen may act on estrogenic receptors in cells.

• E-screen assay –relies on growth response of breast cancer cells that are estrogen sensitive .

Summary

Clinical Guidelines for selecting biocompatible materials :

Define the use of material

Define how the material has been tested

Think in terms of Risk & Benefit

Conclusion

Benefits Benefits RisksRisks

ClinicalClinicalJudgementJudgement

References:-1) Philips’ Science of Dental Materials

- Kenneth J. Anusavice

2) Dental Material Sciences

- Combe

3) Dental Materials – Properties & Manipulation

- Craig

4) Color Atlas of Oral Pathology – 4th Edition

- Robinson & Miller

5) Essentials of Oral Pathology & Oral Medicine

- Cawson & Odell

Thank YouThank You

For a For a PatientPatient

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biocompatibility of dental materials dr.ramashanker associate professor deptt. of prosthodontic 3 rd...

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