COLLEGE OF DENTAL SCIENCES

DEPARTMENT OF CONSERVATIVE DENTISTRY AND ENDODONTICS

SEMINAR ON

“BIOCOMPATIBILITY OF DENTAL MATERIALS”

Presented By : -

Dr. Sharno Mathai Varghese

1

CONTENTS

INTRODUCTION

REQUIREMENTS

TESTS FOR EVALUATION

ALLERGIC RESPONSE TO DENTAL MATERIALS

PULPAL REACTIONS TO RESTORATIONS

o ZINC PHOSPHATE CEMENT

o ZINC POLYCARBOXYLATE CEMENT

o ZINC OXIDE EUGENOL CEMENT

o GLASS IONOMER CEMENTS

o SILICATE CEMENTS

o CALCIUM HYDROXIDE CEMENTS

o VARNISHES

o FILLED AND UNFILLED RESINS

o AMALGAM

PULPAL RESPONSE TO VARIOUS STIMULI / CARIES

CONCLUSION

BIOCOMPATIBILITY OF DENTAL MATERIALS

INTRODUCTION :

The term biocompatible is defined as being harmonious with life and not

having toxic or injurious effects on biologic function. In general,

biocompatibility is measured on the basis of localized cytotoxicity (such as

pulp and mucosal response), systemic responses, allergenicity and

carcinogenicity.

REQUIREMENTS :

1) It should not be harmful to the pulp and soft tissues.

2) It should not contain toxic diffusible substances that can be released and

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

3) It should be free of potentially sensitizing agents that are likely to cause

an allergic response.

4) It should have no carcinogenic potential.

Tests for evaluation :

Group I tests – consist of cytotoxic evaluation in which dental material in a

fresh or cured state are placed directly on tissue culture cells or on membranes

that leach through the barriers.

Eg. Genotoxicity test : Mammalian and non mammalian cells. Bacteria, yeast,

fungi cells are used to determine whether change in chromosome structure,

gene mutation are caused by test materials.

Group II : Secondary tests : The product is evaluated for its potential to create

systemic toxicity.

Eg. Oral median lethal dose, irritation, implantation tests. Dermal toxicity.

Group III : Preclinical usage tests : Approval of the product after it has

successfully pass the primary and secondary tests on the basis that the product

would not be harmful to humans.

1

Eg.

a) 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 is prepared to leave 1 mm or less of tubular dentin

between the floor of cavity preparation anterior the pulp).

b) Pulp capping and pulpotomy usage test (pulp is partially removed / pulp

is merely exposed).

c) Endodontic usage test (Pulp is partially or completely removed and

replaced by the obtaining material. The degree of inflammation is

evaluated).

Allergic Responses to Dental Materials :

a) Allergic contact dermatitis :

Seen commonly first by primary physicians. It is a skin condition caused

by simple chemical insult to the skin. An allergic contact dermatitis associated

with monomers of bonding agent frequently involves the distal parts of the

fingers and patman aspects of finger tips.

Allergy to Latex Products :

Hypersensitivity to latex containing products may represent a true latex

allergy or a reaction to accelerates and an antioxidants used in latex processing.

Thiuram is a chemical used in the fabrication of latex articles that has also been

reported to cause allergic reactions.

Polyether component : Allergy. Localized rashes, Wheezing, Anaphylaxis.

Allergy Contact Stomatitis :

It is the most common adverse reaction to dental material.

It may be local or at distant site.

Dental material contain many components known to be common

allergens, such as chromium cobalt, mercury, eugenol, components of resin

2

based materials, formaldehyde. People who are sensitive to formaldehyde may

develop enhanced tissue responses under this condition.

Free residual methyl methacrylate monomer in autopolymerized acrylic

dentures can cause allergic reactions (to avoid it, dentures are immersed in

water for 24 hours)

Allergic reaction is associated with resin based materials. The

polymerization of composite materials is never complete, there is a percentage

of reactive groups do not participate in polymerization. The incomplete

polymerization of a resin restorative material may predispose to material

degradation. Degradation and wear of the materials release components of the

resin based materials and these may cause reaction both locally and

systemically.

Adverse Reaction :

- Gingival reactions.

- Lichenoid reactions.

Mercury : Minamata Disaster of early 70’s in Japan.

Symptom weakness, fatigue, anorexia, weight loss, insomnia, dizziness,

tremors. 35 g/mL – lowest level of total blood Hg at which non specific

symptoms occur.

Dental Iatrogenesis :

Creation of side effects, problems or complications resulting from

treatment by a physician or dentist.

A favourable situation requires that the intensity of a pulp response, if

any, should be higher initially and decrease with increasing postoperative time

intervals.

3

In most instances, 2 mm of dentin thickness provides an adequate

insulating barrier against traumatic thermal operative techniques and irritating

components of most restorative materials.

At low speed handpiece 6000-20,000 rpm air water sprays a cavity

preparation 2 mm from pulp elicit minimal pulp lesion. At high speed > 50,000

rpm, with adequate low pressure air H2O spray, the pulp response is greatly

reduced.

Pulpal reactions to restorations and various restorative materials.

Some of the properties of materials that might be capable of producing

injury mainly includes ;

a) Acidity

b) Absorption of water during setting

c) Heat evolved during setting

d) Poor marginal adaptation resulting in bacterial contamination.

Plant and Jones (1976) found that pulpal response beneath a material is

not associated with the materials, hydrogen ion concentration. The acid present

in restorative material is probably neutralized by dentin and dentinal fluid.

However placement of an acidic material such as ZnPO4 at luting consistency

in a deep cavity may have a toxic effect on pulp since the diffusion barrier is

extremely thin. They found out that ZnPO4 current showed greatest

temperature rise – an increase of 2.14oC. This amount is not sufficient to

produce tissue injury.

Absorption of water – but compared with removal of fluid from dentin

by an air stream, this injury is insignificant.

In current thinking, pulpal injury is primarily due to microleakage

through gaps between filling material and walls of cavity.

In general, dental materials do not adapt to tooth structure well enough

to provide a hermitic seal. Bacteria may penetrate the gap and create toxic

4

products that can diffuse through the dentinal tubules that evoke an

inflammatory reaction. This has been found to be a major cause in pulpal

injury.

Watts A. (1979) showed that materials such as composite resins,

silicates produced only a localized tissue reaction when placed directly on

exposed pulp in germ free animals.

Brannstrom (1979) found that bacteria did not grow when the outer

portion of restorations were replaced with ZnO eugenol. When bacterial

growth was inhibited, pulpal inflammation was negligible.

Two important factors affecting marginal adaptation are temporary

changes and masticatory forces. If a material was a different coefficient of

thermal expansion than tooth structure, temperature change is likely to produce

gaps between material and cavity wall.

Since at present time, there is no material that can bond chemically to

dentin and thus prevent leakage, the use of a cavity liner to seal dentin is highly

recommended.

Factors that determine whether bacterial growth injure the pulp includes ;

- Pathogenicity of microorganisms.

- Permeability of underlying dentin.

- Ability of irritated pulps to produce reparative dentin.

The antibacterial properties of filling materials may be of considerable

importance (ZnO eugenol, Ca(OH)2, polycarboxylate cements).

Dentin permeability increase with increasing cavity depth due to

difference in size and number of dentin tubules. For most materials, 2 mm of

remaining dentin affords adequate pulp protection.

Coefficient of thermal expansion.

5

If a restoration has a different coefficient thermal expansion than tooth

structure, temperature change is likely to produce gap formation between

material and cavity wall.

Ceramics : 1- 15 ppm/oC

Metals : 10-30 ppm/oC

Polymers : 30-600 ppm/oC

Amalgam : 25 ppm/oC

Tooth : 9-11 ppm/oC

It is important that the CTE of a restorative material be as near as that of tooth

structure.

Microleakage : Is found to occur around all the restorative materials being used

because no material truly adheres to tooth structure. The clinical symptoms are

sensitivity and recurrent caries.

Galvanism : Presence of metallic restoration in mouth cause galvanism. There

is difference in potential between dissimilar fillings resulting in pain.

Thermal Conductivity :

If tooth structure is replaced with metallic restorations, which tend to be

thermal conductors, then it is important to place additional thermal insulator to

protect the pulp from rapid increase or decrease of temperature in the mouth.

Generally, dental cements are used as bases. Dental pulp can withstand small

temperature changes (37oC – 42oC) for relatively short periods (30-60 seconds0

without any permanent damage.

Pulpal reactions to various restorative materials.

ZnPO4 cement : Acts as a luting agent. Commonly used to retain crowns,

inlays, onlays, bridges, orthodontic bands, used as base and temporary

restorative material.

ZnPO4 is considered to be the most irritating of all the intermediary base

materials.

6

a) Acidity during setting : pH of ZnPO4 liquid is approximately 2. As soon as

powder and liquid are combined, the pH level begins to rise 3 minutes after

start of mixing, the pH is approximately 3.5 – 4. The pH then increases rapidly,

but still is only 5.5 at 24 hours, it may take 24 hours before neutrability (7) is

attained. The pH is lower and remains lower for a longer period when thin mix

is employed.

Acidity can be reduced by increasing P:L ratio, increasing surface area

of contact with dentin to take full advantage of buffering capacity of dentin.

The others are microleakage, exothermic heat, depletion underlying

dentin from part of its calcium content.

Studies have shown that in young teeth in wide open dentinal tubules,

the acid from cement can penetrate a dentin thickness as great as 1.5 mm and

result in an intense inflammatory response.

Polycarboxylate Cement :

Uses : Permanent cementation of crowns and bridges, orthodontic bands,

stainless steel crowns and for root canal fillings, cement base.

It has excellent biocompatibility, potential adhesion to tooth structure.

Although polycarboxylate cement liquid, is more acidic than ZnPO4

liquid (1.7), it is neutralized more rapidly during setting process. Polyacrylic

acid has relatively high molecular weight, it is restricted from diffusing through

the dentinal tubules.

Histological studies reveal that the polycarboxylate cements cause a

pulpal response similar to that caused by ZnO eugenol, with a slight to

moderate response after 3 days and only mild, chronic inflammation after 5

weeks, regenerative dentin formation is minimal, they are recommended in

cavities with intact dentin in the floors of the cavity preparation.

7

Zinc Oxide Eugenol : Used as temporary and permanent luting agent, root

canal sealer, thermal insulating base, temporary restorative material,

periodontal pack.

The reason that ZnO eugenol is a good temporary cement and causes

only a mild reaction in pulp is that ;

a) pH is approximately 7 at the time, they are inserted into the tooth.

b) It adapts very close to dentin, thus providing a good marginal seal.

c) Its antibacterial properties inhibits bacterial growth on cavity walls.

When ZnO eugenol comes in direct control with the pulp tissues,

following reaction takes place.

1) Chronic inflammation may remain limited, the area will be walled off by

fibrous tissues followed by matrix formation, mineralization and

bridging of the exposure.

2) Chronic inflammation may propogate to involve all pulp and root canal

tissues with slow, symptomless necrosis.

3) Chronic inflammation may lead to complete fibrosis of pulp and root

canal tissues leaving pulp dentin organ susceptible to any irritation and

with little or no defense.

4) Chronic inflammation may change to acute inflammation leading to

necrosis of pulp and root canal tissues.

Eugenol is slightly acidic and produces palliative or obtundant actions

on the pulp in low concentration. Since eugenol injures cells, one must use

Ca(OH)2 cavity liner in very deep cavity preparation where there is risk of pulp

exposure.

Glass Ionomer Cements :

Used both as luting agent and as a restorative material. They elicit

greater pulp reaction than ZnO eugenol but less than ZnPO4. It contains

polyacrylic acids which are weaker than phosphoric acid and possess higher

molecular weight that may limit their diffusion through the dentinal tubules.

8

However the luting agents pose a greater hazard because of lower

powder : liquid ratio 1.25 – 1.5 g/ml of liquid and a slower setting reaction.

Post operative sensitivity has been associated with cementation of full cast

crowns. It has been suggested that the hydraulic pressure generated during

seating may force some of liquid into the dentinal tubules.

At the time of initial mixing, the cement is highly acidic and have the

potential to produce post operative sensitivity and pulpal irritation. The final

pH value reaches 6-7. Pulpal studies indicate that glass ionomer cements cause

a mild, inflammatory response which is normally resolved in 30 days.

Silicate Cements :

The pH of the liquid is less than 2 and may be as low as 1. After the

liquid and powder are mixed and material is ready for insertion, the pH is less

than 3 and remains below 7 even after 1 month.

Silicate cement is highly irritating to pulp. The pulps of younger

persons are more likely to react severely to these cements than the pulp of older

persons.

A non-irritating base, such as ZnO eugenol should be used under

silicates.

Ca(OH)2 can be an irritant to the pulp if it comes in contact with it. The

irritating ingredients and characteristics could be the forces with which the

material is introduced into the pulp tissue and high alkalinity of the material. If

the effective depth is 100 micrometer or more, a healthy reparative reaction can

be expected.

When Ca(OH)2 comes in contact with the pulp tissues, the layer of tissue

that its contacts directly will undergo chemical necrosis (Coagulation). To

anticipate a favourable pulpal reaction, the following criteria must be met ;

9

a) the pulpal tissue must exhibit no signs of degeneration and have

sufficient vascularity, cellularity.

b) Ca(OH)2 must not be pushed inside the pulp chambers and root canal

space, thereby increase the area to be bridged by reparative dentin.

c) The microbial status at exposure site cannot be controlled.

If these criteria are fulfilled, the pulp tissue next to coagulated surface

area in contact with Ca(OH)2 will deposit an organic matrix which will

mineralize within 4-6 weeks. If Ca(OH)2 comes in contact with degenerating

pulp tissue, the degeneration will be converted to a calcific type of

degeneration that will lead to multiple local isolation of pulp and root canal

tissues which will be devitalized.

Varnishes : Is a solution of one or more resins form natural gums, synthetic

resin. The volatile solvents evaporate quickly when varnish is applied to the

prepared tooth surface, thus leaving a thin resin film. To attain a uniform

continuous coating on all surfaces of prepared cavity, several thin layers should

be applied where the first layer dries. The varnish must be applied in thin

consistency using a brush or a small pledget of cotton.

Varnish produces a positive effect on reducing the pulpal irritation. It

provides a barrier against the passage of irritants from cements or other

restorative materials.

Varnish aid in reduction of post-operative sensitivity when applied to

dentinal surfaces. This could be attributed to the reduced infiltration of oral

fluids at restoration tooth interface into underlying dentin. It prevents

penetration of corrosion products of amalgam into dentinal tubules.

(NB) Not employed under composites it may soften resin and its coating

prevents proper wetting of prepared cavity by bonding agents. Not indicated

when GIC are used.

10

Filled and Unfilled Resin :

Irritating agents

1) Residual monomer

2) Exothermic heat of polymerization

3) Leakage, especially when accompanied by marginal percolation

4) High coefficient of thermal expansion

5) Enamel etching acids acidulating applied on dentin.

Although, they produce a less severe inflammatory reaction of the pulp,

they require use of Ca(OH)2 or GI cavity liner as resins are irritants.

The acid etchant appears to open dentinal tubules and permits greater

penetration of low viscosity bonding agent with potentially irritating low

molecular weight monomer.

Amalgam :

Residual mercury can diffuse form the restoration to the surrounding

dentin. Use of radioactive mercury in silver amalgam has also revealed that

some mercury might even reach pulp. Such mercury has been reported to

poison odontoblasts, subsequently reducing predentin and secondary dentin

formation.

Endodontic Procedures :

As a consequence of pathologic changes in dental pulp, the root cement

system can harbour numerous irritants. As irritants are released form the root

canal system into the periradicular tissue, granulation tissue proliferates and

replaces normal periradicular tissue.

An ideal root canal filling material should meet the following

requirements :

a) It should seal the canal laterally as well as apically.

b) Should not shrink after being inserted.

11

c) Should be impervious to moisture

d) Should be bacteriostatic

e) Should not irritate periradicular tissue.

f) Should not provoke an immune response.

g) Should not be carcinogenic or mutagenic.

Percolation of periradicular exudates into incompletely filled canals is

the greatest cause of endodontic failure. It is presently speculated that the

transudate constantly leaking no partially filled canals arises indirectly from

blood serum. The serum is trapped in cul de-sac of poorly filled canal, away

from influence of blood stream in which it undergoes degradation. Later when

the degradated serum slowly diffuses into periradical tissue, it acts as an irritant

to produce periapical inflammation.

Pulpal Response to Various Stimuli / Caries / Restorative Dental

Procedures :

Tertiary dentin also referred as reactive, reparative or irregular

secondary dentin is produced in reaction to various stimuli such a attrition,

caries or restorative dental procedures. Unlike primary or secondary dentin,

which forms along the centre pulp-dentin border, tertiary dentin is produced

only by cells directly affected by the stimulus. Tertiary dentin may have

regular tubules continuous with those of secondary dentin, tubules sparse in

number and irregularly arranged, or no tubules at all.

12

Management of Dermatitis Associated with Wearing of Protective Gloves

in Dental Practice :

Dermatitis developed in hands

Allergic contact Irritant contact Contact dermatitis Dermatitis Urticaria

Pattern of hand eczema Itchy, dry, Immediate Is suggestive of rubber fissured skin type reactionGlove allergy and chapping Itching, odema

and wheal within 1 hour

Try alternative brand Check handcareOf glove regimen Immediate

referral andavoid contact

Check gloves with rubber Frequently (Emergency

Treatment needed)

Try alternative Brand

If Dermatitis persist

Consult dermatologist

13

Pulpal Reaction to Caries and Dental Procedures :

Dental Caries

Reaction of pulp to caries

Decrease in permeability of dentin.

Formation of new dentin

Inflammatory and immune reactions

Inward diffusion of toxic substances form caries occurs through dentinal

tubules. The most common response to caries is dentin sclerosis. The ability

of pulp to produce reparative dentin below carious lesion is another mechanism

of limiting diffusion of toxic substances to the pulp. The formation of a dead

tract in dentin is yet another reaction that occur in response to caries. But this

is not a defensive reaction. It is an area of dentin where dentinal tubules are

devoid of odontoblast process.

The rate of attack may be influenced by any of the following.

Age of host

Composition of the tooth

Nature of bacterial flora

Salivary flow

Buffering capacity of saliva

Antibacterial substance in saliva

Oral hygiene

Cariogenicity of the diet

Caries inhibiting factors in diet

When the lesions reached to within 0.5 mm of pulp, there is significant

increase in extend of inflammation.

When all of pulp’s defense systems are overwhelmed, a pulpal abscess

may develop. The exudate associated with this reaction is called pus. The pus

14

is formed when neutrophils release their lysosomal enzymes and surrounding

tissue is digested. If drainage is not present, it can result in pulpal necrosis.

In some cases, accumulation of neutrophils may produce surface

ulceration called as chronic ulcerative pulpitis.

In primary and immature permanent teeth, caries exposure can result in

chronic hyperplastic pulpitis or pulp polyp.

Effect of Local Anaesthesia on the Pulp :

Decreases the pulpal blood flow with higher concentration of

vasoconstrictor. Irreversible pulp damage resulting from tooth preparation is

caused by release of vasoactive agents. Under normal circumstances, these

vasoactive agents are quickly removed from pulp by blood stream. However

when blood flow is reduced, then it can result in accumulation of these agents

which result in permanent damage to the pulp. Therefore use of

vasoconstrictor free LA for restorative procedure on vital teeth.

Effect of Cavity and Crown Preparation :

“Cooking the pulp in its own juice” is how Bodecker described tooth

preparation without water coolant. The pulpal response depends on various

factors – thermal injury, transaction of the odotoblastic process, crown

preparation, vibration, desiccation of dentin, pulp exposure, smear layer,

remaining dentin thickness, acid etching.

Cutting of dentin with a rotating bur or stone produces a considerable

amount of frictional heat.

The thermal conductivity of dentin is relatively low. Heat generated

during cutting of cavity in shallow preparation is less. Brushing of teeth seen

during cavity preparation or crown preparation due to frictional heat. It

presents with pinkish hue which is irreversible. However dark purplish color

indicates thrombosis.

15

Effect of Lasers on the Pulp :

Lasers can remove caries, modify the dentin surface for stronger

bonding, eliminate pits and fissures, anaesthetize and treat hypersensitive teeth.

Two requirements critical for effectiveness of cases is laser must

provide superior results over traditional procedures and it must not damage the

vital pulp in the process.

The interaction between laser light and substrate is expressed in terms

of reflection, absorption and transmission which are wavelength dependent.

Clinically CO2 laser and Gr:Yag will do less harm to pulp than Nd:YAG and

diode laser system.

CO2 Laser : Is known for cutting soft tissue without bleeding used in

periodontal and oral surgery procedures. It is not applicable for hard tissue

procedures.

Nd:YAG : has wavelength of 1.06 mm. They have beneficial effect on dentin

but not on the pulp. The pulp damage includes nerve injury and haemorrhage

leading to irreversible damage. Identifying an energy level at given dentin

thickness that provides desired effect on dentin without harming the pulp is an

important step in laser research.

Er :YAG : Can ablate dental hard tissue with minimal damage to dental pulp.

The mechanism is based on its high absorption into the water

component of hard tissue. This may cause a quick temperature increase within

a small volume of the tissue. Thus both enamel and dentin are partly removed

by continuous vaporization process and partly by microexplosion.

Hypersensitive Teeth :

Mechanism : The enamel and cementum covers the dentin when these

protective layer is removed, dentinal tubules are exposed (eg, scaling, caries,

16

#), the teeth often become hypersensitive. Dentin sensitivity is due to a fibres

present in dentinal tubules.

It is characterized by sharp, transient and well localized pain to cold, air

and heat. It can be confused with pulpal pathology. In the latter, it is because

of excitation of C fibres.

Management of Hypersensitive Dentin :

- Agents that block exposed dentinal tubules.

Oxalate Salts :

- Agents that reduce intradental nerve excitability.

Potassium nitrate, potassium bicarbonate, potassium oxalate, silver nitrate,

calcium fluoride.

Current thinking on cense of pulpal reaction to restoration.

Pulpal injury is due to microleakage through gaps between filling

materials and walls of the cavity.

There are 3 possible counts for microleakage.

a) Within or through smear layer.

b) Between smear layer and cavity varnish or cement.

c) Between cavity varnish or cement and restorative material.

Prevention :

Cutting procedures : Use light, intermittent cutting, efficient cooling

system and high speed of rotation.

Avoid dentin desiccation.

Do not apply irritating chemicals to dentin.

Use cavity liner / base whenever necessary.

Do not use excessive force when inserting a restoration.

Avoid excessive polishing procedure.

Choose restorative material carefully.

Do not use caustic cavity sterilizing agents.

17

CONCLUSION :

Tests to evaluate the biological response to dental materials can be

divided into initial, secondary and usage test. Each test level gives additional

information about the biocompatibility of the material. In this way, the initial

tests, which are quicker and less expensive to perform, can screen potential

materials before more complex secondary and usage tests are used. The initial

tests can also delineate the components of materials that might be causing

adverse reactions in the invivo tests. Although there are problems with the

correlation among initial, secondary and usage tests, and although one type of

test cannot be substituted or another at present, each type of test gives

important information about the effect of materials on cell and tissue function.

Continuing efforts to develop further correlations between screening and usage

tests are in progress.

18