biocompatibility of dental materials dr.ramashanker associate professor deptt. of prosthodontic 3 rd...
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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
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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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Allergic Contact Dermatitis
Most common occupational disease
Susceptibility & prior sensitization necessary
Dose independent
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Allergic Contact Dermatitis
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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Allergic Contact Stomatitis
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)
Allergic Contact Stomatitis
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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
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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
Group II : Secondary Tests
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.
Group II : Secondary Tests
3. Skin Sensitization test :-
Sensitization is inflammatory response requiring
participation of an antibody system specific for
material allergen. Done similar to irritation tests
Group II : Secondary 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
ListeningListening