Biological properties of dental materials 1 /certified fixed orthodontic courses by Indian dental academy

SRI GANESH
INDIAN DENTAL ACADEMY
Leader in continuing dental
education
www.indiandentalacademy.com

Biological properties
of Dental materials.

Contents
 Introduction
 Biocompatibility v/s Biological properties
 Components of biocompatibility
 Adverse effects of dental materials
 Toxicity
 Inflammation
 Allergy
 Mutagenicity
 Carcinogenicity
 Local & Systemic effects of materials
 Key principles that determine adverse effects from materials
 Concept of Immunotoxicity
 Oral anatomy that influences the biological response
 Enamel
 Dentine & Pulp
 Bone
 Measuring the biocompatibility
 Invitro tests
 Animal tests
 Usage tests
 Clinical trials

 Advantages & disadvantages of biocompatibility tests
 Correlation among the tests
 How tests are used together ?
 Regulatory standards for measurement of biocompatibility
 Current biocompatibility issues in dentistry
 Reaction of pulp to different materials
 Dentine bonding & Dentine bonding agents
 Dental amalgam
 Dental cements
 Bleaching agents
 Latex
 Impression materials
 Biocompatibility of metals
 Reaction of other oral soft tissues to restorative materials
 Denture base material
 Soft denture liner & adhesives
 Reactions of bone & soft tissues to Implant materials
 Conclusion
 List of references

Introduction

Biological properties of Dental
materials
 Biocompatibility = Lack of interaction
 Biocompatible material = list of negatives
 Non degradable
 Non irritant
 Non toxic
 Non allergic
 Non carcinogenic
 Non mutagenic
 Total inactivity = Passive ignorance ?
 More appropriate – active acceptance
 Biocompatibility : ability of a material to perform with an
appropriate host response, in a specific application.

Components
 Initial Physiochemical interaction
 Effect of the tissue environment
 Local host response
 Transport of products – Systemic effects
 Establishment of solid-liquid interface as any material is
implanted into the tissue
 Protein absorption is the first event
 Immediate response to injury is inflammation
 Very few is know about the factors
 Condition of the host
 Properties of the material
 Context in which the material is used
Eg: Biocompatible as Crown & Bridge but not as an implant material

Adverse effects from Dental
materials

Toxicity
 Placement of a foreign material in the body carries the possibility
of toxicity
 Toxicity can be of 2 types
 Acute toxicity.
 Chronic toxicity.
 Type 1: requires prolonged or repeated administration
 Type 2: requires very few or one dose but long lasting effects
 Type 1 chronic toxicity is a possibility with “Biomaterials”
Eg: metal ions released by gradual corrosion of an implant
 According to J.J.Jacobs et al (1991)
 Vanadium – lungs
 Aluminium – surrounding tissues
 Fortunately, materials causing over toxicity are no longer used in
dentistry.

Inflammation
 May result from toxicity or allergy and often it
precedes toxicity.
 Oedema, inflammatory cell infiltrate
 Current biocompatibility researchwww.indiandentalacademy.com

Allergy

Allergy
 Body specifically recognizes material as foreign &
reacts disproportional to the amount of material
 Gell & Coomb‟s classification of immune responses
 Type 1: Atopic or anaphylactic reaction
 Type 2: Cytotoxic hypersensitivity reaction
 Type 3: Immune complex disease
 Type 4: Delayed or cell mediated hypersensitivity
 Type 5: Stimulating antibody reaction
 Type 6: antibody dependent, cell mediated Cytotoxic
reaction

 Type 1, 2, 3 – quickly. Eosinophils, Mast cells & B
lymphocytes
 Type 4 – delayed. Monocytes & T cells
 Allergic response – individual‟s immune system
recognizes a substance as foreign
 Allergic reactions – initially dose
independent, disproportionate
 Toxic / inflammatory reactions – dose
dependant, proportionate

Mutagenic reactions
 Alteration in base pair sequence (mutation)
 2 types
 Alteration in cellular process that maintain DNA integrity
 Direct interaction
 Can occur from radiations, chemicals, errors in DNA
replication process
 Examples
 Metal ions – nickel, copper, beryllium
 Few components of root canal sealers
 Resin based materials to some extent

Carcinogenic response
 Currently no dental material has been shown to be
carcinogenic for dental applications in patients
 However, carcinogenesis is often exceedingly
difficult to prove or disprove conclusively

Local & Systemic effects of
materials
 Local effects
 Pulp
 Periodontium
 Root apex
 Oral tissues – buccal mucosa, tongue
 Systemic effects
 Function of the distribution of substances released from the materials
 Simple diffusion
 Lymphatics
 Blood vessels
 Access to the body by
 Ingestion & absorption in gut
 Inhalation
 Release at tooth apex
 Absorption into mucosa
 Systemic response depends on
 Duration & concentration of the exposure
 Excretion rate of the substance
 Site of the exposure

Key principles that determine
adverse effects from materials
 A) various types of metal corrosion & other types of
material degradation :
 Biocompatibility depends on the degradation process
 Corrosion is determined not only by material composition
but also by the biological environment
 Many ways for release of products in host
 Metal prosthesis – releases metal ions by
 Electrochemical force
 Particles dislodged by mechanical forces
 Resin composites
 Cyclic stresses
 Salivary esterases

 B) Surface characteristics :
 Surface is quite different from interior
 Examples
 Dental casting alloy containing 70% gold may have 95%
gold at its surface
 Relative unpolymerized state of a sealant at its surface
 The surface composition, roughness, mechanical &
chemical properties are critical to the biocompatibility

Concept of
Immunotoxicity

Concept of Immunotoxicity
“ Based on the principle that small alteration in
the cells of immune systems by materials can
have significant biological consequences ”
 Examples:
 Mercury ions increase the Glutathione but
Palladium decreases Glutathione content of
Monocytes
 HEMA may change the ability of Monocytes to
direct an immune response once challenged by
plaque or others agents

Oral anatomy that influences
the Biological response
 Enamel : “seals” the
tooth
 Peroxides permeate
intact enamel
 Dentine & Pulp :
 Smear layer
 Effective in reducing the
hydrostatic pressure but
not diffusion
 Acid etching

 Bone : Osseointegration & Biointegration
 Osseointegration
 Implant & bone closely approximate to each other
 Approximation less than 100 A
 No fibrous tissue in intervening space
 Titanium alloys
 Biointegration
 Implant & bone are fused to one another & are
continuous
 Occurs with Ceramic & Ceramic coated metal implants
Eg: Calcium & Tri calcium
phosphate, Hydroxyapatite, Bioglass

Measuring the
Biocompatibility
 Is not simple and methods of measurement are
evolving rapidly as more is know about the
interactions between dental materials and oral
tissues & as technologies for testing improves
 Classified as
 In Vitro test
 Animal test
 Usage test
 Clinical trial – special case of a usage test in humans

In Vitro test
 Placement of a material
or component of it in
contact with
cell, enzyme or some
other isolated biological
system
 Direct
 Material in contact
 Physically present or
extract from material
 Indirect
 Some sort of barrier

Types of cells used in In-vitro
assays
 Primary cells :
 Directly from an animal into culture
 Grows for only a limited time
 Continuous cells :
 Primary cells transformed to allow them to grow
indefinitely

Testing procedures & extent of
testing
 Manufacturer‟s responsibility to test new material
 A) Initial tests :deals with general biocompatibility & systemic
effects of a material
 Short term systemic toxicity test
 Short time oral administration
 Toxicity profile
 Acute systemic toxicity test
 I.V administration
 Inhalation toxicity test
 Dental remedies that have significant volatility under usage condition
 Hemolysis test
 In vitro evaluation of hemolytic activity of materials intended for
prolonged tissue contact
 Emes mutagenicity & the dominant lethal test
 To asses the potential carcinogenic activitywww.indiandentalacademy.com

Cytotoxicity tests
 Measures cell count or growth after exposure to a
material
 Method 1 :
 Place the cells in the well of a cell culture dish
 If Cytotoxic - cell may stop growing, exhibit cytopathic
features or detach from the cell
 Method 2 :
 Measurement of cytotoxicity by a change in membrane
permeability
 Loss in membrane permeability is equivalent or very nearly
equivalent to cell death
 Identifies the cells that are alive or dead

Tests
 Sensitization test
 Oral mucous membrane irritation test
 Subcutaneous implant test
 Bone implant test

Usage tests
 Pulp &Dentine test
 Response of dentine & pulp
 Minimum experimental variables
 Pulp capping & Pulpotomy test
 Endodontic usage test
 Assess response of the pulp wound & the periapical tissue
 Influenced by – level at which the pulp tissue is cut off &
total removal of pulp tissue
 Bone implant usage test
 To evaluate all materials that, during their intended
use, penetrate the oral mucosa and the adjacent bone

Correlation among the tests
 Lack of correlation
 Less prominent biological response
 Barriers may exist
 Measure different aspects of the biological
response to the material

Advantages & disadvantages
of Biocompatibility tests
 In-Vitro test
 Advantages
 Quick to perform
 Least expensive
 Standardized
 Large scale screening
 Excellent for mechanisms of interaction
 Disadvantages
 Relevance to In-Vivo questionable

 In- Vivo test
 Advantages
 Allows complex systemic interactions
 More comprehensive
 More relevant
 Disadvantages
 Relevance to use ?
 Expensive
 Time consuming
 Ethical concern
 Difficult to control
 Difficult to interpret & quantify

 Usage test
 Advantages
 Relevance to use of material is assured
 Disadvantages
 Very expensive
 Time consuming
 Major legal / ethical

usage progression
secondary of
primary testing
 Linear paradigm, relies on the accuracy of the primary tests (challenged by
Major et al 1977)
 No prediction of results in usage tests
 Lack of correlation in In-Vitro tests
How the tests are used together
to measure the Biocompatibility

 Non linear thinking
U Progression
S of
P Testing
 All the 3 tests are done
 As test progresses Usage test predominates

 Most common progression
Usage
„Recognizes
Primary Secondary complexity‟

Standards that regulate the
measurement of Biocompatibility
 ANSI / ADA : earliest attempt in 1933
 1972 – The Council on dental
material, instruments & equipment of ANSI / ADA
approved document no. 41 for recommended
standard practices for biological evaluation of
dental materials
 In 1982 updated to include test for mutagenicity
 Uses linear paradigm

 ISO Standard 10993 :
 Not restricted to dental materials only
 First published in 1992
 In 2002 ISO 10993 consisted of 16 parts
 2 types of tests –
 Initial – Cytotoxicity, sensitization & systemic toxicity.
In – Vitro / animal test
 Supplementary – chronic toxicity, carcinogenicity &
bio-degradation. Animals / Humans
 Specialized tests – Eg: dentine barrier test

Current Biocompatibility
issues in dentistry

 Reactions of pulp to
different materials
 Micro leakage :
 If a material does not
bond or debonds at
enamel or dentine
 Previous belief
 Concept of nano leakage
 Between mineralized
dentine & bonded
material. In very small
spaces of
demineralized matrix
into which material did
not penetrate
 Hydrolytic degradation
of dentine – material
bond

 Dentine bonding :
 Bonding to dentine is
difficult –
composition, wetness, lo
w minerals
 Smear layer formation &
removal
 Many studies have
shown
 0.5mm of RDT is
adequate
 Dentine is a buffers of
protons
 Penetration of acids <
100 micrometers

 Dentine bonding agents :
 HEMA is 100 times less cytotoxic in tissue culture
than Bis – GMA
 Bis – GMA, TEGDMA, UDMA

Amalgam

 Dental amalgam :
 Toxic or not ?
 In usage test response of
pulp to amalgam in shallow
or deep lined cavities
 Gallium based amalgam
 Excessive gallium release,
roughness, discolor
 Significant foreign body
reaction
 Absorption : 1 – 3
micrograms / day
 Minimum dose to produce
observable toxic effect is 3
micrograms / kg body
weight

 Dental cements
 Resin based materials :
 Resin composites –
luting or restorative
 Light cured < cytotoxic
than chemically cured
 Pulpal reaction
diminishes after 5 – 8
weeks
 Protective liner or
bonding agent minimizes
Pulpal reaction

 Glass ionomers :
 Luting agent &
restorative material
 Weaker polyacrylic acid
 Fluoride release
 Histological studies in
usage test shows that
any inflammatory
infiltrate to ionomer is
minimal or absent after 1
month

 Zinc phosphate :
 Luting agent & base
 Thermal conductivity closer
to enamel
 Pulpal damage in first 3
days due to initial low
PH(4.2), reaches neutrality
in 48 hours
 When placed in deep
cavities ?
 Inclusion of Ca- OH to the
powder or lowering the
concentration of phosphoric
acid

 Calcium hydroxide :
Suspension form Resin containing
Highly cytotoxic Mild to moderate cytotoxic
Necrosis 1mm or > No necrotic zone
shortly
Neutrophil infiltration Dentine bridge formation
5 to 8 weeks is quick
Slight inflammatory response
wks - months
Dystrophic calcification
Dentine bridge

 Zinc oxide eugenol :
 Suppresses the nerve transmission
 Inhibit synthesis of Prostaglandins & Leukotriens
 Hammesfahr 1987, initiated the search for a
biocompatible resin base system incorporating
Calcium hydroxide “ PRISM VLC DYCAL”

Soft tissue response to the
luting cements
 Apply petroleum jelly
 Clean the excess
 Any residues of cement

 Bleaching agents :
 Usually contain some form of peroxide
 In-Vitro – traverses the dentine & in sufficient
conc. can be cytotoxic
 Penetrates intact enamel & reaches the pulp in
few min.
 May burn gingiva

Latex

 Latex :
 6% to 7% of surgical personnel may be allergic
 42% adverse reactions to occupational materials
 Hypersensitivity may be due to true latex allergy or reaction
to accelerator & antioxidants
White, milky sap
Addition of ammonia
Hydrolyses & degrades the sap proteins to produce allergens

Liquid vulcanization solid
latex sulphur + heat rubber
 Soaked in hot water leaches out allergens
 Allergenicity depends on collecting, preservation
& processing

Impression materials

 Impression materials :
 Price & Whitehead
(1972) – Allergic
contact stomatitis &
Foreign body response
 Sydiskis & Gerhardt
(1993) – some degree
of toxicity in cell culture
 Gabriela Mazzanti et al
(2005) – no significant
evidence of diffuse
inflammation or local
skin reaction www.indiandentalacademy.com

Casting alloys

 Dental casting alloys :
 John c. Wataha 2000
 Release of elements is essential for adverse effects
 Identifying & quantifying the elements that are
released is most relevant measure from stand point of
Biocompatibility
 a) Release of elements from casting alloys
 Multiple phases
 Inherent tendency to release elements – lability
Eg: Cu, Ni, Cd, Zn & Ga – highly labile
 Environmental conditions - PH

 b) Systemic toxicity
 Released metals may not be inside the body
 Route of access – I.V < Peritoneal < Oral
 Distribution – there is no documented proof that
these material cause „Systemic toxicity‟
 c) Local toxicity
 Micro environment exists around casting alloys
 Metal ions can cause local toxicity
 Increased exposure causes increased toxicity

 d) Allergy to dental casting alloys
 Elemental release is essential for allergy
 Metal ions – Haptens
 Allergy & Toxic reaction – difficult to distinguish

 Patch test for metals – controversial
 Application of metal ion to skin in the form of patch
 Injecting small amount of ion below the skin
 Assessment of the response is difficult
 Salt of metal ions important for response
Eg: chloride, sulphate, nitrate salts
 Vehicle – whether its water, oil or petrolatum can vary
the response
 Grimaudo N.J 2001 – true allergic hypersensitivity to
dental casting alloys is rare

 Nickel :
 Common component
 Incidence of allergy 10% – 20%
 Cross reactivity between nickel & palladium (33%
& 100%)
 Nickel ions induces ICAM‟s in the endothelium –
release of cytokines
 It may contribute to any intraoral inflammation
around nickel containing crowns

 Beryllium :
 Used in Ni-Cr alloys in conc. of 1 – 2 wt%
 Forms thin adherent oxides
 Documented carcinogen
 Berylliosis
 Individual is hypersensitive
 Inhalation of beryllium dust, salts, fumes

Reaction of other oral soft tissues
 a) Denture base
materials
 Methacrylates
 Greatest potential for
hyper sensitization
 Acrylic & diacrylic
monomers, curing
agents, antioxidants, ami
nes, formaldehydes
 For the patients most of
these materials have
been reacted in
polymerization and thus
less prone www.indiandentalacademy.com

 True allergy of oral mucosa to denture base
material is very rare
 Residual monomer (methyl methacrylate)
 Allergic acrylic stomatitis
 Heat cured is better

 b) Soft denture liners &
adhesives
 Release of plasticizers
 Extremely cytotoxic
 Effects are masked by
the inflammation
 Denture adhesives show
severe cytotoxic
reactions In-Vitro
 Large amount of
formaldehyde
 Allowed significant
microbial growth

Denture cleansers
 Used to cleanse the prosthesis
 Eg : Hypochlorite, mild acids, etc.
 Biocompatible & cause no harm to the patient

Artificial teeth
 Acrylic & Porcelain teeth
 Acrylic teeth is preferred in poor ridges

Implants

Reaction of bone & soft
tissues to implant material
 Materials – Ceramics, Metals, Carbons & Polymers
 a) Reaction to ceramic implant material
 Very low toxic effects. Oxidized state, corrosion resistant
 Used as a porous or dense coating
 Root surface porosities > 100microns (firmly bound )
 Root surface porosities < 100microns (fibrous ingrowth)
 b) Hydroxyapatite
 Relatively non resorbable form of calcium phosphate
 Coating material & ridge augmentation material
 c) Beta -Tricalcium phosphate
 Another form of calcium phosphate, has been used in
situations where resorption of the material is desirable

 d) Reaction to pure metals & alloys
 „Metal‟ oldest type of oral implant material
 Shares the quality of „strength‟
 Initially selected on the basis of the „Ease of
fabrication‟
 Stainless Steel, Chromium-Cobalt-
Molybdenum, Titanium and its alloys
 Most commonly used is Titanium
 Titanium‟s Biocompatibility is associated with its
fast oxidizing capacity.
 Corrosion resistant & allows Osseointegration

 Soft tissue :
 Epithelium forms bond
with implant similar to
that of tooth
 C.T apparently does not
bond to the titanium, but
forms a tight seal that
seems to limits ingress of
bacteria & its products

Conclusion

List of references
 Restorative dental materials by Craig & Powers
 Phillips‟ Science of dental materials
 Chemistry of medical & dental materials by J.W.Nicholson
 Concise Encyclopedia of medical & dental materials by David Williams
 Dental biomaterials by Arturo N. Natali
 Dent material 2005;21(4):371-74
 JPD 2001 Aug;86(2):203-9
 Gen Dent 2001 Sep-Oct;49(5):498-503
 JPD 2000 Feb;83(2):223-34
 JPD 1998 Sep;80(2):203-9
 JPD 1993;69;431-5
 J Biomater Appl 1987 Jan;1(3):373-81
 BDJ 1972;133:9-14

Precautions to be taken in the
Lab
 Make certain the ventilation system in room is
properly functioning
 During operation of the dental lathe wear a
protective eyewear & a mask
 Clean & disinfect the dental lathe at least
once daily
 Use sterile rag wheels, stones & fresh
pumice for each patient's prosthesis

Thank you
For more details please visit

Biological properties of dental materials 1 /certified fixed orthodontic courses by Indian dental academy

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