Materials in Dentistry 8th May 2009

Institute of Materials, Minerals & Mining, London

Biocompatibility of Dental
Materials
Lucy Di Silvio

Biomaterials, Biomimetics & Biophotonics Group, Dental Institute,

Kings College London, London UK
 INTRODUCTION

Any material or device that is to be

used or placed within the body has
to be evaluated for biocompatibility
to ensure it is safe for human use
 BIOCOMPATIBILITY

Definition:

BIOCOMPATIBILITY IS THE ABILITY

OF A MATERIAL TO PERFORM WITH
AN APPROPRIATE HOST RESPONSE
IN A SPECIFIC APPLICATION

(Williams 1987)
 Biocompatibility involves
two components:

(i) General aspect: "BIOSAFETY"

This concerns and deals with the

exclusion of deleterious effects of a
biomaterial on the organism itself
(toxicity at the cellular level)
(2) Specific aspect:
"BIOFUNCTIONALITY"

This concerns and addresses the

need of a material not only to be free
from damaging effects on the host at
the cellular level, but also to be able
to elicit a beneficial host-response
for optimal functioning of the medical
device
BIOCOMPATIBLITY OF MATERIALS USED
IN DENTISTRY-KEY ELEMENTS

Any dental materials used in the oral cavity should be

harmless to all oral tissue: gingiva, mucosa, pulp, and
bone

Material should contain no toxic, leachable, or diffusible

substance that can be absorbed into the circulatory
system, causing systemic toxic responses/toxicity
(including teratogenic or carcinogenic effects)
e.g.substances released intraorally from dental alloys
and other dental materials

Material should be free of agents that could elicit

sensitization or an allergic response in a sensitized
patient
Tissue-material interface for dental applications
- Those contacting soft tissues in the mouth
- Those contacting hard tissues in the mouth
- Those affecting the vitality of pulp
- Those affecting root canal filling

e.g
Monomers in denture base materials
Allergic reactions to alloys containing nickel
Phosphoric acid- used as an etchant for enamel
Mercury in dental amalgam
Side effects to dental materials are
rare and those reported in restorative
materials may show a toxic, irritative,
or allergic reactions.
This may be manifested as local and/or systemic.

Local reactions involve the gingiva, mucosal tissues, pulp,

and hard tooth tissues

Systemic reactions are

expressed generally as
allergic skin reactions

Side effects may be

acute or chronic
 OFTEN THE RISK IS GREATER TO THE
PRACTITIONER THAN THE PATIENT!

Time dependent exposure when material

being manipulated or during setting

Effects can range from cumulative

irritation to severe allergenic responses

Inhalation of particulates during surgical

procedures can activate immune cells
(e.g dust from alginate impression materials, also some
products containing lead and tin)
Biocompatibility relates to the overall
performance of the (bio) material

When a biomaterial is placed in the body a

two-way biological interaction takes place

1. The effect the body has on the

material (implant)

2. The effect the material (implant)

has on the body
EFFECT THE BODY HAS ON THE IMPLANT
MATERIAL

1. PROTEIN ADSORPTION
Extent dependent on material properties

2. ENVIRONMENTAL
Saliva has corrosive properties, and bacteria are ever
present
3. DEGRADATION
Enzymatic

4. CORROSION
Mainly metals
 EFFECT THE MATERIAL (IMPLANT) HAS ON
THE BODY

1. UPSETS HOMEOSTATIC
EQUILIBRIUM

2. ACUTE INFLAMMATION

3. CHRONIC
INFLAMMATION

4. EVOKES AN IMMUNE
RESPONSE

5. ACTIVATION OF
MACROPHAGES ETC.

6. HEALING
 STANDARDS & TESTING
Until recently, almost all national & international
Dental standards and tests focused on only
physical & chemical aspects

Today, all dental materials require biological

testing

Testing is based on specifications or standards

established by national or international standards
organization, such as the American National
Standards (ANSI) or International Standards
Organization(ISO)
 ASSESSMENT OF BIOCOMPATIBILITY
ISO 10993 under the general title
Biological evaluation of medical devicesis divided
into different parts:
Part 1: Guidance on selection of tests
Part 2: Animal welfare requirements
Part 3: Tests for gentoxicity, carcinogenicity and
reproductive toxicity
Part 4: Selection of tests for interaction with blood
Part 5:Tests for cytotoxicity: in vitro methods
Part 6:Test for local effects after implantation
Part7: Ethylene oxide sterilization residuals
Part8: Clinical investigation
Part9: Degradation of materials related to biological
testing
Part10: Tests for irritation and sensitization
Part11: Tests for systemic toxicity
Part 12: Sample preparation and reference materials
Testing of materials
All dental materials should be subjected to

1.Primary cytotoxicity screening test- to

assess any toxic effect at the cellular level

2.Secondary test- to evaluate tissue

response ( appropriate cell response)

Having passed both 1 and 2

3. Animal tests

4. Clinical trial in humans

 ASSESSMENT OF BIOCOMPATIBILITY

ISO Part 5:Tests for cytotoxicity: in vitro

methods

Many tests available, can assess cell number, growth rate.

Cell metabolism, gene up-regulation, tests are relatively
simple, reproducible, inexpensive, rapid

Can examine:

Nature of the cell- materials interaction

The ability of cells to retain phenotype and functionality
Can test large number of samples; novel and commercial
Can test biofunctionality with appropriate cell model for
both soft and hard tissue
The ISO 10993 does not specify any single test but aims
to define a testing scheme which requires decisions to be
made in a series of steps which should lead to the
selection of the most appropriate test methods

Types of test regimes recommended:

Indirect contact (Extract)

Direct contact

Choice is dependent on:

Type of sample to be tested
Potential site of use
Nature of use
 CYTOTOXICITY TESTS

The material to be tested should be

representative of the components in
the final product and the final product
Requirements for biocompatibility testing methods

SPECIFICTY
Appropriate cells for material being tested

SENSITIVITY
Methods used should be sensitive and
suitable for in vitro cell culture

QUALITY CONTROLS
Both negative and positive and also, material
and cell culture control

ISO-10993 GUIDELINES
Part 5 : in vitro methods
Biocompatibility of common dental
restorative materials
LOCAL REACTIONS

No major adverse effects reported

Lichenoid/white or red erosive

lesions in the oral mucosa reported
in direct contact with dental amalgam,
composite and other restorative
materials

Interestingly, no evidence of
hypersensitivity to dental
restorative materials has been
reported in patients with oral
lichen planus
 RESIN-BASED COMPOSITES

Few documented systemic adverse effects

Associated with numerous organic compounds,
effects of which are unknown
Incomplete polymerisation leads to degradation,
leaching, imperfect bonding
Polymerisation shrinkage
Adverse local pulp and dentin reactions,
development of recurrent caries, and pain
Increased plaque adhesion and Lichenoid
episodes reported
 GLASS INOMER CEMENTS

Few documented systemic adverse effect

Very little irritant effect on pulp reactions, usually

followed by rapid recovery

When used as luting agent, liners are advocated

Hydraulic pressure/etching during placement may

irritate pulp

No undue reactions reported in gingival tissue

Good adhesion, minimal leakage at margins,

Overall, good biocompatibility !

 GOLD FOIL AND CAST ALLOYS

Inert, sensitivities are rare

Potential pulp reactions due to condensation

Rare allergic reactions to alloy metals

CERAMICS
No known reactions except wear on opposing
dentition and restoration

Good biocompatibility- but no long-term data on

biocompatibility available
Most reported adverse effects of dental
materials are allergic reactions:

Large number of dental materials contain components that

are common allergens e.g

Mercury, eugenol, chromium, cobalt, components of resin-

based materials, formaldehyde-containing materials, methyl
methacrylate

Extent of toxicity dependent on

CONCENTRATION & LENGTH OF EXPOSURE

Biofunctionalilty:Cellular interactions
Interactions between material (or implant)
and surrounding tissue are
complex

Restorative materials
may elicit responses
from pulp, gingiva
and oral mucosa

Different cell types involved

 Cell harvesting from dental pulp

Dental pulp tissue explant Migrating cells 2-3- days

Expanding cells 7days in culture Confluent cultures 28 days

Augmentation of Bone defects in
dentistry
Preparation of good bony layer prior to
implantation is mandatory to ensure long term
success of implant

Treatment modes are dependent on defect size

Bone substitutes (e.g bone matrix, TCP, HA)

have been used - usually characterized by long
healing time 6-12 months to achieve sufficient
bone regeneration

The success of these materials is whether they

can give rise to de novo bone and remodelling
that is necessary for the primary stability of
endosseous implants
Commercially available bone substitute
materials for shortening therapy
protocols
NanoBoneTM this comprises nanocrystalline HA in
silica gel matrix-designed to be used with blood to
enhance plasma proteins and assist the attachment of
stem cells to encourage de novo bone formation.
Can be used for:

Sinus floor elevations

Lateral and vertical augmentations
Covering buccal fenestrations
Socket preservation

Others include:
OsseotiteTM
NanoTiteTM
OsseospeedTM
Straumann SLActive
Assessment of Biofunctionality of
bone contacting implants
Reasons for modifying the surface:

Surface modifications play a significant role in

the interaction and success of the implant to the
adjacent tissue-

Study focused on the effect of different chemical

and electrochemical treatment on the
bioactivity of titanium
 Anodic Spark Deposition (ASD)
ASD is an electrochemical
treatment of titanium surface for
use in implantology

This treatment aims to obtain a

thickened titanium oxide layer
doped with calcium (Ca) and
phosphorus (P), known to
enhance osseointegration
properties of titanium implants
 Protein adsorption leading to desired cell
adhesion can be achieved by:
(1) Choice of material
Bioactive materials such as glasses,
ceramics allow the formation of the
hydroxy-carbonate-apatite (HCA) layer
which favour cell adhesion

(2) Design of the implant

Shape, porosity, composite materials,
incorporated factors all have an effect on
cell adhesion.

(3)Surface modifications
Topography, grooves, slits, porosity,
 Hypothesis
1. Surface physicochemical properties
contribute important environment cues
for subsequent bone cell adhesion by
determining preferential protein adsorption
onto modified surfaces, and hence enhancing
osseointegration

2. Surface nano-topography plays a key role

in bone cell behaviour, including cell
adhesion, proliferation, and differentiation.
 Biofunctionality of modified titanium surfaces

1. The physicochemical properties

Surface topography using Scanning
Electron Microscopy (SEM)
Surface chemical composition using
Energy Dispersive X-ray Spectroscopy
(EDS)
Atomic Force Microscopy (AFM)
2. To assess the in vitro cellular response
Cell viability (MTT assay)
Cell Proliferation (Alamar Blue assay,DNA,
protein, cell counts)
Cell adhesion and morphologic study
(SEM)
 Qualitative Observations
BioSpark OsseoSpark

2 2

m m

SEM comparison (x20k)

BS OS

BR cpTi
Toxic effect on cells (e.g.leachables) can cause
alterations in cell membrane function

LIVE-DEAD STAIN: Photo Dynamic Therapy to kill

cells on surfaces

Stained with Fluorescent agents (Calcein AM)

Stains healthy cells GREEN and Dead cells-RED
 MTT assay results
24 hr Elution test 72 hr Elution test

0.7 0.7
0.6 0.6
0.5 0.5
A b s o rb a n c e

A b s o rb a n c e
24 hr exposure 24 hr exposure
0.4 0.4
48 hr exposure 48 hr exposure
0.3 0.3
72 hr Exposure 72 hr Exposure
0.2 0.2
0.1 0.1
0 0
BS OS BR cpTi BS OS BR cpTi
Surfaces Surfaces

24 hr eluant 72 hr eluant
 Summary of Biofucntionality
ASD modified titanium surfaces have a
nanostructured topography enriched in
Calcium and Phosphorus resulting in:

Enhanced selective protein adsorption

(fibronectin)

High osteoblast adhesion and proliferation

High mineralization capability

Potentially enhancing osseointegration

 CONCLUSION
In vitro tests are an integral part of biocompatibility
evaluation prior to in vivo testing

All materials implanted in, or in contact with, the body

should be biocompatible

All current dental materials in use are considered

acceptable and cytocompatible, when properly handled

Adverse systemic effects are rarely documented,self-limiting

and tend to be of an allergic nature

The biomaterial-tissue response should be appropriate such

that the continued safe and effective performance of the
material is ensured
 Acknowledgements
Lertrit Sarinnaphakorn (PhD student)
Paula Coward for excellent technical support

Thank you for your attention