Implant biomaterials seminar/ dentistry curriculum

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

Contents…
Introduction
History
Requirements of implant materials
Classification
Metals and alloys
Ceramics & carbon
Polymers & composites
Surfaces charecteristics

Contents…
Surface cleanliness
Sterilization
Selection of implant material
Biocompatibility
conclusion

Introduction

History….
Chinese (4000 years
ago )
Carved bamboo sticks in
the shape of pegs and
drove them into bone for
fixed tooth replacement

History….
Egyptians (2000 years ago)
Used precious metals with a similar peg
design
Europe
A skull was found with a ferrous metal peg
shaped tooth inserted into it which dated
back to the time of Christ

History….
Central america
(Incas Dynasty)
Took pieces of sea
shells and tapped
them into bone to
replace missing
teeth

History…
Albucasis de Condue
(936 to 1013)
 Used ox bone to replace
missing teeth
 First documented
placement of implants

Recent history
Maggiolo(1809)
Fabricated gold roots which were fixed to pivot
teeth by means of a spring
Harris(1887)
Implanted a platinum post coated with lead
Bonewell (1895)
Used gold or irridium tubes implanted into bone

Recent history
Payne(1898)
Used a silver capsule as an implant
Scholl(1905)
Demonstrated a porcelain corrugated
root implant

Implant
material
requirements
Physical and
mechanical
Corrosion and
biodegradation biological

Mechanical requirements
Strength
 Strength of the implant material should be
tested under tension , compression and shear
force
 For most of the implant materials compressive
strength is usually greater than the tensile and
shear strength

Fatigue strength
 Upper stress limit decreases with an
increase in number of loading cycles
 In general , fatigue limit of metallic implant
materials reaches approximately 50% of
their ultimate tensile strength

Maximum yield strength
 It represents the stress at which permanent
deformation of the material begins
 Should not be exceeded by the masticatory
stresses

Creep deformability
 Creep is defined as the time dependent plastic
deformation of the material under a static load
or constant stress
 Materials with high creep values should be
selected if
o high masticatory forces are expected
o Patient has parafunctional habits

Modulous of Elasticity
 Implant materials and designs should account
for the modification of shape of bone in
response to application of forces
 An attempt to match closely deformability of
bone and implant materials led to
experimentation of polymeric and carbonitic
implant materials

Ductility
 American Society For Testing And Material
(ASTM) , ISO , and ADA :- Require a
minimum of 8% ductility to minimize brittle
fractures of implant materials
 Addition of modifying elements or process
hardening often results in an increase in
strength but decrease in ductility

ductility
 Mixed microstructural phase
hardening of austenitic
materials with nitrogen and
increasing purity of alloys
helps increase strength while
maintaining high level of
plastic deformation

Biodegradation
Williams suggested 3 type of corrosion
were most relevent to dental implant
materials
Galvanic
corrosion
Stress
corrosion
cracking
Fretting
corrosion

Galvanic corrosion
Occurs when two dissimilar metallic materials are
in contact within an electrolyte resulting in current
to flow between the two
Depends on passivity of oxide layers
Lemons et al (1988)
Reported on the formation of electrochemical couples
as a result of oral implant and restorative
procedures
Plank and Zitter(1996)
Galvanic corrosion can be greater for dental implants
than orthopedic implants

Stress corrosion cracking
Corrosion fatigue
Mechanical
stress
Corrosive
environme
nt
Failure
by
cracking

Fretting corrosion
Occurs when there is micromotion and
rubbing contact within a corrosive
environment
Along implant body and
abutment interphase
Along abutment and
superstructure interphase

Biologic considerations
Toxicity
Refers to primary degradation products of
a material

Toxicity
3 factors which decide toxicity of a
material
Amont dissolved by degradation per time unit
• TE (g/day) = TEA(%) x CBR x IS / 100
Amount of material removed by metabolic
activity in the same time unit
Quantities of solid particles and ions deposited
in the tissues and any transfers to the systemic
system

Toxicity
TE( g/day) = TEA (%) x CBR (g/cm2/day)
x
IS(cm2) / 100
 TE toxic element
 TEA toxic elements in alloy
 CBR corrosion biodegradation rate
 IS implant surface

Classification
Implant
materials
metallic ceramic polymeric
Polymeric
composite
Titanium
Titanium
alloys
Co Cr alloys
Stainless
steel
Precious
metals
Bioinert
ceramics
Bioactive and
biodegradable
ceramics

Metallic implant materials
Titanium
Gold standard in implant materials
Atomic number 22
Atomic weight 47.9
0.6% of earth’s crust : million times more
abundant than gold
Exists in nature as 2 ore forms
 Rutile ( TiO2 )
 Ilmenite ( FeTiO3 )

Titanium
Extraction from ore forms
Kroll process
Reduction of TiCl4 by magnesium
Iodide process
 Involves formation of titanium iodide
through reaction of raw titanium with iodine
 Titanium iodide is later decomposed on a
heated titanium wire

Properties
Oxidizes or passivates upon contact with room temp air or
normal tissue fluids
Tensile strength
Wrought soft(root form) and ductile metallurgic (plate form
implants) tensile strength is 1.5 times greater than that of
bone
Fatigue strength
Usually 50% less than tensile strength
Density 4.5g/cm3

Properties
Modulous of elasticity
 5 times greater than that of compact
bone
 Hence enables uniform stress
distribution at bone implant interphase

Advantages
Biologically inert and biocompatible
Excellent resistance to corrosion
Low specific gravity
High heat resistance
High strength comparable to that of
stainless steel

Advantages
Lowenberg et al (1987)
Titanium & zirconium alloy discs are
biocompatible with gingival fibroblasts
J Dent Rest 1987 : 66 : 1000

Biocompatibility of Ti
Titanium oxide surface
Brookite oxide layer
• Amorphous in atomic structure
• Formed in normal temperature or tissue fluid environment
• Usually very adherent and thin in dimension (less than 20 nm)
• Found in case of surgical implants
Rutile or Anatase oxide layer
• Crystalline atomic structure
• Formed by processing Ti at elevated temp or anodizing it in organic
acids at high voltages
• Oxide layer formed is hetrogenous and thick(10 to 100 times thicker)
• More likely to exhibit porosity such as scale

Tissue interactions with Ti Oxide
Highest oxide growth area : bone marrow
site
Lowest oxide growth area : cortical regions
Active exchange of ions at the surface
exhibited by increased levels of Ca & P on
oxide surface

Tissue interactions with Ti
Oxide
Ti Gel conditions
Hydrogen peroxide environment has been shown
to interact with Ti and form a complex gel
Such Ti gel conditions are credited with
 Low apparent toxicity
 Low inflammation
 Bone modelling
 Bactericidal charecteristics

Tissue interactions with Ti
Oxide
Local and systemic release of ions has been
reported with Ti & Ti alloy implants
 Ion release results in an increase in oxide
layer thickness with inclusions of Ca , P & S
 Free Ti ions have shown to inhibit growth of
hydroxyapatite crystals

Advantages of TiO2
 Minimizes biocorrosion in absence of
interfacial motion or adverse environmental
conditions
 In vivo repassivation areas scratched or
abraded during placement repassivate in
vivo
 Solar RJ , Pellack SR , Korostoff F (1979)
Oxide layer tends to increase in thickness
under corrosion testing

Advantages of TiO2
Hoar TP , Meals DC (1966)
Breakdown of this oxide layer is unlikely
in altered solutions such as chlorine
solution
Both et al
Ti allows bone growth directly adjacent
to the oxide surfaces

limitations
High cost

limitations
Difficult & dangerous casting
 A high vacuum or ultrapure gas atmosphere is
needed
 Metal has a high melting point
 Metallic embrittlement may occur due to
propensity to absorption of O , N , & H
 Metal fumes and oxidises rapidly at elevated
temp.  almost explosive reaction may occur

Titanium alloys
3 forms of alloys used in dentistry
 Alpha
 Beta
 Alpha-beta
Most commonly used for dental implants
: alpha-beta variety .e.g Ti -6Al-4V, Ti-
6Al-7Nb

Advantages
Strength  wrought alloy condition is about
6 times stronger than compact bone
 Can be fabricated in thinner sections
MOE slightly greater than that of Ti
 5.6 times of compact bone
Demonstrates oxide formation like Ti
Demonstrates osseointegrated surfaces
Highly resistant to fatigue & corrosion

limitations
Ductility considerably less than Ti
Adverse effects of Al & V biodegradation
on local & systemic tissues
Difficult to cast

Co – Cr – Mo based alloys
Most often used as
 As cast
 Cast & annealed metallurgic condition
High strength permits custom designing

Co – Cr – Mo based alloys
Composition
Co
Cr
Mo
Ni
C
Continuous phase for
basic properties
Corrosion resistance
Strength & bulk corrosion
resistance
Provides strength
ductility

advantages
high strength  4 times that of
compact bone
Excellent biocompatibility profile

disadvantages
Less ductile  bending of finished
implants shhould be avoided

Fe – Cr – Ni based alloys
Surgical stainless steel alloys e.g. 316
low C
Used for orthopedic and dental implant
devices
Used in wrought and heat treated
metallurgic condition

Advantages
High strength
High ductility
Cost effective

Disadvantages
Most subject to crevice and biocorrosion
Ni allergy
Galvanic coupling and biocorrosion with
Ti , Co , Zr and C

Noble metals
Most commonly used noble metals
 Tantalum
 Platinum
 Irridium
 Gold
 Palladium
 Alloys of these metals

Advantages
Inert electrochemically
Easily available esp. gold
Do not depend on surface oxides

Disadvantages
Low strength
Cost per unit weight is high
Weight per unit volume (density) is less

Ceramics & carbon
Ceramics are inorganic , non metallic ,
non polymeric materials manufactured
by compacting and sintering at elevated
temperatures.
2 types
Bioinert ceramics
Bioactive & biodegradable ceramics

Bioinert ceramics
Ceramics from Al , Ti , & Zr oxides
Used as
 root form
 endosteal plate form
 pin type dental implants

properties

Indications
Anterior root form devices

Contraindications
Subperiosteal devices as they have low
fracture resistance and high relative cost
of manufacturing

Advantages
Minimal thermal and electrical conductivity
Minimal biodegradation
Minimal reactions with bone , soft tissue and oral
environment
In certain lab animal and human studies exhibit
direct interfaces with bone like osseointegrated
Ti implants
Gingival attachment zones along sapphire root
form implants in lab animals have demonstrated
localized bonding

Disadvantages
Exposure to steam sterlization------>
measurable decrease in strength
Scratches or notches may introduce
fracture initiation sites
Chemical solutions may leave residues
May abrade other materials

Bioactive & biodegradable
ceramics
Consist of solid or porous particles with
compositions relatively similar to the
mineral phase of bone
Inernal reinforcement through
Mechanical ( central metallic rods )
Physiochemical (coating over another substrate ) techniques

Indications
Ridge retainers : rods and cones for filling tooth
extraction sites
Structural support under high magnitude loading
conditions :
 rods
 Cones
 Blocks
 H- bars
Used in combination with organic compounds such
as
 Collagen
 Drugs
 Bone morphogenic protein

Physical properties
Factors affecting :
 Surface area or form of the product
 Porosity
 crystallinity

Chemical properties
Factors affecting
 Ca – P ratio
 Composition
 Elemental impurities such as carbonate
 Ionic substitutions in atomic structure
 PH of surrounding region

Chemical properties
General formula
M1O
2+ (XO4
3- ) 6 Z2
-1
standard apatite products
 Crystalline monolythic hydroxyapatite
 Crystalline tri calcium phosphate
Indicated for
 Bone augmentation & replacement
 Carriers for organic products
 Coatings for endosteal and subperiosteal implants

Advantages
Chemistry mimics normal biologic tissue
Excellent biocompatibility
Attachment between CPC and hard and
soft tissues
Minimal thermal and electrical
conductivity
MOE closer to bone
Colour similar to hard tissues

Disadvantages
Variable chemical and structural
charecteristics
Low mechanical tensile & shear strengths
under fatigue loading
Low attachment between coating and
substrate
Variable solubility
Variable mechanical stability of coatings under
load bearing conditions
Overuse
Incompatible with steam or water sterilization

Disadvantages
S.C. Guy , M. J. Quade , M. J Schiedt (1993)
Porous hydroxyapatite has demonstrated the
least fibroblast attachment.
Epithelium and gingival fibres forming an
attachment to implant materials has been
reported in the following order
Titanium > non porous HA > porous HA
J Periodontology (1993: 64 : 542 – 546 )

Carbon compounds
Similar to ceramics
 Chemical inertness
 Absence of ductility
Differenence from ceramics
 Electrical & thermal conductivity
A two stage implant system  vitredent : popular in
1970
Design and material limitations significant clinical
failures  withdrawl from clinical use
Used as coatings on metallic & ceramic implants

Polymers
Common polymeric materials
 PTFE
 PET
 PMMA
 UHMW-PE
 PP
 PSF
 PDS
 SR
 Can be combined with
 Particulate or fibres of carbon
 Aluminium oxide
 HA
 Glass ceramics
 Biodegradable calcium phosphate

limitations
Low strength
Low MOE compared to bone
Higher elongation to fractures
High cold flow charecteristics , creep and
fatigue strength
Low resistance to abrasion and wear
Sensitive to sterilization and handling
techniques
Electrostatic surface properties , hence
tend to gather dust

Indications
Tissue attachment , replacement &
augmentation
Coatings for force transfer to soft tissue
and hard tissue regions
Internal force distribution connectors for
O.I implants
Structural scaffolds , plates & screws

Surface charecteristics
Surface
coatings
Passivation
Surface
texturing
Ion
implantation

Surface coatings
Titanium coating
Hydroxyapatite coating

Titanium coating
Introduced by Hahn & Palich
Reported bone in growth in Ti hybrid
powder plasma sprayed implants
inserted in animals

Procedure
Porous or rough Ti surfaces have been
fabricated by plasma spraying a powder form
of molten droplets at high temp.
At temp in the order of 15,000 degree celsius ,
an argon plasma is assosciated with a nozzle
to provide very high velocity ( 600 m/ sec )
partially molten particles of Ti powder (0.05 to
0.1 mm diameter) projected onto a metal or
alloy substrate
Thickness of plasmas sprayed layer : 0.04 to
0.05 mm

Microscopic structure
Round or irregular pores that can be
connected to each other

Advantages
Increases the total surface area upto several
times
Produce attachment by osteoformation
Enhances attachment by increasing ionic
interactions
Dual physical & chemical anchor system
Increase in tensile strength through growth of
bony tissues into 3-D features
Improved force transfer to periimplant area

Disadvantages
Cracking & scaling because of stresses
produced by processing at elevated temp.
Risk of accumulation of abraded material in
the interfacial zone during implanting of Ti
plasma sprayed implants

Hydroxyapatite coating
Introduced to dental profession by de
Groot
Procedure
Majority of commercially available HA
coated implant systems use a plasma
spray technique

procedure
A powdered crystalline HA is introduced
and melted by the hot , high velocity
region of a plasma gun and propelled
onto the metal implant as a partially
melted ceramic

Limitation of plasma spraying
It can alter the nature of crystalline ceramic
powder and can result in the deposition of
a variable % of a resorbable amorphous
phase
Ion beam Sputtering coating technique
Expected to produce dense , more
tennacious and thinner coatings

Advantages
Better organization & mineralization of
adjacent bone
Better biomechanics & initial load
bearing capacity
Improved bone to implant attachment
Increase in bone penetrations
Protective shield
Enhanced coating substrate bond

Disadvantages
Partial resorption of CPC may occur due
to remodelling of the osseous interphase
Resorption of coating in infected &
chronic inflammation areas

Recent advances in HA coatings
Fluorapatite
Heat treated hydroxyapatite coatings ( HA-HT)
Harry et al (1996)
Remaining coating thickness at the end of 24 months:-
HA 38%
FA 95%
HA-HT 97%
Int J Prosthodont 1996 :9 142-148

Passivation
Refers to enhancement of oxide layer to
 Prevent release of metallic ions
 Enhance biocompatibility
2 procedures
 Immersion in 40 % nitric acid  results in a
thin oxide layer
 Anodization electric current is passed
through the metal

Surface texturing
Enhances surface area by upto 6 times
Methods
 Plasma spraying with Ti
 Acid etching
 Particulate Blasting

Acid etching
Ti implants can be etched with
 Nitric acid
 HF acid
Chemically alters the surface
Eliminates some type of contaminants

Particulate blasting
Can be done with various media such as
 Silica
 Alumina
 Glass beads
Provides irregular rough surfacing less
than 10 micron scales
Limitation osteolysis caused by foreign
debris
Resorbable blast media

Ion implantation
Done by bombarding the surface of
implant with high energy ions upto a
surface depth of 0.1 micron
Increases corrosion resistance of Ti
through formation of TiN layer
Increases hardness and abrasion &
wear resistance
Nitrogen implantation & carbon doped
layer deposition recommended for
stainless steel

Strength of implant material
Quality of bone
Bone height
 8 mm bone  Ti implant failure rate was
70% while HA was 4%
 12 mm bone  no significant difference

Fresh extraction sites better initial
stability of HA
Newly grafted sites HA preferred
 Greater implant bone interphase
 Higher shear bond strength
 Higher torsional strength

Surface cleanliness &
sterlization
Alberkston et al (1985)
Implants that seem functional may fail
even after years of function and the
cause may be attributed to improper
ultrasonic cleaning , sterlization or
handling during the surgical placement

Cases of surface contamination
Lausmaa et al showed large variations in C
contamination loads of Ti implants (20% to
60%) in the 0.1 to 3 nm thickness range
Trace amounts of Ca , P , N , Si , S , Cl , Na
Residues of F due to passivation & etching
treatments
Ca , Na & Cl may be incorporated during
autoclaving
Si may be present due to sand & glass bead
blasting procedures

Sterlization
Conventional
steam
sterlization
Radio frequency
glow discharge
technique
(RFGDT)
U.V Light
sterlization
Gamma
radiation
procedures

Radio frequency glow
discharge technique
Sterlization under a controlled noble gas
discharge at very low pressure
Gas ions bombard the surface & remove
surface atoms and molecules which are
adsorbed or are its constituents

Advantages
Baier et al
Provides a clean surface as well as a high
surface energy state
Thinner , more stable oxide films
Improved wettability & tissue adhesion
Principle oxide unchanged
Decrease in bacetrial contamination on HA
coated implants reported
May enhance Ca & P affinity due to an
increase in elemental zone at the surface

U. V light sterlization
Effective on spores
Enhances bioreactivity
Cleans the surface safely & rapidly
Grants high surface energy

Gamma radiation sterlization
Most metallic systems exposed to radiation
doses exceeding 2.5 mega – rads
Advantages
Packaging & all internal parts of assembly
sterlized
Components remain protected , clean &
sterile until inner containers are opened
within the sterile field of surgical procedure

Disadvantages
Some ceramics can get discoloured
Polymers may be degraded by gamma
radiation exposures

Hartman et al (1989)
RFGDT & UV sterlizedimplants show rapid bone
ingrowth and maturation while steam sterlized
implants seem to favour thicker collagen fibres at the
surface
Carlsson et al (1989)
 Reported similar healing responses with RFGDT &
conventionally treated implants
 Cautioned that RFGDT produces much thinner oxide
layer at the surface and may deposit silica oxide
from the glass envelope

Biocompatibility
Boca , Raton , Fla (1981)
An appropriate response to a material
(biomaterial) within a device (design) for a
specific clinical application

History
1960
Emphasis on inert & chemically stable
materials
Classic e.g
 High purity ceramics of aluminium oxide
 Carbon & carbon silicon compounds
 Extra low interstitial grade alloys

History
1970s
Biocompatibility of implants was defined
in terms of minimal harm to the host or
to the biomaterial
Stable interaction - central focus of
B.C.

History
1980s
Focus transferred to bioactive
substrates
Substances which tended to positively
influence tissue response 
considered to be biocompatible

History
1990s
Emphasis is on chemically & mechanically
anisotropic substances
Growth (mitogenic) & inductive (
morphogenic ) traits of material are given
importance while defining biocompatibility

Analysing biocompatibility
Individual constituents :
 Implant materials
 Tissues
Effect on local & systemic tissues
Interfacial zone

ADA criteria
Evaluation of physical properties that ensure sufficient strength
Demonstration of ease of fabrication & sterlization potential
without material degradation
Cytotoxicity testing
Freedom from defects
A minimum of 2 clinical trials , each with a minimum of 50
human subjects conducted for three years  for provisional
acceptance
Clinical trial of 5 years to earn acceptance

Biocompatibility concerns
Titanium
 Normal Ti levels in humans 50ppm
 May reach upto 300 ppm in tissues surrounding Ti
implants
 Tissue discolouration may be visible but is still well
tolerated
Hydroxyapatite
 Disintegration particles (esp smaller than 5 microns)
formed due to dissolution of amorphous substance
 toxic to fibroblasts
 Direct interaction with cells results in irreversible cell
membrane demage

Biocompatibility concerns
Co-Cr alloys & stainless steel
 Potential electrolytic action  galvanic
corrosion
 Release of nickle & beryllium ions
Polymers
 Chronic irritation of surrounding tissue with
fibrous encapsulation
 Reported to cause some allergenic and
carcinogenic reactions
 Bone loss gingival recession peri-implantitis

References
Contemperory implant dentistry : Carl E Misch 3rd
edition
Philips science of dental materials 11 edition
Craig dental materials
DCNA vol 36 no1
JADA dec 1990 vol121
Periodontology 2000 : 1998 vol 17
IJP 1996 vol 9 no.2
JPD sep 1992 vol68 no.3
J Periodontology 1993 vol 64 no.6
JPD 1985 vol 54 no.3

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Implant biomaterials seminar/ dentistry curriculum

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