GOOD MORNING

IMPLANT biomaterials

CONTENTS• Introduction • Terminologies• History• Classification of biomaterials

• Biocompatibility • Biofunctionability• Individual materials

– Metals and alloys – Ceramics and carbon

– Polymers and composite polymers• Surface modifications• Conclusion• References

• For many years, implants of varied types have been used in dentistry to augment or replace hard and soft tissue components of the jaws. Currently, implant materials include grade 2 commercially pure titanium, titanium 6% aluminium 4% vanadium, surgical- grade cobalt-chromium-molybdenum, aluminium oxide in single crystal or polycrystalline form, hydroxyapatite, tricalcium phosphate and calcium aluminate.

• Biocompatibility – (Dorlands illustrated medical dictionary) Being harmonious with life and not having toxic or injurious effects on biofunction.

• Biomaterial – Any substance other than 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.

• Biotolerant – Material that is not necessairly rejected but are surrounded by fibrous layer in the form of a capsule .

TERMINOLOGIES:

• Bio inert – Material that allow close apposition of bone on their surface

• Bioactive - Materials that allow formation of new bone on their surface and ion exchange with host tissue

• Osteoconductive – the materials that forms scaffolding that allows the formation of bone

• Osteoinductive – materials that have capacity to induce bone formation.

• 2500 BC - Ancient Egyptians - gold ligature

• 500 BC - Etruscan population - gold bands incorporating pontics

• 500 BC - Phoenician population - gold wire

• 300 BC - Phoenician population - Carved Ivory teeth

• 600 AD - Mayan population - implantation of pieces of shell

• 18 th century Pierre Fauchard and John Hunter - transplanting the teeth

1913 - Greenfield – 24 gauge iridium platinum wire meshwork forming “basket” implant soldered with 24 carat gold

•1940 - Formiggini - spiral implant - stainless steel wire

• 1937 – Venable et al- vitallium screw to provide anchorage for replacement

1943 - Dahl -Subperiosteal type of implant

1948 - Goldberg and Gershkoff - Extension of frame work

• Early 1960s - Chercheve - Double helical Spiral implant of Cobalt Chromium

• Early 1970s - Grenoble - Vitreous Carbon implants

• 1970 and 1980 - Weiss and Judy - Titanium Mushroom shaped projection (INPLANT)

After 1980s –hollow basket Core vent implant Screw vent implant Screw vent implant with hydroxyapatite coating implant with titanum plasma spray

Biological biocompatibility

Chemical composition Metals Ceramics Polymers

Biotolerant Gold PolyethyleneCobalt-chromium alloys

Polyamide

Stainless steel Polymethylmethacrylate Zirconium Polytetrafluoroethylene Niobium Polyurethane Tantalum

Bioinert Commercially pure titanium

Aluminium oxide

Titanium alloy (Ti-6Al-4V)

Zirconium oxide

Bioactive Bioactive Hydroxyapatite Hydroxyapatite

Tricalcium Tricalcium phosphate phosphate

Calcium Calcium pyrophosphate pyrophosphate

Fluorapatite Fluorapatite Carbon silicon

BioglassBioglass

Classification based on implant design:

1. Sub periosteial 1. Unilateral 2. Bilateral

2. Transosteal (or) Staple bone implant (or) Mandibular staple implant (or) Trans mandibular implant

3. Endosteal implant 1. Cylindrical cones (or) thin plates2. Blade implant 3. Ramus frame implant 4. Root form implant

4. Epithelial implant (or) Sub dermal implant (or) intra mucosal implant.

BIOCOMPATIBILITY Corrosion resistance

Cytotoxicity of corrosion products

Metal contamination

Corrosion – It is defined as loss of metallic ions from the surface of the metal to the surrounding environment

Types of corrosion :

General Galvanic

Pitting Fretting

Crevice Stress corrosion cracking

Williams DF

Williams suggested that three types of corrosion were most relevant to dental implants:

• Stress corrosion cracking• Galvanic corrosion

• Fretting corrosion

Stress corrosion cracking (SCC)

The combination of high magnitudes of applied mechanical stress plus simultaneous exposure to a corrosive environment can result in the failure of metal materials by cracking, where neither condition alone would cause the failure.

William presented this phenomenon of SCC in multicomponent orthopedic implants.

Lemons et al

Hypothesized that it may be responsible for some implant failures in view of high concentrations of forces in the area of the abutment-to-implant body interface.

Most traditional implant body designs under three-dimensional finite element stress analysis show a concentration of stresses at the crest of the bone support and cervical one-third of the implant.

• This tends to support potential SCC at the implant interface area (i.e. a transition zone for altered chemical and mechanical environmental conditions).

• This has also been described in terms of corrosion fatigue (i.e., cyclic load cycle failures accelerated by locally aggressive medium).

Stress Corrosion Cracking

Galvanic corrosion (GC)

GC occurs when two dissimilar metallic materials are in contact and are within an common electrolyte medium, resulting in current to flow

between the two.

The metallic materials with the

dissimilar potentials can have their corrosion currents altered, thereby resulting in a greater corrosion rate..

Galvanic Corrosion

Fretting corrosion (FC)

FC occurs when there is a micromotion and rubbing contact within a corrosive environment such as the perforation of the passive layers and shear-directed loading along adjacent contact surface.

Normally, the passive oxide layers on metallic substrates dissolve at such slower rates that the resultant loss of mass is of no mechanical consequence to the implants.

A more critical problem is irreversible local perforation of the passive layer that is often caused by chloride ions, which may result in localized pitting corrosion.

Pitting Corrosion

PROTECTION AGAINST CORROSION

•Passivation

•Increasing the noble metal content

•Polishing the surface

•Avoid dissimilar metal contact

CYTOTOXICITY OF CORROSION PRODUCTS

The material should undergo only minimal amount of biochemical changes during service.

The material should have minimal reaction with the surrounding bone and the soft tissue

Ideally the corrosion products should not produce any toxicity to the local and systemic environment.

METAL CONTAMINATION

Two different metals in the saline solutions or body fluids may result in a localized difference of electrochemical potential and cause galvanic corrosion. So the instruments that contact titanium implant during insertion procedures either be solid titanium, titanium tipped or treated to prevent metallic transfer.

During storage, sterilization and surgical set up no other type of metal should contact the implant surface.

PHYSICAL AND MECHANICAL PROPERTIES

• The macroscopic distribution of mechanical stress and strain is predominantly controlled by the shape and form of the implant.

• The microscopic distribution is controlled by the basic properties of biomaterials as -Surface chemistry, Microtopography, Modulus of elasticity and Surface attachment to the adjacent tissue.

• Basic problem lies due to the difference in mechanical strength and deformability of the material and the recipient bone.

• The metals can be modified to achieve the required properties by work hardening or alloying.

• Higher the applied load higher the mechanical stress greater the possibility of exceeding the fatigue limit of the material..

MODULUS OF ELASTICITY• the forces applied on the implant leads to stresses within the bone.

• When the applied forces are equal to stresses it acquires the state of

static equilibrium.

• Forces > , it leads to deformation.

• The physiologic importance of modulus of elasticity of biomaterial is related to the modulus of elasticity of the bone.

• The degree of relative movement at the interface determines the health or pathologic state of interface.

• The modulus of elasticity of titanium is very near to bone compared to any other material used. It is almost 6 times more stiff than dense cortical bone.

• The carbon implants has compatible stiffness with bone but fail to have adequate strength to withstand physiologic load leading to microcracks and finally the failure of implant.

• On the other hand the aluminum oxide ceramic implant has high ultimate strength but the stiffness is 33 times greater than the stiffness of the bone which results in apparent stress shielding of interfacial bone

•The modulus of elasticity in subperiosteal implants not an important consideration. The envelopment of the implant in the outer layer of periosteum during healing provides a stable biomechanical situation.

•For unilateral subperiosteal implant the effect of relative movement of metal is minimal.

•For bilateral/total subperiosteal implant may cause excessive relative movement due to its rigidity. So cutting these at the midline or providing individual abutment can increase flexibility.

METALSMost of the materials used for implants are constructed from metals

and their alloys. These includes Titanium, Tantalum, Aluminum, Vanadium, Cobalt, Chromium, Nickel and Molybdenum. These

are selected on the basis of their over all strength. Less frequently used are precious metals as Gold and Platinum.

TITANIUM AND TITANIUM ALLOYS• In 1791 Wilheim Gregor – Discovered in Black Magnetic Sand at

Cornwall.• In 1925 Van Arkel.– Refined into pure form with desirable

properties. • It is extremely reactive and forms tenacious oxide layer that

contribute to its elctrochemical passivity

Uses:

• Pigment industries • Titanium tennis rackets • Eyeglass frames • Largely used in jet engines,

• Fracture site fixation• Deep well drilling• Nuclear waste management• Dental and maxillofacial implants

Titanium alloys can be classified as alpha, beta, and alpha beta

alloys.

Alpha alloy Highest strength, best corrosion resistance, pure titanium, small

amounts of nitrogen and oxygen (CpT1). Aluminium is

stabilizer

Beta alloy Difficult to manufacture (vanadium + aluminium) not used for

implant. Vanadium act as stabilizer

Alpha beta alloys

Most common alloys consisting of 6% of aluminium 4% of

vanadium (T1 & Al64Va)

Good Corrosion resistance

properties Material of choice because of inert, bio compatible nature with

excellent resistant corrosion. Density 4.5 gm/cm2 40 % lighter than steel High heat resistance High strength compatible with S.S Able to maintain fine balance between sufficient strength to

resist # under occlusal forces and lower modulus of elasticity

for a more uniform stress distribution across the bone implant

interface. Titanium – more ductility than titanium alloy High dielectric property osseointegration.

Disadvantages

• Its high cost (although the cost has been reduced over the past few years).

• Titanium is difficult and dangerous to cast. The metal forms oxides so rapidly that an explosive reaction may occur.

(So it is used either in machined or plastic form)

Ti Ore (Carbon and Chlorine)

Heated

TiCl

Reduced in presence of molten Na

Ti Sponge

Fused under Vacuum

Ti Ingots

PRODUCTION

MACHINING &

AUTOCLAVING

Oxide Coatings

• The biocompatibilty of the Ti and Ti alloy is attributed to the ability of formation of passive tenacious surface oxide.

• Minimum of 85 to 95% of pure titanium is required to maintain passivity.

• The pure titanium theoretically may form several oxides as TiO, Ti O2,Ti2O3

• Within a millisecond 10Å thick oxide layer will be formed. In a minute the layer will become 100Å thick.

• The repair of the oxide layer is instantaneous if any damage occurs during insertion of Implant.

• Rate of dissolution is extremely low compared to any implant metals.

Original Branemark fixture

Titanium screw

Cp Ti screw implant

Cobalt Chromium Molybdenum Alloy• These alloys are most often

used in cast-and-annealed metallurgic condition.

• This clears that the alloy is used for fabrication of implants as custom designs such as subperiosteal implants.

The various constituents of alloy with their function-

• 63% Co- provides the continuous phase for basic properties

• C- provides strength, surface abrasion resistance, controls mechanical properties.

• 30% Cr- provides corrosion resistance through the oxide surface

• 5% Mo- provides strength & bulk corrosion resistance.

• Ni- found in traces.

• High modulus (stiffness) and Low ductility.• Outstanding resistance to corrosion• Excellent biocompatibility

Precautions

As cast cobalt alloys are the least ductile of the alloy systems used for dental surgical implants, and bending of finished implants should be avoided.

Iron – Chromium – Nickel based Alloys• Surface is passivated to increase biocorrosion resistance. • High strength and ductility.• Used in wrought and heat treated condition.

Composition (Surgical austenitic steel)– 18% chromium – for corrosion resistance.– 8% nickel – to stabilize austentic structure.– 0.5% carbon – as hardner.

Precautions• Contraindicated in patients sensitive to nickel.• Most susceptible to crevice and pitting corrosion, so care to be

taken to preserve passivated surface.• Has galvanic potential, so avoid contact with dissimilar metal.

OTHER METALS AND ALLOYS

• Early spirals and cages included tantalum, platinum, iridium, gold, palladium, and alloys of these metals.

• More recently, devices made from zirconium, hafnium, tungsten and sapphire have been evaluated.

Ceramics and Carbon as implant Materials

CERAMICS – these are non organic, non metallic, non polymeric materials manufactured by compacting and sintering at elevated temperatures.

• Have low ductility and inherent brittleness are their limitations

can be Classified into Bio active – Ca3(PO4), Hydroxyapatite, tri calcium phosphate

Bio nonreactive – Aluminum Titanium Zirconium oxides

Aluminum Titanium Zirconium Oxides

• Used for endosteal root form, plate form

implants

• Have clear white cream or light grey

color so used for anterior root form

• Minimal biodegradation

• High modulus of elasticity

• Low fracture resistance

• Exhibit direct interface with bone

THE TÜBINGEN IMPLANT OF ALUMINUM OXIDE HAS SPECIFIC MICRO-IRREGULARITIES ON THE SURFACE,

CLAIMED TO ALLOW BONE INGROWTH.

DISADVANTAGES

• Exposure to steam sterilization results in measurable decrease in strength of some ceramics

• So dry heat sterilization is recommended

• Scratches or notches may induce fracture initiating sites

• Although initial testing showed adequate mechanical strengths long term clinical results clearly demonstrate a functional design and material related limitations.

Bioactive and Biodegradable CeramicsCalcium Phosphate Ceramics

• The compositions was relatively similar to bone Ca5(PO4)3OH

• Color similar to bone

• Shows good bonding with bone so it can be used when structural support is

required under high magnitude loading

• It is used as a coating over the metallic implants

• Modulus of elasticity is very near to bone

DISADVANTAGES

• Low mechanical tensile and shear strengths under fatigue loading

• Low attachment strength on some substrates

• Variable solubility depending on the product and their clinical applications

HYDROXYAPATITE

• When the calcium and phosphorus in the ratio of 1.5 to 1.7 are sintered in water containing atmosphere at 1200ºC to 1300ºC a crystallographic end product will be obtained that is Hydroxyapatite.

• This has osseoconductive effect when comes in contact with bone.

• Hydroxyapatite is non porous with angular or spherical shape particles that are examples of crystalline high pure hydroxyapatite.

• Their compressive strength is 500 Mpa and tensile strength is 50-70 Mpa.

PROPERTIES OF BIOACTIVE CERAMICSForms, Microstructure and Mechanical Properties

• Dense polycrystalline ceramics with small crystallites have higher

mechanical strength

• These ceramics are widely used as coatings on metallic implant

substrates

• Calcium phosphate ceramics have become a routine use by plasma

spray technique

• This technique increases the surface area which in turn increases the

osseointegration.

Density, Conductivity and Solubility

• Density of the material increases as the percentage of crystallinity

increases

• As the density / crystallinity increases the solubility decreases

• The solubility also depends on the surface area

• The amorphous products are more slouble because they have less

organized atomic structure

• These are susceptible to enzyme or cell mediated breakdown in the

same way of that of living bone.

• Thse are non conductors of heat and elecctricity.

• The Ceramic implant surface responds to the local Ph changes by releasing Na,Ca,P&Si ions in exchange for H2 ions.

• Si reacts with O2 to form Silica gel

• As the concentration of phosphorus and calcium increases at the surface they combine to form calcium phosphate rich layer and the collagen fibers become incorporated into it.

• This way the functional integration with bone occurs with the help of natural bone cementing substance so the bond formed is strong.

TISSUE RESPONSE

CARBON AND CARBON SILICON COMPOUNDS

• Extensive applications for cardiovascular devices.

• Excellent Biocompatibility profiles and Moduli of elasticity close to that of bone.

ADVANTAGES• Tissue attachment• Thermal and electrical insulation • Color control.• Provides opportunities for attachment of active

biomoleculesLIMITATIONS• Poor Mechanical strength.• Time dependent changes in the physical characteristics.• Biodegradation could adversely affect Stability.

• Minimal resistance to scratching or scraping.

POLYMERS AND COMPOSITES

• These can be designed to match tissue properties and can be fabricated at relatively low cost.

• These include polytetraflouroethylene (PTFE), polyethyleneterephthalate (PET), polymethylmethacrylate (PMMA), polypropylene (PP), polysulfone (PSF), silicon rubber (SR)

Properties • Polymers have low strengths and elastic moduli and higher

elongation to fracture compared with other class of biomaterials.

• Thermal and electric insulators

• Relatively resistant to biodegradation compared to bone

• Most uses have been for internal force distribution connectors intended to better simulate biomechanical conditions for normal tooth functions

• Some are porous where as others are constituted as solid structural forms

DISADVANTAGES• Sensitive to sterilization and handling techniques.

• Electrostatic surface properties and tend to gather dust or other particulate if exposed to semiclean oral environments

• Cleaning the contaminated porous polymers is not possible without a laboratory environment

• So the talc on the gloves or contact with towel or gauze pad or any such contamination must be avoided.

Types of Surface Roughness

1) Macrosurface Roughness.

SURFACE TOPOGRAPHYSurface topography relates to the degree of roughness of the surface and the orientation of surface irregularities.

Screw Hollow basketCore vent

2) Microsurface Roughness.a) Abraded TiO2

Al203

b) Acid EtchedHClH2SO4

c) CoatingTPSHA

ADVANTAGES OF INCREASED SURFACE ROUGHNESS

1) Increased surface areas of the implant adjacent to bone.

2) Improved cell attachment to the bone.

3) Increased bone present at implant surface. 4) Increased biomechanical interaction of the implant with bone.

Blasting with particles of various diameters is one of

the frequently used method of surface alteration.

In this approach, the implant surface is bombarded

with particles of aluminum oxide (Al2O3) or titanium oxide

(TiO2), and by abrasion, a rough surface is produced with

irregular pits and depressions.

BLASTING

Roughness depends on

particle size, time of blasting,

pressure, and distance from the

source of particles to the implant

surface.

Blasting a smooth Ti surface

with Al2 O3 particles of 25 µm, 75

µm, or 250 µm produces surfaces

with roughness values of 1.16 to

1.20, 1.43, and 1.94 to 2.20,

respectively.

SAND BLASTED IMPLANT

SAND BLASTED AND ACID ETCHED IMPLANT

Laser Induced Surface Roughening

Eximer laser – “Used to create roughness”

Regularly oriented surface roughness configuration compared to TPS coating and sandblasting

SEM x 300

SEM x 300SEM x 70

Chemical etching is another process by which surface

roughness can be increased.

The metallic implant is immersed into an acidic solution,

which erodes its surface, creating pits of specific dimensions and

shape.

Concentration of the acidic solution, time, and

temperature are factors determining the result of chemical attack

and microstructure of the surface.

CHEMICAL ETCHING

IRREGULAR SURFACE MORPHOLOGIES

Sandblasted specimen Specimen acid etched for 1 minute.

Specimen acid etched for 5 minutes.

Specimen acid etched for 10 minutes.

Recently, a new surface was introduced that was sandblasted

with large grit and acid-etched (SLA, Straumann).

This surface is produced by a large grit (250 to 500 µm)

blasting process, followed by etching with hydrochloric-sulfuric

acid.

The average ra for the acid-etched surface is 1.3 µm, and the

sandblasted and acid-etched surface, ra=2.0 µm.

SANDBLASTED AND ACID ETCHED (SLA)

Sand blasting Acid etchThe objective

Sand blasting – surface roughness (substractive method)

Acid etching – cleaning

SEM 1000X SEM 7000X

Lima YG et al (2000), Orsini Z et al (2000).

- Acid etching with NaOH, Aq. Nitric acid, hydrofluoric acid.

Decrease in contact angle by 100 – better cell attachment.

increase in osseointegration by removal of aluminium particles (cleaning).

Wennerberg et al 1996. superior bone fixation and bone adaptation

Porous sintered surfaces are produced when spherical powders of metallic or ceramic material becomes a coherent mass with the metallic core of the implant body. Lack of sharp edges is what distinguishes these from rough surfaces.

Porous surfaces are characterized by pore size, pore shape, pore volume, and pore depth, which are affected by the size of spherical particles and the temperature and pressure conditions of the

sintering chamber.

POROUS

POROUS SURFACE: ADVANTAGES

1. A secure, 3-D interlocking interface with bone.

2. Predictable and minimal crestal bone remodelling.

3. Greater surgical options with shorter implant lengths.

4. Shorter initial healing times and

5. Porous coating implants provide the space, volume for cell

migration and attachment, thus support contact osteogenesis.

SURFACE OF A POROUS TITANIUM ALLOY IMPLANT

FIBROBLASTS CULTURED FOR 24 HOURS ON THE SURFACE OF A POROUS

TITANIUM ALLOY IMPLANT.

TITANIUM PLASMA SPRAYED

Titanium Plasma Sprayed Coating (TPS)

Steinemann 1988, Tetsch 1991- 6-10 times increase surface area.

Roughness Depth profile of about 15µm

SURFACE OF A TITANIUM PLASMA-SPRAYED IMPLANT. (SEM, MAGNIFICATION 5,000 X).

HYDROXYAPATITE COATINGS

HA coated implant bioactive surface structure – more rapid osseous healing comparison with smooth surface implant.

↓Increased initial stability

Can be Indicated - Greater bone to implant

contact area - Fresh extraction sites - Newly grafted sites

SEM 100X

• Hydroxyapatite([Ca10(PO4)6OH]2) coating was brought to the dental profession by DeGroot

ADVANTAGES OF HA-COATINGS

1. HA coating can lower the corrosion rate of the same substrate

alloys.

2. HA coatings has been credited with enabling to obtain improved

bone to implant attachment compared with machined surface.

3. The bone adjacent to the implant has been reported to be better

organized than with other implant materials and with a higher

degree of mineralization.

CERAMIC AND CERAMIC COATED IMPLANTS

Ceramic materials are used to coat metallic implants to

produce an ionic ceramic surface, which is thermodynamically

stable and hydrophilic, thereby producing a high strength

attachment to bone and surrounding tissues.

These ceramic can either be plasma sprayed or coated on

to the metal implant to produce bio-active surface.

Aluminum oxide (Al2O3) is used as the gold standard for ceramic implants because of its inertness with no evidence of ion release or immune reaction in vivo.

Zirconia (Zro2) has also demonstrated a high degree of inertness.

THE TÜBINGEN IMPLANT OF ALUMINUM OXIDE HAS SPECIFIC MICRO-IRREGULARITIES ON THE SURFACE,

CLAIMED TO ALLOW BONE INGROWTH.

OTHER SURFACE MODIFICATIONS

Surface modification methods include controlled chemical reactions with nitrogen or other elements or surface ion implantation procedures.

The reaction of nitrogen with "titanium alloys at elevated temperatures results in titanium nitride compounds being formed along the surface.

Electrochemically, the titanium nitrides are similar to the oxides (TiO2), and no adverse electrochemical behavior has been noted if the nitride is lost regionally.

The titanium substrate reoxidizes when the surface layer of nitride is removed.

Doped surfaces that contain various types of bone growth factors or other bone-stimulating agents may prove advantageous in compromised bone beds. However, at present clinical documentation of the efficacy of such surfaces is lacking : BMP = Bone morphogenetic protein.

DOPED SURFACES

•The biomaterials discipline has evolved

significantly over the past decades, and

synthetic biomaterials are now constituted,

fabricated, and provided to health care

professionals as mechanically and chemically

clean devices that have a high predictability

of success when used appropriately within

the surgical disciplines

List of referencs• Implant Dentistry -Carl E Misch.• Principles and practice of implant dentistry -Charls M

Weiss, Adam Weiss.• J Dent Edu 1988; 52: 815-820.• Atlas of Oral implantology - A Norman Cranin.• Sciences of dental materials - Anusavise.• The BRANEMARK system of oral reconstruction - A

clinical atlas.• DCNA 1986 ; 30 (1) 25-47• IJOMI 2000 ;(15) 675-690• D.C.N.A., 1992 ; 36, 1-17• JPD, 1983 ; 50 : 108-113.• JPD, 1983; 50:832-37. • IJP, 1990 ; 3 : 30-41