Titanium Alloys: Clinical Applications

TITANIUM ALLOYSCLINICAL APPLICATIONS

AAMIR GODIL FIRST YEAR P.G.

DEPARTMENT OF PROSTHODONTICSM.A.R.D.C.

OUTLINE• INTRODUCTION• USES OF TITANIUM• CRYSTALLINE FORMS AND GRADES OF TITANIUM• MECHANICAL AND CHEMICAL PROPERTIES• APPLICATIONS IN DENTISTRY

– TITANIUM AND COMPLETE DENTURES– TITANIUM AND CAST PARTIAL DENTURE FRAMEWORK– TITANIUM AND FIXED PARTIAL DENTURES– TITANIUM AND IMPLANTS– TITANIUM AND MAXILLOFACIAL PROSTHESES

• TITANIUM PROCESSING• CONCLUSION

TITANIUM

• Abundant in earth’s crust at oxide = Rutile: TiO2

• Refined to metallic titanium by Kroll’s process• Historically used extensively in– Aerospace– Aeronautical engineering–Marine equipments

High strength and rigidity

Low density and

corresponding low weight

Ability to withstand

high temperatures

Resistance to corrosion

Excellent biocompatibil

ity

USES OF TITANIUMMETAL- CERAMIC RESTORATIONS

DENTAL IMPLANTS

PARTIAL DENTURE FRAMEWORKS

COMPLETE DENTURE BASES

BAR CONNECTORS

MAXILLOFACIAL PROSTHESES

ORTHODONTIC WIRES

DENTAL USES ARTIFICIAL HIP JOINTS

BONE SPLINTS

ARTIFICIAL HEART PUMPS

ARTIFICIAL HEART VALVES PARTS

PACEMAKER CASES

SURGICAL USES

CRYSTALLINE FORMS OF TITANIUM

• The first is alpha which has a hexagonal close-packed crystal structure.

• The second is beta which has a body-centered cubic structure.

Titanium can exist in two crystal forms.

GRADES OF TITANIUMALPHA ALLOYS

• Contain neutral alloying elements (such as tin) and/ or alpha stabilisers (such as aluminium or oxygen) only

• Not heat treatable

• Examples:Ti-5AL-2SN-ELI, Ti-8AL-1MO-1V

NEAR-ALPHA ALLOYS

• Contain small amount of ductile beta-phase

• Alloyed with 1–2% of beta phase stabilizers such as molybdenum, silicon or vanadium

• Examples: Ti-6Al-2Sn-4Zr-2Mo, Ti-5Al-5Sn-2Zr-2Mo, IMI 685, Ti 1100

ALPHA AND BETA ALLOYS

• Metastable and generally include some combination of both alpha and beta stabilisers

• Can be heat treated

• Examples:Ti-6Al-4V, Ti-6Al-4V-ELI, Ti-6Al-6V-2Sn.

BETA AND NEAR BETA ALLOYS

• Metastable and which contain sufficient beta stabilisers

• Examples : Ti-10V-2Fe-3Al, Ti-13V-11Cr-3Al, Ti-8Mo-8V-2Fe-3Al, Beta C, Ti-15-3.

MECHANICAL PROPERTIES

Tensile Strength: 270-740 MPa

Fatigue Limit: 50% of Tensile Strength

Young's Modulus: 105-125 GPa.

Hardness: 120 BHN (highest purity grade)

PROPERTY HIGH NOBLE METAL

Co-Cr Ni-Cr-Be CP Ti

Biocompatibility Excellent Excellent Fair Excellent

Density 14 g/cm2 7.5 g/cm2 8.7 g/cm2 4.5 g/cm2

Elastic Modulus (Stiffness)

90 GPa 145-220 GPa 207 GPa 103GPa

Sag Resistance Poor to excellent Excellent Excellent Fair

Technique Sensitivity Minimal Moderately high Moderately high Extremely high

TITANIUM AND CORROSION

• Titanium-based alloys and alloys containing titanium are prone to gap corrosion and discoloration in the oral cavity.

• Therefore titanium is electrochemically inactivated by the addition of small percentage of a metal of platinum group to improve the anticorrosion properties of the alloys by inducing a firm passive coating.

RESISTANCE TO OXIDATION

Titanium is resistance to oxidation upto about 593°C (1100°F) but it is a reactive metal and can pick up and dissolve interstitial elements like oxygen, nitrogen and hydrogen above this temperature.

TITANIUM IN CONTACT WITH OTHER METALS

In most environments the potential of passive titanium and stainless steel are similar, so galvanic effects do not occur when these metals are connected.

Titanium usually functions as an efficient cathode, and its contact will not lead to significant attack but can cause adverse galvanic effects upon other metals.

TITANIUM IN CHEMICAL ENVIRONMENT

Dry chlorine attacks titanium but is resistant to wet chlorine.

In citric acid 50% strength and trichloracetic acid there is significant corrosion.

It is also resistant to mercury upto 150°C.

In strong solution of caustic alkalis, titanium tends to form soluble titanates and in moderate or low concentration of alkali, there is no significant attack.

APPLICATIONS IN DENTISTRY

• REMOVABLE PARTIAL DENTURE FRAMEWORKS, COMPLETE DENTURES AND OVERDENTURES

• IN FIXED PARTIAL DENTURE

• IMPLANTS

• ORAL AND MAXILLOFACIAL PROSTHESIS

TITANIUM AND COMPLETE DENTURES

The retention of acrylic resin to the titanium base is an important consideration.

Noriyuki Wakabayashi et al confirmed that bond strength between a denture-base resin containing an adhesion-promoting monomer and Ti-6Al-4V alloy that had been airborne particle abraded using aluminum oxide particles was statistically equivalent to that between the same resin and a cobalt-chromium alloy casting.

TITANIUM AND CAST PARTIAL DENTURE

FRAMEWORK

Commercially pure (CP) titanium and titanium alloys containing aluminum and vanadium, or palladium (Ti-O Pd), should be considered potential future materials for removable partial denture frameworks.

The usefulness of Ti as a metal for removable partial denture (RPD) and complete-denture frameworks has been evaluated.

Removable partial denture frameworks that were 0.70 mm thick had better castability than did 0.35 mm thick RPD frameworks, suggesting that if Ti is used for RPD frameworks, a thicker wax pattern is needed than is used in casting of a conventional denture framework with Co-Cr alloys.

In the same study, Ti commonly failed to cast perfect mesh specimens, but Co-Cr alloys did not have this problem.

TITANIUM AND FIXED PARTIAL DENTURES

The low coefficient of thermal expansion (CTE) of titanium (about 10 x 10-6/ºC) compared to those of the conventional low-fusing porcelains (about 13 x 10-6/°C) raised the concern of thermal compatibility.

The difference in the coefficient of the expansion between the alloy and porcelain should be within ±1x10-6 /°C to obtain sufficient bonding strength. Coefficients of thermal expansion of pure titanium and Ti-6A1-4V are 10.37 x 10-6 and 12.43 x 10-6 /ºC, respectively, which are considerably smaller than those of commercial porcelain materials which is about 14 x l0-6 /°C.

• Firing of porcelain over titanium requires a special protocol.

• Metal exposure to temperatures that exceed 8000C leads to the absorption of oxygen and nitrogen, providing the formation of a thick superficial layer of oxide that may attain a thickness up to 1mm and harms the bonding of ceramic to substrate.

Wilson José Garbelini. Evaluation of low-fusing ceramic systems combined with titanium grades ii and v by bending test and scanning electron microscopy; J Appl

Oral Sci 2003; 11(4): 354-60

• Hence compliance with these criteria, low fusion ceramics are used with Titanium.

• Low fusing porcelains are required to adequately match the thermal expansion coefficient of titanium to reduce residual stress, which may result in failure of overlying ceramic.

TITANIUM AND IMPLANTS

Titanium and its alloys are important in dental and surgical implants because of their high degree of biocompatibility, strength and corrosion resistance. Pure titanium, theoretically, may form several oxides. Among these . TiO, Ti02 and Ti2 03. Of these, TiO2 is the most stable and therefore the most commonly used under physiologic conditions. These oxides form spontaneously on exposure of Ti to air.

Titanium, both as a pure metal and as an alloy, is easily passivated, forming a stable Ti02 surface oxide that makes the metal corrosion resistant.

This oxide will repair itself instantaneously on damage thatmight occur during insertion of an implant.

The normal level of Ti in human tissue is 50 ppm. Values of 100 to 300 ppm are frequently observed in soft tissues surrounding Ti implants.

At these levels, tissue discoloration with Ti pigments can be seen.

This rate of dissolution is one of the lowest of all passivated implant metals and seems to be well tolerated by the body.

TITANIUM AND MAXILLOFACIAL PROSTHESES

CRANIAL PROSTHESIS:Titanium has been recently used in fashioning cranial prostheses

This metal is a strong but light material that is soft enough to be swaged in a die-counterdie system.

Moreover it can be strain hardened and thus become stronger with manipulation. Sheets that are 0.6 1mm thick are adequate and its radiodensity permits most radiographic studies.

After the metal prosthesis is shaped, trimmed, and polished, tissue acceptance of the implant is enhanced by anodizing it in a solution of 80% phosphoric acid, 10% sulphuric acid, and 10% water (Gordon and Blair, 1974).

Titanium trays offer the best combination of strength and rigidity with the least bulk of any implant material currently available for restoration of mandibular defects.

Titanium frameworks are also used for rehabilitation of maxillary and mandibular defects like cleft palate.

The osseointegration technique allows the placement of titanium implants in to the orbital bony resin that are capable of supporting a facial prosthesis.

The osseointegration procedure, allows titanium implants in to bone to project through the skin, providing points of attachment for prosthetic devices .

Titanium implants are used for retention of Bone Anchored Hearing Aid (BAHA) .

TITANIUM PROCESSING

Processing of Titanium in the Dental Laboratory

–Dental Melting and Casting Technology

– CAD/CAM Technique

Titanium and Titanium Alloys: Fundamentals and Applications, by Dr. Christoph Leyens, Dr. Manfred Peters

CASTING Difficulties in casting Titanium:

– High melting point– High reactivity– Low casting efficiency– Inadequate expansion of investment– Casting porosity– Requires expensive equipments

• Titanium requires special melting and casting technology and requires some modification of relevant working steps in the dental lab.

• The metal is melted using an electric plasma arc or inductive heating in a melting chamber filled with inert gas or held in a vacuum.

• Pure titanium is usually melted today by argon-arc melting using a copper crucible.

• Casting is done by a vacuum-pressure casting technique.

• Due to the requirements for precision, special investment materials based mainly on silica or silica-modifications are used in dental casting technology.

• Binders used for the investment powder are ethyl-silicates or phosphate/magnesium oxide systems.


• Since the reactivity of molten titanium with these types of investments is very high, they cannot be used for dental titanium castings due to formation of a large α case layer with micro-cracks and increased hardness that renders dental processing extremely difficult.

• This thin layer can be removed completely by usual dental surface treatments like griniding.


• Investment materials used for casting titanium are refractory materials in which the reactivity with titanium is reduced by using components with low standard free energy of oxide, such as alumina, magnesia and zirconium oxide.

Wagner Sotero Fragoso et al, The influence of mold temperature on the fit of cast crownswith commercially pure titanium; Braz Oral Res 2005;19(2):139-43

• Yu Guilin et al conducted a study to evaluate the effects of different investment materials on the formation of α case layer on the titanium casting.

• Conclusion:- Based on the thickness of the surface reaction layer and the surface microhardness of titanium castings, MgO based investment materials may be the best choice for casting these materials.

Yu Guilin, PhD, The effects of different types of investments on the alpha-case layerof titanium castings; J Prosthet Dent 2007;97:157-64.

• One study has shown that use of Zirconia-based coating on the wax pattern substantially reduced the thickness of the complex reaction layer with the investment and yeilded titanium castings with a high-quality surface.Luo XP, et al: Titanium casting into phosphate bonded investment

with zirconate. Dental Mater 18:512,2002.

• The castability of titanium can be influenced by the mold temperature.

• Low mold temperatures have been used to accelerate the solidification of molten titanium, reducing the reactivity with the investment.

• As a result, manufacturers have recommended low mold temperatures to minimize the formation of the reaction layer.

Wagner Sotero Fragoso et al, The influence of mold temperature on the fit of cast crownswith commercially pure titanium; Braz Oral Res 2005;19(2):139-43

It was reported that sprue design commonly used for Co-Cr alloy was not suitable for titanium

Large and multiple sprues found to reduce porosity.

Direction of sprues: lowest porosity in titanium circumferential clasp was obtained when the sprue was attached perpendicular to minor connector

POROSITY OF CAST TITANIUM

A curved sprue design produced significantly less porosity in the circumferential clasp arms of a cast titanium removable partial denture than the conventional straight design.

• New alloys of titanium with nickel that can be cast by more conventional methods are being developed.

• These are reported to release very little ionic nickel and bond well to porcelain.

• New methods of forming titanium crowns and copings by CAD/CAM (computer-aided design/computer-aided milling) technology avoid the problems of casting.

Fundamentals of Fixed Prosthodontics, 3rd edition, Shillingburg

CAD/CAM TECHNIQUE• An optical scanner conducts the data generation from the

master model.

• The design is accomplished by CAD software, adapted to the special demands of dental technology.

• Data generation of milling tracks and manufacturing are done automatically.

• The process starts from rods or plates depending on the system used.


CONCLUSION• Titanium is a useful biomaterial. It will probably continue

to dominate the implant market in the future.

• Titanium is economical and readily available, but the technologies of machining, casting, welding, and veneering it for dental prostheses are new.

• Increased use of titanium in prosthodontics depends on research and clinical trials to compare its effectiveness, as an equivalent or superior metal, to existing metals. The future of titanium in dentistry looks promising.

Thank You

Titanium Alloys: Clinical Applications

Health & Medicine