Biomaterials For Dental Implants

Biomaterials For Dental Implants

Write a short note on implant biomaterial.
Or
Write a short note on biomaterials used in implants.
Answer:

Biomaterial is defined as a non-viable material used in a medicinal device intended to interact with biological systems.

Biomaterials, regardless of use, fall into four general categories:

• Metals and metallic alloys
• Ceramics
• Synthetic polymers
• Natural materials

Metals and metal alloys that utilize oral implants include titanium, tantalum, and alloy of Ti-Al-Va, Co-Cr-Mb, and Fe-Cr-Ni.

These materials are generally selected on the basis of their overall strength properties:

• Bioinert materials allow close approximation of bone on their surface leading to contact osteogenesis.
• These materials allow the formation of new bone on their surface and ion exchange with the tissues leads to the formation of a chemical bonding along the interface bonding osteogenesis.
• Biotolerant are those that are not necessarily rejected when implanted into living tissue.
• They are recombinant human bone morphogenetic protein-2 (rhBMP-2) which induces de novo bone formation.
• Biomimetics are tissue-integrated engineered materials designed to mimic specific biologic processes and help optimize the healing/regenerative response of the host microenvironment.
• Bioinert and bioactive materials are also called osteoconductive, meaning that they can act as scaffolds allowing bone growth on their surface.

Titanium and its Alloys:

Titanium as implant material is most commonly and widely used. It has a good record of being used successfully as an implant material and this success with titanium implants is credited to its excellent biocompatibility due to the formation of a stable oxide layer on its surface.

Titanium and its alloys are of the following types, i.e.

1. Commercially pure titanium (Cp–Ti)
2. Titanium–6 Aluminum–4 Vanadium (Ti–6Al–4Va)

Commercially Pure Titanium:

• The commercially pure titanium (cpTi) is classified into 4 grades which differ in oxygen content.
• Grade 4 is having the most (0.4%) and grade 1 is the least(0.18%) oxygen content.
• The mechanical differences that exist between the different grades of commercially pure titanium is primarily because of the contaminants that are present in minute quantities.
• Iron is added for corrosion resistance and aluminum is added for increased strength and decreased density, while vanadium acts as an aluminum scavenger to prevent corrosion.
• The hexagonal close-packed crystal lattice of Ti is called the α-Ti (α-phase). On heating it at 883°C phase transformation occurs from hexagonal close-packed to body-centered cubic lattce or β- phase
• Ti is reactive as it forms spontaneously a dense oxide fim at its surface.
• Ti is a dimorphic metal, i.e. below 882.5°C it exists as α-phase and above this temperature, it changes from α- phase to β-phase.
• Because of the high passivity, controlled thickness, rapid formation, ability to repair itself instantaneously if damaged, resistance to chemical attack, catalytic activity for a number of chemical reactions, and modulus of elasticity compatible with that of bone o, Ti is the material of choice for intraosseous applications.

Disadvantages its Alloys:

There is an esthetic issue due to the gray color of the titanium and this is more pronounced when the soft tissue situation is not optimal and the dark color shines through the thin mucosa.

Titanium—6 Aluminum—4 Vanadium (Ti—6Al—4Va):

• This is the alloy form of titanium.
• Titanium reacts with several other elements, For example, Silver, Al, Ar, Cu, Fe, Ur, Va, and Zn to form alloys.
• Titanium alloys exist in three forms, i.e. alpha, beta, and α-β.
• These types originate when pure titanium is heated with elements Al, and Va in certain concentrations and cooled, these types originate.
• These added elements play like phase-condition stabilizers.
• Aluminum is an alpha-phase condition stabilizer and it also increases the strength and decreases the weight of the alloy.
• Vanadium acts as a beta-phase stabilizer.
• The temperature at which α-to β transformation occurs changes to a range of temperatures as Al or Va is added to Ti.
• Both α and β forms exist in this range.
• Temperatures to which the desired form is present can be obtained by quenching the alloy at room temperature. To increase the strength, these alloys may be heat treated.
• The alloys most commonly used for dental implants are of the alpha-beta variety. The most common contains 6% Al and 4% Va. (Ti 6 Al 4V)

Iron-Chromium-Nickel Based Alloys: Stainless Steel:

Composition of Stainless Steel:

• 70% iron which is the main constituent
• 18% chromium provides corrosion resistance
• 8% nickel stabilizes the austenitic structure

The alloy is used in wrought and heat-treated conditions which results in high strength and ductility. Passivation is required to maximize biocorrosion resistance. Currently, they are rarely used.

Advantages of Stainless Steel:

• It is corrosion resistance
• It has increased ductility.

Disadvantages of Stainless Steel:

• It is vulnerable to crevice and pitting corrosion
• It is contraindicated in patients allergic to nickel

Ceramics of Stainless Steel:

• Ceramics are inorganic, nonmetallic, and nonpolymeric materials that are either bioactive or bioinert (osteoconductive). Ceramic implants get manufactured by compaction and sintering at high temperatures.
• Bioinert ceramics are used in various implants, i.e. root form, endosteal, plate form, and pin type dental implants.
• Bioactive ceramics are applied to titanium and cobalt alloy substrates by plasma spraying. Plasma spraying provides roughened, biologically acceptable surface for bone growth and ensures anchorage in the jaw. Particles are small-sized crystalline hydroxyapatite ceramics.

Polymers of Stainless Steel:

They are used for manufacturing superstructures. They mainly act as shock absorbers to the load-bearing implants. They are fabricated in porous and solid forms for tissue attachments and replacement augmentation.

Natural Materials of Stainless Steel:

Gold, tantalum, carbon, etc. Materials were used in the past. Recently zirconia and tungsten are used. Titanium has replaced most of these materials. Carbon was recently used as coatings for metallic and ceramic devices. Root form or endosteal plate form, and pin-type dental implants are generally made from high ceramics from aluminum, titanium, and zirconium oxides. The compressive, tensile, and bending strengths exceed the strength of compact bone by 3 to 5 times. These properties combined with high moduli of elasticity and especially with fatigue and fracture strength have resulted in specialized design requirements for this class of biomaterials.