Dental Implants & Biomaterials

• Dental implants are artificial tooth roots placed into the jaw to support a replacement tooth.

Biomaterials

• Biomaterials are compatible with living hard and soft tissues.
• Physical properties, corrosion potential, surface configuration, tissue induction, and inflammation/rejection response potential are key factors.

Biomaterials used for Dental Implants

• Biomaterials for dental implants are classified by chemical composition.
• The three types are metals and alloys, ceramics and carbon, and polymers and composites.

Metals and Alloys

• The most used allow is titanium alloy (Ti-6Al-4V), including Titanium, 6% Aluminium and 4% Vanadium.
• This reactive group of metals and alloys forms oxides in air and oxygenated solutions.
• Oxidized surface reduces biocorrosion, making it the metal of choice for oral implants.
• Titanium has a relatively low modulus of elasticity and tensile strength compared to other alloys.
• Strength values are about 1.5 times greater than compact bone.
• The Titanium alloy (Ti-6Al-4V) is about six times stronger than compact bone.

Disadvantages of Titanium

• Titanium is mostly safe, but concerns remain.Titanium may slowly degrade, increasing metal concentration in the bloodstream.
• Titanium implants may be rejected, though rare.
• Some forms of titanium have harmful health effects.
• For example, titanium tetrachloride is associated with skin irritation and lung damage if inhaled.

Cobalt–Chromium–Molybdenum-based Alloy

• Cobalt-based alloys are often used in castable conditions, allowing for custom designs like subperiosteal frames.
• The alloy elements include Cobalt, Chromium, and Molybdenum.
• Cobalt provides strength, which is 4 times that of compact bone.
• Cobalt also contributes to surface abrasion resistance.
• Chromium offers corrosion resistance via an oxide surface.
• Molybdenum provides strength and corrosion resistance.
• The alloy includes minor concentrations of Nickle, Manganese, and Carbon.
• Nickle has a biocorrosion product and carbon maintains the mechanical properties.

Gold–Platinum and Palladium

• These metals have relatively low strength and this limits implant design.
• In addition to the cost per unit weight limits.

Ceramics and Carbon

• Ceramics are nonorganic, non-metallic, and nonpolymeric.
• Ceramics are manufactured by compacting and sintering at elevated temperatures.
• Ceramics were introduced for surgical implant devices because of their inertness to biodegradation and high strength.
• Ceramics also stand thanks to their physical characteristics, such as minimal thermal and electrical conductivity.
• Ceramics are chemically inert, care is needed in handling due to low ductility and brittleness.
• Zirconia (Artificial Diamond) is a good example of ceramic used in dental applications.

Zirconium Oxides Advantages

• Zirconium dental implants behave similarly to titanium implants.
• Zirconium is a ceramic substance that is white, flexible, strong, and ideal for dental implant material.
• The material is reported as highly resistant to corrosion.
• Some consider zirconium a better implant material than titanium.
• Zirconium implants suit the osseointegration process and are easily accepted by the body.
• These implants have excellent tensile strength, are more durable, and have less risk of breakage.
• The material can withstand drastic temperature changes.
• Being white in color, zirconium implants have an aesthetic advantage over dark titanium implants.

Disadvantages of Zirconium Dental Implants

• Zirconium is a radioactive material and might contain radioactive isotopes.
• Implants give off only a minute level of radioactivity, certified as non-dangerous by manufacturers.
• Zirconium is substantially more costly than titanium.
• These are new products, thus, they lack a successful track record like titanium counterparts.

Carbon and Carbon Silicon Compounds

• Carbon compounds are often classified as ceramics.
• This is owing to their chemical inertness and absence of ductility.

Uses of Carbon and Carbon Silicon Compounds

• There are extensive applications for cardiovascular devices.
• Excellent biocompatibility profiles and moduli of elasticity close to that of bone have resulted in clinical trials in dental and orthopedic prostheses.

Disadvantages of Carbon and Carbon Silicon Compounds

• Mechanical strength properties are relatively poor.
• Biodegradation that could adversely influence tissue stability.
• Time dependent changes in physical characteristics.
• Minimal resistance to scratching or scraping procedures associated with oral hygiene.

Osseointegration

• Osseointegration refers to the direct attachment or connection of osseous tissue to an inert alloplastic material.
• This happens without intervening connective tissue.

Factors Affecting Osseointegration

• Implant biocompatibility
• Implant design
• Implant surface
• Bone quality
• Surgical technique
• Loading condition

Implant Biocompatibility

• The biocompatibility is affected by chemical composition, mechanical properties, electrical charge and surface features.
• A relationship exists between the material toxic reaction and a high corrosion rate.
• Co, Cu, Ni, and V increase degradation and toxicity in this order.
• Metals with corrosion passivation do not trigger a negative tissue response (e.g., Pt, Zr, and Ti).

Implant Design (Root-Form)

• Commercial dental implants can be divided into groups according to shape, type of connection, surface treatment, and surface roughness.
• Shapes include cylindrical, conical, and hybrid.
• Types of connection exist with external hexagon, internal hexagon, and Morse taper.
• Surface treatments involve acid etching, sandblasting, coating by plasma sprays, and laser treatment.
• Surface roughness has: macroroughness, microroughness, and nanoroughness.

Cylindrical Implant

• Some investigators explain the lack of bone steady state by overload due to micromovement.
• Others incriminate an inflammation causing infection.
• This is particularly due to the very rough surfaces typical for these types of implant.
• Threaded implants have demonstrated maintenance of a clear steady state bone response.
• To enhance initial stability and increase surface contact, most implant forms have been developed as a serrated thread.

Implant surface

• The number of threads per unit length is an important factor in implant osseointegration.
• Increased depth between individual threads allows for improved contact area between bone and implant.
• Screw-shaped dental implants dominate the dentistry market as the provide a large contact area between implant and bone.
• The screw shape increases primary stability and reduces shear stress and stress concentration.

Surface Treatment of Titanium Implants

• Sandblasting is uses treatment where the implant is blasted with silicon oxide, aluminum oxide, or titanium oxide.
• Strong acids is treatment where etching roughens titanium implants.
• Routinely used solutions include a mixture of HNO3 and HF or a mixture of HCI and H2SO4.

Sandblasted and Acid-Etched (SLA) Implants

• This type of surface is produced by a large grit 250-500 µm blasting process followed by etching with hydrochloric/sulfuric acid.
• Sandblasting results in surface roughness, and acid etching leads to microtexture and cleaning.
• These surfaces are known to have better bone integration compared to other methods.

Plasma Sprayed and Hydroxyapatite Coating (HA) Surfaces

• Hydroxyapatite coating has improved bone-implant attachment compared to machined surfaces.
• Bone adjacent to such implants has been reported to be better arranged thanks to higher mineralization.
• The most common problem with such surface coatings is the separation of coating from metallic substrate (delamination).

HA Coatings Advantages

• Offers increasing surface area, decreasing corrosion rates, accelerating bone formation via faster osteoblast differentiation, and enhanced bio mechanics so HA coated implants can withstand loads.
• Provides a more organized bone pattern and higher degree of mineralization, as well as, increased bone penetration (which improves fixation).

Bone Quality (Lekholm 1985)

• Type I is composed of homogeneous compact bone, usually in the anterior lower jaw.
• Type II: Has a thick layer of cortical bone surrounding dense trabecular bone, usually in the posterior lower jaw.
• Type III: Has a thin layer of cortical bone surrounding dense trabecular bone.
• It is normally found in the anterior upper jaw but can be seen in the posterior lower jaw and the posterior upper jaw.
• Type IV: Has a very thin layer of cortical bone surrounding a core of low-density trabecular bone.
• It is very soft bone and normally found in the posterior upper jaw, but can be seen in the anterior upper jaw.

Surgical Technique

• Minimal tissue violence during surgery is essential for proper osseointegration.
• Careful cooling while surgical drilling is performed at low rotatory rates
• Use sharp drills and use a grade series of drills.
• The insertion torque is a moderate level to avoid stress concentrations around the implant and subsequent bone resorption.

Loading Condition

• Loading conditions include delayed loading and Immediate loading.
• Delayed loading involves a two-stage or one-stage surgical protocol.
• Immediate loading involves immediate occlusal loading, immediate non-occlusal loading, and early loading.
• Immediate occlusal loading means that the implant is placed within 48 hours after surgery.
• Immediate non-occlusal loading is used in single-tooth or short-span applications.
• Early loading involves prosthetic function within two months.