The success or failure of osseointegration is dependent on the following factors.
a) Biocompatibility of the material - is a vital factor as we have discussed in detail in the preceeding part of this unit. The nature of the material and its surface oxide determine the reaction of tissues around it.
b) Implant design is a factor that determines the primary stability of the implant when it is surgically place. Most commonly used design is a root form endosseous implant which is threaded. More details of the implant design and its implications will be discussed in the next block
c) Surgical technique- The osteotomy preparation is critical both from biologic and biomechanical points of view. The bone drilling should be sequential and with copious irrigation to prevent overheating and subsequent necrosis of surrounding bone. Also the osteotomy site should be mated to the particular implant selected for use to afford primary stability and ensure the success of osseointegration. Soft tissue handling is vital, the flap should be handled with care and a hermetic closure without tension favours osseointegration as any flap tearing etc can lead to infection and failure.
d) Bone density - the most important bone property is density which is influenced by factors such as patient age and genetics. Higher density bones have a better success rate as they provide better stability and better bone implant contact thus favouring osseointegration.
e) Occlusal load – The timing and amount of overload are critical for osseointegration. Occlusal loading early, where the primary stability is low leads to high levels of micromotion and leads to fibrous union. Also if there is no loading after the initial osseointegration process is complete, the remodeling and maturation can be hampered.
f) Infection – Presence of infection at the implant site leads to failure of osseointegration.
g) Implant surface- Surface topography is critical as rough surfaces produce better bone fixation as compared with smooth surfaces, and osteoblast like cells exhibited greater tendency to attach to rough titanium surfaces. Cells flattening and spreading have been observed on both porous and dense hydroxyapatite. Other factors which affect are surface oxide composition, surface contamination.
Machined implant has irregular surface roughness from approximately 10μm grooves and ridges in the machining direction. The roughness of implants can be modified by several methods – sandblasting 1 to 10 μm roughness scale, plasma spraying 10 to 100 μm roughness scale. For producing extremely smooth surfaces (eg. Polished collar of implant) electro polishing is done to 0.1 μm scale.
The biologic interaction between the tissue and the implant material at an interface may result in a variety of phenomena such as leaching, corrosion, mechanical processes, adsorption, denaturation and catalysis.
The biologic response can include:
i) Metabolic disturbance.
ii) Inflammatory response
iii) Immune response
iv) Mutagenesis
v)Carcinogenesis
vi) Adaptation
Metallic implants undergo one or more several surface modifications to enable them to become suitable for implantation. These modifications are passivation, anodization,ion implantation and texturing. Passivation refers to the enhancement of the oxide layer to prevent the release of metallic ions as a result of surface breakdown.Minimizing ion release also enhances the biocompatibility of these materials.Passivation treatments can be performed through immersion in 40 % nitric acid or anodization where an electric current is passed through the metal. The former method of treatment minimally increases the oxide layer thickness whereas the latter results in a thicker oxide layer.
Another surface modification method is ion implantation which consists of bombarding the surface of the implant with high energy ions up to a surface depth of 0.1 micron.This procedure is claimed to increase the corrosion resistance of the metal through the formation of TiN surface layer.A pore size of 100 microns is the most suitable one for bone penetration. If the pore sizes are less than approximately 50 microns, then penetration appears to be poor.Pore sizes of larger than 250 microns are inadvisable as they cause considerable weakening of the structure. Whilst surface pores offer the opportunity for mechanical retention between tissues and the implant, continuous interconnecting pores throughout the material enable tissue cells to permeate the entire mass of the implant, thus producing a tissue/implant composite.
Rough or porous surface exhibited a measurable increase in the strength of the implant-bone bond compared to smooth surfaces. Porous surfaces also show faster initial healing compared to noncoated-porous titanium implants. This is because porosity allows bone formation within porosities during the healing phase. Surface roughening creates an irregular surface composed of grooves, ridges, and pits which are more conducive to cell attachment.Hydroxyapatite coating has been recommended for clinical use. These implants are superior with respect to the degree and rate of fixation in the bone as there is accelerated bone formation and maturation and lower corrosion rate around hydroxyapatite-coated implants. Bone adjacent to the implant is more organized than with other implant materials and with a high degree of mineralization. There is a greater surface area of bone apposition to implant which enhances the biomechanics and initial load-bearing capacity of the system. This enables the hydroxyapatite- coated Ti or Ti alloy implants to obtain improved bone-to-implant attachment. There is an increase in bone penetrations, enhancing fixation in areas of limited initial bone contact. Unfortunately, when implanted these often exhibit cracks or even complete loss of hydroxyapatite coating, and also show heavier colonization of micro-organisms. Therefore, are not necessarily advantageous for the long-term prognosis.Many implants have sandblasted surfaces that are subsequently acid etched. The goal of this combination technique is to render the implant surface rough (sandblasting) and optimally clean (etching).
a) Biocompatibility of the material - is a vital factor as we have discussed in detail in the preceeding part of this unit. The nature of the material and its surface oxide determine the reaction of tissues around it.
b) Implant design is a factor that determines the primary stability of the implant when it is surgically place. Most commonly used design is a root form endosseous implant which is threaded. More details of the implant design and its implications will be discussed in the next block
c) Surgical technique- The osteotomy preparation is critical both from biologic and biomechanical points of view. The bone drilling should be sequential and with copious irrigation to prevent overheating and subsequent necrosis of surrounding bone. Also the osteotomy site should be mated to the particular implant selected for use to afford primary stability and ensure the success of osseointegration. Soft tissue handling is vital, the flap should be handled with care and a hermetic closure without tension favours osseointegration as any flap tearing etc can lead to infection and failure.
d) Bone density - the most important bone property is density which is influenced by factors such as patient age and genetics. Higher density bones have a better success rate as they provide better stability and better bone implant contact thus favouring osseointegration.
e) Occlusal load – The timing and amount of overload are critical for osseointegration. Occlusal loading early, where the primary stability is low leads to high levels of micromotion and leads to fibrous union. Also if there is no loading after the initial osseointegration process is complete, the remodeling and maturation can be hampered.
f) Infection – Presence of infection at the implant site leads to failure of osseointegration.
g) Implant surface- Surface topography is critical as rough surfaces produce better bone fixation as compared with smooth surfaces, and osteoblast like cells exhibited greater tendency to attach to rough titanium surfaces. Cells flattening and spreading have been observed on both porous and dense hydroxyapatite. Other factors which affect are surface oxide composition, surface contamination.
Machined implant has irregular surface roughness from approximately 10μm grooves and ridges in the machining direction. The roughness of implants can be modified by several methods – sandblasting 1 to 10 μm roughness scale, plasma spraying 10 to 100 μm roughness scale. For producing extremely smooth surfaces (eg. Polished collar of implant) electro polishing is done to 0.1 μm scale.
The biologic interaction between the tissue and the implant material at an interface may result in a variety of phenomena such as leaching, corrosion, mechanical processes, adsorption, denaturation and catalysis.
The biologic response can include:
i) Metabolic disturbance.
ii) Inflammatory response
iii) Immune response
iv) Mutagenesis
v)Carcinogenesis
vi) Adaptation
Metallic implants undergo one or more several surface modifications to enable them to become suitable for implantation. These modifications are passivation, anodization,ion implantation and texturing. Passivation refers to the enhancement of the oxide layer to prevent the release of metallic ions as a result of surface breakdown.Minimizing ion release also enhances the biocompatibility of these materials.Passivation treatments can be performed through immersion in 40 % nitric acid or anodization where an electric current is passed through the metal. The former method of treatment minimally increases the oxide layer thickness whereas the latter results in a thicker oxide layer.
Another surface modification method is ion implantation which consists of bombarding the surface of the implant with high energy ions up to a surface depth of 0.1 micron.This procedure is claimed to increase the corrosion resistance of the metal through the formation of TiN surface layer.A pore size of 100 microns is the most suitable one for bone penetration. If the pore sizes are less than approximately 50 microns, then penetration appears to be poor.Pore sizes of larger than 250 microns are inadvisable as they cause considerable weakening of the structure. Whilst surface pores offer the opportunity for mechanical retention between tissues and the implant, continuous interconnecting pores throughout the material enable tissue cells to permeate the entire mass of the implant, thus producing a tissue/implant composite.
Rough or porous surface exhibited a measurable increase in the strength of the implant-bone bond compared to smooth surfaces. Porous surfaces also show faster initial healing compared to noncoated-porous titanium implants. This is because porosity allows bone formation within porosities during the healing phase. Surface roughening creates an irregular surface composed of grooves, ridges, and pits which are more conducive to cell attachment.Hydroxyapatite coating has been recommended for clinical use. These implants are superior with respect to the degree and rate of fixation in the bone as there is accelerated bone formation and maturation and lower corrosion rate around hydroxyapatite-coated implants. Bone adjacent to the implant is more organized than with other implant materials and with a high degree of mineralization. There is a greater surface area of bone apposition to implant which enhances the biomechanics and initial load-bearing capacity of the system. This enables the hydroxyapatite- coated Ti or Ti alloy implants to obtain improved bone-to-implant attachment. There is an increase in bone penetrations, enhancing fixation in areas of limited initial bone contact. Unfortunately, when implanted these often exhibit cracks or even complete loss of hydroxyapatite coating, and also show heavier colonization of micro-organisms. Therefore, are not necessarily advantageous for the long-term prognosis.Many implants have sandblasted surfaces that are subsequently acid etched. The goal of this combination technique is to render the implant surface rough (sandblasting) and optimally clean (etching).
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