There are a plethora of commercially available implant systems and designs.
Qualitative and quantitative nature of the available bone should be carefully analyzed and the implant to be used suitably selected.
1) Improper Implant type in Improper Bone Type
In routine sites with good quality bone, the clinician should prefer implants without any superadded HA coatings and avoiding their added associated risks. However,in poor quality bone where the added coating would enhance the success rate should be a determining factor in implant selection. Though definitive scientific literature is not available to select a particular thread design over others concepts like using the self tapping nature in softer bone while relying on pretapping in densebone help to reduce the trauma on bone and ensure good primary stability and help to prevent failure.
2) Length of the Implant Used
The length of the implant to be used is dictated by the available bone height. The success rate is proportional to the implant length and the quality and the quantity of the available bone. The rate of implant failure can be expected to rise proportionately as the depth of the bone diminishes to less than 10 mm. However, certain implant designs which claim higher surface area (either due to sintered Ti particles) are known to work in shorter lengths. It is a thumb rule to use the longest length possible within anatomical limits as the use of a shorter implant when a longer could be used results in less bone implant surface area, higher stress concentration and thus the associated failures. The crown-implant body ratio affects the appearance of the final prosthesis along with the moment of force on the implant and the crestal surrounding bone. The greater the crown-implant ratio, the greater will be the amount of force with any lateral force. Therefore, the maximum implant length possible should be used for the greatest stability of the overlying prosthesis.
3) Width of the Implant
The width of the implant especially at the interface area is critical towards the success of the implant. It has been recommended that at least 1mm of bone surrounding the implant labially and lingually to ensure the long-term predictability of the treatment as the bone thickness maintains the blood supply. The diameter of the implant is a more critical factor for the surface area than even the length; wider diameter allows for more mechanical engagement of cortical bone and better primary stability and prevents fracture of the implant especially at the cervical area where stresses are high. Using a narrower implant where a wider one was possible leads to increased chances for both mechanical and biological failure. The implant diameter thus should be selected on the basis of the available bone width, esthetic requirements,load and stress analysis, the neighbouring teeth and the arch space available. Using a wider diameter in a narrow ridge situation, results in labial or lingual dehiscence that leaves the implant affected by the damaging shear stresses and leads to cervical bone loss and subsequent implant failure.
4) Number of Implants
The use of more implants decreases the number of pontics and the associated mechanics and strains on the prosthesis, and dissipates stresses more effectively to the bone structure (especially at the crest). It also increases the bone implant interface and improves the ability of the fixed restoration to withstand forces. The selection should be based on bone volume, bone density, occlusion and the opposing dentition, the available proprioception and the implant surface area and distribution.In case the implant number is less than the desired the occlusal overload and the stresses would lead to bone loss, mobility and subsequent loss of the implants.
5) Improper Implant Design
Out of the plethora of implant systems available it is the responsibility of the clinician to select the most suitable. In comparison of the straight cylinder or tapered- the use of tapered is advisable in narrow mesiodistal spaces available to allow for safe distance between the adjacent roots, the tapered design allows for self tapping nature and bone compaction while the straight cylinder offers more surface area. The selection between a press fit design system versus a threaded system is also critical in clinical situations. In poor quality bone like the posterior maxilla the use of osteotomes to prepare the site and using a press fit system can promote bone compaction and achieve expansion if desired thus improving the prognosis of the treatment.
Qualitative and quantitative nature of the available bone should be carefully analyzed and the implant to be used suitably selected.
1) Improper Implant type in Improper Bone Type
In routine sites with good quality bone, the clinician should prefer implants without any superadded HA coatings and avoiding their added associated risks. However,in poor quality bone where the added coating would enhance the success rate should be a determining factor in implant selection. Though definitive scientific literature is not available to select a particular thread design over others concepts like using the self tapping nature in softer bone while relying on pretapping in densebone help to reduce the trauma on bone and ensure good primary stability and help to prevent failure.
2) Length of the Implant Used
The length of the implant to be used is dictated by the available bone height. The success rate is proportional to the implant length and the quality and the quantity of the available bone. The rate of implant failure can be expected to rise proportionately as the depth of the bone diminishes to less than 10 mm. However, certain implant designs which claim higher surface area (either due to sintered Ti particles) are known to work in shorter lengths. It is a thumb rule to use the longest length possible within anatomical limits as the use of a shorter implant when a longer could be used results in less bone implant surface area, higher stress concentration and thus the associated failures. The crown-implant body ratio affects the appearance of the final prosthesis along with the moment of force on the implant and the crestal surrounding bone. The greater the crown-implant ratio, the greater will be the amount of force with any lateral force. Therefore, the maximum implant length possible should be used for the greatest stability of the overlying prosthesis.
3) Width of the Implant
The width of the implant especially at the interface area is critical towards the success of the implant. It has been recommended that at least 1mm of bone surrounding the implant labially and lingually to ensure the long-term predictability of the treatment as the bone thickness maintains the blood supply. The diameter of the implant is a more critical factor for the surface area than even the length; wider diameter allows for more mechanical engagement of cortical bone and better primary stability and prevents fracture of the implant especially at the cervical area where stresses are high. Using a narrower implant where a wider one was possible leads to increased chances for both mechanical and biological failure. The implant diameter thus should be selected on the basis of the available bone width, esthetic requirements,load and stress analysis, the neighbouring teeth and the arch space available. Using a wider diameter in a narrow ridge situation, results in labial or lingual dehiscence that leaves the implant affected by the damaging shear stresses and leads to cervical bone loss and subsequent implant failure.
4) Number of Implants
The use of more implants decreases the number of pontics and the associated mechanics and strains on the prosthesis, and dissipates stresses more effectively to the bone structure (especially at the crest). It also increases the bone implant interface and improves the ability of the fixed restoration to withstand forces. The selection should be based on bone volume, bone density, occlusion and the opposing dentition, the available proprioception and the implant surface area and distribution.In case the implant number is less than the desired the occlusal overload and the stresses would lead to bone loss, mobility and subsequent loss of the implants.
5) Improper Implant Design
Out of the plethora of implant systems available it is the responsibility of the clinician to select the most suitable. In comparison of the straight cylinder or tapered- the use of tapered is advisable in narrow mesiodistal spaces available to allow for safe distance between the adjacent roots, the tapered design allows for self tapping nature and bone compaction while the straight cylinder offers more surface area. The selection between a press fit design system versus a threaded system is also critical in clinical situations. In poor quality bone like the posterior maxilla the use of osteotomes to prepare the site and using a press fit system can promote bone compaction and achieve expansion if desired thus improving the prognosis of the treatment.
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