Contamination of the implant site by organic and inorganic debris can prejudice the achievement of OI. Material such as necrotic tissue, bacteria, chemical reagents and debris from drills can all be harmful in this respect.
It is known that where an implant fits tightly into its osteotomy site then OI is more likely to occur. This is often referred to as primary stability, and where an implant body has this attribute when first placed failure is less probable. This property is related to the quality of fit the implant, its shape, and bone morphology and density. Thus screw-shaped implants will be more capable stable than those with little variation in their surface contour. Soft bone with large marrow spaces and sparse cortices provides a less favorable site for primary stability to be achieved. Some manufacturers produce 'oversized' and self-tapping screw designs to help overcome these problems.
This bone property is well recognized by clinicians but is more difficult to measure scientifically. It is a function of bone density, anatomy and volume, and has been described using a number of criteria. The classifications of Lekholm and Zarb and of Cawood and Howell are widely used to describe bone quality and quantity. The former refers to the thickness and density of cortical and cancellous bone, and the latter to the amount of bone resorption. Bone volume does not by itself influence OI, but is an important determinant of implant placement. Where bone bulk is lacking, then small implants may need to be used, with the consequent risk of mechanical overload and implant failure.
Early implant designs were often associated with downgrowth of oral epithelium, which was originally exteriorized the device. When the newer generation of CPTi devices was introduced great care was taken to prevent this by initially covering the implant body with oral mucosa while OI occurred. The implant body was then exposed and a superstructure added, since it was known that the osseointed interface was resistant to epithelial downgrowth. More recently, there has been a growing interest in using an implant design, which penetrates the mucosa from the time of placement.
While this technique has no long-term data to rival that of the earlier methods, it does appear on the basis of preliminary results to be effective and successful in suitable patients and locations. A recent development of this has been the introduction of a technique for placing a prefabricated superstructure on dental implants, which permits their use within hours of placement.