In a study involving partially edentulous subjects, hard tissue biopsies were sampled from the maxilla and the mandible with the use of trephine drills. The bone tissue was found to include a blend of mainly lamellar bone (46%) and bone marrow (23%) with less amounts of fibrous (12%) and osteoid (4%) tissue. Bone marrow was the dominant tissue element in the anterior maxilla, while dense lamellar bone characterized the anterior portion of the mandible. The cortical cap was consistently comprised of lamellar bone and was wider in the mandible than in the maxilla (1.8 mm vs 0.8 mm, respectively) and substantially more narrow in the anterior maxilla than in the anterior mandible.

Osseointegration

The term osseointegration was coined by Brånemark et al. and was described as bone‐to‐implant contact on the light microscopic level. Later, Albrektsson and Sennerby defined osseointegration as, “a direct functional and structural connection between living bone and the surface of a load‐carrying implant.”

In animal experiments the process of hard tissue healing around implants made of c.p.titanium was described. The individual device had the shape of a solid screw with a modified surface configuration and U‐shaped invaginations (wound chambers) that allowed the ingrowth of bone. The wound chambers were first occupied with a coagulum that after 4 days had been replaced with granulation tissue that contained inflammatory cells and also numerous mesenchymal cells and newly formed vessels. After about 1 week of healing, fingerlike projections of woven bone occurred around vascular structures in the center of the chambers and also in direct contact with small areas of the implant. After 2 to 4 weeks the chambers were filled with woven bone extending from the old bone to reach the surface of the titanium device. In the 6‐ to 12‐week interval the woven bone was replaced with lamellar bone and marrow and bone‐to‐implant contact had been established. At the end of the experiment about 60% of the moderately rough implant surface was occupied with mineralized bone and the marginal bone‐to‐implant contact was located about 0.3 mm from the abutment/implant level. Additional preclinical studies have confirmed that rough surfaces enhance early bone formation and bone‐to‐implant contact. Findings from studies in man confirmed the animal results by documenting that the amount of direct bone (mineralized tissue)‐to‐implant contact was about 60% of the circumference of the implanted device after a healing period of 6 weeks to 3 months.

Crestal bone‐level change

Following implant installation and loading, modeling of the bone occurs, and during this process some crestal bone height is lost. Studies in animals have demonstrated the location of the implant–abutment interface (microgap) determines the amount of this initial marginal bone loss. Thus, the crestal bone reduction that occurs in this healing phase apparently varies between brands and seems to be related to the design of the implant system used. After this initial period about 75% of implants experience no additional bone loss but osseointegration takes place. Most implant sites that exhibit crestal bone loss of > 1 mm appear to be associated with soft tissue inflammation although some sites may have an apparently healthy peri‐implant mucosa.