Bone Density Effect on Implants
In the jaw, we have distinct types of bone compositions based on the different type of loads the two arches receive. In general, the mandible has a very thick cortical plate with a dense trabecular structure that anchors the teeth; whereas, the maxilla has a much thinner cortex and finer trabecular structure. This is because the upper jaw is loaded principally in compression, while the lower jaw is loaded in both compression and torsion.
The edentulous areas of the jaw bone can be classified based on their density; with four groups recognized, starting with dense compacta and decreasing in density to fine trabecular bone.
Is composed almost entirely of dense compacta cortical bone, it is found typically in the anterior mandible. It maintains its shape and density because of its strong muscle attachments, and the stress and flexure they produce. D1 bone feels as hard as oak wood when drilling.
D1 bone can support substantial loads because of its highly mineralized matrix. Bone stability is excellent, even following trauma.
It is a combination of dense, porous compacta cortical bone on the outside and coarse trabecular bone on the inside. It is most commonly located in the anterior mandible, followed by the posterior mandible. Sometimes it is encountered in the anterior maxilla. The tactile sensation when the bone is prepared for implants is similar to that of pine wood.
D2 bone provides excellent rigid healing and osteointegration is very predictable.
Because of the excellent blood supply and rigid initial fixation, adequate bone healing is usually seen within three to four months.
D3 is a combination of the porous compacta of the thinner cortical and fine trabecular bone. It is found mainly in the anterior maxilla, but can also be located in the posterior maxilla or posterior mandible. The tactile sensation when drilling this bone is like drilling balsa wood.
D3 bone is more delicate to handle. Because the amount of D3 bone at the implant-bone interface is less compared with the previous bone categories, an additional implant may be used to improve load distribution and prosthodontic support. Since D3 bone is a greater risk of unpredictable osteointegration, the placement of additional implants during surgery also permits altered prosthodontic restoration, even if a few implants do not integrate.D3 bone in the anterior maxilla is usually not as wide as that in the mandible, and smaller diameter implants are often necessary. Atraumatic healing normally takes four to six month. Although the implant interface develops prior to this time period, the extended time allows the presence of the implant to increase formation of denser, trabecular bone patterns.
D4 is fine trabecular bone with very low density, and little or no cortical crestal bone. D4 is most commonly found in the long – term edentulous posterior maxilla, where the ridges are often very wide with reduced vertical height.
D4 bone is the most difficult in which to obtain rigid osteointegration of any implant system and must be handled with maximum care. Because it is very porous, initial fixation of the implant presents only limited mechanical advantage. Long implants are recommended in this bone density, using one for each tooth to be replaced because of its very low ability to support stress. Six to eight months of undisturbed healing are recommended. For fixed restorations, one implant is used for each replaced tooth. If osteointegration does not occur, an additional implant placed during surgery will improve support if all of the implants integrate.
Dr. Natalia Demianko
DDS / 2015