Bone Volume

Width and height available for bone implant placement can be combined to classify bone by volume. These characteristics are of considerable importance for implant predictability, treatment planning, surgical technique, and final prosthetic outcome.

While in the beginning of implant dentistry bone availability was the only determining factor for implant placement, currently, the gold standard for implant supported prosthetic rehabilitation focuses on implants being placed in the ideal tridimensional position of the missing teeth.

After tooth extraction, resorption of maxillary and mandibular bone occurs towards the midline direction (palatal in the maxilla and lingual in the mandible), which results in less bone available and presents difficulties for implant surgery. The buccal cortical plate often disappears with surgical and prosthetic complications. While the maxillary ridge becomes narrower with tooth loss, the mandibular ridge has a similar resorption that is in a certain way compensated by the fact that the mandible is wider than the original crest.

This classification allows us to understand the extent of bone resorption in patients and aids the planning of an ideal treatment for achieving good esthetic and functional results.

Misch proposed four subdivisions to classify bone volume:

Division A:

Bone is abundant in both dimensions, height is more than 10 mm and width is more than 5 mm. There is no need for bone grafting techniques or osteoplasty prior to implant placement, and surgery can be performed directly.

Division B:

Bone availability is moderate. While height remains more than 10 mm, width has undergone certain atrophy and may be as narrow as 2.5 mm. This can be remedied by using narrower implants or by reconstructive bone techniques. The former does not involve any additional surgery for the patient than placement of the implant, but has as a disadvantage a smaller amount of BIC and therefore less stability and poorer stress distribution around the implant. The latter are associated with longer treatment times and a second surgical procedure, but allow the placement of an implant with larger and optimal dimensions than in the original bone.

Division C:

Bone in this category has already lost a significant portion of its original height (less than 10 mm) and width (less than 2.5 mm). Bone grafting techniques such as sinus augmentation or blocks are preferable prior to implant placement and require additional surgery, professional skills and increased cost to the patient.

Division D:

This bone is severely compromised and has lost its height and width. With this bone type, reconstructive surgery is mandatory prior to implant placement.