Dental implants are becoming an accepted treatment for replacing missing teeth. In many cases, they may be preferable to the alternatives of a bridge or partial denture. However placement of dental implants requires careful evaluation and consideration, especially with respect to the bone where the implant is placed.
Why Worry About Bone?
A dental implant is a metal post placed into the jawbone, and is used as an anchor on top of which a crown (tooth) is placed.
When the implant is placed, the goal is to ensure that it is completely stable (osseointegrated) within the bone, so that it is strong enough to support the tooth on top of it. Great care must be taken to ensure there is enough bone around the implant as this provides the dental implant with its strength and stability.
Thus, a major concern when placing a dental implant is ensuring sufficient volume of bone around it in height, width, and depth.
How Much Bone Is Needed Around a Dental Implant?
As a general guideline, at least 1 mm of bone is required around a dental implant. More space is required when the implant is next to a tooth or another implant (2 and 3 mm respectively). If there is not enough bone to completely envelope the implant, a bone graft will be required.
When evaluating the height of bone, there should simply be enough bone that the implant will be completely submerged. However, it is important to ensure that the implant does not go so deep as to impinge on other anatomic structures (eg the nerve in the bottom jaw, or the sinus in the upper jaw). When placing implants in the upper jaw, there may not be enough room vertically, and a sinus lift may be required to rebuild bone.
Types of Bone Grafts
A bone graft is the addition of bone, or bone-like material, in an effort to increase the volume of bone in the jaw. Typically, the bone is placed and heals before the implant can be placed. The healing period can vary, depending on the type of bone used.
There are many types of bone grafts, but they all fall into one of several categories:
- Autograft – bone used from the patient’s own body.
- Allograft – bone from a genetically similar organism
- Xenograft – bone from a genetically dissimilar organism
- Synthetic – a synthetic biocompatible material
The type of bone graft that will be chosen will depend on the situation, and on the amount of bone required.
Timing of Bone Grafts
Depending on the situation, bone grafts may be placed at the same time as an implant, or before the implant. While it is more convenient to place the implant and graft at the same time (thus saving treatment time), sometimes the clinical situation does not allow it.
If the bone graft must be placed before the implant is put it, it is very important to follow the timelines set out for treatment. If the implant is placed too soon after the graft is placed, the graft will not have had enough time to heal and become solid. If the implant is placed too long after the graft is placed, resorption and melting of the graft may occur with loss of bone volume.
Thus, implant placement is typically scheduled for the “sweet spot” where sufficient healing, but minimal resorption, has occurred.