April 28, 2019
The preservation of jawbone en mass is highly contingent on maintaining good implant health, which is facilitated by positioning of the fixtures in a manner that facilitates hygiene as well as with proper biomechanical considerations.
In my prior article I focused on the causes for bone atrophy, in particular as it relates to Iatrogenic causes and how this can be controlled with timely removal of diseased teeth, avoidance of dentures, and proper positioning of implants.
It was put then to me by a colleague that we are all taught early in our careers that implants preserve the jaw bone, the hard question is: where is the evidence that (well positioned) implants do in-fact preserve jawbone?
If we are talking about alveolar bone that is present around healthy teeth, then as I stated in my prior article on natural atrophy this cannot be stopped, and it cannot be reliably preserved even with implants. What I am talking about in my article is stimulation of deeper basal bone through functional loading.
The picture below illustrates the loss of alveolar bone irrespective of the presence of dental implants …
There is a difference between the alveolar bundle bone which is supported by teeth and periodontal ligament, and basal bone of the jaws, which is unaffected by the presence of a ligament. Bundle bone resorbs with the extraction of teeth, and I am not in any way suggesting that implants will preserve this bone. When placing single implants it is the adjacent teeth that help in preserving the bone level, and in most cases some form of augmentation is required to compensate for the loss of bundle bone.
In full arch cases, for all the reasons that I have mentioned in my prior articles, an alveoplasty eliminates the possibility of further alveolar remodelling from the loss of bundle bone, and the implants are placed in basal bone, which is better quality in terms of its 3-D anatomy and it is better vascularised. It is this jawbone en masse that we now want to preserve. Here preservation of the bone reaction is not dependent on teeth and instead follows Wolff’s law (Wolff J: Das besets der transformation der knochen, Berlin, 1892, August Hirschwald) and the general principles of stimulation through functional loading.
Implants can maintain bone width and height as long as the implant remains healthy (Zarb G , Schmitt A: Edentulous predicament . 1. A prospective study of the effectiveness of implant-supported fixed prostheses. J Am Dent Assoc 127:59-72, 1996), and functional loading can maintain bone mass (Marks SC, Popoff SN: Bone cell biology: the regulation of development, structure and function in the skeleton, Am J Anat 183:1-44. 1988). Having said that, there is no literature that I am aware of to prove Wolff’s Law applies specifically for implants, but considering the clear evidence that implants do in fact osseointegrate, we can rely on what is available elsewhere in the literature in other areas on the topic of preservation of bone through functional stimulation to draw a parallel (search “bone reaction to functional load” on Pubmed). This is also covered in Carl Misch’s book Contemporary Implant Dentistry (Second Ed. Chapter 22: 317-328).
Sometimes we don’t have literature that answers a very specific question, especially because some things are difficult or impossible to actually measure. Empirical evidence is often what we rely on in such cases, and this derived from the experience and insight of our own and that of our teachers, as well as the parallels that can be drawn to literature that does exist.
The question put to me by my colleague is not a hard question. I can’t help who accepts my answers, but we can all certainly do something about what our patients are likely or unlikely to accept (and enjoy) in terms of treatment that we offer them, as I outlined in my original article Definitive Solutions for Our Patients