Dental implants

An implant fixture is not "screwed into" bone the way a screw goes into a wall. After placement, bone-forming cells migrate to the fixture surface and lay down new bone directly onto the titanium — this is osseointegration, and it takes the time biology takes. Paying more does not shorten it.

How fast it happens depends on the bone density at the site. Dense bone in the lower front jaw (types D1 – D2) is usually stable after 2 to 3 months. The softer bone in the upper back jaw (types D3 – D4) needs 4 to 6 months. So two patients with the same brand of fixture can be given crown appointments months apart — that is a difference in bone, not in service.

Before the crown goes on, fixture stability should be measured with a dedicated device rather than judged by hand feel and elapsed time. Only a sufficiently high stability reading justifies loading it. Putting a tooth onto a fixture that has not finished integrating is the shortest route to losing the whole case.

An implant cannot decay, and that leads many people to assume it is immune to everything. In fact the tissue around an implant is more vulnerable than the tissue around a natural tooth: a natural tooth has a periodontal ligament with its own blood supply and a ring of fibres attaching around the neck, whereas around an implant the fibres run lengthways only and resist bacteria far less well.

So when plaque accumulates at the neck of the fixture, inflammation travels down to the bone faster and usually without pain — the patient only notices once the fixture is loose, by which point a lot of bone has gone. This is why an implant with a lifetime warranty can still fail: the warranty protects you against a material defect, not against plaque.

Prevention comes down to three things: cleaning around the neck of the fixture daily with implant-specific floss or a water flosser, six-monthly maintenance using instruments that do not scratch the titanium surface, and an annual X-ray to compare the bone level against the film taken right after placement.

Modern implantology works backwards from the result: first the final tooth is designed, and only then is it determined where the fixture must sit, at what angle and at what depth to support that tooth along the line of chewing force.

Doing it the other way round — placing wherever the bone is thickest because it is easier — produces a fixture off-axis. The crown then has to be built out to compensate, which puts a twisting load on the fixture, creates a ledge that traps food, and in the front of the mouth makes an acceptable aesthetic result nearly unachievable.

This is the entire reason for the Cone Beam CT, the software planning and the printed surgical guide. The guide turns a plan on a screen into a drill in the right place in the mouth, with far less deviation than free-hand placement.