We often come across patients who have lost one or several molars from the back of their jaw. Furthermore, these pieces have often been missing for several years, meaning that the bone has decreased in height and width; i.e. it has atrophied and represents a problem when fitting implants.
When patients have been using a removable prosthesis for several years, which often moves excessively due to poor fitting, the bone loss tends to be rather important.
During the last 30 years the solution has been to add bone in order to fit implants. This means proceeding with a graft of autologous bone, or in other words, taken from the patient themselves. Bone is taken from another part of the jaw, such as the chin or ramus, and grafted to the area requiring implants, normally the back molars. Bone can also be taken from the top of the skull.
Another option is regeneration using artificial bone particles held together with collagen, titanium or Gore-Tex membranes. The problem is that the lower jaw is hard and cortical, meaning that grafts have difficulty adhering to it. In the case of the upper jaw grafts tend to take more easily because the bone is spongy, full of little cavities in which the veins and nerves grow and the new bone forms.
Another point to be taken into account is that the rear jaw houses the lower dental nerve, which we cannot touch, meaning that there is very little available bone.
Today the solution lies in short implants. Implant surfaces have improved enormously and can now strongly adhere to the bone. We are currently using implants of 8.5mm, 7.5mm, 6.5mm and even 5mm to solve our cases. These are known as extra-short implants. In order to provide a decent surface for anchorage, these implants must be wider than the ones commonly used. They generally have a width of 4.5mm, 5mm, 5.5mm and even 6mm. Sometimes they have more width than depth.
It has been demonstrated that most of the tooth strength lies in the first 3-5 mm of the implant, meaning that the rate of implant survival and bone level are the same in short implants as they are in the standard 10mm and over.
It used to be said that the crown of the tooth couldn’t be bigger than the implant; however, today it is considered perfectly acceptable for crowns to be double the size or even more than the implants themselves.
These short implants, when fitted in such a way that their crowns are joined together, will show greater resistance than if they were individual teeth.
This means that less vertical bone regeneration is required for back jaw implants. The result is that short implants now mean that surgery is faster and simpler, with improved post-operatory recovery and lower cost.