Restorations supported by implants are a predictable treatment for the replacement of missing teeth. The success rate of dental implants is very high but there are situations in which the implant may fail and it will need to be removed. For the patient, the failure of an implant implies a higher cost and additional procedures.
Among the predictors of the success or failure of dental implants, we find different possibilities: the factors that depend on the patient (the general health of the patient, the smoking habit, quality and quantity of bone or oral hygiene and maintenance), the characteristics of the implant (dimensions, surface of the implant, loading times) the location of the implant and the experience of the dentist, surgeon or periodontist.
The success criteria in dental implants were usually defined as: absence of mobility, marginal bone loss less than 1.5 mm during the first year of function and 0.2 mm per year, plus absence of pain and paresthesia. Currently, the bone loss accepted around the implant must be less than 1 mm because of the implants and connections we use. The failure of the implant can be due to a multifactorial process. There are many causes related to the early failure of the implant and others that are related to late failure.
The early failures correspond to those implants that do not survive before the prosthetic load and the late failures are those that do not work after the loading of the implant. Incorrect osseointegration will result in early implant failure. There are different risk factors that can cause alterations in the osseointegration of the implant. The main ones are: smoking, characteristics of the implant, infection or quantity and quality of the bone.
Osseointegration is a structural connection between living bone and the surface of the implant that supports a load. For the initial healing is very important the first month after the implant placement. If there is an imbalance between apposition and bone resorption, osseointegration may fail. When osseointegration does not occur or is lost for some reason, fibrous connective tissue forms around the implant. This fibrointegration can occur when there is a discrepancy between the diameter of the implant and the diameter of the milling, when there is no primary stability, in traumatic and septic surgeries, when there are remains of fibrous tissue in the new alveolus or when the implant material is not biocompatible.
Other factors that may imply an implant rejection
Some factors depend neither on the operator nor on the patient, but on the implant itself. The operator can choose between different implants according to his knowledge and this will depend on the greater or lesser success in the placement of the implants. The majority of implants today are made of titanium since it is a very biocompatible material that has been studied extensively. The state of the implant surface can also influence osseointegration independently of the implant material. The implant can not come into contact with any type of contaminants such as talcum powder or serum before its placement. This could affect the bond between the bone and the titanium oxide on the surface of the implant.
The infection is one of the causes of the early failure of dental implants. It is not a very common cause unless the surgical conditions are septic. This contamination can occur through the external environment or by a pre-existing infection in the area of implant placement.
In the preparation of the implant receiving bed, trauma to the bone can be caused, which if it is the case it will inevitably cause an area to be necroseed. The main factor that can compromise the correct healing of the bone is the heat that the drills generate when preparing the implant bed.
The failures usually appear quickly, during the first 3 months and before the placement of the prosthesis. Some failures used to appear a few months after loading. The use of provisional prostheses allows among many other things to assess this fundamental stage of prosthetic reconstruction. After this period, implant failures are very rare. Today implant osseointegration is assessed by a software machine with the RFA index. When these measurements are higher than 65 the implant has a moderate to high osseointegration and failure is very rare to happen.
Most times, after a failure of an implant and its explantation, it is possible to reposition another implant at the time of removing the first implant, or after a certain time, such as 2-3 months, in the same place. Normally the second surgery is successful.