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That brings us to the next issue, namely - the feasibility of connecting implants to natural dentition. This is a very complex issue and is difficult to study in the laboratory. In addition, clinical situations offer great variability with regard to the periodontal status of potential abutment teeth, bone anchorage of the implants, the length of the edentulous span of the bridge, flexure of the mandible and occlusal loading factors. |
| However, I am confident about one issue, namely that it is very unwise to connect single implants to natural dentition with non-rigid-semi precision type attachments as is shown here. |   |
| When the bridge is designed in this way, a cantilever is created, leading to load magnification and loss of bone around the implants as shown in this patient here . |  |
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Other clinical problems, such as impaction of the abutment tooth into the alveolar ridge can also occur . It is interesting to note in the previous patient that the bone loss occurred even though the occlusal loads were minimal - the opposing arch was restored with a complete denture. When we connect rigid type implants to natural dentition we recommend it be done in a rigid fashion, either with rigid screw retained attachments or with copings with permanent cement as seen here. The case for such rigid connections has been eloquently made by the data presented by Gulbranson at the 6th International Congress on Preprosthetic Surgery in 1994. He clearly showed that if one connects an implant to natural dentition with a rigid system of attachment the implant failure and complication rates such as screw loosening were dramatically reduced. |
| So, in view of all these data and in view of our past clinical experience what do we at UCLA recommend for posterior quadrants. First lets talk about the number of implants required to restore posterior quadrants.In the maxilla we believe that three is the minimum number in most patients. Two implants have been used successfully in some patients, particularly those with significant amount of vertical overlap of the anterior teeth, but the addition of the third implant improves the biomechanics of the restoration and minimizes the risk of load magnification. The addition of the third implant will provide an extra margin of safety that will improve the predictability of your restoration. In addition, when possible we recommend that the implant portion of the restoration be designed so it is independent of natural dentition. This simplifies the restorative treatment and reduces cost to the patient. |   |
| Here are a few examples of some of our implant failures in the maxilla before we recognized the importance of these principles. Note this patient |  |  |
where two implants were placed on the right and one on the left. The one on the left was connected to natural dentition with a semiprecision attachment. The implants on the right were used to suggest a fixed partial denture. The bridge was independent of natural dentition and failed after 18 months. The implant on the left failed one year later. Today we would have designed this case quite differently. We would have placed 3 to 4 implants on the right and at least 3 implants on the left side. Both restorations would be designed so that the implant portion of the restoration would be independent of natural dentition. If there is insufficient bone to receive the implants a sinus lift and graft would have been considered.
Here is another case.
Two implants have been placed to restore a four unit span. Within 2 1/2 years the implants failed. Note the bone loss around each of these implants. Today we would have placed 3-4 implants into this area or an implant for every tooth to be restored.
Here is another patient . Only two implants have been used to restore this posterior maxillary quadrant. These implants failed after 4 1/2 years. As a result of these failures, and other complications we began to use more implants in the posterior quadrant cases. At least 3 implants are used in all maxillary quadrants and usually 1 implant is placed for every posterior tooth restored. Our success rates have dramatically increased and the complication rate has been reduced with this practice.
Here are a couple of patients to demonstrate this practice .
In this patient 3 implants have been placed and the restoration was designed to be independent of natural dentition.
In the following case 3 implants have been positioned but one has been placed through the tuberosity of the maxilla at an angle so as to engage the pterygoid plate.
Note how the restoration has been designed. It is wise to over engineer these linear quadrant cases. In this way more successful and predictable results are achieved. To sum up in the maxilla, at least 3 implants should be used and sometimes 4 when all 4 posterior teeth are to be restored and when using most implant systems, the restoration is best designed so as to be independent of the natural dentition. You can't use too many implants when restoring the posterior maxillary quadrants. More is better for most patients.
I must admit however, that we do have patients in which we have successfully restored the maxillary posterior quadrant with 2 implants as is shown in this patient.
However, in the successful cases, the patients demonstrated very pronounced vertical overlap of the anterior dentition and consequently had very steep anterior guidance. The posterior cusp inclinations were made very flat in these patients, and combined with the significant vertical overlap anteriorly, occlusal forces were primarily axially directed.
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In the posterior mandible the bone implant interface or bone anchorage is better than that which can be achieved in the posterior maxilla and therefore we believe 2 implants is sufficient for many patients. |
| Three is recommended only when poor quality bone is encountered at surgery which was the case in this patient |  |  |
| or when a tendency toward clenching and bruxism is noted as was the case in this patient. |  |