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Next I would like to speak to the issue of using standard 3.75 to 4.0mm diameter implants to restore single tooth defects in the posterior quadrants of the maxilla or mandible. First, let us discuss the UCLA results in the molar region. In the 1980's we at UCLA attempted to restore mandibular 1st molar defects with conventional 3.75 or 4.0mm diameter implants. Unfortunately, the results were quite disappointing. |
| We had cases where occlusal overload lead to loss of bone around the implant and eventually to implant failure as seen here, |  |  |
| and other cases that resulted in implant fixture fracture as seen here. |  |
Most often observed however, the problem was the screw retaining the restoration coming loose. This is caused by the fact that the diameter of the head of the implant was so much smaller than the size of occlusal surface that we could not prevent tipping of the restoration. This tipping eventually lead to loosening of the screw that secured the crown to the implant fixture.
Here in these cases you can see the problem.
One can control the buccal-lingual width of the crown - we can keep that to a minimum - but we do not have control over the mesial distal dimension - we must fill this space. When the bolus of food becomes positioned on the mesial side of this crown, tipping forces are generated which eventually leads to loosening the screw retaining the crown. Theoretically, using the wide diameter implants will resolve the screw loosening complication. However, although the initial clinical data is promising, the use of solitary wide diameter implants to restore the molar region needs more clinical study.
| If the 1st molar is lost and suitable abutments are available on both sides, we therefore recommend a conventional three unit fixed partial denture as shown in this patient .This restoration is very cost effective and quite predictable. |
In distal extension areas restoring one molar tooth, we recommend that you place two conventionally sized implants close together as is shown here.
This restoration is biomechanically sound and as you can see can be designed to allow adequate hygiene access.
| We are confident that single implants can be used in the mandibular and maxillary bicuspid area . The bone implant interface achieved in this area is good and the size of the occlusal surface is generally small. Success rates have been very high at this site. Likewise our success rates in the maxillary bicuspid region has been good. However, we recommend that you use implants 13mm in length or longer to restore these sites, because the bone implant interface is not ideal in these regions. To conclude this discussion, I would like to highlight a few design principles which are important to observe if you want to achieve predictable results with the types of implant supported restorations used to restore posterior quadrants we have discussed. |   |
First, I would recommend that you use tapered healing abutments of the type shown here .
The taper allows the tissue to heal in a contour that permits the development of more preferable emergence profiles in your final restoration. In addition, we prefer healing abutments that have polished surfaces as opposed to machined surfaces because they retain less plaque, are more easily cleaned by the patient and therefore promote faster and more effective healing of the tissues after second stage surgery.
Second, following adequate healing we recommend you make your impressions at the fixture level as is shown here. In this way you will obtain a master cast with fixture analogues embedded. This allows you to select the type of abutment that best fits the needs of the patient.
