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| The purpose of my lecture is to discuss the UCLA experience using implants to restore the posterior quadrants of the maxilla and mandible in partially edentulous patients such as you see on the right. Like most of you, our initial experiences with osseointegrated implants were in edentulous patients and the implants were placed in the anterior region of the maxilla or mandible. | |
In these patients 4 to 6 implants were placed and fixed edentulous bridges were fabricated for the patients. The implant success rates were quite high and comparable with other international groups. These success rates were very high because the anterior bone sites in both the mandible and the maxilla were of good quality and quantity, the design of the prosthetic restoration had been perfected over many years of clinical testing, and the biomechanics of these types of implant supported prostheses were quite favorable to supporting bone.
| However, when osseointegrated implants were used to restore the posterior quadrants in partially edentulous patients the success rates were not as high. The reason for the lower rates of success are just now becoming clear. In order to understand why the success rates were less, and in order to maximize the rate of success in partially edentulous patients we need to discuss the following issues. First - Pertinent dental history findings. |  |
The most important is a dental history of severe chronic bruxism. The question is whether or not it is advisable to restore posterior quadrants with unilateral implant supported fixed partial dentures. Next, we need to understand that the biomechanics of the linear implant configurations that are most commonly encountered in these partially edentulous patients are different. In restorations restoring posterior quadrants, implants are generally positioned in a linear configuration as opposed to the curvilinear configuration possible when restoring the entire arch of an edentulous patients. The biomechanics of the linear arrangements are much less favorable to the supporting bone than those of the curvilinear implant configurations.
The next issue I am going to discuss is the effect anatomic limitations have in implant length and angulation. In posterior quadrants the presence of the maxillary sinus and the inferior alveolar nerve limit the length of the implants. In response, our surgical colleagues have developed techniques aimed at increasing the vertical height of the implant bone site with bone grafts and in the case of the mandible, surgeons have perfected means of displacing the inferior alveolar nerve laterally in order to increase the length of implants used. The critical questions are whether these techniques are effective and appropriate and just what place they should occupy in our clinical practice.
Next, what are the minimum lengths that should be used to support implant supported fixed partial dentures that restore posterior quadrants of the maxilla and the mandible. I will provide you with some data accumulated at UCLA which provides the basis for my recommendations.
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The next issue I will discuss is whether or not it is wise to expose implants configured in a linear fashion to nonaxial loading. This in turn affects the status of the use of cantilevers in these quadrant restorations and the practice of connecting implants to natural dentition with implant supported fixed partial dentures. |
The practice of progressive loading with temporary restorations is the next issue I am going to discuss. This issue is a controversial one and I will give you my opinion based on some of the research conducted at UCLA and other institutions.
Next, based on the clinical studies performed at UCLA, I will discuss the number of implants that are necessary to restore posterior quadrants of either the maxilla or the mandible.
Last, I will discuss the wisdom of using solitary implants in the posterior quadrants based on the success-failure rates and complication rates seen on the basis of our UCLA experience. When I have completed this discussion, I will briefly provide some clinical and technical suggestions regarding the design and fabrication of implant supported restorations used to restore posterior quadrants of the mandible and maxilla.
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Let us begin. First let us discuss Dental History Findings of importance. The most important as I mentioned previously, is a history of chronic bruxism. |
Patients who are bruxers demonstrate an exceedingly high implant complication and implant failure rate. The screw type 3.75 millimeter diameter implants originally distributed by Nobelpharma are quite susceptible to fracture in these types of patients and here shown are examples of fractures.
| In a recent article by Rangert, (1994) more than 75% of the implant fractures he reported occurred in patients who had signs and a history of chronic bruxism. The occlusal forces these patients generate are quite significant and the screw type implant of the Branemark design is quite susceptible to fracture. We recommend that in patients with moderate bruxism that either cylindrical types implants such as the G.C. type be used, shown here next to a Branemark type that the implants be used as overlay denture abutments for removable partial dentures or in the case of severe bruxism, that implants not be used at all. The cylindrical type with titanium plasma spray coating develops a better bone implant interface and is much stronger and therefore less likely to fracture. |  |  |