RESULTS.
Implant Survival.
No patient withdrew during the follow-up period. Two of 61 implants were lost, both from the same patient. This patient had a maxillary arch fixed bridge as antagonist, and the implants were placed at the same session as the extraction of the residual mandibular dentition. The failed implants did not show signs of infection, but they had clinical mobility, and the patient had functional discomfort. The 59 remaining implants were clinically immobile, asymptomatic, and free of any radiolucency for the entire follow-up period, with a maximum of 18 months and an average of 8 months. Thus, the implant survival rate was 96.7% for the follow-up period.
The prostheses success rate was 92.3%; a previously planned fixed/ detachable prosthesis had to be converted into an overdenture because the patient refused to have the two lost implants replaced.

Marginal Bone Loss.
Marginal bone loss was generally very limited (always ,1 mm). Only two implants showed a marginal bone loss .1 mm. Excluding them, the preliminary cumulative success rate was 93.4%.

Complications.
Tissue healing occurred without any significant complications in all of the patients. During the first 4 months of using the transitional prosthesis, the most frequent prosthetic complications were three cases of fractured cantilevered portions (15%) (Fig. 7), two of them in the same patient, probably in relation to incorrect occlusal adjustment. Another prosthetic complication was the loosening of screws in 23% of the prostheses. None of the complications prevented the prostheses from functioning and, therefore, cannot be considered as failures.

DISCUSSION.
This study, carried out in a private clinic, confirms earlier reports on the immediate loading of implants in the interforaminal zone as a safe method. Despite the limited number of cases and the short follow-up period, the preliminary results of this study are significant because, apart from those presenting the aforementioned exclusion criteria, all patients in need of a mandibular prosthesis were included. These results are comparable to those obtained from similar studies on fixed/detachable mandibular prostheses, hybrid type.
In the case of the patient who lost two implants, there was occlusal pathology with considerable anterolateral discrepancy between the centric relation and the intercuspal position and some oral muscular tension. Furthermore, at the time of her treatment, she was suffering from intense emotional stress. Thus, her altered oral function cannot be ruled out as the cause of the two implant failures. Because she refused to have the two implants replaced, her prosthodontic plan was changed to a bar on the three remaining implants and an overdenture.
It should be stressed that 32 implants (53%) were placed in the same session as the extraction of the residual dentition. In another 13 implants (21%), the time between extractions and implantation was only 2 months. Only 16 implants (26%) were inserted on bone that had been edentulous for more than 12 months. Despite these different circumstances, all of the implants were immediately loaded, and no negative influence was noticed with implant success rate. Until now, this option of immediately placing and loading implants has rarely been reported in clinical studies8,11 and never discussed by their authors. The present results suggest that implants placed into extraction sockets and immediately loaded show a positive clinical response if a strong primary stability is achieved and there are no periapical infections in the surgical zone.
Some authors reported a slight improvement in marginal periimplant bone loss for immediate loading protocols. 14 Recent experimental studies have demonstrated greater density in the bone surrounding immediately loaded implants,18,19 or a better boneimplant contact in rotation-mobile implants compared with the corresponding control group of totally stable implants.27 These authors speculate that these results could be due to the immediate transmission of functional forces acting as an osteogenic stimulus. This was postulated by Frost,28 who called it regional acceleratory phenomenon (RAP). Our study confirms that marginal bone loss rates of immediately loaded implants were well within the clinically acceptable parameter: ,1.5 mm, as documented for Brånemarklike implants after 12 months of functional loading.1 This measurement is always taken at the time of prosthesis installation, thus disregarding the initial postsurgical osseous remodelling. Interestingly, in the present study, this initial bone loss is included in the measurement because our baseline is the immediate postsurgical x-ray. One of the two implants with bone loss .1.5 mm was located in the center of the mandibular arch, and the surgical wound suffered a dehiscence in a central relief incision, probably in relation to masticatory traumatism (although this hypothesis cannot be confirmed).
The fact that four different implant designs were used in this study without significant differences in success rates indicates that the results are not dependent on a particular implant design or surface, but rather that different root-form implants clinically behave in the same manner when in the same clinical conditions.
The prosthetic complications were easily managed and seem to be partly related to an imprecise working model or inaccurate intermaxillary registration. Fractured prostheses were attributed to the fatigue of wire reinforcement. (Our initial concern was the rapid placement of the fixed prostheses so that a cast framework was not made.) Technical development during the time of the study resulted in better prosthetic procedures and a reduction in the number of complications.
The rapid restoration of oral function through the immediate loading of the prostheses has been a great advantage for the patients compared with conventional delayed loading protocols. In particular, this protocol has completely eliminated decubital lesions or soreness due to pressure on the mucosa as well as uncontrolled forces transmitted to unsplinted implants through the overlying denture. These problems are frequently seen because implants are commonly placed in a nonsubmerged or semisubmerged position. A substantial improvement in function and psychological well-being was experienced by 100% of the patients included in this study, resulting in a high level of satisfaction with the treatment.

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