This retrospective case series study evaluated clinical outcomes, patient satisfaction, and OHRQoL after rehabilitation of AEM with six implants placed simultaneously with bilateral MSFA, immediate loading on the four anterior implants through the all-on-4 PFP, and delayed loading on the two posterior implants through the all-on-6 DFP. The main findings revealed: 1. A high rate of implant and prosthesis survival and success after an average of 20 months of follow-up. 2. Stable peri-implant soft tissue condition without biological complications. 3. Stable MBL over time, with no statistically significant difference between implants placed in native and augmented bone. 4. low post-operative pain and swelling; and high patient satisfaction. 5. Significant improvement in OHRQoL after shifting from the provisional all-on-4 to the final all-on-6 prosthesis.
The present study reported a 100% Implant survival rate. This result was similar to previous studies that evaluated the short-term outcome of the ISFP. [40] assessed the outcomes of 37 patients rehabilitated with full-arch hybrid PEEK-acrylic resin prostheses through the all-on-four concept and reported 100% implant survival after one year. [41] investigated implant and prosthesis survival rates for immediate FP supported by 4,5 or 6 implants with and without bicortical anchorage up to 2 years of follow-up. They reported a 99.7% overall implant survival rate. In a study similar to our study concept, [42] evaluated an immediately fixed implant restoration of the AEM after bilateral sinus floor augmentation. The author reported 98.7% of implant survival after one year. Similar results were recorded in a five-year follow-up study by [43]. The previous study compared the immediately loaded maxillary cross-arch fixed dental prosthesis supported by four or six implants and found 98.6% implant survival up to 5 years of loading.
Placement of implants in combination with maxillary sinus floor elevation is a predictable treatment with a 98.3% implant survival rate after three years [44]. In our study, the maxillary sinus augmentation was performed with simultaneous implant placement, and no implant loss was reported during follow-up. These results were in line with those reported in the previous study that used the same grafting material as our research (DBB) with simultaneous implant placement and reported a 100% cumulative implant survival rate after 60 months of loading [45]. This high implant survival rate could also be compared with those recently reported when the same graft material (DBBM) was used with delayed implant placement; 100% implant survival was recorded after 20 months of functional loading [46]. Furthermore, our results agreed with the previous reports [42] that did not find a significant difference in the survival rate of the implants inserted in sinus grafted compared with native sites at one year of loading.
The modified preparation technique used to improve primary stability and the characteristics of the implant surface may have played a role in the high implant survival observed in this study. In addition, the rigid splint through a titanium CAD/CAM milled framework may help prevent micromotion and thus improve implant survival. Moreover, the implants in augmented sinus were lift submerged from 6 to 9 months. This sufficient time had allowed the bone consolidation and implant osseointegration without a patient complaint and/or impinge on the healing tissue [23] since the patients were using their provisional screw-retained fixed all-on-4 prosthesis well for daily mouth activities. The previous may play a role in implant survival in augmented sinuses.
The wide anteroposterior distribution of the implants to the first or second molar allowed the construction of 12–14 elements of the final prosthesis without a distal cantilever, resulting in the optimized distribution of occlusal loading. The preceding may have played a role in the absence of prosthetic complications during the follow-up period, which resulted in 100% prosthesis success.
The plaque accumulation was more observed in smokers; however, both smokers and non-smokers reported difficulty maintaining oral hygiene. This is a well-known disadvantage associated with an increased number of implants, as in all-on-6 rehabilitation; thus, every patient received strict dental hygiene instructions as well as self-performed plaque control training. Moreover, the tissue surface of the prosthesis was relieved when needed to facilitate using a super-floss.
The MBL remained stable throughout the study period, with a mean MBL of 0.09 ± 0.06 mm after 12 to 36 months of follow-up. These minor changes in MBL were consistent with those reported in an RCT [43], which compared four and six implants in the maxilla using NobelSpeedy Groovy implants (Nobel BioCare AG, Balsberg, Switzerland), and reported.08 mm (± 0.05), 0.00 mm (± 0.07), and 0.03 mm (± 0.03) of MBL changes between 0–12 months, 12–24 months, and 24–36. In a recent clinical retrospective study [47], the MBL after using the all-on-4 (5 or 6) immediate-loading treatment were 0.74 ± 0.10 mm, 0.37 ± 0.12 mm, and 0.15 ± 0.14 mm in 1, 2, and 3-to-4-year follow-up, respectively. This trend of marginal bone change could be compared favorably with previous reports on immediate loading in fully edentulous maxillae; [48] reported bone losses of 0.45 mm (± 0.73), 0.44 mm (± 0.79), and 0.57 mm (± 1.12) at 6 months, 1 year, and 3 years from the baseline, respectively.
Moreover, no significant difference in MBL was found between implants placed in native and sinus augmented bone (P = 0.078), which was consistent with the findings of [49], who registered no significant difference in MBL between simultaneous and different implantations in patients undergoing sinus bone grafting after a mean follow-up of 4.6 ± 1.4 years. In contrast, [50] found a greater mesial and distal MBL at 18 months with simultaneous versus deferred implant placement. The high precision and passive fit of the CAD/CAM titanium framework that splinted all implants together and a platform switching concept [51] may be associated with maintaining a stable marginal bone level. Furthermore, the abutments were seated simultaneously with the implant and never removed, reducing the frequency of disconnection and reconnection procedures, which may reduce the risk of marginal bone resorption [52].
Interestingly, most patients in the current study did not experience significant postoperative pain and/or swelling within the first week after surgery; some patients experienced a slight swelling that lasted 3–5 days. [42], on the other hand, used autogenous bone harvested from the mandibular ramus to augment the sinus bone and confirmed that patients experienced almost double pain and swelling after sinus augmentation compared to implant surgery. This was consistent with previous studies, which found that using autogenous bone grafts is associated with additional surgical procedures, a higher risk of donor site morbidity, and a lower postoperative Oral health-related Quality of Life (OHRQoL) [53, 54]. The use of DBB instead of an autogenous bone graft, as well as the small access window (3 to 5 mm vertical height performed in the current study, may be related to the apparent limitation in postoperative complications and discomfort, consequently increased willingness to undergo similar surgical procedures if necessary.
The VAS assessed patient satisfaction following functional loading with the all-on-6 DFP. The mean general satisfaction scores were very high (91.75 ± 7.06), which supported previous studies that used VAS and found high general satisfaction after rehabilitation with ISFP [55, 56]. The esthetic satisfaction was rated with high scores, 91.58 ± 9.08, except for one patient who was not very satisfied and rated the esthetic satisfaction with 68%. This patient was a heavy smoker (20 cigarettes per day), and some stains appeared on his denture. The increase in esthetic satisfaction could be related to the provisional all-on-4 prosthesis that provides the patient with immediate esthetic and helps adapt and contour the soft tissue under the prosthesis before delivering the final prosthesis. It also allowed patients to visualize and evaluate the final prosthesis, assisting in acceptance and/or guiding the clinician on changes that needed to be made for the final restoration.
The higher satisfaction with comfort and chewing ability in the current study could be attributed to the increased retention and stability of ISFP, which allows patients to apply higher masticatory forces without pain during food grinding. This was evident in previous studies that used VAS to compare satisfaction with ISFP versus overdenture or complete denture and found high satisfaction with ISFP [57, 58]. The highest level of satisfaction was registered for speaking, while the lowest was recorded for ease of cleaning. This is considered one of the disadvantages of using fixed complete denture (FCD) supported by more implants. The reduced inter-implant space, combined with the bulk of artificial gingiva used to compensate for horizontal and vertical ridge deficiencies, may complicate hygienic maintenance. Therefore, the importance of hygienic maintenance and regular checkups in the long-term success of ISFP should be emphasized and discussed with patients seeking such prosthesis treatment before surgery.
The current study compared the OHRQoL before treatment (T0), during PFP (T1), and after DFP (T2) using OHIP-14 and found that QoL improved more after treatment than before treatment. The difference in the improvement of OHRQoL between time intervals T0, T1, and T2 was statistically significant (P < 0.001), with lower OHIP scores recorded during T2 compared with T1, indicating more improvement in QoL during the DFP. During PFP (T1) interval, there was a statistically significant improvement (P < 0.05) in the following domains (items) of OHRQoL: functional limitation (taste), physical pain (painful aching, comfort on eating), physical disability (interrupting meals), psychologic disability, social disability, and handicap (life in general). The improvement in previous OHIP dimensions after transitioning from pretreatment (toothless or complete denture) to PFP could be attributed to the improved retention and stability of the screw-retained all-on-4 PFP which allowed the patient to apply the required masticatory force without pain. This was consistent with previous studies that recorded more improvement in the OHRQoL with ISFP compared with conventional treatment or overdenture [58–60]. Transitioning from All-on-4 PFP to All-on-6 DFP resulted in significant improvement in all OHIP dimensions. The extra extension of the definitive All-on-6 posteriorly, combined with adding one or two molars bilaterally, which may have contributed to optimizing the distribution of the occlusal loads in the area of the highest masticatory force, could be attributed to the superiority of All-on-6 prosthesis in functional limitation, physical pain, and physical disability.
The retrospective design of the current study is considered one of the limitations. Where the participants were requested to recollect their experiences with implant surgery and to assess their QoL before the treatment, there may have been recalled bias. However, this was the first experience for participants with implant surgery, and they confirmed that the memory of the surgery is still fresh. Another limitation was the relatively short follow-up time of 20 (12–36) months. However, the follow-up was assumed from the insertion of the all-on-6 DFP (after about 7–12 months from immediate loading on all-on-4 DFP and osteointegration of the implant in the augmented sinus. Moreover, according to previous studies, MBL changes are more pronounced during the first years of function [61], and more than half of implant failure occurs in more than half of implant failures within the first year [62]. The limited sample size was the main limitation of our study. We suggest future clinical studies on this approach with large sample size and more extended follow-up periods. Although the higher cost associated with the use of graft material and an increased number of implants was one of the shortcomings of this treatment method, all patients showed high levels of satisfaction and a willingness to repeat the same procedures if necessary.