Background Modern implantology has made it possible to reduce patients' rehabilitation time compared with traditional protocols introduced by Brånemark. Immediate load rehabilitations of partially or totally edentulous patients allow patients to restore esthetic, masticatory and phonetic function within 24-48 hours (Pera P 2014, Menini M et al. 2012) allowing patients to immediately return to their usual social and working life. Although this type of rehabilitation is increasingly popular, knowledge of the factors that may influence implant survival and clinical success is still limited and a frequent subject of discussion in the dental scientific community. Clinical outcome is in fact the result of a multifactorial etiology that includes patient-related factors, factors related to the surgical-prosthetic protocol adopted, and operator-related factors. Purpose of the research The purpose of this research is to clinically evaluate possible factors that may influence the survival and success of immediate partial and full-arch immediate loading rehabilitations. Materials and Methods The study was carried out at the Prosthodontics and Implant Prosthodontics Division of the Department of Surgical Sciences (DISC) of the University of Genoa and involves a retrospective analysis of patients already rehabilitated by immediate loading (phase 1) and a prospective analysis of patients undergoing immediate loading investigating possible variables that might affect the clinical outcomes (phase 2). Phase 1: Retrospective study Patients rehabilitated with full-arch immediate loading prostheses of the upper or lower arch following the Columbus Bridge surgical-prosthetic protocol were included. Follow-up included recording of peri-implant soft tissue health parameters (PD, BOP and IP) and radiographic analysis of peri-implant bone level. In addition, survival and prosthetic complications were recorded. Phase 2: Prospective studies Prospective studies included patients undergoing full-arch immediate loading rehabilitation of the lower or upper arch following the Columbus Bridge surgical-prosthetic protocol (Tealdo T et al. 2014) or a partial immediate loading rehabilitation. Two randomized split-mouth studies were carried on comparing implant thread morphology (regular vs. large) and implant connection (internal vs. external hexagonal connection). Each patient received the two different implant morphology in a different hemiarch. AGGIUNGI DATI COME PER ZIGOMATICI Endoral radiographs were taken to monitor peri-implant bone remodeling at time 0 (implant placement), 3 months, 6 months and 1 year post implant placement and then annually. Periodontal indices (plaque index (PI), bleeding on probing (BoP), probing depth (PD)) were recorded to assess peri-implant tissue health at 3, 6 and 12 months of healing and then annually. Any surgical and prosthetic complication was also recorded The third prospective study investigated whether patients with extreme maxillary atrophy and who cannot be rehabilitated exclusively with traditional implants, can be treated by immediate loading full-arch rehabilitations with the placement of zygomatic implants following the hybrid zygoma concept. Eighteen patients were enrolled and follow-up visits were planned after 1, and 3 weeks, 4, 6 months and then annually. At the last follow-up appointment (mean: 36 months after surgery; range: 24-52 months), prostheses were unscrewed, and the implants and peri-implant tissues were examined. Implant success was the primary outcome evaluated: following the criteria proposed by Aparicio implant success was classified in four grades, with grade I representing the best condition and grade IV representing a failure. At the annual check-up patients were asked to fill-up a questionnaire to evaluate their satisfaction towards their oral rehabilitation. Results Retrospective study? The first prospective study showed that mean bone resorption did not differ significantly between patients treated with implants with internal and external hexagonal connection. The mean difference in bone levels between EHC and IHC was 0.25 mm at implant placement. The mean difference between IHC and EHC was -0.01 mm at 3 months, 0.13 mm at 6 months and 0.11 mm at 12 months and 0.04 mm at 36 months. All implants showed good periodontal health at the 1-year function visit, with no statistically significant differences between groups. The second prospective study showed that average bone resorption did not differ significantly between patients treated with implants with a wide thread and implants with a regular thread. No dropouts occurred during the follow-up period. Implant and prosthetic survivals were 100 %. No biological complications were evidenced. No significant differences were found between SY and SL implants comparing the number of threads exposed when inserting the implant with an insertion torque of 30 N (T student test p=.142 and U test p=.164). At 50 N no threads were visible in either group. The final torque insertion values were higher for SL (mean: 48.42 Ncm) than SY implants (mean: 43.42 Ncm) without a statistically significant difference. All implants showed good clinical results at one year. In the third prospective study 80 implants (34 zygomatic and 46 regular implants) were inserted. One zygomatic implant was lost in one patient and two regular implants failed in other two patients. 24 zygomatic implants (70.6%) presented a success grade I, 9 (26.5%) a success of grade II, and 1 (2.9%) a grade IV. Sinusitis was the most common biological complication and occurred in 2 patients (5.6%). Two patients showed unilateral upper lip paraesthesia, persistent at the latest follow-up. At the annual follow-up visit, from the data of the questionnaire, 72%, 89% and 94% of patients declared to be satisfied with their phonetic ability, chewing ability and aesthetics respectively. Conclusion In conclusion, we can argue that, thanks to the advancement of techniques and continuous scientific research in recent years, the operative protocol involving the placement of implants for immediate-loading full-arch rehabilitations with traditional implants can be considered a procedure capable of producing predictable results, with a very high success rate. Thread morphology and implant connection did not significantly affect the clinical outcomes. In cases of extremely severe atrophies, the traditional protocol can be modified by the placement of zygomatic implants in the posterior areas of the maxilla together with traditional implants in the anterior area with predictable results over time. The factors investigated in the present research do not seem to influence the success of this rehabilitation method, however, further studies with larger sample size and longer follow-up period are be needed to confirm the results.
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