135 Summary was to assess the clinical usability of the developed template and the corresponding implant placement accuracy in patients with edentulous atrophic maxillae. Twenty-four implants were placed in eleven patients. All implants could be placed with good primary stability. The implants had high accuracy at the implant shoulder (global deviation 1.1±0.5mm, lateral deviation 0.8±0.5mm) and a mean angular deviation of 7.2±3.4°. Therefore, it was concluded that the developed surgical template offers stabilised and secure template placement in the edentulous atrophic maxilla, resulting in satisfying implant placement accuracy when using a semiguided approach. Chapter 4 aimed to compare marginal bone level change, implant, and overdenture survival, clinical, masticatory, and patient related outcomes of bar-retained maxillary implant overdentures supported by two or four implants in a randomised controlled trial with a follow-up of 1 year. Forty edentulous patients were randomly allocated to two groups (n=20), receiving two or four implants in the maxilla. After healing, all the participants received an implant overdenture retained by a bar-clip system. After one year, the marginal bone level change was -0.03mm in the 2-implant group and -0.16mm in the 4-implant group (p=0.21). Implant survival was 83.3% in the 2-implant group and 94.4% in the 4-implant group (p=0.03). Median pocket depth change and clinical outcomes were low, masticatory performance and patient related outcomes improved in both groups and did not differ significantly between groups. It was concluded that maxillary 4-implant overdentures perform better than maxillary 2-implant overdentures when retained by bars in terms of implant and overdenture survival, though 2 and 4-implant maxillary overdentures perform similarly terms of marginal bone level change, clinical, masticatory, and patient related outcomes. The aim of chapter 5 was to assess treatment outcomes of 2-implant overdentures with a solitary attachment system in patients who had insufficient bone volume to place at least four implants and were unwilling to be treated with reconstructive surgery. Fifteen consecutive patients were included in this case series. The participants received two implants under local anaesthesia and after three months of osseointegration, an overdenture with palatal coverage and solitary attachments was fabricated. Implant and overdenture survival rate were 89.3% and 85.7%, respectively. Change in marginal bone level (-0.5±0.7mm), change in probing depth (0.0±1.0mm), and clinical outcomes were favourable. Masticatory performance and patient related outcomes improved significantly compared to baseline. It was concluded that patients with extreme resorption of the maxilla that are unwilling to be treated with reconstructive surgery, benefit from 2-implant maxillary overdentures retained by solitary attachments in terms of improved masticatory functioning and denture satisfaction, but have relatively high risk of implant loss. The aim of chapter 6 was to assess the incidence of peri-implant mucositis and peri-implantitis in fully edentulous patients with implant-retained maxillary overdentures during a 10-year follow-up period. One hundred and sixteen patients treated with implant-supported maxillary overdentures were available from two clinical trials. The patient level incidence of peri-implant A
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