77 Maxillary implant overdentures: two implants in atrophic jaws 5.1 INTRODUCTION Though there is an ongoing debate on the number of implants and the preferable superstructure in the edentulous maxilla1, an implant overdenture (IOD) retained by four implants is a good treatment option for patients experiencing problems with their conventional maxillary denture2-4. After a follow-up of at least five years, marginal bone level change (MBLC), implant and overdenture survival, and clinical parameters such as probing depth change (PDC), plaque and bleeding on probing are favourable, mastication is improved, and patient satisfaction is high2-5. In case of extreme bone resorption where no reliable implant placement is possible, reconstructive surgery using bone augmentation may be needed or zygomatic implants can be used. Both therapies are reliable and safe, but can be invasive, can induce some morbidity and due to its extent it is often performed under general anaesthesia6. A maxillary IOD can also be supported by less than four implants. Placing less than four implants to support a maxillary IOD may avoid the need for reconstructive surgery, is less invasive and less time-consuming and enables implant placement in an outpatient treatment setting. However, current evidence of such treatment is still sparse and show variable clinical, radiographical and patient related outcomes7-11. With an increasingly aging population and subsequent age-associated comorbidities, the demand for less invasive elective surgical procedures is increasing. Therefore, the aim of this case series was to assess the implant survival rate (primary outcome), prosthesis survival rates, the clinical, radiographical and patient related outcome measures, and the masticatory performance (secondary outcomes) of maxillary overdentures supported by two implants (2-IOD) and solitary attachments in patients with an atrophic maxilla. 5.2 MATERIALS AND METHODS Between September 2017 and September 2020 all patients experiencing problems with their maxillary conventional denture that were referred to the Department of Oral and Maxillofacial Surgery (University Medical Center Groningen, the Netherlands) were screened if they were eligible for maxillary implant overdenture therapy. Patients that had insufficient bone volume to place at least four implants in the edentulous maxilla and were unwilling to be treated with reconstructive surgery, were asked to participate in this case series. To be able to participate, the bone volume in the anterior maxilla, as assessed on a cone beam computed tomography (CBCT), had to be sufficient for the placement of two implants. A participant had to be at least 18 years of age, fully edentulous for at least one year and did not have an American Society of Anesthesiologists score (ASA) of IV or higher12. In this study the participants were treated following an existing procedure and was therefore not considered research performed on test-subjects as meant in the Medical Research Involving Human Subjects Act (WMO) (MEC-reference M19.224998). The study was registered in the UMCG Trial Register (RR201900060). This study was conducted in accordance with the 2008 revised requirements of the Helsinki Declaration of 1975. 5
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