61 Maxillary implant overdentures: four or two implants Outcome measures The primary outcome measure was MBLC. The secondary outcome measures were implant survival, overdenture survival, clinical outcomes (presence of plaque and calculus, mucosal health, bleeding on probing and pocket depth change (PDC), masticatory performance, PROMs and complications. Clinical and radiographic evaluations took place one month (T1) and 12 months (T12) after the prosthetic loading. Masticatory performance and PROMs were evaluated prior to treatment (T0) and at T12. Marginal bone level change Standardised intra-oral radiographs were made at T1 and T12 using a paralleling extension-cone system (RINN, Dentsply, Elgin, IL, USA). The radiographs were assessed with a computer software (Biomedical Engineering, UMCG, the Netherlands), which utilises the implant diameter (3.5mm) for calibration purposes. To enable blinded assessment, the superstructures were cropped from the digital radiographs. The assessments were performed by one experienced examiner (HJAM). Measurements were taken at the mesial and distal side of each implant. MBLC was defined as the difference in bone height between the radiographs taken at T1 and T12. The side of each implant that had experienced the largest amount of bone loss (mesial or distal) was used for the analysis. Implant and overdenture survival Implant survival was defined as the percentage of implants still present and not mobile at the follow-up evaluation. Implant mobility was assessed using a percussion test, which was tested after removing the bar. Maxillary overdenture survival was defined as the percentage of the initially placed overdentures still present at the T12 follow-up. Clinical outcomes The clinical outcomes were measured by one experienced examiner (PO). • Probing depth (PD) was measured at the distal, vestibular, mesial and oral site of each implant using a manual periodontal probe. Probing depth was defined as the distance between the marginal border of the mucosa and the tip of the periodontal probe. Subtracting the measurements of T1 from T12 resulted in the PDC value. • The presence of plaque was assessed by using the index described by Loë and Silness16 (range 0-3: no plaque detection (0); plaque accumulation after probing (1); visible plaque detection (2); and an abundance of visible plaque (3)). • The presence of calculus was scored with a 0 or 1 (absence (0) or presence of calculus (1)). • Peri-implant gingival health was assessed by using the modified Löe and Silness index16 (range 0-3: normal mucosa (0); mild inflammation with slight oedema and redness (1), moderate inflammation with oedema, redness and glazing (2); and severe inflammation with marked redness, oedema and ulceration (3)). • Bleeding on probing was assessed by using the Mombelli et al. index17 (range 0-3: no bleeding (0); isolated bleeding (1); confluent bleeding along the mucosal margin (2); and heavy or profuse bleeding (3)). 4
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