70 Chapter 4 the implants can only be splinted in a mediolateral orientation, which could actually be an additional factor that can explain the low implant survival in our 2-implant group. Clinical outcomes The present study’s clinical outcomes were favourable in both groups, as was the median probing depth change. This is in line with other studies reporting on maxillary overdentures retained by bars1,26. Therefore, it is not likely that the difference in implant survival rates between the groups can be attributed to clinical outcomes. Masticatory performance Both groups’ masticatory performance had significantly improved. The MAI values are comparable to other studies that performed the MAT after maxillary overdenture treatment2. Therefore, the improved circumstances that are created by retaining a maxillary IOD, regardless of the number of implants, enable the patient to chew their food more effectively. Interestingly, masticatory ability, which is tested subjectively with the chewing ability questionnaire, did differ significantly between groups, favouring the 4-implant group at T12. This could possibly be explained by the number of clips used, which was higher in the 4-implant group, therefore have a higher load bearing area, thereby enhancing the chewing experience, especially when eating hard foods. Patient related outcomes The PROMs showed improved circumstances compared to the baseline in both groups. However, we could not test the intra-participant preference. This was tested by Kappel et al (2021), who provided 24 participants with four implants during their cross-over study27. The overdentures were first retained with two solitary attachments in the anterior or posterior region, then inverted after three months and subsequently converted to 4-IOD after another three months27. The preferable 2-implant retention (anterior/posterior) was equally distributed among all the participants but, interestingly, 23 out of 24 participants preferred the 4-IOD over the 2-IOD. This indicates that even though both groups’ PROMs had improved compared to a conventional denture, as reported in the present study, 4-IODs may also be the preferred choice in terms of PROMs. Strengths, limitations and future research The study was designed to assess MBLC non-inferiority in the two described groups. Unfortunately, the unexpected low implant survival rate in the 2-implant group combined with the lossto-follow up may have resulted in an underpowered MBLC result. Simultaneously, the present study clearly demonstrates a higher risk of implant loss in the experimental group, which indicates that 4-IODs should still remain the gold standard in maxillary overdenture therapy. It must be recognised that the present study included the use of narrow diameter implants (3.5mm), which may limit the generalisability to the use of regular diameter implants. Yet, compromised bone conditions are often present in patients experiencing complaints of their conventional maxillary denture, which may require more pre-prosthetic reconstructive surgery to be able to
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