122 Chapter 8 The general aim of the research described in this thesis was to assess the treatment outcomes of a number of maxillary implant overdenture treatment modalities for the atrophic edentulous maxilla in patients experiencing problems with their conventional denture. The implant survival rate in maxillary overdentures retained by four implants and a bar attachment was higher than that of four implants with solitary attachments, two implants and a bar attachment or two implants with solitary attachments. Implant survival The implant survival rate was the highest in patients with maxillary overdentures retained by four implants and a bar attachment compared to the studied alternatives (chapters 2 and 4). The 1-year case-series (chapter 5) also reported a relatively low survival rate. Other research focused on 4-IOD retained with bars and report high survival rates that are in line with our results on 4-IOD retained with bars1-5. Considering research on 4-IOD’s retained by solitary attachments, only one study with 5-year results is available, which also reports survival rates for solitary attachments compared to bar attachment6. Comparative research on 2-IOD’s retained by bars or solitary attachments is limited to two prospective studies with a limited amount of patients7,8, which report more favourable results than the present thesis’ studies. A third, more recent cohort study on 2-IOD on solitary attachments also reported a high survival rate after one year9. However, the limited number of participants, the relatively short follow-up time, limited number of studies on 2-implant IODs and varying results between these studies are insufficient to formulate a definite conclusion about maxillary IOD treatment with two implants. Moreover, the circumstances may not be comparable since no information was added about the participants’ bone properties. Since the treated participants in the present thesis all had atrophic maxillae, these circumstances may have resulted in the lower survival rates. However, the influence of bone properties in edentulous maxillae has not yet been studied. Considering these results, reports with a longer follow-up can contribute to a more firm conclusion. In general, based on the implant survival rates reported in the present thesis and in other studies, in relation to the length of the evaluation period, and the number of participants, it can be concluded that maxillary implant overdenture treatment using four implants and a bar attachment system remains the gold standard. This is further confirmed by the studies reporting the ten years follow-up of this system, reporting an enduring high implant survival10,11. A similar implant survival rate is expected during the long-term follow-up of the present thesis’ studies with a similar construction. Marginal bone level change The 5-years RCT (chapter 2) reported a more favourable marginal bone level change in 4-IODs on bars compared to 4-IODs with solitary attachments. The 1-year RCT did not report any statistically significant differences between 4-IODs and 2-IODs on bars. Together with the 1-year case series, the reported mean marginal bone level change was within the 1 mm that can be expected during the first year of bone remodelling12. However, it must be noted that for the latter two studies the implant survival rate for 2-IODs was lower than desirable. In case the lost implant had survived the 1-year evaluation period, the marginal bone level change outcomes may have
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