65 Maxillary implant overdentures: four or two implants Marginal bone level change The median MBLC was -0.03mm for the 2-implant group and -0.16mm for the 4-implant group. The MBLC was not statistically different between both groups (p=0.21). A frequency distribution of the MBLC is depicted in Table 4.1. Implant and overdenture survival At the end of the osseointegration period, four implants in one of the 4-implant group participants and six implants in four of the 2-implant group participants were lost. This resulted in a one year implant survival rate of 83.3% in the 2-implant group and 94.4% in the 4-implant group (p=0.03; Table 4.2). Consequently, four IODs in the 2-implant group and one IOD in the 4-implant group were lost because the number of remaining implants was too low to retain the IOD, resulting in an IOD survival rate of 77.8% in the 2-implant group and a 94.4% in the 4-implant group (p=0.32; Table 4.2). Table 4.2 | Implant and overdenture survival 1 year after overdenture placement. 2-implant group 4-implant group p-value Implants 36 72 Implants lost 6 4 Implant survival in % 83.3% 94.4% 0.03a Overdentures 18 18 Overdentures lost 3 1 Overdenture survival in % 77.8% 94.4% 0.32a aDifferences between the study groups were tested with the Log-rank test. Table 4.3 | Median changes and interquartile ranges at baseline and 1 year after overdenture placement for plaque-index, bleeding-index, gingival-index, presence of calculus and probing depth change. Baseline After 1 years 2-implant IOD (n = 18) 4-implant IOD (n = 18) p- value 2-implant IOD (n = 15) 4-implant IOD (n = 17) p- value Plaque-index [Q1 - Q3] 0 [0 – 1] 0 [0 – 0] 0.15 0 [0 – 0] 0 [0 – 0] 0.63a Bleeding-index [Q1 - Q3] 0 [0 – 0] 0 [0 – 0] 0.66 0 [0 – 1] 0 [0 – 0] 0.90a Gingival-index [Q1 - Q3] 0 [0 – 1] 0 [0 – 1] 0.42 0 [0 – 0.25] 0 [0 – 1] 0.37a Calculus-presence [Q1 - Q3] 0 [0 – 0] 0 [0 – 0] 0.16 0 [0 – 0] 0 [0 – 0] 1.00a Median Probing depth change in mm [Q1 – Q3] NA NA NA 0 [0 – 1.25] 0 [0 – 1] 0.53a aDifferences between the study groups were tested with the Mann–Whitney U test. [Q1 - Q3]: interquartile range; NA: not applicable. 4
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