## 3 Results  
The results of \(n\) = 254,141 implants sold are shown in Table 1.  
Group C consisted of \(n\) = 178,201 implants; the rest belonged to the two-piece group of implants. The overall return rate of implants was 0.282%. The estimated complaint rates and associated confidence intervals with respect to the overall return rate are shown in Figure 1. There were no complaints regarding polished two-piece implants designed mainly for the tubero-pterygoid region. However, only 350 sold pieces were included in the comparison. Rough implants with a large neck diameter (4.8 mm and larger) showed the highest complaint rate (2.77%). The complaint rate for single-piece basal screw implants (Category 2, Systems: BCS, BECES, GBC) was approx. 23.3 times lower than for all other two-piece implants. Prior to group analyses, categories 4 and 5, and 3, 6, and 11 (Table 1) were tested for significant within-group differences. Thereby, the comparison of categories 4 and 5 yielded significant differences in complaint rates, \(\chi^{2}\) (1) = 26.349, \(p\) < 0.001, whereas the results of comparing categories 3, 6, and 11 indicated no significant effects, \(\chi^{2}\) (2) = 0.119, n.s. Comparing categories 4 and 5 (pc = 1.182%) against category 10 (pc = 0.913%) showed no significant difference in complaint rates, \(\chi^{2}\) (1) = 1.818, n.s., OR = 1.297 (0.907; 1.853). However, when comparing implants in categories 4 and 5 against implants in categories 3, 6, and 11 (pc = 0.527%), the results indicated a significant difference in return rates, \(\chi^{2}\) (1) = 77.097, \(p\) < 0.001. The odds of observing a complaint in categories 4 and 5 were OR = 2.257 (1.875; 2.717) times higher than in categories 3, 6, and 11. When comparing category 4 (pc = 1.059%) against category 9 (pc = 1.418%), no significant difference emerged, \(\chi^{2}\) (1) = 3.440, n.s., OR = 0.745 (0.552; 1.005). Various implant designs based on the treatment protocol (immediate loading, two-stage, etc.) and surface properties (rough vs. polished surface) are presented in Table 2. Complaint rates of categories 3, 6, and 11 (two-stage-implants with conical core and more aggressive threads) were significantly different compared to category 9 (Bone Level Plus), \(\chi^{2}\) (1) = 49.975, \(p\) < 0.001. Complaints in categories 3, 6, and 11 are OR = 0.368 (0.277; 0.490) times less likely to be observed than in category 9. Comparison of polished (pc = 0.037%) and rough (pc = 0.393%) surfaces yields a significant difference in complaint rates, \(\chi^{2}\) (1) = 245.130, \(p\) < 0.001. Thereby, the odds of observing complaints in the group of rough implants is OR = 10.777 (7.429; 15.630) times higher than for polished implants. With regard to implant design, two-piece implants (pc = 0.741%) showed significantly higher complaint rates than single-piece implants (pc = 0.089%), \(\chi^{2}\) (1) = 795.968, \(p\) < 0.001. The odds for implant complaints were OR = 8.408 (7.044; 10.040) higher for two-piece implants compared to single-piece implants. The implant's core also shows a significant impact on the complaint rates, \(\chi^{2}\) (1) = 291.216, \(p\) < 0.001. Thereby, conical implants (pc = 0.309%) exhibit OR = 3.856 (3.266; 4.553) times lower odds of being returned compared to cylindrical implants (1.182%). Thread types are also significantly related to the outcome, \(\chi^{2}\) (3) = 982.317, \(p\) < 0.001. Aggressive threaded implants for 2 nd-cortical engagement showed the lowest rates of complaint (pc = 0.033%), followed by compression screws (pc = 0.159%), cutting threads (pc = 0.527%), and cylindrical implants with minimal threads (pc = 1.229%). When comparing groups C and D against each other, it must be noticed that in group C mainly single-piece implants were found (99.7%), whereas the percentage of single-piece implants in group D was only 57.1%.