Page 56 - Peri-implant health: the effect of implant design and surgical procedure on bone and soft tissue stability

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follow‐up time of 8 years based on implants in function from 3 years up to 16 years of follow‐up. One could debate whether it is appropriate to sample implants with a large range in function time as being one group or whether cohort analysis based on function periods would be more justified.
Bone loss is in most of the studies expressed as a mean value with a standard deviation, which may hide outliers in the analysis. When reporting mean values of bone loss in a study population, it implies that the data are normally distributed. If this were the case, the mean and standard deviation would suffice to estimate the percentage of implants with a defined bone loss. Doornewaard and colleagues applied this in a systematic review and calculated the proportion of implants with bone loss over 1, 2 and 3 mm, respectively.1 The same approach was applied as a post hoc analysis using the 13 papers that reported both the mean and standard deviation and also gave a frequency distribution of bone loss as presented in Table 6. We observed that the calculated proportion of implants with bone loss was an overestimation when compared to the frequency distribution reported. Hence, bone loss is probably not normally distributed within the study population but positively skewed. Hence, nonparametric statistics is appropriate including statistical parameters median, interquartile ranges as well as frequency distributions. This could refine the prevalence figures in scientific reports. Only four of the 13 previously mentioned papers reported their data in this proposed way (Donati et al., 2015; Ekfeldt et al., 2017; Frisch et al., 2013; van Velzen, Ofec, Schulten & Ten Bruggenkate, 2015) and all reported lower medians than means.77,92,95,97 This may suggest that few implants with an extensive bone loss have a big impact on the mean and the standard deviation. This is confirmed by Donati who detected three of the 35 evaluated implants with bone loss of 5, 7, and 9 mm.77 They reported a median of 0.2 mm and an interquartile range of −0.7 to 0.5 mm. Ekfeldt and colleagues showed comparable results where only two of the 30 evaluated implants lost, respectively, 1.8 mm and 2.4 mm bone.92 This resulted in a higher mean bone loss of 0.26 mm compared to a median of 0.0 mm. It is obvious that the methodology applied in our review yielded overestimated proportions of implants with a certain threshold of bone loss.
The pooled data from this review did not demonstrate a relationship between mean function time and mean implant survival or peri‐implantitis prevalence. This could be partially explained by dropouts of implants that are not further assessed during follow‐up.
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