Mean values (± SD) of recorded maximum RF values, calculated indirect ISQ values, and direct recorded ISQ values for Ankylos (A) and Straumann (S) test implants are shown in Table 2.

Using the Shapiro-Wilk test for indirect ISQ (p = 0.05) and direct ISQ (p = 0.02), we can conclude that both indirect and direct ISQ measures are not drawn from a normal distribution (data not shown). Both variables show a negative skewness and kurtosis (skewness indirect ISQ = − 6.22; skewness direct ISQ = − 0.491; kurtosis indirect ISQ = − 0.786; kurtosis direct ISQ = − 0.850).

The mean indirect ISQ value is on average 0.535 IDSQ units higher than the direct ISQ value although this is not significantly different from 0 (paired t test t = 2.018, df = 19, p = 0.058). This is confirmed by the Wilcoxon signed rank test (Z = 1.867, p = 0.062). Figure 4 graphically represents the match between both outcome variables for all test implants. Differences are noted between Ankylos and Straumann implants and furthermore between the different length-diameter clusters of the Straumann implants.

The Pearson product-moment correlation between indirect and direct ISQ values equals 0.990 with p = 0.000 indicating a significantly high linear relationship between both measures.