The protocol used for measuring the distances in every radiograph was described by the author [6] and is outlined in Figs. 4 and 5. Crucial is the determination of a reliable reference line for every implant type. Rather than measuring only the bone level, the “coronal bone defect,” described by the author in 1995 [6], is assessed, which is the extent to which the part of the implant that is meant for osseointegration failed to be osseointegrated.

All these distances were recorded on special evaluation forms, independent for each radiograph.

The obtained data was transmitted to the SAS JMP program (JMP 9, SAS Institute, Cary, USA) for further processing.

Since radiographic images are known to have a distortion, all distances had to be multiplied with a factor that was individual for each radiograph. Therefore, the length of the most coronal step was needed. When subtracting this number from the implant length provided by the manufacturer, the exact length from the apical point of the implant to the reference line is obtained. Dividing the distance gathered from the radiograph with the absolute distance provides the factor that is needed to convert all distances measured vertically. The factor for the horizontal distances is similarly obtained by using the measured implant diameter and the real implant diameter provided by the manufacturer.

The formula used for calculating the coronal bone defect (CBD) is provided in Table 3. The different values added to the depth of the bone defect (DD) are based on the various lengths of the upper most part of the Frialit.

After converting the data from the measured lengths (radiolucency) to the “coronal bone defect” by calculation, the results for the mesial and distal parts were plotted in a chronological sequence. This was carried out to check for outliers and also served as an assessment of plausibility. If an anomaly was found, the radiographs were measured again and the documentation forms were reassessed. Using this technique, errors due to false transmission or measurement errors could be identified and rectified.