Changes in marginal bone level were measured using the routinely made digital panoramic radiographs if these were available. The measurement tool was calibrated with the known respective implant length. To evaluate the bone loss, the difference was formed between the bone level at follow-up examination (Fig. 5) and at implant placement which is the baseline.

An implant was considered as successful if it fulfilled its function without pain or discomfort or clinically detectable mobility and if no peri-implant radiolucency or peri-implant infection was detectable.

Descriptive statistics, including mean values and standard deviations, were calculated for the continuous parameters using SPSS software (ver. 17.0; SPSS Inc., Munich, Germany).

The measured values were tested for normal distribution with the Kolmogorov-Smirnov goodness-of-fit test. t test or nonparametric test was used for the evaluation of differences between dependent or independent samples.

The null hypothesis was that there is a significant difference between measured parameters between tilted and axially inserted implants. The alternative hypothesis was that the differences would be purely random. A significance level of 5% was determined as statistically significant.

To assess the suitability of the two stability parameters ISQ and PT values as potential predictors for the risk of non-osseointegration of immediately loaded splinted maxillary implants in this collective, sensitivity values were plotted against complementary specificity values in receiver operating characteristic (ROC) curves [13, 14]. The area under the curve (AUC) of the ROC analysis is a measure for the quality of the parameter analyzed as a prognostic test. An area of 1 represents a perfect test; an area of 0.5 represents an ineffective test.