Methods
handedness, learning gain, a learning gain
REGRESSION
Surgical training in knot tying and suturing techniques was provided to 124 preclinical and clinical dental students in a controlled-randomized study between December 2016 and July 2019. This knot tying and suturing course was offered exclusively as part of this study as an elective course.The case number calculation was performed with an alpha level of 0.05, a power of 0.8, and an assumed mean effect size with a Cohens d of 0.5. This resulted in a group size of 64 or a total of 128 students. The following online calculator was used for this calculation: [The study was conducted as a controlled, randomized prospective trial. All subjects consented to study participation and the use of their data prior to study initiation. The surgical knotting technique was practiced on knotting boards and the suturing technique was practiced as single button suturing on suture pads.Prior to training, a screening was performed to determine handedness using the Sattler questionnaire based on everyday activities [The training followed the 4-step method according to Peyton. In the first step, the students were shown in real time how to perform a surgical knot or how to perform a surgical suture. In the second step, a slow demonstration was given in individual steps with detailed explanations. In the third step, the instructor performed surgical knot tying or suturing according to students' instructions. In the fourth step, the learners demonstrated knot tying and suturing. This was followed by an assessment of the performed suture and knot technique with the dominant hand using the OSATS. Based on the OSATS assessment (initial measurement), students received structured feedback [For the subsequent training phase, students were randomized into three groups. For randomization, equally distributed, identical-looking tickets were drawn from the students, which assigned each student to the respective training groups (DH, NDH, or AT) with equal probability. In group DH, training was done on knotting and suturing techniques with the dominant hand. In group NDH, training occurred with the non-dominant hand, and in group AT, learners completed alternative training. This involved writing a sentence and tracing a maze with the non-dominant hand. The exercises in each group were repeated twenty times without additional self-training. The number of repetitions was determined based on a preliminary study. Immediately after the last repetition, final OSATS measurements were taken. The raters were surgical residents trained with the OSATS. The trainers and the OSATS raters were different individuals who acted independently of each other.The learners performed a new self-assessment of their skills after the training phase. Learning growth was determined as the difference between the OSATS score before and after the training phase. The evaluation of the skills and their quality according to the OSATS was based on the criteria: 
tissue handling, movement, handling of the thread, fluidity, theoretical knowledge, knots, result and overall evaluation.For each criterion, between one point for poor performance and five points for very good performance can be awarded (see attachment 1 , supplementary tables S1, S2).Learning gain was defined as an improvement in the OSATS score of 4 or more points in a subsequent analysis. This threshold was chosen, because a significant improvement in the OSATS score was observed when training with the DH with a median OSATS increase of 7 points for knot technique and a median OSATS increase of 5.5 points for suture technique while the median OSATS increase after training with the NDH or an AT was found to be 3 points for knot technique and 4 and 3 points for suture technique, respectively. Based on this characteristic, two groups of students were formed to further characterize the characteristics of those participants who demonstrated learning success.The Kolmogorov-Smirnov and Shapiro-Wilk tests were used to test the discrete variables for normal distribution. If one of the two tests reached the respective significance level (Kolmogorov-Smirnov p<0.010 or Shapiro-Wilk p<0.01), a non-parametric distribution was assumed. Because several variables were not parametrically distributed, the Wilcoxon rank-sum test was used to determine significance levels for two-sided group comparisons. For binary variables, significance levels were determined using the ChiA correlation matrix was created to determine correlations between parameters. A relevant correlation between two variables was defined as |r|>0.500. Binary logistic regression analysis was used to identify predictors for a learning gain with an increase in OSATS≥4. Multivariable linear regression analysis was performed to identify independent predictors of learning gain measured in OSATS score increase after training.