The aim of the study was to evaluate the training effect of CTP and DTP with regard to scaling with either a sonic scaler (AIR) or GRA. Furthermore, the participants of both training concepts assessed themselves with regard to their subgingival scaling effort, treatment time, handling, root surface roughness/destruction and effectiveness.
Forty-nine participating students were without randomization assigned, (1) in their 7th semester in the autumn of 2018 to the CTP group, while the students present in the spring of 2019 were assigned to the DTP group. In the DTP group, one student refused to take part in the study (n = 30). In the CTP group, one student failed to finish the training phase (no data at the test visit because of breaks during the preclinical course) (n = 19).
Data for all the participants regarding age, gender, handedness, regularity of playing computer games/consoles and previous dental/technical or medical education were retrieved pseudonymously.
During the practical evaluation, with an equivalent structure for all participants, artificial root surfaces were instrumented either with GRA normal shapes 5/6, 7/8, 11/12 and 13/14 (American Eagle Instruments, Missoula, MT, USA) or AIR (Synea, W&H, Bürmoos, Austria) with air pressure and water cooling (30 ml/min), as recommended by the manufacturer at level 2, i.e., "medium" amplitude, combined with a straight, right and left curved, slender tip (1AP, 2APr, 2APl, W&H, Bürmoos, Austria). Simultaneously, a total of 14 questions per participant had to be answered. Four of the fourteen questions were recorded separately for AIR and GRA, resulting in 18 questions in total. In addition, the instrumentation time of each participant was recorded for the two different instruments.
Student training program and instrumentation procedures
At the beginning of the study, all the participants received a two-hour theoretical introduction to both instruments and to one of the two training programs, either CTP or DTP, but without practical exercises.
The participants in the DTP group received training for both types of instruments, with 10 sessions of 45 min each over a period of 12 weeks. DTP is intended to support the teaching of the necessary work steps and ergonomic aspects for each instrument separately, e.g., with animated GIF (graphics interchange format) or short video sequences to explain the entire construction, technique and seating position of the participants and patient. Therefore, the number of staff and time of supervision (three periodontists with board certificates; one out of ten students) could be reduced compared to the CTP group.
The CTP group also received systematic training over the same period of time according to the continuously modified conventional teaching program from 1994 . This group was supervised and monitored by five periodontists with board certificates (one per four students) without any digital interaction (e.g., no possibility for self-performed working steps or self-control of handling).
In addition, all 49 participants were clinically calibrated during the training courses with regard to application pressure (3–5 N for GRA and < 1 N for AIR). No measurements of root surface destruction or roughness were made.
After 12 weeks (end of the training period), the effectiveness of all the participants (DTP/CTP) was evaluated, and their self-assessment was determined by questionnaire. During practical evaluation, 12 comparable test teeth had to be instrumented with GRA (tooth: 11, 14, 16, 31, 37, 45) and with AIR (tooth: 21, 25, 17, 34, 36, 43). The sequence of both instruments was initially randomized (Microsoft Excel 16, Microsoft Corporation, One Microsoft Way Redmond, WA, USA) for each participant. The participants were asked to instrument the test teeth until they reached the subjective maximum elimination of hard and soft simulated deposits. For each participant, the time required to treat the six teeth per instrument was recorded. The time for changing instruments was considered. Further details including timetables, etc. have been described in detail elsewhere .
Manikin heads, test teeth and planimetric evaluation
All participants performed subgingival scaling on similar manikin heads, which were equipped with modified periodontitis models (Frasaco, Tettnang, Germany). The models exhibited pronounced periodontitis with moderate to advanced horizontal bone loss and isolated and deep vertical pockets. Consequently, the difficulty of instrumenting the teeth differed regarding both anatomy and accessibility. The mean (SD) pocket probing depth (PPD) was 5.8 (2.1) mm (range, 3–11 mm). The test teeth were coated with a thin layer of transparent fluorescent varnish (Shiny White, Rival de Loop Young, Berlin, Germany) between the artificial cementoenamel junction and the alveolar bone. Adhering plaque was simulated with commercial varnish (A-CK, Frasaco, Tettnang, Germany), modified by the ratio of varnish to thickener to simulate the adhesion of subgingival hard deposits. Details of the reproducible and standardized procedure for coating and planimetric evaluation of cleaning efficiency have been described in detail elsewhere [11, 12].
During the practical evaluation visit at the end of the 12-week training phase, a questionnaire had to be answered. Before the test, all the participants had to give six statements, rated on a response scale ranging from 1 to 5, according their own personal assessment of the two different scaling instruments used (Additional file 1). Furthermore, four questions aimed at the fatigue effect, treatment time requirement, handling and effectiveness and had to be answered after using each group of scaling instruments (Additional file 2). The evaluation was performed pseudonymously and assigned to a processed model.
The effectiveness (cleaned area in %) and the treatment time when using GRA or AIR were analyzed in relation to the DTP or CTP group. This study focuses on the evaluation of the questionnaires (personal assessments of the participants). In particular, the training groups (DTP vs. CTP) and GRA versus AIR were compared according to the individual statements on a 5-point Likert scale, differentiated in 25% steps. The answers of each group were counted for every possible answer.
As the aim of the study was to compare two different teaching concepts during a regularly running course, participants were selected consecutively. Hence, a power calculation was not feasible. Data acquisition and collection were performed with Microsoft Excel (Microsoft Excel 16, Microsoft Corporation, One Microsoft Way Redmond, WA, USA). Tables were created and entered into SPSS Statistics (SPSS Statistics 24, IBM, Chicago, IL, USA) for statistical analysis. The normal distribution of questions 1 to 4 and statements 1 to 6 within the two different groups (DTP vs. CTP) between AIR and GRA were tested by the Kolmogorov–Smirnov and Shapiro–Wilk tests. For all questions and statements, there was no normal distribution. Subsequently, a mean value comparison was performed using the Mann–Whitney U-test, and significant differences were found both within the DTP and CTP groups with regard to the AIR versus GRA group. A linear regression model was constructed using RCE-b after treatment as the dependent variable, while age, gender, handedness (right/left/two-handed), playing computer games/consoles regularly (no/yes), previous education in medicine/dentistry (no/yes), instrument (AIR/GRA) and group of training (DTP/CTP) were the independent variables. All tests were two-sided; statistical significance was assumed if p ≤ 0.05.