Comparison of accuracy of pilot-drill guided and full-guided implant insertion

When comparing the values for the accuracy of the implant insertion using the fully guided mode all values were higher when compared to the pilot-drill guided. This is in line with the findings of previous laboratory studies [5, 6, 9, 25]. The closer guidance provided by the fully guided implant insertion might be beneficial for inexperienced surgeons as extended mistakes are unlikely when the manufacturer’s protocol is followed. When beginning with implant dentistry, the safety for inexperienced surgeons might thus increase. However, even with fully guided implant insertion a residual error has to be considered. First, there might be a mismatch when superimposing the surface scan over the data set obtained by cone beam computed tomography. Furthermore, the template itself must have a clearance fit in order to be positioned on the model. In the current study, the offset was 0.2 mm for the templates. Additionally, the guiding sleeve must have tolerance in order to allow a smooth gliding of the implant bur. This tolerance was reported with 60 μm for the sleeve and might cause a deviation of 200 μm on the tip of the bur depending on its lengths [26]. However, all these factors were leveled as the same procedure and materials were used except for the guiding mode. When using the fully guided implant insertion, the mean mismatch was less than 1 mm, and the mean angular deviation was 2.24 degrees. Those findings are comparable to the findings of Ebeling et al. who were comparing the deviation between undergraduates and implantologists using the same system [22]. The slightly higher deviations in their study compared to the current examination might be due to the use of phantom heads. In our study, the models were not fixed in a phantom head so that the participants were able to have an overview of and access to the model from all directions enabling enhanced visual control and possibility for corrections.

For the vertical mismatch, there was a tendency that the implants were not inserted deep enough. One potential reason might be the consistency of the resin that the models were made from. As the drilling experience was rather rigid, a higher torque was needed to insert the implants. Another reason might be that the preparation of the cavities was performed without irrigation. Thus, debris might not have been fully cleared from the implant cavity and has prevented the implant from being inserted to the vertical stop position. Considering the vertical mismatch, no value either for the fully guided nor for the pilot-drill guided implant insertion was more than 2 mm. Certainly, this might be important as a regular safety margin is 2 mm. Thus, an injury of the adjacent anatomical structures e.g. the inferior alveolar nerve, would be unlikely when using a template. When comparing the results of fully guided and pilot-drill guided implant insertion, it can be stated that both methods provide sufficient accuracy within the safety margin of 2 mm.

Influence of individual factors on the accuracy

The influence of the individual factors is a bit controversial as only single parameters have reached statistical significance. This is in accordance with previous examinations having analyzed undergraduate students [7,8,9]. In contrast, van de Wiele et al. found a higher accuracy in right-handed surgeons for implant placement on the right site and for left-handed implant placement on the left site in the inexperienced group [27]. One reason could be that in the present examination tooth-borne templates were used in a laboratory set-up whereas Van de Wiele et al. used mucosa-borne templates in a clinical set-up. In different studies, tooth-borne templates showed a higher accuracy when compared to mucosa-borne templates [28, 29]. This might be due to the higher resilience of the mucosa compared to natural teeth or bone. Furthermore, the positioning of the templates is more reliable when teeth are available for fixation. Another potential reason for not finding statistically significant differences considering the individual factors in the present examination might be that the examination used a laboratory set-up. Thus, the participants were able to overview the surgical site without restrictions and the models were not fixed so that they could be positioned according to the participant’s need.

Time required for implant insertion

In the current examination, the participants needed statistically significantly more time to insert the implants fully guided compared to the pilot-drill guided implant insertion. This might be explained by the fact that the pilot-drill guided implant insertion requires only once the application of the drill into the sleeve, whereas the full-guided implant insertion requires this procedure seven times potentially leading to an extended time for implant cavity preparation and implant insertion. The literature reporting the time required for implant insertion is contradictory [7, 9]. In one study, the participants needed statistical significantly less time for fully guided implant insertion [7] while in another examination the fully guided implant insertion took longer even though the difference reached no statistical significance [9]. In a recent study, mandibular models were mounted in a phantom head and fully guided implant insertion was performed with two different guides, the time required for the procedure was comparable to time recorded in the current study 16:26 ± 5:52 min versus 15:22 ± 05:22 min [30]. In general, the participants in the current study required more time for implant insertion in general and statistically significantly more for fully guided implant insertion. Another potential reason for the longer time required for fully guided implant placement in the current study could be the implant system. In the studies mentioned, a surgical tray using drill sleeves already placed on the respective burr was used. The currently applied guided surgery tray uses a drill handle that has to be placed into the sleeve in the template. Especially when the gap is narrow, placing the drill handle in the template sleeve correctly without twisting can be challenging. For the pilot-drill guided implant insertion, the pilot drill has to be placed into the template sleeve without the drill handle. As the participants were not familiar with the guided surgery tray, the correct positioning of the drill handle might be the reason for the longer time observed in the current study.

Questionnaire

The completion of the questionnaire was divided into one part prior to and one part after participation in the hands-on course. Surprisingly, a majority had only theoretical knowledge in implant dentistry although 26 of the participants had a dentistry-related professional education prior to studying dentistry. This fact is specific to our Dental School as applicants with a completed education as dental assistant or dental technician get a bonus in the university election process for the allocation of places in higher education. In a recent study, a comparable ratio of students with completed dentistry-related education could be observed [30]. Initially, most of the participants stated to have insufficient knowledge in implant dentistry which is in line with a previous examination at a German Dental School [9]. A potential explanation might be the hygiene restriction during the COVID-19 pandemic. In this term, practical education was reduced, and elective surgery had to be postponed which reduced the possibility for the students to obtain practical experience considering implant dentistry. After the course, the interest in implant dentistry could be increased according to the questionnaires. These results are in line with findings from other countries where the surveys were yielding an extended interest in implant dentistry [17, 31]. However, combinations of theory and practical training are time-consuming and require staff. According to a survey in the United Kingdom, major limiting factors in teaching implant dentistry are limited time and funding and insurance liability [32]. This is in line with the situation in the presented examination. As funding is the most urgent limiting factor, there is the necessity of support from implant providers. However, this fact always raises the concern of a lack of independence in dental education. A potential way to overcome this concern might be partnerships with multiple different implant providers in order to avoid a bias toward one specific system [32].

Teaching method

The teaching method applied in the current study was a three-step procedure. First, the theoretical lesson was performed online. The digital planning of the implant position was the second step. Subsequently, the practical training followed. It would have been advantageous to integrate blended learning into the course e.g. the digital planning of the implant position as an online course in advance to the practical part as it has shown beneficial long-time results [33]. However, due to the license management of the planning software, it was not possible to perform the planning online. Thus, the planning part was done on-site on licensed workstations. Furthermore, a long-term evaluation was not part of the current study. One drawback of hands-on teaching is that it is cost-intensive and time-consuming. When totalizing the material costs per participant, it is adding up to 150 € not included the working time of the staff. This fact leads to another disadvantage: The application of the Peyton-4-step approach was not possible due to limited resources. In a recent study of our department, promising results could be shown for the use of this method for the teaching of surgical sutures [34]. As the 4-step approach contains demonstration–deconstruction–comprehension, and performance by the learner the procedure of the implant insertion by the instructor would have been necessarily performed multiple times during the course. However, due to the limited resources considering the material, this was not possible. In future courses, a video sequence of the instructor performing the implant insertion would be advantageous.

Limitations

As the examination was in a laboratory set-up, the results have to be interpreted with caution. The implants were inserted into mandibular models with a gingiva mask in the region of implant placement that were not mounted into a phantom head. Constricting factors being present in a clinical situation, e.g. bleeding, soft tissue, limited mouth opening, or saliva were absent. The participants were able to have a clear view and access from all directions to the model. Thus, the implant insertion in the presented study might be considered as easier compared to a clinical situation [3]. Furthermore, it can be assumed that the time required for implant insertion is different from a clinical situation. The mandibular models are another limiting factor. The resin is not imitating the structure of natural bone [22]. Furthermore, the resin debris cannot be removed by irrigation so that it might remain in the implant cavity potentially leading to deviations, certainly vertical, when inserting the implant. On the other hand, laboratory training is an important step before performing surgery in real patients. Offering the opportunity for the instructors to give direct feedback to the participants considering their accuracy provides a quality-controlled training which has been reported to have a positive effect on the patients’ safety [23]. Another factor potentially influencing the results is the fact that, due to hygiene restrictions caused by the COVID-19 pandemic, the course was only possible in small groups of four students. Thus, closer support and supervision was assured compared to larger groups. This close supervision might lead to more accurate results as errors could be identified early and corrected compared to the hands-on courses in larger groups. However, teaching in small groups is favored but has higher staff and time requirements. Therefore, considering the limited resources available in dental education, training in small groups is preferred but a return to courses in larger groups might be unavoidable.