Dimensional reliability in CAD/CAM production of complete denture bases: A comparative study of milling and various 3D printing technologies.

This study aims to assess the dimensional accuracy of complete denture bases fabricated from different CAD/CAM technologies and a conventional method, including milling (CNC), PolyJet (PJ), laser sintering (SLS), digital light processing (DLP), and injection molding (IM). It also examines the influence of the removal of technology-specific connectors or support structures when present. Denture base surfaces were digitized using a laboratory scanner, and virtual measurement points were calculated with tetrahedral reference geometries. Defined distances were measured in all spatial directions and compared to design data (p<0.05), revealing significant differences in sagittal (p=0.004), transversal (p<0.001), and vertical (p<0.001) dimensions. Connector removal had no significant impact for CNC but significantly affected DLP. All technologies yielded clinically acceptable results, with CNC milling demonstrating the best overall outcome.

Impact of a virtual prosthetic case planning environment on perceived immersion, cognitive load, authenticity and learning motivation in dental students.

INTRODUCTION: The application of virtual reality (VR) presents a big trend in medical education. The aim of this investigation was the presentation and assessment of a multi-user virtual prosthetic case planning environment using criteria such as perceived immersion, cognitive load, authenticity and students´ learning motivation during a virtual seminar. MATERIALS AND METHODS: The virtual case planning environment consisted of two different virtual environments - the entrance area and the case planning environment. Students and lecturers visited it with the used VR glasses Oculus Quest 2 (Meta Quest). All participants appeared as tooth avatars (molars) during the prosthetic case planning seminar and were able to communicate. These voluntary virtual case planning seminars took place in the clinical prosthetic courses (4th and 5th year). Students were asked to fill in the questionnaire comprising 15 questions separated into four categories, each assessed by a 11-point Likert scale: perceived presence/immersion, cognitive load, motivation and authenticity. A negative and a positive focus group were built, each consisting of three students answering three guiding questions. An exploratory data analysis was performed with the significance level set at p = .05. RESULTS: A total of 64 students out of 98 participated in the virtual seminars. The results demonstrated that the students felt very comfortable in the virtual seminar environment and were able to focus well on the content, demonstrated in predominantly positive results for presence/immersion. Cognitive load and authenticity presented positive results. In particular, the motivation of the students showed a high score (median: 2.1-2.6; IQR: 3.9). The cognitive load should be reduced if necessary to increase focus. The cyber sickness is a challenge for some students as well as the technical requirements of the internet connection, which needs to be addressed. Nevertheless, virtual case planning seminars are an essential tool for motivating the new generation of students. CONCLUSIONS: The results of the investigation demonstrate that the students felt very comfortable in the virtual seminar environment and were able to focus well on the content. The prosthetic case plannings were well understood and the students quickly become familiar with the environment. The cognitive load could be reduced to increase focus. In particular, the motivation of the students showed a high score. The cyber sickness is a challenge for some students as well as the technical requirements of the internet connection, which needs to be addressed.

Effect of Dentin Bonding Agents, Various Resin Composites and Curing Modes on Bond Strength to Human Dentin.

This study investigated the influence of several dentin bonding agents, resin composites and curing modes on push-out bond strength to human dentin. 360 extracted caries-free third molars were prepared, cut into slices, embedded in epoxy resin and perforated centrally. One half of the specimens (180) were treated by using one-step adhesive systems and the other half (180) with multi-step adhesive systems. Subsequently, the cavities were filled with either universal, flowable or bulk-fill resin composite according to the manufactures' product line and cured with either turbo or soft start program. After storage the push-out test was performed. The data was analyzed using Kolmogorov-Smirnov, three- and one-way ANOVA followed by the Scheffé post-hoc test, unpaired two-sample t-test (p < 0.05). The strongest influence on push-out bond strength was exerted by the resin composite type (partial eta squared ηP2 = 0.505, p < 0.001), followed by the adhesive system (ηP2 = 0.138, p < 0.001), while the choice of the curing intensity was not significant (p = 0.465). The effect of the binary or ternary combinations of the three parameters was significant for the combinations resin composite type coupled adhesive system (ηP2 = 0.054, p < 0.001), only. The flowable resin composites showed predominantly mixed, while the universal and bulk-fill resin composite showed adhesive failure types. Cohesive failure types were not observed in any group. Multi-step adhesive systems are preferable to one-step adhesive systems due to their higher bond strength to dentin. Flowable resin composites showed the highest bond strength and should become more important as restoration material especially in cavity lining. The use of a soft start modus for polymerization of resin composites does not enhance the bond strength to dentin.