Influence of additive and subtractive zirconia and lithium disilicate manufacturing on tensile bond strength and surface topography.

STATEMENT OF PROBLEM: Although bonding is important for long-term clinical success, studies on the bonding of additively manufactured ceramics are sparse. PURPOSE: The purpose of this in vitro study was to determine the influence of manufacturing methods, additive (LCM) versus subtractive (CAM). and ceramic materials, zirconia (ZrO2) and lithium disilicate (LiSi), on the tensile bond strength (TBS), failure mode, and surface roughness of ceramics. MATERIAL AND METHODS: A total of 240 ceramic specimens (n=60/group; 2×2×10 mm) were prepared. Two additively manufactured (LCM-printed) ceramics, LiSi and ZrO2 (Lithoz), subtractively manufactured LiSi (IPS e.max CAD), and subtractively manufactured ZrO2 (KATANA Zirconia HTML PLUS) were evaluated. From each material, 40 specimens were bonded together (n=20 ceramic-ceramic specimens/group), and 20 specimens were bonded to equally sized human dentin specimens (n=20 ceramic-dentin specimens/group). The ZrO2 specimens were airborne-particle abraded (Al2O3, 50 µm, 0.1 MPa), and the LiSi specimens were etched with hydrofluoric acid. Then, a universal primer (Monobond Plus) was applied. After the dentin was coated with an etch-and-rinse adhesive (Syntac Classic), the specimens were bonded with luting composite resin (Variolink Esthetic DC), light polymerized for 40 seconds, thermally aged (10 000 cycles between 5 °C and 55 °C), tested for TBS, and statistically analyzed (1- and 3-way ANOVA and Weibull analysis). The ceramic surface was examined with scanning electron microscopy, and surface roughness was measured with digital microscopy before and after surface pretreatment. RESULTS: TBS varied between 5.88 ±2.22 MPa and 6.34 ±2.26 MPa in the ceramic-dentin groups and 12.40 ±1.56 MPa and 18.82 ±5.92 MPa in the ceramic-ceramic groups. No significant difference was observed regarding the manufacturing method and material for different bonding conditions (P>.05). Additive and subtractive LiSi showed the highest reliability with m=18.27. The ceramic-ceramic specimens failed cohesively in the luting composite resin, whereas the ceramic-dentin specimens failed adhesively. CONCLUSIONS: The manufacturing method and material used had little effect on bond strength values or surface properties. The recently introduced printed materials performed similarly to conventionally milled materials.

Comparing accuracy in guided endodontics: dynamic real-time navigation, static guides, and manual approaches for access cavity preparation - an in vitro study using 3D printed teeth.

OBJECTIVES: To assess root canal localization accuracy using a dynamic approach, surgical guides and freehand technique in vitro. MATERIALS AND METHODS: Access cavities were prepared for 4 different 3D printed tooth types by 4 operators (n = 144). Deviations from the planning in angle and bur positioning were compared and operating time as well as tooth substance loss were evaluated (Kruskal-Wallis Test, ANOVA). Operating method, tooth type, and operator effects were analyzed (partial eta-squared statistic). RESULTS: Angle deviation varied significantly between the operating methods (p < .0001): freehand (9.53 ± 6.36°), dynamic (2.82 ± 1.8°) and static navigation (1.12 ± 0.85°). The highest effect size was calculated for operating method (ηP²=0.524), followed by tooth type (0.364), and operator (0.08). Regarding deviation of bur base and tip localization no significant difference was found between the methods. Operating method mainly influenced both parameters (ηP²=0.471, 0.379) with minor effects of tooth type (0.157) and operator. Freehand technique caused most substance loss (p < .001), dynamic navigation least (p < .0001). Operating time was the shortest for freehand followed by static and dynamic navigation. CONCLUSIONS: Guided endodontic access may aid in precise root canal localization and save tooth structure. CLINICAL RELEVANCE: Although guided endodontic access preparation may require more time compared to the freehand technique, the guided navigation is more accurate and saves tooth structure.

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.

Correlation between theoretical knowledge and the difference between self- and teaching doctor-assessment.

OBJECTIVES: The right intuition for self-assessment without overestimating or underestimating oneself compared to theoretical knowledge is a skill that requires conscious practice and is very often paradoxically opposed to the level of knowledge. Self-assessment is an essential skill for dental professionals for lifelong learning and improvement. The objective of our study was to assess the correlation between theoretical knowledge and the difference between self- and teaching doctor-assessment. METHODS: The app "digital course organizer" for organization and assessment was used for the self- and teaching doctor-assessment of students for each day of patient treatment during the clinical courses at a university hospital. The difference between the self- and teaching doctor-assessment was compared to the score of an initial theoretical written test at the beginning of the eighth semester to assess the correlation between overestimation or underestimation and theoretical knowledge. RESULTS: A total of 309 dental students over four semesters in the clinical study phase (fourth and fifth years; eighth and 10th semesters) participated in the investigation. The overall view of all values showed very low correlations (<0.2) of the assessment difference values of both practical courses for the initial written test. CONCLUSION: There were very low correlations between the initial written test (theoretical knowledge) and the difference between self- and teaching doctor-assessment as well as no evidence of overestimation and underestimation.

Evaluation of one-piece zirconia dental implants: An 8-year follow-up study.

OBJECTIVES: Long-term studies of modern zirconia implants are still insufficient. This prospective 8-year follow-up study investigated one-piece zirconia implants. MATERIALS AND METHODS: Patients who had received a one-piece zirconia dental implant (PURE ceramic implant, Institut Straumann GmbH, Basel, Switzerland) were included in this study. Next to the implant survival and success rates, the radiographic and clinical implant parameters were assessed. RESULTS: The overall survival rate of 67 zirconia implants in 39 patients was 100%. The overall success rate was 89.6%. Around the immediate zirconia implants, the success rate was 94.7%, and around the delayed implants, 87.5%. The immediate implants showed a significantly higher bone crest compared to the delayed implants (p = 0.0120). According to the pink esthetic score, the immediate implants revealed more favorable esthetic results compared to the delayed implants after an 8-year follow-up (p = 0.0002). CONCLUSIONS: After 8 years, the one-piece zirconia implants presented an 89.6% success rate. Regarding the timing of implantation, in individual cases, immediate implantation can have slight advantages over delayed implantation. CLINICAL RELEVANCE: Immediate implants can also be considered for zirconia implants and should not be excluded on principle.

Three-Dimensional Printed Resin: Impact of Different Cleaning Protocols on Degree of Conversion and Tensile Bond Strength to a Composite Resin Using Various Adhesive Systems.

The present investigation tested the effect of cleaning methods and adhesives on the tensile bond strength (TBS) of a resin-based composite luted to a temporary 3D printed resin. Substrates (n= 360) were printed using a Rapidshape D20II and cleaned with a butyldiglycol-based solution, isopropanol, or by centrifugation. Specimens were air-abraded with Al2O3 (mean particle size 50 µm) at 0.1 MPa followed by pretreatment (n = 30/subgroup) with: (1) Clearfil Ceramic Primer (CCP); (2) Clearfil Universal Bond (CUB); (3) Scotchbond Universal Plus (SUP) or 4. Visio.link (VL) and luted to PanaviaV5. TBS (n = 15/subgroup) was measured initially (24 h at 37 °C water) or after thermal cycling (10,000×, 5/55 °C). The degree of conversion (DC) for each cleaning method was determined prior and after air-abrasion. Univariate ANOVA followed by post-hoc Scheffé test was computed (p < 0.05). Using Ciba-Geigy tables and chi-square, failure types were analyzed. The DC values were >85% after all cleaning methods, with centrifugation showing the lowest. CCP pretreatment exhibited the lowest TBS values, with predominantly adhesive failures. The combination of CCP and centrifugation increased the TBS values (p < 0.001) compared to the chemical cleaning. CUB, SUP, and VL, regardless of cleaning, can increase the bond strength between the 3D printed resin and the conventional luting resin.

Impact of polishing system on surface roughness of different ceramic surfaces after various pretreatments and bracket debonding.

OBJECTIVE: Evaluating various polishing methods after bracket debonding and excessive attachment material removal for different ceramics and pretreatments. MATERIAL AND METHODS: Zirconia (ZrO2), leucite (LEU) and lithium disilicate (LiSi) specimens were pretreated with a) silica coated alumina particles (CoJet); LEU and LiSi additionally with b) hydrofluoric acid (HF), c) Monobond Etch&Prime (MEP), d) silicium carbide grinder (SiC) before bracket bonding, shearing off, ARI evaluation, excessive attachment material removal and polishing with i) Sof-Lex Discs (Soflex), ii) polishing paste (Paste), iii) polishing set (Set). Before/after polishing surface roughness (Ra) was measured with a profilometer. Martens hardness parameter were also assessed. RESULTS: Irrespective of pretreatment Ra of LEU increased the most, followed by LiSi and ZrO2 (p < 0.001, SiC: p = 0.012), in accordance with the measured Martens hardness parameter. CoJet/SiC caused greater roughness as HF/MEP (p < 0.001). The ZrO2 surface was rougher after polishing with Paste/Set (p < 0.001; p = 0.047). Ra improved in the LEU/CoJet, LEU/SiC and LiSi/SiC groups with Soflex/Set (p < 0.001), in the LiSi/CoJet and LEU/HF groups by Soflex (p = 0.003, p < 0.001) and worsened by Paste (p = 0.017, p < 0.001). Polishing of HF or MEP pretreated LiSi with Set increased Ra (p = 0.001, p < 0.001), so did Paste in the LEU/MEP group (p < 0.001). CONCLUSIONS: Paste couldn't improve the surfaces. Soflex was the only method decreasing Ra on rough surfaces and not causing roughness worsening. Polishing of LEU/LiSi after MEP, LEU after HF pretreatment doesn´t seem to have any benefit. CLINICAL RELEVANCE: To avoid long-term damage to ceramic restorations, special attention should be paid to the polishing method after orthodontic treatment.

Impact of material combinations and removal and insertion cycles on the retention force of telescopic systems.

OBJECTIVES: A variety of dental materials are available for the fabrication of telescopic crowns. The aim was to investigate the impact of material combinations and removal and insertion cycles on their retention forces. MATERIALS AND METHODS: CAD/CAM-fabricated cobalt-chromium-molybdenum (CoCr) and zirconia (ZrO2) primary crowns were combined with polyetheretherketone (PEEK), polyetherketoneketone (PEKK), CoCr, and ZrO2 secondary crowns (four combinations included PEEK/PEKK secondary crowns in a thickness of 0.5 mm bonded to the CoCr tertiary construction), resulting in 12 different material combinations: CoCr-PEEK; CoCr-PEKK; CoCr-ZrO2; CoCr-CoCr; CoCr-PEEK 0.5; CoCr-PEKK 0.5; ZrO2-PEEK; ZrO2-PEKK; ZrO2-ZrO2, ZrO2-CoCr; ZrO2-PEEK 0.5; and ZrO2-PEKK 0.5 (n = 15 pairings per material combination). Pull-off tests were performed with a universal testing machine initially and after 500, 5000, and 10,000 removal and insertion cycles in a mastication simulator. Descriptive statistics with the Kolmogorov-Smirnov, Kruskal-Wallis, and Mann-Whitney U tests were computed (α = 0.05). RESULTS: The tested parameters, material combination, and removal and insertion cycles had significant impact on the retention force values (p < 0.001). An increase in removal and insertion cycles was associated with a decrease in retention forces within CoCr and ZrO2 secondary crowns, regardless of the primary crown material. In contrast, PEEK and PEKK secondary crowns presented higher retention load values after 10,000 cycles than initially. CONCLUSION: Different material combinations behaved differently after simulated removal and insertion regimens. This difference should be considered during treatment planning. CLINICAL RELEVANCE: Telescopic crown systems should be made of materials with predictable retention forces that do not deteriorate with time. The implementation of new materials and technologies facilitates reproducibility and time-saving fabrication.

Impact of high-speed sintering and choice of preshaded monochrome or multilayered blanks on fatigue behavior of 4 mol% yttria-stabilized tetragonal zirconia polycrystal.

STATEMENT OF PROBLEM: High-speed sintering allows the rapid fabrication of esthetic restorations with adequate flexural strength. However, data on the fatigue behavior of high-speed sintered 4 mol% yttria-stabilized tetragonal zirconia polycrystal (4Y-TZP) are lacking. PURPOSE: The purpose of this in vitro study was to examine the effect of high-speed sintering and the preshading of blanks (monochrome versus multilayer) on the fatigue behavior of 4Y-TZP ceramics. MATERIAL AND METHODS: Four-point flexural strength specimens (N=405) were fabricated from high-speed sintered multilayer 4Y-TZP (Zolid DRS) processed at 1580 °C for about 20 minutes and conventionally sintered at 1450 °C for about 10 hours, multilayer 4Y-TZP (Zolid Gen-x), and monochrome 4Y-TZP (Ceramill Zolid HT+PS), the control group. The specimens were loaded under 5 different dynamic test conditions for fatigue testing (P1-P5). Three were step-stress protocols (P1: 50 N for 5000 cycles; P2: 10 N for 1000 cycles, P3: 5% for 5000 cycles), 1 was tested with a constant force of 720 N (P4), and 1 was tested for different constant load levels (P5). For analysis of P1-P3, the Kaplan-Meier test and Mantel Cox test were performed (α=.05). P4 was analyzed with the Kolmogorov-Smirnov, Kruskal-Wallis, and Mann-Whitney U tests, and P5 by creating a load-cycle diagram. A fracture analysis was performed. RESULTS: ZMLC showed better fatigue behavior than ZMLH (P≤.006) and ZMOC (P≤.002) in all 3 step-stress protocols (P1-P3). ZMLH showed results comparable with those for ZMOC (P≥.285). In P4 and P5, all materials showed comparable values (P=.163 for P4). CONCLUSIONS: The multilayer technique showed a positive effect on the fatigue behavior of 4Y-TZP. In contrast, high-speed sintering negatively influenced the fatigue behavior of multilayer 4Y-TZP. The high-speed sintered material showed no deterioration compared with the conventional sintered monochrome material.

Food Solutions and Cigarette Smoke-Dependent Changes in Color and Surface Texture of CAD/CAM Composite Resins-An In Vitro Study.

PURPOSE: To investigate the discoloration and surface properties of four CAD/CAM composite resins following storage in various food solutions and exposure to cigarette smoke. MATERIALS AND METHODS: A total of 74 specimens (N = 370) were prepared for five materials: Brilliant Crios (BC), Cerasmart (GC), Lava Ultimate (LU), Shofu Block HC (SH), and Sonic Fill 2 (SO). Discoloration (ΔE) was investigated with a spectrophotometer. Measurements were taken before immersion in storage media (carrot juice, curry, cigarette smoke, red wine, energy drink, and distilled water), after 2 weeks of immersion, and after manual polishing of the specimens following immersion. The average surface roughness (Ra) was measured with a profilometer. Qualitative surface observation was performed with scanning electron microscopy (SEM). Data were analyzed using Kolmogorov-Smirnov test, Mann-Whitney U test, and one-way ANOVA with Tukey post hoc test. RESULTS: The highest influence on ΔE after immersion was observed for storage medium (ηηP2 = 0.878, P < .001), followed by the interaction between storage medium and material (ηP2 = 0.770, P < .001) and material (ηP2 = 0.306, P < .001). For ΔE after polishing, the highest influence was indicated by the interaction between material and medium (ηP2 = 0.554, P < .001), followed by medium (ηP2 = 0.244, P < .001) and material (ηP2 = 0.196, P < .001). Immersion in carrot juice led to the highest color change (ΔE: 8.0 to 10.4), whereas the lowest values were recorded in distilled water (ΔE: 2.0 to 2.4). Carrot juice and the energy drink caused the highest Ra values (0.120 µm to 0.355 µm). SEM pictures indicated a loss of the organic matrix after manual polishing. CONCLUSION: The different materials reacted dissimilarly to the various storage media in terms of discoloration. Surface roughness increased after immersion or polishing. Neither discoloration nor surface roughness could be reset to default by manual polishing. Int J Prosthodont 2023;36:194-202. doi: 10.11607/ijp.6950.

Clinical and Radiographic Outcomes of Dental Implants in Patients Treated With Antiresorptive Drugs: A Consecutive Case Series.

Medication-related osteonecrosis of the jaw (MRONJ) is a serious concern for dentists as well as maxillofacial surgeons. Therefore, the safety of dental implant placement in patient receiving antiresorptive drugs (ARDs) has been the subject of controversial debate for several years and remains a source of uncertainty for surgeons and patients. This consecutive case series assessed the clinical and radiographic outcomes of dental implants placed in patients under antiresorptive therapy. Patients who received at least one dental implant at the Department of Oral and Maxillofacial Surgery, Ludwig Maximilian University (LMU), Munich, Germany, between 2010 and 2019 with a history of current or past antiresorptive medication were included the study. The main outcomes were occurrence of MRONJ, implant success, and survival rate. A total of 16 patients were treated with 39 implants. No implant loss or MRONJ occurred in the respective patients. The reasons for antiresorptive intake were osteoporosis, malignancy, edema of bone marrow, or diffuse sclerosing osteomyelitis (DSO). MRONJ occurred neither around implants nor in other locations. Cumulative implant success was 92.6% (25 of 27). No subjective complaints or postoperative complications were documented. Mean bone loss was 0.60 ± 0.98 mm. The prevalence of peri-implantitis was 30% on patient level and 29.6% on implant level. None of the patients had failed implants. No major complications after implant placement under antiresorptives could be detected. As long as implant surgery follows a specific protocol, implant placement in patients treated with antiresorptive therapy seems to be safe and predictable.

Bond strength between temporary 3D printable resin and conventional resin composite: influence of cleaning methods and air-abrasion parameters.

OBJECTIVES: The influence of different cleaning methods, air-abrasion parameters, and aging on shear bond strength (SBS) and tensile bond strength (TBS) of 3D resin luted to composite resin. MATERIALS AND METHODS: Nine hundred resin substrates were 3D printed (D20II, Rapid Shape) and cleaned with either isopropanol (ISO), butyldiglycol-based solution (BUT), or centrifugation (CEN). After 24-h storage in 37 °C water, specimens were air-abraded (mean particle size 50 µm; n = 60) with either alumina at 0.1 MPa (AL0.1) or 0.4 MPa (AL0.4) and glass pearls at 0.1 MPa (GP0.1) and 0.4 MPa (GP0.4) or conditioned with visio.link (control) and luted with PanaviaV5. Initially (24 h, 37 °C water storage) or after aging (10,000 thermal cycles), SBS and TBS were measured, and fracture types were examined. Surface free energy (SFE) and roughness (Ra) were determined after air-abrasion. Kolmogorov-Smirnov, Kruskal-Wallis H, Mann-Whitney U, chi-square, and partial eta-squared were computed. RESULTS: SBS measurements presented higher values than TBS (p < 0.001-0.033). Within the pretreatment groups, CEN showed the highest SBS and TBS values compared to cleaning with ISO or BUT (p < 0.001-0.040). Pretreatment with GP0.1 displayed the lowest bond strength values (p < 0.001-0.049), and mostly adhesive fractures occurred. The highest Ra values (p < 0.001) were observed for AL0.4 pretreatment. CONCLUSIONS: Pretreatment with AL0.4 and the control group mainly presented the highest bond strength values. Thermocycling had a positive effect on the bond strength. CLINICAL RELEVANCE: According to this study, 3D-printed restorations should be pretreated with AL0.4 or with visio.link before adhesive luting, regardless of their cleaning.

Prospective Clinical Split-Mouth Study of Two-Wing­Retained Resin-Bonded Anterior Fixed Dental Prostheses with Metallic and Ceramic Frameworks: 5-year Results

PURPOSE: To analyze the clinical performance of two-wing­retained resin-bonded fixed dental prostheses (RBFDPs) after 5 years of clinical use with respect to technical and biologic complications, as well as survival and success rates. MATERIALS AND METHODS: RBFDPs were fabricated from 3Y-TZP zirconia layered by hand (Lava Frame veneered with Lava Ceram; 3M ESPE) or metal (Remanium Star, Dentaurum; layered with Reflex, Wieland). The primary endpoints were debonding and fracture. The secondary endpoints (marginal integrity, marginal discoloration, abrasion of antagonist dentition, patient satisfaction, Gingival Index, and side effects) were evaluated at baseline and after 5 years. Survival and success rates were calculated using the Kaplan-Meier method. Log-rank test was used to compare the survival and success rates of the different materials. RESULTS: The mean observation time was 6 years and 10 months. The estimated cumulative success rate after 5 years was 88.9% ± 10% for metal-supported and 33% ± 16% for all-ceramic two-wing RBFDPs. After conversion into one-wing RBFDPs, the survival rate was 100% in both groups. Debonding of one of the two wings was the major complication. One zirconia framework fracture occurred. Metal-based two-wing RBFDPs showed a significantly higher success rate, but lower esthetic evaluation. CONCLUSION: Due to a reduction in technical complication rate and less invasiveness, one-wing RBFDPs should be preferred over two-wing RBFDPs whenever possible.

Mobile virtual tooth morphology teaching environment for preclinical dental students.

OBJECTIVES: Extended reality as an additional digital learning concept comprises virtual reality (VR), augmented reality, and mixed reality. In particular, VR allows an interaction in the virtual world. The aim of this study was to evaluate the students' attitude toward a mobile VR application for teaching tooth morphologies. METHODS: Eighty-two first year dental students were enrolled. After using the VR learning environment with mobile VR glasses at home for 1 week, the students were asked to fill in a questionnaire with 21 questions regarding intuitive handling, and supplemental learning information in comparison to the use of conventional textbooks. Nine questions provided predefined answer options, another nine had the form of a visual analog scale (VAS, range 0%-highly negative to 100%-highly positive), and three allowed free text answers. The data were checked for normal distribution (Kolmogorov-Smirnov test) and was analyzed descriptively. RESULTS: Forty-four percent of the students rated their perception of understanding of dental morphologies much better with VR than with conventional learning. The potential of the VR learning environment for further dental topics was assessed with a median VAS score of 75.8%. Its intuitive handling was evaluated with a median VAS score of 67.1%. The haptic, visual, and auditory supplemental learning information was consistently rated positively with VAS scores of 73.9%, 80.0%, and 71.6%, respectively. Overall, a majority of the students (85.5%) recommended the VR learning environment for dental morphology. CONCLUSIONS: The VR dental learning environment allows dental students an additional learning opportunity of dental morphologies, recommended by more than 85% of students.

Pressable lithium disilicate ceramic versus CAD/CAM resin composite restorations in patients with moderate to severe tooth wear: Clinical observations up to 13 years.

OBJECTIVE: To report the long-term clinical survival and failure rates of single-tooth restorations made of pressable lithium disilicate ceramics (LS2 ) and CAD/CAM resin composite (RC) by two separate clinical observations. MATERIALS AND METHODS: Twenty-one patients (12 female, nine male) were treated with 436 minimally invasive single-tooth restorations made of 274 pressed LS2 (n = 12; posterior: monolithic IPS e.max Press; anterior: IPS e.max Ceram veneered, Ivoclar) or 162 milled from RC (n = 9; monolithic exp. CAD/CAM resin composite, Ivoclar). The mean age of patients was 44.1 ± 9.3 years and the mean observation time was 86.2 ± 13.5 months (7.7 ± 1.1 years), with 8.5 ± 2.7 years for LS2 and 6.7 ± 0.5 years for RC. All restorations were observed for technical/biological failures using the modified criteria of the United States Public Health Service (USPHS). Collected data were analyzed using Kaplan-Meier survival analysis and log-rank test (α < 0.025). RESULTS: The 274 LS2 restorations showed a survival of 100% and a total failure rate of 5.5%. The 162 RC restorations showed a survival of 100% and a total failure rate of 25.3%. RC restorations exhibited more material fractures (p = 0.020) and higher discoloration rates (p < 0.001). CONCLUSIONS: Pressed LS2 single-tooth restorations showed lower long-term failure rates than restorations made of RC. CLINICAL SIGNIFICANCE: Despite the limitations of the clinical observations, single-tooth restorations of both materials can be recommended for permanent use in patients with severe tooth wear.

First evaluation of an app to optimize and organize the processes and assessments in dental clinical courses.

BACKGROUND: Digital teaching and learning tools, such as computer/mobile apps, are becoming an important factor in modern university education. The objective of our study was to introduce, analyze, and assess an organization and dual assessment app for clinical courses in dental medicine. METHODS: This was a survey-based study of dental students from the clinical study phase (4th/5th year; 8th/10th semester) of a department of prosthetic dentistry at a German university hospital about the benefits of a novel web-based and mobile app for organization and dual assessment of dental clinical courses. A total of eight questions were answered in an anonymous online survey. Data were analyzed using the Kolmogorov-Smirnov test, followed by an exploratory data analysis (α < 0.05). RESULTS: The app was given an average grade of 2.4, whereby 56.9% of the respondents rated the app with a grade of 2 (2 = good). In all, 94.6% of the study participants had not experienced any technical problems when using the app. Concerning the assessment, teaching doctor assessment (51.5 [IQR: 44.0]) was rated significantly better (p = 0.002) than self-assessment (39.5 [IQR: 32.8]). CONCLUSIONS: This investigation evaluated a newly introduced app to optimize dental clinical course workflows and assessment. The organizational feature was rated as good, while the daily self- and teaching doctor assessments were evaluated as less important. The results outline how the use of app technologies can provide an infrastructure for managing organization and daily assessments in dental education.

Dental education during the COVID-19 pandemic in Germany - cross-sectional lecturer-side evaluation for the application of digital teaching concepts.

Background: The COVID-19 pandemic resulted in significant restrictions on dental teaching. The aim of this investigation was to evaluate the attitudes of faculty members towards digital teaching formats and the effort creating digital lectures. We hypothesized that on the lecturer side there is no difference between the various digital teaching concepts in terms of workload and effort and that there is no increase in workload and effort when switching to digital teaching concepts. Methods: All German dental faculties were invited to the online survey by an anonymous voluntary questionnaire from January to April 2021. The questionnaire consisted of 27 questions that could be answered with a visual analog scale, free text answers, or with fixed answer options. Data was analyzed using the Kolmogorov-Smirnov test and an exploratory data analysis (α=0.05). Results: Before the pandemic, 24.8% of the participating lecturers were using digital teaching and 64.4% had no previous experience. After the outbreak of the pandemic 100% of the dental teaching was initially held online. More than 80% of the lecturers stated that they offer online lectures (86.1%), online seminars (81.2%), and/or online bedside teaching (33.7%). 88.1% see face-to-face teaching as the preferred teaching format. The lecturers also see the greatest opportunities for interaction in the area of analog teaching and significantly worse in synchronous and asynchronous digital teaching. In the course of the pandemic, respondents' attitudes towards online teaching improved in the median of 24.0 to a median of 50.0. Conclusions: Faculty members have positively changed their attitudes towards online teaching formats over the course of the pandemic. Although they see the greatest learning success in conventional face-to-face teaching formats and the creation of digital lectures is associated with a higher effort, they want more online lessons in the future.

Impact of multiple firings on fracture load of veneered zirconia restorations.

OBJECTIVES: This investigation evaluated the impact of multiple firings during the veneering process of anterior all-ceramic restorations on the fracture load (FL) of zirconia crowns veneered with different ceramics (ZRT, ZRO, HFZ, STR). METHODS: All-ceramic crowns with anatomically reduced zirconia frameworks were prepared using four different veneering ceramics (N = 192/n = 48 per veneering ceramic). The crowns were fired 2 and 10 times. Half of them were thermocycled (5000 cycles, 5 °C/55 °C, 20s). FL using Voss shear test was measured. Data was analyzed using ANOVA with partial eta squared and post-hoc Scheffé-test as well as t-test and Weibull analysis. RESULTS: Regarding FL, greatest differences were among the number of firings (p<0.001, ηp2 = 0.369). FL was not influenced by the interaction of both number of firings and aging level (p = 0.231) and the interaction of number of firings and veneering ceramic (p = 0.222). Differences were found comparing FL values of ZRT and STR (p<0.001) and of HFZ and STR (p<0.001). No differences occurred among the veneering ceramics after 2 (p = 0.430) and after 10 firings (p = 0.057) in respect to initial FL. For all initially tested veneering ceramics, FL showed higher values after 10 firings (p≤0.001-0.014). When aged, ZRO, HFZ, and STR also provided higher FL values after 10 firings (p≤0.001). For ZRT, FL values differed between initial and aged testing after 2 firings (p = 0.001) with aged specimens providing higher FL values. After 10 firings, none of the veneering ceramics showed differences regarding FL values between initial and aged testing. Weibull modulus was higher for ZRT specimens after 10 firings when tested initially (m = 10.1) and for aged ZRT specimens after 2 firings (m = 11.1). Failures occurred either with chipping of the veneer or total fracture. SIGNIFICANCE: Veneered zirconia restorations tested presented higher FL after 10 firings compared to 2 firings. Aging via thermocycling showed a positive effect on the FL.

Fracture load of different veneered and implant-supported 4-UNIT cantilever PEEK fixed dental prostheses.

OBJECTIVES: To determine the fracture load before and after artificial aging of implant-supported 4-unit cantilever fixed dental prostheses (FDP) with frameworks made of two differently filled polyetheretherketone (PEEK) compounds and veneered using three different techniques. METHODS: A total of 120 duplicate 4-unit FDP frameworks were produced (n = 60 milled from PEEK, 20% TiO2 filled and n = 60 pressed from PEEK, 30% TiO2 filled) and veneered using three different techniques: (i) digital veneerings, (ii) conventional resin composite veneerings and (iii) prefabricated veneers (n = 20 per subgroup). The FDPs were adhesively bonded to titanium abutments and the fracture load was measured in a universal testing machine (1 mm/min) before and after artificial aging in a mastication simulator (1,200,000 cycles, 50 N, TC: 5/55 °C, 6000 cycles). The fracture patterns were analyzed using digital microscopy. Data were analyzed using the Kolmogorov-Smirnov test, two-way ANOVA, post hoc Scheffé, Chi2-test (p < 0.05), and Weibull modulus m, as well as fracture patterns using the Ciba-Geigy table. RESULTS: Veneering technique and filler content significantly affected the fracture load (p < 0.001). Prefabricated veneers showed higher fracture load (p ≤ 0.001) whereas digital and conventional veneerings were similar (p = 0.451). PEEK with 30% filler content presented higher fracture load (p < 0.001) compared with PEEK with 20%. Aging showed no effect on fracture load (p = 0.176). Regarding fracture types, no significant differences were found among the groups (p = 0.055). CONCLUSIONS: Filler content of PEEK compound as well as veneering technique influenced fracture load while aging had no effect on fracture load. FDPs made of PEEK with 30% of filler content veneered using prefabricated veneers had the highest fracture resistance.