Monolithic hybrid abutment crowns: Influence of crown height, crown morphology and material on the implant-abutment complex.

PURPOSE: This in vitro study investigated the influence of material selection, crown morphology, and vertical crown height on the biomechanical behavior of monolithic hybrid abutment crowns (HACs). METHODS: Ninety implants were embedded in accordance with ISO standard 14801; ninety HACs were mounted (N=90). Monolithic crowns with varying group-specific designs were luted using titanium bases. HACs were fabricated from monolithic lithium disilicate ceramic (LD) or zirconia-reinforced lithium silicate ceramic (ZLS). The crown morphology was either maxillary premolar (LD_PM, ZLS_PM) or molar (LD_MO). The three groups were further divided into three subgroups of ten specimens, each designed with a small (7.5 mm), middle (10.5 mm), and high (13.5 mm) configuration of crown heights (N=10). A load-to-failure test at 30° off-axis was conducted using a universal testing machine until failure. For statistical analysis, Kolmogorov-Smirnov and Mann-Whitney U tests were conducted (P < 0.05). RESULTS: All LD_MO groups presented the highest failure values (808.7 to 947.9 N), followed by the LD_PM (525.8 to 722.8 N) and ZLS_PM groups (312.6 to 478.8N). A comparison between LD and ZLS materials (P < 0.001) as well as the crown morphology (P < 0.001) showed significant differences in failure values. The values in the subgroups of ZLS_PM (low, middle, high) decreased as the crown height increased. The fracture modes showed no consistent patterns across the test groups. CONCLUSIONS: Material selection, crown morphology, and vertical crown height appear to be important factors that may influence the clinical failure values and patterns of HACs.

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.

In Vitro Survival and Fracture Force of Lithium-Disilicate Hybrid Abutment Crowns.

PURPOSE: To evaluate the behavior of hybrid abutment crowns fabricated from monolithic lithium disilicate ceramic (LDC) and to compare the influence of different in-vitro artificial aging protocols. MATERIAL AND METHODS: 32 monolithic hybrid abutment crowns of monolithic LDC were fabricated. 24 were artificially aged applying 3 different protocols up to a 20 year-simulation (1.2 × 106, 2.4 × 106, 4.8 × 106 chewing cycles, thermocycling), one control group underwent no artificial aging (N=32, n=8). Load-to-failure tests were conducted for all specimens and failure values were compared (p<0.05). RESULTS/CONCLUSIONS: All specimens passed in-vitro aging. Mean failure load values between 532.6 and 562.8 N were found but did neither differ significantly among the test groups nor from the control group. Within the limitations of this in-vitro pilot study, hybrid abutment crowns manufactured from monolithic LDC seem to offer appropriate long-lasting mechanical stability over a simulation period up to 20 years. The failure values and complication pattern seem to be independent of several aging protocols in this test set-up.

Biomechanical behavior of implants with different diameters in relation to simulated bone loss- an in vitro study.

OBJECTIVES: Bone resorption around implants could influence the resistance of the implant abutment complex (IAC). The present in vitro study aimed to assess the stability to static fatigue of implants presenting different levels of bone losses and diameters. MATERIALS AND METHODS: Ninety implants with an internal conical connection with 3 different implant diameters (3.3 mm (I33), 3.8 mm (I38), and 4.3 mm (I43)) and 3 simulated bone loss settings (1.5 mm (I_15), 3.0 mm (I_30), and 4.5 mm (I_45) (n = 10)) were embedded and standard abutments were mounted. All specimens were artificially aged (1,200,000 cycles, 50 N, simultaneous thermocycling) and underwent subsequently load-to-fracture test. For statistical analysis, Kolmogorov-Smirnov test, Kruskal-Wallis test, and Mann-Whitney U test (p < 0.05) were applied. RESULTS: All test specimens withstood the artificial aging without damage. The mean failure values were 382.1 (± 59.2) N (I3315), 347.0 (± 35.7) N (I3330), 315.9 N (± 30.9) (I3345), 531.4 (± 36.2) N (I3815), 514.5 (± 40.8) N (I3830), 477.9 (± 26.3) N (I3845), 710.1 (± 38.2) N (I4315), 697.9 (± 65.2) N (I4330), and 662.2 N (± 45.9) (I4345). The stability of the IACs decreased in all groups when bone loss inclined. Merely, the failure load values did not significantly differ among subgroups of I43. CONCLUSIONS: Larger implant diameters and minor circular bone loss around the implant lead to a higher stability of the IAC. The smaller the implant diameter was, the more the stability was affected by the circumferential bone level. CLINICAL RELEVANCE: Preserving crestal bone level is important to ensure biomechanical sustainability at implant systems with a conical interface. It seems sensible to take the effect of eventual bone loss around implants into account during implant planning processes and restorative considerations.

The Fracture Load as a Function of the Material Thickness: The Key to Computing the Strength of Monolithic All-Ceramic Materials?

The thickness of a material has a significant impact on its fracture load. The aim of the study was to find and describe a mathematical relationship between the material thickness and the fracture load for dental all-ceramics. In total, 180 specimens were prepared from a leucite silicate ceramic (ESS), a lithium disilicate ceramic (EMX), and a 3Y-TZP zirconia ceramic (LP) in five thicknesses (0.4, 0.7, 1.0, 1.3, and 1.6 mm; n = 12). The fracture load of all specimens was determined using the biaxial bending test according to the DIN EN ISO 6872. The regression analyses for the linear, quadratic, and cubic curve characteristics of the materials were conducted, and the cubic regression curves showed the best correlation (coefficients of determination (R2): ESS R2 = 0.974, EMX R2 = 0.947, LP R2 = 0.969) for the fracture load values as a function of the material thickness. A cubic relationship could be described for the materials investigated. Applying the cubic function and material-specific fracture-load coefficients, the respective fracture load values can be calculated for the individual material thicknesses. These results help to improve and objectify the estimation of the fracture loads of restorations, to enable a more patient- and indication-centered situation-dependent material choice.

Predictable esthetics in hybrid and resin-based CAD/CAM restorative materials: Translucency as a function of material thickness.

AIM: The CAM of esthetically pleasing monolithic dental restorations presents with specific challenges. One vital parameter to consider is the translucency of the materials. Previous studies have proven a correlation between translucency and material thickness for various all-ceramic materials. The aim of the present study was to assess and define the relationship between thickness and translucency in modern resin-based restorative materials. MATERIALS AND METHODS: Specimens fabricated from two resin nano-ceramics (Cerasmart, Lava Ultimate), a polymer-infiltrated ceramic network (Vita Enamic), and a polymethyl methacrylate (Telio CAD) were examined, representing these different material classes. For each material, 12 specimens (n = 12) were fabricated in five thicknesses (0.4, 0.7, 1.0, 1.3, and 1.6 mm; N = 240). The translucency was measured with a spectrophotometer. The total light transmittance for each specimen was calculated applying specialized software. Regression curves were fitted to the results and their coefficient of determination (R2) fit was determined. RESULTS: Logarithmic regression curves showed the best R2 approximation (Cerasmart: R2 = 0.994; Vita Enamic: R2 = 0.978; Lava Ultimate: R2 = 0.997; Telio CAD: R2 = 0.997) to the light transmission values. CONCLUSIONS: The results of the present study indicate that the translucency of resin-based materials can be calculated using a mathematic approach to estimate their optical behavior. Cerasmart, Lava Ultimate, Vita Enamic, and Telio CAD exhibit a logarithmic relationship between material thickness and translucency. By determining material-specific coefficients for this logarithmic function, the resulting translucency can be computed for any given material thickness.

Influence of monolithic restorative materials on the implant-abutment interface of hybrid abutment crowns: An in vitro investigation.

Purpose This in vitro study aimed to investigate the long-term performance, stability, and fracture mode of monolithic hybrid abutment crowns, and the effect of different materials on the implant-abutment interface (IAI).Methods Eighty monolithic hybrid abutment crowns luted on titanium bases were manufactured from 3Y-TZP zirconia (ZY3), "Gradient Technology" zirconia (ZY35), 5Y-TZP zirconia (ZY5), lithium disilicate ceramic (LDS), zirconia-reinforced lithium silicate ceramic (ZLS), polymer-infiltrated ceramic network (MHY), polymethylmethacrylate (PMA), and 3D-printed hybrid composite (PHC) (n = 10 for each material). Eighty implants (Camlog Progressive-Line, diameter: 3.8 mm) were embedded in accordance with ISO standard 14801, and crowns were mounted. After artificial aging (1.2 × 106 cycles, 50 N, thermocycling), intact specimens were loaded 30° off-axis in a universal testing machine until failure.Results Seven specimens in the PHC group failed during artificial aging, and all the others survived. There were two subgroups based on the one-way analysis of variance and Dunnett's test (P < 0.05) of the mean fracture load values. The first comprised Z3Y, ZY35, Z5Y, and LDS, with mean fracture loads between 499.4 and 529.7 N, while the second included ZLS, MHY, and PMA, with values in the 346.2-416.0 N range. ZY3, ZY35, ZY5, and LDS exhibited irreversible, visible deformations of the implant shoulders with varying dimensions after load-to-fracture tests.Conclusions Crowns made of LDS, ZLS, MHY, and PMA may act as potential stress breakers, and prevent possible deformation at IAIs. Further clinical studies need to assess if these materials also withstand relevant loads in-vivo.

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.

Influence of Pre-Treatment and Artificial Aging on the Retention of 3D-Printed Permanent Composite Crowns.

The aim of this in vitro study is to investigate the bonding properties of a 3D-printable permanent composite material in comparison to milled composite materials. The tested materials are 3D-printed BEGO VarseoSmile Crown plus (VA1_ab, VA1_nt, VA2_ab, VA2_nt), Vita Enamic (EN1, EN2), and 3M Lava Ultimate (UL1, UL2) (N = 64; n = 8). For this purpose, all crowns are luted to polymer tooth stumps #46 (FDI) using dual-curing luting composite, strictly according to the manufacturer's instructions. VA1_ab and VA2_ab are additionally airborne-particle abraded. 4 groups (VA2_ab, VA2_nt, EN2, UL2) are artificially aged (1,200,000 cycles, 50 N, 10,000 thermocycles), whereby no specimen has failed. All 64 specimens undergo pull-off testing until retention loss. The mean forces of retention-loss is 786.6 ± 137.6 N (VA1_nt, *), 988.6 ± 212.1 N (VA2_nt, *, Ɨ), 1223.8 ± 119.2 N (VA1_ab, Ɨ, ǂ), 1051.9 ± 107.2 N (VA2_ab, *, Ɨ), 1185.9 ± 211.8 N (EN1, Ɨ, ǂ), 1485.0 ± 198.2 N EN2, ǂ), 1533.8 ± 42.4 N (UL1, ǂ), and 1521.8 ± 343.4 N (UL2, ǂ) (one-way ANOVA (Scheffé method); p < 0.05; *, Ɨ, ǂ: group distribution). No characteristic failure modes can be detected. In conclusion, all of the pull-off forces reflect retention values that seem to be sufficiently high for clinical use. Additional airborne-particle abrasion of VA does not result in significantly better retention but can be recommended.

Up to 10-Year Incidence of Complications in Fixed vs Removable Implant-Supported Restorations for Edentulous Arches.

PURPOSE: To retrospectively compare the incidence of biologic and prosthetic complications in implant-supported fixed dental prostheses (FDP) and removable dental prostheses (RDP) in edentulous patients after up to 10 years. MATERIALS AND METHODS: A total of 13 patients (mean age: 58.8 years, women = 9, men = 4) who had received 14 implant-supported FDPs and a total of 43 patients (mean age: 64.4 years, 22 women, 21 men) who were provided with 50 implant-supported RDPs were included in the study. The RDPs were fixed using locator attachments, ball heads, bars, or double-crowns. Technical, biologic, and prosthetic complications were assessed over a 73.3-month (± 37.7) follow-up period, and the collected data covered the period between 2000 and 2016. Using Kaplan-Meier curve and Breslow tests, the data were statistically analyzed. The level of peri-implant bone margins was determined at least every 2 years. RESULTS: Of the 328 implants placed, 2 had to be removed during the follow-up period. All implant superstructures were still in situ at the end of the observation period. The mean overall complication rate was 0.24 per restoration per year for FDPs and 0.37 per year for RDPs. Reasonable therapeutic interventions allowed for preserving and reestablishing the integrity of all implants and full operability of all superstructures. Prosthetic complications occurred about four to five times more frequently than biologic ones; however, according to Breslow test, the distribution of biologic and prosthetic complications was not significantly different (P > .05) when comparing FDPs and RDPs over 10 years. CONCLUSION: Implant-supported FDPs were not significantly more prone to complications than implant-supported RDPs over time. Prosthetic intervention was required more often than biologic interventions in both approaches.

Accuracy of surface adaptation of complete denture bases fabricated using milling, material jetting, selective laser sintering, digital light processing, and conventional injection molding.

AIM: Milling-based, subtractive fabrication of digital complete dentures represents the computer-engineered manufacturing method of choice. However, efficient additive manufacturing technologies might also prove beneficial for the indication. The aim of the present study was to evaluate the accuracy of surface adaptation of complete denture bases fabricated using subtractive, additive, and conventional manufacturing techniques. MATERIALS AND METHODS: A standardized edentulous maxillary model was digitally designed and milled. Twelve duplicated plaster casts were scanned and virtual denture bases designed accordingly. Physical complete denture bases (n = 12 per technique) were manufactured applying different digital and conventional fabrication methods: 1) CNC milling (MIL); 2) material jetting (MJ); 3) selective laser sintering (SLS); 4) digital light processing (DLP); and 5) conventional injection molding (INJ). The INJ group served as control. The intaglio surfaces of the denture bases were digitized and superposed with the surface data of the casts using a best-fit algorithm. Accuracy of surface adaptation was assessed by examining deviations. Statistical analysis was conducted using SPSS (P < 0.05). RESULTS: The milling of denture bases led to significantly better surface adaptation compared with all the other technologies (P < 0.001). The other fabrication methods in the study, including conventional manufacturing, revealed no considerable overall differences. CONCLUSIONS: As regards the accuracy of surface adaptation, all the investigated technologies adequately produced complete denture bases, with milled denture bases presenting the most superior results.

Virtual dental teaching and its effect on test success - A cross-over study.

OBJECTIVES: The aim of this cross-over investigation was to analyze the effect of virtual teaching using virtual reality (VR) within a dental learning environment by preclinical students with or without dental professional experience on test performance. METHODS: Preclinical students (N = 82) were randomly divided into two groups for cross-over testing of tooth morphology knowledge: (a) anterior VR-group (group 1) using the VR-glasses as an additional learning tool for the anterior tooth morphologies and (b) posterior VR-group (group 2) using it for the posterior tooth morphologies also in addition to conventional learning. All students used the VR-glasses for 1 week independent of time and location depending on group. The students had to recognize teeth (anterior or posterior within two separate tests after three [anterior test] and 6 weeks [posterior test] of practical course) and note the tooth number and characteristics in written form. Former dental experience (dental technician/assistance) was noted. Test results were analyzed to quantify the effect of virtual teaching on test scores. Data were analyzed with the Kolmogorov-Smirnov and Mann-Whitney U test (p = 0.05). RESULTS: By differentiating the two student groups (use of VR glasses for anterior/posterior teeth) within the dental experience group, significantly better test results (p = 0.040) were shown for group 1 in the total posterior teeth test score. Furthermore, no other significant differences, but a possible tendency, in the test results and thus no effect of the use of the VR glasses on both VR groups could be analyzed (p ≥ 0.051). CONCLUSIONS: Using the VR tooth learning environment predominantly did not lead to a significant improvement of test results. Anterior teeth test scores predominantly showed significantly better results than posterior teeth test scores.

Impact of Missing Teeth on Oral-Health-Related Quality of Life: A Prospective Bicenter Clinical Trial.

PURPOSE: To investigate the effect of missing teeth on patients' oral health-related quality of life (OHRQoL). MATERIALS AND METHODS: A total of 151 patients participated in this prospective bicenter clinical study (mean age: 64.7 ± 10.5 years; 71 women). Four subgroups were defined based on the number of missing teeth. OHRQoL was assessed using the German version of the Oral Health Impact Profile-49/53 (OHIP-G49/53) and visual analog scale (VAS) questionnaires. The effect of missing teeth on OHIP (total and by dimension) and VAS scores before and after prosthetic treatment was investigated at baseline (T0), 1 week (T1), and 3 months (T2) after prosthetic treatment. Scores were analyzed using Kolmogorov-Smirnov, Kruskal-Wallis, and Mann-Whitney U tests. Correlations were assessed using Spearman rho correlation. The level of significance was set at P = .05. RESULTS: Initial OHIP and VAS scores were highest for patients with 11 to 28 missing teeth. Scores improved among all groups between T0 and T1/T2. After prosthetic rehabilitation (T1), improvements in total OHIP scores were greatest for patients with no missing teeth or with 11 to 28 missing teeth. Patients with no missing teeth or with 1 to 4 missing teeth before treatment had the lowest posttreatment OHIP scores. Total OHIP scores among the groups were in the same value range (P > .185). No direct correlation was found between the VAS and total OHIP scores. CONCLUSION: OHIP and VAS scores for OHRQoL were associated with the number of missing teeth. Prosthetic treatment resulted in improved OHRQoL and oral function among all groups. The use of a VAS yielded additional detailed information.

Short communication: In vitro pilot study: Are monolithic 3Y-TZP zirconia crowns too strong for titanium Implants?

PURPOSE: To report on pilot tests for a planned study on single implant-supported crowns made from different restorative materials using finite element analysis (FEA) and in vitro load-to-failure testing. MATERIALS AND METHODS: Within this pilot study, FEA was conducted using Ansys 2019 R2 to simulate stress and deformation for implant-supported crowns made of lithium disilicate ceramic (LiS2) and zirconia (3Y-TZP). Additionally, an in vitro load to failure test was conducted using two specimens per group to evaluate the failure mode and to confirm the findings from the FEA. RESULTS/CONCLUSION: FEA revealed stress areas at the palatal cervical areas of the crowns. In the load to failure test, both hybrid abutment crowns made of LiS2 fractured (410 N and 510 N) before plastic deformation of the metal implant components occurred. The monolithic hybrid abutment crowns made of 3Y-TZP did not fracture until tests were interrupted at 646-N and 690-N occlusal force, when plastic deformation of the metal implant components was visually observed.

CAD/CAM-milled versus conventionally cast secondary crowns fabricated from high noble metal alloy: an in vitro study of retentive force.

AIM: To investigate retentive forces (RFs) of CAD/CAM-milled and conventionally cast secondary crowns (SCs) after artificial aging in an in vitro study. MATERIALS AND METHODS: Forty artificial premolars were manufactured and provided with 40 primary crowns (PCs) milled from a high noble metal alloy. SCs were fabricated from the same alloy. Ten SCs were produced with the help of a tactile scanning method (group A), 10 with the help of a photo-optical scan (spray; group B), 10 with the help of a photo-optical scan (acrylic dye; group C), and 10 using a conventional casting technique (group D). Cycles of separation were performed and RFs were measured at baseline and after 5,000 and 10,000 cycles. Surfaces were examined under a scanning electron microscope (SEM). Statistical analysis was conducted at a significance level of P ≤ 0.05. RESULTS: Group D showed the highest median RFs with respective interquartile ranges (IQRs) - baseline: 7.0(2.5) N; 5,000 cycles: 5.5(2.0) N; 10,000 cycles: 5.4(1.5) N compared with groups A, B, and C - baseline: 5.2(8.4)/3.4(11.3)/1.3(1.5) N; 5,000 cycles: 1.8(0.8)/2.1(1.7)/1.0(1.3) N; 10,000 cycles: 1.9(1.6)/2.4(2.5)/1.0(1.4) N, respectively. In contrast to groups A, B, and C, group D did not gain RF when RF values were compared after 5,000 and 10,000 cycles. The loss of RF between baseline (7.0 N) and after 10,000 cycles (5.4 N) was significant only for group D (P = 0.007), but not for groups A, B, and C. CONCLUSION: Both CAD/CAM-milled and conventionally cast SCs from a high noble metal alloy can provide sufficient RF after 10,000 cycles of artificial aging. However, groups A, B, and C showed constantly lower RF values compared with group D.

In-vivo-wear in composite and ceramic full mouth rehabilitations over 3 years.

The aim of this study was to quantify and to compare the wear rates of premolar (PM) and molar (M) restorations of lithium disilicate ceramic (LS2) and an experimental CAD/CAM polymer (COMP) in cases of complex rehabilitations with changes in vertical dimension of occlusion (VDO). Twelve patients with severe tooth wear underwent prosthetic rehabilitation, restoring the VDO with antagonistic occlusal coverage restorations either out of LS2 (n = 6 patients, n = 16 posterior restorations/patient; N = 96 restorations/year) or COMP (n = 6 patients; n = 16 posterior restorations/patient; N = 96 restorations/year). Data was obtained by digitalization of plaster casts with a laboratory scanner at annual recalls (350 ± 86 days; 755 ± 92 days; 1102 ± 97 days). Each annual recall dataset of premolar and molar restorations (N = 192) was overlaid individually with the corresponding baseline dataset using an iterative best-fit method. Mean vertical loss of the occlusal contact areas (OCAs) was calculated for each restoration and recall time. For LS2 restorations, the mean wear rate per month over 1 year was 7.5 ± 3.4 µm (PM), 7.8 ± 2.0 µm (M), over 2 years 3.8 ± 1.6 µm (PM), 4.4 ± 1.5 µm (M), over 3 years 2.8 ± 1.3 µm (PM), 3.4 ± 1.7 µm (M). For COMP restorations, the mean wear rate per month over 1 year was 15.5 ± 8.9 µm (PM), 28.5 ± 20.2 µm (M), over 2 years 9.2 ± 5.9 µm (PM), 16.7 ± 14.9 µm (M), over 3 years 8.6 ± 5.3 µm (PM), 9.5 ± 8.0 µm (M). Three COMP restorations fractured after two years and therefore were not considered in the 3-year results. The wear rates in the LS2 group showed significant differences between premolars and molars restorations (p = 0.041; p = 0.023; p = 0.045). The wear rates in COMP group differed significantly between premolars and molars only in the first two years (p < 0.0001; p = 0.007). COMP restorations show much higher wear rates compared to LS2. The presented results suggest that with increasing time in situ, the monthly wear rates for both materials decreased over time. On the basis of this limited dataset, both LS2 and COMP restorations show reasonable clinical wear rates after 3 years follow-up. Wear of COMP restorations was higher, however prosthodontic treatment was less invasive. LS2 showed less wear, yet tooth preparation was necessary. Clinicians should balance well between necessary preparation invasiveness and long-term occlusal stability in patients with worn dentitions.