Cutting Efficiency of Diamond Grinders on Composite and Zirconia.

This in vitro study was carried out to compare the cutting efficiency of diamond grinders on zirconia and resin-based composite materials. Grinders were employed with a special holder for the handpiece to apply a constant load (160 g) for resin-based composite (8 cuts, 40 s each) and zirconia materials (4 cuts, 5 min each; n = 10 for each material and grinder). To assess the efficiency of the grinders, weight measurements of the material were taken before and after the grinding process. Scanning electron micrographs were captured for instrument surfaces before and after testing and for the resulting surface of the materials. In the resin-based composite group, there were significant differences in weight removal between the burs for both the baseline (first cut; p = 0.009) and removal after the eighth cut (p = 0.049). Statistically significant decreases in weight removal compared to the baseline values were noted for the third, fourth, sixth, and seventh steps (p ≤ 0.046). For the zirconia group, significant differences existed in weight removal between the burs for the baseline (first cut; p < 0.001) and removal after the fourth cut (p < 0.001). A significant positive correlation was observed between removal and the number of cuts (Pearson: 0.673; p < 0.001). A statistically significant decrease in removal compared to the respective baseline value was found for the fourth step (p = 0.006). The initial wear removal and durability significantly differed between the grinders used on resin-based composite and zirconia. Achieving comparable weight removal took five times longer when grinding zirconia compared to the resin-based composite.

Pull-Off Behavior of Hand-Cast, Thermoformed, Milled, and 3D-Printed Splints.

PURPOSE: To investigate the insertion/pull-out performance of splints produced by hand casting, thermoforming, milling, and 3D printing. MATERIALS AND METHODS: A total of 120 identical mandibular splints (n = 8 specimens per group) were manufactured with hand casting, thermoforming, milling, and 3D printing. The splints were stored in water at 37°C for 10 days and then placed onto cobalt-chromium arches and fixed on one side. Forces were applied to the other side (centric, perpendicular 50 N, 1 Hz) at two different positions (teeth 46 and 44/45) to pull out, and the test was then reset. The number of pull-out cycles until failure was recorded. The fracture behavior of the splints was investigated and characterized as fracture in the loading position, fracture at the fixation, or combined fracture. Splints were pulled off until fracture as a control (v = 1 mm/minute). Finite element analysis was used to verify the results. Statistical analyses were conducted with one-way ANOVA, post hoc Bonferroni, Pearson correlation, and Kaplan-Meier log-rank tests (α = .05). RESULTS: The mean pull-off cycles varied from 7,839 (V-Print) to 1,600,000 (Optimill) at the tooth 46 position (FDI numbering system) and from 9,064 (Splint Comfort) to 797,750 (Optimill) at the 44/45 position. Log-rank test showed significantly (P < .001) different pull-out cycles between the systems (chi-square: 61,792 to 122,377). The thickness of the splints varied between 1.6 ± 0.2 mm (Splint Comfort) and 2.3 ± 0.1 mm (V-Print). Thickness and number of cycles were correlated (Pearson: 0.164; P = .074). The pull-off forces of the control varied significantly (P ≤ .040), ranging from 13.0 N (Keysplint) to 82.2 N (Optimill) at the tooth 46 position and from 25.2 N (Keysplint) to 139.0 N (Optimill) at the 44/45 position. CONCLUSIONS: The milled and cast splints survived more pull-off cycles than the printed or thermoformed splints. The pullout performance showed differences among the tested splint systems and indicated the influence of the material properties and processing.

Finite Element Analysis of Occlusal Interferences in Dental Prosthetics Caused by Occlusal Adjustment.

PURPOSE: To investigate the influence of occlusal interference using finite element analysis (FEA). MATERIALS AND METHODS: The FEA model designed for this study centered on an all-ceramic, bilayered, fixed partial denture (FPD) retained on the maxillary first premolar and first molar, with the second premolar replaced by a pontic. The surrounding structures-such as the neighboring teeth, antagonists, and periodontium-were modeled. Four different loading cases were designed at occlusal interferences of 0, 8, 12, and 24 µm and were loaded by a simulated bite force of 300 N. Principal and von Mises stresses, as well as strain, were evaluated for all included structures. RESULTS: For interferences of 12 and 24 µm, failure-relevant tensile stresses in the veneering layer were observed at the occlusal surfaces. Stress found in the zirconia FPD did not reach fatigue or flexural strength for any test load. CONCLUSION: Peak tensile stress was observed in close proximity to occlusal contact points, increasing with increasing occlusal interference. The FEA results suggest that the majority of occlusal stress is absorbed by the deformation of the periodontal ligament. Framework failure caused by the simulated interferences was not expected. Surface defects may ultimately lead to failure due to fracture or chipping, especially in cases of weaker ceramics or veneering.

Microstructure, composition, and flexural strength of different layers within zirconia materials with strength gradient.

OBJECTIVES: The aim of this study was to compare composition, microstructure, and mechanical strength of current multilayer zirconia blanks. METHODS: Bar shaped specimens were made from several layers of multilayer zirconia blanks (Cercon ht ML, Dentsply Sirona, US; Katana Zirconia YML, Kuraray, J;SHOFU Disk ZR Lucent Supra, Shofu, J; priti multidisc ZrO2 Multi Translucent, Pritidenta, D; IPS e.max ZirCAD Prime, Ivoclar Vivadent, FL). Flexural strength was determined in a three-point bending test on extra-thin bars. X-ray diffraction (XRD) with Rietveld refinement was used to assess crystal structure and scanning electron microscopy (SEM) imaging to visualize the microstructure of each material and layer. RESULTS: Mean flexural strength varied between 467.5 ± 97.5 MPa (top layer, IPS e.max ZirCAD Prime) and 898.0 ± 188.5 MPa (bottom layer, Cercon ht ML) with significant (p ≤ 0.055) differences between the individual layers. XRD indicated 5Y-TZP for enamel-layers, 3Y-TZP for dentine-layers, individual mixtures of 3Y-TZP, 4Y-TZP, or 5 Y-TZP for intermediate layers. SEM analysis showed grain sizes between approx. 0.15 and 4 µm. Grain size tended to decrease from top to bottom layers. SIGNIFICANCE: The investigated blanks differ predominantly in the intermediate layers. In addition to dimensioning of restorations, the milling position in the blanks must also be taken into account when using multilayer zirconia as restorative material.

Survival dependence of 3D-printed temporary materials on the filler content.

AIM: The aim of the present study was the evaluation of the in vitro performance and fracture force of 3D-printed anterior implant-supported temporary partial dentures (TPDs) with different filler content. MATERIALS AND METHODS: Identical anterior resin-based TPDs (tooth sites 11 to 13; n = eight per material) were 3D printed from methacrylate resins with different filler content. A cartridge polymethyl methacrylate (PMMA) material was used as a reference. After temporary cementation, combined thermal cycling and mechanical loading (TCML) was performed on all the restorations to mimic clinical application. Behavior during TCML and fracture force was determined, and failures were analyzed. Data were statistically investigated (Kolmogorov-Smirnov test, one-way ANOVA; post hoc Bonferroni, Kaplan-Meier survival; α = 0.05). RESULTS: Failure during TCML varied between three failures and total failure during loading time. Mean survival time varied between 93 ± 206 x 103 cycles and 329 ± 84 x 103 cycles. Significantly different survival cycles between the individual materials could be determined (Mantel Cox log-rank test: chi-square: 21,861; degrees of freedom (df) = 4, P < 0.001). A correlation between filler level and survival cycles could be found (Pearson: 0.186, P = 0.065). Fracture values of the surviving TPDs varied between 499 and 835 N. Failures were characterized by fracture of the connector (n = 24) followed by fractures at the abutment (n = 10). CONCLUSIONS: TDPs showed different filler-dependent survival. Individual 3D-printed materials provided comparable or even better performance than a standard cartridge system and might be sufficient for temporary application of at least half a year.

Pull-off behavior of hand-cast, thermoformed, milled and 3D printed splints.

PURPOSE: To investigate the insertion/pull-out performance of splints produced by hand casting, thermoforming, milling, and 3D printing. MATERIALS AND METHODS: A total of 120 identical mandibular splints (n = 8 per group) were manufactured with hand casting, thermoforming, milling, and 3D printing. The splints were stored in water at 37°C for 10 days and then placed onto cobalt-chromium arches and fixed on one side. Forces were applied to the other side (centric, perpendicular 50 N, 1 Hz) at two different positions (teeth 46 and 44/45) to pull out, and the test was then reset. The number of pull-out cycles until failure was recorded. The fracture behavior of the splints was investigated and characterized as fracture in the loading position, fracture at the fixation, or combined fracture. Splints were pulled off until fracture as a control (v = 1 mm/minute). Finite element analysis was used to verify the results. Statistical analyses were conducted with one-way-ANOVA, post hoc Bonferroni, Pearson correlation, and Kaplan-Meier log-rank tests (α = .05). RESULTS: The mean pull-off cycles varied from 7,839 (V-Print) to 1,600,000 (Optimill) at the tooth 46 position and from 9,064 (Splint Flex) to 797,750 (Optimill) at the 44/45 position. Log-rank test showed significantly (P < .001) different pull-out cycles between the systems (χ2: 61,792 to 122,377). The thickness of the splints varied between 1.6 ± 0.2 mm (Splint Flex) and 2.3 ± 0.1 mm (V-Print Splint). Thickness and number of cycles were correlated (Pearson 0.164; P = .074). The pull-off forces of the control varied significantly (P ≤ .040), from 13.0 N (Keysplint) to 82.2 N (Optimill) at the tooth 46 position and from 25.2 N (Keysplint) to 139.0 N (Optimill) at the 44/45 position. CONCLUSION: The milled and cast splints survived more pull-off cycles than the printed or thermoformed splints. The pull-out performance showed differences among the tested splint systems and indicated the influence of the material properties and the processing.

Inadequate Reporting of Complications in Randomized Controlled Trials Cited as Supporting Evidence Underpinning AAOS CPG Recommendations for Hip and Knee Osteoarthritis: Application of the CONSORT Harms Checklist.

BACKGROUND: Randomized controlled trials (RCTs) have been shown to influence clinical decision-making and health policy. Therefore, it is essential that trial outcomes-including harms-are completely reported. METHODS: We included all RCTs cited as supporting evidence for the American Academy of Orthopaedic Surgeons Surgical Management of Osteoarthritis of the Knee, Osteoarthritis of the Knee, and Osteoarthritis of theHip Clinical Practice Guideline recommendations. Manuscripts were analyzed for compliance with the Consolidated Standards of Reporting Trials (CONSORT) Extension for Harms items. We determined the Extension for Harms' influence on harms reporting by comparing RCTs published before and after the extension's release. RESULTS: One hundred and seventy-three RCTs were included, of which 81 (47%) adequately reported ≥50% of the checklist and 75 (43%) reported ≤33% of the checklist items. The mean number of checklist items reported was 8 items (of 18; 45%). Our interrupted time-series analysis suggests the implementation of the CONSORT Extension for Harms did not have a statistically significant effect on the completeness of harms reporting (P = .35; 95% Confidence interval = -0.0041 to 0.0014). CONCLUSION: Harms-related data are poorly reported within RCTs cited as supporting evidence for the American Academy of Orthopaedic Surgeons management for hip and knee OA Clinical Practice Guideline. Our time series analysis illustrates the failure of the CONSORT Extension for Harms on improving the reporting of harms-related data. Future efforts to improve the quality of harms reporting is crucial for patients, clinicians, and policy makers to perform thorough risk-benefit appraisals as RCT results directly influence clinical decision-making in orthopaedic surgery.

In Vitro Mastication Simulation and Wear Test of Virgilite and Advanced Lithium Disilicate Ceramics.

PURPOSE: To compare wear behavior, durability during in vitro mastication simulation, and fracture force of an established and a novel lithium disilicate CAD/CAM material, as well as to examine the impact of cementation and reduced ceramic thickness on durability and fracture force. MATERIALS AND METHODS: Specimens (n = 8 per group) were prepared from lithium disilicate (LS2; IPS e.max, Ivoclar Vivadent) and advanced lithium disilicate (ALD; Cerec Tessera, Dentsply Sirona). Specimens were polished, and two-body wear test and thermocycling were performed (50 N, 120,000 cycles, 1.6 Hz, H2O dist., 5°C/55°C, 600 cycles). Maximum vertical loss, surface roughness, surface roughness depth, and antagonist wear were determined. Single crowns (n = 8 per group; thickness 1.5 mm/1.0 mm) were manufactured from LS2 and ALD and mounted on human molar teeth with adhesive resin (AB; CalibraCeram, Dentsply Sirona), glass-ionomer cement (GIC; Ketac Cem, 3M ESPE), and hybrid glass-ionomer cement (HGIC; Calibra Bio, Dentsply Sirona). Thermocycling and mechanical loading (2 × 3000 × 5°C/55°C, 2 minutes, H20 dist., 1.2 × 106 50 N) were performed. Fracture force was determined by a universal testing machine (1446, ZwickRoell), and one-way analysis and Bonferroni post hoc test (α = .05) were used for statistical analyses. RESULTS: Mean (ALD: 210 ± 42.4 µm; LS2: 264.3 ± 56.1 µm) and maximum (ALD: 391.1 ± 86.3 µm; LS2: 518.3 ± 113.2 µm) wear between groups were significantly different (P ≤ .047). Fracture force varied between 1,911.4 ± 468.4 N (ALD/AB 1 mm) and 2,995.3 ± 880.6 N (LS2/GIC), without significant differences (P ≥ .152). CONCLUSION: ALD showed better wear behavior than LS2, but provided similar fracture force. Cementation and reduction of ceramic thickness had only minor effects on fracture force.

Effects of storage and toothbrush simulation on color, gloss, and roughness of CAD/CAM, hand-cast, thermoforming, and 3D-printed splint materials.

OBJECTIVES: The aim was to investigate color, gloss, or roughness of splint materials after storage in liquids and toothbrush simulation. MATERIALS AND METHODS: A total of 58 × 8 (n = 10 per material and group) specimens were fabricated (hand-cast, thermoforming, CAD/CAM-milled, 3D-printed materials); stored in air, water, coffee, red wine, and cleaning tablets; and investigated after fabrication, 24 h, two-, and four-week storage or toothbrushing. Color values (L*, a*, b*; ISO 11664-4:2008; CM-3500d, Konica-Minolta), gloss (ISO 2813:2014), and roughness values were determined (3D laser-scanning-microscope, KJ 3D, Keyence) before and after simulation or storage. STATISTICS: Levene-test, one-way ANOVA, Bonferroni post hoc test, between-subjects effects, Pearson correlation (α = 0.05). RESULTS: Color, gloss, and roughness altered due to contact with staining solutions/toothbrush simulation. Highest impact on color, gloss, and roughness presented the material followed by storage time (ΔE material (η2 = 0.239/p < 0.001), storage time (η2 = 0.179/p < 0.001); gloss (η2 = 0.751/p < 0.001) (η2 = 0.401/p < 0.001); Ra/Rz (η2 ≥ 0.801/p < 0.001) (η2 ≥ 0.416/p < 0.001)). Correlations were found between Rz and Ra (Pearson 0.887/p ≤ 0.001) or Rz and ΔE (0.517/p ≤ 0.001) or Ra and ΔE (0.460/p ≤ 0.001). CONCLUSIONS: Storage and toothbrushing were accompanied by a change in color, gloss, and roughness. Almost all materials showed visible discoloration after 4 weeks of storage. Gloss values decreased as storage time increased. The initial roughness and polishability were better with harder materials. CLINICAL RELEVANCE: Milled and 3D printed splints show good color, gloss, and roughness resistance after 4-week storage or toothbrush application.

Multilayer zirconia: Influence of positioning within blank and sintering conditions on the in vitro performance of 3-unit fixed partial dentures.

STATEMENT OF PROBLEM: Multilayer zirconia blanks comprise material layers with different optical and mechanical properties. Whether positioning within the blank, as well as variation in the sintering procedure, will lead to restorations with different properties is unclear. PURPOSE: The purpose of this in vitro study was to test the influence of sintering procedures and positioning in a multilayer blank on the in vitro performance of 3-unit zirconia fixed partial dentures. MATERIAL AND METHODS: Human molars were embedded in acrylic resin and prepared for 3-unit fixed partial dentures. Anatomic contour prostheses were milled from zirconia blanks (ZirCAD Prime 16 mm) in 3 different positions: above (cusp-top at the top of the blank), central (center of the prosthesis in the center of the blank), and bottom (margins at the lower edge of the blank). Sintering time (2:26, 4:25, 9:50 hours:minutes) was varied for the central and bottom prostheses. All prostheses were glazed and adhesively bonded. Thermocycling and mechanical loading was performed at 2×3000×5 °C/55 °C in distilled water for 1.2×106 cycles at a 50-N load. Then, fracture force was determined with a universal testing device by using central loading, a Ø12-mm steel ball, a 1-mm tin foil, and a rate of 1 mm/min. Failure was defined as 10% force drop or acoustic signal (crack). Statistical analysis was performed with 1-way ANOVA and Bonferroni correction (α=.05). RESULTS: All fixed partial dentures survived thermocycling and mechanical loading. Fracture forces varied between 1002 ±446 N (above; 9:50 hours) and 1760 ±607 N (central; 9:50 hours). The 1-way ANOVA revealed no statistically significant differences (P=.059) among the groups. Individual significant differences (P=.048) were found between prostheses from positions above, 9:50 hours, and central, 9:50 hours. For normal and long sintering times, fracture forces were highest in the central position. CONCLUSIONS: The sintering process and positioning of restorations within a multilayer zirconia blank have little effect on the mechanical properties of the prostheses.

In vitro performance of CAD/CAM and conventional removable dentures.

AIM: Innovations in CAD/CAM technology and materials science offer new methodologies for removable prosthodontics. As clinical data are still rare, in vitro performance of both CAD/CAM and comparable conventional materials may help to estimate the clinical outcome. MATERIALS AND METHODS: Specimens (n = 8 per group) from teeth (CediTEC, SR VivodentCAD, Vitapan), base materials (V-Print dentbase, IvoBase CAD, Paladur), adhesives (CediTEC Primer/Adhesive, IvoBase CAD Bond), and a fully printed specimen (Try-In) were created. All specimens underwent thermal cycling and mechanical loading (TCML): 1,200,000 × 50 N; 2x3000 x 5°C/55°C; H2O. Surviving specimens were loaded to fracture. Statistical tests used were the Shapiro-Wilk test and the Kaplan-Meier survival, with the level of significance set to α = 0.05. RESULTS: Mean loading cycles until failure varied between 100 and 621,667 cycles. Up to five specimens per group failed during TCML. With one exception, all specimens of the entirely CAD/CAM-fabricated group survived TCML. The log-rank (Mantel-Cox) test showed significantly different (P = 0.000) loading cycles between the systems (chi-square test: 28,247; degree of freedom: 8). Failure of the dentures during TCML was characterized by failure of the denture base (2x), denture tooth (13x), mixed base/tooth (3x) or adhesive between base and tooth (1x). CONCLUSION: TCML and fracture testing showed different aspects of denture tooth restoration. The results indicated no correlation between fracture force, fracture pattern, and survival cycles. Denture teeth (milled, heat-pressed), bases (milled, printed, pressed), and primer should be matched up to optimize the performance of dentures.

Thermoanalytical Investigations on the Influence of Storage Time in Water of Resin-Based CAD/CAM Materials.

New resin-based composites and resin-infiltrated ceramics are used to fabricate computer-aided design (CAD) and computer-aided manufacturing (CAM)-based restorations, although little information is available on the long-term performance of these materials. The aim of this investigation was to determine the effects of storage time (24 h, 90 days, 180 days) on the thermophysical properties of resin-based CAD/CAM materials. Thermogravimetric Analysis (TGA), differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) were used in the study. TGA provided insight into the composition of the resin-based materials and the influence of internal plasticization and water sorption. Resin-based composites showed different decomposition, heat energy and mechanical behavior, which was influenced by storage time in water. Individual materials such as Grandio bloc showed lower influence of water storage while maintaining good mechanical properties.

The role of medical school prestige and location in neurosurgery residency placement: An analysis of data from 2016 to 2020.

OBJECTIVE: There remains a gap in the literature analyzing how categorical variables may affect the highly competitive neurosurgery residency application process for MD Seniors in the United States. We aimed to improve understanding of the impact of medical school prestige and geographic location on candidacy for neurosurgery residency. METHODS: Schools were stratified into high and low prestige cohorts based on the U.S. News and World Report Rankings and by geographic location. Publicly available match data displayed by websites of included medical schools from 2016 to 2020 were examined, and neurosurgery residency placement rates were then compared. Analysis was performed using Fisher's exact test and chi-square analysis, with a p-value of 0.05. RESULTS: There were 6685 total matches in the high-prestige cohort and 12,997 total matches in the low-prestige cohort, with 115 (1.72%) and 113 (0.87%) neurosurgery matches, respectively (OR = 2.00, p < 0.0001). Considering geographic location, there were 5244 total matches in the Midwest, 3456 total matches in the West, 4994 total matches in the South, and 6053 total matches in the Northeast, with 51 (0.97%), 24 (0.69%), 83 (1.66%), and 114 (1.88%) being neurosurgery residency placements, respectively (p < 0.0001). CONCLUSIONS: Neurosurgery residency placement may be correlated with attending more prestigious medical schools and those located in the Northeast or South United States. Further elucidation of similar variables may prove to be important as neurosurgery residency becomes more competitive and the evaluation process changes.

Investigating the mechanical and optical properties of novel Urethandimethacrylate (UDMA) and Urethanmethacrylate (UMA) based rapid prototyping materials.

OBJECTIVE: This study is focused on testing experimental rapid prototyping materials for occlusal splints made from Urethandimethacrylate (UDMA) and Urethanmethacrylate (UMA). METHODS: Materials were mixed from UDMA and UMA in ratios of 1.0:0.0, 0.75:0.25, 0.5:0.5, 0.25:0.75 and 0.0:1.0. Specimens were printed using digital light processing (DLP). After post-processing, the specimens underwent testing on flexural strength, modulus of elasticity, hardness, wear behavior, surface roughness, gloss and color stability. All tests were performed after 24 h (baseline) and 10 days of water storage (aging). Splints underwent cyclic pull-off and insertion testing, which was alongside simulated using finite element analysis. RESULTS: The mechanical properties were significantly influenced by changes in the UDMA:UMA ratio. Statistical analysis revealed that increased amounts of UMA correlated with a decrease in flexural strength (92.0 to 30.7 MPa), modulus of elasticity (2.4 to 0.6 GPa), hardness (155.1 to 102.0 N/mm2) and wear resistance (-1394.9 to -1742.1 µm). Materials with higher amounts of UMA were also more likely to be influenced by water storage. Specimens with 75% and 100% UMA content were partly not analyzable due to soft consistency. Optical properties showed only minor influence from UMA content and aging. Differences in surface roughness (3.9 to 2.4 µm) and color stability were insignificant. Gloss was partly influenced by the UDMA:UMA ratio and water storage. Mean survival rates for cyclic pull-off and insertion testing ranged from 2537 to 23,857 cycles. A correlation between the amount of UMA and survival rates was observed. SIGNIFICANCE: The addition of up to 25% UMA showed promising results, complying with clinical standards and delivering acceptable results in the cyclic pull-off and insertion test. Further investigation on increments between 0 and 25% UMA could help to find an optimum.

Correction to: Temporary materials: comparison of in vivo and in vitro performance.

A Correction to this paper has been published: https://doi.org/10.1007/s00784-021-04067-4.

Machine-driven simulation of removing luting agent remnants from implant surfaces: An investigator-independent assessment of cleaning protocols.

INTRODUCTION: To simulate removing luting agent remnants from crowns fixed onto implant-abutment analogs using a standardized machine-driven protocol including a scaler and air polishing or sonic. MATERIAL AND METHODS: A motor-driven device was constructed that controlled the rotational speed of the specimens, machining distance, contact pressure, and working time. A standardized layer of cement (Provicol, VOCO; Cuxhaven, G; Ketac Cem, 3MEspe; Seefeld, G; or Rely X Unicem, 3MEspe, Seefeld, G) was placed onto the finishing line of the crowns luted onto titanium-abutment analogs. The cement layer was scaled with a fresh titanium scaler maneuvered by the motor-driven device and treated with air polishing or sonic. Protocol 1: Scaling only for 20s, 40s, or 60s; n=20; protocol 2: 40s of scaling plus 20s of air polishing; protocol 3: 20s of scaling plus 40s of air polishing; protocol 4: 20s of scaling plus 40s of sonic; protocol 5: 40s of scaling plus 20s of sonic; protocols 2-5: n=10. Cement remnants were counted digitally as "percentage of remnants". STATISTICS: mean, standard deviation, Bonferroni post hoc tests; α=0.05. RESULTS: Ketac Cem was easily removed by scaling only and Provicol by scaling and air polishing, but the self-adhesive resin composite cement Rely X Unicem was not removable with the device. Only remnants of Provicol could be significantly reduced by further treatment after scaling (p<0.001). CONCLUSION: The presented motor-driven device enables reproducible investigations of various cleaning protocols and is thus useful to create an overview of cleaning protocols needed for the different types of cement.

Long-term clinical performance and complications of zirconia-based tooth- and implant-supported fixed prosthodontic restorations: A summary of systematic reviews.

OBJECTIVES: To present an overview on systematic reviews on prosthodontic zirconia restorations and to discuss long-term complications as well as information on anatomical and functional changes to the masticatory system. DATA/SOURCES: MEDLINE, EMBASE, Trip medical, and Cochrane Library databases were searched for systematic reviews up to February 2021. Bias was assessed and clinical survival and complications were analyzed. STUDY SELECTION: 38 eligible articles published between 2006 and 2021 were included. The reviews were based on 128 in vivo studies on approximately 10,000 zirconia restorations. 5-year cumulative survival rates varied between 91.2% and 95.9% for tooth-supported (TS) single crowns (SC), 89.4% and 100% for TS multi-unit fixed dental prostheses (FDP), 97.1% and 97.6% for implant-supported (IS) SCs and 93.0% and 100% for IS FDPs. Chipping was the most often technical complication, followed by framework fracture, loss of retention, marginal discrepancies/discoloration, occlusal roughness and abutment/screw loosening. Color mismatch was the only esthetic complication. Biological complications were caries, endodontic complications, tooth fracture, periodontal disease, abrasion/attrition, persisting pain, high sensitivity, peri­implantitis and soft tissue issues. Patients with bruxism were only examined sporadically. CONCLUSIONS: 5-year results for zirconia restorations were satisfactory. The predominant technical problem of veneering fractures could be overcome with adapted design or fabrication and application of monolithic restorations, but reviews of clinical studies on this subject are rare. The impact of zirconia restorations on the masticatory system remains unclear. CLINICAL SIGNIFICANCE: Zirconia restorations are experiencing a rapidly increasing use in dental practice. Being highly wear-resistant, hard and durable, it can be assumed that they do not follow natural abrasion and changes in the masticatory system. Possible long-term effects on the stomatognathic system as a whole should therefore be considered.

Pilot in-vitro study on insertion/removal performance of hand-cast, milled and 3D printed splints.

OBJECTIVES: The aim of this in-vitro pilot study was to establish a splint testing method and compare insertion/removal performance of dental splints. MATERIALS AND METHODS: 56 identical lower jaw splints (n = 8 per group) were manufactured from 2x methacrylate (MA) hand-cast (reference material), deep-drawn Polyethyleneterephthalate, combined deep-draw MA hand-cast, 2x CAD/CAM-milled MA and 3D-printed MA systems. After 10 days water storage (37 °C), cyclic pull-off and insertion performance on a metal jaw was investigated. Statistics; Shapiro-Wilk-test, one-way-ANOVA; post-hoc-Bonferroni, Kaplan-Meier-survival, α = 0.05. RESULTS: Mean insertion/pull-off cycles varied significantly (p = 0.000) between 864 cycles (MA) and 202640 cycles (Deep Draw MA). Fracture of the splints was characterized by brittle individual fractures in the 31-34 region and most fractures in region 35 (44 of 56 splints). Finite element analysis confirmed the type and location of failure. CONCLUSIONS: Deep-draw, cast methacrylate and combined systems showed longer insertion/pull-off system cycles in comparison to printed or milled splints. Insertion/pull-off performance showed differences between the tested splint systems and indicates the influence of the processing. CLINICAL RELEVANCE: The presented in-vitro test allowed for estimating the clinical insertion/pull-off performance of dental splints.

In vitro performance and fracture resistance of interim conventional or CAD-CAM implant-supported screw- or cement-retained anterior fixed partial dentures.

STATEMENT OF PROBLEM: Interim restorations represent an essential clinical treatment step; however, limited information is available concerning the performance of computer-aided design and computer-aided manufacturing (CAD-CAM) interim materials. PURPOSE: The purpose of this in vitro study was to evaluate the performance and fracture load of resin anterior implant-supported interim fixed partial dentures (IFPDs). MATERIAL AND METHODS: Identical anterior resin IFPDs (maxillary central incisor to canine; n=16 per material) were milled from polymethylmethacrylate (PMMA) or di-methacrylate (DMA) systems with different filler content. The IFPD groups were split to simulate a chairside (cemented implant-supported prosthesis) or laboratory procedure (screw-retained implant-supported prosthesis). A cartridge DMA material served as a control. After interim cementation, combined thermocycling and mechanical loading (TCML) was performed on all restorations to approximate a maximum of 2.5 years of clinical function. Behavior during TCML and fracture force was determined, and failures were analyzed. The data were statistically investigated (Kolmogorov-Smirnov test, 1-way-ANOVA; post hoc Bonferroni, Kaplan-Meier survival, α=.05). RESULTS: Drop out during TCML varied between no failures and complete failure during loading. For most systems, failure occurred between 120 000 and 600 000 mechanical loading cycles. For IFPDs without a screw channel fracture, values varied between 644 ±263 N and 987 ±101 N. Those with a screw channel fracture failed between 493 ±89 N and 951 ±248 N. Individual IFPDs had significantly higher mean fracture loads (P<.002), but the mean fracture values between IFPDs with and without a screw channel were not significantly different (P>.137). Failures were characterized by fracture of the connector (n=53) followed by mixed failures (n=22) or fractures at the abutment (n=21). CONCLUSIONS: These interim materials are sufficiently fracture resistant for the fabrication of implant-supported anterior IFPDs and are expected to survive between 6 months and 2 years before failure. The stability of IFPDs depended on the type of material but not on the restoration design (with or without a screw channel).

Fatigue and wear behaviour of zirconia materials.

OBJECTIVES: Comparison of in-vitro fatigue and wear performance of 3Y-, 4Y-, 5Y-TZP and lithiumdisilicate ceramic, multilayer/monolayer 4Y-TZP and variation of wall thickness at 5Y-TZP. METHOD AND MATERIALS: Crowns (n = 96; 6 groups à 16) were made of 3Y-TZP-LA, 4Y-TZP (multilayer and monolayer), 5Y-TZP (0,5mm/1 mm wall thickness) and lithiumdisilicate. 8 per group were stored in water (24hrs), 8 underwent TCML (1.200.000 × 50N; 2x3000x5°/55 °C; H2O, 2min cycle). Fracture force was determined by static loading (v = 1 mm/min, steel sphere with tin foil, diameter = 12 mm). Pin-on-block wear test was performed (steatite antagonist d = 3 mm; 50N, 120,000 cycles, 1.2Hz, lateral motion: 1 mm, antagonist lift: 1 mm, n = 8). Roughness, wear depth [µm] and antagonist wear were determined (3-D-laser-microscope, KJ3D, Keyence, J). STATISTICS: one-way-ANOVA; Bonferroni-post-hoc-test; α = 0.05. RESULTS: Fracture forces varied between 1211N (5Y,TCML) and 3952N (4Y-Mult,TCML). Individual significant differences (p ≤ 0.025) were found between materials. Increase of wall thickness (5Y; 0.5 mm/1.0 mm) lead to a non-significant (p ≥ 0.442) increase of fracture force. 4Y and 4Y-multilayer zirconia showed no significantly different (p ≥ 0.073) fracture forces. Zirconia mean wear (3Y:10.0 ± 3.9 µm, 4Y:19.8 ± 3.8 µm, 5Y:10.9 ± 6.8 µm) was not significantly (p = 1.000) different. Lithiumdisilicate ceramic (149.3 ± 45.4 µm) and human enamel (434.2 ± 131.3 µm) provided significantly (p ≤ 0.002) higher wear. Antagonistic wear against lithiumdisilicate (17.5 ± 3.9%) and human enamel (6.7 ± 3.0%) was significantly (p ≤ 0.007) lower than against zirconia (4Y:31.9 ± 8.0% - 5Y:27.6 ± 5.8%). CONCLUSION: Fracture force of 5Y-TZP differs from 4- or 3-Y-TZP. Mechanical characteristics and dimensional requirement of 5Y-TZP are comparable to lithiumdisilicate. Mono- or multilayer 4Y-TZP provided comparable fracture forces. Wear was comparable between zirconia systems and lower in comparison to lithiumdisilicate or enamel.