The Influence of Contamination and Different Cleaning Methods and the Effect of Plasma Treatment of CoCr Alloy on Tensile Bond Strength to Composite Resin.

PURPOSE: To investigate the influence of contamination and different cleaning methods on resin bonding to cobalt-chro- mium (CoCr) alloy disks. MATERIALS AND METHODS: A total of 160 CoCr disks were divided into 3 groups. The first group (N = 64) was air abraded with alumina particles and contaminated with a silicone disclosing agent and saliva; the second group (N = 64) was air abraded but not contaminated; the third group (N = 32) was neither air abraded nor contaminated. The first two groups were di- vided into 4 subgroups (N = 16) according to the cleaning method: ultrasonic bath in 99% isopropanol, use of a cleaning suspension of zirconium oxide particles, use of a cleaning suspension based on 10-MDP salt, and treatment with atmo- spheric plasma. The third group was divided into 2 subgroups (N = 16): treatment with atmospheric plasma and no treat- ment. All CoCr specimens were bonded to plexiglas tubes filled with a bonding resin that contained phosphate monomer. Tensile bond strength (TBS) was examined by tensile testing after 3 and 150 days of water storage plus 37,500 thermal cy- cles (N = 8). RESULTS: After contamination, TBS was significantly reduced after 150 days of water storage. Groups without air abrasion showed initially low TBS and debonded spontaneously after 150 days of water storage. CONCLUSION: None of the cleaning methods was able to remove saliva and silicone disclosing agent on CoCr-alloy sur- faces. Surface activation by plasma treatment has no long-term effect on the bond strength.

Long-term effect of simulated five years professional mechanical biofilm removal on the luting gap of ceramic restorations.

BACKGROUND: Achieving sufficient professional mechanical biofilm removal (PMPR) can be challenging in supportive periodontal therapy (SPT), particularly in patients with prosthetic restorations. This experimental study aimed to simulate five years of SPT with periodic PMPR near the luting gap of ceramic restorations using a rubber cup with polishing paste (RCP), air polishing with two different low-abrasive powders (LAPA-1: glycine powder, LAPA-2: erythritol powder), and non-professional mechanical cleaning (control group) to measure the extent of volume loss in the luting gap after baseline (∆V = Vbaseline-V1-5; in µm3). METHODS: Two operators randomly performed PMPR ten times for thirty seconds on one of four sides of 30 crown replicas fixed with glass-ionomer cement (CGIZ: n = 15) or adhesive bonding (CAB: n = 15). The replicas were separated in a template during PMPR, and afterward, cleaned for five seconds per side with a sonic brush under flowing water. The artificial aging process between two PMPRs simulated a 5-year SPT with two PMPRs per year. Profilometric measurements were performed at baseline and after each second PMPR to obtain the mean change of ∆V. The statistical evaluation of the data was carried out using nonparametric tests with Bonferroni correction applied for multiple tests. RESULTS: Ninety-six out of 120 sides could be included in the analysis. PMPR methods showed a loss of substance in the luting gap with a ∆V (mean(standard deviation)) of -4.35 × 106(4.8 × 106)µm3 versus 8.79 × 104(1.05 × 106)µm3 for control at V5 (p ≤ 0.001). No significant differences of ∆V1-5 values could be identified in the control (p > 0.05), whereat all PMPRs showed a significant increasing loss of substance per simulated year (p ≤ 0.001). Intergroup comparison identified LAPA-1 as having the highest significant loss of substance determined on CAB (∆V: -1.05 × 107 (7,2 × 106) µm3), followed by LAPA-2 on CAB (∆V: -6.29 × 106 (4,24 × 106) µm3), LAPA-1 on CGIZ (∆V: -4.15 × 106 (3,25 × 106) µm3), LAPA-2 on CGIZ (∆V: -3.0 × 106 (2,23 × 106) µm3), RCP on CAB (∆V: -1.86 × 106 (2,23 × 106) µm3) and CGIZ (∆V: -1.2 × 106 (1,31 × 106) µm3; p ≤ 0.001)). CONCLUSIONS: Within study limitations, all PMPRs caused a significantly higher loss of substance in the luting gap versus control without professional intervention, with the highest values in the CAB group for LAPA-1, LAPA-2 and RCP. Similar findings were observed for CGIZ, although the loss values were lower.

3D-printed versus conventionally milled zirconia for dental clinical applications: Trueness, precision, accuracy, biological and esthetic aspects.

OBJECTIVES: This systematic review aimed to compare the clinical outcome, internal gap, trueness, precision, and biocompatibility of 3D-printed (AM) compared to milled (SM) zirconia restorations. DATA SOURCE: A thorough search of Internet databases was conducted up to September 2023. The search retrieved studies compared AM zirconia to SM zirconia restorations regarding clinical outcome, fit, trueness, precision, and biocompatibility. STUDY SELECTION: Of 1736 records, only 59 were screened for eligibility, and 22 records were included in this review. The quality of studies was assessed using the revised Cochrane risk-of-bias tool (ROB2), and the Modified Consort Statement. One clinical study exhibited a low risk of bias. All laboratory studies revealed some bias concerns. Short-term observation showed 100 % survival with no signs of periodontal complications. 3D-printed zirconia crowns showed statistically significant lower ΔE and a better match to adjacent teeth (p ≤ 0.5). The fit, trueness, and precision vary with the printing technique and the tooth surface. CONCLUSIONS: 3D-printed zirconia crowns provide better aesthetic color and contour match to adjacent natural teeth than milled crowns. Both 3D printing and milling result in crowns within the clinically acceptable internal and marginal fit. Except for nanoparticle jetting, the marginal gap of SM crowns was smaller than AM crowns, however, both were clinically acceptable. Laminate veneers might be more accurately produced by 3D printing. 3D-printed axial surface trueness was better than milled axial surfaces. Long-term RCTs are recommended to confirm the clinical applicability of 3D-printed restorations. CLINICAL SIGNIFICANCE: Internal fit and gap, precision, and trueness are fundamental requirements for successful dental restorations. Both techniques produce restorations with clinically acceptable marginal and internal fit. Axial surfaces and narrow or constricted areas favored 3D-printed than conventionally milled zirconia.

Influence of post material and ferrule thickness on the fracture resistance of endodontically treated premolars: A laboratory study.

STATEMENT OF PROBLEM: The influence of the ferrule thickness and post materials on the fracture resistance of endodontically treated teeth remains unclear. PURPOSE: The purpose of this laboratory study was to evaluate the influence of post material and ferrule thickness on the fracture resistance of endodontically treated mandibular premolars. MATERIAL AND METHODS: Sixty-four extracted and endodontically treated mandibular first premolars were used and divided into 4 test groups (n=16) depending on the ferrule thickness: F-0: without a ferrule, F-0.5: with a 0.5-mm ferrule thickness, F-1: with a 1-mm ferrule thickness, and F-1.5: with a 1.5-mm ferrule thickness. In groups with ferrules, the height ranged from 2 mm buccally/lingually to 1 mm proximally. Teeth in subgroups (n=8) were restored with either prefabricated glass fiber (FF) or titanium posts (FT) (ISO size 70 and length of 7.5 mm) and then adhesively restored with composite resin foundation materials. After foundation procedures, each specimen was restored with a cobalt chromium crown which was cemented with glass-ionomer cement. All specimens were subjected to dynamic loading in a masticatory simulator for 1 200 000 loading cycles with a nominal load of 5 Kg at 1.2 Hz and simultaneous thermocycling (5 to 55 °C). Specimens were then quasistatically loaded at 30 degrees in a universal testing machine until fracture. Fracture loads were analyzed by using 2-way ANOVA followed by the Tukey honestly significant difference test (α=.05). RESULTS: Fracture loads ranged from 610 ±45 N (no ferrule - glass fiber post) to 1216 ±169 N (1.5 mm ferrule thickness - glass fiber post). A statistically significant increase in fracture resistance was observed with increasing ferrule thickness (P<.001). However, post materials did not show a statistically significant influence (P=.977). CONCLUSIONS: Under the conditions of this laboratory study, increasing the ferrule thickness had a significant effect on the fracture resistance of endodontically treated teeth after thermomechanical fatigue, irrespective of post materials.

Durability of Resin Bonding to Dental 3Y-TZP Zirconia Using Different Adhesive Systems.

This laboratory study was conducted to evaluate and compare the resin bond strength of different adhesive resin systems in different combinations and the durability of their bonds with zirconia ceramic. MATERIALS AND METHODS: One hundred and twenty-eight specimens were milled from 3Y-TZP zirconia ceramic. The bonding surfaces of all disks were wet polished, steam cleaned, airborne-particle abraded and ultrasonically cleaned in 99% isopropanol. The specimens were randomly divided into four main groups according to the applied resin system; two conventional and two self-adhesive systems were used. Each group was further subdivided into two subgroups; the first was conditioned with the specified primer for conventional luting resins or not conditioned for the self-adhesive systems, whereas the second subgroup of each was conditioned with the same phosphate monomer-containing primer (Alloy Primer). The zirconia specimens were adhesively bonded, using the allocated luting resin, to plexiglass tubes filled with self-curing composite resin (Clearfil FII). Half of the specimens of each subgroup were stored in distilled water at 37 °C for 3 days, whereas the other half were subjected to artificial aging, 150 days of storage and additional thermal cycling. Thereafter, all specimens were subjected to TBS testing using a universal testing machine. Statistical analysis was conducted using two-way ANOVA followed by separate one-way ANOVAs. The Games-Howell post-hoc test was applied for pairwise comparisons. RESULTS: All specimens survived storage with thermal cycling. The mean TBS values ranged from a minimum of 43.4 ± 5.0 MPa to a maximum of 66.4 ± 3.5 after 3 days and from a minimum of 13.6 ± 2.5 MPa to a maximum of 50.1 ± 9.4 MPa after 150 days. CONCLUSIONS: Artificial aging had a significantly negative effect on all test groups. The chosen adhesive-resin system had a significant effect on the resulting TBS values. The highest TBS values were achieved for the self-adhesive luting resin G-Cem One but were statistically comparable to the results obtained for the dual-cure luting resin G-Cem LinkForce.

Long-term clinical outcome of three-unit fixed-fixed posterior zirconia ceramic inlay-retained FDPs with a modified design.

OBJECTIVES: To assess the long-term clinical outcome of posterior inlay-retained fixed dental prostheses (IRFDPs) with a modified design made from zirconia ceramic. METHODS: In 30 patients thirty 3-unit IRFDPs were placed to replace 7 premolars (4 in the maxilla, 3 in the mandible), and 23 first molars (15 in the maxilla, 8 in the mandible). Preparations were accomplished in agreement with the general principles for ceramic inlay restorations and modified with a short retainer-wing bevel preparation within the enamel at the buccal and oral sides. The frameworks were milled from 3Y-TZP ceramic, and the pontics were veneered with feldspathic ceramic. All IRFDPs were bonded with a phosphate monomer containing luting resin after air-abrasion of the intaglio surfaces. The patients were recalled 6-12 months after placement, and then annually. Kaplan-Meier analysis was used to calculate the survival and complication rates of the IRFDPs. RESULTS: The mean observation time was 10.6 ± 1.5 years. The 10-year cumulative survival rate was 89% with 4 failures, two of them were due to deep secondary caries with loss of retention, one due to repeated debonding with enamel fractures, and one due to generalized progressive periodontitis. The most common complication was chipping of the veneering ceramic (20.1%). Eighteen IRFDPs were free of any type of complication up to 15.4 years, which corresponds to a 10-year cumulative success rate of 70.4%. CONCLUSION: The long-term clinical performance of modified IRFDPs made of veneered zirconia ceramics was favorable after 10 years, therefore, they represent a treatment alternative to replace posterior single missing teeth. CLINICAL SIGNIFICANCE: Zirconia-based IRFDPs fabricated in the modified design may represent a substance-preserving alternative to conventional posterior FDPs to replace posterior single missing teeth, particularly in cases where implants cannot be placed, and when the adjacent teeth already have small restorations or defects.

Outcomes of resin-bonded attachments for removable dental prostheses.

PURPOSE: This clinical study aimed to evaluate the outcomes of resin-bonded attachments (RBAs) for precision-retained removable dental prostheses (RDPs) after at least two years of clinical maintenance. METHODS: Since December 1998, 205 RBAs (44 bonded to posterior teeth, 161 to anterior teeth) have been inserted in 123 patients (62 females and 61 males; mean age, 63.6 ± 9.6 years) who were recalled annually. The abutment teeth underwent a minimally invasive preparation limited to the enamel. RBAs were cast in a cobalt-chromium alloy with a minimum thickness of 0.5 mm and adhesively luted with a luting composite resin (Panavia 21 Ex or Panavia V5, Kuraray, Japan). We evaluated caries activity, plaque index, periodontal condition, and tooth vitality. The Kaplan-Meier survival curves were used to account for the reasons for failure. RESULTS: The mean observation time of RBAs until the last recall visit was 84.5 ± 51.3 months (range, 3.6-270.6). During the observation period, 33 RBAs debonded in 27 patients (16.1%). The 10-year success rate according to the Kaplan-Meier analysis was 58.4%, which dropped to 46.2% after 15 years of observation if debonding was considered a failure. If rebonded RBAs were regarded as surviving, the 10- and 15-year survival rates would be 68.3% and 61%, respectively. CONCLUSIONS: The use of RBAs for precision-retained RDPs appears to be a promising alternative to conventionally retained RDPs. As reported in the literature, the survival rate and frequency of complications were comparable with those of conventional crown-retained attachments for RDPs.

Effect of Thermomechanical Dynamic Loading on the Retention of Metallic and Nonmetallic Telescopic Mandibular Overdentures.

PURPOSE: To evaluate the effect of thermomechanical dynamic loading on the retention of telescopic mandibular overdentures with different metallic and nonmetallic material combinations. MATERIALS AND METHODS: Four groups were tested: (1) ZP (zirconia abutments/PEEK framework); (2) PP (PEEK abutments/PEEK framework); (3) TP (titanium abutments/PEEK framework); and (4) TG (titanium abutments/gold copings/cobalt-chromium framework). Each specimen contained four implants positioned over a polyvinylchloride-cylindrical base. After 10,000 removal/insertion cycles, the specimens were subjected to thermomechanical dynamic load in a chewing simulator for 1,200,000 loading cycles, corresponding to 5-year clinical fatigue. A screw was used to receive the chewing load, and 0.5 mm was permitted between the screw and the metal top fixed into the base to simulate the resilience of the posterior residual ridge tissues. Vertical chewing loads of 60 N were applied at a speed of 30 mm/second. Thermocycling was applied with a temperature ranging between 5°C and 55°C. The retentive force was measured using a universal testing machine 10 times before and after the thermomechanical dynamic loading test with a speed of 8 mm/second. RESULTS: The mean retentive force increased significantly from 13.2 (± 4.6) N to 16.4 (± 6.1) N in group ZP (P = .002), while in group TP, it decreased significantly from 4.9 (± 2.1) N to 3.3 (± 1.7) N (P = .046). There was no statistically significant change in the retentive force for groups PP and TG. CONCLUSIONS: The investigated metallic and nonmetallic combinations of double-crown-retained mandibular overdentures maintained acceptable levels of retention after thermomechanical dynamic loading. Further laboratory and clinical studies are needed before their routine clinical use can be recommended.

Influence of Post Length, Post Material, and Substance Loss on the Fracture Resistance of Endodontically Treated Teeth: A Laboratory Study

PURPOSE: To evaluate the effects of post length, post material, and substance loss on the fracture resistance of endodontically treated mandibular premolars. MATERIALS AND METHODS: A total of 96 extracted human mandibular first premolars were endodontically treated and divided into 12 test groups (n = 8 each) based on the number of residual walls (one/two), post material (glass-fiber/titanium), and post length (5 mm, 7.5 mm, and 10 mm). After luting the posts, specimens received a composite resin core and a crown preparation with a 1.5-mm ferrule. Cast cobalt-chromium crowns were cemented using glass-ionomer cement. After 1,200,000 chewing cycles with a load of 49 N and simultaneous thermocycling (5°C to 55°C), specimens were quasi-statically loaded at 30 degrees to the longitudinal axis of the tooth until fracture. Fracture loads were analyzed using three-way, two-way, and one-way ANOVA (α = .05). Fracture modes were examined under a stereomicroscope (×25 magnification) and recorded. RESULTS: The mean ± SD fracture loads ranged from 642 ± 190 N (one wall, glass fiber, 5 mm) to 1,170 ± 130 N (two walls, titanium, 7.5 mm). The mean fracture load of titanium posts was significantly higher than that of glass-fiber posts (P < .001), and the 7.5-mm post length exhibited significantly higher fracture loads than groups with 5-mm and 10-mm post length (P = .008). CONCLUSIONS: Teeth restored with titanium posts revealed considerably higher fracture resistance than teeth restored with glass-fiber posts, especially if 7.5-mm-length posts were used.

Extrusion-based 3D printing of osteoinductive scaffolds with a spongiosa-inspired structure.

Critical-sized bone defects resulting from trauma, inflammation, and tumor resections are individual in their size and shape. Implants for the treatment of such defects have to consider biomechanical and biomedical factors, as well as the individual conditions within the implantation site. In this context, 3D printing technologies offer new possibilities to design and produce patient-specific implants reflecting the outer shape and internal structure of the replaced bone tissue. The selection or modification of materials used in 3D printing enables the adaption of the implant, by enhancing the osteoinductive or biomechanical properties. In this study, scaffolds with bone spongiosa-inspired structure for extrusion-based 3D printing were generated. The computer aided design process resulted in an up scaled and simplified version of the bone spongiosa. To enhance the osteoinductive properties of the 3D printed construct, polycaprolactone (PCL) was combined with 20% (wt) calcium phosphate nano powder (CaP). The implants were designed in form of a ring structure and revealed an irregular and interconnected porous structure with a calculated porosity of 35.2% and a compression strength within the range of the natural cancellous bone. The implants were assessed in terms of biocompatibility and osteoinductivity using the osteosarcoma cell line MG63 and patient-derived mesenchymal stem cells in selected experiments. Cell growth and differentiation over 14 days were monitored using confocal laser scanning microscopy, scanning electron microscopy, deoxyribonucleic acid (DNA) quantification, gene expression analysis, and quantitative assessment of calcification. MG63 cells and human mesenchymal stem cells (hMSC) adhered to the printed implants and revealed a typical elongated morphology as indicated by microscopy. Using DNA quantification, no differences for PCL or PCL-CaP in the initial adhesion of MG63 cells were observed, while the PCL-based scaffolds favored cell proliferation in the early phases of culture up to 7 days. In contrast, on PCL-CaP, cell proliferation for MG63 cells was not evident, while data from PCR and the levels of calcification, or alkaline phosphatase activity, indicated osteogenic differentiation within the PCL-CaP constructs over time. For hMSC, the highest levels in the total calcium content were observed for the PCL-CaP constructs, thus underlining the osteoinductive properties.

The Effect of Sterilization on the Accuracy and Fit of 3D-Printed Surgical Guides.

This study was conducted to evaluate the accuracy of 3D-printed surgical guides before and after sterilization in a steam sterilizer. A test-model incorporating three implant replicas was customized. A total of forty guides were printed from five printable resins. A group made from a self-curing composite served as control group. The guides were checked for fit. Vertical discrepancies between the model and guides were measured at standardized points at a load of 500 g (P1). The guides were connected to implant replicas and scanned, and their angles were digitally measured. The specimens were sterilized in a steam sterilizer at 121 °C for 20 min at 2 bar pressure. Vertical discrepancies (P2) and angulations were remeasured. Additionally, the specimens were repositioned with an increased load, and measurements were repeated (P3). All specimens were repositionable after sterilization. The smallest variation in discrepancy at a 500 g load was 428 µm, whereas the greatest was 1487 µm. Under an increased force, the smallest change was 94 µm, while the greatest was 260 µm. The level of significance α = 0.05 (95% confidence interval) was set for all tests. The variation in the measured angles was not statistically significant (Kruskal-Wallis's test, p > 0.05). The accuracy was affected by the material and sterilization, but it was clinically acceptable when an increased load was applied during repositioning.

Comparison of bond strength to three restorative materials after contamination and the use of two cleaning agents.

STATEMENT OF PROBLEM: Scientific data on the decontamination effectiveness of a newly introduced cleaning agent are lacking. PURPOSE: The purpose of this in vitro study was to evaluate and compare the tensile bond strength (TBS) of 3 different restorative bonding surfaces after contamination with saliva following different cleaning protocols. MATERIAL AND METHODS: A total of 192 disk specimens were made out of 3 materials (n=64); Katana Avencia (A), Katana Zirconia (Z), and e.max CAD (L). The bonding surfaces of all disks were polished, steam cleaned, and then pretreated by following the recommended protocol for each material. The specimens of each group were divided into 4 subgroups (n=16). The first subgroup served as the reference (R), where no contamination was applied. The 3 other subgroups were contaminated with saliva and subsequently rinsed with water for 20 seconds and dried with oil- and water-free air spray. They were then either not treated with any cleaning method (0), cleaned with Katana Cleaner (K), or cleaned with Ivoclean (I). The bonding surfaces of the specimens were perpendicularly luted to plexiglass tubes filled with dual-polymerizing composite resin (Clearfil DC Core) with resin cement (Panavia V5) after the recommended surface conditioning. Each subgroup was further subdivided into 2 groups: stored in 37 °C water for 3 days or subjected to thermal-cyclic loading for 150 days with 37 500 thermal cycles (7500 per month), temperature 5 to 55 °C, and dwell time of 30 seconds. All specimens were subjected to TBS testing in a universal testing machine. Three-way ANOVA was applied. A significant interaction (P<.01) was detected between the 3 different variables (material, treatment, aging). After significant interactions had been revealed by 3-way ANOVA, additional statistical analysis was performed by using separate 2-way ANOVAs, then separate 1-way ANOVAs followed by the Tukey-HSD test for post hoc pairwise comparisons among groups (α=.05 for all tests). All specimens underwent failure mode analysis after TBS testing RESULTS: All specimens survived the storage with thermocycling except for group Z-0, where all specimens debonded during thermocycling. The mean ±standard deviation TBS values ranged from 18.3 ±5.3 MPa to 34.0 ±5.4 MPa after 3 days and from 6.7 ±5.5 MPa to 26.9 ±5.4 MPa after 150 days. CONCLUSIONS: Contaminated groups that did not receive any cleaning had significantly lower TBS. Thermocycling had a negative effect on the TBS but was not statistically significant for all groups. Using the same cleaning method, the restorative material did had a significant effect on the TBS after 150 days.

Failure resistance of single-implant crowns assembled from polyetheretherketone and lithium disilicate abutments and different crown materials after artificial aging.

AIM: To investigate the effect of using different materials for the fabrication of implant abutments and crowns on the mechanical behavior of implant-supported single crowns after artificial aging. The materials were tested in different combinations to reveal whether using stiff or resilient materials as an abutment or a crown material might influence the fracture strength of the whole structure. MATERIALS AND METHODS: A total of 40 implants (blueSKY, bredent GmbH & Co. KG) were restored with identical custom-made CAD/CAM abutments milled out of lithium disilicate or ceramic-reinforced PEEK and were divided into 5 test groups (n = 8 each). Forty crowns made of three different materials (zirconia, lithium disilicate, and ceramic-reinforced PEEK) were used to restore the abutments. Specimens were subjected to mechanical load up to 1,200,000 cycles in a chewing simulator (Kausimulator, Willytech) with additional thermal cycling. The surviving specimens were subjected to quasi-static loading using a universal testing machine (Z010, Zwick). RESULTS: PEEK abutments with zirconia crowns showed the highest median failure load (3890.5 N), while PEEK abutments with lithium disilicate crowns exhibited the lowest (1920 N). Fracture and deformation occurred in both crowns and abutments. CONCLUSION: The failure load of the restorations was influenced by the material of the abutment and the crown. Restoring PEEK abutments with zirconia crowns showed a high failure load and no screw loosening.

Wear resistance of CAD/CAM one-piece screw-retained hybrid-abutmentcCrowns made from different restorative materials.

INTRODUCTION: The aim of this study was to measure the wear progress of three high performance polymers (HPP) materials as well as that of zirconia after artificial aging (simulated 2.5- and 5-year of clinical service with thermo-mechanical loading) and compare it with the well-documented wear of lithium disilicate. METHODS: Forty implants were used to restore a maxillary first premolar, where the abutment and the crown were manufactured as hybrid-abutment-crown and connected to the implant using a titanium insert. The implants were randomly divided, according to the restorative materials used, into five groups: 3Y-TZP zirconia (Z), lithium disilicate (L), ceramic-reinforced polyetheretherketon (P), nano-hybrid composite resin (C) and polymer-infiltrated ceramic-network (E). All hybrid-abutment-crowns were produced using CAD/CAM technology. A design of a maxillary first premolar was created with an angle of 120° between the buccal and palatal cusps, which were designed as planes. The restorations were adhesively luted onto the titanium inserts, according to the manufacturers' recommendations for each material individually, by means of dual-curing luting resin with the exception of group P, where the blocks were pre-fitted (heat-pressed) with an integrated titanium insert. The suprastructures were assembled onto the implants through titanium screws. The screw channels were sealed with Teflon tape and composite resin filling material that was polished to high-gloss. All specimens underwent 1 200 000 thermo-dynamic loading cycles with 49 N in a dual-axis chewing simulator. Elastomeric impressions were made for all specimens after 600 000 and after 1 200 000 cycles. The corresponding impressions were imaged using a laser scanning microscope and then 3D-analyzed using the software (Geomagic Wrap) to measure the volume loss of the wear area for all specimens. Statistical analysis was performed using Wilcoxon-Test regarding the two different time measurements for each material. For the analysis of the material variable, Kruskal-Wallis test was conducted followed by Mann-Whitney test. RESULTS: Group Z showed statistically the lowest volume loss compared to the other test materials, both after 600 000 and 1 200 000 cycles of artificial aging, with a median value of 0.002 mm3 volume loss after 1 200 000 cycles. In contrast, group E showed the highest volume loss with median values of 0.18 and 0.3 mm3 after 600 000 and 1 200 000 cycles, respectively. Artificial aging had significantly negative effect on the volume loss for all test materials. In addition, the choice of material had statistical influence on the outcome. CONCLUSION: Monolithic zirconia ceramic demonstrated lower wear than that reported for enamel after simulated 5-year of clinical service, whereas all other test materials showed higher volume loss after artificial aging.

Influence of shading on zirconia's phase transformation and flexural strength after artificial aging.

OBJECTIVES: The aim of this study was to determine the phase transformation and the influence of aging on the flexural strength of different colored zirconia. The effect of hydrothermal aging in an autoclave was compared with the effect of mechanical stress by simulating chewing. METHODS: High-strength zirconia (3Y-TZP) was investigated in three different colors: uncolored, A3, and D3. Disc-shaped specimens (N = 3) were analyzed by X-ray diffraction (XRD), and flexural strength was determined on bar-shaped specimens (N = 15) in a 4-point bending test before and after performing two different aging protocols: aging in an autoclave (134 °C, 70 h) and aging in a chewing simulator (5 kg load, 1.2 million cycles). During autoclave aging, the fraction of monoclinic phase on the surface was determined every 5 h. Once this exceeded 25 vol%, aging of the bar specimens was stopped. RESULTS: While in the unstained group the mean value of the proportion of monoclinic phase already exceeded 25 vol% after 30 h in the autoclave, this was the case in both stained groups only after 70 h. No measurable phase transformation could be detected after chewing simulation. Only color A3 showed a statistically significant (p ≤ 0.05) decrease in flexural strength after aging in the chewing simulator. SIGNIFICANCE: The colored zirconia showed a higher resistance to phase transformation through hydrothermal aging. The metal oxides in the staining solutions are assumed to hinder the phase transformation in the zirconia. Therefore, the significant reduction in the stained zirconia after chewing simulation is particularly interesting.

The Single Midline Implant in the Edentulous Mandible-Current Status of Clinical Trials.

The single midline implant in the edentulous mandible is a treatment concept that has often been controversially discussed. Nearly 30 years ago, the first available clinical results revealed high implant survival rates and remarkable improvements in oral comfort, function, patient satisfaction and oral health-related quality of life for edentulous patients compared to the situation with no implant. However, the clinical trials were predominantly conducted with a small number of patients over a short to medium follow-up period. Today, numerous clinical investigations on the single midline implant in the edentulous mandible, which increasingly include longer-term observation periods, are available. It is the aim of this overview to present the current literature and to highlight the clinical problems. This article is a 2023 update of a review published by the authors in the German language in 2021 in the German journal Implantologie. In total, 19 prospective clinical trials with a follow-up period of 0.5-10 years were analyzed. Over this observation period, single implants with modern rough implant surfaces in the edentulous mandible reveal high implant survival rates of between 90.9 and 100% when a conventional delayed loading protocol was applied.

Survival and debonding resistance of posterior cantilever resin-bonded fixed dental prostheses for moderately and severely worn dentition during thermomechanical loading.

OBJECTIVES: The purpose of this study was to investigate the survival rate, the debonding resistance, and the failure modes of different occlusal veneer designs when used as a retainer for posterior cantilever, resin-bonded fixed dental prostheses (RBFDPs) at two tooth wear levels. METHODS: Four test groups were assigned: two groups with occlusal-proximal preparation (PT1 and PT2 for grade 2 and 3 wear), and two groups for occlusal-proximal and lingual preparation (PLT1 and PLT2 for grade 2 and 3 wear) Monolithic zirconia ceramic (3Y-TZP) RBFDPs were luted with an adhesive bonding system (Panavia V5). The specimens underwent a chewing simulation for 1.200.000 cycles with a load of 5 kg and thermocycling for 7500 cycles between 5 °C and 55 °C. The surviving restorations were debonded under quasi-static conditions. The results were analyzed with ANOVA. RESULTS: The specimens exhibited a 100 % survival rate after thermomechanical fatigue loading. The debonding resistance was statistically significant higher for group PLT1 than for group PT1 (P = 0.004), and higher for group PT2 than group PT1 (P ≤ 0.001). However, the debonding resistance showed no statistically significant difference between groups PT2 and PLT2 (P = 0.343), and groups PLT1 and PLT2 (P = 0.222). Groups PT1 and PT2 showed favorable failure modes in 62.5 % and 0.00 % of the specimens, respectively. While groups PLT1 and PLT2 presented 25 % favorable failure modes. SIGNIFICANCE: Occlusal veneers showed promising results as a retainer for cantilever RBFDPs. The lingual extension might increase debonding resistance. Nevertheless, conservative designs with lingual and proximal bevels are to be recommended, irrespective of the level of tooth wear.

Comparison of properties and cost efficiency of zirconia processed by DIW printing, casting and CAD/CAM-milling.

OBJECTIVES: The aim of this study was to evaluate the mechanical properties and cost efficiency of direct ink writing (DIW) printing of two different zirconia inks compared to casting and subtractive manufacturing. METHODS: Zirconia disks were manufactured by DIW printing and the casting process and divided into six subgroups (n = 20) according to sintering temperatures (1350 °C, 1450 °C and 1550 °C) and two different ink compositions (Ink 1, Ink 2). A CAD/CAM-milled high strength zirconia (3Y-TZP) was added as reference group. The biaxial flexural strength (BFS) was measured using the piston-on-three-balls test. X-ray-diffraction (XRD) was used for microstructural analysis. The cost efficiency was compared for DIW printing and subtractive manufacturing by calculation of the manufacturing costs of one dental crown. RESULTS: Using XRD, monoclinic and tetragonal phases were detected for Ink 1, for all other groups no monoclinic phase was detected. The CAD/CAM-milled ceramic showed a significantly higher BFS than all other groups. The BFS of Ink 2 was significantly higher than the BFS of Ink 1. At a sintering temperature of 1550 °C the mean BFS of the printed Ink 2 was 822 ± 174 MPa. The BFS of the cast materials did not show a significantly higher BFS than the corresponding printed group for any tested parameter-set. The manufacturing costs of DIW printed crowns are lower than the manufacturing costs of CAD/CAM-milled crowns. CONCLUSION: DIW has a high potential to replace subtractive processes for dental applications, as it shows promising mechanical properties for appropriate ink compositions and facilitates a highly cost effective production.

Metabolic role of the hepatic valine/3-hydroxyisobutyrate (3-HIB) pathway in fatty liver disease.

BACKGROUND: The valine (branched-chain amino acid) metabolite 3-hydroxyisobutyrate (3-HIB), produced by 3-Hydroxyisobutyryl-CoA Hydrolase (HIBCH), is associated with insulin resistance and type 2 diabetes, but implicated tissues and cellular mechanisms are poorly understood. We hypothesized that HIBCH and 3-HIB regulate hepatic lipid accumulation. METHODS: HIBCH mRNA in human liver biopsies ("Liver cohort") and plasma 3-HIB ("CARBFUNC" cohort) were correlated with fatty liver and metabolic markers. Human Huh7 hepatocytes were supplemented with fatty acids (FAs) to induce lipid accumulation. Following HIBCH overexpression, siRNA knockdown, inhibition of PDK4 (a marker of FA ß-oxidation) or 3-HIB supplementation, we performed RNA-seq, Western blotting, targeted metabolite analyses and functional assays. FINDINGS: We identify a regulatory feedback loop between the valine/3-HIB pathway and PDK4 that shapes hepatic FA metabolism and metabolic health and responds to 3-HIB treatment of hepatocytes. HIBCH overexpression increased 3-HIB release and FA uptake, while knockdown increased cellular respiration and decreased reactive oxygen species (ROS) associated with metabolic shifts via PDK4 upregulation. Treatment with PDK4 inhibitor lowered 3-HIB release and increased FA uptake, while increasing HIBCH mRNA. Implicating this regulatory loop in fatty liver, human cohorts show positive correlations of liver fat with hepatic HIBCH and PDK4 expression (Liver cohort) and plasma 3-HIB (CARBFUNC cohort). Hepatocyte 3-HIB supplementation lowered HIBCH expression and FA uptake and increased cellular respiration and ROS. INTERPRETATION: These data implicate the hepatic valine/3-HIB pathway in mechanisms of fatty liver, reflected in increased plasma 3-HIB concentrations, and present possible targets for therapeutic intervention. FUNDING: Funding was provided by the Research Council of Norway (263124/F20), the University of Bergen, the Western Norway Health Authorities, Novo Nordisk Scandinavia AS, the Trond Mohn Foundation and the Norwegian Diabetes Association.

Zirconia restorations and the tool diameter compensation.

AIM: The aim of the present article is to describe a new method to reduce the undesirable loss of material thickness that results from overmilling due to the tool diameter compensation correction of common CAD/CAM software. MATERIALS AND METHODS: Today's CAD/CAM software (eg, 3Shape or Exocad) specifies the same tool diameter compensation for different ceramics. In the case of zirconia ceramics milled in the raw state, this leads to excessive milling of the inner surfaces of crowns, which results in unnecessarily large cementation gaps and a restoration that is thinned out from the inside. By manually reducing the preset correction in the digital design process by the volumetric sintering shrinkage factor specified by the manufacturer, excessive thinning of the zirconia can be avoided. RESULTS: The inner geometry of the restorations changes only slightly after manually reducing the preset tool diameter compensation correction. Consequently, a design of the restoration with the required minimum interocclusal thickness yet with accurate passive seating and marginal fit is possible without any further interventions. CONCLUSIONS: Understanding the specifics of the subtractive fabrication process as well as the properties of the restorative materials is a key factor in achieving optimal clinical outcomes with all-ceramic restorations fabricated with CAD/CAM technology. The use of monolithic zirconia combined with a calculated reduction in the preset tool diameter compensation correction might be beneficial in cases with thin or uneven geometry.