The International Journal of Prosthodontics, 06/2021

Purpose: To compare in a randomized controlled trial the 5-year clinical outcomes of (1) 3-unit fiber-reinforced resin-bonded fixed dental prostheses (RBFDPs) to 3-unit metal-ceramic RBFDPs; and (2) 3-unit fiber-reinforced RBFDPs to 2-unit cantilevered metal-ceramic RBFDPs. Materials and methods: A consecutive sample of 50 young adult patients with tooth agenesis or trauma in the anterior region was included. The recruitment period was from 2005 to 2009, during which a total of 62 RBFDPs were inserted. In group A, 27 participants were randomly treated with 18 metal-ceramic 3-unit RBFDPs and 15 3-unit fiber-reinforced RBFDPs. In group B, 23 participants were randomly treated with 16 metal-ceramic 2-unit RBFDPs and 13 3-unit fiber-reinforced RBFDPs. All patients were followed up at baseline registration and at 1, 3, and 5 years. The primary outcome parameter was survival rate of the RBFDPs, and the secondary outcome parameters were periodontal and technical/esthetic outcomes and patient-reported evaluation of the RBFDPs. Results: Seven patients dropped out of the study during the 5-year observation period. In group A, the fiber-reinforced RBFDPs had a cumulative survival rate of 23% after 5 years, which was significantly less than for the 3-unit metal-ceramic RBFDPs. In group B, the cumulative 5-year survival rate was 36% for the fiber-reinforced RBFDPs and 91% for the 2-unit cantilevered metal-ceramic RBFDPs. Conclusion: The 3- and 2-unit metal-ceramic RBFDPs had a significantly higher 5-year survival rate than the 3-unit fiber-reinforced RBFDPs. The accessibility for oral hygiene practice was better with 2-unit compared to 3-unit RBFDPs, and the degree of gingivitis was lower. The esthetic outcome was better for the RBFDPs with ceramic pontics than the composite ones.

Purpose: To evaluate the efficacy of manual and machine-aided cleaning to remove matured plaque from removable partial dentures (RPD). Materials and methods: A total of 32 patients with bilateral free-end saddle RPDs were included. The plaque was stained, and the RPD was photographed on all sides. One saddle was randomly allocated to manual cleaning, while the other was allocated to no cleaning. The patient manually cleaned the saddle by applying a denture brush and gel. The whole RPD was then cleaned with the aide of a machine using a rotating needle device. After each step, plaque dyeing and photographing were repeated. The plaque proportions (% pixel) were measured using special software. For statistical analysis, mixed models were used to adjust for baseline covariates, including plaque and surfaces, and to cover all time points. Results: The mean plaque area without cleaning at the fitting surface was higher than at the buccal/lingual surfaces (32.8% [95% CI: 28.1% to 36.4%] vs 15.3% [13.1% to 17.4%], respectively). Manual cleaning was not substantially better than no cleaning (4.6% [-0.1% to 9.2%] for the difference at fitting surfaces; disclaiming a substantial difference of > 10%; the difference found was even smaller at buccal/lingual surfaces). Machine-aided cleaning was substantially better than manual cleaning (16.1% [12.0% to 20.2%] for the difference at fitting surfaces and 7.3% [4.6% to 10.0%] at buccal/lingual surfaces). The combination of manual and machine-aided cleaning was not better than machine-aided cleaning alone (-0.2% [-2.6% to 2.1%] difference at fitting surface). Conclusion: Manual cleaning is insufficient in removing matured denture plaque. Machine-aided cleaning is clearly superior to manual cleaning, especially at fitting surfaces.

Purpose: To assess the survival rate of 3 mol % yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) minimally invasive anterior and posterior single and double partial retainer fixed dental prostheses (PRFDPs). Materials and methods: Twenty-three patients (18 women and 5 men, age range: 20 to 66 years) with single-tooth gaps received 28 3Y-TZP PRFDPs. Eight PRFDPs had two partial retainers and one pontic, two PRFDPs had two partial retainers and one pontic with a mesial cantilever, and 18 PRFDPs had one retainer and one cantilever. The abutment teeth were prepared following specific guidelines for all-ceramic restorations, considering existing direct restorations, carious processes, and occlusal conditions. The restorations were made of 3Y-TZP using CAD/CAM technology. Cementation was performed either conventionally, using resin-modified glass-ionomer (n = 6), or adhesively, using dual-polymerized resin cement (n = 22). Kaplan-Meier survival analysis was conducted. A P value of .05 was considered statistically significant. Results: During the observation period (5.92 ± 1.74 years, minimum = 2 years, maximum = 10 years), three debondings occurred, all in the two-retainer group and the mandible. The survival rates for the two types of intervention were different, with 100% for a single retainer and 70% for a double retainer, but without a significant difference (log-rank test χ²(1) = 0.200, P = .655). Conclusion: The 3Y-TZP PRFDPs presented in this study showed no failure when bonded and not conventionally cemented. Therefore, they can be used in cases where implant therapy is not possible or indicated.

Purpose: To compare the fit and clinical performance of screw-retained monolithic zirconia implant fixed dental prostheses (FDPs) based on either intraoral optical scanning (IOS) or conventional impressions. Materials  and methods: Patients with two posterior tissue-level implants (Straumann Regular Neck) replacing two or three adjacent teeth were recruited. Impressions were taken with both IOS (True Definition Scanner, 3M ESPE) and a conventional (polyether) pick-up impression. Double-blind randomization was performed after impression-taking, and patients were to receive an FDP based on either the digital or the conventional impression. The fit was evaluated, and the time required for adjustments was recorded. Additionally, survival and technical complication rates with a follow-up of 1 year were documented. Results: A total of 38 patients requiring 45 FDPs were included: 24 FDPs in the test (IOS) and 21 in the control (conventional) group. The average adjustment time was 6.92 minutes (SD: ± 10.84, range: 0 to 49 minutes) for digital vs 12.38 minutes (SD: ± 14.52, range: 0 to 54 minutes) for conventional impressions (P = .090). A proper fit (no adjustments) was achieved in 33.3% of the digital and 28.6% of the conventional group. Forty-two FDPs could be placed within the two planned appointments, and 3 FDPs exhibited an unacceptable fit and required an extra appointment. Eight technical complications occurred during the first year of function. The overall restoration survival rate was 100%. Conclusion: The clinical fit of CAD/CAM FDPs based on digital impressions is comparable to conventional impressions. Screw-retained monolithic zirconia FDPs on Ti-base abutments show low major complication and survival rates in the short term.

Purpose: To evaluate and compare the wear of natural enamel against a metal-ceramic and a monolithic zirconia crown, with the null hypothesis that there is no difference in the wear of enamel between antagonist metal-ceramic and monolithic zirconia crowns. Materials and methods: In 30 subjects (irrespective of sex and within the age range of 18 to 40 years), two bilaterally opposing molars (maxillary/mandibular) were prepared to receive monolithic zirconia or metal-ceramic crowns with feldspathic porcelain veneer. A polyvinyl siloxane impression of the opposing arch was taken at the time of cementation and 1 year after cementation. Casts were poured in type III gypsum and scanned, and the images were superimposed on each other. AutoCAD was used to calculate the difference between two images, which corresponded to the linear wear of the antagonist teeth. Statistical analysis of the data was done using one-way analysis of variance (ANOVA) and post hoc Tukey honest significant difference test for intergroup comparison. The P value obtained by one-way ANOVA was 1.1102e^-16 (< .05), and by post hoc Tukey test was .001 (< .01). Results: The mean wear of enamel against enamel was 14.8 ± 1.3 μm, enamel against metal-ceramic was 87.1 ± 18.3 μm, and enamel against monolithic zirconia was 59.4 ± 13.6 μm. The P values obtained; ie, 1.1102e^-16 (one-way ANOVA) and 0.001 (post hoc Tukey), indicated that the difference in wear of the antagonist tooth between monolithic zirconia and feldspathic porcelain was significant. Conclusion: It can be concluded that monolithic zirconia causes less wear of the antagonist tooth than feldspathic porcelain.

Taking a conventional implant abutment-level impression with the gingival retraction technique can cause side effects such as gingival recession and bleeding. In order to overcome these problems, an impression technique using digital superimposition of the customized abutment is newly introduced. In this technique, digital impression data and pre-scanned abutment data are superimposed to reproduce the abutment's location and shape on computer-aided design software. The present investigation was conducted to evaluate the clinical accuracy of the newly adapted digital superimposition impression technique by assessing the fit of fabricated prostheses. The results showed clinical efficacy of this technique, satisfying both convenience and clinically acceptable marginal and internal fit.

Purpose: To evaluate the accuracy (trueness and precision) achievable with four intraoral scanners (IOSs) and different preparation geometries. Materials and methods: A model of a maxillary arch with different preparation geometries (onlay, inlay, veneer, full-crown) served as the reference master model (RMM). The RMM was scanned 10 times using four commonly used IOSs (Trios 2 [TR], 3Shape; Omnicam [OC], Dentsply Sirona; True-Definition [TD], 3M ESPE; and Primescan [PS], Dentsply Sirona). Scans were matched using a 3D measurement software (Inspect 2019, GOM) and a best-fit algorithm, and the accuracy (trueness and precision) of the preparation types of the scanning data was evaluated for positive and negative deviations separately. All data were subjected to univariate analysis of variance using SPSS version 24 (IBM). Results: Mean (± SD) positive deviations ranged from 4.6 ± 0.7 μm (TR, veneer) to 25.9 ± 2.4μm (OC, full crown). Mean negative deviations ranged from -7.2 ± 0.6 μm (TR, veneer) to -26.4 ± 3.8 μm (OC, full crown). There were significant differences (P < .05) in terms of trueness and precision among the different IOSs and preparation geometries. Conclusion: The transfer accuracy of simple geometries was significantly more accurate than those of the more complex prosthetic geometries. Overall, however, the IOSs used in this study yielded results that were clinically useful for the investigated preparation types, and the mean positive and negative deviations were in clinically acceptable ranges.

Purpose: To evaluate the failure load of 3D-printed denture resin material and teeth before and after dynamic loading. Materials and methods: A total of 40 specimens were fabricated following ISO/TS 19736 and were divided into two equal groups. In the test group, the cylindrical base and denture teeth were 3D printed separately and then luted together. In the control group, the specimens were fabricated from conventional heat-cured polymethyl methacrylate (PMMA) and commercially available denture teeth using the compression-molding technique. Ten specimens from each group were subjected to dynamic load of 50 N for 250,000 cycles in a chewing simulator. All specimens were subjected to static load of 50 N using Instron machine with a crosshead speed of 1 mm/minute until fracture. The fractured surfaces were analyzed using field emission scanning electron microscopy. The failure loads were calculated and compared using analysis of variance (P < .05). Results: All specimens survived the loading, undergoing 250,000 cycles without fracture. The mean failure load was influenced by fabrication technique and was significantly higher for the 3D-printed test group (P = .028). 3D-printed teeth showed a mixed mode of fracture, whereas in the control group, the specimens showed cohesive fracture within the teeth. Conclusion: The fabrication technique has an influence on the mode of failure between acrylic teeth and resin base material. Cohesive failure in teeth was predominant in the conventional group, suggesting possibly higher bond strength between the teeth and resin base in this group. The observed failure modes reveal that both fabrication techniques exhibited satisfactory bond strength. Chewing simulation did not significantly influence the bond strength of any of the tested groups.

Purpose: To investigate the impact of high-speed sintering on the accuracy (trueness and reproducibility) and fit of 4Y-TZP full-coverage single-unit fixed dental prostheses (FDPs) and three-unit FDPs. Materials and methods: Single-unit FDPs, conventional three-unit FDPs, and cantilever three-unit FDPs (N = 108; n = 12 per subgroup) were fabricated from: (1) high-speed sintered (1,580°C, about 20 minutes) multi-layer 4Y-TZP (Zolid RS, Amann Girrbach; ZMLH group), as well as two conventionally sintered (1,450°C, about 10 hours) materials: (2) multi-layer 4Y-TZP (Zolid Gen-X, Amann Girrbach; ZMLC group) and (3) monochrome 4Y-TZP (Ceramill Zolid HT+ PS, Amann Girrbach; ZMOC group). All specimens were scanned. Trueness, reproducibility, and fit were measured with 3D analysis software. For data analysis, Kolmogorov-Smirnov, Kruskal-Wallis, and Mann-Whitney U tests were performed (α = .05). Results: Three-unit FDPs made from ZMLH presented a deterioration of accuracy in comparison to ZMLC (P ≤ .001 to .008). The influence of highspeed sintering on marginal and general fit was not clinically relevant (P = .154 to .877). Conclusion: High-speed sintering influenced the accuracy of 4Y-TZP full-coverage single-unit and three-unit FDPs. However, no clinically relevant impact on fit was observed.

Purpose: To investigate the influence of different cleaning methods for additively manufactured fixed dental prostheses (FDPs) for long-term temporary use on the degree of conversion (DC), surface roughness, Martens parameters, and biaxial flexural strength. Materials and methods: A total of 180 specimens per material (3Delta Etemp, DeltaMed; Freeprint Temp, Detax; Temp PRINT, GC Europe; Temp C&B and C&B MFH, NextDent; N = 180) were additively manufactured (D20 II, Rapid Shape) and subsequently cleaned by different methods: by rinsing for 5 minutes in acetone (Höfer Chemie; 99.5%); butyl glycol (Algin Chemie; 100%); ethanol (Otto Fischar; 96%); isopropanol (SAV LP; 100%); Yellow Magic 7 (Bradley Systems; 100%); or by applying centrifugal force for 4 minutes (n = 30 per subgroup). After postpolymerization (Otoflash G171, NK-Optik), the DC was measured using Raman spectroscopy, and the surface roughness, as well as the Martens parameters, were recorded. Biaxial flexural strength was investigated after artificial aging (thermocycling for 10,000 cycles). Data were statistically analyzed (Kolmogorov-Smirnov, Kruskal-Wallis, and Mann-Whitney U tests, and Pearson correlation coefficient). Results: The highest DC was recorded after the use of butyl glycol or isopropyl (P < .001 to P = .047). The highest surface roughness was measured after the use of butyl glycol (P < .001 to P = .024). The use of centrifugal force or Yellow Magic resulted in the highest Martens parameter values (P < .001 to P = .036) and the highest biaxial flexural strength (P < .001 to P = .013), while acetone and butyl glycol led to the lowest values. Conclusion: The use of centrifugal force and Yellow Magic resulted in the highest Martens parameter values and the highest biaxial flexural strength. Concerning Yellow Magic, no negative effect on the mechanical properties was observed. The 3Delta Etemp material especially was prone to degradation after chemical cleaning.

Purpose: To evaluate the effectiveness of nonthermal atmospheric plasma (NTAP) and priming on the shear bond strength (SBS) of a resin cement to two zirconia ceramics after 24 hours and 1 year of water storage. Materials and methods: A total of 120 plates (9 x 7 x 2 mm) were obtained from two types of zirconia (Katana, Kuraray Noritake; and ZirCAD, Ivoclar Vivadent) plates randomly divided into 12 groups (n = 10 each). Zirconia ceramic plates were submitted to the following treatments: (1) untreated (control); (2) treated with ZPrime Plus (Bisco Dental) primer; (3) NTAP (Surface Plasma Tool Model SAP, Surface Engineering and Plasma Solution) application for 10 seconds; (4) NTAP for 30 seconds; (5) NTAP for 10 seconds followed by priming; and (6) NTAP for 30 seconds followed by priming. Two silicone molds (2.37-mm diameter x 2-mm height) were positioned on the treated surface of each zirconia plate, and the resin cement (Panavia F 2.0, Kuraray Noritake) was manipulated and inserted into the molds. After light activation, two resin cement cylinders (specimens) were obtained from each plate. One specimen was tested after 24 hours, and the other after 1 year. The shear load was applied to the base of the resin cement cylinders until failure. Data were analyzed using three-way ANOVA and post hoc Tukey test (α = .05). Results: NTAP application alone (groups 3 and 4) increased SBS compared to the control group only at 24 hours. After 1 year, the NTAP/primer combination showed higher SBS than the other groups. Water storage for 1 year reduced the bond strength for all groups. Conclusion: NTAP, combined or not combined with primer, had a beneficial effect on adhesion after 24 hours and after 1 year. Water storage negatively influenced the adhesion in all groups.

Purpose: To compare the flexural strength and flexural modulus of soft liner-retained overdentures to ball-and-socket-retained overdentures, as well as to evaluate the effect of using glass fiber as a reinforcement material for soft liner-retained overdentures on such mechanical properties. Materials and methods: A total of 80 overdenture specimens were fabricated and divided equally into four groups (n = 20 each): specimens with a metal matrix (group 1); a silicone soft liner matrix (group 2); reinforced with one bundle of unidirectional glass fiber sticks placed above the silicone soft liner matrix (group 3); and reinforced with four layers of bidirectional Stick Net glass fiber weaves placed above the silicone soft liner matrix (group 4). Half of the specimens from each group were stored in water at room temperature (23°C ± 1°C) for 24 hours, while the other half were stored in water at 37°C for 30 days before being subjected to a static 3-point loading test. Results: After 1 day of water storage, the flexural strength and flexural modulus values of groups 1, 3, and 4 were not significantly different from each other (P = .788, P = .084), but were significantly higher than group 2 (P < .05). Water storage for 30 days significantly decreased the flexural strength and modulus values of group 1 only (P < .001) and not the other three groups (P >.05). Conclusion: After 30 days of water storage, the flexural strength and flexural modulus values of overdentures retained with a metal housing were not significantly different from those of overdentures retained with a silicone soft liner housing. Placing uni- and bidirectional glass fiber reinforcement above soft liner matrices increases the fracture resistance of a soft liner-retained overdenture.

Purpose: To conduct a systematic review to evaluate the influence of materials and surfaces used for dental implant abutments on the proliferation of human gingival fibroblasts. Materials and methods: The focus question of this review was: Which material/surface characteristics used for dental implant abutments influence/enhance proliferation of human gingival fibroblasts? The Medline/PubMed, Embase, and Cochrane Library databases were searched using "gingiva," "fibroblasts," "proliferation," and "dental implant abutments" as main keywords with AND/OR as Boolean operators. In vitro studies reporting 3 to 4 or 6 to 7 days of cell proliferation, surface hydrophilicity, and roughness were included. A quality assessment of the selected studies was performed using the web-based Science in Risk Assessment and Policy (SciRAP) tool. Results: The search identified 1,144 studies, and 44 were eligible for inclusion. The average reporting quality SciRAP score was 82.87 ± 10.68, and the average methodologic quality SciRAP score was 87.35 ± 10.55. Machined, polished, and coated titanium and zirconia surfaces were most commonly investigated. Several studies analyzed aluminum oxide, cobalt-chrome-molybdenum alloy, lithium disilicate, polyether ether ketone, polymer-infiltrated ceramic network, and bioglass. The best cell proliferation was observed on zirconia and on titanium harboring nanotubules or microgrooves. UV treatment, polydopamine, and nitride coatings also improved cell proliferation. Due to the heterogeneity of the data, no correlation could be established between cell profileration and surface hydrophilicity or roughness. However, surface roughness in the range of R_a = 15 to 145 nm and Sa = 19 to 500 nm on titanium and zirconia proved most suitable. Conclusion: Titanium surfaces with directional guidance patterning and zirconia surfaces best supported cell proliferation during the first week of cell culture. Lack of standardization in surface definitions (machined or polished), methodology, and reporting prevented analytical comparison and should be imposed in future studies.

Purpose: To describe a digitally designed device for improving esthetic and occlusal planning for full-arch implant-supported rehabilitations. Materials and methods: A step-by-step clinical and technical protocol is described to obtain an esthetic rim. Alternatives in terms of design and case requirements and the clinical use of the device are also described. Results/conclusion: An integral approach based on esthetic and functional needs is mandatory in full-arch restorations. The proposed device can improve teamwork and communication, minimizing possible errors. Future proposals are needed to achieve a fully digital protocol in the fabrication of these rehabilitations.