Journal of Advanced Prosthodontics最新文献

Purpose: This study aimed to evaluate the effects of fatigue and misfit on the reverse torque, load-bearing capacity, and failure modes of cemented and screw-retained two-implant-supported fixed dental prostheses (FDPs).

Materials and methods: Eighty CAD-CAM zirconia frameworks with porcelain veneering were assigned to three groups based on engaging (E) and non-engaging (N) abutment configurations: N-N, N-E, and E-E. Misfit scenarios included a control cast and 100 µm horizontal or vertical misfits. Frameworks were mounted on implants as screw-retained or cement-retained 3-unit FDPs, forming seven test groups and one control group (n = 10). Reverse torque was measured before and after thermomechanical cycling, followed by maximum failure load (Fmax) testing and failure mode analysis. Fmax was evaluated using two-way ANOVA, and reverse torque using mixed-effects ANOVA accounting for engagement, misfit, and implant position (α = 0.05).

Results: No significant differences in Fmax were observed across zirconia specimen groups or engagement configurations under various misfit conditions (P > .05). Engagement configuration did not significantly impact fracture strength or reverse torque (P = .421). A significant difference was found in the horizontal misfit group compared to controls (P < .001). Reverse torque values differed between distal (13.5 ± 0.5 Ncm) and mesial implants (18.6 ± 0.5 Ncm) (P = .000), suggesting distal implants may be more prone to preload loss and mechanical issues.

Conclusion: The engagement configuration of implants did not significantly affect reverse torque, fracture strength, or failure modes of cemented and screw-retained restorations, although horizontal misfit reduced load-bearing capacity.

Purpose: This study evaluated the clinical efficiency and geometric fidelity of the library-selected anatomical prefabricated abutments (LAPA) compared with custom abutments (CA) and stock abutments (SA) by using a novel sector-based deviation analysis (SBDA) method.

Materials and methods: Two posterior single-implant cases, the mandibular left first molar and right second premolar, were selected for in vitro analysis. Twenty-four dental professionals (15 prosthodontic residents and 9 board-certified prosthodontists) performed three tasks: CA design, LAPA selection, and SA selection. The recorded time required for CA design and LAPA selection was compared. Overall geometric conformity was assessed using in-tolerance analysis (± 0.50 mm, ± 0.70 mm), and margin-level fidelity was evaluated by sector-based and vector-based deviation analyses. The Wilcoxon signed-rank test was used to evaluate the clinical efficiency and geometric fidelity at a significance level of α = 0.05.

Results: LAPA required significantly less design time than the custom abutment (CA) (P < .001). Both LAPA and SA showed high overall conformity to CA within clinically acceptable limits. Sector- and vector-based analyses demonstrated that LAPA more closely replicated CA margin positions than SA, indicating superior morphological consistency with greater time efficiency.

Conclusion: Within the limitations of this in vitro study, the library-selected anatomical prefabricated abutment showed a balanced performance between clinical efficiency and morphological fidelity.

Purpose: This prospective clinical study aimed to evaluate the accuracy of intraoral scanning (IOS) as an alternative to the conventional window technique impression (WTI) for recording maxillary flabby ridges in edentulous patients.

Materials and methods: Twelve edentulous participants with maxillary flabby ridges underwent both IOS (TRIOS 5, 3Shape, Denmark) and WTI. WTI impressions were made using zinc oxide-eugenol paste and plaster of Paris as the reference. All scans were exported in STL format. Accuracy was assessed via trueness and precision, using RMS, average negative, and average positive deviations, calculated with Medit Compare software.

Results: IOS showed significantly higher trueness than WTI in RMS (mean difference (MD) = -0.11, 95% CI: -0.15 to -0.06, P = .0001) and average negative deviation (MD = 0.13, 95% CI: 0.07 to 0.19, P = .0001). The average positive deviation had no significant difference (MD = 0.02, 95% CI: -0.01 to 0.05, P = .11). In terms of precision, IOS had significantly higher precision across all parameters: RMS (MD = 0.23, 95% CI: 0.21 to 0.26, P = .0001), average positive deviation (MD = 0.14, 95% CI: 0.11 to 0.17, P = .0001), and average negative deviation (MD = -0.15, 95% CI: -0.17 to -0.13, P = .0001).

Conclusion: This study suggests that IOS may provide improved accuracy compared to the conventional window impression technique for capturing maxillary flabby ridges in edentulous patients. Further research with larger sample size and clinical outcome assessments is needed to confirm its efficacy.

Purpose: This study aimed to investigate the effects of blank position and thermo-mechanical aging on the fracture force of strength-gradient multilayer (SGM) zirconia crowns.

Materials and methods: Eighty premolar SGM zirconia crowns (KATANA™ Zirconia YML) were assigned to eight groups (n = 10), based on four blank positions (1, 2, 3, and 4 mm below the top edge) and two conditions (with and without thermo-mechanical aging). Aging simulated five years of clinical service through 6,000 thermocycles (5℃ - 55℃) and cyclic fatigue (50 N, 1.2 Hz, 1,200,000 cycles). Fracture force was measured using a universal testing machine. Failure modes and fractographic features were examined. Data were assessed using two-way ANOVA, Bonferroni post hoc tests, independent t-tests, and Spearman correlation (P < .05).

Results: Fracture force was significantly influenced by both blank position and thermo-mechanical aging. Crowns from the 1 - 2 mm regions demonstrated significantly lower fracture force and more severe failure modes (Types I - V), while those from the 3 - 4 mm regions showed significantly higher fracture force and milder modes (Types I - III). Thermo-mechanical aging reduced fracture force in all groups, supported by fractographic analysis. A strong negative correlation existed between position depth and failure severity.

Conclusion: Both blank position and thermo-mechanical aging significantly affected fracture force and failure behavior. Lower blank positions provide better mechanical performance and are recommended for posterior restorations. Conversely, upper blank positions-offering improved translucency-are suitable for anterior restorations where esthetics are prioritized. These findings offer clinically relevant guidance for optimizing strength and appearance in zirconia crown fabrication.

Purpose: Accurate planning for occlusal vertical dimension (OVD) increase is crucial for prosthodontic success. This study evaluates the effects of different OVD increase amounts (2 mm or 5 mm), methods (articulator-based or intraoral) and virtual facebow use on occlusal contacts.

Materials and methods: Twenty-one individuals were initially recruited; three dropped out, leaving 18 participants. Digital impressions, bite records in maximum intercuspal position (MIP) and facial scans were obtained. Each participant received eight occlusal splints, varying by OVD increase method, amount and facebow use. Centric relation contacts and MIP were recorded using articulator paper and a scannable bite material. These scans were superimposed with Group D (2 mm intraoral increase without facebow) serving as the reference baseline. Deviations in the X (lateral), Y (anteroposterior) and Z (superoinferior) directions were analyzed using non-parametric tests with Bonferroni correction for pairwise comparisons.

Results: No significant deviations were observed in the X-direction. However, significant deviations occurred in the Y and Z-directions in certain groups, particularly with a 5 mm intraoral increase. Effect size analysis indicated that most Y-direction differences were minor, whereas Z-direction deviations at higher OVD increases were more clinically relevant.

Conclusion: Regardless of the method, increasing the OVD by 2 or 5 mm and using a virtual facebow did not significantly affect the number of occlusal contacts. However, spatial deviations of contacts were detected, with articulator-based 5 mm increase producing fewer deviations than intraoral methods. Within the limitations of this study, the virtual facebow did not substantially reduce deviations.

[This corrects the article on p. 292 in vol. 17, PMID: 41180326.].

Purpose: The aim of the present study was to evaluate whether the accuracy of digital definitive implant casts is affected by both the process of best fit (BF) alignment of the scan bodies (SBs) with the CAD library and the type of scanner used.

Materials and methods: Scans of the upper and lower arches of a totally edentulous patient, each with eight implants, were performed using the Trios-3 (T) and True-Definition (TD) intraoral scanners and the Identica-Light extraoral scanner (EO) for casts. Two types of alignment of the SB with the CAD implant library were performed, using either 3/3 or 1/3 of its mesh. Twelve virtual definitive implant casts were generated, each with a designed prosthetic bar. Analysis included absolute differences in 28 inter-implant distances and 7 relative angles of the bar implant abutments.

Results: Descriptive statistical analysis was carried out, including the calculation of means ± standard deviations and maximum and minimum values for both distances and angles.

Conclusion: In conclusion, the accuracy of digital definitive casts with multiple implants was influenced by both the amount of mesh selected in the SBs during the BF alignment with the CAD library and the optical impression system used.

Purpose: This study aimed to compare the marginal adaptation and fracture strength of monolayered and multilayered monolithic zirconia crowns fabricated at three distinct milling depths.

Materials and methods: Eighty-four epoxy resin dies of prepared premolars were fabricated. Crowns were designed in software and milled from two monolayered zirconia materials [3Y-TZP (VITA YZ HT)(3-VYZ) and 4Y-TZP (Priti^®multidisc ZrO₂ Extra Translucent)(4-ET)], three multilayered zirconia materials [3/5Y-TZP (IPS e.max ZirCAD Prime)(3/5-ZP), 4/5Y-TZP (IPS e.max ZirCAD Prime Esthetic)(4/5-ZPE), and 4/5Y-TZP (Priti^®multidisc ZrO₂ Multi Translucent Plus)(4/5-MTP)], at three milling depths [above (A), center (C), below (B)], and a zirconia-reinforced lithium silicate glass ceramic block (VITA Suprinity)(VS) (n = 7). After sintering and glazing, marginal gaps (MG) were measured using silicone replica technique. Crowns were cemented with dualcure resin (SpeedCEM Plus, Ivoclar Vivadent), subjected to 5000 thermal cycles. Fracture strength (FS) test was performed perpendicularly to occlusal surface at 1 mm/min. Data were analyzed (SPSS 26, one-way ANOVA, Tukey post-hoc tests, P = .05), and fracture types were classified. SEM analysis was performed on representative specimens.

Results: MG differences among groups were insignificant (P > .05). The highest FS values were observed in 3-VYZ (1587.14 ± 228.26 N), 3/5ZP-B (1537.28 ± 268.81 N), and 4-ET (1364.86 ± 196.98 N) (P > .05). The lowest FS values were found in VS (483.86 ± 47.10 N)(P > .05). B-positioned multilayered crowns exhibited numerically higher FS than A or C positions.

Conclusion: Monolayered (3Y-TZP and 4Y-TZP) or multilayered 3/5Y-TZP zirconia milled from below layer may be preferred for posterior region, whereas multilayered 3/5Y-TZP milled from upper layer and all configurations of multilayered 4/5Y-TZP may be more suitable for anterior.

Purpose: The aim of the present study was to assess the influence of various implant angulations, camera positions and number of implant references on the accuracy of a photogrammetry device for complete arch implant prostheses.

Materials and methods: 2 edentulous models, one with 6 parallel implants (PM) and other with 6 angled implants (AM), underwent digitalization with a coordinate measuring machine (CMM) to establish a reference standard. Both models underwent 20 impressions with 2 different camera positions and 3 different implant references, with a total of 240 impressions. Euclidean linear and angular measurements were obtained on the reference cast and each experimental scan and compared. Absolute (n) and relative frequencies (%) of true and precise measurements at 95% confidence intervals (CI) were calculated. Chi-squared tests were used to assess differences in trueness and precision between these factors.

Results: 3660 distances and 1440 angles were analyzed for trueness. The absolute difference was 54 ± 46 µm and 0.341 ± 0.301°. Precision was 18 ± 23 µm from 68400 measured distances and 0.048 ± 0.074° for the 22800 angulations measured. Statistically significant differences (P < .05) were identified between PM and Am, A1 and A2 and number of references in both distances and angulations for trueness and precision.

Conclusion: Implant angulations, camera positions and number of implant references used affected the precision and trueness of Precise Implant Capture (PIC) system. However, these differences did not show clinically relevant values.

Purpose: This study aimed to assess the osseointegration effects of niobia-modified yttria-stabilized tetragonal zirconia ((Y,Nb)-TZP) implants, compared to titanium implants and 3 mol% yttria-stabilized tetragonal zirconia (3Y-TZP) implants in a rabbit tibia model.

Materials and methods: Sandblasted (Y,Nb)-TZP implants (YNb), sandblasted and acid-etched titanium implants (SLA), and smooth-surface 3D-printed 3Y-TZP implants (3Y) were prepared. Surface characteristics of the specimens were evaluated using scanning electron microscopy and confocal laser scanning microscopy. Implants were inserted into the tibiae of 16 rabbits, with eight rabbits euthanized at each time point (2 and 6 weeks). To estimate periodic bone remodeling, tetracycline and xylenol orange were administered to the rabbits euthanized at 6 weeks. Undecalcified specimens were prepared to measure the periodic bone remodeling ratio (PBR), bone-to-implant contact (BIC) and bone area (BA). Data analysis was conducted using one-way ANOVA with Bonferroni post hoc analysis and the Wilcoxon signed-rank test at a significance level of 0.05.

Results: At both the 2-week and 6-week intervals, YNb group exhibited significantly higher BIC values than the SLA and 3Y groups. No significant differences (P > .05) were found in PBR and BA across all comparisons.

Conclusion: Sandblasted (Y,Nb)-TZP implants indicated superior osseointegration in comparison to SLA titanium and smooth-surface 3D-printed 3Y-TZP implants. The enhanced osseointegration observed in this study supports the clinical potential of (Y,Nb)-TZP as a next-generation zirconia implant material.