Journal of Advanced Prosthodontics最新文献

Purpose: The purpose of this in vitro study was to evaluate how variations in scan body geometry, specifically body height and the length of the flat indexing surface (FIS), affect linear and angular accuracy when combined with truncated or full-geometry library files.

Materials and methods: Nine scan body geometries were fabricated by combining three body heights (4, 5, and 6 mm) with three FIS lengths (1, 2, and 3 mm). Digital impressions were superimposed onto truncated or full-geometry library files. Linear deviation (ΔD) and angular deviation (ΔA) were calculated by comparing aligned scan bodies with coordinate measuring machine references. Linear and angular deviations were compared between library types using the Mann-Whitney U test, and differences among body heights and FIS lengths were evaluated using the Kruskal-Wallis test with Dunn's post-hoc test (α = .05).

Results: Linear deviation remained within a comparable range, and most geometry-library comparisons did not show a significant difference from body height, FIS length, or library morphology (P > .05). Angular deviation demonstrated geometry-dependent behavior, increasing only in the 4-mm body paired with larger FIS lengths, particularly when full-geometry libraries were used. No significant angular differences were observed in the 5-mm or 6-mm body groups.

Conclusion: Digital implant registration remained stable across most configurations. Shortened scan bodies performed reliably when FIS dimensions were preserved. Angular accuracy was more sensitive to geometry-library interactions, with truncated libraries improving stability.

Purpose: This study aimed to compare the wear depth and volume loss of 3D-printed resin denture teeth with prefabricated and milled acrylic denture teeth under chewing simulation.

Materials and methods: Four groups of denture teeth (n = 9) were evaluated: prefabricated acrylic teeth (PT), milled acrylic teeth (MT), 3D-printed methacrylate-based resin teeth (3DT), and glazed 3D-printed resin teeth (3DT+G). Samples were embedded in self-curing resin, and antagonists were fabricated from the same materials. A chewing simulator was utilized to apply a cyclic occlusal load of 49.05 N (5 kg) for 120,000 cycles in distilled water. Wear depth (µm) and volume loss (mm³) were measured using a 3D laser profilometer. Surface morphology was qualitatively analyzed via scanning electron microscopy (SEM). Data normality was verified, and statistical significance was determined using one-way ANOVA followed by Tukey's HSD test (α=0.05).

Results: Significant differences in wear depth and volume loss were observed among the groups (P < .05). No significant differences were found between PT and MT, or between 3DT and 3DT+G. However, the 3DT and 3DT+G groups exhibited significantly lower wear depth and volume loss compared to the PT and MT groups (P < .05). SEM analysis revealed that the PT group displayed a more uniform and homogenous surface morphology compared to the other groups, while 3DT+G showed evidence of glaze depletion within the wear facets.

Conclusion: 3D-printed resin denture teeth demonstrated superior wear resistance compared to prefabricated and milled alternatives under simulated chewing conditions. Furthermore, the application of a 50 µm surface glaze did not significantly enhance wear resistance of the 3D-printed resin.

Purpose: This study aims to evaluate how the fit between implant-abutment connection surfaces and the proximal contact tightness of crowns affect abutment screw loosening.

Materials and methods: Forty implants with internal hex connections were placed in stainless steel models in the maxillary right first molar region. Monolithic zirconia crowns with standard and 15 µm reduced proximal contacts were used with abutments with standard and 25 µm horizontally reduced hex connections. After cementation, four groups of specimens-standard abutment/standard proximal contact (control), reduced fit abutment/standard proximal contact (RS), standard abutment/reduced proximal contact (SR), and reduced fit abutment/reduced proximal contact (RR)-were subjected to simultaneous thermocycling (± 5 - 55℃) and chewing cycles (100 N, 1.6 Hz, 40 mm/sec lateral and vertical speed, lateral movement: 6 mm, vertical movement: 0.5 mm). Removal torque values (RTVs) were measured using a digital torque meter. Data were analyzed using two-way ANOVA and the Bonferroni test (α = .05).

Results: All groups exhibited statistically significant differences compared to each other and the control group (P < .05). The RR group had the lowest removal torque values (RTVs) (21.70 ± 0.99 N·cm), while the control group had the highest (26.82 ± 0.70 N·cm). The RS group (24.78 ± 0.89 N·cm) had lower RTVs than the SR group (25.51 ± 0.52 N·cm).

Conclusion: The findings indicate that inadequate proximal contacts and horizontal misfit of the implant-abutment connection may lead to torque loss and screw loosening.

Purpose: This study evaluated the fracture resistance of premolar screw-retained implant-supported hybrid abutment crowns (HACs) fabricated from different monolithic restorative materials following artificial aging.

Materials and methods: Forty-four titanium implant analogs were restored with HACs fabricated from four materials: 5 mol% yttria-partially stabilized monolithic zirconia (ST), strength-gradient multilayered zirconia (YM), lithium disilicate ceramic (LD), and resin composite containing dispersed nanoparticles (CM) (n = 11 per group). All specimens were subjected to thermocycling (10,000 cycles) and mechanical loading (1.2 million cycles) to simulate 5 years of clinical service. Fracture resistance was evaluated under compressive loading, and failure modes were analyzed using optical microscopy and scanning electron microscopy. Statistical analysis was performed using the Kruskal-Wallis and Steel-Dwass tests (α = 0.05).

Results: Significant differences were found among all groups (P = 0.00033-0.0022). The YM group exhibited the highest median fracture resistance (2.06 kN, IQR: 2.00 - 2.60 kN), followed by ST (1.74 kN, IQR: 1.69 - 1.80 kN), LD (1.29 kN, IQR: 1.14 - 1.41 kN), and CM (0.87 kN, IQR: 0.79 - 0.92 kN). All specimens survived the artificial aging protocols. Distinct fracture patterns were observed depending on the restorative material, with zirconia-based groups showing more favorable resistance than resin composite.

Conclusion: All tested HACs exhibited fracture resistance values exceeding maximum bite forces, supporting their clinical applicability. Strength-gradient multilayered zirconia demonstrated superior reliability after simulated 5-year aging, emphasizing its structural advantage and broader safety margin compared with other restorative materials.

Purpose: This study aimed to evaluate the influence of implant placement depth on the accuracy of five full-arch digital impression techniques: 2 photogrammetry systems (Imetric [PGI] and Oxo Core [PGO]) and 3 intraoral scanning (IOS) routes (standard IOS, IOS with crown-shaped [IOS+C], and IOS with laterally-extending [IOS+LE] scanning aids).

Materials and methods: Three master models including 5 implants with 2-, 4-, and 6-mm subgingival implant depths were fabricated. Implant positions were recorded using each of the 5 techniques (n = 15). The resultant scans were compared to reference data generated by a laboratory scanner. Deviations were 3-dimensionally assessed using root mean square values to quantify both trueness and precision. Angular deviations (AD) were calculated to provide a detailed assessment of spatial inconsistencies. Data were statistically analyzed (α = 0.05).

Results: Implant depth and impression technique, as well as their interaction, significantly affected trueness, precision, and angular deviation values (P < .001). PGI demonstrated the highest accuracy, with the lowest mean AD values across all implant positions (0.24 - 0.32°) and the highest trueness (26.57 µm) and precision (7.72 µm). IOS exhibited the largest distortions, with AD values up to 1.77° and trueness values of 74.84 µm. Precision of both photogrammetry systems were not influenced by implant depth.

Conclusion: Implant depth significantly impacts the accuracy metrics of full-arch digital impressions. The Imetric system outperformed the other groups. Since laterally-extending scanning aids effectively improved accuracy, it may be recommended as a clinically viable alternative to standard IOS.

Purpose: The purpose of this study was to evaluate the interrelationships among the determinants of Hanau's Quint - condylar guidance, occlusal plane, compensating curve, incisal guidance, and cusp height - according to the laws of articulation, using a novel digital method.

Materials and methods: Fully edentulous casts with 9 sets of occlusion rims (7, 8, and 9 inches curvature; standard, +5°, and -5° inclination) were mounted on a semi-adjustable articulator to simulate analog experimental conditions (AECs). The same settings were reproduced in a 2-dimensional virtual articulator in a lateral view (Adobe Photoshop), with the addition of cusp height as a variable, to generate digital experimental conditions (DECs). Whenever an increase in one determinant produced occlusal disharmony, other factors were modified until bilateral balanced occlusion (BBO) was reestablished. The results were compared with Hanau's predicted interactions.

Results: Both analog and digital methods demonstrated consistent interrelationships among the occlusal plane, compensating curve, condylar guidance, and incisal guidance, as described in Hanau's Quint. Cusp height, tested digitally, showed a predictable compensatory role.

Conclusion: The interrelationships among the determinants of Hanau's Quint in achieving BBO were validated digitally using a simple and reproducible digital methodology confirmed by an analog articulator. This study may help clinicians better understand BBO and Hanau's principles in complete denture treatment planning.

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.