Journal of Advanced Prosthodontics最新文献

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.

Purpose: Removable partial dentures (RPDs) require metal frameworks for support, stability, and retention. Conventional impression methods are time-consuming and may introduce inaccuracies that affect framework fit. Intraoral scanning (IOS) offers a digital alternative that may improve accuracy and efficiency; however, few studies have quantitatively compared frameworks fabricated using IOS data with those fabricated using conventional methods. This study aimed to compare the accuracy of RPD frameworks fabricated using conventional and IOS-based methods.

Materials and methods: This study included 15 arches from 13 patients requiring RPDs. Each arch received two metal frameworks, one fabricated using the conventional impression method (CON group) and the other using IOS (IOS group). Qualitative evaluations included visual inspection and pressing with a plugger, whereas quantitative evaluations were performed using three-dimensional superimposition and gap measurements at the rest-seat areas. Paired t-tests were used to compare the accuracy, and two-way analysis of variance was used to evaluate the interaction between the fabrication method and tooth position.

Results: All frameworks met the qualitative evaluation criteria. In the quantitative evaluation, the IOS group exhibited a significantly smaller mean gap (201 ± 78 µm) than the CON group (239 ± 83 µm) (P = .015). Furthermore, the IOS group demonstrated significantly greater accuracy, particularly at the terminal abutments of distal-extension RPDs.

Conclusion: Clinically acceptable RPD framework accuracy was achieved in both groups. However, accuracy was significantly better in the IOS group, especially at the terminal abutments of distal-extension RPDs.

Purpose: The biomechanical advantage of selective pressure impressions over mucocompressive techniques remains unclear. This study aimed to determine whether selective pressure techniques offer substantial biomechanical advantage over mucocompressive impressions using clinical computer simulation.

Materials and methods: Two models were analyzed: Model C, with mucocompressive impression tray, and Model S, with selective pressure impression tray with 10-mm diameter circular relief in the midline. Each model included the tray, polyvinyl siloxane (PVS), mucosa, cortical, and cancellous bone. Seven locations were designated, from which the results were analyzed. With a vertical load of 49 N on the palatal area, pressure, von Mises stress, and displacement were evaluated. Statistical analysis was performed using paired-samples t-test and effect size estimation (Cohen's d).

Results: Both models generated mucosal displacement and stress transmission to the underlying structures upon load application. In Location 3, where the relief was placed, Model S exhibited lower pressure, stress, and displacement than Model C, indicating localized force reduction. Conversely, other locations exhibited higher values in Model S than in Model C. Low stress in bone for both trays suggested that tray design had minimal effect on bone. All variations demonstrated small effect sizes (d ≤ 0.2), despite statistical significance (P < .007).

Conclusion: Selective pressure trays modified tissue loading locally at the relief site; however, these did not seem to provide a substantial biomechanical advantage, particularly on bone. Their clinical relevance remains limited and needs further supporting evidence.

Purpose: Material surfaces can influence the biological response of soft tissues, particularly during the early stages of healing and maturation. This study assessed whether the type of surface finish (glazed or polished) of monolithic zirconia single crowns impacts the health of peri-implant soft tissues during the first 6 months of clinical function. Infrared thermography was employed to assess soft tissue conditions.

Materials and methods: This was a prospective, randomized, intra-participant clinical trial. Twenty single crowns, supported by posterior implants, were fabricated in monolithic zirconia using computer-aided design/computer-aided manufacturing. For each crown, the mesial and distal surfaces were randomly allocated to receive either a glazed or a polished surface finish. Data were collected at 7 (T1) and 180 days (T2) following crown placement, using clinical examinations (assessing pain/discomfort, biofilm formation, bleeding, inflammation, and suppuration) and infrared thermography (to record thermogram values in Celsius). The data were analyzed using both descriptive and inferential statistics.

Results: No significant clinical differences in peri-implant soft tissue health were identified between the glazed and polished surface treatments at T1, T2, or across the evaluation period. Infrared thermography revealed a significant decrease in temperature from T1 to T2 for some polished and/or glazed subgroups when comparing the peri-implant mucosal phenotype, dental arch, and tooth regions. However, no significant differences were observed between the polished and glazed groups.

Conclusion: Both glazing and polishing are suitable surface treatments for monolithic zirconia and do not adversely affect peri-implant soft tissue health within 6 months after crown installation. Infrared thermography has the potential to be a complementary tool for the objective evaluation of soft tissue healing.