Journal of Prosthetic Dentistry最新文献

Statement of problem: Acrylic resin denture teeth have been widely used in prosthodontics because of their affordability and ease of fabrication. However, their susceptibility to discoloration over time poses a significant esthetic challenge for denture wearers. Various intrinsic and extrinsic factors influence color stability, yet the impact of material composition and different brands remains inadequately explored.

Purpose: This systematic review and meta-analysis aimed to assess the impact of material composition and different brands of acrylic resin teeth on their color stability.

Material and methods: The PubMed, Scopus, Web of Science, Science Direct, and Cochrane Collaboration databases were analyzed. Studies from 2019 to 2023 on the color stability of acrylic resin denture teeth were assessed, and 11 articles were selected based on specific inclusion criteria.

Results: All the included studies showed that acrylic resin teeth were susceptible to discoloration, with variations by brand and material, influenced by composition, staining agents, and immersion duration. Brands of acrylic resin teeth such as Ivoclar (Ivoclar AG) and SR Orthosit PE (Ivoclar, AG) demonstrated superior resistance to discoloration, while Tritone (Vipi), SR Phonares II (Ivoclar AG), and Z250 (Filtek, 3M ESPE) showed higher color changes in various staining solutions. Polymethyl methacrylate teeth showed discoloration, while the cross-linked polymethyl methacrylate and nanohybrid composite resin formulations offered better color stability. Brands incorporating hydrophobic materials and reinforced polymer matrices generally maintained color stability more effectively over extended immersion time periods.

Conclusions: Material composition and brand significantly affected the color stability of acrylic resin denture teeth. Advanced resin formulations and composite-based materials exhibited improved resistance to discoloration.

Statement of problem: The consistency of the placement force provided by striking friction-locked abutments remains uncertain.

Purpose: The purpose of this in vitro study was to evaluate different strikes and repeated reconnection-disconnection cycles on the connection strength of a locking taper implant system with varying wells.

Material and methods: Sixty-three implant-abutment replica specimens (IARSs) with 2-, 2.5-, and 3-mm wells with a 1.5-degree locking taper design were fabricated from grade 5 titanium (Ti). Specimens were divided into 3 striking groups (3T, 6T, 12T, n=21/group) and 3 well subgroups (3T2, 3T2.5, 3T3; 6T2, 6T2.5, 6T3, and 12T2, 12T2.5, 12T3, n=7/subgroup). For subgroups 3T2, 3T2.5, and 3T3, the abutments were seated in the implants with finger load and then struck 3 times with a calibrated striker. The abutments were then disconnected using rotational movements and the removal torque values were recorded with a digital torque meter in newton centimeter (Ncm). This seating, striking, and removal cycle was repeated 7 times by the same operator. The same procedure was applied to the second and third subgroups with 6 and 12 strikes respectively. ANOVA and post hoc Bonferroni tests were used to analyze the data. Repeated measures ANOVA with the Greenhouse-Geisser correction was applied when the sphericity assumption was violated (α=.05).

Results: Removal torque values varied significantly with well diameter and the number of strikes (P<.001), peaking at 3 mm with 12 strikes. Torque values were statistically similar after repeated disconnection-reconnection cycles (P>.05).

Conclusions: Although wider wells and higher striking cycles tended to increase the removal torque and repeated disconnection-reconnection tended to decrease it, the values remained statistically similar.

Statement of problem: The nasal prosthesis is an artificial solution to the restoration of tissue in the nasal region, traditionally requiring time-intensive manual sculpting directly on the patient's face. Whether a novel, automated approach using Convolutional Neural Networks (CNNs) can reconstruct the nasofacial region from 2-dimensional (2D) photography is unclear.

Purpose: The purpose of this study was to evaluate whether the automated approach could generate 3-dimensional (3D) models suitable for direct 3D printing.

Material and methods: The Residual U-Net architecture was trained on a dataset derived from CelebA-HQ comprising 12 000 image pairs (input images with trapezoidal masks and corresponding mask-free output images). The dataset's normalized and square-aligned images facilitated efficient training, with the masked area prioritized during reconstruction through weighted loss functions. The model's performance was evaluated using Peak Signal-to-Noise Ratio (PSNR).

Results: Accurate reconstruction of nasal geometries that harmonized well with the overall facial structure were demonstrated. Visual assessments confirmed the approach's effectiveness, although minor limitations such as inconsistent texture modeling were observed under nonideal conditions. Beyond technical validation, this automated solution should reduce laboratory and clinical time requirements, minimizing patient travel and emotional stress and enhance accessibility to personalized prosthetic care. By leveraging advancements in CNNs and image-to-3D model conversion and manufacturing techniques, this approach offered a suitable path toward automating the creation of nasal prostheses.

Conclusions: This work represents a significant step toward automating the creation of nasal prostheses, enabling faster, more cost-effective, and patient-friendly solutions for patients with midfacial deficiency.

Statement of problem: Airborne-particle abrasion and tribochemical silica coating are well established as surface treatments to enhance the metal-ceramic bond strength of cobalt chromium (Co-Cr) alloys, but nanosecond ytterbium fiber and femtosecond Ti:sapphire laser texturing have been proposed as alternatives. However, their effects on the metal-ceramic bond strength, surface roughness, and surface chemistry of selective laser melted Co-Cr frameworks have not been directly compared.

Purpose: The purpose of this in vitro study was to compare, on selective laser melting Co Cr frameworks, the effects of airborne-particle abrasion, tribochemical silica coating, nanosecond ytterbium fiber laser texturing, and femtosecond Ti:sapphire laser texturing on metal-ceramic bond strength and to relate bond strength to surface roughness (Ra, Rz) and surface elemental composition using energy-dispersive X-ray spectroscopy (EDS).

Material and methods: Fifty-two selective laser melting Co-Cr bars were randomly allocated to 4 surface treatment groups: airborne-particle abrasion (APA) with 110-µm Al₂O₃, tribochemical silica coating (TC), nanosecond ytterbium fiber laser (NS), and femtosecond Ti:sapphire laser (FS). After surface treatment, a feldspathic porcelain was applied, and metal-ceramic bond strength was evaluated using 3-point bending. Surface roughness parameters (Ra, Rz) were measured using contact profilometry, and surface elemental composition was analyzed using EDS. Data were analyzed using parametric and nonparametric tests (α=.05).

Results: Mean ±standard deviation bond strengths (MPa) were 32.0 ±5.2 (APA), 32.6 ±7.2 (TC), 32.7 ±6.0 (NS), and 27.2 ±5.4 (FS). Bond strength was significantly lower in the FS group than in the other groups (P<.05), with no significant differences among APA, TC, and NS (P>.05). NS produced the highest Ra and Rz values, whereas FS produced the lowest Rz. Bond strength showed a weak positive correlation with Rz but no significant correlation with Ra. EDS revealed the lowest oxygen content in the FS group (3.73%) and the highest oxygen and silica contents in the TC group (26.20% and 15.17%, respectively).

Conclusions: On selective laser melting Co-Cr frameworks, airborne-particle abrasion, tribochemical silica coating, and nanosecond laser texturing produced comparable metal-ceramic bond strengths that exceeded the 25-MPa minimum requirement. Femtosecond laser texturing resulted in significantly lower, although still acceptable, bond strength values with the parameters used.

Statement of problem: Despite rapid development in dynamic computer-assisted implant surgery (d-CAIS) registration methods, a systematic comparison of their accuracy and efficiency is lacking.

Purpose: The purpose of this in vitro study was to compare the implant placement accuracy and efficiency of 5 different registration methods in d-CAIS.

Material and methods: A standard partially edentulous mandibular model with a replaceable component for inserting a single implant into a polyurethane foam block was designed. D-CAIS was performed using 5 registration methods (n=12 per group): the standard registration (S), the standard screw registration (SS), the orthodontic screw registration (OS), the tooth cusp registration (TC), and the tooth surface registration (TS). The duration of registration was recorded. A postoperative cone beam computed tomography (CBCT) scan was acquired to evaluate the positional accuracy of the implants. Statistical analysis was performed using the Shapiro-Wilk test, 1-way ANOVA, Kruskal-Wallis test, and Bonferroni-adjusted Spearman correlation (α=.05).

Results: For both platform and apex 3-dimensional (3D) deviations, the TC group showed significantly lower accuracy than the S (P<.001 and P<.001 respectively), SS (P<.001 and P<.001 respectively), and OS (P=.009 and P=.008 respectively) groups, exhibiting 1.5 to 2 times of the mean 3D deviation at the platform level than the S group. No significant difference in the angular deviation was observed among the 5 groups (P=.354). The registration duration of the OS and TC groups was significantly longer than that of the S group (P<.001 and P<.001 respectively), with a median duration of more than 2 minutes.

Conclusions: Caution should be exercised when using the cuspate or surficial registration for d-CAIS because of the increased systematic error. Both standard screw and orthodontic screw registration demonstrated accuracy close to the standard registration.

Creating a natural appearance with proper shade matching is critical for achieving successful esthetic outcomes of dental ceramic restorations. Ceramic materials with high translucency are often preferred when restoring teeth with a normal stump shade. However, ceramic materials with increased opacity, such as zirconia, offer significant advantages when restoring discolored teeth. This video presentation describes 4 different ceramic material options that enable clinicians to effectively mask dark stump shades while maintaining the natural appearance of dental ceramic restorations.

A straightforward technique for a complete mouth rehabilitation under complete isolation using the resin stamp technique and planned and executed using a digital workflow is described. A preoperative scan was recorded under dental dam isolation, ensuring a controlled environment identical to that of the actual procedure and using the same isolation procedures. A virtual diagnostic waxing was designed, followed by the manufacturing of printed clear index guides relined with transparent silicone. For the restorative steps, packable and flowable composite resins were inserted into the relined guide and light polymerized. This technique enabled dental dam isolation, reduced silicone index deformation, and prevented adhesion issues between the printed indices and composite resin material.

Statement of problem: Bruxism (BX) involves repetitive or sustained dental movements by the masticatory muscles, potentially stressing the masticatory system. Despite this, diagnosis remains challenging. Understanding the impact of BX on the stomatognathic system is crucial for improving diagnosis and treatment.

Purpose: The purpose of this clinical study was to evaluate the fractal analysis of and mandibular radiomorphometric indices in panoramic radiographs of individuals with and without possible BX.

Material and methods: Panoramic radiographs and medical records from patients at the Federal University of Ceará's College of Dentistry were analyzed. Fractal analysis was conducted using the box-counting method on regions of interest in the mandible. The mandibular panoramic index, mandibular cortical index, gonial index, antegonial index, mental index, mandibular bone resorption index, mandibular notch index, mandibular condyle height index, and coronoid process index were obtained. The data were analyzed with a 95% confidence level.

Results: In 66 panoramic radiographs (33 with possible BX, 33 without BX), the antegonial index was lower in those with possible BX. Individuals with possible BX also exhibited more wear facets, marked mucosa, and facial fatigue. Fractal analysis values were lower in individuals with possible BX across 3 regions of interest. Statistically significant differences in trabecular bone morphology were observed between groups (P<.05).

Conclusions: Further research is needed to better understand the impact of BX on the stomatognathic system and to assess the applicability of fractal analysis and mandibular indices in evaluating mandibular bone in the panoramic radiographs of individuals with possible BX.