Purpose: This systematic review aimed to investigate and compare peri-implant soft-tissue responses to tooth-colored abutment materials frequently used in implant dentistry.

Study selection: A comprehensive electronic search was performed in three databases (MEDLINE via PubMed, Google Scholar, and Scopus) to identify relevant literature. The study-selection criteria included original research articles written in English that investigated the effects of various tooth-colored abutment materials on peri-implant soft-tissue responses.

Results: In total, 136 articles were included in this systematic review. Tooth-colored abutment materials, particularly zirconia and polyetheretherketone (PEEK), facilitated favorable soft-tissue adaptation, enhanced esthetics, and contributed to long-term implant success. Zirconia demonstrated excellent biocompatibility, enhanced cell viability and attachment, and lower inflammatory responses compared to titanium, suggesting improved soft-tissue integration and reduced biofilm-related risks. PEEK exhibited favorable mechanical properties and biocompatibility but limited cell attachment due to its hydrophobicity, indicating the need for surface modification. Titanium remains the clinical standard for integration but is associated with greater inflammation and biofilm formation than tooth-colored materials.

Conclusions: This review highlights the effects of tooth-colored abutment materials on peri-implant soft-tissue responses and emphasizes the importance of selecting appropriate materials for successful dental implants. Zirconia represents a promising biological alternative to titanium, promoting a stable soft-tissue barrier that contributes to minimizing inflammation and maintaining long-term tissue health. Conversely, while PEEK offers strong mechanical properties, it faces challenges regarding cell proliferation and matrix production, limiting its optimal biological performance. Further research will provide deeper insights into the best options for enhancing patient and esthetic outcomes.

Purpose: This review examined clinical and technological factors that influence implant placement accuracy in computer-assisted implant surgery (CAIS) systems.

Study selection: A systematic search of PubMed, Scopus, and Embase identified English-language studies published between January 2015 and January 2025. The eligible studies included randomized controlled trials, observational studies, systematic reviews, in vitro investigations, and case reports. Data extraction focused on the coronal, apical, and angular deviations. Methodological quality was appraised using the Oxford Centre for Evidence-Based Medicine (CEBM) framework and validated bias assessment tools.

Results: Fifty-three studies were included. Accuracy was influenced by patient-related factors (arch type, bone density, and edentulous span), surgical variables (flap design, operator experience, and guide protocol), and technological parameters (imaging modality, fiducial markers, and calibration). Static systems achieved high accuracy in dentate cases with stable guide support, but were less reliable in posterior or edentulous jaws. Dynamic navigation provided intraoperative flexibility and consistent performance across arches, although outcomes depended on calibration precision and operator learning curves. Robotic-assisted systems achieved the lowest mean deviations through trajectory control and haptic feedback, although evidence remains limited to early clinical and in vitro studies.

Conclusions: Although all CAIS systems achieve high accuracy, their performance varies according to the design of the system and clinical context. Static systems are effective when stabilization is ensured, while dynamic navigation offers adaptable accuracy across scenarios, and robotics exhibit the greatest consistency by reducing operator variability. Further multicenter randomized trials and standardized reporting are needed to strengthen the available evidence and guide clinical selection.

Purpose: This was a prospective study conducted alongside a randomized controlled trial (RCT) that evaluated the incidence of fractures and associated risk factors in single-implant overdentures (1-IOD) compared with two-implant overdentures (2-IOD).

Methods: The participants received either a mandibular 1-IOD or 2-IOD (attachments: Straumann® retentive anchor and elliptical titanium matrix with gold insert; implants: 4.1 mm diameter, Straumann® Standard Plus SLActive® Regular Neck), within the context of a randomized clinical trial. The primary outcome of interest was the incidence of IOD fractures at 5-year follow-up. Prosthetic factors, such as area and cervico-incisal height in the attachment region, and volume at the inter-canine region, were measured. Patient-related factors including age, sex, handgrip strength, manual dexterity, bite force, and chewing performance were assessed. Data analysis included descriptive statistics, bivariate tests, Kaplan-Meier plots, and linear discriminant analysis with log₁₀ transformation for variable normalization.

Results: A total of 47 patients were recruited, and 34 (n = 34, 1-IOD = 16, 2-IOD = 18; mean-age: 63.9 ± 8.6 years; 79.4% women) completed the 5-year follow-up. There were no differences in the incidence of fractures between the 1-IOD and 2-IOD groups (P < 0.05). Fractures were more frequent in younger patients, and reduced cervico-incisal IOD height was significantly associated with fractures (P = 0.040). Linear discriminant analysis predicted fractures with 84.4% accuracy and identified cervico-incisal height and age as key predictors.

Conclusions: There were no significant differences in the incidence of overdenture fractures between groups. Reduced cervico-incisal denture height in the attachment region of ball-retained IODs was associated with mandibular IOD fractures. Further studies with larger cohorts are recommended to identify additional risk factors for mandibular IODs.

Purpose: Evaluation of the impact of ultraviolet (UV) photofunctionalization on titanium–cement interfaces, specifically its ability to transform titanium into a high-energy surface and enhance crown retention.

Methods: Commercial titanium abutments (standard: 4.0 mm; long: 5.5 mm) were treated with vacuum UV (VUV) light at 172 nm for 1 min. Milled polymethyl methacrylate crowns were cemented using resin-modified glass ionomer cement. Tensile testing quantified the maximum tensile load and interfacial energy. Surface changes were analyzed using contact angle measurements and X-ray photoelectron spectroscopy (XPS). Post-failure interfaces were examined via scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX).

Results: UV-treated standard-length abutments exhibited a 4.1-fold increase in maximum tensile load and 27-fold increase in bonding energy compared with untreated control counterparts. UV-treated long abutments showed a 4.6-fold increase in maximum tensile load and 54-fold increase in bonding energy. UV treatment rendered the titanium surface superhydrophilic and low in carbon, whereas untreated specimens remained carbon-rich and hydrophobic. UV-treated long abutments exhibited 3.1-fold higher energy than UV-treated standard abutments. Notably, long abutments without UV treatment did not outperform standard untreated abutments. SEM and EDX confirmed extensive residual cement on UV-treated abutments, indicating cohesive failure and strong interfacial bonding.

Conclusions: A 1-min UV photofunctionalization transforms titanium into a superhydrophilic, high-energy surface that significantly enhances cement bonding. This physicochemical surface strategy outperforms geometric modifications alone. As a rapid, non-invasive approach, UV photofunctionalization may establish a new standard for durable implant-supported restorations, reducing prosthetic failure and influencing both material selection and clinical and laboratory workflows.

Purpose: To clarify the intra- and inter-examiner reliability of an occlusal force-measuring device equipped with a capacitive-type pressure-mapping sensor sheet in older adults.

Methods: Thirty-eight individuals (23 women) aged ≥65 (mean ± SD: 79.3±6.1) years were included. The numbers of present and functional teeth were visually examined. Occlusal force was measured using the Oramo-bf device (Sumitomo Riko Co., Aichi, Japan). To evaluate intra-examiner reliability, one dentist measured each participant’s occlusal force thrice and calculated the intraclass correlation coefficient (ICC; case 1) and the coefficient of variation (CV). To examine inter-examiner reliability, three dentists measured the occlusal force once per participant and calculated the ICC case 2.

Results: The median (first quartile–third quartile [Q1–Q3]) numbers of present and functional teeth were 22.5 (18–27) and 28 (26–28), respectively. The median (Q1-Q3) occlusal force measured by a single examiner across the measurements was 604.8 (261.7–731.5) N. The ICC for a single measurement by one examiner based on all three measurements per participant was 0.982 (95% confidence interval [CI]: 0.969–0.990). The ICC (1,3) for the mean of three repeated measurements by one examiner was 0.994 (95% CI: 0.990–0.997). The mean ± SD CV was 0.052 ± 0.046. The ICC (2,1) for inter-examiner reliability was 0.950 (95% CI: 0.917–0.972).

Conclusions: This study revealed high intra- and inter-examiner reliability of measurements obtained using an occlusal force-measuring device equipped with a capacitive-type pressure-mapping sensor sheet. This device may provide reliable results with a single measurement, regardless of the examiner.

Purpose: This study proposes the development of “Motion-DSD”, an artificial intelligence-assisted workflow for digital smile design (DSD), which enables a dynamic 2-dimensional (2D) simulation of digital diagnostic waxing by transferring an intraoral design onto a frontal facial video, and validates its clinical feasibility.

Methods: A total of 2,000 facial and 190 intraoral images were used to fine-tune the pre-trained neural network, Segment Anything model (SAM), via two sets of low-rank adaptation (LoRA) modules for facial structures and teeth segmentation respectively. A transformation algorithm incorporating a “standard” facial image was developed to align intraoral and facial structures. A Flask-based web user interface (web-UI) was developed for clinical deployment. A participant sample set was prepared to validate the workflow’s performance in a clinical setting.

Results: Two fine-tuned SAMs achieved robust segmentation performance, with a mean Dice score coefficient of 0.886 for the facial dataset and 0.969 for the intraoral dataset. The alignment algorithm effectively transferred the intraoral DSD design onto the participant’s frontal facial video and enabled a 2D simulation of digital diagnostic waxing under various facial expressions, demonstrating its clinical feasibility. The web-UI allows dentists to interactively refine the design and preview simulation results in real time.

Conclusions: Motion-DSD enables the 2D simulation of digital diagnostic waxing from intraoral DSD designs in a dynamic facial context. The workflow overcomes the limitations of static imaging methods and manual alignment, bringing dynamics prior to the physical mockup phase. Further investigations are warranted to quantitatively validate the simulation accuracy and demonstrate its potential advantages over conventional static methods.

Purpose: Conventional handheld pH meters have measurement limitations. Therefore, this study aimed to continuously measure the salivary pH at two intraoral locations using a newly developed sensor system.

Methods: In this pilot study, we developed custom-made intraoral mouthguards (MG) with two pH sensors in the anterior region (Channel 1: Ch1) and the buccal side of the maxillary molar (Channel 2: Ch2) to continuously monitor salivary pH at two different locations in the oral cavity.

Results: The coefficient of determination (R²) for all MG sensor measurements was ≥0.99, with a high level of accuracy. Both sensor channels exhibited similar mean pH values for standard solutions, with small and constant variations. However, notable unstable differences in intraoral measurements were observed during rehydration owing to positional differences. Nonetheless, the MG sensors demonstrated excellent reliability with consistently high Intraclass Correlation Coefficients ranging from 0.977 to 0.999.

Conclusions: This pilot study provides valuable insights into salivary pH fluctuations, particularly during exercise, through continuous measurements using a sensor system for the simultaneous acquisition of real-time data from different anatomical sites. These results emphasize the potential of developing an intraoral sensor system that can detect subtle variations in salivary pH.

Purpose: This study evaluated the wear behavior of dental materials for definitive fixed prostheses, including computer-aided design (CAD)- and manufacturing (CAM) composite resins, polyether-ether-ketone (PEEK), Ag-Pd-Au alloys, titanium, and zirconia, under standardized experimental conditions.

Methods: Three CAD-CAM-produced composite resins (HC, HCH, and CS), PEEK (SPE), Ag-Pd-Au alloys (CW), pure titanium class II (TJ), and zirconia (ZL) were tested. Two-body wear tests were conducted using an abrasion-testing machine under wet conditions using stainless-steel styluses as antagonists. Wear traces were examined using laser confocal scanning microscopy and scanning electron microscopy (SEM). Wear depths and heights were analyzed by one-way analysis of variance with Tukey’s multiple comparison test.

Results: The wear depths of CS and TJ were significantly greater than those of the other materials (P < 0.05), whereas ZL exhibited the lowest wear depth. No significant differences were found among HC, HCH, SPE, and CW. The stylus opposing the SPE exhibited the smallest wear height, whereas TJ caused the most antagonist wear. SEM revealed distinct wear mechanisms, including adhesive and abrasive wear, depending on the material.

Conclusions: The SPE and CW showed similar wear behavior. CAD/CAM composite resins demonstrated variable wear rates, which was likely attributable to variations in the composition and morphology of the constituent fillers. The TJ exhibited excessive antagonist wear, suggesting the need for improved tribological properties. These findings provide guidance for selecting materials that preserve occlusion and prevent excessive wear.

Purpose: To evaluate the trueness of denture bases fabricated using digital light processing (DLP) and milling methods using three-dimensional (3D) models with varying residual ridge morphologies.

Methods: Edentulous mandibular 3D models representing a well-rounded ridge (WR), knife-edge ridge (KR), and flat ridge (FR) were designed using computer-aided design (CAD) software. Denture bases for these models were created using dental CAD software and fabricated via DLP 3D printing at build angles of 0 and 45 degrees (DLP0 and DLP45) and by milling (MIL). A total of 90 denture bases were fabricated, with 10 bases per model–method combination. These bases were digitized and compared to their original CAD data to assess the adaptation across three regions: denture border, alveolar ridge, and retromolar pad. Measurements were performed at three time points: before water storage, after 1 day of water storage, and after 7 days of water storage.

Results: The MIL bases exhibited significantly lower 3D surface deviations than the DLP0 and DLP45 bases. The KR models generally exhibited greater 3D surface deviations than the WR and FR models. Temporal changes in the denture bases were significant across almost all ridge types and manufacturing methods.

Conclusions: The trueness of digitally fabricated denture bases is influenced by the residual ridge morphology and manufacturing method. Milling demonstrated superior trueness compared to DLP. Temporal dimensional changes were observed in almost all the bases.

Purpose: To investigate the effects of coffee and orange juice on 3 different esthetic ceramic materials regarding color changes, Vickers microhardness, and solubility & sorption changes among patients with reflux.

Methods: A glass-ceramic material (IPS Emax CAD), a polymer-infiltrated ceramic material (Vita Enamic), and a nano-hybrid ceramic material (Cerasmart) were selected for this study (n=32/group). Following the polishing procedure, all the samples were immersed in artificial saliva for 21 days. Half the samples were assigned to the control group and exposed only to artificial saliva (pH 7.3). The remaining 16 samples were exposed to saliva or simulated gastric acid. Sixteen samples from each group were exposed to gastric acid 3 times daily for 30 seconds. The color, Vickers microhardness, and solubility & sorption were then measured. Following this procedure, the samples were exposed to coffee and orange juice (n=8/per group). The samples were exposed to the solutions for 16 hours and 48 minutes to simulate 21 days of consumption. Final measurements were then obtained. Statistical significance was determined using Levene’s test to compare variances, and three-way analysis of variance (ANOVA) followed by Tukey’s post-hoc test, Welch’s ANOVA, and Games–Howell’s test were applied to reveal differences between groups.

Results: According to ANOVA, restorative material type and immersion media had a significant effect on color change (P < 0.001), microhardness (P < 0.001), and solubility & sorption (P < 0.001).

Conclusions: The choice of material is crucial for erosion-prone patients.

Purpose: To assess the time efficiency of an innovative workflow (SafetyCrown) for implant-supported rehabilitation of posterior single-tooth sites against the standard workflow. The hypothesis was that there is no difference in treatment duration and accuracy, as represented by the number of clinical adjustments and additional visits required.

Methods: 31 participants (16 females, 15 males) were included in this analysis from a randomized clinical trial. Participants were randomly assigned to the test group (SafetyCrown workflow, three visits) or control group (conventional digital workflow, six visits). The SafetyCrown workflow combined immediate restoration with a prefabricated definitive abutment and chairside provisional restoration. The control group followed a conventional digital approach in six visits. Treatment times per visit were recorded with a stopwatch; clinical adjustments and additional visits were documented.

Results: The SafetyCrown workflow was completed in three visits in 53% of cases, with a mean of 3.5 visits compared with 6.1 visits in the control group. The total treatment time differed insignificantly by 10 minutes (test: 126.4 minutes; 95% CI: 116.4–136.5; control: 116.8 minutes; 95% CI: 104.4–129.3; P = 0.232), and individual visits lasted longer in the test group (e.g., surgical visit: 62 minutes vs. 33 minutes in control). Clinical adjustments were common in both groups when using model-free workflows.

Conclusions: Limitations aside, the SafetyCrown workflow reduced the total visits while maintaining the overall treatment time despite longer individual appointments, thus increasing efficiency. Both fully digital workflows were feasible, although frequent adjustments highlight the need to investigate sources of inaccuracy to improve the precision and efficiency further.

Purpose: Hard reline procedures are commonly used to improve denture fit; however, the long-term durability of reline materials remains unclear. This study evaluated time-dependent changes in the surface properties and biofilm adhesion of light- and auto-polymerizing hard reline materials following long-term immersion in artificial saliva. The findings may help determine optimal timing for clinical intervention and enhance prosthesis longevity.

Methods: Specimens of three materials—light-polymerizing reline, auto-polymerizing reline, and heat-polymerizing denture base polymethyl methacrylate—were immersed in artificial saliva for up to 180 days. Auto-polymerizing materials continue to polymerize over time, whereas light-polymerizing materials require light irradiation. The surface properties were evaluated based on Vickers hardness, surface roughness, color stability, contact angle, and Candida albicans (C. albicans) biofilm adhesion.

Results: After 180 days, the light-polymerizing material exhibited a significant increase in hardness (P < 0.001), whereas the auto-polymerizing material exhibited an increase from day 120 (P < 0.001). Contrastingly, the heat-polymerizing PMMA exhibited a significant decrease in hardness. The surface roughness increased nearly threefold for the auto-polymerizing material, indicating pronounced degradation. Color changes in the light-polymerizing material were weaker than those in the auto-polymerizing material at all time points except at 60 and 150 days. C. albicans adhesion increased significantly in the auto-polymerizing material (P = 0.034), whereas the light-polymerized material showed no significant change (P = 0.258).

Conclusions: Time-dependent changes in surface characteristics were observed in both reline materials. The light-polymerizing material superior stability throughout the immersion period compared with that of the auto-polymerizing material, indicating superior long-term performance.

Purpose: This study evaluates the effects of different abutment screw tightening protocols and implant materials on screw loosening and morphological changes after cyclic torsional loading of two-piece implants.

Methods: Titanium (T) and zirconia (Z) two-piece implants were used. Abutment screws were tightened to 35 Ncm. Three protocols were tested: (A) retightening after 5 min, (B) immediate retightening, and (C) no retightening (n = 6 each). All samples underwent 100,000 cycles of cyclic torsional loading. Removal torque values before and after loading (RT-pre and RT-post) and torque loss percentage (TL) were calculated. Surface morphology was assessed using scanning electron microscopy (SEM), and dimensional changes were quantified using root mean square (RMS) values from three-dimensional data.

Results: In the titanium group, protocol A (TA) had lower RT-post values than protocols B (TB) and C (TC) (P < 0.001), and TB was lower than TC (P < 0.05). In the zirconia group, protocol A (ZA) was significantly lower than protocols B (ZB) and C (ZC) (P < 0.05, P < 0.001, respectively). RT-post and RT-pre were significantly lower in the zirconia group than in the titanium group under all conditions (P < 0.001). No differences were observed in TL. SEM revealed wear on the screw heads and threads in all groups. RMS values were significantly lower in the zirconia group (P < 0.05).

Conclusions: Abutment screw retightening does not consistently enhance torque maintenance under torsional loading. The implant material affects torque retention and deformation, where titanium implants demonstrating greater stability than zirconia implants.

Purpose: To elucidate how the combination of acidic and sulfur-based monomers enhances bonding to oxidized noble metal alloy surfaces.

Methods: Two types of gold alloys were used: one with a low copper content (DG) and the other with a high copper content (IV). Three primers were used: a sulfur-based monomer primer (VP), a phosphate-based acidic monomer primer (PZ), and a combination of both (MC). Two conditions were used: heated and non-heated. The shear bond strengths before and after thermocycling were determined and compared for each condition. Surface chemical analysis was performed using X-ray photoelectron spectroscopy (XPS).

Results: After thermocycling, the bond strength of MC was significantly higher than that of the VP under all conditions. In the comparison of alloys under heating conditions, IV showed a significantly higher bond strength than that of DG for the PZ and MC groups. XPS revealed peaks attributed to copper oxide (CuO) formation on the heated IV surface.

Conclusions: Multipurpose primers are effective for bonding oxidized noble metal alloys and acrylic resins. The formation of CuO improves the performance of 10-methacryloyloxydecyl dihydrogen phosphate, and its combination with sulfur-based monomers is particularly effective for noble metal alloy surfaces with high copper content.

Purpose: Polyetheretherketone (PEEK), a high-performance thermoplastic polymer, has been explored as a dental material because of its excellent mechanical strength and biocompatibility. Composite resin has been reported as a viable prosthetic material when appropriate surface treatment is applied to PEEK. We evaluated the effects of ultraviolet and ozone (UV/ozone) irradiation on the bond strength of PEEK.

Methods: Eighty-six rectangular PEEK specimens were fabricated and divided into two surface-pretreatment groups: untreated (CO) and UV/ozone-treated (UV). The contact angle, surface roughness, and chemical composition were analyzed using contact angle goniometry, laser scanning microscopy, and X-ray photoelectron spectroscopy (XPS), respectively. The remaining specimens were assigned to two conditioning groups: no conditioning (NT) and primer conditioning (AD). Cylindrical specimens fabricated by Computer-Aided Design, Computer-Aided Manufacturing (CAD-CAM) composite resin blocks were bonded to the PEEK surface using resin cement. Half of the specimens in each group were subjected to 5000 thermal cycles. The shear bond strength was tested using a universal testing machine and the fracture surfaces were examined under a stereomicroscope. Statistical analyses were performed using t-tests (α = 0.05).

Results: UV/ozone treatment significantly reduced the contact angle, improved the surface wettability, and caused slight changes in the surface roughness. XPS analysis revealed a decrease in the C=O bonds and an increase in the C-OH bonds in the UV/ozone-treated group. The shear bond strength improved significantly, particularly in the AD group.

Conclusions: UV/ozone treatment of PEEK surfaces increased the wettability and significantly improved the shear bond strength of the composite resin blocks.

Purpose: This study aimed to determine whether the maximum compressive force exerted on denture base materials by test foods varies depending on the presence and type of resilient denture liners.

Methods: The maximum compressive forces of gummy jelly and peanuts were measured using a texture analyzer equipped with a 500 N load cell, operating at a crosshead speed of 9.78 mm/s. Tests were conducted on rectangular prism-shaped specimens (30 mm × 30 mm × 4 mm) fabricated from various denture base materials. Three commercial silicone-based resilient denture liners—Sofreliner Supersoft (SS), Sofreliner Mediumsoft (MS), and Sofreliner Tough Medium (TM)—and a conventional heat-cured acrylic resin (Urban, UR) were used. Additionally, the Shore A hardness of each material was measured using a hardness tester.

Results: The maximum compressive forces applied to gummy jelly and peanuts on UR specimens were significantly higher than those on TM, MS, and SS specimens. Similarly, the Shore A hardness of UR was higher than that of the other materials. A statistically significant positive correlation was observed between the maximum compressive force of the test foods and the Shore A hardness of the denture base materials.

Conclusions: The maximum compressive force applied to food varied according to the type of denture base materials. In particular, resilient denture liners effectively reduced the force transmitted to the food compared with conventional hard acrylic resin.

Purpose: We aimed to verify the hypothesis that patients who undergo prosthetic treatment with a definitive obturator following maxillectomy for oral tumors show decreased oral functions when the maxillary defects are extensive.

Methods: This study comprised 77 patients (46 men, 31 women; mean age, 71.0 years) who underwent prosthetic treatment with definitive obturators designed to restore maxillary defects following maxillectomy owing to an oral tumor. Oral function, masticatory performance, maximum bite force, tongue pressure, and tongue-lip motor function (oral diadochokinesis /pa/, /ta/, /ka/) were evaluated. The extent of maxillary defects was evaluated based on Aramany’s classification. The maxillary defects were classified into three groups, namely, no oroantral communication (NOC), small oroantral communication (SOC), and large oroantral communication (LOC) groups. Multiple regression analyses were performed with each oral function as the objective variable and age, sex, maximal mouth opening, history of radiotherapy, number of functional teeth, and the extent of the maxillary defect as explanatory variables.

Results: The number of functional teeth and LOC were significant as explanatory variables for masticatory performance, while sex, number of functional teeth, and LOC were significant as explanatory variables for maximum bite force. Regarding other oral functions, the extent of the jaw defect was not significant as an explanatory variable.

Conclusions: In patients with maxillary defects wearing definitive obturators, a defect exceeding half of the palate and communicating with the nasal cavity was significantly associated with lower masticatory performance and maximum bite force.

Purpose: The purpose of this study was to establish chevron-notched beam (CNB) finite element analysis (FEA) models to investigate the fracture toughness of zirconia ceramics.

Methods: Experimental four-point flexural strength data (n = 9; previously published) for 3 mol% yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP; 3M Oral Care, Seefeld, Germany) were combined with numerical data (calculated using the inverse finite element method) to evaluate the input material properties of the CNB-FEA models. These models (n = 8) were then simulated and validated against the CNB test data of specimens with the same geometries (n = 8). The validation criteria included the margin of error, coefficient of determination, and linear regression. FEA was used to evaluate the volumetric strain distribution during deformation.

Results: 3Y-TZP has static elastic modulus and fracture strain values of 144.5 GPa and 0.0056, respectively. The fracture toughness of the CNB-FEA models closely matched those of the corresponding test specimens (±3% error). Linear regression yielded a coefficient of determination (R²) of 0.94 (P < 0.05), demonstrating an excellent predictive performance. The CNB-FEA models accurately reflected the actual fracture behaviors of the zirconia ceramics, with the volumetric strain localized at the notch tip.

Conclusions: The volumetric strains of the CNB-FEA models could be determined using the FEA and measured four-point flexural strength data. Thus, CNB-FEA was found to be a valuable method for predicting the fracture toughness of zirconia ceramics.

Purpose: Masticatory exercise promotes systemic health and cognitive function. Although acute masticatory stimuli enhance prefrontal cortical activity, the effects of increased habitual chewing on cortical activity remain unclear. This study evaluated the effects of habitual chewing on cortical activity in young adults.

Methods: Forty-one young adults (aged 21-31 years) were randomly assigned to an intervention group, which used a wearable device to increase attentional chewing strokes during meals for 1 month, or a control group that did not use the device. We monitored the cortical activity during gum chewing using functional near-infrared spectroscopy at baseline and immediately after intervention. We recorded the number of chews per rice ball at baseline, immediately after intervention, and at 3 months post-intervention. Changes across different time points in each group were compared using one-sample t-tests with Bonferroni correction.

Results: The intervention group showed a significant increase in the number of chews after the intervention and at the 3-month follow-up, whereas the control group exhibited no changes. Moreover, the intervention group demonstrated significantly higher activity in the dorsolateral prefrontal cortex (DLPFC) and premotor cortex compared with the control group. A voxel-based correlation analysis revealed a positive correlation between increase in chewing strokes and activity in these brain regions in the intervention group (family-wise error-corrected, P < 0.05).

Conclusions: Intentional chewing, enhanced through an attentional intervention, led to increased activation in the DLPFC and premotor cortex during mastication. These results demonstrated the objective neural effects of interventions targeting habitual masticatory behavior.