Purpose: This systematic review evaluated the effect of different printing orientations on the physical-mechanical properties and accuracy of resin denture bases and related specimens.

Study selection: Utilizing PRISMA 2020 guidelines, a comprehensive search of PubMed, Web of Science, Cochrane, and Scopus databases was conducted until June 2024. Included studies examined the accuracy, volumetric changes, and mechanical or physical properties of 3D-printed denture bases in various orientations. Studies without relevant data were excluded. Bias risk was assessed using a modified CONSORT checklist.

Results: This review included 24 studies on 3D-printed denture base resins, mainly based on stereolithography and digital light processing. Horizontal orientation (0°) generally enhanced flexural strength, while tilted and vertical orientations (90°) reduced it. Microhardness results varied due to differences in materials, layer thicknesses, and post-curing. Surface roughness was highest at 45°. Vertical orientation uses less material but is less time-efficient. Microbial adhesion, influenced by surface roughness, varied with printing orientation without a clear consensus on the optimal direction.

Conclusions: Printing orientation significantly impacts the physical and mechanical properties and accuracy of 3D-printed resin dentures. A horizontal orientation (0°) improved flexural strength, while accuracy and adaptability were better at 45° and 90°. Surface roughness, translucency, and chemical stability are also affected by orientation, post-curing, and material choice. Although a 90° orientation reduces material use, it increases printing time. Standardized study designs are recommended for drawing definitive conclusions in future research.

Purpose: To investigate the accuracy of static and dynamic computer-aided implant surgery (s/d-CAIS) for immediate implant placement for single-tooth replacement in healthy individuals with partially edentulous zones.

Study selection: A systematic search of six electronic databases for clinical studies reporting on Type 1 implant placement identified 15 eligible articles (seven RCTs, two prospective studies, and six retrospective studies) involving 383 patients. The focus question addressed population, intervention, comparison, and outcome criteria. A meta-analysis was performed using a random-effects model to obtain pooled estimates, presented as forest plots with weighted mean differences and 95% confidence intervals. Quality assessment was conducted using the Robin-I and RoB2 tools.

Results: The meta-analysis revealed that s/d-CAIS demonstrated significantly lower global platform and apex deviation compared to freehand placement, with mean differences of -0.70 mm (95% CI -0.74, -0.66; P < 0.001) and -0.86 mm (95% CI -1.00, -0.73; P < 0.001) respectively. The mean difference in platform depth deviation was statistically significant in favor of CAIS, with a mean difference of -0.73 mm (95% CI -1.04, -0.43; P < 0.001). High heterogeneity was observed across studies. The average global coronal, global apex, and angulation deviation for d-CAIS and s-CAIS were 0.72 mm, 0.81 mm, and 2.04 degrees, and 0.80 mm, 1.10 mm, and 2.12 degrees, respectively.

Conclusions: Data on Type 1 implant placement suggest that s/d-CAIS may enhance implant placement accuracy in several dimensions compared with freehand placement, with d-CAIS demonstrating marginally better control over angulation. However, the high heterogeneity across studies with a moderate-to-high risk of bias limits the generalizability of these findings.

Purpose: To determine the effects of K18 quaternary ammonium methacryloxy silane (QAS) on tissue conditioner materials and their antimicrobial properties.

Methods: 30% K18 QAS in methyl methacrylate (MMA; K18-MMA; 0%, 15%, and 20% w/w) was incorporated into a commercial tissue conditioner (Coe comfort). The degree of curing (Shore A hardness), hydrophilicity (contact angle), flow, liquid sorption, mass loss, and antimicrobial properties of Streptococcus mutans, Streptococcus sanguinis, and Candida albicans were determined. Statistical analysis included analysis of variance with Tukey HSD and Kruskal–Wallis with Bonferroni correction.

Results: Hardness increased significantly at higher K18-MMA concentrations. The contact angles did not differ between the groups. Although the control and K18-containing tissue conditioner flow decreased significantly at each successive time point and with increasing K18 QAS MMA concentration, the flow was still within the ISO 10139-1 specifications for class 2 (high-flow) soft lining materials until 2 min 30 s. The highest liquid sorption happened between 1 and 4 weeks. The controls absorbed more acid than water or base, and the K18 groups absorbed more water and acid than base. With increasing K18-MMA concentration, the mass loss increased at all times and in all three media, except in base, after 4 weeks. Both 15% and 20% K18-MMA showed significant antimicrobial activity against S. mutans, S. sanguinis, and C. albicans.

Conclusions: K18-MMA imparted significant antimicrobial properties to tissue conditioners against S. mutans, S. sanguinis, and C. albicans without compromising the flow, hardness, or hydrophilicity. However, K18-MMA addition led to increased water sorption and mass loss after 4 weeks.

Purpose: Human flourishing is a multidimensional concept that encompasses happiness and life satisfaction (happiness), mental and physical health (health), meaning and purpose (purpose), character and virtue (character), and close social relationships (social), which are characterized by comprehensive well-being. This cross-sectional study investigated the association of oral health, number of remaining teeth, and prosthesis use with multidimensional flourishing.

Methods: Data was sourced from the 2022 wave of the Japan Gerontological Evaluation Study, a population-based survey of independent individuals aged 65 years or older. This study utilized multilevel linear regression with multiple imputations. The covariates included sex, age, income, education, marital status, smoking status, diabetes history, instrumental activities of daily living, and depressive symptoms.

Results: This study included 87,201 participants with a mean age of 74.87 years [standard deviation (SD)=6.30], and mean±SD composite flourishing index of 6.77±1.64. Multilevel multivariable regression showed that individuals with dental prostheses or more teeth had a higher flourishing index. Among individuals without dental prostheses, those with >20 teeth showed a composite flourishing index of 0.34 units higher (95% confidence interval (95% CI): 0.26-0.42, P < 0.001) than those with 0-9 teeth. Among those with 0-9 teeth, individuals with dental prostheses showed 0.21 (95% CI: 0.12-0.29, P < 0.001) higher units compared to those without prostheses. The interaction analysis showed that dental prosthesis use was significantly associated with higher indices, especially among those with fewer teeth.

Conclusions: Teeth and prostheses were independently associated with multidimensional flourishing. Using dental prostheses may enhance multidimensional flourishing among individuals with fewer remaining teeth.

Purpose: This study was aimed at investigating the thermal stresses in monolithic zirconia crowns (MZC) of various thicknesses and elucidating their thermal behavior under cooling or heating changes in the oral cavity. Additionally, the clinical availability and potential issues of MZC were examined by comparing them with other crown materials.

Methods: Finite element models comprising MZC (0.5-, 1.0-, and 1.5-mm thick), cement layers, and abutment teeth were subjected to thermal changes from 37 to 5 °C or 60 °C. Using a thermal distribution at 5 s, the thermal stress was calculated and compared with those of gold alloy and resin composite crowns. The loads corresponding to the thermal stresses were also estimated by comparing them with the stresses induced by vertical loading on the occlusal surface.

Results: Tensile stress occurred primarily in the crowns and cement during cooling, whereas compressive stress was generated during heating. Thermal stresses increased from 16.0 to 27.2 MPa with decreasing crown thickness from 1.5 to 0.5 mm and varied with different materials. Although the MZC exhibited the highest thermal stress, the estimated load (200 N) corresponding to the thermal stress was smaller than that of the resin composite (1280 N).

Conclusions: Thinner crowns exhibited higher thermal stress, suggesting an increased risk of failure owing to thermal changes. Despite the higher thermal stress in thinner MZC, the stresses were below the fatigue strength of the material, indicating sufficient resistance to thermal changes in the oral cavity.

Purpose: In this cross-sectional study, we aimed to investigate the association among dietary diversity, ingestible food profiles, and the type of prosthodontic treatment (i.e., removable partial or complete dentures [RD] vs. implant-supported dentures [ID], including implant-supported fixed prostheses and implant-assisted overdentures) in older Japanese outpatients.

Methods: We included 297 patients aged ≥65 years (mean age, 75.3 years) undergoing maintenance therapy for RD or ID. Dietary diversity was assessed using the Dietary Variety Score (DVS) questionnaire. The ingestible food profile, a subjective quantification of the ability to consume foods with high masticatory difficulty, was evaluated using a validated ingestible food questionnaire and assessed using the ingestible food score (IFS). DVS- and IFS-related factors were identified using multiple regression analyses.

Results: The median IFS of the ID group (100.0) was significantly higher than that of the RD group (84.5); however, the median DVS showed no statistically significant difference between the two groups. After adjusting for confounding factors, prosthodontic treatment type (RD) and the number of present teeth (≤20) were found to be significantly associated with low IFS, whereas young age and presence of cardiovascular disease were significantly associated with low DVS.

Conclusions: Older individuals with ID had a better ingestible food profile than those with RD; however, dietary diversity did not differ significantly between the two groups. RD is a potential risk factor for poor ingestible food profile, whereas the prosthodontic treatment type is not a direct risk factor for low dietary diversity.

Purpose: This study examined the effect of assistive device use on the precision of digital impressions for multiple implants placed in a fully edentulous maxilla in vivo.

Methods: A total of eight participants with fully edentulous maxillae and four implants at position #15, #12, #22, and #25 were included in the study. The assistive device was made using CAD/CAM technology. Digital impressions were obtained using an intraoral scanner with (AD+) and without (AD-) the assistive device that attached to the scan bodies. Each participant underwent five digital and conventional impressions (verification casts (VC)). Dimensional deviations for each impression method were measured using the least-squares best-fit method to assess precision. Statistical analysis was performed using one-way analysis of variance (ANOVA) with Tukey’s post-hoc adjustments for multiple comparisons.

Results: The dimensional deviations were as follows: AD- (37.56 ± 7.43 µm), AD+ (16.23 ± 2.56 µm), and VC (26.48 ± 5.13 µm). One-way ANOVA revealed significant differences between the groups (F = 31.04, P < 0.0001), which remained after Tukey adjustment (P < 0.01). The AD+ group exhibited the highest precision, while the AD- group had the lowest.

Conclusions: For implants placed in a fully edentulous maxilla in vivo, digital impressions with assistive devices demonstrated superior precision compared with those obtained without assistive devices or conventional impressions obtained with an implant indexing device.

Purpose: Excessive occlusal forces resulting from inadequate dental prosthesis, along with periodontal infection (PI), lead to severe periodontitis; however, the roles of senescent cells and their involvement in the mechanisms underlying this process remain unclear. Therefore, this study aimed to elucidate the roles of senescent cells and their cell types in severe periodontitis with excessive force (occlusal trauma [OT]).

Methods: To determine whether senescent cells exacerbate alveolar bone resorption, we developed a severe periodontitis rat model by inducing PI and OT and assessed the presence of senescent cells and bone resorption. Senolytics (dasatinib + quercetin [DQ]) were administered to evaluate the changes in the appearance of senescent cells and bone resorption.

Results: PI and OT + PI increased senescent cells as well as osteoclasts. Furthermore, p21 and receptor activator of nuclear factor-kappa B ligand (RANKL) co-expressing cells were observed in the OT + PI group rats, suggesting a correlation between bone resorption and senescent cells. Cell type analysis identified osteoblasts and Th17 cells as RANKL⁺ cells expressing p21 or p16. DQ administration reduced senescent cells and osteoclasts, thereby preventing alveolar bone resorption.

Conclusions: RANKL⁺ senescent osteoblasts and Th17 cells are involved in osteoclastogenesis and bone resorption. Our findings highlight a new target for the prosthetic treatment of severe periodontitis.

Purpose: Spark-discharged anodic oxidation coating on commercially pure titanium (SAc.p.Ti) has been shown to promote bone conduction and bone matrix mineralization during new bone formation. This study hypothesized that the combination of SAc.p.Ti with dental pulp stem cells (DPSCs) would enhance new bone formation. The objective was to evaluate the effect of this combination in a rat bone defect model.

Methods: DPSCs were isolated from Sprague–Dawley (SD) rat incisors and cultured. Calvarial bone defects were created in SD rats, followed by transplantation of commercially pure titanium (c.p.Ti), SAc.p.Ti, or SAc.p.Ti combined with DPSCs. Bone formation was assessed using micro-computed tomography (micro-CT). Toluidine blue O staining was employed to evaluate bone-implant contact and the newly formed bone area. Hematoxylin–eosin (HE) staining was performed to identify osteoblast-like cells.

Results: Micro-CT analysis revealed hard tissue formation on the surface of SAc.p.Ti. Toluidine blue O staining showed significantly greater bone-implant contact and newly formed bone area in the SAc.p.Ti/DPSC group compared to the c.p.Ti and SAc.p.Ti groups. HE staining confirmed the presence of osteoblast-like cells at the defect margins, with evidence of new bone formation on the surface of SAc.p.Ti and in the SAc.p.Ti/DPSC groups.

Conclusions: The combination of SAc.p.Ti and DPSCs presents a promising strategy for promoting new bone formation in rat calvarial defect model.

Purpose: To investigate the optimal post-polymerization temperature and time to enhance the mechanical properties of three-dimensional (3D)-printed nanocomposites.

Methods: A control group of pure 3D-printed resin was used to fabricate specimens post-polymerized at 40 °C for 15 min (n = 6). Next, 3-wt% functionalized yttria-stabilized zirconia (YSZ) nanoparticles were dispersed in a 3D-printed resin to fabricate YSZ-based nanocomposites for the experimental groups. The post-polymerization conditions of six experimental groups (n = 6) were set as two temperatures (40 °C and 80 °C) and three time periods (30, 60, and 90 min). The degree of conversion (DC), flexural strength, modulus, fractography, and hardness values of each group were evaluated. One-way and two-way analysis of variance were applied to analyze significant differences among the control and experimental groups and interaction effect of temperature and time of post-polymerization, respectively (α = 0.05).

Results: Significant reductions in DC values were noted in the experimental groups compared to the control group. The experimental groups demonstrated significantly higher flexural strengths and moduli than those of the control group. At 80 °C, no significant differences were observed for different post-polymerization times. Compared to post-polymerization at 40 °C, the flexural strength, modulus, and hardness were significantly enhanced when the post-polymerization temperature was increased to 80 °C.

Conclusions: Optimal mechanical properties of 3D-printed YSZ-based nanocomposites could be achieved under post-polymerization at 80 °C and 30 min.

Purpose: This clinical study aimed to evaluate the effects of various head positions within physiological movement limits on occlusal contacts (OCs) in digital bite registrations (BRs) obtained using an intraoral scanner (IOS).

Methods: This study included 36 individuals with natural dentition without missing teeth. Maxillary and mandibular scans were performed using an IOS (Trios4). The natural (NHP), forward (FHP), and backward (BHP) head positions were determined using a manual goniometer, and three BRs were obtained using an IOS. A new assessment method, the “digital occlusion analysis” module (oJMA, Zebris), was used to assess the OCs in these BRs. Dental arch scans and BRs were imported into the digital occlusion module. OC evaluation was performed on buccal-lingual cross-sections obtained at 1 mm intervals on the four left and right posterior teeth of the mandible. Each section was evaluated for the number, intensity, and location of OCs between pairwise comparison groups of head positions.

Results: The number of OCs significantly decreased in the BHP-FHP group with respect to contact points (P = 0.03). OC intensity was similar among the three groups. However, OC location was significantly reduced in the NHP-BHP and NHP-FHP groups compared with the NHP group, specifically for functional cusp contacts (P = 0.03, P = 0.018).

Conclusions: Digital BRs obtained in different head positions showed significant differences only in the OC locations in the FHP and BHP compared with the NHP. The effect on the number of OCs was observed as the angle between the head positions increased from FHP to BHP.

Purpose: To evaluate stress distribution in short-crowned molars with distal subgingival defects with various restorations and materials.

Methods: Residual crowns were restored using a post-and-core crown (model A), a full crown (model B), a fissure-post endocrown (model C), an endocrown (model D), an onlay (model E), and an overlay (model F). The ceramic materials used were IPS e.max (EM), Vita Enamic (VE), and Lava Ultimate (LU). Subsequently, finite element analysis was performed by applying 600 N vertical load (0° to the long axis) and 200 N oblique load (45° to the long axis) to simulate chewing loads.

Results: As the elastic modulus of the material increased, the stress on the restorations also increased, particularly under an oblique loading condition. Under vertical and oblique loading conditions, the peak maximum principal stress (MPS) in the dentin was lowest in Group A-EM (17.28 MPa and 5.61 MPa, respectively), following the trend A < B, C < D, F < E. The MPS within the cement was lowest in Group A-EM (2.74 MPa and 2.58 MPa under vertical and oblique loading conditions, respectively). The MPS within the cement in Group H (4.11 MPa) was reduced to approximately one-third of that in Group G (12.35 MPa).

Conclusions: EM exhibited a more uniform stress distribution than other materials and is a promising material for short-crowned molars. A fissure-post endocrown design is a potentially favorable restorative option for short-crowned molars. Fiber posts should be used with full crown restorations.

Purpose: This study evaluated the use of pre-sintered cobalt-chromium (Co-Cr) alloy discs in the fabrication of clasps for removable partial dentures, comparing their accuracy and mechanical properties, as determined via tensile testing, with those of conventional fabrication methods.

Methods: Accuracy of the clasps was assessed by obtaining three-dimensional (3D) data (design data) of the Akers clasp. The clasps were fabricated under three conditions: (1) pre-sintered, fabricated from pre-sintered Co-Cr alloy discs; (2) fully sintered, fabricated from fully sintered Co-Cr alloy discs; and (3) cast, fabricated via casting. For each method, 3D data were collected (fabrication data). The design and fabrication data were subsequently superimposed, and the accuracy of the clasps was investigated based on their inner surfaces. The mechanical properties were assessed via tensile testing of dumbbell-shaped Co-Cr alloy specimens fabricated under the same conditions used for accuracy testing (pre-sintered, fully sintered, and cast).

Results: Cast clasps typically exhibited the highest trueness values and fully sintered clasps exhibited the highest precision values. The pre-sintered clasps exhibited high trueness in every part of the rest area; however, the accuracy at the clasp tip was low. In terms of mechanical properties, the pre-sintered clasps exhibited the highest elongation, meeting the standards for Type 4 metals as specified by ISO 22674:2022.

Conclusions: The present study demonstrates that pre-sintered Co-Cr alloy discs are suitable for fabrication of clasps with good fit and mechanical properties, provided that the accuracy of the clasp tip is improved.

Purpose: The hyoid bone plays a key role in several physiological functions by interacting with the attached muscles. Understanding its kinematics and positional stability is essential for evaluating its functions: swallowing, mastication, intraoral transport, vocalization, and respiration. This study aimed to assess the position of the hyoid bone relative to the cranial base and mandible using cephalometric imaging and to examine its stability.

Methods: Cephalometric images of 140 patients were analyzed using specialized software. The positional relationship between the cranial base and hyoid bone was assessed by measuring the Porion-Hyoid distance (Po-Hy) and the angle between the Po-Hy and the Nasion-Porion line (∠CB-Hy). The relationship between the mandible and the hyoid bone and the cervical angle was also evaluated.

Results: The ∠CB-Hy showed a narrow distribution (mean ± SD: 89.2 ± 5.12°). A weak, but statistically significant, correlation was observed between age and the ∠CB-Hy. Additionally, a significant negative correlation was found between the number of missing molars and ∠CB-Hy, while a strong positive correlation was identified between the cervical angle and ∠CB-Hy. The relationship between the cervical angle and ∠CB-Hy was represented by the following linear regression equation: ∠CB-Hy = 0.484 × Cervical angle + 37.4.

Conclusions: Our findings suggest that the hyoid bone maintains a relatively stable position with respect to the cranial base with only slight variation. However, a significant relationship exists between ∠CB-Hy and cervical inclination. Clinicians and researchers should consider this relationship when assessing the hyoid position in clinical and research settings.

Purpose: To evaluate the influence of cleaning methods on bonding to zirconia ceramic over a long period after airborne-particle abrasion (APA).

Methods: A total of 140 disc-shaped zirconia specimens were divided into five groups based on the cleaning methods after a 72-hour delay between APA and bonding: A-(alcohol), V-(Ivoclean), K-(Katana Cleaner), P2-(Clearfil Ceramic Primer Plus after 72 hours), and P1-(Clearfil Ceramic Primer Plus directly after APA). The specimens were APA-treated with 50-µm alumina particles (Al₂O₃) and stored at room temperature for 72 hours (n=28/group). Surface free energy (SFE) was measured for 12 specimens per group using a goniometer. For each group, 16 Plexiglas tubes filled with composite resin were bonded to zirconia specimens using a self-adhesive luting resin. Tensile bond strength (TBS) was tested for subgroups of eight specimens after 3 days of water storage and 150 days with 37500 thermal cycles. Failure modes were categorized as adhesive or cohesive using light microscopy.

Results: SFE increased significantly in groups V (68.4 mN/m) and A (61.8 mN/m) (P ≤ 0.05), but decreased in group K (33.1 mN/m) (P ≤ 0.05). TBS after 3 days of water storage ranged from 60.7 MPa in group A to 51.6 MPa in group P2 without significant difference between the tested groups (P > 0.05), and after 150 days with thermocycling, it ranged from (45.4 MPa) in group K to 33.9 MPa in group P2 with a significant difference between groups K and P2 (P ≤ 0.05).

Conclusions: Cleaning significantly affected the strength and durability of bonding in non-retentive zirconia restorations when there was a considerable time gap between APA and bonding.

Patients: Three residents of a long-term care home volunteered to participate in a rehabilitation program involving a virtual reality blowgun game. The participants played the game 5 days a week as a new exercise routine. After 4 weeks of intervention, tongue pressure and forced expiratory volume in 1 s improved in all participants. In addition, the jaw-opening force and forced expiratory volume in 6 s improved in two participants. All three participants rated the virtual reality blowgun game as more enjoyable than their regular rehabilitation programs.

Discussion: Previous studies have shown that gamification can be useful in dysphagia rehabilitation. However, there are no previous reports describing the use of virtual reality in rehabilitation programs aimed at improving swallowing and respiratory functions in older adults while investigating participant motivation. The outcomes of the cases described herein suggest that such programs can be as effective as conventional expiratory training. Furthermore, gamification can enhance enjoyment, even in exercises designed to improve physical function.

Conclusions: These cases indicate that the virtual reality blowgun game may effectively improve swallowing and respiratory functions in older adults while being enjoyable.

Purpose: This guideline aimed to make evidence-based clinical practice guidelines for the primary treatment of temporomandibular disorders (TMDs) for general practitioners who do not specialize in TMD.

Review process: Following the principles of evidence-based medicine, a systematic review and network meta-analysis (NMA) of multiple treatments was conducted, assessing the certainty of evidence using the Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) approach. Randomized controlled trials published between January 2000 and December 2020 were included. Patients diagnosed with TMD according to the Diagnostic Criteria for Temporomandibular Disorders were considered. Myalgia, arthralgia, and maximal mouth opening were selected as outcomes, and 12 treatments were included in the NMA. The modified Delphi method was used to reach a consensus on recommendations during clinical guideline panel meetings of the Japanese Society for the Temporomandibular Joint.

Results: Self-administered mouth opening exercises, stabilization-type oral appliances, and low-level laser therapy (LLLT) were recognized as effective primary treatments, although the evidence level was graded as “very low” (Grade 2D). During the clinical guideline panel meetings, decisions were developed based on the NMA results, and recommendations for clinical practice guidelines were finalized following consensus.

Conclusions: This guideline recommends mouth opening exercises and the use of stabilization-type oral appliances as primary treatments for TMD. Additionally, it suggests that LLLT be a conditional recommendation, supplemented with additional considerations.