Purpose: This systematic review examined the effectiveness of soft denture relining (SDR) materials.

Study selection: A comprehensive search of MEDLINE, Cochrane Library, and ICHUSHI was conducted up to July 26, 2020. Target outcomes were patient satisfaction, oral health-related quality of life (OHRQOL), masticatory ability (MA), denture functional duration, residual ridge resorption (RRR), and microbial contamination. An organization specializing in literature searches performed the reference searches, and two reviewers independently selected the literature sources, extracted the data, and assessed the risk of bias. The reviewers resolved any disagreements concerning the assortment of literature sources through discussion. SDR included acrylic- and silicone-based materials, which were evaluated separately.

Results: Reviewers selected 7, 5, 11, 1, 4, and 6 studies to assess patient satisfaction, OHRQOL, MA, functional duration, RRR, and microbial contamination, respectively. The results confirmed that SDR improved patient satisfaction, OHRQOL, MA, and RRR. However, the functional duration of SDR material is shorter than that of hard denture relining (HDR) or acrylic resin material. Furthermore, SDR material is more susceptible to microbial contamination in the long term. The risk of bias for the included studies tended to be high because of specific issues (difficulty in blinding SDR versus HDR).

Conclusions: For patients who wear complete dentures, SDR often provides beneficial outcomes such as pain reduction and recovery from MA. However, caution should be exercised regarding their use owing to insufficient functional duration and the possibility of microbial contamination during long-term use.

Purpose: Dental implant osseointegration comprises two types of bone formation—contact and distance osteogenesis—which result in bone formation originating from the implant surface or bone edges, respectively. The physicochemical properties of the implant surface regulate initial contact osteogenesis by directly tuning the osteoprogenitor cells in the peri-implant environment. However, whether these implant surface properties can regulate osteoprogenitor cells distant from the implant remains unclear. Innate immune cells, including neutrophils and macrophages, govern bone metabolism, suggesting their involvement in osseointegration and distance osteogenesis. This narrative review discusses the role of innate immunity in osseointegration and the effects of implant surface properties on distant osteogenesis, focusing on innate immune regulation.

Study selection: The role of innate immunity in bone formation and the effects of implant surface properties on innate immune function were reviewed based on clinical, animal, and in vitro studies.

Results: Neutrophils and macrophages are responsible for bone formation during osseointegration, via inflammatory mediators. The microroughness and hydrophilic status of titanium implants have the potential to alleviate this inflammatory response of neutrophils, and induce an anti-inflammatory response in macrophages, to tune both contact and distance osteogenesis through the activation of osteoblasts. Thus, the surface micro-roughness and hydrophilicity of implants can regulate the function of distant osteoprogenitor cells through innate immune cells.

Conclusions: Surface modification of implants aimed at regulating innate immunity may be useful in promoting further osteogenesis and overcoming the limitations encountered in severe situations, such as early loading protocol application.

Purpose: This scoping review aimed to identify and discuss the recyclability of dental zirconia residuals along with the factors influencing the properties of dental recycled zirconia.

Study selection: In vitro studies written in both English and Chinese that evaluated the recyclability of dental zirconia residue were selected. A literature search was conducted in Medline, PubMed, Web of Science, and Cochrane Library databases with no restrictions on the publication year.

Results: Sixteen studies were included in this review. Residual dental zirconia can be recycled. Cold isostatic pressing improved the density of recycled zirconia compared with uniaxial pressing. Recycled zirconia powder with fine particles enhanced the performance of recycled zirconia compared with coarse particles. A presintering temperature of 950 to 1100°C was suitable for preparing recycled zirconia presintered bodies. Recycled zirconia may require a higher sintering temperature (≥1500°C) compared with commercially available zirconia. Additionally, recycled zirconia powder can enhance the properties of polymethylmethacrylate as a reinforcing filler and can be combined with alumina powder to obtain an alumina/zirconia composite material.

Conclusions: Despite a limited body of literature, the recycling and reutilization of dental zirconia residuals are feasible and reliable, and can reduce economic and environmental losses. Nevertheless, several factors influence the recycling effect, including the particle size, molding techniques, and sintering parameters. In addition, recycled zirconia powder can act as a reinforcing filler, potentially enhancing the mechanical properties of other materials. To realize commercially viable recycled zirconia materials, further studies are essential to comprehensively explore and understand their recycling performance.

Purpose: This study investigated the fracture resistance of 0.5-mm-thick restorations for minimally invasive therapy. Anterior partial-coverage crowns composed of three-dimensional (3D)-printed 3-mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP; Lithacon 3Y210, Lithoz) and 3D-printed composite (Varseo Smile Crown plus, Bego) were compared with a control group made from milled 3Y-TZP (Cercon ht, DentsplySirona).

Methods: Three groups each with 27 restorations were produced. For milled 3Y-TZP partial-coverage crowns, drill compensation was needed so the milling bur could access the inner surface at the incisal edge. Restoration fit was verified by cross-sectioning 12 specimens in each group. The remaining 15 restorations were sandblasted (Al2O3, 0.1 MPa) and adhesively cemented (Panavia SA, Kuraray) onto CoCr teeth. Static load-to-failure tests were performed. The load was induced on the incisal edge. The forces needed to fracture the specimens were analyzed using the Welch analysis of variance and post hoc Dunnet-T3 tests. The Weibull parameters were also calculated.

Results: Drill compensation increased cement thickness at the loading area by 200 µm in milled 3Y-TZP restorations compared with the 3D-printed partial-coverage crowns. Fracture resistance was the highest in 3D-printed 3Y-TZP restorations (1570±661N) followed by milled 3Y-TZP (886±164N) and 3D-printed composite partial-coverage crowns (570±233 N). Milled 3Y-TZP was associated with a substantially higher Weibull modulus (m=6) than the 3D-printed materials (m=2), suggesting greater reliability.

Conclusions: Fracture resistance increased with tighter fit, demonstrating the benefit of the geometric freedom associated with 3D-printing. Future research should focus on making 3D-printed 3Y-TZP more reliable to increase its safety in clinical use.

Purpose: Some patients with mild-to-moderate obstructive sleep apnea (OSA) undergoing mandibular advancement device (MAD) therapy may exhibit residual sleep-breathing abnormalities. These cases require adjunctive treatment to further reduce the remaining airway inadequacy, which may affect the health and quality of life. This clinical trial was conducted since the oropharyngeal exercise, which aims to enhance the muscular function of the upper airway, combined with MAD, is unknown. We assessed the possible improvements in respiratory event parameters and lip and tongue physiological properties in patients with OSA who received oropharyngeal exercises for 2 months as an adjunct to MAD therapy.

Methods: Twenty-three participants with OSA who had been using MAD but still had residual apnea-hypopnea were randomly allocated to either the oropharyngeal exercise (OE group; N=12) or the sham exercise group (N=11). Lip and tongue strength, endurance, daytime sleepiness, respiratory event index (REI), and the lowest oxygen saturation (SpO₂ nadir) were determined.

Results: Within and between the treatment groups, no significant improvement in the REI or SpO₂ nadir was found. In both groups, there was a significant reduction in the Epworth Sleepiness Scale at 2 months (OE, P = 0.02; control, P = 0.02). In the OE group, lip endurance (P = 0.03), anterior tongue strength (P = 0.02), and endurance (P = 0.02) increased after 2-month of exercise, but only anterior tongue endurance increased significantly compared with the sham control (P = 0.01).

Conclusions: This study found that adjunctive OE to MAD showed no additive effect in treating patients with moderate OSA who had a mild residual apnea-hypopnea index following MAD treatment. However, the exercises successfully enhanced lip and anterior tongue endurance, as well as anterior tongue strength.

Purpose: To evaluate the effect of chemical, mechanical, and combination surface treatments on the shear bond strength (SBS) of autopolymerizing repair resin to conventional heat-cured, computer aided design (CAD)-computer aided manufacturing (CAM) milled, and three-dimensionally (3D) printed denture base materials.

Methods: Specimens were fabricated and divided according to the surface treatment as follows: no surface treatment (control group), monomer treatment (monomer group), resin remover treatment (resin remover group), roughening with 180 FEPA grit abrasive paper followed by monomer treatment (180-grit plus monomer group), and air particle abrasion (air abrasion group). Autopolymerizing resin cylinders were attached before accelerated aging of the specimens in water at 100 °C for 16 h. The SBS was tested using a universal testing machine. Surface roughness was evaluated using a 3D optical profilometer. Scanning electron microscopy (SEM) and stereomicroscopy were used for surface analysis. Data was collected and analyzed using analysis of variance (ANOVA) and Kruskall–Wallis tests (α = 0.05).

Results: The denture base material and surface treatment significantly affected the SBS. The milled Temp Basic Tissue demonstrated the highest SBS values across all surface treatments, whereas the two 3D-printed denture base materials exhibited the lowest SBS values.

Conclusions: The bond strength of CAD-CAM-milled denture base resins to autopolymerizing repair resin is comparable to that of heat-cured resins. Surface roughening using air particle abrasion or 180-grit carbide paper can enhance the bond strength of the autopolymerizing repair resin to 3D-printed denture base materials.

Purpose: To investigate the effects of the number of ethylene oxide units in bis-EMA on the physical properties of additively manufactured occlusal splints.

Methods: Seven experimental materials containing bis-EMAs with three and 10 ethylene oxide units (BE3 and BE10, respectively) were prepared at different BE10 content rates (BE10-0%, -20%, -30%, -40%, -50%, -60%, and -80%). Half the specimens of each material were aged in boiling water. Flexural strength (FS), flexural modulus (FM), fracture toughness (FT), microwear depth (MD), degree of conversion (DC), water sorption (WSP), water solubility (WSL), color difference between non-aged and aged series (ΔE), and translucency (TP) were evaluated. All the evaluated properties other than FS and MD were analyzed by 1-way ANOVA and Tukey’s post hoc analysis, while FS and MD were analyzed by Kruskal–Wallis’s test and Bonferroni correction (α=0.05).

Results: BE10-80% revealed the lowest FS (P < 0.01 for BE10-0%, -20%, and -30%) and FM (P < 0.01, for all), while revealing the highest DC, WSP, WSL (P < 0.01 for all) and TP (P < 0.01 for all other than BE10-60%). BE10-50% showed the highest FT (P < 0.01 for all). BE10-50%, -60%, and -80% revealed significantly lower ΔE than others (P < 0.01) and lower MD than BE10-0% (P < 0.05). Regardless of the BE10 content, FS, FM, and FT decreased with aging.

Conclusions: The number of ethylene oxide units affects the physical properties of additively manufactured occlusal splints. The higher number of ethylene oxide units in bis-EMA enhanced the microwear resistance, DC, WSP, WSL, color stability, and translucency, whereas it deteriorated the FS and FM.

Purpose: This study aimed to determine the usefulness of machine learning techniques, specifically supervised and unsupervised learning, for assessing the cementation condition between a fixed partial denture (FPD) and its abutment using a resonance frequency analysis (RFA) system.

Methods: An in vitro mandibular model was used with a single crown and three-unit bridge made of a high-gold alloy. Two cementation conditions for the single crown and its abutment were set: cemented and uncemented. Four cementation conditions were set for the bridge and abutments: both crowns were firmly cemented, only the premolar crown was cemented, only the molar crown was cemented, and both crowns were uncemented. For RFA under cementation conditions, 16 impulsive forces were directly applied to the buccal side of the tested tooth at a frequency of 4 Hz using a Periotest device. Frequency responses were measured using a 3D accelerometer mounted on the occlusal surface of the tested tooth. Both supervised and unsupervised learning methods were used to analyze the datasets.

Results: Using supervised learning, the fully cemented condition had the highest feature importance scores at approximately 3000 Hz; the partially cemented condition had the highest scores between 1000 and 2000 Hz; and the highest scores for the uncemented condition were observed between 0 and 500 Hz. Using unsupervised learning, the uncemented and partially cemented conditions exhibited the highest anomaly scores.

Conclusions: Machine learning combined with RFA exhibits good potential to assess the cementation condition of an FPD and hence facilitate the early diagnosis of FPD retention loss.

Purpose: Depression is a leading cause of disability. Although tooth loss increases the risk of depressive symptoms, it is unclear whether dental prosthesis use moderates this risk. This study aimed to investigate whether dental prosthesis use moderates the association between tooth loss and new depressive symptoms in older adults.

Methods: This cohort study used data from the 2016 and 2019 Japan Gerontological Evaluation Study (JAGES). The participants were independent older adults aged ≥65 years without depressive symptoms in 2016. The onset of depressive symptoms in 2019 was the outcome variable. The exposure variables were dental status (≥20 teeth, 10–19 teeth with or without dental prostheses, and 0–9 teeth with or without dental prostheses) in 2016. Risk ratios (RRs) and 95% confidence intervals (CIs) were estimated using Poisson regression models with potential confounders as covariates.

Results: The analysis included 50,169 participants (mean age: 72.8 [standard deviation, 5.4] years). During follow-up, the incidence of depressive symptoms was 11.3%. Compared to those who had ≥20 teeth, the RR of depressive symptom onset was highest among those who had 0–9 teeth without dental prostheses (RR, 1.27; 95% CI, 1.04–1.56), after the adjustment for confounders. However, this risk was lower in those with 0–9 teeth and dental prostheses (RR, 1.08; 95% CI, 1.01–1.15).

Conclusions: These data highlight the potential of dental prostheses as an important factor in reducing the risk of depressive symptoms among individuals with severe tooth loss.

Purpose: This study aimed to investigate the effects of the age and sex of tooth donors on dentin bond strength.

Methods: A total of 38 extracted teeth (12 male and 26 female donors; age range: 17–82 years) were used in this study. In addition to donor age and sex, four other microtensile bond strength (μTBS) test specimen factors were evaluated: dentin position, bonding area, presence of voids at the interface, and computed tomography (CT) values of dentin. The μTBS was measured immediately (24 h) and 6 months after storage in water. After the μTBS testing, linear mixed and nonlinear regression models were used to analyze the effects of these factors on the μTBS data.

Results: The results from the linear mixed model revealed that the bonding area (P = 0.02), presence of voids at the interface (P = 0.04), and storage time (P < 0.001) significantly affected bond strength. In contrast, no correlation was observed between the μ TBS and dentin position (P = 0.08) or sex (P = 0.07). The results of the nonlinear regression model with robust variance–covariance estimators revealed that age significantly affected bond strength (P < 0.001). In addition, a significant positive correlation was found between μTBS and age (P < 0.001), with nonlinearity (P = 0.002). However, no correlation was observed between the μTBS and CT values (P = 0.69) without nonlinearity (P = 0.39).

Conclusions: These findings suggest that bond strength increases with age until 60 years but not afterward.

Purpose: The processes and methods of treating and polishing additive-manufactured (AMed) cobalt-chromium (Co–Cr) alloy clasps were assessed in vitro to determine their suitability for constant clinical use and the reduction of dental technician work.

Methods: AMed Aker clasps were fabricated by selective laser sintering of approximately 50 μm Co–Cr alloy powders. After the nodules and fins on the inner surface of the AMed clasps were removed and morphological correction was performed, a dental technician manually polished the clasps as a control. Four surface treatments, barrel finishing, shot peening, and wet and dry electropolishing, were performed to obtain smooth surfaces. In addition, hybrid manufacturing, which integrates repeated laser sintering and high-speed milling for one-process molding, was added to this study. After observing the treated surfaces using SEM and Hybrid Laser Microscope (HLM) the surface roughness, fitness accuracy, and retentive forces of the treated AMed clasps were measured, and their polishing efficiencies were compared.

Results: Similar to manual polishing, dry electropolishing yielded the smoothest surfaces in all treatments. The fitness accuracy of all clasp regions and treatment methods ranged from 80 to 140 μm, without significant differences among the treatment methods. All treated clasps showed acceptable retentive forces for clinical use, and hybrid manufacturing and wet electropolishing showed significantly higher forces.

Conclusions: AMed Co–Cr clasps with all surface treatments could be clinically used if additional slight manual polishing was performed; however, each processing condition should be carefully selected.

Purpose: This prospective cohort study examined the effects of the number of present and functional teeth on mortality among older Japanese adults requiring nursing care in an environment of comprehensive oral hygiene and nutritional management.

Methods: The study included 174 older adults (mean age: 84.4 ± 8.3 years; male/female: 49/125) in need of support or long-term care, who resided in either a local specialized healthcare facility or their own homes, and received daily oral hygiene and nutritional support at facilities in Okayama, Japan. The initial clinical oral examination along with assessment of general physical condition and nursing environment of the participants were performed in July 2013 and followed up for one year.

Results: All-cause mortality occurred in 28 (mean age: 88.7 ±13.4 years; male/female: 6 /22) individuals during the follow-up period. Cox proportional hazard analysis indicated that older age, low performance in activities of daily living (Barthel Index <40), and underweight status (body mass index <18.5) were significant risk factors for mortality. The number of present and functional teeth were not found to be significant risk factors for mortality.

Conclusions: During the one-year follow-up period, the number of present and functional teeth did not have a significant impact on mortality among older Japanese adults requiring nursing care in a well-managed environment of oral hygiene and nutritional status.

Purpose: This in vitro study investigated the influence of material selection, crown morphology, and vertical crown height on the biomechanical behavior of screw-retained monolithic hybrid abutment crowns (HACs).

Methods: Ninety implants were embedded in accordance with ISO standard 14801; ninety HACs were mounted (N=90). Monolithic crowns with varying group-specific designs were luted using titanium bases. HACs were fabricated from monolithic lithium disilicate ceramic (LD) or zirconia-reinforced lithium silicate ceramic (ZLS). The crown morphology was either maxillary premolar (LD_PM, ZLS_PM) or molar (LD_MO). The three groups were further divided into three subgroups of ten specimens, each designed with a small (7.5 mm), middle (10.5 mm), and high (13.5 mm) configuration of crown heights (N=10). A load-to-failure test at 30° off-axis was conducted using a universal testing machine until failure. For statistical analysis, Kolmogorov–Smirnov and Mann–Whitney U tests were conducted (P < 0.05).

Results: All LD_MO groups presented the highest failure values (808.7 to 947.9 N), followed by the LD_PM (525.8 to 722.8 N) and ZLS_PM groups (312.6 to 478.8N). A comparison between LD and ZLS materials (P < 0.001) as well as the crown morphology (P < 0.001) showed significant differences in failure values. The values in the subgroups of ZLS_PM (low, middle, high) decreased as the crown height increased. The fracture modes showed no consistent patterns across the test groups.

Conclusions: Material selection, crown morphology, and vertical crown height appear to be important factors that may influence the clinical failure values and patterns of screw-retained single implant crowns.

Purpose: This study aimed to investigate whether the presence of a mesial cantilever influences the biomechanical behavior and screw loosening in fixed partial dentures (FPDs) with a distally tilted implant in the atrophic posterior maxilla and where to best place the distal implant.

Methods: Two configurations of implant-supported four-unit FPDs were modelled using finite element analysis. Five interabutment distances were considered. The stress and strain distributions in the implants, abutments, and prosthetic screws were verified under occlusal loading. The development of the axial force on the abutments and screws was also examined. Two-sample t-tests were used to identify differences (P < 0.05).

Results: The von Mises stress distributions of the components in the two configurations were similar, as were the maximum plastic strains of the distal prosthetic screws, distal implants, and 30° abutments. The difference in the maximum plastic strains of the straight abutments was statistically significant. The preload of the 30° abutment screws was significantly reduced after the initial loading. In the absence of a mesial cantilever, the axial force on the straight abutments increased. However, when a mesial cantilever was used, the preload of the straight abutments was maintained, and the axial force on the prosthetic screws fluctuated less. The axial force fluctuation of the abutments gradually decreased as the interabutment distance increased.

Conclusions: Mesial cantilever usage had minimal effect on stress or strain distribution in FPD implants, abutments, or prostheses. However, it helped resist screw loosening. The distal screw access hole was preferably positioned close to the prosthetic end.

Purpose: This study aimed to evaluate the 10-year outcomes of partial fixed dental prostheses (P-FDPs) fabricated using metal-free fiber-reinforced composite (FRC) resin frameworks veneered with composite resin and supported by short and extra-short implants.

Methods: This study included 28 patients with 38 FRC prostheses supported by 96 implants. Implant and prosthesis survival and success rates were evaluated using Kaplan-Meier analysis.

Results: The 10-year implant survival and success rate, as determined by Kaplan-Meier analysis, was 96.9%, and the prosthesis survival and success rates were 94.7% and 92.0%, respectively. None of the parameters under investigation were significantly correlated with prosthetic survival or successful outcomes, but three parameters were correlated with higher peri-implant bone levels: implant placement in the mandible as opposed to the maxilla, shorter P-FDP spans, and natural teeth on the opposing arch.

Conclusions: FRC P-FDPs supported by short and extra-short implants presented high, up to 10-year, survival and success rates, when used to restore partially edentulous arches.

Purpose: This study investigated the influence of different palatal morphologies on the accuracy of intraoral scanning (TRIOS 4) of edentulous maxillae.

Methods: Six typodonts were fabricated for different palatal morphologies with flat (F), medium (M), and deep (D) palates, with palatal wrinkles (W), or smooth palates (S), resulting in six groups: WF, WM, WD and SF, SM, SD. Ten scans were performed for each group; standard tessellation language files obtained were imported into a software to measure trueness and precision in micrometer. Trueness was calculated as the mean of the standard deviation values obtained by superimposing each scan onto the reference scan. Precision was achieved by overlapping each scan with that with the best trueness in the group. Descriptive and post-hoc analyses were conducted.

Results: The mean values for trueness were as follows: WM=48.7±4.7, WD=161.7±18.4, WF=85.9±16, SM=48.1±2.4, SD=349.9±8.8, and SF=349.1±25.5. The precision values were as follows: WM=46.7±7.3, WD=46.9±9, WF=48.9±6.7, SM=46±2.7, SD=105.9±17.4, SF=72.6±10.8. Significant differences were observed for trueness between SM and SD (P < 0.001), SM and SF (P < 0.001), and WF and SF (P = 0.003); whereas for precision, significant differences were reported between WD and SD (P = 0.015). Regarding trueness and precision, no difference was found between WM and SM (P = 1.0).

Conclusions: Medium palatal depth showed the best accuracy. The mean accuracy values were within the clinical acceptability thresholds for all palatal morphologies. The presence of rugae improved the precision of deeper palates and the trueness of flat palates. No differences were observed in the medium palates with or without rugae.

Purpose: To determine whether the number of functional teeth, including the remaining natural teeth and prosthetically restored missing teeth, is associated with the dietary inflammatory index (DII), a quantitative measure of the inflammatory potential of the overall diet, in middle-aged and older Japanese adults.

Methods: National survey data from a non-institutionalized Japanese population aged ≥45 years was analyzed. Multivariable linear regression analyses were performed to assess the association between the DII score, which was calculated based on dietary records, and the number of functional teeth, which was determined during dental examination. All regression analyses were stratified according to the age groups 45–64, 65–74, and ≥75 years. The association between functional tooth units (FTUs) and the DII was assessed using sensitivity analysis.

Results: In total, 2407 individuals (1053 men and 1354 women; mean age = 66.7 years) were included. Multivariable analysis revealed that the number of functional teeth was significantly inversely associated with the DII score among participants aged ≥75 years (regression coefficient per increase of one in the number of functional teeth = -0.050; 95% confidence interval = -0.089 to -0.010). The number of functional teeth was not associated with the DII score in younger age categories (i.e., those aged 45–74 years). As in the primary analysis, the number of FTUs was significantly inversely associated with the DII score only in the group aged ≥75 years.

Conclusions: A greater number of functional teeth was associated with a lower DII (i.e., diet with greater anti-inflammatory potential) in Japanese adults aged ≥75 years.

Purpose: Color-changeable chewing gums are used to evaluate masticatory performance, as measured by a colorimeter or visually based on a color scale. Although anyone can use a color scale, the evaluation accuracy depends on the evaluator. We develop an application that can determine the degree of color change in chewing gum using smartphone images, making color evaluation accurate and easy to measure.

Methods: For the application, 60 chewed gum samples were prepared. Two shots were captured using two smartphone models. To create the application algorithm, a formula was developed to approximately map the color value from the smartphone images to the true value using a colorimeter. A basic validation was performed on 60 new samples covering a range of colors, followed by a field validation on 100 healthy dentate participants aged 20–39 years.

Results: The intraclass correlation coefficient for two repeated shots had a high value ≥ 0.97 in the basic and field validations, confirming reliability. No significant differences were observed in the paired t-test and Wilcoxon signed-rank test, and a significant and strong correlation (correlation coefficient ≥ 0.92) was observed between the evaluation values using the colorimeter and the basic and field validations. Bland–Altman plots further confirmed the validity of the application.

Conclusions: A software application was developed to enable easy, quick, and accurate determination of the masticatory performance of a chewing gum from images taken using a smartphone with highly reliable and validated results.

Purpose: Based on a self-controlled case, this study evaluated the finite element analysis (FEA) results of a single missing molar with wide mesiodistal length (MDL) restored by a single or double implant-supported crown.

Methods: A case of a missing bilateral mandibular first molar with wide MDL was restored using a single or double implant-supported crown. The implant survival and peri-implant bone were compared. FEA was conducted in coordination with the case using eight models with different MDLs (12, 13, 14, and 15 mm). Von Mises stress was calculated in the FEA to evaluate the biomechanical responses of the implants under increasing vertical and lateral loading, including the stress values of the implant, abutment, screw, crown, and cortical bone.

Results: The restorations on the left and right sides supported by double implants have been used for 6 and 12 years, respectively, and so far have shown excellent osseointegration radiographically.

The von Mises stress calculated in the FEA showed that when the MDL was >14 mm, both the bone and prosthetic components bore more stress in the single implant-supported strategy. The strength was 188.62–201.37 MPa and 201.85–215.9 MPa when the MDL was 14 mm and 15 mm, respectively, which significantly exceeded the allowable yield stress (180 MPa).

Conclusions: Compared with the single implant-supported crown, the double implant-supported crown reduced peri-implant bone stress and produced a more appropriate stress transfer model at the implant-bone interface when the MDL of the single missing molar was ≥14 mm.

Patients: This case report presents a minimally invasive approach to replace a missing mandibular lateral incisor using a dual-injection molding technique with flowable composite resins. Integrated with a comprehensive digital workflow, this method achieves a structurally and esthetically biomimetic, bi-layered prosthetic solution. A 34-year-old woman with congenital absence of a mandibular lateral incisor was successfully rehabilitated using a direct composite resin-bonded fixed partial denture (RBFPD).

Discussion: Two specialized three-dimensional (3D)-printed flexible indices stabilized by a custom-designed 3D-printed rigid holder were employed to ensure the meticulous injection molding of flowable composite resins formulated to emulate the inherent chromatic gradations between dentin and enamel. The inherent flexibility of the indices, combined with the holder, facilitated accurate and seamless adaptation to the complex morphological features of the dental arch, thereby mitigating the challenges commonly associated with rigid 3D-printed resin indices.

Conclusions: The bilayered direct composite RBFPD using 3D printed flexible indices prepared with a full digital workflow has several advantages over other dental prosthetic solutions, including noninvasiveness, cost-effectiveness, biomimetic esthetics, repairability, and shortened treatment times. Although the initial results are promising, further longitudinal studies with larger patient cohorts are required to confirm the long-term efficacy of this approach.