Effect of the Material Properties and Knee Position to the Bone Bruise Pattern in Skeletally Mature and Immature Subjects.

A bone bruise is generated by a bony collision that could occur when the anterior cruciate ligament (ACL) is injured, and its pattern reflects the injury mechanism and skeletal maturity. Thus, the bone bruise pattern is useful to predict a subject-specific injury mechanism, although the sensitivity and/or effect of the material property and the knee position at injury is still unclear. The objective of the present study was to determine the effect of the material property and knee position on the bone bruise pattern in skeletally mature and immature subjects using finite element analysis. Finite element models were created from a magnetic resonance (MR) image in the sagittal plane of a skeletally mature (25 y. o.) and immature (9 y. o.) male subject. The femur and tibia were collided at 2 m/s to simulate the impact trauma and determine the maximum principal stress. The analysis was performed at 15, 30, and 45 deg of knee flexion, and neutral, 10 mm anterior and posterior translated position at each knee flexion angle. Although high stress was distributed toward the metaphysis area in the mature model, the stress did not cross the growth plate in the immature model. The size of the stress area was larger in the mature model than those in the immature model. The location of the stress area changed depending on the joint position. Young's modulus of cartilage and trabecular bone also affected the location of the stress area. The Young's modulus for the cartilage affected peak stress during impact, while the size of the stress area had almost no change. These results indicate that the bone bruise pattern is strongly associated with subject-specific parameters. In addition, the bone bruise pattern was affected not only by knee position but also by tissue qualities. In conclusion, although the bone bruise distribution was generally called footprint of the injury, the combined evaluation of the quality of the structure and the bone bruise distribution is necessary for properly diagnosing tissue injury based on the MR imaging.

Biomechanical behavior of all-on-4 concept and alternative designs under different occlusal load configurations for completely edentulous mandible: a 3-D finite element analysis.

The aim of this study was to evaluate the effect of the All-on-4 design and 4 alternative implant-supported fixed prosthesis designs on stress distribution in implants, peri-implant bone, and prosthetic framework in the edentulous mandible under different loading conditions using three-dimensional finite element analysis (3D-FEA).Five different experimental finite element models (Model A (unsplinted 6), Model B (splinted 6), Model C (All-on-4), Model D (axial; 2 anterior, 2 posterior), and Model E (4 interforaminal)) were created. Three different loading conditions were applied (canine loading, unilateral I-loading, and unilateral II-loading). The highest minimum (Pmin) and the maximum (Pmax) principal stress values were acquired for cortical and trabecular bones; the highest von Mises (mvM) stress values were obtained for implants and metal frameworks. Model B and Model D showed the most favorable stress distribution. The All-on-4 design (Model C) also showed acceptable stress values close to those of Model B and Model D in the cortical and trabecular bones. In accordance with the stress values in the bone structure, the lowest stress values were measured in the implants and Co-Cr framework in Model B and Model D. The highest stress values in all structures were measured for unilateral loading- II, while the lowest values were found for canine loading. It was concluded that Model B and Model D experimental models showed better biomechanical performance in all structures. Furthermore, the use of a splinted framework, avoiding cantilevers, results in lower stress transmission. On the other hand, canine loading and unilateral loading-I exhibited the best loading conditions.

Influence of prosthetic index structures and implant materials on stress distribution in implant restorations: a three-dimensional finite element analysis.

BACKGROUND: Mechanical complications affect the stability of implant restorations and are a key concern for clinicians, especially with the frequent introduction of new implant designs featuring various structures and materials. This study evaluated the effect of different prosthetic index structure types and implant materials on the stress distribution of implant restorations using both in silico and in vitro methods. METHODS: Four finite element analysis (FEA) models of implant restorations were created, incorporating two prosthetic index structures (cross-fit (CF) and torc-fit (TF)) and two implant materials (titanium and titanium-zirconium). A static load was applied to each group. An in vitro study using digital image correlation (DIC) with a research scenario identical to that of the FEA was conducted for validation. The primary strain, sensitivity index, and equivalent von Mises stress were used to evaluate the outcomes. RESULTS: Changing the implant material from titanium to titanium-zirconium did not significantly affect the stress distribution or maximum stress value of other components, except for the implant itself. In the CF group, implants with a lower elastic modulus increased the stress on the screw. The TF group showed better stress distribution on the abutment and a lower stress value on the screw. The TF group demonstrated similar sensitivity for all components. DIC analysis revealed significant differences between TF-TiZr and CF-Ti in terms of the maximum (P < 0.001) and minimum principal strains (P < 0.05) on the implants and the minimum principal strains on the investment materials in both groups (P < 0.001). CONCLUSIONS: Changes in the implant material significantly affected the maximum stress of the implant. The TF group exhibited better structural integrity and reliability.

Comparison of stress distribution around all-on-four implants of different angulations and zygoma implants: a 7-model finite element analysis.

BACKGROUND: In recent years, zygomatic implants and the all-on-four treatment concept have been increasingly preferred for rehabilitation of atrophic maxillae. However, debate continues regarding the optimal configuration and angulation of the implants. The aim of this study was to analyze the biomechanical stress in implants and peri-implant bone in an edentulous maxilla with zygomatic implants and the all-on-four concept, using multiple implant configurations. METHODS: A total of 7 models consisting different combinations of 4-tilted dental implants and zygomatic implants were included in the study. In each model, a total of 200 N perpendicular to the posterior teeth and 50 N with 45° to the lateral tooth were applied. A finite element analysis was performed for determination of stress distribution on implants and peri-implant bone for each model. RESULTS: Higher stress values were observed in both cortical and trabecular bone around the 45°-tilted posterior implants in all-on-four models when compared to zygomatic implants. In cortical bone, the highest stress was established in an all-on-four model including 45°-tilted posterior implant with 4,346 megapascal (MPa), while the lowest stress was determined in the model including anterior dental implant combined with zygomatic implants with 0.817 MPa. In trabecular bone, the highest stress was determined in an all-on-four model including 30°-tilted posterior implant with 0.872 MPa while the lowest stress was observed in quad-zygoma model with 0.119 MPa. Regarding von Mises values, the highest stress among anterior implants was observed in an all-on-four model including 17° buccally tilted anterior implant with 38.141 MPa, while the lowest was in the including anterior dental implant combined with zygomatic implants with 20,446 MPa. Among posterior implants, the highest von Mises value was observed in the all-on-four model including 30°-tilted posterior implant with 97.002 MPa and the lowest stress was in quad zygoma model with 35.802 MPa. CONCLUSIONS: Within the limits of the present study, the use of zygoma implants may provide benefit in decreasing biomechanical stress around both dental and zygoma implants. Regarding the all-on-four concept, a 17° buccal angulation of anterior implants may not cause a significant stress increase while tilting the posterior implant from 30° to 45° may cause an increase in the stress around these implants.

Stress analysis of mandibular Kennedy class I partial overdenture submitted to different implant length and clasp designs - An in vitro study.

PURPOSE: To analyze the distribution of stresses for mandibular Kennedy class I removable partial overdentures submitted to different implant lengths and clasp designs. MATERIALS AND METHODS: Twenty-seven heat-cured acrylic resin casts with a uniform soft acrylic layer were constructed from models representing the mandibular Kennedy class I removable partial denture with the first premolars terminal abutment on both sides. The casts were grouped into a control group, group I, and group II with three casts of each for designing a different clasp on the last abutment with Rest, Proximal plate, Aker circumferential (RPA), Rest, Proximal plate, I-bar (RPI), and wrought wire (WW). All casts were submitted to vertical load for stress analysis after preparing channels at the buccal/distal surface of abutments, the crest of the ridge, and the buccal/lingual of the implant for placement of uniaxial strain gauges that can convert the electro-signals to micro-strain by using the software. Kolmogorov-Smirnov normality test, independent t-test, and one-way anlysis of Variance (ANOVA) test followed by Tukey`s Post Hoc for multiple comparisons test were used for statistical analysis. RESULTS: The control group results revealed more significant stresses on the ridge with RPA and RPI clasps but on the abutment with WW clasp as P < 0.05. In group I, the ridge was significantly stressed more than the implant followed by the abutment when the RPA clasp was used while there was insignificance on the implant with RPA and RPI as p > 0.05. In group II, the stresses were more on the abutment with RPA, RPI, and WW clasps followed by lower on the implant and lowest on the ridge. CONCLUSIONS: Proper implant and clasp type selection are critical for stress distribution on the ridge, abutment, and implant when using removable partial overdenture. The stresses on longer implants are tolerated and more widely distributed than shorter ones.

Co-Influence of Restoration Bonding and Inlay Cavity Design on Fracture Load of Restored Tooth.

INTRODUCTION: The aim of this study was to investigate the co-influence of indirect mesio- occlusal-distal (MOD) cavity geometry and inlay restoration bonding on quasi-static fracture load of the restored tooth. METHODS: Forty-eight intact human molar teeth were selected and prepared for standardized edge-shaped or round-shaped MOD cavities. The resin composite (Cerasmart, GC) inlays were bonded with the state-of-the-art inlay bonding protocol or with intentionally deteriorated bonding using n-hexane-wax solution for preconditioning. Restored teeth were loaded along the long axis of the tooth. Ultimate fracture load was recorded, and the type of fracture was visually determined and classified. Statistical analysis of load values was performed by Kruskal-Wallis test. RESULTS: Round-shaped cavity design with bonded restoration presented the highest fracture load (1658N). Bonding had significant influence on the fracture load of roundshaped cavity design (p=0.0003), whereas cavity design had no influence when the bonding was deteriorated (p=0.8075). In the case of deteriorated bonding, either the inlay or tooth fractured separately whereas in the bonded inlays fractures were commonly found both in the tooth and inlay. CONCLUSIONS: According to this study, bonded inlay restoration increased fracture resistance, while cavity design had no statistical difference on fracture resistance of the restored tooth.

Carbon Nanotube-Reinforced Dual Carbon Stress-Buffering for Highly Stable Silicon Anode Material in Lithium-Ion Battery.

Silicon (Si) anode suffers from huge volume expansion which causes poor structural stability in terms of electrode material, solid electrolyte interface, and electrode, limiting its practical application in high-energy-density lithium-ion batteries. Rationally designing architectures to optimize the stress distribution of Si/carbon (Si/C) composites has been proven to be effective in enhancing their structural stability and cycling stability, but this remains a big challenge. Here, metal-organic frameworks (ZIF-67)-derived carbon nanotube-reinforced carbon framework is employed as an outer protective layer to encapsulate the inner carbon-coated Si nanoparticles (Si@C@CNTs), which features dual carbon stress-buffering to enhance the structural stability of Si/C composite and prolong their cycling lifetime. Finite element simulation proves the structural advantage of dual carbon stress-buffering through significantly relieving stress concentration when Si lithiation. The outer carbon framework also accelerates the charge transfer efficiency during charging/discharging by the improvement of lithium-ion diffusion and electron transport. As a result, the Si@C@CNTs electrode exhibits excellent long-term lifetime and good rate capability, showing a specific capacity of 680 mAh g-1 even at a high rate of 1 A g-1 after 1000 cycles. This work provides insight into the design of robust architectures for Si/C composites by stress optimization.

Quasi-3D dynamic photoelastic analysis of stress distribution during preparation of simulated canals with 13 mechanical preparation systems.

AIM: The aim of this study is to compare the stress produced on the internal walls of simulated canals by nine rotary and four reciprocating systems. METHODOLOGY: Sixty-five isotropic transparent blocks containing a 60° curved and tapered simulated canal were selected and distributed into 13 groups (n = 5) according to the preparation system: BioRace, HyFlex EDM, iRaCe, Mtwo, One RECI, ProTaper Next, RaCe EVO, Reciproc, Reciproc Blue, R-Motion, VDW.ROTATE, XP-Endo Rise Shaper, and XP-Endo Shaper. Each resin block was mounted in a vice and a digital camera recorded the entire sequence of each preparation system through a circular polariscope set for dark field analysis. The video frames when each instrument reached the end of the coronal, middle, and apical thirds of the canal were extracted from the recordings and analysed by two independent observers regarding the stress generated on the canal walls using a semi-quantitative evaluation on a 0-5 scale. Intra- and inter-observer agreement were subjected to the Cohen's Kappa coefficient test, whilst the experimental results were compared using Kruskal-Wallis test post hoc pairwise comparisons with Bonferroni correction (α = 5%). RESULTS: The inter- and intra-observer agreement were 0.98 and 1, respectively. Most instruments demonstrated acceptable performance (scores ≤ 2) in all thirds. Other instruments, such as the HyFlex EDM 25.12 (coronal and middle thirds), Reciproc Blue R25 and Reciproc R25 (coronal and apical thirds), R-Motion 30.04 (apical third), and VDW.ROTATE 20.05 (apical third) showed scores higher than 3. Statistical analysis revealed a significant difference amongst the tested systems at the coronal, middle, and apical thirds (p < .05). CONCLUSION: None of the canal instrumentation protocols were stress-free, showing varying levels of stress concentrations. Various factors seemed to influence the magnitude of stress and its distribution pattern on the canal walls. Overall, instruments characterized by a larger taper, lower speed, reciprocating motion, and made of heat-treated NiTi alloy exhibited higher patterns of stress distribution.

Effects of different treatment modalities on biomechanical behavior of maxillary incisors with external invasive cervical resorption at different progression levels.

BACKGROUND/AIM: This study aimed to evaluate the biomechanical behavior of maxillary incisors with external invasive cervical resorption (EICR) at different progression levels after receiving different modes of treatment under occlusal forces using finite element analysis (FEA). MATERIALS AND METHODS: Three-dimensional (3D) models of intact maxillary central incisors were constructed and modified to include EICR cavities with different progression levels in the buccal cervical areas. The EICR cavities confined to dentin were repaired using Biodentine™ (Septodont Ltd., Saint Maur des Fausse ́s, France), resin composite, or glass ionomer cement (GIC) . Additionally, EICR cavities with pulp invasion requiring direct pulp capping were simulated as repaired using Biodentine only or 1 mm thick Biodentine and either resin composite or GIC for the rest of the cavity. Moreover, models with root canal treatment and EICR defects repaired using Biodentine, resin composites, or GIC were also generated. A force of 240 N was applied to the incisal edge. The principal stresses in the dentin were evaluated. RESULTS: GIC showed more favorable results than the other materials in EICR cavities confined to the dentin. However, Biodentine alone resulted in more favorable minimum principal stresses (Pmin ) compared to other materials in EICR cavities with close pulp proximity. Exceptionally, the models localized in the coronal third of the root with a circumferential extension of the cavity >90° showed more favorable results for GIC. The presence of root canal treatment had no significant effect on stress values. CONCLUSIONS: Based on this FEA study the use of GIC in EICR lesions confined to the dentin is recommended. However, Biodentine may be a better option for restoring EICR lesions close to the pulp with or without root canal treatment. Except when the circumferential extension of the cavity is >90°, the use of GIC may be more advantageous.

Effect of abutment type and creep behavior on the mechanical properties of implant restorations in the anterior region: A finite element analysis.

PURPOSE: This study aimed to assess the effect of abutment variation and creep on dental implant restorations. MATERIALS AND METHODS: Three finite element analysis (FEA) models of implant restorations were created, which were restored by conventional one-piece abutment (CA), hybrid abutment crown (HAC), and multi-unit abutment (MUA). The contacts were considered intimate (no friction), except for implant/abutment, abutment/screw, and abutment/screw/crown (HAC) attachments. The related mechanical parameters were used to improve the authenticity of the study. Instantaneous loads and constant loads (100 s) of 130 N were applied at a 30° angle to the palatal portion of the crown. Results were qualitatively and quantitatively evaluated using the equivalent von Mises stress, micro-gap distance of the implant-abutment interface (IAI), preload changes, and safety index. RESULTS: The stress state of each component differed depending on the restoration type, from CA and HAC to MUA. Implants and screws were the structures that suffered the most stress under instantaneous loads. Each metal structure exhibited a substantial decrease in stress during a constant loading period. The screws of the MUA abutment showed more preload loss (62.1 N) after constant loads for 100 s. MUA base produced less micro-gap (0.72 µm) at the IAI when it was compared with the CA group (0.93 µm) and HAC group (3.29 µm). CONCLUSIONS: The abutment type influences the mechanical properties and performance of implant restorations. The creep effect decreases the maximum stress level and increases the safety factors of each structure, indicating that stress-related mechanical complications may not occur more easily.

Finite Element Modeling of Powder Compaction: Mini-Tablets in Comparison with Conventionally Sized Tablets.

INTRODUCTION: Mini-tablets are considered a promising solid dosage form in the pharmaceutical industry due to advantages such as dosing accuracy, efficiency as a drug delivery system, and alleged improvement in mechanical properties. Nevertheless, only a few experimental studies are available in the literature regarding this topic and technical aspects, such as punch's shape and size effect on the stress and density distribution in the compact mini-tablets, are still not fully investigated. OBJECTIVES: In this paper, the influence of powder properties and process parameters, such as punch shape and size, on the evolution of mechanical properties during the tableting process and the potential occurrence of tablet defects are investigated using the mechanistic modeling approach, Finite Element Method (FEM). METHODS: The numerical simulation cases consist of four different die sizes, mini-tablets of 2 mm, and 3 mm, and conventionally sized tablets of 8 mm and 11.28 mm. Each tablet size is simulated using four distinctive excipients, Avicel® PH-102, Kollidon® VA64, Pearlitol® 100SD, and Supertab® 11SD, and two different punch geometries, a flat-face punch, and a bevel edge punch. RESULTS: The model predictions in terms of stress and density distribution at different stages of the compaction process indicate similar behavior in terms of density and stress distribution profiles between the conventionally sized tablets and mini-tablets for a particular excipient. CONCLUSIONS: Based on tablet size, small localized differences are noted (e.g., low-density regions, high shear bands, and heterogeneous density profiles), suggesting a possible risk of tableting defects for conventionally sized tablets compared to mini-tablets. Furthermore, it is observed that bevel-edged tablets could facilitate the formation of cracks, leading to possible capping failure.

Stress on the posteromedial region of the proximal tibia increased over time after anterior cruciate ligament injury.

PURPOSE: Anterior cruciate ligament (ACL) injury induces anterior and rotatory instability of the knee. However, the effect of this instability on the stress distribution in the knee joint in living participants is not clear. The aim of this study was to compare the distribution pattern of subchondral bone density across the proximal tibia in the knees with and without ACL injury, and to investigate the correlation between the distribution patterns of the subchondral bone density and the duration of ACL-deficiency. METHODS: Radiographic and computed tomography (CT) data pertaining to 20 patients with unilateral ACL injury without combined injury (ACL-deficient group) and 19 nontraumatic subjects (control group) were collected retrospectively. Subchondral bone density of the proximal tibia was assessed using CT-osteoabsorptiometry. Both the medial and lateral compartments of the proximal tibia were divided into three subregions of equal width in the sagittal direction. The percentage of high subchondral bone density areas (HDA%) in each subregion was quantitatively analyzed. RESULTS: HDA% of the posteromedial region was significantly higher in the ACL-deficient group (mean: 21.6%) than in the control group (14.7%) (p = 0.002). In contrast, HDA% of the anteromedial region was significantly lower in the ACL-deficient group (9.4%) than in the control group (15.3%) (p = 0.048). The logarithm of the time elapsed from ACL injury to CT examination showed a significant correlation with HDA% in the posteromedial region (p = 0.032). CONCLUSIONS: Subchondral bone density in the posteromedial region significantly increased after ACL injury and correlated with the duration of ACL-deficiency in semi-log manner in meniscus intact knees. The increase in stress on the posteromedial region after ACL injury, which induces a change in the subchondral bone density, justifies early ACL reconstruction after ACL injury.

Fracture resistance and stress distribution of weakened teeth reinforced with a bundled glass fiber-reinforced resin post.

OBJECTIVES: To make an in vitro assessment of fracture resistance of weakened and non-weakened teeth receiving intraradicular reinforcement using Rebilda bundled glass fiber-reinforced composite posts (GT), Rebilda conventional glass fiber posts (RP), or both systems combined (GT + RP). MATERIALS AND METHODS: Eighty sound bovine incisors were prepared and divided randomly into eight groups as follows: (a) nWnR: without simulating weakness, and without intraradicular reinforcement; (b) WnR: simulating weakness, but without intraradicular reinforcement; (c) nWGT: without simulating weakness, but with GT; (d) WGT: simulating weakness, and with GT; (e) nWRP: without simulating weakness, but with RP; (f) WRP: simulating weakness, and with RP; (g) nWGTRP: without simulating weakness, but with GT + RP; (h) WGTRP: simulating weakness, and with GT + RP. The specimens were subjected to the load-to-fracture test using the DL-2000MF universal testing machine. The finite element method assessed the mechanical behavior and stress distribution in endodontically treated teeth. RESULTS: The groups nWGTRP and WGTRP presented the best results in the load-to-fracture test, with the former being better than the latter, but with no statistically significant difference (P > 0.05). However, there was a significant difference between these and the other groups (P < 0.05), except for nWRP. Stress distribution inside the canal wall was different among the groups, with promising mechanical behavior for nWGTRP and nWRP. CONCLUSIONS: The Rebilda conventional fiber post (RP), combined with the Rebilda bundled glass fiber-reinforced composite post (GT) improves the resistance and stress distribution of immature teeth. CLINICAL RELEVANCE: Longitudinal fracture is less frequent in teeth restored with GT and RP posts.

Estimation of national stress index using socioeconomic antecedents - a case of MIMIC model.

Developed economies are at the forefront of facing the brunt of non-communicable diseases (NCD). The majority of the health expenditures are routed in managing obesity and mental disorder-related patients, and there is a fall in the productivity of the distressed and NCD prone labour. Several indicators of stress are used in literature to assess its implications. However, empirically no database has maintained the longitudinal data of national stress level. This study focused on constructing the socioeconomic antecedent of non-communicable stress which is leading to several NCDs. For this Multiple Indicator and Multiple Causes (MIMIC) model is utilized for 151 countries between 2008 and 2018. The results show that macroeconomic conditions, trade, and environmental quality follow fundamentals in explaining stress. While, national stress index is a significant source of smoking and mental disorder prevalence.

Impact of different axial wall designs on the fracture strength and stress distribution of ceramic restorations in mandibular first molar.

BACKGROUND: The purpose of this study was to investigate the fracture strength and stress distribution of four ceramic restorations. METHODS: Forty human mandibular first molars were collected and randomized into four groups after establishing the distal defect: full crown group with 4 mm axial wall height (AWH) (FC4); short AWH crown group with 2 mm AWH (SC2); occlusal veneer group with 0 mm AWH (OV0); occlusal distal veneer group with only the distal surface prepared, and 4 mm AWH (OD4). The teeth were prepared according to the groups and the ceramic restorations were completed using celtra duo ceramic blocks. The ceramic thickness of the occlusal surface is about 1.5 mm and the edge is about 1 mm. The failure load values and fracture modes of each group were detected by mechanical test in vitro. According to the groups to establish three-dimensional finite element analysis (FEA) models, a 600 N loading force was applied vertically using a hemispherical indenter with a diameter of 6 mm. and compare the stress distribution under the condition of different restorations. RESULTS: In vitro mechanical tests showed that the failure load values were SC2 (3232.80 ± 708.12 N) > OD4 (2886.90 ± 338.72 N) > VO0 (2133.20 ± 376.15 N) > FC4(1635.40 ± 413.05 N). The failure load values of the short AWH crown and occlusal distal veneer were significantly higher than that of occlusal veneer and full crown (P<0.05). The fracture modes of the full crown and occlusal veneer groups were mainly ceramic fractures and some were restorable tooth fractures. The short AWH crown and occlusal distal veneer groups presented with three fracture modes, the proportion of non-restorable tooth fracture was higher. The results of FEA show that under the spherical loading condition, the stress of ceramic was concentrated in the contact area of the loading head, the maximum von Mises stress values were FC4 (356.2 MPa) > VO0 (214.3 MPa) > OD4 (197.9 MPa) > SC2 (163.1 MPa). The stress of enamel was concentrated in the area where the remaining enamel was thinner, the maximum von Mises stress values was OD4 (246.2 MPa) ≈ FC4 (212.4 MPa) > VO0 (61.8 MPa) ≈ SC2 (45.81 MPa). The stress of dentin is concentrated in the root furcation and the upper third region of the root. However, stress concentration was observed at the tooth cervix in the full crown. CONCLUSION: Under certain conditions, the occlusal distal veneer shows better performance than the full crown.

Finite Element Analysis of the Stress Distribution Associated With Different Implant Designs for Different Bone Densities.

PURPOSE: The main objective of this study was to investigate the influence of implant design, bone type, and abutment angulation on stress distribution around dental implants. MATERIALS AND METHODS: Two implant designs with different thread designs, but with the same length and brand were used. The three-dimensional geometry of the bone was simulated with four different bone types, for two different abutment angulations. A 30° oblique load of 200 N was applied to the implant abutments. Maximum principal stress and minimum principal stresses were obtained for bone and Von misses stresses were obtained for dental implants. RESULTS: The distribution of the load was concentrated at the coronal portion of the bone and implants. The stress distributions to the D4 type bone were higher for implant models. Increased bone density and increased cortical bone thickness cause less stress on bone and implants. All implants showed a good distribution of forces for non-axial loads, with higher stresses concentrated at the crestal region of the bone-implant interface. In implant types using straight abutments there was a decrease in stress as the bone density decreased. The change in the abutment angle also caused an increase in stress. CONCLUSIONS: The use of different implant threads and angled abutments affects the stress on the surrounding bone and implant. In addition, it was observed that a decrease in density in trabecular bone and a decrease in cortical bone thickness increased stress.

Effect of Different Customized Abutment Types on Stress Distribution in Implant-Supported Single Crown: A 3D Finite Element Analysis.

PURPOSE: The purpose was to investigate stress distribution among 4 different customized abutment types: titanium abutment (Ti), titanium hybrid-abutment-crown (Ti-Hybrid), zirconia abutment with titanium base (Zir-TiBase), and zirconia hybrid-abutment-crown with titanium base (Zir-Hybrid-TiBase). MATERIALS AND METHODS: To achieve this purpose, 4 types of abutment configurations were simulated. A static load of 200 N (vertical) and 100 N (oblique) were applied to the models. The volume average, maximum, and stress distribution of von Mises stress, including percentage difference, were analyzed with 3D finite element analysis. RESULTS: According to the volume average von Mises stress, the Ti and Zir-TiBase comparison group showed that the Zir-TiBase group dominantly generated the higher value at Ti-base (22.57 MPa) and screw (17.68 MPa). To evaluate the effect of the hybrid-abutment-crown on volume average von Mises stress by comparing the Ti-Hybrid and Zir-Hybrid-TiBase groups, it was revealed that the combination of abutment and crown in the Ti-Hybrid group generated the worst stress concentration at the screw (12.42 MPa), while in the Zir-Hybrid-TiBase group presented stress concentration at the implant (8.90 MPa). CONCLUSIONS: A titanium base improved stress distribution at implant in zirconia abutment with titanium base by absorbing stress itself. Customized titanium hybrid-abutment-crown and zirconia hybrid-abutment-crown with titanium base created concentrated stress at screw and implant; respectively. Both abutment types should be cautiously used and maintenanced regularly.

Influence of Different Cements and Cement Thickness on the Stress Distribution under Occlusal Surfaces of Porcelain-fused-to-metal and Porcelain-fused-to-zirconium Crowns: A Finite Element Analysis.

AIM: The purpose of this study is to compare and evaluate the influence of two different cement space settings and two different cement types on the stress distribution under occlusal surfaces of tooth restored with two different types of crowns and studied by using three-dimensional (3D) finite element analysis (FEA). MATERIALS AND METHODS: Eight 3D finite element models (FEMs) representing a mandibular first molar tooth restored with crowns of, porcelain-fused-to-metal (PFM) and porcelain-fused-to-zirconia (PFZ) crowns with two cement space settings (50 and 80 µm) and with two different types of cement were constructed, using an FEA software (ANSYS, version 10). Each model was subjected to a distributed load simulating normal masticatory bite force of 225 N and was applied axial direction. Also, von Mises stress of each individual part in the system of models was calculated. RESULTS: The PFM crowns undergo less stress distribution than the PFZ crowns. The PFM crowns are more compatible with self-adhesive cements, and the PFZ crowns are more compatible with resin-modified glass ionomer cements. CONCLUSION: The PFM crowns with G-Cem Link Ace with 50 µm and PFZ crowns with RelyX Luting Plus with 80 µm combinations displayed less amount of stress distribution under normal masticatory bite force. CLINICAL SIGNIFICANCE: Self-adhesive resin cements with PFM crowns and PFZ with resin-modified glass ionomer cements show more benefits in stress distribution under occlusal surfaces under normal masticatory bite force.

[Experimental design of the lower jaw functional loading for implant-supported restoration in unfavorable clinical conditions]. / Eksperimental'noe modelirovanie funktsional'noi nagruzki nizhnei chelyusti pri protezirovanii s oporoi na implantaty v neblagopriyatnykh klinicheskikh usloviyakh.

THE AIM OF THE STUDY: Was to create a finite element design to evaluate the masticatory stress distribution on the full fixed prosthesis with three supporting implants and the mandibular bone in the conditions most closely resembling the real ones. MATERIALS AND METHODS: The geometric design was created with the results of a CBCT of a real patient. The transfer of the DICOM into STL format was carried out in the Mimics Medical 21 program, in which the author's splinting device for the implant was designed. The actual thicknesses of the patient's compact and cancellous bone layers were measured with Romexis ver. 4.5.1. Scanning of the artificial dentition was performed with the iTero Element 2 Version 1.7 which created an object in STL format. Design was performed in the package for finite element analysis Ansys 19.3. Tetrahedral elements of the second order were used for calculation. The structural elements were connected in the model by a rigid «Bonded¼ contact. RESULTS: A finite element model has been created for the experimental load design on the lower jaw for immediate implant restoration with few supports in combination with a device for stabilizing the implant in unfavorable clinical conditions. It is shown that the designed finite element model takes into account the biomechanics of the prosthesis with few supports. When calculating, the entire model was fixed to the mandibular process at its base, and was loaded with a force of 500 N, distributed over the teeth. The values of the maximum stresses obtained in the elements were 51.8 MPa for the compact layer and 245 MPa for titanium elements. CONCLUSION: Thus, we created personalized geometric and finite element models for calculating the distribution of functional load on a long full fixed implant-supported prosthesis with few artificial supports, which makes the experimental results more accurate and correct.

Cementum thickening leads to lower whole tooth mobility and reduced root stresses: An in silico study on aging effects during mastication.

In the course of a lifetime the crowns of teeth wear off, cementum thickens and the pulp closes-in or may stiffen. Little is known about how these changes affect the tooth response to load. Using a series of finite element models of teeth attached to the jawbone, and by comparing these to a validated model of a 'young' pig 3-rooted tooth, the effects of these structural changes were studied. Models of altered teeth show a stiffer response to mastication even when material properties used are identical to those found in 'young' teeth. This stiffening response to occlusal loads is mostly caused by the thicker cementum found in 'old' teeth. Tensile stresses associated with bending of dentine in the roots fall into a narrower distribution range with lower peak values. It is speculated that this is a possible protective adaptation mechanism of the aging tooth to avoid fracture. The greatest reduction in lateral motion was seen in the bucco-lingual direction. We propose that greater tooth motion during mastication is typical for the young growing animal. This motion is reduced in adulthood, favoring less off-axis loading, possibly to counteract natural bone resorption and consequent compromised anchoring.