Unilateral Loading Research Articles

MAGNET VERSUS OLS ATTACHMENTS FOR IMPLANT OVERDENTURES: A STRESS ANALYSIS STUDY

Objectives: to compare between the microstrains transmitted to the implants with magnetic and OLS attachments in 2-implant overdentures. Methodology: two dummy implants 3.7 mm in diameter and 12mm in length were placed in an acrylic resin model resembling a completely edentulous mandible. Attachment pick up was done for the magnetic attachment followed by loading and measurement. Four Strain gauges were used to measure microstrains around the implants during unilateral and bilateral loading using a universal testing machine and a multi-channel strain meter. The procedure was repeated for the OLS attachment. Measurements were tabulated and statistically analyzed. Results: loading sides demonstrated significantly higher microstrains around the implants with the two attachments than non-loading sides. OLS attachment showed significantly higher microstrains than magnetic attachment for both loading and non-loading sides during unilateral loading. During bilateral loading, there was no significant difference between the two attachments. Conclusion: implant overdentures retained by magnetic attachments transmit less stresses to the implants than OLS attachments with PEEK retentive matrices during unilateral loading. During bilateral loading, the stresses transmitted by the two attachments were comparable.

THE EFFECT OF MAGNETIC AND LOCATOR ATTACHMENTS ON STRAIN AROUND IMPLANTS RETAINING MANDIBULAR OVERDENTURE: AN IN VITRO STUDY

Objectives: This in-vitro strain gauge study was conducted to compare between magnetic and locator attachments regarding strain induced around two implants supporting a mandibular overdenture. Methodology: The study was performed on acrylic models of a completely edentulous mandibular arch with two implants installed bilaterally at the canine areas. The strain induced around the implants was studied during unilateral and bilateral loading at the first molar area using a universal testing machine. Results: The results of this study showed that there was no statistically significant difference between the two studied groups during unilateral loading with higher values in the locator attachment group while during bilateral loading there was a statistically significant difference between the two groups but with higher micro-strain values for the magnetic attachment group Conclusion: Within the limitation of this in-vitro study, it could be conclude that the attachment type could have an effect on the amount of load that will be transmitted to the implants supporting an over denture. Clinical studies are required to evaluate the effect of type of attachment on peri-implant crestal alveolar bone loss and correlate it with the results of the current study.

Gait training assist system of a lower limb prosthetic visualizing muscle activation pattern using a color-depth sensor.

Some unilateral lower-limb amputees load the intact limb more than the prosthetic limb. This can cause chronic pains, fatigue, lumbago, and joint diseases, including knee osteoarthritis. To avoid and counteract these symptoms it is necessary to improve their asymmetric gait. Increasing the function of the hip abductor muscle is important to maintaining symmetrical weight distribution. Therefore, the purpose of this study is to develop a training assist system, which estimates and visualizes an abductor muscle by using a color-depth sensor. To estimate the muscle activation, first, the floor reaction force is calculated using a simple dynamic model. Then, the hip torque is calculated using joint angles. The floor reaction force and, the muscle length are calculated based on a human musculoskeletal model. Muscle activity is estimated by these parameters. Evaluation experiments of this proposed method were performed on healthy persons and unilateral trans femoral amputees, and the effectiveness of this proposed algorithm has been confirmed.

Effects of different numbers of mini-dental implants on alveolar ridge strain distribution under mandibular implant-retained overdentures

PurposeTo investigate the strains around mini-dental implants (MDIs) and retromolar edentulous areas when using different numbers of MDIs in order to retain mandibular overdentures. Materials and methodsFour different prosthetic situations were fabricated on an edentulous mandibular model including a complete denture (CD), and three overdentures, retained by four, three or two MDIs in the interforaminal region with retentive attachments. A static load of 200N was applied on the posterior teeth of the dentures under bilateral or unilateral loading conditions. The strains at the mesial and distal of the MDIs and the retromolar edentulous ridges were measured using twelve strain gauges. Comparisons of the mean microstrains among all strain gauges in all situations were analyzed. ResultsThe strain distribution determined during bilateral loading experienced a symmetrical distribution; while during unilateral loading, the recorded strains tended to change from compressive strains on the loaded side to tensile strains. Overall, the number of MDIs was found to be passively correlated to the generated compressive strain. The highest strains were recorded in the four MDIs followed by three, two MDIs retained overdenture and CD situations, respectively. The highest strain was found around the terminal MDI. ConclusionsThe use of a low number of MDIs tends to produce low strain values in the retromolar denture-bearing area and around the terminal MDIs during posterior loadings. However, when using a high number of MDIs, the overdenture tends to have more stability during function.

Effect of Buccal Implant Inclination on Stresses Around Two-Implant-Retained Overdentures with Resilient Stud Attachments.

This study aimed to evaluate the effect of buccal implant inclination on stresses around two-implant-retained overdentures with resilient stud attachments. Four acrylic models representing a mandibular edentulous ridge were constructed. For each model, two implants were placed at canine areas. Models were classified into four types according to the degree of buccal implant inclination: Group I (GI, 0 degrees), Group II (GII, 10 degrees), Group III (GIII, 20 degrees), and Group IV (GIV, 30 degrees). Overdentures were connected to the implants with Locator attachments. Regular light-retention inserts were used for all groups, and extended range inserts were also used for GIV (GIVext), making a fifth comparison group. Four strain gauges were bonded at the buccal, lingual, mesial, and distal surfaces of each implant to monitor the stresses during bilateral and unilateral load application. Tensile stresses were recorded at distal and lingual gauges, and compressive stresses were recorded at mesial and buccal gauges for all groups. GIV recorded the highest stresses, followed by GIII, GII, GIVext, and GI. Distal position recorded the highest stresses, followed by lingual, mesial, and buccal. Nonloading side was associated with significantly higher stresses than loading side. The peri-implant stresses increase as the buccal implant inclination increases when resilient stud attachments are used for implant overdentures. Therefore, it is recommended to insert the implants parallel to each other to decrease peri-implant stresses. However, when buccal inclination is inevitable due to anatomical limitations, it should be limited to 10 degrees for standard nylon inserts, or extended range inserts are recommended.

Экспериментальное обоснование мероприятий по совершенствованию проектных решений строительных конструкций зданий и сооружений АЭС

In recent time requirements for security of building constructions, an internal inventory and personnel at action of special inertial reaction taking into account increase in their predicted intensity are toughened. It is possible to carry to similar special types of loadings: seismic influence, blow of the plane, the fire, a loading of designs air shockwaves, the unauthorized armed attacking actions and so forth. These circumstances cause need of identification of stocks of design durability, the detailed description of features of formation of zones of destruction, distribution of indignations for the actual designs including equipped with tools shock-, vibration- and fire-protection. The central element of design protection of the modern NPP is the pressure-tight cover of the reactor (containment) capable to maintain not only extreme external mechanical influences (earthquakes, hurricanes, plane crash, etc.), but also intrinsic pressure up to 0,4 MPa. However, at damage of building constructions because of emergence of cracks, through holes, a dehiscence of a reinforcing layer mechanical strength and a limit of their fire proofness can change considerably. Thus, preservation of a wholeness of building constructions of the NPP becomes one of decisive factors for safety of operation of the reactor in the conditions of emergency situation. Now new approaches to increase in design protection of envelopes of the NPP are developed. In particular, tests of perspective concrete goods with “non-contact” joints of fittings are carried out (like loopback joints, and also direct or bent restart-up with various anchor devices). Within the pilot studies full-scale tests of reinforced concrete linear elements with unwelding joints of metal mountings in various conditions were carried out. Tests were carried out at the hydrostatic stand of LLC “Stroydinamika”. Sizes of models 4700´400´400 mm. The class of durability of concrete of reinforced concrete models declared by the manufacturer is B25. The generalized test data for option of multiple sign-variable mechanical influence are provided on the chart “loading movement”. During tests for the first time it was succeeded to investigate features of destruction of a loopback joint on slanting section. Destruction of a loopback joint on slanting section is reached only at a unilateral loading in the conditions of the application of loading immediately near a joint. The crack arises at loadings 0,7-0,8 from maximal. For development of recommendations about application, calculated justification and designing of the offered options of a joint tests of designs on the inertial unidirectional and reversal load began. These tests are intended to give the answer to a question of effectiveness of use of loopback joints of metal mountings for decrease in intensity of destructions at shock and explosion.

EXPERIENCE AND PRACTICE IN CARRYING A HEAVY, UNILATERAL LOAD: FOOTPRINT EVIDENCE

Although a significant amount of research has examined the biomechanical effects of carrying a load on human walking, most has focussed on fore and aft loads, or evenly balanced loads. In addition, most research on human walking no longer considers footprint analysis, despite its ease of use and its effectiveness in studies of balance. However, one project, with a small number of subjects, suggested that people carrying a heavy load in one hand (e.g., a suitcase or toolbox) make two sorts of adjustments to the placement of their feet on the substrate. The first and most obvious change is a decrease in foot angle (in-toeing) on the unloaded side. This puts the anterior part of the foot further under the center of mass when carrying a load in the contralateral hand and has been amply documented in subsequent studies. The second and more subtle change is a decrease in step width, a practice which also moves the foot on the unloaded side closer to the center of mass. However, tests subsequent to the original study did not show a consistent or significant use of this technique. This discrepancy between original and subsequent results in step width can be explained by the level of expertise which various subjects have. Experience carrying heavy loads may be required for most subjects to develop ways of accommodating loads. For this project, subjects were tested under two conditions: carrying an empty canvas bag; carrying the same bag with 21% of their body weight in it. All subjects walked on paper runners, wearing paint-soaked socks to leave footprint trails. Subjects were asked to walk once with no weights followed by three more times with weights. They were then given 10–15[Formula: see text]min of practice with the weighted bag, then asked to repeat the protocol, for a total of eight trials (two unweighted and six weighted). Foot angle and step width were measured for all trials. Results show that practice does indeed make a difference in the use of a narrower step when carrying a heavy load. Specifically, the first three weighted trials show a decrease in step width that is nonsignificant, but the last three evince a significant reduction as compared to unweighted trials. In addition, lifetime experience carrying a heavy load led to more immediate changes in foot placement. We conclude that the initial study involved subjects who already had experience carrying a unilateral heavy load and that, as with other activities, mechanically more effective movements are acquired with greater experience and practice.

Carrying asymmetric loads during stair negotiation

Individuals often carry items in one hand instead of both hands during activities of daily living. The combined effects of carrying asymmetric loads and stair negotiation may create even higher demands on the low back and lower extremity. The purpose of this study was to investigate the effect of symmetric and asymmetric loading conditions on L5/S1 and lower extremity moments during stair negotiation. Twenty-two college students performed stair ascent and stair descent on a three-step staircase (step height 18.5cm, tread depth 29.5cm) at preferred pace under five load conditions: no load, 10% body weight (BW) unilateral load, 20% BW unilateral load, 10% BW bilateral load, and 20% BW bilateral load. Video cameras and force platforms were used to collect kinematic and kinetic data. Inverse dynamics was used to calculate frontal plane moments for the L5/S1 and lower extremity. A 20% BW unilateral load resulted in significantly higher peak L5/S1 lateral bending, hip abduction, and external knee varus moments than nearly all other loading conditions during stair ascent and stair descent. Therefore, we suggest potential benefits when carrying symmetrical loads as compared to an asymmetric load in order to decrease the frontal joint moments, particularly at 20% BW load.

Effect of Implant Position and Edentulous Span Length on Stresses Around Implants Assisting Claspless Distal Extension Partial Overdentures: An In Vitro Study.

The aim of this in vitro study was to evaluate the effect of implant position and edentulous span length on stresses around implants assisting claspless distal extension partial overdentures. Four bilateral mandibular distal extension acrylic models were constructed. Two implants were inserted in the distal extension ridges parallel to each other and perpendicular to the ridges. Based on the implant position, models were categorized into two groups: Group I, mesial implants position and Group II, distal implant position. Each group was subdivided into 2 subgroups according to the length of edentulous span: Subgroup a, long span and Subgroup b, short span. Four claspless partial overdentures were fabricated on the models and retained to the implants with ball-and-socket attachments. Three strain gauges were cemented to the acrylic resin at buccal, lingual, and distal sides of each implant. Static unilateral vertical load of 60N was applied in the central fossae of the first molar, and peri-implant stresses were measured on loading and nonloading sides. Distal implant placements recorded significantly higher peri-implant stresses than did mesial implant placements. Long saddle recorded significantly higher stresses than did short saddle. The greatest peri-implant stresses were recorded with distal placement and long saddle at the loading side. At loading and nonloading sides, the mesial placement with a short saddle recorded the lowest strain. For mandibular distal extension partial overdentures, a mesially placed implant combined with short saddle may be preferable to a distally placed implant combined with long saddle, as the former was associated with reduced peri-implant stresses.

Effect of implant- and occlusal load location on stress distribution in Locator attachments of mandibular overdenture. A finite element study

PURPOSEThe aim of this study is to evaluate and compare the stress distribution in Locator attachments in mandibular two-implant overdentures according to implant locations and different loading conditions.MATERIALS AND METHODSFour three-dimensional finite element models were created, simulating two osseointegrated implants in the mandible to support two Locator attachments and an overdenture. The models simulated an overdenture with implants located in the position of the level of lateral incisors, canines, second premolars, and crossed implant. A 150 N vertical unilateral and bilateral load was applied at different locations and 40 N was also applied when combined with anterior load at the midline. Data for von Mises stresses in the abutment (matrix) of the attachment and the plastic insert (patrix) of the attachment were produced numerically, color-coded, and compared between the models for attachments and loading conditions.RESULTSRegardless of the load, the greatest stress values were recorded in the overdenture attachments with implants at lateral incisor locations. In all models and load conditions, the attachment abutment (matrix) withstood a much greater stress than the insert plastic (patrix). Regardless of the model, when a unilateral load was applied, the load side Locator attachments recorded a much higher stress compared to the contralateral side. However, with load bilateral posterior alone or combined at midline load, the stress distribution was more symmetrical. The stress is distributed primarily in the occlusal and lateral surface of the insert plastic patrix and threadless area of the abutment (matrix).CONCLUSIONThe overdenture model with lateral incisor level implants is the worst design in terms of biomechanical environment for the attachment components. The bilateral load in general favors a more uniform stress distribution in both attachments compared to a much greater stress registered with unilateral load in the load side attachments. Regardless of the implant positions and the occlusal load application site, the stress transferred to the insert plastic is much lower than that registered in the abutment.

Peri-implant strain around mesially inclined two-implant-retained mandibular overdentures with Locator attachments.

This study aimed to evaluate the peri-implant strain around mesially inclined implants used to retain mandibular overdentures with Locator resilient attachments. Four mandibular edentulous acrylic resin models received two implants in the canine areas with 0°, 5°, 10°, and 20° mesial inclinations. Overdentures were connected to the implants using Locator attachments. Pink nylon inserts (light retention) were used for all implant inclinations, and red inserts were used for 20° inclination (20°red). Four strain gages were bonded on the mesial (M), distal (D), buccal (B), and lingual (L) surfaces of each implant. Peri-implant strains were measured during bilateral and unilateral loading. The 20° inclination showed the highest strain, followed by 10° and 5°, and both 0° and 20°red presented with the lowest strain. Site D was associated with the highest strain, followed by M, B, and L, which showed the lowest strain values. Unilateral loading and the loading side presented with significantly higher strain values than bilateral loading and the nonloading side, respectively. Hence, in this study, strains around the two-implant-retained overdentures with Locator attachments increased with increases in mesial implant angulation, except when red male inserts were used.

The Impact of Distal Cantilever Extension on the Stress Around Four Implants Connected by a Bar Retained Palateless Overdenture (In Vitro Stress Analysis)

Aim: This in vitro research was aimed to compare the impact of distal cantilever extension on the stress around four implants retained palateless overdenture by means of a bar. Materials and methods: Four implants were placed bilaterally in lateral incisor and the first premolar positions of edentulous acrylic resin maxillary model; connected bar with 7 mm distal cantilever extension with soft liner female retentive element was used. Eight strain gauges were bonded to the acrylic resin at the mesial and distal surfaces of each implant, stress was measured, then the 7 mm cantilever extension was trimmed and the stress measured for the bar without distal cantilever extension. Results: Bar with distal cantilever extension demonstrate a significant increase in stress compared to the bar without distal cantilever extension in unilateral loading and bilateral loading. During unilateral loading in bar with distal cantilever extension and bar without distal cantilever extension the maximum stress was recorded at mesial side of posterior implant of loading side. Conclusion: The four implants connected with the bar without distal cantilever extension demonstrates lower stress than bar with distal cantilever extension.

钢锚板式钢-混组合索塔锚固体系单侧受荷承载力数值分析

采用非线性有限元仿真分析方法，研究在单侧受荷下钢锚板式钢-混组合索塔锚固体系的极限承载力。分析结果表明，单侧索力作用时的极限承载能力状态，非加载侧下横隔板与底板之间靠近侧板处混凝土发生破坏，此时，最大主压应力出现在加载侧侧板与上横隔板交界处所对应的混凝土角点处。锚固区普通钢筋最大轴向应力出现在加载侧侧板与上横隔板交界处所对应的外侧钢筋位置。随着荷载系数的增大，混凝土裂缝从加载侧向非加载侧发展，当荷载系数达到3.04时，混凝土塔柱发生破坏。 The ultimate bearing capacity of steel-concrete composite cable-pylon anchorage system with steel anchor slab under the unilateral cable force has been studied using nonlinear finite element analysis method. The analysis result showed that under unilateral load, the concrete between the bulkhead and floor in the non-load side has been broken. At this time the maximum principal compressive stress appeared in the concrete corner point of the junction between the load side plates and upper diaphragm. The maximum axial stress in reinforced anchorage area appeared in the junction between the load side plates and upper diaphragm. With the increase of load, the concrete cracks were developing from the load side to the non-load side. When the load factor reached 3.04, the concrete of tower has been destructed.

The Relationship Between 2-Dimensional Knee-Valgus Angles During Single-Leg Squat, Single-Leg-Land, and Drop-Jump Screening Tests.

Injuries to the anterior cruciate ligament (ACL) and patellofemoral joint (PFJ) are a significant problem in female athletes. A number of screening tasks have been used in the literature to identify those at greatest risk of injury. To date, no study has examined the relationship in 2-dimensional (2D) knee valgus between common screening tasks to determine whether individuals exhibit similar movement patterns across tasks. To establish whether frontal-plane projection angle (FPPA) during the single-leg squat (SLS), single-leg land (SLL), and drop jump (DJ) are related. Cross-sectional study. University laboratory. 52 national-league female football players and 36 national-league female basketball players. 2D FPPA during the SLS, SLL, and DJ screening tasks. Significant correlations were found between tasks. FPPA in the SLS was significantly correlated with SLL (r = .52) and DJ (r = .30), whereas FPPA in the SLL was also significantly correlated to DJ (r = .33). FPPA was significantly greater in the SLS than in the SLL (P < .001) and DJ (P < .001) and in the SLL than in the DJ (P < .001). The results showed that 2D FPPA is correlated across the SLS, SLL, and DJ tasks. However, significantly greater FPPA values in the unilateral tasks suggest that the DJ may not identify risk of injury in sports where primary injury mechanisms are during unilateral loading tasks. Therefore, it is recommended that both unilateral and bilateral tasks be included when screening for ACL and PFJ injury risk.

Calculation of the strain-deformation condition of the spinal motor segment during loading

A mathematical model is proposed to analyze the spinal strain-deformation condition resulting from axial and lateral g-loads that are generated by changes in the gravity field and/or pilot’s actions during high-performance aircraft maneuvering under flight overload conditions. An algorithm of solution has been developed, which takes into account changes in the intervertebral disk pressure and the fibrous ring shape at the time when loading reaches close-to-critical g-values. Calculation of the spinal-strain deformation condition was implemented using the SPLEN computer system (KOMMEK, Russia). Analysis of the spinal straindeformation condition was made for two types of external loads: normal load and unilateral load with the bending moment. Maximum permissible loads on the spinal segment were evaluated, and a pattern of distribution of strain intensity and mean strains, spinal deformation, and the destruction field was described. The developed computer models can be used as a basis for developing a technique of predicting characteristic spinal injuries due to different extreme loads and pathologies.

Hybrid Finite Element Modeling for Seismic Structural Response Analysis of a Reinforced Concrete Structure

For rational seismic structural response analysis of a Reinforced Concrete (RC) structure, this paper presents a solid element in which a sophisticated concrete constitutive relation and cracking functionality are implemented. Hybrid finite element modeling that uses solid and beam elements for concrete and steel rebar is proposed, made tougher with a method of constructing the hybrid finite element. Well-balanced modeling is possible by first generating beam elements for the steel rebars and then generating solid elements for the concrete with nodes of the beam elements being shared by the solid element. A numerical experiment was carried out for a RC column subjected to unilateral loading, in order to examine the potential applicability of the hybrid finite element modeling. The computed results are compared with the experimental data, and the nonlinear relation between the displacement and reaction force is reproduced to some extent.

Old age and the associated impairment of bones' adaptation to loading are associated with transcriptomic changes in cellular metabolism, cell-matrix interactions and the cell cycle

In old animals, bone's ability to adapt its mass and architecture to functional load-bearing requirements is diminished, resulting in bone loss characteristic of osteoporosis. Here we investigate transcriptomic changes associated with this impaired adaptive response. Young adult (19-week-old) and aged (19-month-old) female mice were subjected to unilateral axial tibial loading and their cortical shells harvested for microarray analysis between 1h and 24h following loading (36 mice per age group, 6 mice per loading group at 6 time points). In non-loaded aged bones, down-regulated genes are enriched for MAPK, Wnt and cell cycle components, including E2F1. E2F1 is the transcription factor most closely associated with genes down-regulated by ageing and is down-regulated at the protein level in osteocytes. Genes up-regulated in aged bone are enriched for carbohydrate metabolism, TNFα and TGFβ superfamily components. Loading stimulates rapid and sustained transcriptional responses in both age groups. However, genes related to proliferation are predominantly up-regulated in the young and down-regulated in the aged following loading, whereas those implicated in bioenergetics are down-regulated in the young and up-regulated in the aged. Networks of inter-related transcription factors regulated by E2F1 are loading-responsive in both age groups. Loading regulates genes involved in similar signalling cascades in both age groups, but these responses are more sustained in the young than aged. From this we conclude that cells in aged bone retain the capability to sense and transduce loading-related stimuli, but their ability to translate acute responses into functionally relevant outcomes is diminished.

Effects of two different degrees of lateral-wedge insoles on unilateral lower extremity load-bearing line in patients with medial knee osteoarthritis

ObjectiveThe aim of this study is to assess the effect of 5 and 10° lateral-wedge insoles on unilateral lower extremity load carrying line in patients with medial knee osteoarthritis using the L.A.S.A.R. posture alignment system. Patients and methodsTwenty subjects (10 females and 10 males, mean age 67.7 ± 5.4 years (range: 58–78) with bilateral medial knee osteoarthritis were included in the study. The laser line projected on the person by the L.A.S.A.R. posture alignment system showed joint load carrying line. The location of the joint load carrying line in static standing with one foot on the force plate was assessed with barefoot, and 5° and 10° lateral-wedge insoles. Displacement of the load carrying line was measured using a ruler placed tangentially to the patella at the level of joint line. ResultsThe load carrying lines measured with 5° and 10° lateral-wedge insoles were significantly laterally located compared to that without wearing insole (p < 0.001). 10° lateral-wedge insole caused a significant more lateral shifting of the load carrying line than 5° lateral-wedge insole (p < 0.001). ConclusionBoth wedge insoles was effective in moving of the unilateral lower extremity load carrying line to the lateral. Lateral wedged insoles are biomechanically effective and reduce loading of the medial compartment in patients with medial knee osteoarthritis.

Maxillary “All-On-Four” treatment using zygomatic implants. A mechanical analysis

Zygomatic implants may be used for dental rehabilitation in atrophic maxillae. The aim of this study was to establish experimentally the areas of stress distribution using 2 kinds of "All-On-Four" maxillary procedures. The best position to insert the implants was selected using polyurethane craniomaxillary models and surgical guides were made. Group 1 was designed with two posterior zygomatic implants and two conventional anterior implants, and group 2 with two posterior zygomatic implants and two anterior zygomatic implants. A titanium bar was built to link the 4 implants in both groups. Photoelastic replicas of these models were made and the implants were inserted using the surgical guides. An Instrom 4411 testing machine was used to perform a unilateral compressive loading at the level of the right first molar until 2mm of displacement was obtained. Group 1 showed a high strain concentration in the right lateral orbital region at the level of the apex of the zygomatic implant. Less strain was noticed at the apical levels of the conventional implants in the anterior sector and of the contralateral zygomatic implant. Group 2 showed high strains in the lateral inferior orbital area. The load was low in the alveolar bone sector. Zygomatic bone and paranasal structures are loaded at high levels when zygomatic implants are used to stabilize a full maxillary prosthodontic rehabilitation on 4 implants. The use of 4 zygomatic implants loads the alveolar bone to a lower extent and seems better suited from a mechanical point of view than the use of 2 zygomatic implants.

Finite element analysis on stress distribution of maxillary implant-retained overdentures depending on the Bar attachment design and palatal coverage.

PURPOSEThe purpose of this study was to determine the effect of anchorage systems and palatal coverage of denture base on load transfer in maxillary implant-retained overdenture.MATERIALS AND METHODSMaxillary implant-retained overdentures with 4 implants placed in the anterior region of edentulous maxilla were converted into a 3-D numerical model, and stress distribution patterns in implant supporting bone in the case of unilateral vertical loading on maxillary right first molar were compared with each other depending on various types of anchorage system and palatal coverage extent of denture base using three-dimensional finite element analysis.RESULTSIn all experimental models, the highest stress was concentrated on the most distal implant and implant supporting bone on loaded side. The stress at the most distal implant-supporting bone was concentrated on the cortical bone. In all anchorage system without palatal coverage of denture base, higher stresses were concentrated on the most distal implant and implant supporting bone on loaded side.CONCLUSIONIt could be suggested that when making maxillary implant retained overdenture, using Hader bar instead of milled bar and full palatal coverage rather than partial palatal coverage are more beneficial in distributing the stress that is applied on implant supporting bone.