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Purpose: Implant overdentures with splinted attachments have been used in clinical practice, and the effect of splinting on implants has been reported frequently. However, the effect of implant configuration of more than four implants and covering the palate with an overdenture has not been sufficiently examined. The purpose of this study was to reveal the effects of implant configuration and palatal coverage on both implant and denture strain in maxillary implant overdentures using splinted implants., Materials and Methods: Six implants were placed in the anterior, premolar, and molar areas in a maxillary edentulous model. Four strain gauges were attached to the implant surface, and Dolder bar attachments were used to splint implants distributed in various configurations. Two types of maxillary experimental dentures (with/without palatal coverage) were fabricated, and two strain gauges were attached at the midline. A vertical load of 98 N was applied, and the strains on the dentures and implants were measured. The strain measurements were compared using one-way analysis of variance and t test (P = .05)., Results: When comparing the implant strains, the strain was significantly smaller on the anterior and premolar implants when six implants were used, but there was no significant difference among the different implant configurations in the strain on the molar implants. Strains on anterior implants of the palateless overdenture were significantly greater than those of the overdenture with palatal coverage. When four implants were used, the strain on the palatal side of dentures without palate was significantly greater than that on those with palatal coverage. When six implants were used, there was no significant difference in the strain on either side between two types of dentures., Conclusion: When implants were splinted to each other using a denture without palatal coverage, the strain of dentures when six or two anterior and two posterior implants were used was lower. The difference of denture strains between two types of dentures was not significant when six implants were used, but was significant for all other configurations. Also, the difference of implant strains between two dentures was significant in anterior implants regardless of implant configuration.

Purpose: To examine the effect of the attachment features (abutment height, retention, and freedom of rotation) of implant overdentures on the bending strain around implants under an overdenture., Materials and Methods: Mandibular and maxillary edentulous models were fabricated and covered with silicone rubber. Strain gauges were attached to the four sides of each implant. Two implants (tissue-level implant, 4.1-mm diameter, 10-mm length) were placed bilaterally in the area between the mandibular canines and lateral incisors. A maxillary conventional denture and a mandibular overdenture were made to fit the edentulous models. Three levels of peri-implant bone resorption were created sequentially: no bone resorption, 0.8 mm, and 1.5 mm. Three kinds of attachments (magnetic, stud, and ball attachments) were used. Bending strains generated from a 98-N occlusal load through the maxillary denture were measured using a sensor interface, and the data were analyzed using the Kruskal-Wallis and Bonferroni tests. Multiple regression analysis was used to find the relationship between independent variables (peri-implant bone resorption level, abutment height, retention, and freedom of rotation) and the dependent variable (bending strain)., Results: For all attachment types, the bending strains were smallest with no bone resorption and largest with 1.5-mm bone resorption (P < .05). Multiple regression analysis showed that abutment height had the greatest impact on the reduction of bending strain (beta = .413), followed by freedom of rotation (beta = -.349), and retention (beta = .107)., Conclusion: Low abutment height, large freedom of rotation, and low retention can minimize bending strain around implants.

Purpose: The purpose of this study was to evaluate the biomechanical effects of bone loss on peri-implant bending strain underneath overdentures., Materials and Methods: One mandibular and one maxillary edentulous model were created and covered with 2 to 4 mm of silicone rubber to simulate the oral mucosa. Four strain gauges were attached to four sides of each implant. In the mandibular model, two implants were inserted, and the implant was placed bilaterally in the area between the mandibular canines and lateral incisors. A maxillary conventional denture and mandibular overdenture were fabricated with acrylic resin to fit the edentulous models. Five bone loss levels were created: no bone loss, 0.8 mm bone loss on only the left implant, 0.8 mm bone loss bilaterally, 1.5 mm bone loss on only the left implant, and 1.5 mm bone loss bilaterally. Magnetic attachments were used to retain the denture. The bending strains generated from three types of unilateral loading were measured by a sensor interface, and the data were analyzed using the Kruskal-Wallis test and Bonferroni's post hoc test., Results: Bending strain increased with decreasing bone levels on the loading side. On the nonloading side, bending strains were greater at even bone loss (0.8 mm or 1.5 mm bone loss bilaterally) than at uneven bone loss (0.8 mm or 1.5 mm bone loss on only the left implant). Strains under loading at the left first premolar were approximately equal to that under loading with a cotton roll; these strains were higher than those generated with loading at the left first molar., Conclusion: Peri-implant bending strains rapidly increased on the loading side as bone loss levels increased. Peri-implant bending strains on the nonloading side were higher at bilaterally even bone loss than at unilateral bone loss.

Purpose: The purpose of this study was to determine the optimal positioning of implants for maxillary implant-supported overdentures (MIODs) using finite element analysis (FEA)., Materials and Methods: Three-dimensional (3D) finite element models were built incorporating the maxilla, mucous membrane, removable denture, and artificial teeth using FEA software. Four models were prepared: one without an implant; one with two implants in the region of the lateral incisor; one with two implants in the first premolar region; and one with four implants in the lateral incisor and first premolar regions. Occlusal load was applied to the model, and denture displacement and the distribution of stress in the surrounding bone and mucous membrane were observed and measured., Results: The maximum equivalent stresses to the bone and mucous membrane were highest in the premolar and anterior areas, respectively. Stress to the bone was concentrated around the implants, whereas stress in the mucous membrane was concentrated along the posterior margin. Denture displacement in the anterior direction was highest in the model without implants, while denture displacement in the posterior direction was less affected by the presence of implants. Overall, denture displacement in the four-implant model was smaller than that in the other models. Implant angle affected the stress distribution, with highest stress to the bone when the implant was positioned in a palatal direction and highest stress to the mucous membrane when placed mesially. However, implant angle had little impact on denture displacement, with almost the same stress for implants at all tested angles., Conclusion: Optimal implant position can stabilize overdentures and reduce stress to the bone and mucous membrane. Stress is reduced when implants are inserted in the premolar area and when the direction of the implant is perpendicular to the occlusal plane.

Purpose: Palateless maxillary implant overdentures are often used for patients experiencing problems with a full-palate denture. However, palateless overdentures are reported to be a risk factor for implant complications. The purpose of this study was to examine the strain on implants beneath palateless overdentures with unsplinted attachments under various implant distributions., Materials and Methods: A maxillary edentulous model with implants and an experimental palateless overdenture were fabricated. Four strain gauges were attached to each implant, positioned in the anterior, premolar, and molar areas. Three types of unsplinted attachments (ball, locator, and magnet) were set on the implants under various implant distributions. A vertical occlusal load of 98 N was applied through the mandibular complete denture, and the bending strain on the implants was compared using the Kruskal-Wallis test (P = .05)., Results: When comparing the strain among different attachments, those using a magnet attachment were the smallest and those using a ball attachment were the greatest, and this difference was significant in most situations (P < .05). When comparing the strain among different implant distributions, the strain on a four-implant distribution was significantly smaller than that on a two-implant distribution in most situations (P < .05), and those using premolar and molar implants recorded the smallest strain. The strain on implants using a locator attachment tended to be midway between those using ball and magnet attachments, regardless of the implant distribution., Conclusion: In most implant distributions, magnet attachments decrease the strain on implants more than ball and locator attachments. The most favorable unsplinted attachments for use beneath palateless overdentures to decrease the implant strain are magnet attachments and four implants placed in the premolar and molar areas.

Purpose: The aim of this study was to examine the deformation modality of palateless maxillary implant overdentures using isolated attachments under various implant configurations., Materials and Methods: A maxillary edentulous model with implants inserted in the anterior, premolar, and molar areas was fabricated, and three types of unsplinted attachments-ball, locator, and magnet-were set on the implants distributed in various configurations. Experimental palateless dentures were fabricated, and two strain gauges were attached at the anterior midline of the labial and palatal sides. A vertical occlusal load of 98 N was applied, and the shear strains of dentures were measured. The measurements of strains were compared with the Kruskal-Wallis test (P = .05)., Results: The strains of the labial side were much larger than those of the palatal side except for those using the ball attachment. The strains using the magnet attachment on anterior implants were significantly larger than those using other attachments (P < .05). Those using anterior implants were significantly smaller than those using premolar or molar implants (P < .05)., Conclusion: The strains of palateless overdentures were different according to the attachments and implant distribution. However, when using molar implants, there was no significant difference among the three attachments.

Purpose: Implant overdentures with attachments have been used in clinical practice and the effect of attachments on implant strain has been frequently reported. However, most studies have focused on mandibular overdentures; there are few reports on maxillary overdentures. The purpose of this study was to examine the influence of attachment type on implant strain in maxillary overdentures under various implant configurations., Materials and Methods: A maxillary edentulous model with implants and experimental overdentures were fabricated. Four strain gauges were attached to each implant, positioned in anterior, premolar, and molar areas. Three types of unsplinted attachments-ball, locator, and magnet-were set on the implants under various implant configurations. A vertical occlusal load of 98 N was applied through the mandibular complete denture, and implant strain was compared using the Kruskal-Wallis test., Results: Ball attachments caused the greatest amount of strain, while magnet attachments caused the least amount under all conditions. For all attachments, two anterior implants caused significantly more strain than four implants (P < .05). No significant difference was observed between subtypes in four-implant configurations except when using locator attachments., Conclusion: When using unsplinted attachments for maxillary implant overdentures, magnet attachments are recommended to reduce implant stress. Using only two implants, especially two anterior implants, is not recommended regardless of attachment type.

Purpose: The purpose of this preliminary study was to examine the influence of overdenture attachment height and shape on lateral force on implants and denture displacement., Materials and Methods: A straight model was fabricated to simulate the edentulous ridge. Two strain gauges were attached to the mesial and distal surfaces of the implant in the canine area. Five types of ball attachments and three types of Locator attachments with three types of replacement male attachments were used. A vertical load of 49 N was applied. The lateral force on the implant and the denture displacement were measured. Statistical comparisons were performed using one-way analysis of variance, Tukey post hoc comparison test, and multivariate analysis. P < .05 was considered significant., Results: Ball attachments of 4-mm height exerted the highest lateral force on the implant, and the greatest displacement was also observed with attachments of 4-mm height. Different lateral forces were observed for different shapes of ball attachments, but there were no significant differences in denture displacement among the shapes. For Locator attachments, the highest lateral force was observed with the white male type, and the greatest denture displacement occurred with attachments of 4-mm height. There were no significant differences among male white, pink, and blue types., Conclusion: The height of the stud attachments in implant overdentures had a marked effect on the lateral force on implants and on denture displacement. To protect implants supporting an overdenture and to prevent bone resorption, the height of the attachment should be carefully considered.

Purpose: This study examined the effects of attachments on strain in maxillary implant overdentures supported by two or four implants., Materials and Methods: A maxillary edentulous model with implants inserted into anterior, premolar, and molar areas was fabricated, and three types of unsplinted attachments-ball, locator, and magnet-were set on the implants distributed under various conditions. Maxillary experimental dentures were fabricated, and two strain gauges were attached at the anterior midline on the labial and palatal sides. A vertical occlusal load of 98 N was applied and shear strain of the dentures was measured., Results: On both sides, magnet attachments resulted in the lowest shear strain, while ball attachments resulted in the highest shear strain under most conditions. However, differences in shear strain among the three attachment types were not significant when supported by four implants, especially molar implants., Conclusion: Shear strain of the maxillary implant overdenture was lowest when using magnet attachments. Magnet attachments mounted on four implants are recommended to prevent denture complications when using maxillary implant overdentures.

Purpose: The aim of this study was to determine the optimal number and location of mini-implants retaining an overdenture to resist lateral forces., Materials and Methods: A strain gauge was attached to a mini-implant and placed in an edentulous mandible model. The following different implant locations were evaluated: one mini-implant at the midline, two mini-implants in the lateral incisor regions, two mini-implants in the canine regions, and four mini-implants., Results: Lateral forces on mandibular overdentures retained by one mini-implant at the midline or two mini-implants in the lateral incisor regions appeared to be advantageous when compared with placing two mini-implants in the canine regions or four mini-implants., Conclusion: Fewer mini-implants resulted in less lateral stress, while four were associated with an unequal stress distribution.

Purpose: Maxillary implant overdentures are often designed without palatal coverage to maximize wearer comfort. Although palateless dentures have been reported to be less rigid than conventional dentures, and require reinforcement to prevent complications, there is little documentation about the effects of such reinforcement. The purpose of this study was to examine the effects of reinforcement on the strain on maxillary implant overdentures supported by implants in a variety of configurations., Materials and Methods: A maxillary edentulous model with implants inserted in the anterior, premolar, and molar area was fabricated. Five types of experimental overdentures, with and without reinforcement, were fabricated, and two strain gauges were attached at the anterior midline of the labial and palatal sides. A vertical occlusal load of 98 N was applied through a mandibular complete denture, and the shear strain on the denture was measured. The measurements were compared using the Kruskal-Wallis test (P = .05)., Results: On both the labial and palatal sides, the strain on the palateless dentures with reinforcement was significantly lower than the strain on palateless dentures without reinforcement in all implant configurations (P < .05). The labial strain on the palateless dentures with reinforcement was almost as low as the labial strain on dentures with palatal coverage in most implant configurations., Conclusion: Reinforcement of a palateless implant overdenture with residual ridge reinforcement and a palatal bar could reduce the strain in the anterior midline to almost the same level as a denture with palatal coverage. This type of reinforcement may prevent prosthetic and implant complications.

Purpose: Maxillary implant overdentures are often used in clinical practice. However, there is no agreement or established guidelines regarding prosthetic design or optimal implant placement configuration. The purpose of this study was to examine the influence of palatal coverage and implant number and distribution in relation to impact strain under maxillary implant overdentures., Materials and Methods: A maxillary edentulous model with implants and experimental overdentures with and without palatal coverage was fabricated. Four strain gauges were attached to each implant, and they were positioned in the anterior, premolar, and molar areas. A vertical occlusal load of 98 N was applied through a mandibular complete denture, and the implant strains were compared using one-way analysis of variance (P = .05)., Results: The palatolabial strain was much higher on anterior implants than on other implants in both denture types. Although there was no significant difference between the strain under dentures with and without palatal coverage, palateless dentures tended to result in higher implant strain than dentures with palatal coverage. Dentures supported by only two implants registered higher strain than those supported by four or six implants., Conclusion: Implants under palateless dentures registered higher strain than those under dentures with palatal coverage. Anterior implants exhibited higher palatolabial strain than other implants regardless of palatal coverage and implant configuration; it is therefore recommended that maxillary implant overdentures should be supported by six implants with support extending to the distal end of the arch.

Purpose: As maxillary implant overdentures are being increasingly used in clinical practice, prosthodontic complications related to these dentures are also reported more often. The purpose of this study was to examine the influence of palatal coverage and implant distribution on the shear strain of maxillary implant overdentures., Materials and Methods: A maxillary edentulous model with implants inserted in the anterior, premolar, and molar areas was fabricated. Two kinds of experimental overdentures, with and without palatal coverage, were also fabricated, and two strain gauges were attached at the midline of the labial and palatal sides. A vertical occlusal load of 98 N was applied through a mandibular complete denture, and the shear strain in each denture was compared by analysis of variance (P = .05)., Results: In all situations, the shear strain in palateless dentures was significantly higher than in dentures with palate on both sides (P < .05). In dentures with palate, the shear strain was lower when anterior implants were present., Conclusion: Palateless maxillary implant overdentures exhibited much higher strain than overdentures with palate regardless of the implant distribution; this may cause more prosthodontic and implant complications. The most favorable configuration to prevent complications in maxillary implant overdentures was palatal coverage that was supported by more than four widely distributed implants.

Purpose: The purpose of this study was to examine the influence of reinforcement of an embedded cast on the strains within maxillary implant overdentures., Materials and Methods: A maxillary edentulous model with implants placed bilaterally in the canine positions, dome-shaped copings, and experimental overdentures was fabricated. Rosette-type strain gauges were attached in the canine positions and at three points along the midline of the polished surface of the denture and connected to the sensor interface controlled by a personal computer. Experimental dentures with five different reinforcements were tested: without reinforcement; with a cast cobalt-chrome reinforcement over the residual ridge and the tops of the copings; with the same reinforcement from first molar to first molar, over the residual ridge and the tops of the copings; with the same reinforcement over the residual ridge and the sides of the copings; and with the same reinforcement from first molar to first molar, over the residual ridge and the sides of the copings. A vertical occlusal load of 49 N was applied to the first premolar and then to the first molar, and the strains were measured and compared by analysis of variance., Results: In both loading situations, significantly less strain was recorded in dentures with reinforcement than in those without reinforcement. When the first premolar was loaded on dentures with and without palatal reinforcement at the first premolars, the strains on the denture with reinforcement over the tops of the copings were significantly lower than on the denture with reinforcement over the sides of the copings at the canine position., Conclusion: Cast reinforcement over the residual ridge and the top of copings embedded in an acrylic base reduced the strain from occlusal stress on maxillary implant overdentures.

Objective: Lateral force to mini-implants should be avoided because mini-implants are weak mechanically because of its small diameter. Overdentures retained by mini-implants are usually formed using ball attachments. However, bar attachments can offer the advantage of splinting the mini-implants. This study examined the effect of attachments in withstanding these lateral forces in tilted mini-implants of overdentures., Materials and Methods: Strain gauges were attached to the mini-implants (2.5 × 18 mm) embedded in an acrylic resin block. Two mini-implants were inserted vertically (Control) or with one mini-implant inclined at 10° or 20° (10-inclined and 20-inclined, respectively). The female portions of the attachments were secured to the denture base. A prefabricated ball attachment and CAD/CAM-fabricated bar attachment were compared. A vertical load of 49 N was applied to the occlusal surface at a distance 10 mm away from the center of two mini-implants. The lateral force borne by the mini-implants was measured via the attached strain gauge. Mann-Whitney U-test and an analysis of Bonferroni correction were used to compare differences between the two attachments and among the three models (P < 0.05)., Results: The lateral force exerted to the inclined mini-implant was significantly greater than that borne by a vertical mini-implant for both attachment types. The lateral force on the 20° inclined mini-implants with bar attachments was smaller than that on mini-implants with ball attachments., Conclusion: Inclined mini-implants are subjected to greater stresses than vertical ones, and a bar attachment can reduce the lateral forces borne by the mini-implant when one mini-implant inclined at 20°., (© 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

This study evaluated how the contact height between the magnetic attachment and denture base influences stability and bending strain. An implant modified with strain gauges and a magnetic attachment mounted in an acrylic resin block were used to characterize systems with varying degrees or heights of contact with the abutment. Bending strain under lateral loading increased significantly as the contact height decreased. In the no contact and resilient contact groups, magnetic assemblies separated at reduced bending strain in all loading conditions. The contact height of the magnetic attachment influenced the stability and the amount of bending strain on the implant.

The purpose of this study was to examine the influence of reinforcing the structure of an overdenture on stress distribution in the residual ridge using the three dimensional finite element method. Four models of mandibular overdentures with various reinforcement methods were analyzed, including (1) without reinforcement, (2) with chrome-cobalt reinforcing wire, (3) with a reinforcing structure (a cast metal framework) and no reinforcement on the coping top, and (4) with a reinforcing structure and reinforcement on the coping top. The reinforcement adjacent to the top of the coping and the medial part reduces the stress beneath the loading side of dentures and widely and evenly distributes the stress of the residual alveolar ridge.

The purpose of this study was to examine a longitudinal clinical performance of magnetic attachments used for natural overdenture abutments. The study included 131 patients who had used removable prostheses (complete overdentures 31%, partial dentures 69%) more than 5 years (40-90 years old) with 211 magnetic attachments on natural abutments (Magfit 400 or 600; Aichi Steel co., Aichi, Japan) treated in 15 clinics using a standardized protocol. Analyses were performed on the degree of patient satisfaction regarding retention, complications of magnets (corrosion, detachment from denture base), abutments (pain during mastication, periodontal pocket formation, inflammation, mobility), and dentures (fracture etc.). Ninety-seven percent of patients were satisfied with the retention and stability of their dentures. No corrosion of magnet was observed, and 19 magnets were detached. Most frequent complication of abutments was periodontal pocket formation (52%), followed by the inflammation (29%), increase in mobility (27%) and pain (4%). Magnetic attachment on natural tooth abutments provided a viable and long-term treatment option., (© 2013 Blackwell Publishing Ltd.)

Objective: To evaluate the retentive force and lateral force of an implant with various types of attachments for overdentures in relation to implant inclination., Material and Methods: An implant (3.75 × 13 mm) was embedded into an acrylic resin block, simulating the edentulous ridge. Four different attachment systems were used, including: (1) Locator black and blue, (2) a ball attachment, (3) a flat-type magnetic attachment and (4) a self-adjusting magnetic attachment, which has vertical and rotational movement. All of the attachments were under a constant dislodging force with an angle of the implant at 0°, 15°, 30° and 45°, and the experiments were repeated 10 times using a universal testing machine to measure the retentive force. The lateral force to the implant was measured by strain gauges attached on the implant surface. Statistical analysis was performed by multiple comparisons with Bonferroni's correction. P<0.05 was considered statistically significant., Results: At 0°, the significantly highest retentive force was observed in the Locator blue, followed by the Locator black, ball, flat-type and self-adjusting magnetic attachments. The Locator blue and ball attachment maintained the retentive force until a 30° inclination; however, the lateral force increased significantly, especially with the ball attachment. The retentive force of the magnetic attachment was significantly lower at 0°, as well as the lateral force in the self-adjusting magnetic attachment., Conclusion: Within the limitations of this study, we conclude that the retentive force decreases with an increase in implant inclination, whereas the lateral force increases, except for in magnetic attachments., (© 2011 John Wiley & Sons A/S.)

The aim of this study was to establish a method for in vivo examination of the load-bearing ratio between mucosa and abutments beneath an overdenture. Two patients wearing a four tooth-supported or a four implant-supported overdenture were enrolled in this study. Recordings were performed with the metal framework only or with a metal framework and a denture base. The force value with the framework only was designated as 100%, and the tissue-supporting ratio (TSR) with the denture base was calculated. The TSR was approximately 30% to 40% in both subjects, regardless of the load. These data suggest that measurement of a TSR beneath an overdenture is feasible.

Statement of Problem: While 2 to 4 implants are preferred to retain and stabilize an implant overdenture, some reports suggest a single implant is adequate to retain an overdenture. Denture fracture is one of the common complications with overdentures; however, there is no information on the incidence of fractures when dentures are retained by 1 implant., Purpose: The purpose of this study was to compare the fracture incidence of mandibular overdentures retained by 1 and 2 implants., Material and Methods: The records of 85 subjects enrolled in the Vancouver Implant Prosthesis (VIP) clinical trial between 2003 and 2008 and followed up for at least 17 months were reviewed retrospectively. From the clinical records, subjects who had experienced a fractured overdenture were identified. A fracture was considered as either a visible crack in the acrylic resin or complete separation of the denture parts. The same clinical records listed 3 denture fracture sites: over the implant, elsewhere, or unknown. A chi-square test was used to compare the incidence of fracture (alpha=.05). Kaplan-Meier and log rank tests were used to compare the survival rate of overdenture or "time to fracture" (alpha=.05)., Results: Forty-two subjects received a single implant, and 43 received 2 implants. In total, there were 17 fractures recorded for 13 subjects. Nine single-implant subjects experienced 11 denture fractures, while 4 double-implant subjects experienced 6 fractures. There was no significant difference in the incidence of denture fractures in prostheses retained by 1 or 2 implants. When denture fractures did occur, they were found most frequently in areas adjacent to the implant(s)., Conclusions: The incidence of denture base fractures was not significantly different between overdentures retained by 1 implant and those retained by 2 implants. When fractures did occur, they tended to be in areas adjacent to implants., ((c) 2010 The Editorial Council of the Journal of Prosthetic Dentistry. Published by Mosby, Inc. All rights reserved.)

Because the abutment becomes the fulcrum, and the denture base over the coping is usually thin, the overdenture is susceptible to fracture. We hypothesized that rational reinforcement can reduce strain and prevent deformation and fracture of the overdenture. We investigated the effect of reinforcement on overdenture strain around the copings and at a midline. A mandibular edentulous model with a 2-mm-thick artificial mucosa and abutment teeth installed bilaterally in the canine position was produced. The coping had a dome-shaped upper surface with a height of 6 mm. On the lingual polished surface, strain gauges were attached at the canine position and at the midline. A vertical load of 49 N was applied on the occlusal surface. Among several kinds of reinforcements, the cast metal reinforcement that covers both the midline and the coping top significantly reduced the strain on the overdenture. It is suggested that this simple reinforcement is effective in preventing deformation and fracture of the overdenture.

The purpose of this study was to investigate the influence of coping heights on the strain around the abutment teeth and at the middle part of mandibular overdentures, using strain gauges. A mandibular edentulous model with a silicone artificial mucosa of thickness 2 mm was made. Two artificial roots were embedded on both sides in the canine position. The coping had a dome-shaped upper surface at a height of 0, 2, 4 and 6 mm. On the lingual polished surface of the overdenture, three strain gauges were attached in the left canine position at the vertical level corresponding to the top of the 6, 4 and 2 mm copings and two strain gauges were attached in the middle section (upper and lower). A vertical loading of 49 N was applied on the occlusal surface of first premolar, first molar and second molar. When loading on the first premolar adjacent to an abutment, the largest tensile strain was observed on the overdenture surface close to the top of each coping, independent of coping heights. When loading on the first premolar on the opposite side, the tensile strains around the coping were remarkably smaller. In the middle part of the overdenture, the compressive strains became larger by reducing the coping height or loading on distal point. The largest tensile strain was observed on the overdenture surface close to the top of copings, independent of coping heights.

Recently, a newly developed magnetic attachment with stress breaker was used in retentive components in overdentures. Excessive lateral stress has a more harmful effect on natural teeth than axial stress, and the magnetic attachment with stress breaker is expected to reduce lateral forces on abutment teeth and protect it teeth from excessive stress. However, the properties of this retainer have not yet been determined experimentally. This study compares the lateral forces on abutment teeth for three retainers under loading on the denture base in a model study. A mandibular simulation model is constructed to measure lateral stress. Three types of retentive devices are attached to the canine root. These devices include the conventional root coping, the conventional magnetic attachment and the new magnetic attachment with stress breaker. For each retentive device, load is generated on the occlusal table of the model overdenture, and the lateral stress on the canine root and the displacement of the overdenture measured. The magnetic attachment with stress breaker does not displace the denture and exhibits lower lateral stress in the canine root than conventional root coping and magnetic attachments.