Search

Purpose: To examine the influence of posterior residual ridge resorption (PRRR) and relining on bending strain around implants under an overdenture., Materials and Methods: Maxillary and mandibular edentulous models were made and covered with white silicone. Four strain gauges were placed on four sides of each implant. Two tissue-level implants were placed bilaterally in the part between the lateral incisors and canines of the mandible. A maxillary conventional denture and a mandibular overdenture were fabricated to fit the models. Three levels of bone resorption around the implant were created: 0, 0.8, and 1.5 mm. The surface of the residual ridge was uniformly removed from the area near the distal side of the implant to the retromolar section, and three levels of PRRR were created (0, 1, and 1.5 mm). After the measurement, the experimental denture of the PRRR of 1 mm and 1.5 mm were relined. Locator attachments were used. A 98-N occlusal force was applied, and bending strains around the implant were measured. The Kruskal-Wallis test and Bonferroni correction were employed to analyze the data., Results: Without relining, at each bone resorption level around the implant, the bending strain was smallest with PRRR of 0 mm and largest with PRRR of 1.5 mm. The bending strain after relining was smaller than the bending strain with ridge resorption. Bending strains after relining were smaller than bending strains with no ridge resorption, but there was no significant difference in bending strain between these three groups., Conclusion: As PRRR increased, the bending strain increased without relining. As bone resorption around the implant progressed, PRRR enhanced the increase in the peri-implant bending strain. Bending strain was reduced when relining was performed.

Purpose This study aimed to determine the influence of mandibular free-end partial edentulism and use of conventional or implant-supported removable dental prostheses in the partially edentulous area on the load exerted on the maxillary anterior teeth.Methods A jaw model with mandibular free-end missing teeth was used, and a distal extension, removable partial dental prosthesis was fabricated to replace the missing posterior teeth. Four experimental conditions were set up: 1) without prosthesis, 2) with a conventional removable partial dental prosthesis, 3) with an implant-supported removable partial dental prosthesis, and 4) with a complete dental arch. Strain gauges were attached to the root surface of the maxillary left central incisor, canine, first premolar, and first molar. The load exerted on them was calculated based on the calibration coefficient. An occlusal load of 49 N was applied, and the forces were compared using a Kruskal-Wallis test (P < 0.05). Results The load exerted on the maxillary anterior teeth increased significantly with no prosthesis, decreased significantly with a conventional removable partial dental prosthesis, and decreased even more significantly with an implant-supported removable partial dental prosthesis. Conclusions The burden on the maxillary anterior teeth decreased with the use of a removable partial dental prosthesis and decreased even further with the use of an implant-supported dental prosthesis. The use of an implant to support a distal extension removable partial dental prosthesis is potentially effective in preserving the remaining teeth and tissues by reducing excessive stress in patients with mandibular free-end partial edentulism.

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 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 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: The aim of this study was to investigate strain on implants used for adjunctive support of distal extension removable partial dentures., Materials and Methods: An implant with strain gauges was used for testing purposes in two positions, parallel and inclined. Three loading scenarios--loading apparatus (LA), artificial teeth via cotton roll (CR), and artificial teeth (UT)--were studied and strains compared via the Kruskal-Wallis test (P=.05)., Results: Strain under CR was significantly larger than UT in parallel (P<.05). However, the opposite was observed in inclined., Conclusions: Strain in parallel was smallest for UT, whereas in inclined it was largest for CR.

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.)

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.)

Seven implants provided with strain gauges were placed in an acrylic block to evaluate the biomechanical performance of short implants in splinted restorations. Two 7-mm-long implants with the same diameter (3.8, 4.4, or 5.0 mm) were splinted together (short-short implant splinted restoration [SS]) or individually with a 4.4 ? 12.0-mm implant (short-long implant splinted restoration [SL]), and a 50-N oblique load was applied to both restorations. The strain decreased significantly with an increase in implant diameter in both the SS and SL restorations, and the observed strain was identical between splinted implants of the same diameter and those splinted with the long implant, suggesting that splinting of two short implants has the same biomechanical effectiveness as splinting with a single long implant.

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.)