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

Abstract

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.

Five‐year study of mandibular overdentures on stud abutments: Clinical outcome, patient satisfaction and prosthetic maintenance—Influence of bone resorption and implant position

“…The canine region is considered the most favourable implant location for a 2IOD, yielding the least bone stress and optimal transfer of mastication load on the mucosa (Bonnet, Dubois, Daas, & Lipinski, ). Although most clinical studies followed this approach, in vitro research results are inconclusive whether the second premolar or the lateral incisors position is biomechanically the best locus for dental implants in an overdenture solution (Alvarez‐Arenal et al, ; Hong et al, ; Scherer, McGlumphy, Seghi, & Campagni, ). Clinical research associated a higher inter‐implant distance with a better OHRQoL score (Geckili et al, ).…”

Biomechanical behavior of overdentures supported by different implant position and angulation using Micro ERA® system

“…Regarding the tensile stress, which will assume the most likely region to suffer resorption, the higher values was presented for the LI-0º group, in which the stress was located in the cortical layers around the implant first treads ( Fig 4C) 22,37 . The results suggest that overdentures with lateral incisor implants is the worst design in terms of biomechanical environment for the bone, moreover, it may favor much greater stress registered into the attachment component 38 . For FEA, when two bodies with different Young modulus (cortical bone and titanium implant) come into contact, the highest stress is presented at the beginning of the contact surface 9,39 .…”

“…This finding shows that the location mentioned may be the one with greatest nylon wear, promoting retention loss and a higher maintenance costs. Equally, a FEA study 38 compared the stress distribution in mandibular two-implant overdentures according to implant locations (lateral incisors and canines), and observed the worst biomechanical environment for the lateral incisor position. In addition to be the worst model for the attachment components 38 .…”

“…Equally, a FEA study 38 compared the stress distribution in mandibular two-implant overdentures according to implant locations (lateral incisors and canines), and observed the worst biomechanical environment for the lateral incisor position. In addition to be the worst model for the attachment components 38 . For the different angulations, a previous study found that implant/attachments perpendicular to the occlusal plane were appropriately retentive in the first year and the retentive capacity of the nylon component was affected by implant inclinations 41 .…”

Balanced occlusion aided locator abutment retained overdenture with no implant placed within anterior region: A case report

“…Locator abutment, together with its negative modules, was a modified ball‐cap retained module . It was not so easy to fracture as ball‐cap modules, while for the locator abutment retained overdenture, in order to fulfill the stability of overdenture, the partial implants were always located at the anterior region of an edentulous arch . As far as this case was concerned, the patient was unwilling to undergo the larger operation and could not afford the higher medical expense, and 4‐implants located at the posterior area for overdenture stability seemed to be the best solution.…”