Comparison of the retention of three types of attachment systems for mandibular two-implant overdentures: Legacy Locator®, Locator R-Tx® and OT Equator®: In vitro study.

Description :

On a simulation of a completely edentulous mandible, two implants (dummies with an external hexagon of Biomet 3I) will be placed parallel to each other in the symphyseal region, spaced by 22mm (simulating the position of the canines). Three identical master models, each with two implant analogs, will be issued from this simulation of the mandible. The model 1 will be loaded with two Legacy Locator® abutments, the model 2 with two Locator R-Tx® abutments and the model 3 with two OT Equator® abutments. Six corresponding acrylic resin bases will be fabricated, each one containing 2 identical metal housings with 2 pink nylon retention inserts of the attachment systems: 2 bases containing each one 2 Legacy Locators, 2 bases containing each one 2 Locators R-Tx and 2 bases containing each one 2 OT Equators. The six prostheses containing the three types of attachment systems, will be immersed in distilled water in a thermocycler and subjected to 1000 cycles consisting of alternating 30-second exposures to temperatures of 5 ± 1°C and 55 ± 1°C (8), then will be soaked in a 0.02N (=0.48 g/L) citric acid aqueous solution in an incubator, for 12 days (9). This procedure will be repeated twice, which means that in total, the specimens will undergo 2000 cycles in the thermocycler simulating thermal changes inside an oral environment for 2 years of clinical denture use (8), and 24 days of immersion in citric acid solution equivalent to 2 years of consumption (9). Then the bases will be adapted to the three identical models and will be machine tested to measure the dislodgment forces after 2000 insertion and removal cycles (equivalent to the number of cycles for 2 years, if we consider that the patient removes his prosthesis 3 times a day). Thus, we will be able to verify the deterioration of the material of each attachment system due to acid action, by comparing the dislodgement time and the retention forces among these three attachment systems.