Mechanical aging and Retention Forces Assessment of Three Different Modalities of Titanium Milled bar in Implant Retained Mandibular Overdenture: An in-vitro study

Aim: To evaluate the axial retention forces of three different titanium milled bar ‎attachment systems: milled bar , milled bar with supra OT equator, milled bar with supra ‎ball for in implant-retained mandibular overdenture.‎ Materials and methods: An epoxy resin model was constructed simulating completely ‎edentulous mandible. Two implants were inserted in canine regions ,and one in the left ‎central incisor region. Bar attachments designs were constructed by CAD/ CAM ‎technology. Experimental overdentures were to connected to either implants with milled ‎titanium bar attachment (group I), or milled bar with supra ball attachments (group II),or ‎milled bar with supra OT equator attachment (group III). The axial retention force was ‎measured in Newton by universal testing machine for each attachment system at base line ‎‎(T0) to (T11) which simulating five years of the overdenture function (T11 after 5400 ‎cycles of insertion and removal).‎ To compare the three groups to each other; one way-ANOVA followed by Tukey post hoc ‎test, were used to compare between more than two groups in non-related samples.‎ Results: The milled bar with supra ball attachments had a significantly highest retention ‎forces (142 Newton) followed by milled bar with equator attachments (118.65 Newton), ‎while the lowest one was milled bar (111.40 Newton) at base line. The loss of retention ‎force continued throughout the study to reach (22.96 Newton) for milled bar with ball, ‎‎(20.6 Newton) for milled bar with equator, and for milled bar (18.74 Newton) at the end of ‎the study. ‎ conclusion: The retention forces for the milled bar with ball attachment systems ‎demonstrated significantly higher retention forces than those for the milled bar with OT ‎equator, milled bar after cyclic insertion and removal. ‎