Objectives: This in vivo study aimed to compare the effect of different types of implant attachments; ball and locator, on masticatory muscles activity for two implants retained mandibular overdentures.
Material and methods: Six completely edentulous healthy patients were selected for this study. Using two-stages surgical technique, two inter-foraminal implants were inserted for each patient in canine areas of the mandible, implants were left unloaded for three months. The implants were exposed and connected to the acrylic mandibular overdentures with ball attachment at first (group1), then EMG recordings were carried out after one week and repeated one monthpost insertion. The same denture was modified to receive locator attachments (group 2) and the same measures were carried out .Electromyographic evaluation of both temporalis and masseter muscles activity during static (maximum voluntary clenching) and dynamic (wafer and peanut chewing) was done at the periods of study.
Results: On the static test, there was significant difference between  both groups at different periods in the right side of masseter (P=0.047) and temporalis muscles (P=0.009) and insignificant difference in the left side. On the dynamic test, there was insignificant difference between groups (P>0.05) during mastication for all muscles except in peanut chewing at the end of follow up period in the right sideof masseter (p=0.05) and temporalis (P=0.028). The highest median values were for locator in static and dynamic test.
Conclusion:Although, both groups of attachment showed nearly the same results, but locator attachment was more reliable treatment option.