PURPOSE: The purpose of this study was to examine and compare the strain distribution around long and short implant mandibular overdentures retained either by ball or self-aligning stud (Positioner) attachments. MATERIAL AND METHODS: Two completely edentulous mandibular models made of epoxy resin were used with implants placed equidistantly in the canine region. In the first model, two long implants were inserted, while two short implants were inserted in the second model. Two attachment mechanisms were examined for each model. A total of twentyfour identical mandibular overdentures were constructed and divided into two groups for each model (n = 12). Each model had two subgroups: ball attachments (n = 6) and Positioner attachments (n = 6). Two linear strain gauges were bonded to the epoxy at their corresponding prepared sites around each implant, where the microstrain was measured under bilateral and unilateral vertical loads of 100N. One-way ANOVA with post-hoc pairwise comparison and an independent t-test were used to analyze the microstrain value data (α =.05). RESULTS: When comparing ball and Positioner attachments, the Positioner showed significantly higher microstrain than the ball attachment (P <
0.001) for both bilateral and unilateral loading. When long and short implants were compared, no statistically significant difference was found in bilateral loading (P = 0.22) or unilateral loading (P = 0.19
P = 0.16) on both loading and nonloading sides. CONCLUSIONS: A higher strain distribution around implants was induced by the Positioner attachment compared to the ball attachment, regardless of the implant length. Increasing the implant length was not advantageous. Thus, the use of short implants for retaining mandibular overdentures can be a viable alternative treatment option.