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Purpose: The aim of this study was to compare the stresses and retention force of two different attachment systems in implant retained maxillary obturator. Material & Methods: an acrylic model was constructed to simulate edentulous case with maxillary defect and three implants were inserted in the pre-maxillary region. The obturator was constructed with the first design bar with equator attachment (BEA) and screwed to the implants. The retention was measured at the base line and after 90,270,540,810,1080,1620,2160 cycles of insertion and removal respectively. Then the second design bar and clip attachment was constructed, screwed and retention testing procedures repeated as that for the first design. Universal testing machine was used for measuring the retentive forces of each retainer type. The vertical static load of 60 and 90 N was applied (loading machine) at three loading points on the obturator prosthesis for the two bar designs. The readings were tabulated and statistically analyzed. Results: Two-factor ANOVA followed by pair-wise Newman-Keuls post-hoc tests were performed to detect significance between variables (Attachment type and aging). Bar and clip design recorded slightly lesser retention force than that of BEA at base line and at all cycles of insertion and removal but with no significant difference between the two designs. But regarding the effect of aging within each group; there was a significant difference at different cycles of insertion and removal. But regarding the stress analysis Bar and clip recorded to some extent less microstrain values than BEA in most of surfaces at different points of loading. Conclusion: The retention force of Bar and clip was slightly lesser than BEA at any given cycle of insertion and removal. Reduction of mean retentive force continues to occur over time within each group. Bar and clip recorded less micro-strain values than BEA at most of the surfaces specially when applying the load on the posterior intact side. (908) Amr Mohamed Ismail Badr E.D.J. Vol. 63, No. 1

EVALUATION OF STRESSES AND RETENTION IN TWO DIFFERENT TYPES OF BAR ATTACHMENT USED IN IMPLANT RETAINED MAXILLARY OBTURATOR