| Summary: | Introduction: The aim of this in vitro study was to evaluate the effect of modification of the attachment on stress transmitted to the abutment tooth and residual ridges in lower unilateral distal extension partial dentures. Materials and Methods: An acrylic lower unilateral distal extension cast with the first premolar as the main abutment was constructed. Three types of commonly used extracoronal castable attachments were selected, namely: (1) Preci-vertix standard, CEKA attachment, (2) Preci-sagix mini size, CEKA attachment, (3) OT–cap normal, Rhein 83. They underwent a simple new modification and their effect on stress distribution was studied. Six attachment retained removable partial dentures were constructed: among them, three with nonmodified attachments, and three with modified attachments. Four strain gauges were installed on the acrylic cast to measure the microstrain induced around the abutment tooth and residual ridges. A unilateral static vertical load of 300 Newton was applied on the first premolar and the first molar at a crosshead speed of 2 mm/min and microstrain was recorded using specific miniature Universal Testing Machine. Data were collected and analyzed using the Wilcoxon test for comparison between attachments before and after modification. Results: The highest microstrain was recorded for modified OT cap and modified Preci-sagix attachment around the abutment tooth and residual ridges respectively. While modified PV attachment showed the lowest microstrain around abutment and residual ridges. Conclusion: Maximum strain induced around the tooth and residual ridges in cases of OT cap and Preci-sagix attachments. Among all attachments, the use of Preci-vertix showed better stress distribution around both abutment and residual ridges.
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