Purpose: This 5-year retrospective study aimed to investigate and compare the effect of bar designs of two-implant-retained overdentures (2-IRO) on pattern of the residual ridge resorption (RRR) of the posterior mandibles using 3-D Cone Beam Computed Tomography (CBCT) imaging. Materials and Methods: Forty five edentulous patients treated with mandibular 2-IRO opposing maxillary complete denture were selected for the study. According to bar designs; the enrolled patients were divided into three groups: Group BC (n=19) patients treated with two-implant overdentures retained by a bar joint with a plastic retentive clip. Group BL (n=14) patients treated with two-implant overdentures retained by locator attachments on the top of milled bar. Group BD (n=12) patients treated with two-implant overdentures retained by a straight bar with a plastic retentive clip & distally cantilevered ball attachments. The pattern of posterior RRR was evaluated by using CBCT imaging after 5 years post-treatment. Results: The overall vertical means of RRR differences were highly significant between three bar groups (BC, BD, and BL) using One Way ANOVA test with LSD post hoc. For group BL, no significant differences were revealed in height and width (for both buccal and lingual sides) of alveolar bone when comparing molar and premolar areas. For group BD, the reduction in RRR recorded highly significant differences (p<0.001) in height and width (for lingual side only) with statistical significant increase at molar than premolar areas. Conclusion: Taking the limitation of this study into considerations; Mandibular posterior residual ridge resorption occurs irrespective of 2-IRO design. The impact of bar design on the rate of residual ridge resorption is a matter of controversy. Unless limited by the available restorative space; milled bar design with locator retainer could be considered the bar design of choice regarding the rate and pattern of RRR.
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