Objectives: The purpose of the present study is to determine the influence of the reinforcing structure on the strain of an overdenture around a coping and at the median part. Methods: A mandibular edentulous model having a 2-mm-thick artificial mucosa was produced. Abutment teeth were installed on both sides in the canine position. The upper surface of the abutment coping was dome-shaped, and the height was 6 mm. On the lingual polished surface, four strain gauges were attached on the left canine position and two strain gauges were attached in the median part. Four types of overdentures were fabricated. 1. Without reinforcement (S). 2. With chrome-cobalt wire reinforcement (diameter: 1.2 mm) (W), 3. With reinforcing structure (width: 4 mm, thickness: 1 mm) but no reinforcement on the coping top (CA), 4. With reinforcing structure and reinforcement on the coping top (CB). The loaded positions were located at six points on the occlusal surface, and a vertical load of 49 N was applied. We used analysis of variance (ANOVA) and multiple comparisons to compare the mean values. Results: When loaded at the left first premolar, in the strain gauge at the coping top the strain of S was significantly larger than those of W, CA, and CB. The strain of CB was significantly smaller than those of S, W, and CA. When loaded at the left and right first and second molars, in the median part, the strains of CA and CB were significantly smaller than the strains of S and W. Conclusion: Overdentures having a reinforcing structure covering the coping top can reduce the strain on the polished lingual surface not only in the median part but also in the canine. It is suggested that a reinforcing structure can prevent deformation and facture of the overdenture base.

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