Three-dimensional finite element analysis and comparison of stress distribution in overdentures supported with bar attachments and telescopic crowns.
OBJECTIVE: To determine which one of the overdenture (OD) retainers was more beneficial to the abutments--the bar or the telescopic crown--and if a tooth could be used as an OD abutment when the supporting bone decreased to half of the root. MATERIALS AND METHODS: The three-dimensional finite element method was used to investigate the stress distribution in a mandible with an overdenture supported by the roots of two canines. The two teeth were either connected with a bar attachment or restored with telescopic crowns, and were then restored with a complete overdenture. For each type of superstructure, the influence of bone height around the roots (no alveolar resorption and resorption to half of the root length) was analyzed under three loading conditions. RESULTS: The most extreme stress values were located at the alveolar ridge crest of the bone around the root of the abutment. In the case of anterior loading, the largest compressive stress (LCS) in telescopic crown overdenture (TOD) was lower. When loaded posteriorly there was no obvious difference between bar attachment overdenture (BOD) and TOD. At the alveolar ridge crest around the root of the abutment, the stress value in the model with decreased bone level was higher than in the model with normal bone level, but the range was not significant. CONCLUSION: 1. In terms of stress in the alveolar bone, complete overdenture over telescopic crowns is more convenient than over bar attachments. 2. Stress increases as the height of the bone around the roots decreases, but the increment is less than 30%. It is important for an abutment with bone resorption to perform root amputation to obtain an acceptable crown/root ratio.