The effects of dowel design and load direction on dowel-and-core restorations

Statement of problem. Complications such as loosening of the dowel and core or fracture of the remaining tooth root can be influenced by many factors, including the amount of remaining dentin, direction of the occlusal load, and design of the dowel. Most stress analyses of dowel and cores were conducted without including all aspects of the restorations and supporting structures. Purpose. The purpose of this study was to investigate the influence of occlusal stresses on various dowel designs in a restored, endodontically treated maxillary incisor by using a 2-dimensional finite element analysis model. Material and methods. A 2-dimensional finite element model was constructed in a labiolingual cross-sectional view of a maxillary central incisor, a dowel, a core, and the supporting tissues to investigate stresses in various dowel designs. As a control, a metal-ceramic crown on an endodontically treated tooth without a dowel and core was modeled. A 10-kg force was applied as follows: (1) in a vertical load on the incisal edge, (2) in a horizontal load on the labial surface, and (3) in a 20-degree diagonal load on the lingual surface. Results. The use of a dowel reduced the peak dentinal stress to 75% of the magnitude of the control. When a vertical force was applied, the magnitudes of stress of the various dowel designs were similar; however, when loaded horizontally, the short dowel produced the greatest dentinal stress concentration, and the tapered dowel showed the greatest stress concentration within the cement layer. Greater deflections and higher stresses were generated with horizontal loading. Conclusion. The dowel and core provided little reinforcement to the remaining tooth. The direction of the functional load had a greater effect than dowel design on maximum stress and displacement. Parallel-sided dowel and cores with a length of 12 mm distributed the stress widely in the restoration and dentin, resulting in the smallest stresses. (J Prosthet Dent 2001;85:558-67.)