In their April JADA article, "Vertical Root Fractures: Clinical and Radiographic Diagnosis," Drs. Stephen Cohen, Lucia Blanco and Louis Berman stated that the majority of the vertical root fractures in their study were "caused by poorly designed dowels (too long, too wide or both)." Nevertheless, this cause-and-effect statement related to the length of the posts is speculative, and contradicts the results of the majority of previously published studies on this issue.
A classic retrospective study by Sorensen and Martinoff 1 indicated that longer posts had the highest probability of clinical success. When the length of the posts equaled the length of the clinical crowns, the failure rate reported by Sorensen and Martinoff was 2.5 percent. Posts that were one-quarter the length of their respective clinical crowns recorded a failure rate of 25 percent—a tenfold increase.
A prior study of teeth with vertical root fractures by Fuss and colleagues2 reported that two-thirds of the posts associated with vertically fractured teeth were extremely short, terminating in the cervical third of the roots. In vitro biomechanical studies also have suggested that better stress distribution occurs with longer posts.3–5
Furthermore, the authors’ conclusions concerning the lengths of the posts appear to be inconsistent with the radiographs displayed in their article. Many of the teeth illustrated received less-than-optimal dentistry, such as inadequate endodontic obturation with ill-fitting artificial crowns, and most of the posts were too wide. However, most posts could be judged too short, not too long. Moreover, it appeared that most restorations lacked a ferrule, and this deficiency probably represented the primary factor contributing to the root fractures.6
The topic of restoring pulp-less teeth with posts and cores is complex and controversial, but few authorities on the subject would advocate short posts. Preservation of sound coronal and radicular tooth structure is critical. Tooth preparations for artificial crowns should preserve as much tooth structure as practical to ensure an adequate ferrule, and the post channel should be as narrow as possible.7
With regard to length, the potential for clinical success is enhanced when the post is as long as practical, consistent with anatomical limitations of the root and the need to maintain the apical seal.6
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