Some notes on vertiprep

Perhaps the most important factor related to the survivability of an endodontically treated tooth is the amount of coronal and radicular tooth structure that remains prior to restoration. This factor appears to be of paramount importance and will be considered in detail later in this chapter. The tooth structure that will be available following tooth preparation should be visualized and should be assessed for the provision of adequate retention and resistance form for the subsequent crown. Key to this factor is the presence of an adequate ferrule. The term ferrule describes the band of circumferential material that encircles the cervical area of a tooth restored with a crown.18 As commonly used in dentistry, ferrule also refers to the dimension of remaining vertical tooth structure from the anticipated margin of the preparation to its coronal extent, which is available for encirclement by the crown. The "ferrule effect" serves to reinforce the remaining tooth structure and helps the restoration withstand lateral forces.19 The ferrule provides resistance form and enhances longevity.20 Ferrule length was found to be more important than post length in increasing fracture resistance to cyclic loading of crowned teeth.21Indeed, some authors have noted that the effect of the remaining dentin height is so significant as to make the effect of the type of post and core employed irrelevant with respect to tooth survival.22Lack of an adequate ferrule increases the risk of failure because of post-crown dislodgment, post fracture, and root fracture.23,24 Sorensen and Engelman19 noted that a ferrule of only 1.0 mm in vertical height doubles the resistance to fracture of a tooth without remaining coronal tooth structure. Optimal beneficial effect can be expected from a ferrule of at least 1.5 to 2.0 mm of vertical height. Adequate sound tooth structure should be present to allow placement of a restoration margin that will not encroach on the biologic width, which will ensure continued periodontal health. Biologic widthhas been defined as "the dimension of the junctional epithelium and connective tissue attachment to the root above the alveolar crest" and has been estimated to be approximately 2 mm.26 Violation of this dimension with a restorative margin may result in persistent periodontal inflammation.27 Given the requirement of a minimal ferrule height of 2 mm, at least 4 mm of sound supra-alveolar tooth structure is necessary for mechanical stability and periodontal health. Maxillary premolar roots are often fluted and may be curved, presenting a high risk of strip perforation during preparation of the post space.60 The palatal root has been shown to have a larger and straighter canal than the buccal and should be utilized for post placement.61 For the molar tooth, the decisions are more clear-cut. The forces on posterior teeth are predominately vertical. Therefore, development of additional resistance form to withstand lateral forces is not as commonly needed as in anterior teeth. Because of the morbidity associated with post placement (Fig 21-8), a post is indicated in a posterior tooth only when other more conservative retention and resistance features cannot be used for the core. These features include chamber/canal orifice retention, amalgam pins, and threaded pins, all of which have been shown to be exceedingly effective.62 When a post is deemed necessary, the palatal canal of maxillary molars and the distal canal of mandibular molars are usually the best choice.