When the apical end of a root is removed, the remaining surface of the root is described as having been “beveled” [6]. The shape and direction of the bevel can strongly influence both success rate of the whole procedure and the incidence of complications that may occur.

Historically, a long bevel was proposed in order to obtain a better visualization, especially in posterior regions, of the root end and an easier access while preparing the retrograde cavity. However, nowadays, several drawbacks can be evaluated and considered while using a large bevel which has to be avoided due to the improvements in technique and instruments available. Main complications and drawbacks can be:

Crown-to-root ratio is defined as the physical relationship between the portion of the tooth within the alveolar bone and the portion not within the alveolar bone, as determined radiographically [8]. While an ideal crown-to-root ratio of 1:2 has been suggested for a tooth to serve as an abutment, it is rarely observed in practice. The original guidelines for crown-to-root ratio in the selection of abutments were found to be exceptionally conservative and treatment limiting, and 1:1 ratio might be adequate in cases with a carefully designed occlusion and controlled periodontal inflammation [9].

Various clinical procedures have been reported to directly affect the crown-to-root ratio such as abutment preparation for overdentures, surgical crown lengthening, and forced eruption [5].

Endodontic surgery cuts off the apical root and may result in an unfavorable crown-to-root ratio.

While most roots have a conical shape, molars have root trunk portion with wider surface area than just conical root portion. Thus, on these teeth the loss of apical root is less significant for alveolar bone support [10].

The most common cause of increased crown-to-root ratio is marginal periodontitis [11]. Cervical bone support is the most important to sustain the stresses from occlusal load. Therefore, periodontal bone loss is detrimental to the prognosis of abutment tooth. On the contrary, apical root resection is not as harmful as periodontal bone loss because the occlusal stress concentrates on the cervical area, not on the apical area [10].

However, from an anatomical point of view, the amputation of the apex, which decreases the longitudinal distance between alveolar bone margin and resected root end, can increase the risk of endo-perio communication, increasing the risk of infection spread.

The preservation of an adequate crown-to-root ratio should be considered essential in endodontic surgery. The use of a minimum bevel allows a greater preservation of the tooth structure than a larger bevel does. However, it should be taken into consideration that the main goal of endodontic surgery remains the regeneration of periapical tissues after the removal of the infectious periapical noxa. As reported, the aim of preserving tooth structure must not compromise the goal of endodontic surgery [12].

Missed multiple canals or missed complete roots are among the most severe complications because it may compromise the success of the procedure due to persistence of pathogens in contact with the tooth surrounding the tissues.

This occurrence can be caused by an inadequate root resection or incomplete visualization of the anatomy both in planning and in surgical phases. Missing root canal anatomy is strictly linked to the anatomy of the tooth or of the root that has to be treated (Fig. 9.4).

It is known that many variations can be observed in the root canal anatomy of the tooth, as described by Vertucci [13]. In his publications the authors described a number of different root canal anatomical features, classifying them on the basis of the number of canals and isthmus or communications among them (Fig. 9.5).

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So, the shape of the root canal end after resection can be different on the basis of the position of the resection plane, affecting the three-dimensional sealing procedure. A deep knowledge of root canal anatomy allows an appropriate planning of the procedure and, during the surgery, can reduce the risk of missing root anatomy.

The preparation of the root-end cavity aims to create the conditions for a tridimensional obturation of the root end, eliminating the pathways of the source of infection from the root canal into periradicular tissues.

The ideal root-end cavity preparation should be at least 3–5 mm deep Black class-I cavity, with walls parallel to the long axis of the root [14], and should incorporate the root canal anatomy and retain the retrograde filling material [15].

Several complications can occur during root-end preparation due to inadequate instrumentation or visualization of the surgical site: