Canines guide the teeth into proper bite, and have therefore specific functions in chewing and in excursive movements of the mandible. According to Fiedler and Alling in 1968 1 and Mead and Monsen in 1965 2, canines present proprioceptive and reflexive fibres which protect and stabilize occlusion. Due to their position, they provide an aesthetic and harmonious transition between the anterior and posterior segments of the dental arch. Canines have the longest roots and are the most resistant teeth 34 and thus are often displaced or impacted 5. The prevalence of maxillary canine impaction seems to be related to the ethnic origin 6. The lowest frequency (0.27%) is seen among Japanese individuals 7, while the highest (1.8%) is observed in Iceland 8. Impacted canines occur more frequently in females than males, with a proportion of 2.5:1 9.

Maxillary canines travel a long, tortuous path before they erupt, and the long axis may adopt an inclined or horizontal position related to the occlusal plane. Impaction might occur due to general or local factors. The etiopathological investigation of impaction may reveal the existence of systemic diseases such as cleidocranial dysplasia, or Gardner and Gorlin-Goltz syndromes. However, many local problems may be involved, particularly those related to alterations in bone or dental structures and volumes. Bone condensation, alveolar ridge, dental arch length discrepancy, ankylosis and root dilaceration are among the local causes of impaction. Dentoalveolar or oral maxillofacial traumas are among the possible local causes of impaction, in variable combinations involving factors such as the kind of trauma or the age of the patient at diagnosis 10.

Surgical intervention for impacted canines can be classified as: exposure for spontaneous eruption, exposure for orthodontic traction with bonding devices and extraction 111213141516. Planning the adequate surgical strategy depends on radiographic analyses or computed tomography (CT), that show the position of the impacted tooth, its eruption path, the stage of root formation, root anatomy 17 and indicate the most adequate orthodontic treatment.

Based on an investigation of the root apex's location and its relationship with the Ennis inverted Y, Puricelli described in 1987 an ortho-surgical procedure to treat upper canine impaction 17. The eruption of impacted teeth is induced by the guided fracture of the root apex, called apicotomy, resulting from the impact of hammer and chisel, followed by elastic traction of the corono-radicular structure with orthodontic methods 101718. The present work aims to describe in greater detail the method, that has been succesfully used for the past 20 years.

For the surgical fracture of the root apex, the author designed a 16.5 mm long, double-bezel chisel with an angle of 135°. Its active region is 3.5 mm wide, 4.0 mm thick and 5.0 mm long (Figure 1). This design allows a shallow intrusion, with immediate segmentation of the root stucture and minimal risk of damage of the pulp tissue. A surgical hammer, weighing 150 g, is part of the basic instruments involved in the surgical technique.

As part of the surgical planning, clinical examination includes local inspection to confirm the existence of space in the dental arch and orthodontic treatment devices. Panoramic and lateral cephalometric extra-oral radiographs, associated with maxillary occlusal and periapical intra-oral radiographs (Figure 2) are the diagnostic image exams indicated. Computed tomography of the maxilla in coronal and axial planes allows the visual examination of the relationships among nasal, sinusal and vestibular intercorticals. Dilacerations or ankylosis of the apical region of the root of the impacted tooth can be thoroughly observed with these images (Figure 3). The root, contained in a reduced spongeous medullary space, might be connected to one, two or even the three mentioned corticals. Surgery can be performed with local or general anesthesia.

During the deciduos dentition period, the germ of the permanent upper canine is located in a medullary space of pyramidal, triangular shape, which is delimited by the nasal, sinusal and maxillary anterior corticals. Since developing roots are plastic and shaped, apparently, according to their environment, root apices of upper canines may present dilacerations or ankylosis 17, determined by the close relationship with the above mentioned corticals. Seiler and Pajarola 20 recommend that, in some cases of partial ankylosis, induction of a mild luxation of the tooth before attaching an orthodontic traction device may be useful to induce an adequate eruption. In our experience, the ankylosis process affecting the apical region of the root may, also, be particularly related to luxations performed in previous surgical interventions. Presently, CT analysis and anamnesis with history of previous interventions allow, preoperatively, to presume the diagnosis of apical root ankylosis near the so-called Ennis inverted Y. Routine radiographic examination is less favourable for the observation of this apical ankylosis, but allows the identification of apical dilacerations. The intrabuccal lateral maxillary oclusal incidence is particularly indicated.

The technique of apicotomy proposed by Puricelli in 1987 17 includes the separation and isolation of the affected apical region, allowing the usage, in the dental arch, of the two root thirds and the intact crown of the upper canine. Application of orthodontic traction five to seven days after the surgical procedure is recommended. According to Andreasen 21, a fractured root region has extensive communication with the periodontal tissues, so that blood supply to the pulp tissue can be more easily reestablished through the periodontal ligament. The development of a pulp tissue edema, which represents another important factor, is resolved by extravasation of fluids through the fracture zone, lowering the pressure on the delicate pulp tissue vessels. Since the vascular circulation is not interrupted in the pulp apical region, necrosis of this segment is very rare in root fractures 22. The apical fragment does not present infectious postoperative complications 18. Vitality tests are not indicated in the corono-radicular complex during the traction period, and should be initiated only after complete exposure of the tooth crown in the oral cavity. Negative responses to sensitivity stimuli, however, do not necessarily indicate pulp necrosis 18. Electric testing of the pulp aims to stimulate an answer from the sensorial fibres in its interior through electrical excitation. The response given by the patient does not suggest pulp integrity, but just the continued existence of vital sensorial fibres. The test does not provide any information about the blood supply available to the pulp, which is the real determinant of pulp tissues vitality. Thermical tests are thus indispensable, and absence of response may indicate a non-vital pulp. The absence of response might also, nevertheless, represent a false-positive result due to excessive calcification, or to an incompletely formed apex, a recent trauma or to the previous use of drugs 2223. No pulp alterations, of infectious nature or related to tooth mobility, were observed since the technique was developed. A slight colour modification of the crown, clinically similar to the signs observed in teeth submitted to dental trauma, is seen.

In apicotomy, according to the technique originally described by Puricelli 17, the transversal groove which runs along the root path of the dental element should be shallow over the surgical exposed apical region, so that the pulp structure is not affected. Technically, rupture of the pulp tissue is avoided during the induction of fracture and the light movements aiming at inducing luxation in the fracture line. In vitro experiments confirm that the pulp tissue is maintained. The design of the double-bezel chisel proposed by Puricelli is essential for maintenance of integrity of the pulp tissues.

Radiologic analyses show that the corono-radicular and apical fragments may, or may not, undergo increasing separation during the progression of the orthodontic traction. This means that the apical fragments, even if fractured, may be displaced with the corono-radicular portion by the orthodontic traction. A progressive obliteration of the pulp chamber and the root conduct in the corono-radicular element is observed 1718 (Figures 1 and 6). The phenomenon is well recognized in vital teeth where root fractures were performed 2122. In these cases, the conduct may be partially or completely obliterated. Partial obliteration is more frequent in the fracture area and in the apical fragment, whereas total obliteration is characterized by an uniform reduction on the size of the pulp cavity as a whole 21. The apical region and the periodontal space of the apicotomized erupted tooth present, at radiographic examination, a hard periodontal layer with regular borders 18.

Since 1987, when the technique began to be used, the teeth aligned and leveled in the dental arch have kept stable and functional.

Apicotomy is a technique which has been successfully used during the past twenty years, for conservative intervention in cases of impacted upper canines with dilaceration or apical root-ankylosis. Currently, it could also be indicated for lower canines. The technique aims at freeing the tooth from its dilacerated or ankylosed portion inducing, thus, its traction and eruption. It was initially indicated after failure of conservative techniques for inducing spontaneous eruption and orthodontic traction. At the moment, image examinations allow precise diagnosis and its indication as a first surgical therapeutic option. The technique is counter-indicated for young patients with incomplete rhizogenesis or for teeth with total root ankylosis.

The author(s) declare that they have no competing interests.