33rd Annual Scientific Meeting proceedings

In human medicine cone beam computed tomography (CBCT) has become a mainstay in various fields of oral and maxillofacial surgery, allowing practitioners to plan appropriately, operate with confidence, and assess results post-operatively.¹ Furthermore, the acquired CT image data can be used for computer-assisted surgery (CAS), by coupling a surgical navigation system with a (CB)CT scanner, and this has found great utility in implant dentistry and in craniomaxillofacial surgery.² With the help of CAS, the surgeon can precisely plan and execute complex surgical procedures in an efficient manner. These features are highly desireable in equine veterinary dentistry, where intraoperative orientation is an imperative for challenging cases. The focus of this presentation will be on pre-operative planning, intra-operative imaging and image-guided surgery, more specifically how CAS can be used for surgical case management.

Although the great majority of cheek teeth can be successfully extracted with a standing oral extraction technique⁴, the veterinary dentist will be faced with limitations on a regular basis that can make these procedures technically challenging and potentially afflicted with considerable iatrogenic damage. These limitations include tooth fractures with or without missing parts of the clinical crown, variations in the shape of the tooth crown or roots, supernumerary or ectopic teeth, impacted teeth, restricted surgical access, and other issues. This is reflected by numerous complementing and alternative techniques, which have been described to accomplish exodontia in such challenging cases.^5-12 These can be performed in standing sedated or in recumbent anesthetized horses, and include a minimally invasive transbuccal screw extraction (MITSE)⁶, tooth segmentation⁷, trephination and repulsion techniques^8-10, or exodontia via an invasive lateral buccotomy approach.^10-12 Because of the considerable risk of inadvertent iatrogenic damage to adjacent dental, bony or soft tissue structures^8,11, some form of intra-operative imaging is indispensable for the majority of these surgeries.

The mobile CBCT unit (O-arm, Medtronic) used at the authors’ institution was primarily developed for intraoperative use in humans and can be coupled with a surgical navigation system (StealthStation, Medtronic). In standing, sedated horses, we use the CBCT scanner primarily for the diagnostic workup of dental and paranasal sinus disease.³ Once it is clear which dental structure is affected, the imaging data is screened for additional information to help plan surgical case management. This includes a comprehensive 3-dimensional evaluation of the targeted dental structure and the associated anatomy, i.e. the surrounding alveolar bone, the adjacent nasal passages or paranasal sinuses, as well as important neurovascular structures.

Having the CAS technology available at the authors’ institution, and gained first experience with its use in computer-assisted orthopaedic surgery^13-14, we started applying this technology in equine dentistry for selected cases in 2015. Today, we are using CAS routinely for the surgical case management of challenging interventions involving the equine dentition and (para)nasal cavities.

The use of CAS has greatly improved preoperative planning and intraoperative orientation for such surgical interventions, and has proved to be particularly useful in surgeries where exact instrumentation and multiplanar orientation are indispensable. Simultaneously, CAS facilitates minimally invasive approaches and potentially allows to decrease collateral damage and improve the overall outcome of numerous procedures.

Based on our experience, we believe that CAS provides the operating surgeon with unmatched intraoperative orientation and real-time control over the instrumentation during these procedures. While this may not be necessary in most procedures, it is nonetheless very useful to have in many cases, and in rare instances even indispensable to insure a safe procedure. An example for the latter is documented and illustrated in a recently published case report of CAS-guided removal of an ectopic tooth in the mandibular fossa via a condylectomy approach.¹⁵

Although not indispensable, CAS is of great value and help when performing mandibular or maxillary cheek teeth repulsions. There, CAS provides intraoperative guidance for important steps like performing an osteotomy and for correctly positioning and aiming the dental punch used for the forceful repulsion. These steps are readily controlled in real time, eliminating the need of repeated intraoperative radiographic or CT imaging. In cases where transoral extraction and MITSE failed in removing a maxillary cheek tooth, and repulsion is elected to finish the job, meticulous intraoperative guidance can become indispensable. The main objectives for the use of intraoperative guidance are then to avoid the infraorbital canal and directing the dental punch through a trephination to the apical region of the tooth and aligning the long axis of the punch with the long axis of the tooth. When using CAS, this can be done under real-time intraoperative guidance. Moreover, a high speed drill (Midas, Medtronic) can be navigated and used to remove hard dental material of teeth with enlargement of their roots because of chronic periodontal changes, before applying the dental punch and to allow successful removal. Once familiar with the principles of CAS, this technology is readily be applied to control or even enhance many of the described techniques used to accomplish challenging tooth extractions or complete failed transoral extractions. Furthermore, the mobile CBCT scanner alone is sometimes used as an intraoperative imaging modality to confirm complete removal of residual dental structures or bone sequestra.

In summary, CAS can aid challenging dental procedures based on the following 3 inherent features: (1) It provides 3D preoperative imaging that allows to complement any previous diagnostic imaging that has been performed and thus provide a comprehensive diagnosis. (2) It provides the best possible real-time intraoperative orientation to implement minimally invasive approaches, and (3) it allows for the real-time guidance of navigated surgical instruments for the precise execution of the surgical plan.

By using computerized technology, today's veterinary equine dentists have the possibility of increasing surgical accuracy when performing challenging cheek tooth extractions, sinus surgery, or other interventions that carry a high risk of iatrogenic damage. This will help us to further reduce surgery-related morbidity^8,16-19 and improve the overall success rates and outcomes.

References

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