Several delicate, complex, and important structures necessary for an individual’s existence are found in the oral and cranio-maxillofacial region. Therefore, surgery in this area requires a great degree of precision to provide the best potential outcome, both esthetically and functionally. To attain this precision, several creative tools and concepts have emerged during the past few decades. Interactive visual-guided surgical interventions are one such area of ongoing research and development, with the most recent addition being the use of virtual and augmented reality in the surgical arena. This literature review gives insight into the existing and future applications of this rapidly emerging technology in oral and maxillofacial surgery.
Review Article
Virtual and Augmented Reality in Oral and Maxillofacial Surgery: Current Trends and Future
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Abstract
INTRODUCTION
Oral and cranio-maxillofacial surgery (OCMS) is a specialty concerned with the diagnosis and treatment of disorders affecting the mouth, face, jaws, head, and neck. Due to the fact that this surgical specialty is frequently associated with intricate surgical procedures involving delicate and important anatomical components, it has a significant potential for image-guided technology. Thus, it should come as no surprise that OCMS was one of the first specialties to be studied in terms of medical-augmented reality (AR) (which was first introduced in 1995 by Wagner et al.).[1] Since then, AR has been extensively used in trauma cases, oncology, orthognathic surgeries, and maxillofacial implantology.[2,3] Virtual reality (VR) can be understood as the art and science of introducing a virtually created environment that provides a predictable, secure, and customizable interface for the evaluation of various anatomical regions to help with the examination, diagnosis, and ultimately, the required treatment planning.[4] This artificially created interface can also be put to use in surgical training and understanding. Thus, VR represents a three-dimensional (3D)-generated world that can be readily explored and engaged with by an individual. On the other hand, AR combines VR with a 3D real environment that is specific to each patient, utilizing a complex registration process to create an integrated image that enhances the virtual scene with the real one.[2,4] Hence, the integrated image is superimposed on real surroundings. According to Azuma, for an interface to be considered an AR, it should be incorporated with the following attributes:[5] (1) combination of real and virtual elements, (2) interaction in real-time, and (3) 3D registration. VR and AR differ in that the former fully engrosses users into a virtual environment without being subjected to any awareness of the real world, while the latter technique enhances the sense of reality by instantaneously superimposing virtual images over the actual scene. All these advanced technologies broadly fall under the umbrella of mixed reality, which in addition to these also contains telepresence.
A variety of devices, including display units, input devices, tracking, and computers, are used in AR technology.[6] There are three main types of displays used in the fabrication of AR: head-mounted devices (HMD), hand-held displays, and spatial displays (video/optical see-through).[4,6] Contact lenses and more recent innovations, such as virtual retina displays, are being used by some AR systems these days (wherein the display is scanned onto the viewer’s retina).[6] Nowadays, there are various kinds of input devices available, and tracking devices consist of wireless sensors, accelerometers, digital cameras, other optical sensors, and Global Positioning Systems.
Currently, in the field of surgery, the navigation data/output is now shown on one or more monitors positioned around the site of surgery, which is a demanding process as a whole owing to space limitations and line-of-sight restrictions. For this reason, the operator has to divide his attention between the patient and the navigation display while coordinating the use of surgical instruments at the same time. AR has lately been used in maxillofacial surgery to overcome the aforementioned problems. Using AR, real and virtual pictures are combined into a unified scenario, enabling direct viewing of the patient imaging overlaid to the surgical field thus, subtly improving the impression of the surrounding environment.[4] This eliminates the need to take the operator’s focus away from the surgical field by enabling them to see both the projected images and the surgical field at the same time.
DISCUSSION
A number of elements must be incorporated to fabricate a successful AR system.[2,6] The first component is a scanning device in the form of a camera or a sensor, for capturing the objects and real-life images. The computer unit is the second crucial component; which processes the captured images and motion, analyzes its location, and finally, adds up depth to the captured images, thereby converting them into three-dimensional entities. A display system to show the virtual and 3D objects in the real world makes up the third component. Finally, a device is used to register and actively track the user during the entire process to achieve real-time visualization.[7] Marker-free registration, which uses lasers to scan the skin’s surface, and marker-based registration, which makes use of anatomical landmarks, bone screws, and skin adhesive markers, are the two primary categories of registration procedures.[8,9] The tracking systems are employed to monitor the motions of the patient, the instruments, and the operator. In addition, the virtual objects can be viewed from different perspectives.[7-10] Two methods are employed for tracking: (a) The fiducially markers: based on anatomical landmarks identified by X-rays and (b) surface matching: that relies on position sensors which are attached to both the patient and the device being used.[10]
First reported in the late 1980s, computer-assisted head-and-neck procedures have now been integrated into several cranio-maxillofacial subspecialties, as a means of performing precise and minimally invasive procedures. A review was conducted in 2019 by Ayoub and Pulijala. reveal maxillofacial surgery to be the primary area of application of AR-based technologies, as compared to any other dental specialty.[4] Maximum studies that have been conducted till date report orthognathic surgeries to be the most active domain of its employment, followed by implantology, traumatology, oncology, and others. Other than its surgical application AR is being very popularly used as a learning/teaching tool making visualization of the complex anatomical structures and associated surgical techniques much more easier and understandable.[3-5] These applications have been described in detail in the following paragraphs:
ORTHOGNATHIC SURGERIES
The most commonly employed application of AR and/or VR in orthognathic surgeries is in its treatment planning phase.[4,6] Recently, following the improvements in the speed and image quality AR is being utilized intraoperatively to visualize the important underlying anatomical structures helping to prevent any surgical mishaps. The desired treatment outcome that was planned during the treatment planning phase is directly superimposed on the patient in the operative setting helping in visualizing the amount of osteotomy, advancement, or setback that is required individually.[11]
In an article published in 2018, Zhu et al. compared the use of the AR system with the free-hand technique during a mandibular angle osteotomy.[8] The study’s findings indicated that while the AR system required more time during the preoperative phase than the free-hand technique, it took less time during the procedure. This was consistent with findings from Zinser et al.’s 46 orthognathic surgeries, wherein operating times were found to be approximately 60 min longer overall when utilizing the AR system compared to free-hand procedures. However, the technique utilizing AR navigation was noted to be superior to conventional in terms of precision, ease of planning, and specific clinical requirements, resulting in more predictable and favorable patient outcomes.[12] In 2019, Han et al. used this technology in seven patients’ “synostoticplagiocephaly surgery,” reporting adequate compliance between the preoperative plan and the surgical outcome.[13] It has been further reported in the literature that the usage of AR as a navigational system can potentially reduce the mean positional errors to approximately 0.7 mm.[12]
DENTAL IMPLANTOLOGY
Precise placement of dental implants is essential to meet the functional and esthetic requirements in dental implantology. Preoperative cone-beam computed tomography has been used extensively to determine the implant’s size, position, orientation, and proximity to important structures by means of the use of VR.[3,4,6] One of the main advantages of dynamic navigation is the operator’s ability to adjust the position of the implant to avoid a compromised bone foundation and anatomical entities that might not have been identified during the presurgical planning phase. The image-guiding implantology technique has been found to be highly accurate, with an overall navigation error of 0.35 mm (and a mean angular deviation of < 4°). When compared to manual operations, implant AR-supplemented navigation systems are known to produce more precise outcomes and lower variance. Moreover, it decreases the chances of iatrogenic errors such as sinus perforations, dehiscence, fenestrations, and nerve injury.[3,4]
ONCOLOGY
With concern to oncology, the clinician can physically mark the boundaries of the tumor as an overlay making use of the VR programming tools onto the processed radiographic informational indices.[8] Many studies conducted in this regard have elicited the efficacy of virtual planning in mandibular and maxillary reconstructive surgeries. Profeta et al. in their experiment utilized AR for guiding free-hand single-photon emission computed tomography in sentinel lymph node biopsy of head-and-neck oncology cases.[14] Scolozzi and Bijlenga in 2017 presented a case report of their case wherein an augmented operating microscope was used for the removal of tumor from intraorbital region.[15] In this case, to achieve a better view of the tumor’s deeper extensions, a surface exhibiting the tumor was placed within the microscope. In selected cases of tumor removal followed by reconstruction of maxillofacial region. estimated the AR-based navigation system error to be around 1 mm.
TRAUMA SURGERIES
Reduction and fixation of fractures are made easier by thorough intraoperative visualization of the underlying vital structures, thereby significantly reducing the chances of intraoperative bleed and postoperative paresthesia. Furthermore, retrieval of foreign bodies can be accomplished in more safe and accurate manner by utilizing this image-guided navigation technology.
SURGICAL TRAINING
VR in conjugation with the haptic feedback simulation system is being used as an integral training tool for surgical and dental students in many institutions. This provides the students with the opportunity to prepare themselves by practicing the complex surgical procedures and instrument handling in a real life-like virtual surgical field before they get to work on real patients. Many such training systems are now being introduced in dental colleges to help students grasp the complex anatomical aspects by 3D visualization and simulation. Study conducted by Pulijala et al. employing VR for training students in orthognathic surgery, got feedback of the system being very reliable and easier to understand.[16] Thus, improving the operative skills among trainees. The incorporation of haptic technology, which gives the user a tactile sensation of the touched structure or object held in their hands, has enhanced VR and created a more realistic setting for surgical training.
TEMPOROMANDIBULAR JOINT SURGERIES
In the case of temporomandibular joint (TMJ) surgeries, the innovative AR applications allow the surgeon to visualize the patient’s anatomy by viewing the underlying anatomical structures superimposed on the patient’s face.[17] There are two ways to track in AR surgical navigation systems: external tracking and integrated cameras.[18] The first method uses specialized equipment such as visible light tracking (Micron tracker) or infrared tracking (NDI Polaris-Northern Digital Inc) are frequently used for external tracking. In the second approach, cameras are utilized for either marker-based or marker-less tracking of surface characteristics or markers in the surgical site. In addition, it aids in the diagnosis of changed TMJ kinematics, visualizes narrow jaw areas, and enhances surgical precision.
DRAWBACKS OF AUGMENTED REALITY
- Longer preoperative duration
- The technical application and accuracy are still in the developing stage with the evolving technologies thus restricting its routine usage in the surgical field which demands high level of precision
- High expenses
- The use of HMD devices has been reported to cause vertigo, eye strain, nausea, blurred vision, and headaches. This augments a thorough evaluation of the potential occurrences of these side effects before the first use
- AR cannot be utilized for emergency treatments since it involves extensive and lengthy preoperative investigations.