Abstract
Navigation-guided surgery has recently been introduced into various surgical disciplines, including oral and maxillofacial surgery. Since the advent of dental implants, dental computed tomography (CT) scans have been used as a diagnostic tool for preoperative planning, but not as part of the surgical phase.
This article explains the principles of computer-assisted surgery and describes the use of a computer-guided navigation system in dental implantology. The system uses preoperative dental CT scans for planning and as an integral part of the surgical procedure. This system allows continuous intraoperative coordination of the implantation phase with the preoperative plan, optimizing the accuracy of implant surgery. Deviations from the planned location of the implants are minimal. Several cases are discussed.
Introduction
Image-guided surgery (IGS), also called computer-assisted surgery, was recently introduced in many surgical specialties. These systems are similar in principle to the Global Positioning System; they combine tracking technology with a highly accurate road map of a patient’s anatomy, so that the surgeon can navigate within the surgical field.
The high-speed processing unit can track the movement of the surgical instruments, calculate their position within the surgical field, and display the instruments in relation to the patient’s anatomy detailed from the imaging data. During the surgical procedure, the surgeon can view an image of the surgical instruments superimposed on the detailed image of the patient’s anatomy (Figure 1).
History
Image-guided surgery was first introduced into neurosurgery, followed by other surgical fields, including oral and maxillofacial surgery. However, the implementation of this technology to the field of dental implantology was delayed because of two obstacles.
The first obstacle was related to the fact that conventional IGS had to be performed under full anesthesia with a completely fixed surgical field. Early attempts to use this technology with dental implants were limited to the fixed upper jaw. The second obstacle was related to the accuracy of the available systems. Accuracy was reported to be in the range of 2 mm to 5 mm. Although this level of accuracy is beneficial in some surgical procedures, it is unacceptable for dental implant surgery.
Tracking Technologies
Two elements require tracking during IGS: the real-time position of the patient and the position of the surgeon-operated handpiece. Currently, there are four types of tracking technologies: electromechanical, sonic, electromagnetic, and optical.
- Electromechanical tracking relies on detectors located within the joints of a mechanical arm system. It is cumbersome and doesn’t achieve the required accuracy because of imprecise registration and elasticity of the arms and joints.
- Sonic tracking determines position by measuring the time needed for the sound from an emitter to travel to a microphone array of known geometry. This technique is influenced by temperature changes, which may lead to inaccuracies.
- Electromagnetic tracking superimposes a magnetic field around the area of interest. The position can be determined by using a probe that can detect gradients in the magnetic field. Ferromagnetic substances, aluminum, and electromagnetic radiation may distort the magnetic fields and impair the accuracy of localization.
- Optical tracking is the most commonly used technology. This technique is based on arranging infrared light-emitting diodes (LEDs) in a known geometric pattern, attaching them to the patient in proximity to the surgical field, and installing them on the surgical instruments. The infrared emission is detected by a camera and transferred to a processing unit that reconstructs the position of the patient and the surgical instruments.
Image-Guided Implantology System
The Image-Guided Implantology (IGI) is a newly developed, optically based navigational system that is specifically designed to facilitate planning and execution of dental implant placement (Figure 2). Because the system uses a special appliance to track the patient’s head and jaw movements, immobilization is not required. The system’s mean spatial navigation error was established to be 0.35 mm. In a controlled environment, it allows the transfer of the preoperative plan with a deviation of less than 1 mm, which is acceptable for dental implants.
The surgeon uses the software to plan the implants’ positions based on the reconstructed dental computed tomography (CT) image. The surgeon assesses the alveolar bone and then identifies and marks critical anatomical structures to be avoided. With a simulation of the future restoration, the surgeon can correlate the implants’ position with the patient’s occlusion, establishing optimal implant placement for bone morphology and prosthetic needs. The system then guides the surgeon in placing the implants.