Zygomatic implants are indicated for the rehabilitation of the severely atrophic maxilla. Similar to standard implant placement, gaining an optimal position of the zygomatic implants is essential for a predictable prosthetic-driven treatment outcome. Stereolithographic templates, either bone-supported or mucosa-supported, have been used to install zygomatic implants in the planned position based on computer-assisted planning. However, there is no effective mechanism to physically control the drilling trajectory for the zygomatic implants. Therefore, deviation between the actual and planned implant position is inevitable. A novel device designed to increase the precision of the guided surgical placement of zygomatic implants that guides the osteotomy from the entry point to the exit point, allowing optimal positioning, is presented herein.
Zygomatic implants are indicated for implant rehabilitation of the atrophic edentulous maxilla as a graftless solution. The original protocol employs a two-stage approach to the placement of the zygomatic implants, which pass internally through the maxillary sinus before entering the zygoma bone. Despite the original protocol being a proven technique, it is associated with a few drawbacks, such as difficulty of surgical access, palatal position of the implant heads, and potential risk of maxillary sinusitis. Therefore clinicians have developed new protocols or have modified techniques to address these issues.
There are surgical techniques for external placement, such as the slot technique, extra-sinus methods, and extra-maxillary method. These different methods allow the placement of zygomatic implants in the optimal position. In order to achieve prosthetic-driven outcomes, computer-based planning has also been introduced for zygomatic implants. To optimize treatment outcomes with computer-assisted planning, clinicians have also attempted static or dynamic guided surgical techniques to place the zygomatic implants in the planned position.
It is important to place the zygomatic implants in the optimal position for a predictable treatment outcome. Optimal positioning of the zygomatic implant is defined by the location of the head and the tip of the implant and the path of its insertion. The location of the head of the zygomatic implant should fulfil the prosthetic-driven considerations in order to achieve favourable biomechanics, facilitate hygiene maintenance, and prevent complications. The location of the tip of the zygomatic implant should maximize bone anchorage, enhance initial stability, and avoid penetration into the orbit. The path of insertion is better external to the maxillary sinus to eliminate the risk of maxillary sinusitis.
The zygomatic implant is an extra-long implant that enters the residual maxillary ridge in the premolar–molar region and exits at the outer surface of the zygoma bone. When installing a zygomatic implant through a stereolithographic template, it is possible to locate the entry point as planned, but there is no effective mechanism to control where it exits. The lack of precise control with regard to the exit point is due to the following factors: (1) limited access and poor visibility during surgery; (2) flexibility of the long twist drills for zygomatic implant osteotomy; and (3) curved or irregular bony surface at the base of the zygoma bone around the exit area.
A zygoma drill guide designed to maximize the benefits of the template-guided placement of zygomatic implants was developed by the author of this article.
Materials and methods
In order to control the exit point, a device designed to guide the tip of the drill into the correct location when performing template-guided placement of zygomatic implants was developed. This device has been called a ‘zygoma drill guide’. The zygoma drill guide was designed using computer-aided design (CAD) software, and a prototype was printed for testing ( Figs 1 and 2 ). Subsequently, a zygoma drill guide made of stainless steel was produced by milling ( Fig. 3 ). The milled zygoma drill guide could be disassembled for cleaning and autoclaving. The zygoma drill guide was designed for use on the right and left sides of the maxilla and for different patients after sterilization.
The zygoma drill guide consists of two heads in co-axial alignment that guide the drill at the entry point and the exit point. These two heads are metal rings with an internal diameter of 2.9 mm; these are connected by a sliding arm consisting of a rod enclosed in a tube with an open end. The entry head is inserted into the drill sleeve of the surgical template and the exit head is positioned at the base of the zygoma bone ( Fig. 4 ). When passing a drill through the surgical template, the drill enters the entry head at the drill sleeve and engages the exit head before entering the zygoma bone. The co-axial alignment of these two heads guides the twist drill along the pre-determined path of insertion and limits any deviation of the drill tip when engaging the bony surface at the base of the zygoma bone.