Computer-assisted surgical planning in head and neck reconstruction: Mandible and dental restoration

Introduction

The free fibula flap has become the workhorse for mandible reconstruction. It was popularized by Hidalgo in 1989 and in its early iterations, involved creating intraoperative templates to guide osteotomies and hand-bend plates. Although this involved great artistry and skill, this method also carried a greater margin for error and could be time consuming.

In the decades following, advancements have improved the planning, accuracy, and efficiency of osseous free flap mandible reconstruction. In the 1990s, surgeons translated technology utilized in craniofacial surgery, and printed three-dimensional (3D) models of recipient defects and reconstructive templates to aid flap shaping. This also allowed the ability to bend plates preoperatively. In the early 2000s, cutting jigs to create more precise osteotomies were used. Soon after, surgeons started performing preoperative “virtual surgery” to fabricate more precise cutting guides. Next, custom milled plates, which are thinner, stronger, and configured to specifically fit the defect were utilized.

Dental restoration has evolved in parallel. Placement of immediate dental implants was introduced at the same time the free fibula was popularized for mandible reconstruction. However, patients still underwent a period of osseointegration before the implants were loaded with a prosthesis, and the initial reconstructive plan was often not centered around occlusion. This led to greater challenges providing ultimate dental restoration. Over time, the use of computer-assisted surgical planning (CaSP) to refine dental implant placement ^, and earlier functional loading has expedited the process and allowed the possibility of “jaw in a day” surgery. ^,

Clinical considerations

It is important for the ablative, dental, and reconstructive surgeons to plan the surgery together. Because the fibula is the most often used flap for mandible reconstruction, we will focus on details related to this option. However, there are situations where other flaps may be better suited and CaSP can be utilized to assist reconstruction.

One of the first aspects to consider is the anticipated bony and soft tissue defect location and size. Unless this is a benign case with adequate gingiva, there will likely be a need for a skin paddle. One can plan to place the bony segments centered around the perforators depending on where the needed soft tissue is located. One needs to also determine if a second skin paddle or free flap will be necessary. Situations that may require this additional soft tissue are when there is an external skin defect or other oral cavity structures, such as the floor of mouth or tongue, that are involved.

Another key determination is whether the vascular pedicle will run anterior or posterior. This may be determined by recipient vessel quality and availability, and whether the condyle needs to be reconstructed. This orientation will affect the soft tissue inset and planned laterality of the donor site. There are different schools of thought on how to orient and drape the skin paddle. Traditional thinking is to have the skin paddle septum drape over the posterior fibula in the lingual direction. However, tighter inset may be better suited for dental implants, leading some to advocate having the septum drape over the lateral fibula and reconstruction plate in the buccal direction. This helps avoid skin paddle bulk and creates a buccal sulcus from the pull of the septum.

Once the fibula laterality and orientation are decided, the next step is to determine how many osteotomies to perform for reconstruction. The native mandible can be ghosted or mirrored to help with optimal configuration. If the defect is anterior, a double-barrel configuration to help with lip support, and chin height and projection may be considered. However, the planning needs to maintain enough restorative space for dental rehabilitation.

When planning for dental rehabilitation, it is important to ensure the reconstructed mandible will align with the opposing maxillary dentition, and that the implants are aligned through the occlusal or lingual surface of the teeth. Another consideration is the positioning of the fibula in the superior/inferior direction and its effects on dental rehabilitation versus optimizing lower mandible contour. There may be advantages to aligning the fibula along the mandible alveolus rather than the inferior border, which allows better prosthetic abutment-to-implant ratio. Regardless, one needs to allow at least 15 mm of restorative space for dental rehabilitation. When planning the location of the dental implants along the bone, there may be certain areas of the fibula that are better shaped and suited for placement of implants which will affect where the fibula is harvested in the proximal/distal direction.

Workflow for computer-assisted design/computer-assisted manufacturing

Please see Fig. 8.1 .