Computer-assisted planning in maxillofacial prosthetics

Introduction

Six separate procedures will be described in this chapter. Each demonstrates the value of computer-assisted planning and the interaction between the craniofacial surgeon and other members of the prosthetics and design team. In each case, the definitive outcome is first visualized and then planning for the actual procedure commences with an eye toward this goal. This is restorative-driven care. This is analogous to the construction of a new home where one first selects the appearance of the desired structure, then goes about planning and designing to achieve this outcome. Fig. 27.1 depicts the digital workflow common to all procedures described.

• 1.

  Single tooth replacement with an osseointegrated implant. In cases of cleft lip and palate it is common for a tooth to be congenitally missing in the line of the clefted alveolus. The placement of an osseointegrated implant in the edentulous site of a congenitally missing tooth has become a standard in cleft care. It allows for an aesthetic and functional restoration while avoiding the need to unnecessarily restore adjacent teeth or connect teeth together, creating a more hygienic oral environment. It may require hard and/or soft tissue grafting of the site prior to implant placement.

• 2 and 3.

  Complex oral rehabilitation: reconstruction of maxilla/mandible with microvascular free flap/osseointegrated implants/fixed prosthesis. The same basic principles, protocol, and workflow for computer-assisted surgery and restoration of a single missing tooth apply to more complex craniofacial cases that involve multiple missing teeth and often, segments of the jaw and soft tissues. These situations arise most commonly in connection with a tumor resection but may be the result of craniofacial trauma or a congenital condition. In addition to replacing missing teeth, the restorative process may require the addition of bone with or without soft tissue. The cases demonstrated in Videos 27.2 and 27.3 required microvascular flap reconstruction following oncologic resection. In each situation, computer-assisted surgical planning (CaSP) and prosthesis design and fabrication yielded a predictable outcome that is both aesthetic and functional.

• 4.

  Soft tissue augmentation. When surgery is performed to augment deficient soft tissue facial contours, computer-assisted planning and computer-generated surgical guides assist the surgeon to achieve a more symmetrical, predictable appearance.

• 5.

  Autologous ear construction. When craniofacial reconstruction with autologous tissue is possible, the prosthetics team provides computer-assisted planning and surgical guides that enable the surgeon to achieve ideal position and form of the reconstruction.

• 6.

  Implant-retained facial prosthesis. In congenital or acquired situations where an ear, nose, or orbit is missing or deformed, surgical correction using autologous tissues is the most natural means of restoring form and function. However, the nature and location of the defect, the lack of available soft tissue, the patient’s medical condition, or their preference may preclude a reconstruction that is purely autologous. In such cases, prosthetic rehabilitation with osseointegrated craniofacial implants is a preferred option. An implant-retained facial prosthesis utilizing a computer-assisted surgical plan and prosthetic design and fabrication offers improved aesthetics, retention, and patient comfort over an adhesive retained one.

Clinical considerations

• 1.

  Single tooth replacement with an osseointegrated implant. The edentulous site must be of appropriate clinical and radiographic width to allow for an aesthetic restoration without interfering with the roots of adjacent teeth. In a cleft-related edentulous space, the maxillofacial prosthodontist must work closely with the orthodontist to establish and maintain proper tooth spacing and root alignment of adjacent teeth so as not to impose on the ideal implant position. A cone-beam computed tomography (CBCT) scan will detect root position and bone volume (height and width) at the site. If there is inadequate bone volume at the implant site and a bone graft is required, computer-assisted planning helps to guide proper positioning of the bone graft to allow for later ideal implant placement.

• 2 and 3.

  Complex oral rehabilitation: reconstruction of maxilla/mandible with microvascular free flap/osseointegrated implants/fixed prosthesis. When placing osseointegrated implants and a fixed dental restoration as part of an extensive oral rehabilitation, there are many more considerations than with a single tooth replacement. Intricate planning sessions with the surgeon, maxillofacial prosthodontist, and the biomedical technologist are required for such complex surgeries. When an autogenous microvascular free flap and osseointegrated implants will be part of the reconstruction, three-dimensional (3D) spiral and CBCTs, a comprehensive oral examination, and an intraoral scan are necessary data. Anatomical and clinical considerations for this procedure include location of the defect, dimensions of the bony replacement, occlusal relationships, donor site selection, perfusion of the planned flap, and orientation of the bone segment relative to pedicle position. The location of nerves and vessels and position of the reconstruction plate and screws must be identified so the planned position of each implant will not interfere. The additional use of virtual reality software provides unique visualization capabilities at both the donor and host sites and enhance the surgeon’s ability to evaluate the anatomy and plan the surgery along with the other members of the rehabilitation team.

• 4.

  Soft tissue augmentation. The goal of this procedure is to achieve facial symmetry and aesthetic improvement that can provide the patient with a sense of psychological well-being and confidence in both a social or work-related environment and improve their quality of life. The surgeon, working with the maxillofacial prosthetics team, can develop a computer-assisted plan to achieve the desired augmentation and then a computer-generated surgical guide to be used during the surgery to insure the desired outcome.

• 5.

  Autologous ear construction. Autologous reconstruction is one of the most difficult tasks for the reconstructive surgeon. The goal of this procedure is to create an external ear that mimics the contralateral side in size, shape, position, and orientation. This becomes a challenge during the procedure when the unaffected ear is draped and inaccessible for reference. Computer-assisted planning and surgical guides provided by the maxillofacial prosthetics team assist the surgeon in all stages of the reconstruction.

• 6.

  Implant-retained facial prosthesis. The use of osseointegrated craniofacial implants to retain a facial prosthesis significantly improves the overall success of the restoration. The most common application sites are the auricular, nasal, and orbital areas. Depending on skin quality and contour at the defect site, and the visual acuity and manual dexterity of the patient or caregiver, adhesive-retained facial prostheses may be difficult to properly position and retain. There is also additional time and maintenance required due to the daily required application and removal of skin adhesive as well as potential skin irritation from the adhesive. An implant-retained facial prosthesis overcomes all of these problems. It is a more retentive and aesthetic restoration that is easier to position and remove. It is easier to maintain as the daily preparation and cleaning regimen is less cumbersome and there is no skin irritation from adhesives.

Considerations in planning for such a prosthesis are the presence of adequate bone and the condition of the skin through which the implants will pass. Digital information including a CT scan, a facial scan, and computerized imaging of the planned prosthesis will assist in determining the location of the implants to avoid anatomical structures, such as the mastoid air cells (auricular), frontal and maxillary sinuses (nasal), infraorbital nerve, and frontal sinus (orbital).