A classification of mandibular defects based on functional as well as aesthetic factors is presented. By taking into account the difficulties in restoring form and function and not simply relying on traditional anatomic landmarks, it is hoped that this method will allow different types of reconstructions to be fairly evaluated. It also should help surgeons to tailor individual reconstructive techniques to specific clinical situations. Major difficulties in mandibular reconstruction arise when a condyle requires replacement, when there is a mucosal and/or skin component to the defect, and when the area to be reconstructed involves the anterior arch.
The classification is based on three upper-case and three lower-case characters: H, C, L and o, m, s. H defects are lateral defects of any length, including the condyle but not significantly crossing the midline; L defects are the same only without the condyle; C defects consist of the entire central segment containing the four incisors and the two canines. Combinations of these letters are possible (an angle-to-angle defect, for example, is represented as LCL). Thus H and L defects may reach or even extend slightly beyond the midline but are not referred to as LC or HC unless they contain the entire central segment. The letters o (neither a skin nor a mucosal component), s (skin), m (mucosa), and sm (skin plus mucosa) are added to denote the epithelial requirement.
Current strategies for jaw reconstruction require multiple procedures, first to repair the bone defect to offer sufficient support, and then to place the tooth implant. The entire procedure can be painful and time-consuming, and the desired esthetic and functional repair can be achieved only when both steps are successful. Although the patient's quality of life can be improved significantly, the prognosis is often unpredictable, especially in young patients, whose jaws continue to grow, while the implant remains fixed. The ability to bioengineer combined tooth and bone constructs, which would grow in a coordinated fashion with the surrounding tissues, could potentially improve the clinical outcomes, and also reduce patient suffering.
Under the guidance of Dr. Pamela C. Yelick, a research team at Tufts University (Boston, MA) has examined the feasibility of simultaneously reconstructing both teeth and bone. In 2002, the group first reported the regeneration of tooth crowns, from cultured tooth bud cells seeded onto biodegradable scaffolds and implanted into rat hosts. The morphology of the developing tissue-engineered tooth crowns closely resembled that of naturally formed teeth. Next, they generated a hybrid tooth-bone construct, by combining a bone-marrow-derived stem-cell-seeded scaffold with the previously used tooth model, implanted and grown in the omenta (tissues connecting abdominal structures) of rat hosts. In this case, the formation of not only the tooth crowns but also tooth root and surrounding alveolar bone was observed. However, since the omentum offers an environment quite distinct from that of the natural tooth site, the jawbone, the team examined hybrid tooth-bone construct development using third molar tooth bud cells and bone marrow derived from, and implanted back into, the same minipig.