Correction of Dentofacial Deformities

Prevalence of Dentofacial Deformities

Epidemiologic surveys demonstrate that a large percentage of the U.S. population has a significant malocclusion. Very little data describe the exact prevalence of significant skeletal facial deformity. This information can be extrapolated from studies that have evaluated the prevalence of severe malocclusion. The National Health and Nutrition Examination Survey III, conducted from 1989 to 1994, obtained a sample of 14,000 individuals ages 8 through 50 years, which roughly approximates the general U.S. population. In this study, information was collected describing overjet and reverse overjet, vertical overlap (deep bite and open bite), and posterior cross-bites. It can be assumed that patients with extreme values in each of these categories have underlying facial deformities ( Table 26.1 ). Because many patients have dental compensations for skeletal growth abnormalities (described later in this chapter), this study likely underestimates the severity of skeletal abnormalities. This type of data, combined with other criteria that clearly define the most severe characteristics of a malocclusion such as overjet versus crowding, can help estimate more accurately the prevalence of skeletal abnormality that may require surgical correction as part of the treatment for malocclusion.

It appears that about 2% of the U.S. population has mandibular deficiency, vertical maxillary excess that is severe enough to be considered a handicap, or both. Other abnormalities and their percentages of prevalence in the population include mandibular excess, maxillary deficiency, or both, 0.3%; open bite, 0.3%; and asymmetry, 0.1%. Therefore it appears that approximately 2.7% of the U.S. population may have a dentofacial deformity contributing to malocclusion that requires surgical treatment for correction.

Historically, treatment of malocclusions, even those associated with dentofacial deformities, has been aimed at correction of dental abnormalities, with little attention to the accompanying deformity of the facial skeleton. In the last 60 years, surgical techniques have been developed to allow positioning of the entire midface complex, the mandible, or dentoalveolar segments to any desired position. The combining of surgical and orthodontic procedures for dentofacial deformities has become an integral part of the correction of malocclusions and facial abnormalities.

Causes of Dentofacial Deformity

Malocclusion and associated abnormalities of the skeletal components of the face can occur as a result of a variety of factors, including inherited tendencies, prenatal problems, systemic conditions that occur during growth, trauma, and environmental influences. Although it is not within the scope of this book to present a detailed discussion of facial growth, an understanding of basic principles as they relate to the development of dentofacial deformities is essential. Enlow and Han's Essentials of Facial Growth should be reviewed for a more complete discussion of the principles of facial growth.

General Principles of Facial Growth

The development of proper craniofacial form and function is a complex process affected by many factors. In the area of the craniofacial complex, some parts appear to have their own intrinsic growth potential, including the spheno-occipital and sphenoethmoidal synchondroses and the nasal septum. In addition, the majority of growth of the bones of the face occurs in response to adjacent soft tissue and the functional demands placed on underlying bone. These soft tissue influences include the nasal, oral, and hypopharyngeal airway; facial muscles; and muscles of mastication.

The general direction of normal growth of the face is downward and forward with lateral expansion. The maxilla and the mandible appear to grow by remodeling or differential apposition and resorption of bone, producing changes in three dimensions. Enlow and Hans describe this phenomenon as area relocation , with the maxillary–mandibular complex enlarging in the downward and forward direction as an “expanding pyramid” ( Fig. 26.1 ). The direction and amount of growth characterize an individual's growth pattern. Alterations in the pattern of growth or in the rate at which this growth occurs may result in abnormal skeletal morphology of the face and an accompanying malocclusion.

Genetic and Environmental Influences

Genetic influence certainly plays a role in dentofacial deformities. Patterns of inheritance such as a familial tendency toward a prognathic or deficient mandible are often seen in a patient with a dentofacial deformity. However, the multifactorial nature of facial development precludes the prediction of an inherited pattern of a particular facial abnormality.

Abnormal facial growth and associated malocclusions are sometimes associated with congenital abnormalities and syndromes. Some of these syndromes, such as hemifacial microsomia and mandibulofacial dysostosis (Treacher Collins syndrome), are related to embryonic abnormalities of neural crest cells. Other congenital abnormalities affecting jaw growth include cleft lip and palate and craniosynostosis (premature fusions of craniofacial sutures). Facial growth abnormalities may be caused by conditions related to maternal systemic influences, for example, fetal alcohol syndrome, which may result in hypoplasia of midface structures.

Environmental influences also play a role in the development of dentofacial deformities. As early as the prenatal stage, intrauterine molding of the developing fetal head may result in a severe mandibular deficiency. Abnormal function after birth also may result in altered facial growth because soft tissue and muscular function often influence the position of teeth and growth of the jaws. Abnormal tongue position or size can affect the position and growth of the maxilla and the mandible ( Fig. 26.2 ). Respiratory difficulty, mouth breathing, and abnormal tongue and lip postures can adversely influence facial growth. Trauma to the bones of the face can result in severe abnormalities of the facial skeleton and the occlusion. In addition to the abnormality that occurs as an immediate result of trauma, further effects on the development of facial bones may occur. In the case of temporomandibular joint (TMJ) trauma in a growing child, significant restriction of jaw function may occur as a result of scarring or bony or fibrous ankylosis. Subsequent alteration of growth may result with deficient or asymmetric mandibular growth ( Fig. 26.3 ).

Evaluation of Patients With Dentofacial Deformity

In the past, patients with dentofacial deformities were often treated by individual practitioners. Some patients have been treated with orthodontics alone, with a resultant acceptable occlusion but a compromise in facial aesthetics. Other patients have had surgery without orthodontics in an attempt to correct a skeletal deformity, which resulted in improved facial aesthetics but a less than ideal occlusion. In addition to orthodontic and surgical needs, these patients often have many other problems requiring periodontic, endodontic, complex restorative, and prosthetic considerations.

Many areas of dental practice, in addition to orthodontics and surgery, must be integrated to address the complex problems of patients with dental deformities. This integrated approach, used throughout the evaluation, presurgical, and postsurgical phases of patient care, provides the best possible results for these patients.

The most important phase in patient care centers on evaluation of the existing problems and definition of treatment goals. At the initial appointment, a thorough interview should be conducted with the patient to discuss the patient's perception of the problems and the goals of any possible treatment. The patient's current health status and any medical or psychological problems that may affect treatment are also discussed at this time.

The involved orthodontist and oral-maxillofacial surgeon should conduct a thorough examination of facial structure, with consideration of frontal and profile aesthetics.

Evaluation of facial aesthetics in the frontal view should assess the presence of asymmetries and evaluate overall facial balance. The evaluation should include assessment of the position of the forehead, eyes, infraorbital rims, and malar eminences; configuration of the nose, including the width of the alar base; paranasal areas; lip morphology; relationship of the lips to incisors; and overall proportional relationships of the face in the vertical and transverse dimensions. Fig. 26.4 demonstrates normal facial proportions. The profile evaluation allows an assessment of the anteroposterior and vertical relationships of all components of the face. The soft tissue configuration of the throat should also be evaluated. Photographic documentation of the pretreatment condition of the patient should be a standard part of the evaluation. Video and digital computerized images have been introduced over the past decade as an additional aid in evaluating facial morphology.

A complete dental examination should include assessment of dental arch form, symmetry, tooth alignment, and occlusal abnormalities in the transverse, anteroposterior, and vertical dimensions. The muscles of mastication and TMJ function should also be evaluated. A screening periodontal examination, including probing, should assess the patient's hygiene and current periodontal health status. Impressions and a bite registration for dental cast construction and evaluation should also be obtained at this time.

Lateral cephalometric and panoramic radiographs are routinely used in the patient evaluation and are an important part of the initial assessment. Initially these were created with conventional radiographic technology. Currently cone-beam computerized tomography (CBCT) has become state of the art for most radiographic examinations of facial bones for the purpose of planning orthognathic surgery. Cephalometric and panoramic views are then reconstructed from the CBCT. In addition to these views, other images, including posterior-anterior views, TMJ images, and detailed three-dimensional (3D) views of any or all of the boney structures of the facial skeleton, can be easily evaluated. The cephalometric radiograph can be evaluated by several techniques to aid in the determination of the nature of the skeletal abnormality ( Fig. 26.5 ; Table 26.2 ). An important note, however, is that cephalometric radiographs are only a part of the evaluation process; they are used as adjunctive diagnostic tools in the clinical assessment of the patient's facial structure and occlusion. In difficult, complex cases, it may be helpful to view detailed 3D images of the facial skeleton ( Fig. 26.6A ). A stereolithic 3D model constructed from computed tomography (CT) data may also provide useful information for surgical planning (see Fig. 26.6B ). Computerized digital technology helps integrate cephalometric data with digital images of the face to improve evaluation of the relationship of the underlying facial skeleton and overlying soft tissue. After careful clinical assessment and evaluation of the diagnostic records, a problem list and treatment plan should be developed, combining the opinions of all practitioners participating in the patient's care, including the orthodontist, oral-maxillofacial surgeon, periodontist, and restorative dentist.

Presurgical Treatment Phase

Periodontal Considerations

As the first step in treatment, gingival inflammation must be brought under control and the patient's cooperation ensured. In patients who are unwilling or unable to clean their teeth properly before the placement of orthodontic appliances, oral hygiene procedures will be even less effective when complicated by orthodontic band placement.

Periodontal therapy includes oral hygiene instruction, scaling, and root planing; in certain instances, flap surgery to gain access for root planing may be necessary to provide proper tissue health. Whenever possible, it is advisable to delay comprehensive treatment until adequate patient compliance and control of inflammation are achieved.

As a result of the periodontal examination findings and proposed orthodontic and surgical plan, mucogingival surgery is often accomplished during this initial phase of therapy to provide a zone of attached keratinized tissue that is more resistant to potential orthodontic and surgical trauma. Soft tissue grafting is indicated in areas that have no keratinized gingiva or where only a thin band of keratinized tissue with little or no attachment is found when an increase in tissue trauma is likely ( Fig. 26.7 ). Such trauma to these areas includes labial orthodontic movement of teeth or a surgical procedure such as an inferior border osteotomy or segmental osteotomies in interdental areas.