Cleft and craniofacial orthognathic surgery

Growth and development

The maxilla and mandible develop from derivatives of the first pharyngeal arch beginning around the seventh week of gestation and proceed to grow primarily by intramembranous ossification. Although there is significant variability between genders and among individuals, skeletal maturation generally progresses in a cranial-to-caudal direction with the cranial vault reaching close to its final size in early adolescence, then the upper face in the early teen years, the maxilla in the mid teen years, and the mandible in the late teen years.

The maxilla forms from the ventral migration and eventual fusion of the paired maxillary prominences from its original more dorsal location near the mandibular prominences. The developing maxilla interacts with the nasal placodes and medial and lateral nasal prominences to form the nose, lips, and palate. The primary palate develops from the deep part of the intermaxillary segment of the maxilla and fusion of the median palatine processes. The secondary palate develops one week after the primary palate from shelf-like processes called the lateral palatine processes. The lateral palatine processes fuse in the midline and with the nasal septum and posterior part of the primary palate. The posterior part of the lateral palatine processes do not ossify and instead extend posteriorly beyond the nasal septum to form the soft palate. Postnatally from infancy through late adolescence to early adulthood, the maxilla grows in vertical height, transverse width, and anteroposterior length via intramembranous ossification at multiple sutures: frontonasal, frontomaxillary, zygomaticomaxillary, zygomaticotemporal, and pterygopalatine. Growth proceeds in a cranial-to-caudal and posterior-to-anterior direction in response to primary displacement of the bony structures at the sutures and then secondary bony ingrowth and remodeling. The bony palate expands in transverse width via growth at the midpalatine suture and lengths in the anteroposterior dimension via growth at the palatomaxillary suture. The alveolar ridge grows to allow for dental eruption. The maxillary sinus develops from pneumatization, a process whereby bone is resorbed on the sinus side and the deposits on the anterior side. Complete ossification of the maxilla occurs after that of the mandible in late adolescence.

The mandible develops from Meckel’s cartilage which is derived from the first branchial arch. Meckel’s cartilage extends from the otic capsule to the symphyseal midline and provides a template to guide the growth of the mandible. Just lateral to Meckel’s cartilage, a mandibular prominence forms on either side and then induces ossification for eventual fusion of the two mandibular prominences. Postnatally, the mandible grows in width first, then length, and then height. Mandibular width is nearly complete prior to adolescence, though the intercanine, molar, and bicondylar widths do slightly increase until mandibular length completes. Growth in length occurs through puberty typically ending around 15 years in girls and 18 years in boys. The primary sites of mandibular growth are the condylar cartilage, posterior rami, and alveolar ridges. During the growth process, the mandible displaces anteriorly and caudally. The mandible lengthens vertically to match the growth of the pharynx and middle cranial fossa to accommodate the vertical nasomaxillary growth and continues after horizontal growth has ceased in order to match the vertical growth of the midface.

Dental placodes initiate tooth development in the maxilla and mandible. These mesenchymal structures initially form a bud, which later becomes a cap and bell. Spatial and temporal induction of the dental mesenchyme determines the cusp patterns of individual teeth. Dental eruption patterns proceed in a similar stepwise fashion, and the transition from mixed dentition (6–12 years of age) to permanent dentition (12–20 years of age) mirrors the maturation of the maxillofacial skeleton. In a reciprocal fashion, midface and lower face development is also affected by the budding deciduous and permanent dentition, providing regional signals to the alveolus and stimulating bony deposition. During this period, an alteration of tooth position can alter the direction of growth of both the maxilla and mandible. Orthodontists take advantage of this active phase of development through their use of braces, palatal expanders, and various external devices to alter maxillary and mandibular growth trajectories. For this reason, surgical intervention is usually delayed until skeletal maturity is reached and orthodontic movements are no longer effective.

Nonsyndromic maxillomandibular skeletal dysplasia

Dentofacial deformities or skeletal dysplasias of the jaws affect about 20 percent of the population with the majority not being associated with a congenital anomaly. In North America the most encountered jaw deformity is mandibular retrognathia with or without microgenia. In Asia, the most frequent abnormality is mandibular prognathism. In contrast to North America, there is broad acceptance of orthognathic surgery to correct maxillomandibular skeletal dysplasias in Asian countries such as Korea, Japan, Taiwan, and China. In the United States, a more conservative approach to malocclusion associated with skeletal dysplasia has historically been the standard.

The apprehension to undergo orthognathic surgery in the United States is due to the feeling that the procedure is complex, the recovery difficult, and the risk of complications high. In all but the most severe cases of jaw dysplasia, parents opt for a non-surgical treatment that involves dental compensation with possible dental extractions. The introduction of skeletal anchorage devices has improved the orthodontist’s ability to modify skeletal growth. However, despite achieving a class I occlusion, many of these patients suffer adverse aesthetic consequences on facial form that are a direct result from uncorrected jaw deformities in combination with dental compensation. To correct an overbite with dental compensation, the upper incisors are retroclined and the lower incisors proclined. As the upper anterior teeth are retroclined, the upper lip support is compromised, reducing upper lip fullness. This upper lip retraction contributes to the illusion of excessive nasal projection which, in combination with the weak pogonion projection associated with the underlying mandibular retrognathia, results in an undesirable facial appearance ( Fig. 21.11.3 ). To correct the adverse aesthetic sequelae of uncorrected jaw deformities, patients seek orthognathic camouflage procedures – procedures that mask the underlying jaw deformity to enhance facial appearance. Typical procedures used in orthognathic camouflage are chin augmentation, rhinoplasty, dermal fillers, and alloplastic facial implants.

Recently, two factors seem to be leading to an increased acceptance for orthognathic surgery in North America: greater appreciation for the adverse aesthetic consequences of the uncorrected skeletal deformity and an improved perioperative experience for the patient. An increasing number of patients are aware of the impact that an uncorrected skeletal dysplasia of the jaw will have on their nose and chin. Moreover, as patients age, the compromised skeletal support of the facial soft tissue contributes to a prematurely aged appearance as marionette lines, nasolabial creases, and submandibular laxity appear earlier than if the underlying skeletal support was normal ( Fig. 21.11.4 ). Even a reluctant adolescent will accept surgery when shown the image of the retrognathic facial rejuvenation patient who presents with soft-tissue laxity due to suboptimal skeletal support.

A second advance is in the perioperative process for orthognathic surgery. The two most significant improvements for patients are clear aligner orthodontic therapy and CASS. Clear aligner orthodontic treatment such as Invisalign has eliminated the need for the patient to wear visible metallic or ceramic orthodontic brackets. The patients wear the trays up to the day of surgery and then a screw-anchored arch bar is placed intra-operatively for intra-operative maxillomandibular fixation and postoperative elastics. The arch bars can be removed in the office or the surgery center after postoperative elastic therapy is complete. The majority of the author’s patients undergo perioperative orthodontic therapy with clear aligners.

CASS also contributes to the precision and efficiency of the perioperative process. The diagnosis of the skeletal deformity is viewed in three planes to evaluate symmetry, overlap of mandibular segments, and the occlusal plane. The planned movements are measured to the hundredth of a millimeter, and occlusal interferences are noted on a heat map to show the surgeon the location and degree of any necessary occlusal equilibration. Surgical splints are accurate and can be customized to the surgeon’s specifications. If desired, custom plates can be designed. The author has incorporated the routine use of custom maxillary plates to reduce operative time and increase the accuracy of maxillary position. The author has noted that the incorporation of these advances has led to much faster recovery periods than those of his patients prior to CASS.

A final note is that there is a growing population of patients seeking treatment: those with a retrognathic jaw with a normal chin–lip relationship. The patients express dissatisfaction with facial appearance and typically present for chin augmentation, submental liposuction, or a necklift. These patients have little submental fat, minimal tissue laxity, and a normal chin–lip relationship. The examination reveals a short neck to pogonion distance and a lower lip retrusion compared to upper lip ( Fig. 21.11.5 ). Given that these patients have had orthodontics in youth, there is no excess dental overjet to allow mandibular advancement. The only treatment to achieve their aesthetic goal is to reverse the previous dental compensation to recreate the overjet necessary to allow mandibular advancement. When the patient is shown a prediction of mandibular advancement, they frequently respond that the prediction image is the aesthetic result they were seeking but did not know how to articulate the problem. Prior to clear aligner therapy for orthodontic treatment, very few patients selected this approach. Since the introduction of clear aligner orthodontics, the bar has been lowered and many patients agree to undergo reversal of their previous orthodontic treatment to restore a normal jaw alignment through orthognathic surgery.

Cleft lip and palate

Patients with cleft lip/palate commonly present with midface hypoplasia. The maxilla is commonly deficient in the anteroposterior, transverse, and vertical dimensions and is accompanied by dental arch constriction ( Fig. 21.11.6 ). It is unclear whether the cause of maxillary hypoplasia is intrinsic to the embryologic pathogenesis of the cleft, extrinsic from the trauma and scar formation and contracture from multiple surgeries at a young age, or due to a combination of both.

The presentation of maxillary hypoplasia varies with cleft type. Patients with a unilateral cleft lip and palate have a hypoplastic maxillary lesser segment that is displaced superiorly, posteriorly, and medially, and the maxillary midline is shifted toward the cleft side. Patients with a bilateral cleft lip/­palate have a narrow maxilla in the transverse direction posteriorly, which can result in a bilateral posterior crossbite. The premaxilla segment is more often anteriorly protruded than posteriorly retruded and can be either superiorly or inferiorly displaced. Patients with cleft lip and palate generally have normal mandibular anatomy in all three dimensions.

The reported incidence of orthognathic surgery in patients with cleft lip and palate varies significantly. A review of 177 nonsyndromic patients with cleft lip and palate found that 20.9% of patients underwent a Le Fort I osteotomy. No patients with a cleft lip alone (0/69) or cleft palate alone (0/35) required orthognathic surgery in this study. Some 47.4% (37/78) of patients with cleft lip and palate required a Le Fort I osteotomy with higher rates in patients with complete clefts and bilateral clefts compared to those with incomplete and unilateral clefts. Similarly, a review of 211 patients with complete unilateral cleft lip and palate and 129 patients with complete bilateral cleft lip and palate demonstrated that the rate of orthognathic surgery was significantly higher in patients with bilateral cleft lip and palate: 65.1% (84/129) versus 48.3% (102/211). A review of 189 nonsyndromic patients with isolated cleft palate found that 13.2% (25/189) required orthognathic surgery. A systematic review reported that the overall incidence of orthognathic surgery was 38.1% for patients with bilateral cleft lip and palate, 30.2% for unilateral cleft lip and palate, 4.4% for isolated cleft palate, and 1.8% for isolated cleft lip. There is inconsistent evidence if timing of lip/palate repair, technique of repair, or whether or not the repair is staged impacts the need for later orthognathic surgery. Some centers have advocated early use of cephalometrics and more advanced facial imaging to predict which patients may need orthognathic surgery later in life to better counsel parents and coordinate with dentists.

Craniosynostosis

Patients with craniosynostosis have an increased risk of dental malocclusion. Premature fusion of the cranial sutures may lead to premature fusion of the facial sutures, restricting mid and lower face growth. Genetic mutations, such as those in FGF, seen in syndromic craniosynostosis can also predispose to premature facial suture fusion. Patients with cranial base restriction most commonly also present with class III malocclusion because of maxillary hypoplasia. Syndromic craniosynostosis can present with varied but often certain common patterns of mid and lower face restriction. Patients with Crouzon syndrome present with midface hypoplasia involving the orbits, zygoma, nose, and maxilla. Patients with Apert syndrome commonly present with mandibular protrusion with class III malocclusion, an anterior open bite, maxillary hypoplasia, and pronounced and overcrowded teeth. Patients with Treacher Collins syndrome present with both maxillary and mandibular hypoplasia in the anteroposterior dimension, but the mandibular hypoplasia is particularly severe, characterized by a short ramus and an antegonial notch with pronounced curvature and posterior rotation. Patients with Muenke syndrome present with midfacial hypoplasia with associated dental crowding.

Hemifacial microsomia

Hemifacial or craniofacial microsomia (HFM) is a hypoplastic disorder of the first and second branchial arches on one side of the face leading to soft-tissue and skeletal facial asymmetry. The presentation of HFM varies greatly but can result in restricted growth of the maxilla and mandible in the sagittal, transverse, and vertical dimensions as well as hypoplasia of the midface and lower face musculature. The mandible is generally more affected than the maxilla and can present with an absent condyle and significantly shortened ramus. Patients may present with facial imbalance asymmetric class II or III malocclusion with possible open bite, chin deviation, and an occlusal cant. The skeletal and soft-tissue imbalances, in addition to the aesthetic deformity, can affect eating and speech.

Condylar hyperplasia

Condylar hyperplasia presents as asymmetric excessive growth of one of the mandibular condyles and presents with painless facial skeletal asymmetry resulting in an occlusal cant, crossbite, open bite, and other occlusal abnormalities. The etiology of condylar hyperplasia is unknown but most commonly presents in adolescence and early adulthood and affects women more commonly than men. Two growth patterns have been described: type 1 characterized by excessive horizontal growth, and type 2 characterized by excessive vertical growth, with type 1 more common than type 2. Various morphologies of the condylar head and neck have been described including normal, enlarged, elongated, and deformed. The different morphologies of condylar hyperplasia translate to differing types of facial asymmetry. These have been categorized into vertical asymmetry resulting in no occlusal alteration but a posterior open bite on the affected side, transverse asymmetry resulting in a crossbite and suboptimal intercuspation and deviation of the dental apical midlines, chin deviation, and combinations of the three. Technetium scans can assist in the diagnosis.

For minor cases of condylar hyperplasia, compensatory orthodontics to align the dental midlines or close a small open bite is preferred. In more severe cases, the best treatment approach is to perform a high condylectomy, generally 4–5 mm from the upper pole of the condyle, or low or proportional condylectomy, followed by additional orthognathic surgery to rotate or move the maxilla, mandible, and/or chin to achieve symmetric skeletal and soft-tissue balance. A systematic review of 11 studies and 289 patients concluded that the optimal timing for intervention is late adolescence or early adulthood, right after skeletal maturity to allow the disease process to burn out and to prevent compensatory soft-tissue changes from longstanding condylar hyperplasia. Performing orthognathic surgery alone to correct asymmetries resulted in high rates of relapse, whereas combining orthognathic surgery with condylectomy produced much lower relapse rates. Furthermore, a minimum of 3 mm of the condyle should be taken off. There are numerous surgical techniques including removing the entire condylar head, removing a segment of the condylar neck, and removing the head to recontour it and then replate it in situ . Most patients undergoing orthognathic surgery to correct for aesthetic facial asymmetries were pleased. There is some evidence that a proportional condylectomy, which better removes the hyperactive growth center and can better level the occlusal plane relative to the contralateral normal side, has lower rates of revision surgery compared to high condylectomy.

Congenital myopathies and congenital muscular dystrophies

There are numerous types of congenital myopathies and congenital muscular dystrophies, and while all are different, they can all present with malocclusion, difficulty with mastication, and aesthetic deformities. The mid and lower face skeletal deformities that patients present with vary significantly but are generally secondary to weakened and imbalanced muscular forces that lead to secondary bony changes. Common skeletal abnormalities in this patient population include a transversely constricted but high-arched palate, vertically elongated mandibular ramus, dental crowding, and apertognathia. When treating these patients, it is important to recognize the high rates of osteopenia and osteoporosis which may make achieving rigid fixation more challenging. The skeletal abnormalities can be corrected with the same workhorse orthognathic techniques: Le Fort I osteotomy, maxillary expansion, mandibular bilateral sagittal splint osteotomy, and genioplasty. Because patients with congenital myopathies or congenital muscular dystrophies often have multisystemic manifestations, it is important to have a preoperative consultation with anesthesiology.

History and physical examination

It is important to obtain a thorough medical, dental, and surgical history from every patient. Systemic diseases such as juvenile rheumatoid arthritis, diabetes, and scleroderma can affect treatment planning. Multiple past cleft and craniofacial surgeries increase the scar burden and may make maxillary advancement surgery difficult. With jaw asymmetries, a history of hyperplasia or hypoplasia from syndromic, traumatic, postsurgical, or neoplastic etiologies affects treatment considerations. Each patient should be questioned regarding symptoms of temporomandibular joint disease or myofascial pain syndrome. Finally, a history of snoring or obstructive sleep apnea (OSA) is important to note. If there is any question regarding OSA, a formal sleep study and evaluation is obtained prior to developing a treatment plan.

Orthognathic surgery is one of the most powerful procedures to alter facial form. Although most patients present for correction of occlusion, orthognathic surgery is an opportunity for the patient and the surgeon to address other concerns of facial appearance. Once the bones are mobile, they can be placed in any position with minimal differences in invasiveness or recovery. Any concerns of symmetry, soft-tissue laxity, facial shape or proportion should be addressed and incorporated into the treatment plan as indicated.

Motivation and realistic expectations are important for an optimal outcome. It is likewise important for patients to have a clear understanding of the procedure, recovery, and anticipated result. In younger patients, a family discussion in nontechnical terms helps to alleviate preoperative anxiety. Orthognathic surgery is a major undertaking, and the patient and family must be appropriately motivated to undergo necessary preoperative and postoperative orthodontic treatment in addition to the surgery itself.