Stability and Relapse in Orthognathic Surgery

Neeraj Panchal, DDS, MD, MA

Christine Ellis, DDS, MSD

Paul Tiwana, DDS, MD, MS, FACS

less complex, also demands rigorous INTRODUCTION precision from start to finish. From the The long-term success of orthognathic first consultation, the surgeon must begin reconstructive surgery is dependent upon to factor the aesthetic, functional, and long-term stability of the surgical stability related demands of the anticipated correction. Stability is defined as the surgical correction. Failure to do so risks maintenance of the skeleton and the introduction of errors that ultimately associated dental structures in the increase the likelihood of surgical relapse. intended position over time. Failure to Pre-operative planning/execution errors, achieve stability, also called surgical intra-operative errors at the time of relapse, can result in a compromised final surgery, or post-operative wound healing result. There are multiple reasons surgical errors all contribute to early surgical relapse occurs. These reasons can be relapse. divided into both short and long-term causative factors. Short-term relapse occurs in the immediate post-operative period, and is most often due to surgical planning/model surgery errors, intra- PRE-OPERATIVE ERRORS operative surgical errors, or wound healing problems. Long-term relapse, on the other CONTRIBUTING TO EARLY hand, is influenced by three major factors; RELAPSE growth, physiologic adaptation, and post- Success of the surgical plan depends on operative changes due to orthodontic or sound knowledge of the physiology and surgical relapse. Although equally critical, function of the jaws, including the this article will not cover the role that limitations of any proposed surgical orthodontic preparation, finishing, and movements. Surgical planning that maintenance of the orthognathic patient by disregard the limitations, in both direction the orthodontist play in contributing to and magnitude of skeletal movement, post-operative stability. increases the risk of early relapse. When anterior-posterior movement of any EARLY RELAPSE one jaw exceeds one centimeter, the Successful double-jaw orthognathic surgeon should consider an alternative surgery requires methodical surgical surgical technique like distraction accuracy, making it one of the most osteogenesis or concomitant bone grafting challenging surgical procedures provided in addition to or instead of a standard Le within the scope of a modern maxillofacial Fort or BSSO to improve stability. surgery practice. Single jaw surgery, while Treatment planning surgical movements under anesthesia and in the supine that result in excessive counter-clockwise position. rotation of the facial skeleton should be Another example of a records collection avoided. Excessive counter-clockwise error is an inaccurate face bow transfer. rotation contributes to early relapse and Care must be taken to ensure the usually manifests as a newly developed acquisition of an accurate face bow anterior open bite on clinical examination. transfer, otherwise, the model surgery and To limit excessive counter-clockwise splint fabrication will be predicated on an rotation, the surgeon should employ erroneous dental and skeletal relationship. techniques such as grafting to the Other examples of records collection errors posterior maxilla, changing the mandibular include alginate model inaccuracies or ramus osteotomy to lie outside the warped dental stone models. muscular sling (extra-oral inverted-L osteotomy), or incorporating a TMJ related Presently, surgical work ups assisted by procedure such as total alloplastic joint computer-based planning are becoming replacement. Patients diagnosed with more common. To prevent the introduction short posterior face height are at particular of treatment planning errors, digital risk for this type of relapse. Even with planning with error-free models, an technique modification, this sub-group of accurate centric bite and ideal transfer of patients should be approached with natural head position must occur. caution and deliberate planning. Irrespective of whether the articulator or computer is used, the surgeon must accurately transfer the patient’s records to eliminate the introduction of records EXECUTION ERRORS collection errors that may affect post- Accurate patient records are critical to surgical stability. surgical planning, therefore, obtaining surgical records and model surgery planning must be executed with attention to detail. Errors made while obtaining surgical records or during model surgery EARLY RELAPSE DUE TO planning will translate into an error in the INTRA-OPERATIVE FACTORS patient’s final outcome. Consequently, Also of importance to early surgical relapse errors of records collection or model are factors secondary to intra-operative surgery planning may ultimately become errors that prevent passive and repeatable factors related to post-operative relapse, occlusion in the surgical splint. One such especially in complex two-jaw or bi- factor is failure to seat the patient’s maxillary surgery. condyles into the condylar fossae during An inaccurate centric bite is one example surgery. Whether one- or two-jaw of a records collection error. The centric surgery, the mandibular condyles must be bite must be taken with care and seated passively in the most posterior- confirmed several times to ensure that superior position of the fossa with good both of the patient’s condyles are seated in inter-maxillary fixation during stabilization their respective condylar fossa. If the of the surgical correction with plates and centric bite is taken with the condyles not screws. Failure to do so will result in a seated, an immediate change in the post-operative occlusal relationship that is planned occlusion will occur intra- different from the one that was intended. operatively as the condyle(s) return to the Dislocation of the mandibular condyles, true centric position while the patient is may occur during Le Fort I osteotomy if there is inadequate removal or relief of posterior interferences. This leads to growth is the usual culprit in these dislocation of the mandibular condyles as situations. Proffit, Turvey, and Phillips the maxillomandibular complex is rotated have determined that growth affects post- superiorly to the correct vertical position of operative stability by asymmetrically the midface. Similarly, during mandibular changing the untreated and treated areas surgery, the proximal (condylar) segment of the facial skeleton.1 The possibility of must be seated adequately to ensure the continued facial growth must be appropriate surgical correction. Some considered in both the pediatric and adult surgeons will employ clamps or plates that populations. Most, but not all patients will run from the maxilla to the proximal complete the majority of their craniofacial segment to limit this possibility. However, growth by the late teenage years, with the in the authors opinion, this is usually mandible finishing last in both genders. It unnecessary. If the occlusion obtained is important to note that although immediately after rigid fixation is not craniofacial skeletal changes occur passive and repeatable in the intermediate throughout adulthood, most of these (maxillary) or final (mandibular) inter- changes are normal, symmetric physiologic occlusal splints, a rigidly fixed error has changes, and do not contribute to occurred. The surgeon must correct this observable post-operative relapse. In error at the time of surgery; post- 1927, Milo Hellman termed “morphological operative elastics will do little to correct differentiation” to describe these normal this error post-operatively. changes to the facial skeleton that occur throughout a patient’s lifetime.2 Pathologic Finally, unintended intra-operative conditions of the facial skeleton like complications also may result in early unilateral condylar hyperplasia, on the relapse. One example is a “bad” split of other hand, differ from normal physiologic the mandible during sagittal splitting. If changes and can contribute to post- inadvertent fractures of the skeleton occur surgical relapse. Patients suspected of during the osteotomy, the surgeon must experiencing pathologic, hyperplastic first identify the complication and then use growth should ideally not undergo surgical an appropriate and stable surgical correction until after cessation of the technique to correct the mandible. If the growth has been verified. However a rigid fixation employed either to correct an disadvantage of this philosophy is that as inadvertent fracture or during routine unremitting unilateral pathologic growth fixation is overcome by the function and continues, compensatory changes occur in physiologic demands of the jaws during other unaffected bones of the skeleton and convalescence, infection, mal-union, or therefore increase the magnitude of non-union of the affected osteotomy site surgical correction when finally performed. may result. This problem is classified as a This obviously may also contribute to wound healing related factor contributing instability over the long-term. to early relapse. Clinically, these issues Consideration can be given by the surgeon will be readily visible as acute changes of to perform condylectomy or condylar the occlusal relationship and will require shave as a first stage procedure where further surgery to correct. appropriate to limit this problem. Final surgical correction prior to cessation of pathologic or hyperplastic growth greatly increases the risk of late post-operative LATE RELAPSE relapse. One of the most common causes of late post-operative instability is continued growth of the patient following surgical correction. Continued or late mandibular FUNCTIONAL MATRIX OTHER FACTORS AFFECTING HYPOTHESIS LONG-TERM STABILITY Over a half century ago, Melvin Moss For a period of time following surgery, postulated the Functional Matrix neuromuscular adaptation to skeletal Hypothesis.3 He presented a theory of modification occurs. For example, when growth which credited primarily epigenetic the position of the maxilla is changed, the rather than genomic factors, as the postural position of the mandible adapts to primary contributor to the final form of the the new maxillary position. The skeleton. Moss determined that “bones do proprioceptors located in the periodontal not grow, they are grown,” as the skeleton ligament of maxillary posterior teeth, in responds to the “functional matrix” coordination with the central nervous surrounding them. Applying the functional system, control the posture of the matrix hypothesis, function and growth are mandible to an independently determined primarily responsible for determining the normal position. As a result, the post- form of bones like the angle of the operative inter-occlusal space remains mandible and the shape of the coronoid essentially unchanged from the pre- process. Orthognathic surgery changes operative distance,1 the functional matrix as muscular and soft Similarly, the functional position of the tissue tension is changed following surgical tongue changes following any direction of movements. Consequently, an mandible or maxilla repositioning. Post- understanding of Melvin Moss’ functional operatively, the tongue’s position relative matrix hypothesis is essential, particularly to the anterior teeth duplicates the exact to aid the surgeon in determining which pre-surgical contact with the palate and surgical movements will contribute to or teeth post-operatively. Surgical changes prevent relapse. that decrease the size of the oral cavity, Surgical movements that increase the such as inferior repositioning of the maxilla stretch of a muscle or soft tissue change and mandibular setback can be affected by the functional matrix by introducing the function of the tongue. As the oral tension. Surgical movements that cavity decreases in size, pressure from minimize soft tissue or muscle tension tongue function on the structures in direct improve long-term post-operative stability. contact with the tongue will increase. The In contrast, surgical movements that result may negatively impact post- increase the tension applied to the bone by operative stability. Surgical movements soft tissue or muscle function also increase that increase the size of the oral cavity like the chances of long-term post-operative superior repositioning of the maxilla, relapse. The functional matrix hypothesis advancement of maxilla in anterior- explains the well-documented high risk of posterior dimension, and mandibular long-term relapse following surgical advancement, result in less pressure from maxillary expansion as the maxilla tongue function on the accompanying response to increased tension of the structures and consequently contribute to palatal soft tissue in the transverse greater post-operative stability. Actual dimension. In summary, the surgeon must tongue position within the orofacial take care to ensure that changes to the complex can change in response to functional matrix are factored into the surgical movements as well. Following a surgical plan to minimize the effect of mandibular set back, the tongue and floor these changes on the long-term stability of of mouth musculature potentially increase the case. functional pressure against the anterior dentition. Over time, as the tongue repositions downward along with the hyoid bone and adapts to the new oral cavity Newer methods of fixation with resorbable size, the impact of tongue function on materials have demonstrated similar post-operative relapse is minimized. The favorable outcomes in terms of stability adaptation of the temporomandibular joint and should be considered affective options (TMJ) occurs in response to changes as well.8 affecting condylar orientation, position, or arc of rotation around condylar axis following orthognathic surgery. Most patients respond to these changes with minimal difficulty, however the current EVIDENCE literature regarding treatment and Until recently, the evidence of post- management of the TMJ is controversial surgical stability has been based on two- regarding the effect of orthognathic dimensional lateral cephalogram analysis. surgery on stability. Clinical studies have The introduction of three-dimensional demonstrated a reduction in pain and digital imaging promises the opportunity dysfunction following mandibular ramus for more detailed data collection and a osteotomies.4 However, some authors also deeper understanding of craniofacial have demonstrated condylar changes relationships. As three-dimensional following mandibular ramus osteotomies. craniofacial analyses are developed, Consequently, the recommendation of changes in the craniofacial complex will be concomitant TMJ and orthognathic surgery better understood. Relapse in multiple may be elected to remove the risk of dimensions, as opposed to only those relapse or other problems associated with evident on a cephalometric x-ray, will post-surgical condylar changes.5,6 certainly aid the surgeon in refining surgical techniques in the future. Finally, patients presenting with Progressive Condylar Resorption (PCR) Much of the scientific data currently represent a unique and small group of available on the stability of orthognathic patients with long term post-surgical surgery has come from the analysis of relapse. PCR is associated with several patient records in the Dentofacial factors including female sex selection, pre- Deformities Program at the University of existing TMJ disease, patients with a high North Carolina. The lead investigators, mandibular plane angle, and patients William R. Proffit, Timothy A. Turvey and requiring large magnitude mandibular Ceib Phillips, have evaluated the stability advancement.7 Although no specific of orthognathic surgery in the same group etiology has been positively identified, PCR of patients for over four decades. A visual has been associated with both hormonal understanding of the implications for long- factors and avascular necrosis of the term stability in orthognathic surgery is involved condyle. gained by reviewing Figure 1, which summarizes the potential for relapse based It is important to recognize what role the on common patterns of dento-facial type of skeletal fixation, either wire or rigid deformity and the associated directional fixation, plays in the stability of movements. orthognathic surgery. In the modern era of orthognathic surgery, titanium based rigid internal fixation has become the standard of care at most institutions and has been found to aid post-surgical stability in most cases. While wire fixation is still effective and utilized for specific scenarios, fixation that compromises post- operative stability is not recommended. skeletal changes that may occur resulting in minimal clinically noticeable occlusal changes.10,11

CORRECTION OF VERTICAL MAXILLARY DEFICIENCY Vertical maxillary deficiency can be corrected with a Le Fort I osteotomy with inferior repositioning, however with far less predictability than surgical correction of vertical maxillary excess. Achieving post- operative stability following a LeFort I inferior repositioning is difficult. There is Figure 1: Hierarchy of Stability. a strong tendency for the maxilla to return to the original superior position due to the CORRECTION OF VERTICAL significant upward occlusal forces applied MAXILLARY EXCESS by the mandibular teeth during function. Studies have found that up to 50% of The Le Fort I osteotomy came into patients experience greater than two common use in the late 1960s. For millimeters of post-operative change, and patients seeking correction of vertical up to 20% experience greater than four maxillary excess, the Le Fort I osteotomy millimeters of change following surgical allows the maxilla to be superiorly inferior repositioning of the maxilla. repositioned (vertically impacted). After Furthermore, post-operative stability is superior repositioning of the maxilla, the highly dependent upon the type of fixation mandible autorotates to maintain dental employed. Almost all vertical change is occlusion. Despite early concerns that the lost with wire fixation. Even with rigid maxilla would relapse back downward, fixation, there is a strong tendency for superior repositioning of the maxilla has significant post-operative relapse. been found to be one of the most stable Although surgical correction of vertical surgical movements available, regardless maxillary deficiency is inherently far less of the type of fixation used. A better than stable than other surgical procedures, 90% chance of excellent post-operative three approaches have been proposed to skeletal stability following maxillary improve stability: (1) placement of heavy superior repositioning has been fixation plates from the zygomatic body to demonstrated. maxillary posterior segment; (2) For patients in which wire fixation is used, interposition of a synthetic hydroxyapatite a “telescoping effect can result in a graft to provide mechanical rigidity; and minimal continued superior movement that (3) simultaneous ramus osteotomy to is on average only a one millimeter decrease occlusal forces.12 Two additional difference from the stability achieved with techniques have also been employed by rigid fixation in the immediate post- osteotomy modification. During Le Fort I surgical period.”9 Long-term studies osteotomy if the buttress osteotomy is examining patients over five years show placed at a higher level than the pyriform that only about one-third of all patients rim, as the maxilla is advanced it will be undergoing maxillary superior positioned inferiorly. This is described as repositioning experience a continuation of “ramping”. Another technique is to a downward movement of the maxilla. complete a “step” osteotomy in the region Fortunately in these cases, eruption of the of the pyriform rim that accomplishes the incisors appear to compensate for the same goal. It must be mentioned that irrespective of the technique employed, Studies have found good long term post- stability of the correction is questionable operative stability of the BSSO in cases of over the long-term as a result of the mandibular deficiency, demonstrating a change in facial height. better than 90% chance of less than 2 mm of change one year after surgical correction, regardless of the type of fixation used.15 Other post-operative CORRECTION OF MAXILLARY changes have been observed. The majority of patients experience greater ANTERIOR-POSTERIOR than 2 mm of remodeling of the gonion in an upward direction during the first year DEFICIENCY after the BSSO advancement. Also, about The Le Fort I osteotomy with advancement 20% of patients experience condylar of the maxilla can predictably correct a remodeling 1 to 5 years after surgery, maxillary anterior-posterior (Class III) resulting in decreased mandibular length deficiency. In fact, research has found and ramus height. These patients also that patients have an 80% chance of experience long term post-operative dental immediate post-operative stability, and adaptation. Lower incisor proclination only a 20% chance of two to four occurs in about 50% of the cases, with the millimeters of relapse one year following other half experiencing an increase in surgery. If a larger magnitude overjet.1 (Figure 2) advancement is planned (greater than 5 mm), heavier plates and screws with simultaneous autogenous bone grafting can aid the post-operative stability. Distraction osteogenesis, with either internal or externally placed distractors, may be considered for patients requiring maxillary advancements of greater than 10 mm. Patients with midface deficiency resulting from cleft lip and palate and other craniofacial anomalies present a unique challenge to achieving long-term Figure 2A: Preoperative Occlusion. Demonstration of post-operative stability. For these patients, Relapse Due To Condylar Resorption One Year After even small magnitude surgical movements Bilateral Sagittal Split Osteotomy To Correct should be reinforced with the addition of Apertognathia and Mandibular Deficiency. bone grafts.

CORRECTION OF MANDIBULAR DEFICIENCY Since the late 1970s, the most common mandibular surgery has been the Bilateral Sagittal Split Osteotomy (BSSO), which allows the surgeon to move the mandible in either a more anterior or more posterior position. Trauner and Obwegeser first described the BSSO, which has undergone several subsequent modifications.13,14

Figure 2B: Preoperative Frontal Repose. Figure 2D: Preoperative Cephalometric Radiograph.

Figure 2E: 6-month Postoperative Occlusion.

Figure 2C: Preoperative Frontal Smile.

Figure 2F: 6-month Postoperative Frontal Repose.

Figure 2H: 6-month Postoperative Cephalometric Radiograph.

Figure 2I: 12-month Postoperative Occlusion.

Figure 2G: 6-month Postoperative Frontal Smile.

Figure 2K: 12-month Postoperative Frontal Smile. Figure 2J: 12-month Postoperative Frontal Repose.

Figure 2L: 12-month Postoperative Cephalometric Radiograph. significant. For patients stabilized with CORRECTION OF MANDIBULAR wire fixation, approximately 20% of ANTERIOR-POSTERIOR EXCESS patients experience a slight upward and rotational movement of the maxilla, while Mandibular setback can be accomplished about 50% experience backward by either an Intraoral Vertical Ramus mandibular movement, six weeks after Osteotomy (IVRO) or BSSO with surgery. Furthermore, no return toward mandibular setback. Post-operative the original surgical position can be stability, while clinically acceptable in both expected to occur, with nearly one-third of cases, varies depending on which surgical these patients experiencing continuing technique is used. One year following relapse. One year after surgery, only 60% IVRO, there is a chance of either forward of patients stabilized with wire fixation or backward movement of the mandible. have an excellent clinical result. In With a BSSO there is no post-surgical contrast, patients stabilized with rigid backward movement, but forward relapse fixation demonstrate greater stability in is more frequent. both the maxilla and mandible six weeks Regardless of surgical technique, up to after surgery. One year after surgery, 50% of patients experience more than two 90% of patients stabilized with rigid millimeters of post-operative change fixation are judged to have excellent post- following a mandibular setback, with 20% surgical results. Consequently, rigid of these patients experiencing change of fixation provides significantly more stability more than four millimeters. For patients for the simultaneous correction of vertical experiencing significant post-surgical maxillary excess and mandibular relapse following a mandibular setback, deficiency. the cause may be the result of a technical problem. During surgery, the position of the ramus (proximal segment with condyle) can inadvertently be pushed SIMULTANEOUS CORRECTION posteriorly into the condylar fossa. Following surgery, the ramus will return OF MAXILLARY ANTERIOR- back to its original orientation. POSTERIOR DEFICIENCY AND MANDIBULAR EXCESS SIMULTANEOUS CORRECTION Some severe skeletal Class III dentofacial deformities can be corrected with a OF VERTICAL MAXILLARY combined maxillary Le Fort I osteotomy with advancement, and mandibular EXCESS AND MANDIBULAR intraoral vertical ramus osteotomy or DEFICIENCY bilateral sagittal split osteotomy. The data on stability for this particular surgical Patients often present with complex correction is limited, however it appears to dentofacial deformities that require double be similar to the findings of post-operative jaw surgery to correct. A Le Fort I stability seen in each jaw after maxillary maxillary osteotomy with superior advancement or mandibular setback alone. repositioning and mandibular advancement Of particular interest, the type of fixation with bilateral sagittal split osteotomy used once again significantly affects post- constitute the typical procedures used to operative stability. Ninety percent of correct both vertical maxillary excess and patients with rigid fixation following double mandibular deficiency. For this particular jaw correction of a Class III dentofacial type of surgery, the influence of the type deformity were judged to have an of fixation used for long-term stability is excellent clinical result compared to only 60% of patients with wire fixation one year following surgery. (Figure 3)

Figure 3A: Preoperative Cephalometric Radiograph. Maintenance of Stability One Year After LeFort 1 Osteotomy with Maxillary Superior Repositioning and Advancement, Bilateral Sagittal Split Ramus Osteotomy with Mandibular Advancement and Genioplasty.

Figure 3C: Preoperative Frontal Smile.

Figure 3D: Preoperative Lateral Repose. Figure 3B: Preoperative Frontal Repose.

Figure 3E: Preoperative Occlusion.

Figure 3G: 12-month Postoperative Frontal Repose.

Figure 3F: 12-month Postoperative Cephalometric Radiograph..

Figure 3H: 12-month Postoperative Frontal Smile. CORRECTION OF MAXILLARY TRANSVERSE DEFICIENCY Surgical transverse widening of the maxilla can be accomplished with either a segmental Le Fort I osteotomy or Surgically Assisted Rapid Palatal Expansion (SARPE). The selection of surgical technique depends at least in part on the presenting dentofacial deformity of the patient. If only a transverse deficiency exists, then a SARPE is a reasonable alternative. If other accompanying maxillary deformities exist, for example, maxillary constriction and anterior open bite, then a segmental Le Fort I may be the best surgical option. Surgeon and/or orthodontist preference will also play a role in the selection of transverse surgical technique. Vanarssdall has documented a preference of SARPE over segmental Le Fort I on the basis of an improved periodontium.16 Post-operative stability must be considered in both cases as surgical maxillary expansion is the least stable of all orthognathic surgical procedures. As discussed earlier in this chapter, widening Figure 3I: 12-month Postoperative Lateral Repose. the maxilla causes a stretching of the palatal mucosa. As predicted by the functional matrix theory, the tension of the stretched palatal tissue applies a constricting force to the recently operated maxilla. The result is relapse of surgical expansion. In fact, studies have found that approximately 50% of the expansion in the 2nd molar area resulting from Le Fort I segmental surgery is lost within one year of surgery. Stability data on SARPE is similar to that of segmental Le Fort I osteotomy. It has been reported that about 60% of patients undergoing SARPE have dental relapse of greater than two millimeters of the posterior teeth with lingual movement of the teeth.17 Figure 3J: 12-month Postoperative Frontal Occlusion. Techniques to control transverse relapse

following surgery include over-correction of the transverse deficiency, immediate post- surgical placement of a heavy orthodontic palatal bar and/or a palate covering retainer. Many authors recommend that when the transverse expansion of the (titanium or resorbable) has greatly maxilla requires more than 6-7 mm of increased the stability of certain movement, a staged approach consisting orthognathic procedures like double jaw of first stage SARPE followed by Le Fort I surgery. adds to the overall long-term stability of the correction.18,19 With different institutions advocating REFERENCES different techniques to manage transverse deficiency of the maxilla, the literature is 1. 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