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S E A S O NE D S E A S O NE D Practitioner’s Practitioner’s Corner Corner Surgical-Orthodontic Cases Part 2: Class III Treatment Dr. Terry McDonald Interviews Dr. Richard McLaughlin See Part I of this interview (Winter 2009 PCSO Bulletin), where Dr. Terry McDonald interviewed Dr. Richard McLaughlin about Surgical-Orthodontic Cases — Class II Treatment. Dr. McLaughlin Dr. McDonald CURRICULUM VITAE: RICHARD P. McLAUGHLIN, DDS D R. RICHARD MCLAUGHLIN completed his orthodontic training at the University of Southern California in 1976. Since then, he has been in the full time practice of orthodontics in San Diego, CA. He has lectured extensively in the United States as well as internationally. He is a member of the Pacific Coast Society of Orthodontists, the American Association of Orthodontists, and a Diplomate of the American Board of Orthodontics. He is the Component Director of the Southern California Component of the Edward H. Angle Society. He is the 2009 American Board of Orthodontics recipient of the Dale Wade Award. In addition, Dr. McLaughlin is a clinical professor at the University of Southern California, Department of Orthodontics, in Los Angeles, California, and an associate professor at St. Louis University, Department of Orthodontics. Terry McDonald: What are you general comments on Class III surgical cases? Richard McLaughlin: Thinking among orthodontists and oral surgeons has somewhat changed over the years concerning Class III surgical treatment. In the early days of orthognathic surgery, most severe Class III cases were treated with mandibular setbacks. With time, and the awareness that many Class III cases showed a component of midface deficiency, maxillary surgical techniques were developed to address the mid face concerns. With this advancement, Class III cases could be treated with either lower jaw surgery or upper jaw surgery, or a combination of both. As knowledge of the causes of sleep apnea has increased along with the awareness that sleep apnea patients are being significantly helped by combined orthodontic-surgical procedures, the pendulum for Class III surgery has swung more toward forward and downward placement of the maxilla with resultant backward mandibular rotation, and minimal need for mandibular setback. TM: With this as a background, please give us your ideas for Class III surgical treatment that can be accomplished with mandibular surgery only. RM: In terms of diagnosis and treatment planning, many of the principles described in Part I of this discussion (Class II surgical treatment) are applicable to Class III treatment as well. In order for Class III cases to be treated with mandibular surgery only, the maxilla must be in an ideal or at least an acceptable position in three planes of space. Transversely, the maxilla must be wide enough posteriorly Transversely to accommodate the retracted mandibular position. A high percentage of Class III cases are narrow in the maxilla relative to the corrected mandibular position. As with most cases, the Curve of Wilson should be level in the upper arch, which is very difficult to achieve in the maxilla in Class III cases. Also, cants in the maxilla must be minimal, or at least acceptable to the patient. Horizontally, the airway should be evaluated to assure that carrying out a mandibular setback will continue to assure an SPRING 2010 • PCSO BULLETIN 11 S E A S O NE D Practitioner’s Corner adequate airway. The upper incisors must be located in an acceptable position, or be movable to that position orthodontically. Correct incisor torque position must be achievable orthodontically (110o to 115o to the palatal plane, and 55o to 59o to the maxillary occlusal plane). Ideally, with normal lip thickness, the upper central incisors should be positioned approximately 9mm behind the true vertical line. (Editor’s note: see part one of this interview regarding the true vertical line.) With thin lips, the incisors can be positioned slightly more anteriorly, and with thick lips, slightly more posteriorly. Crowding must be managed either with interproximal reduction or extractions to accommodate upper incisor horizontal position. Distal lateral spaces may be needed along with lower incisor stripping to assure proper overbite and overjet in the corrected Class I position. Vertically, the maxillary dentition should be relatively flat. When vertical “steps” are present, surgical leveling is preferred over orthodontic leveling. Vertical incisor exposure should be in the range of 2mm to 5mm. (Class III patients frequently show inadequate vertical development of the maxilla and lack of incisor exposure). In order to avoid post-surgical disappointment, it is critical that modifications from this range be thoroughly discussed with the patient prior to surgery. The maxillary occlusal plane should be close to a normal range (94o to 98o to the true vertical line), as it cannot be adjusted when surgery is confined to the mandible only. When the occlusal plane is very flat or very steep in these cases, the distally positioned mandible may be either too prominent or too retrusive. Chin reductions can be helpful in this regard, but this procedure has its limitations. In summary, for mandibular surgery only to be successful, maxillary tooth and jaw position requirements are significant, and the above three-dimensional considerations should be carefully evaluated. In the mandible, Transversely, the Curve of Wilson should be leveled, usually with buccal uprighting. Horizontally, the incisors should be positioned as close to an ideal position as possible, 90o to 95o to the mandibular plane and 62o to 66o to the mandibular occlusal plane. Frequently the lower incisors are retroclined in Class III cases, and it is a challenge to procline them far enough forward. The shape of the symphisis and lower lip pressure create a resistance to this movement. Crowding should be managed either with interproximal re- 12 duction or extractions to accommodate correct lower incisor position. Vertically, mandibular Curve of Spee leveling should be completed orthodontically prior to surgery. This allows for more accurate positioning of the occlusion by the surgeon, and minimizes the need for a surgical splint. As with Class II cases, when teeth are properly aligned, including Curve of Spee leveling, the occlusion acts as an excellent splint, and very little orthodontic tooth movement is required post-surgically. For general upper and lower tooth alignment in these cases, as with Class II cases, the American Board requirements serve as excellent guidelines for the orthodontist. Concerning mandibular surgical fixation technique, there is great controversy among surgeons concerning fixation screws versus mini-plates. My experience has been that the use of mini-plates allows for more accurate condyle positioning, with fewer post-surgical symptoms, than do fixation screws. TM: What are your indications and requirements for Class III maxillary surgery only? RM: As stated above, this is becoming a far more common surgical procedure than in the past. This is due to the awareness that: 1. when possible, eliminating mandibular setback surgery and treating the Class III patient with maxillary surgery only can contribute to the prevention of that patient developing sleep apnea, and 2. Class III malocclusions are more frequently the result of maxillary deficiency versus mandibular prognatism. So, when surgery is completed in the maxilla only, the mandible must be located in an adequate position in the face, or in a position where it can be rotated clockwise to an acceptable position by forward and downward positioning of the maxilla. This is often a good choice, as frequently the maxilla in Class III patients is short vertically, with inadequate incisor exposure. Care must be taken to reduce or eliminate clenching during the healing process (with anti-clenching medication) so that re-impaction of the maxilla does not occur. Asymmetries in the mandible eliminate the alternative of maxillary surgery only. Finally, in cases where surgery is limited to the maxila only, the steepening of the occlusal plane can be achieved by moving the maxilla down such that the mandible rotates in a clockwise direction. Segmental maxillary surgery may be PCSO BULLETIN • SPRING 2010 SEASONE D Practitioner’s Corner required in these cases because of a vertical “two-step” occlusion, a transverse maxillary discrepancy or both. Segmental maxillary surgery will be discussed below under two-jaw surgery. If maxillary surgical positioning and the resultant mandibular rotation produces a good occlusion and a satisfactory facial result, but does not produce an adequate airway, then two-jaw surgery is indicated. Pre-surgical orthodontic tooth alignment can be carried out in a manner similar to mandibular setback cases, as described above. TM: Please discuss your ideas on two-jaw Class III surgical cases. RM: The limitations and indications for single Class III jaw surgery were described above. When the limitations present themselves, then two-jaw surgery is indicated. Such cases require maximum attention and skill, but they do allow for the most amount of flexibility and, hence, the best possible facial, airway and occlusal results. More specifically, the corrected occlusion can be properly placed between the airway posteriorly and the face anteriorly. This is greatly aided by setting the occlusal plane in an ideal position, which is frequently not possible with single-jaw surgeries. Pre-surgical orthodontic alignment considerations in the mandible were described above in the discussion on mandibular surgical only and apply similarly in two-jaw surgeries. The maxillary surgical portion of the treatment can be completed with a single piece LeForte procedure if there are no vertical or transverse discrepancies in the maxilla. Segmental maxillary surgery is required in cases that have a “two-step” occlusion vertically in the maxilla. The most common area where vertical steps occur is between the lateral incisors and cuspids. Therefore, this is the most common area (about 90% of segmental cases) for sectioning the arch wires pre-surgically. The step may also occur between the cuspids and first bicuspids (about 10% of the time) in which case arch wire sectioning would occur in this location. Very infrequently, other segmental locations may be required. Arch wire segments can be properly shaped by first coordinating the upper and lower arch wires, and then sectioning the upper arch wire in the appropriate locations. This allows the positioned maxillary segments to fit the lower arch properly at the time of sur- SPRING 2010 • PCSO BULLETIN gery. When there is a transverse discrepancy in the maxilla (usually maxillary narrowing), a significant surgical decision is required. Many surgeons are uncomfortable with large segmental expansions (5mm to 10mm) in the maxilla. Their concerns are related to the tendency for transverse relapse to occur. Therefore, some surgeons prefer to do a SARPE procedure prior to orthodontic alignment to correct the maxillary transverse problem, and then a second surgery for vertical and horizontal positioning of the arches after orthodontic alignment. However, a second surgery is not popular with patients. Fortunately, surgeons are improving their techniques in dealing with transverse discrepancies so that all needed maxillary correction can be accomplished with a single surgical procedure with stable results. In particular, rather than single sectioning in the mid-palatal suture area, a cut can be made on each side of the suture. This divides the amount of widening into two areas, thereby increasing the chances for stability. Final surgical splints are also not required in these two-jaw cases if the pre-surgical orthodontic alignment is satisfactory and the upper arch wire segments are connected during surgery using acrylic across the upper surgical sites. This method forms a single stable upper arch because of the formation of a very solid single arch wire. Most surgeons complete upper jaw surgery first in these cases, using the original mandiblar position and an interim surgical splint as a baseline for maxillary positioning. Others complete mandibular surgery first, contending that there are frequently discrepancies between seated positions of the condyles in patients that are awake versus the positions in patients that are anesthetized (no matter how much care is taken). When this discrepancy occurs, the usual result is a mandible that is seated more posteriorly than planned. Thus, the more retrusive anesthetized mandibular reference position and interim splint set the maxilla more posterior than desired. While completing mandibular surgery first requires great accuracy, the argument for this approach is valid and compelling. TM: Thank you, Dr. McLaughlin, for your experienced and valuable comments. 13