Accurate orthognathic surgery predictions for the obstructive sleep apnea patient

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Accurate orthognathic surgery predictions for the obstructive sleep apnea patient

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Dr R. Scott Conley
R. Scott Conley, USA

By R. Scott Conley, USA

Thu. 19. February 2009

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Orthognathic surgery has been performed routinely since the mid- 1970s to correct severe skeletal malocclusion. Since its inception, various forms of prediction have been utilized to attempt to educate the patient regarding potential profile changes. Initially, lateral cephalometric tracings were used to create a visual treatment objective. Later, with the advent of computers and computer imaging, multiple computer programs were developed to assist the process. Now, surgical predictions have become a routine part of the standard of care for offices recommending orthognathic surgery to their patients.

Instead of utilizing surgery as a tool merely for the correction of skeletal malocclusion, it is now being used as one of the more successful treatment modalities in the treatment of severe obstructive sleep apnea (Riley, Powell et al. 2000). Surgery for the obstructive sleep apnea patient typically involves large surgical advancement of both the maxilla and the mandible. With these larger surgical advancements, questions have developed regarding the accuracy of surgical predictions. Are the values that were developed for use with single jaw surgery still valid? Do the previous prediction methods over-estimate or underestimate the potential treatment changes?

Orthognathic surgery history

One of the earliest reported maxillary surgical procedures was performed by Cheever in 1864. The precursor of today’s LeFort I osteotomy was performed to remove a nasopharyngeal carcinoma from the patient. Anesthesia and sterilization techniques were quite nascent at the time. The surgery was a success, the tumor was resected, but the patient died approximately three days later. Around the turn of the 20th century, surgical procedures to correct severe skeletal malocclusions were again attempted. This time, surgery was attempted in the mandible. Because the biological basis for orthognathic surgery was not yet well understood, surgery was generally reserved for individuals with severe facial deformities, or to address a traumatic injury. These early surgical procedures were largely unsuccessful and unpredictable in both the short term (intra-operative and immediate post-operative time) as well as the long term (months to years postoperative). With the advent of the bilateral sagittal split ramus osteotomy by Obwegeser in the late 1950s, predictable and successful advancement of the mandible became possible (Trauner and Obwegeser 1957). However, successful routine maxillary surgery took nearly another quarter century. In 1975, Bell performed a microangiographic study of Macaca mulatta monkeys who had undergone maxillary surgery to begin to understand the healing process (Bell, Fonseca et al. 1975). This landmark paper led to a significant increase in both the frequency and success of maxillary surgery.

History of obstructive sleep apnea

The first paper describing what is now classified as obstructive sleep apnea (OSA) referred to the disease as Pickwickian Syndrome (Bicklemann, Burwell et al. 1956). The description reportedly refers to a character from Charles Dickens’ The Pickwick Papers serial from the 1830s, where one of the characters was severely overweight. The character was further described as being able to fall asleep nearly anytime of the day regardless of the setting or circumstances. In recent years, the condition has become much more studied across several disciplines of medicine.

One of the early reported forms of surgical treatment included man-dibular advancement surgery (Bear and Priest 1980). Later, other authors describe performing two-jaw surgery to augment the flow of oxygen during sleep (Hochban, Brandenburg et al. 1994; Riley, Powell et al. 1993; Prinsell 2002). Though patients underwent surgery for severe quality of life reasons, little information was presented regarding the effect orthognathic surgery would have on the facial profile since the advancements were nearly 10 mm.

Effects of maxillary and mandibular surgery on the profil

Several papers have been written to examine the effects of jaw surgery on the overlying soft tissue profile. One of the earlier papers found that the soft tissue changes were approximately 40 per cent of the hard tissue changes (Dann, Fonseca et al. 1976). The paper reported changes based on only eight patients, two of whom had surgery to address the growth inhibition due to cleft lip and palate. A subsequent paper examined 21 patients and demonstrated a 46 per cent soft tissue to hard tissue ratio (Stella, Streater et al. 1989).

A subsequent paper that became the standard set of predictive rules also utilized 21 patients, however only 14 were advancement only patients; the other seven were maxillary impaction (Mansour, Burstone et al. 1983). Their results demonstrated an increased soft tissue to hard tissue change of 60 per cent when examining the change in the upper lip position. With the advent of distraction osteogenesis, investigators theorized that greater soft tissue changes would be observed due to the simultaneous distraction histeogenesis that reportedly occurs. In recent papers examining the effects of distraction osteogenesis on the profile, an 80 per cent soft tissue to hard tissue change is reported for the upper lip. In addition, a 96 per cent soft tissue to hard tissue change was observed at the superior sulcus (soft tissue A point) (Wen-Ching Ko, Figueroa et al. 2000). One limiting factor of this paper is that it only examined 16 patients, all of whom were syndromic.

With mandibular surgery, relative consistency is present for advancement surgery. Two of the many papers written both describe approximately one-to-one soft tissue to hard tissue changes (Quast, Biggerstaff et al. 1983; Ewing and Ross 1992). When distraction osteogenesis was evaluated, soft tissue changes were reported to be very close to those observed following standard mandibular advancement surgery (Melugin, Hanson et al. 2006).

One of the few papers describing the soft tissue changes in obstructive sleep apnea patients was published in 2001 and describes an 80 per cent soft tissue to hard tissue change when examining the upper lip (Louis, Austin et al. 2001). One weakness of the paper is the relatively small study group of 15 patients. Another weakness is that only three locations were studied, so only a very limited knowledge of the soft tissue change was presented.

Tremendous benefit would come from a better understanding of all of the regional changes that should be expected with two-jaw surgery. A new investigation that was just published examines the entire soft tissue changes that were observed following maxillomandibular advancement for sleep apnea (Conley and Boyd 2007). The changes reported are significantly larger than previous reports.

Current predictive software products such as Dolphin, Vistadent, etc. have 'default' soft tissue to hard tissue rules built into their programs. These values are based on previous published investigations. With only one paper describing the soft tissue to hard tissue changes available, it is theorized that current computer programs lack the necessary information to adequately predict the changes that will occur with MMA surgery.

Materials and methods

Two predictions were performed for a patient using Dolphin. The pretreatment lateral cephalometric radiograph was taken and loaded into Dolphin. The lateral cephalometric radiograph was then digitally traced. Two treatment forecasts were fabricated using Dolphin’s treatment planning module. The first prediction was performed using the stock or 'default' values for a LeFort I ad-vancement. A second prediction was performed using the same pretreatment digitally traced lateral cephalometric radiograph. The second treatment forecast was performed using the newly developed soft tissue to hard tissue changes reported by Conley and Boyd. The amount of advancement used was the same in both treatment forecasts. The amount of advancement was 8.9 mm, which was the average advancement of the patients examined by Conley and Boyd.

The default values for the Dolphin program are shown in Figure 1. The computer schematic representing the predicted facial changes using the stock values is shown in Figure 2. The second prediction was performed with the newly developed soft tissue to hard tissue rations that were previously mentioned (Conley and Boyd 2007). Figure 3 shows how to enter the custom soft tissue to hard tissue ratios within Dolphin. The resulting schematic from the custom ratios is shown in Figure 4. The predictions were then viewed side by side to determine qualitative differences (Fig. 5).

Results

Qualitatively, it is readily apparent that there are significant differences between the two predictive schemes. Most notably, the 'default' computer program values underestimate the changes that occur at the base of the nose, and the superior to middle portion of the upper lip. As the observer can see, the more inferior portions of the upper lip, labrale superiorus, the two predictive schemas more closely approximate one another. However, the change is still underestimated using the 'stock' computer soft tissue rules when predicting the change. For evaluation of the predicted final outcome, the full prediction tracing has been included (Fig. 6).

Discussion

The soft tissue changes reported by Conley and Boyd are significantly larger than most previous reports. Several potential causes for the difference exist. First, the average patient age in the Conley and Boyd paper was older than most previous orthognathic surgery study populations. The increased age could result in an increased tissue laxity, making the soft tissue more accommodating to skeletal changes.

Another possibility is the type of tissue. The majority of the obstructive sleep apnea study group included overweight to obese individuals. Previous soft tissue studies have predominantly investigated normal body habitus patients. The increased adipose tissue combined with the previously mentioned tissue laxity may combine for an increased soft tissue response.

Another consideration must be the type of closure technique used during the surgery. The previous paper describing the profile changes in obstructive sleep apnea patients, (Louis, Austin et al.), reports that no adjunctive soft tissue closure techniques were utilized. Conley and Boyd used a V-Y or a double V-Y soft tissue closure technique. The technique was first described by Carlotti and Schendel (Schendel and Williamson 1983; Carlotti, Aschaffenburg et al. 1986; Schendel and Carlotti 1991).

The technique is performed to draw the soft tissue of the maxilla forward during closure. This results in the soft tissue gathering in the anterior maxilla. This gathering provides bulk to the area and results in larger soft tissue support for the base of the nose and the superior portion of the upper lip. This change is maintained even over the course of the time (one year) studied. The result of the V-Y or double V-Y closure technique is a more parallel advancement of the soft tissues. Without the technique, more soft tissue change is observed inferiorly because the teeth hold the lip in a more forward position.

Though patients are undergoing MMA surgery to reduce the negative effects of obstructive sleep apnea, they and their family have questions and concerns regarding the potential facial changes that may occur. To provide appropriate informed consent, as well as allaying their fears and concerns, it is important to share as much information as is available. Using predictive programs such as Dolphin or other computer packages can help the patient and family see the likely facial changes.

However, when doing such predictions, it is necessary to inform the family that these changes are predictions, and actual results may be different. Neither the surgeon nor the orthodontist should guarantee results that exactly duplicate the prediction. When performing the predictions, it is important to show the most accurate information possible. The newly developed soft tissue ratios can be an adjunct in the presentation of these predictions.

Conclusion

Though the orthodontist does not perform the surgery, it is often the orthodontist who receives questions regarding the potential surgical changes due to the relationship that builds as treatment is provided over many months. For accurate prediction of the soft tissue changes, several factors must be considered regardless of whether the prediction is performed by computer or by hand. Patient age, body mass and tissue tonicity must be considered along with the type of surgery to be performed. In addition, the soft tissue closure technique along with any other adjunctive procedures (piriformplasty, trimming of ANS, etc.) can play a dramatic role in the types of change a patient can expect. Discussion with the surgeon who will be treating the patient is essential so that the orthodontist can provide the most accurate information possible.

Editorial note: A complete list of references is available from the publisher.

Contact info

Dr R. Scott Conley
Clinical Assistant Professor
University of Michigan
School of Dentistry
Department of Orthodontics
and Pediatric Dentistry
1011 N. University Avenue
Ann Arbor, MI 48109-1078
USA

Tel.: +1 734 936 3919
E-mail: rsconley@umich.edu

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