Abstract
The treatment of maxillary transverse deficiency in post-pubertal patients has been an area of disagreement among orthodontists. Much of the controversy is over the timing of when it is appropriate for these patients to be referred to an oral and maxillofacial surgeon for an adjunctive surgical procedure or whether traditional orthodontic mechanics should be attempted. The decision, therefore, by an orthodontist of when to refer a patient for surgery appears to be an individual one. The question then becomes which of the three basic surgical procedures would be most appropriate for the patient. Specifically, consideration must be given to surgically assisted rapid palatal expansion, segmental LeFort I osteotomy, or mandibular midline osteotomy with constriction.
Introduction
The treatment of maxillary transverse deficiency in post-pubertal patients has long been an area of disagreement among orthodontists. Much of the controversy is over the timing of when it is appropriate for these patients to be referred to an oral and maxillofacial surgeon for an adjunctive surgical procedure or whether traditional orthodontic mechanics should be attempted. Since the timing of maxillary palatal suture maturation is variable, there are not clear guidelines in the orthodontic literature to assist with this decision. Traditionally, orthodontists have relied on Melsen’s work on autopsy specimens in which she found that there was evidence of midpalatal sutural fusion as early as 15 years of age in females and 17 years of age in males. Later, Pierson and Thilander showed that the midpalatal suture can remain patent until the mid-30 s. Following cessation of facial growth, sutures do not typically initiate immediate fusion but, rather, undergo morphologic alteration as they become less functional and are no longer active sites for growth adjustment. Facial sutures more typically become more interlocking or interdigitated with age making expansion more difficult through resistance rather than through actual fusion of the suture. Consequently, a recent systematic review of the literature on this topic could not come to a definitive conclusion as to the reliability of using skeletal age as a criterion for the success, or failure, of conventional rapid maxillary expansion in nongrowing-growing individuals. The decision, therefore, by an orthodontist of when to refer a patient for surgery appears to be an individual one. Clearly, there are patients in whom most would agree that surgery should be considered. Those situations may include previous unsuccessful attempts at conventional orthopedic expansion, adult patients with significant bilateral or asymmetric unilateral crossbites, and patients with other accompanying facial skeletal discrepancies. The decision then becomes which of the three basic surgical procedures would be best for the patient. Specifically, consideration must be given to surgically assisted rapid palatal expansion, segmental LeFort I osteotomy, or mandibular midline osteotomy with constriction.
Surgically assisted rapid palatal expansion (SARPE or SARME)
Surgically assisted expansion is a natural progression from consideration of conventional orthopedic palatal expansion in treating patients with posterior transverse deficiency. As with conventional maxillary expansion, the major limitation to surgically assisted rapid palatal expansion, is that the skeletal problem needs to be limited to maxillary deficiency in the transverse plane. One advantage of surgically assisted rapid palatal expansion over conventional orthopedic expansion is that it can be effectively used in the correction of a unilateral crossbite.
The use of an expander concomitant with maxillary osteotomies is a technique first described by Lines in 1975. He described a surgical approach similar to one that is commonly utilized at the present time. Following a soft tissue incision from canine to the molar region, a horizontal bone cut is made from piriform rim to the pterygoid plate. This is accomplished bilaterally followed by a midpalatal incision made from behind the nasopalatine papilla back to just before the end of the hard palate. After elevating palatal tissue on either side of the suture a bone cut is made angling the bur to either side of the septum. This cut is made from the posterior hard palate forward to just behind the nasopalatine foramen. Lines did not attempt to separate the tuberosity from the pterygoid plate and he waited two to three weeks following surgery before initiating the active expansion. The primary difference between Lines’ technique and the procedure that is commonly used is the addition of the use of a fine osteotome, driving it to a depth of approximately 5–10 mm between the apices of the central incisors. Differences in the timing and amount of activation vary among surgeons. We have had excellent success in starting the activation immediately after cementing the appliance in place then expanding at 1.0 mm per day until the desired maxillary width is obtained.
There are several variations of this basic technique with the most controversial being the use of a vertical cut at the pterygomaxillary suture. This has been shown to be of minimal, if any, benefit. There is also the possibility of damaging blood vessels in that region. One of the advantages of the SARPE procedure promoted by many surgeons is that it can be safely and comfortably done in an office environment under sedation and local anesthesia. The risk of excess bleeding from the pterygomaxillary cut makes this additional procedure impractical in an office setting.
Some surgeons prefer not to make a direct palatal incision, but instead use a sharp osteotome, driving it posteriorly between the apices of the central incisors approximately 1.5 cm. Besides requiring care to avoid a tear of the palatal tissue, this technique may contribute to a common undesired side effect of surgically assisted rapid palatal expansion, that of unequal expansion. This potential complication has been associated with the restraining effect of the vomer and septum being attached to one of the halves of the maxilla.
A final major technique variation is the use of bone-borne instead of tooth-borne expanders. Interestingly, the benefit of applying pressure directly to the bone is not as clearly supported by literature as would be expected.
A greater amount of skeletal movement does seem to occur with the bone-borne expander, but the claims by some surgeons of minimal buccal dentoalveolar tipping have not been supported by the literature. The inability to show much difference between the two approaches may lay with the difficulty of placing the bone contacts close to the horizontal shelf of the palate. A deep, narrow vault limits the size of the expander and makes access difficult for placing the bone screws. Thus, the expander ends up putting pressure on the dental alveolus which is not significantly different from a tooth-borne appliance. Lee presented what he called the mini-screw assisted rapid palatal expander (MARPE) which he used for conventional expansion without osteotomies. This expander is connected to the horizontal plate of the palate on either side of the suture with small screws, but again its use is limited by the size of the expander. Based on the minor differences in the response and the limitations of application of the bone-borne expander, it appears that the traditional tooth-borne expander is most appropriate when significant expansion of the maxilla is required.
Complications associated with the use of surgically assisted rapid palatal expansion are rare with asymmetric expansion, as previously noted, being the most common. Postoperative relapse does occur, but it has been shown to be similar in amount when compared to conventional orthopedic expansion in adolescents. The evidence indicates that the clinician should anticipate a loss of approximately one third (33%) of the transverse dental expansion obtained with SARPE while the skeletal expansion achieved is quite stable. Because both surgically assisted rapid palatal expansion and conventional orthopedic expansion both have a similar response of increase in buccal crown torque and dentoalveolar tipping, it is generally recommended that the expansion continue until the maxillary palatal cusps are in contact with the buccal cusps of the mandibular dentition. Most surgically assisted expansion reports in the literature are greater than 5 mm although it is possible to expand up to 15 mm using additional expansion appliances. The length of retention after expansion also varies but it is recommended that fixed retention be maintained for at least twelve weeks following surgery and preferably longer.
Recently, two variations of surgically assisted rapid palatal expansion have been suggested in treatment of obstructive sleep apnea. The first has been called the DOME procedure (distraction osteogenesis for maxillary expansion). The other is the EASE procedure (endoscopically assisted surgical expansion). Neither procedure appears to offer any advantages over conventional surgically assisted rapid palatal expansion done on an outpatient basis.
Additional benefits of surgically assisted rapid palatal expansion over maxillary segmental osteotomy need to be emphasized: Equal expansion can be achieved from the molar to canine regions, thus providing an increase in arch perimeter to reduce an existing arch length deficiency ; intercanine width can be predictably increased for finishing in situations of narrow intercanine distance and/or significant anterior crowding; and the buccal incisions can be limited to about 1.5 cm thus minimizing the potential negative labial and paranasal soft tissue aesthetic changes that have been associated with maxillary LeFort I osteotomies ( Fig. 1 a–f).
Maxillary LeFort I segmental osteotomy
The use of a segmental LeFort I osteotomy in treatment of maxillary constriction is an old and traditional surgical procedure. The primary benefit of the maxillary segmental osteotomy over surgically assisted rapid palatal expansion is the ability to control the maxillary segments in all three planes of space. When the maxilla is segmented in two or more segments, the immediate postoperative occlusion is predictable. However, the long-term maintenance of that transverse correction is of concern with instability being the primary disadvantage of this surgical procedure. Consequently, there are two dilemmas facing the clinician when planning to use a maxillary segmental osteotomy for the treatment of a transverse deficiency. First is to determine the appropriate amount of overcorrection and second is how to best hold the correction following surgery. This issue is emphasized in the most recent “Hierarchy of Stability” article based on the ongoing research at the University of North Carolina. They found that relapse occurred in almost all of the cases they reviewed and that 30% of the patients had more than 3.0 mm of postoperative constriction. An additional potential complicating factor in dealing with stability is the possible introduction of transverse dental relapse. If an orthodontist attempts to conventionally expand the arch prior to surgery and tips the buccal segments out, the surgeon is then limited in the amount of skeletal overcorrection possible without placing the dentition in complete buccal crossbite. Accordingly, the probability of both skeletal and dental relapse occurring is increased if dental tipping occurs during the presurgical orthodontic phase. As in all orthognathic treatment planning, it is important that there is close cooperation between the surgeon and the orthodontist prior to surgery. It is strongly recommended that the orthodontist try to minimize any dental expansion during the presurgical phase but, rather, work on optimizing axial inclinations of the posterior teeth. This way, if surgical relapse does occur, the orthodontist still has an opportunity to compensate with conventional orthodontic tooth movement. Unfortunately, the ability to correct an excessive curve of Wilson prior to surgery in situations such as anterior open bite and Class III malocclusions may be extremely difficult for the orthodontist. In situations where curve of Wilson is still present to some degree going into surgery, maximal overcorrection is best achieved by placing the maxillary lingual cusps over the mandibular buccal cusps. Any greater over correction is generally not advisable because of the difficulty controlling the vertical position of the molars after surgery and during orthodontic finishing.
Various methods of holding the transverse change, in addition to over correction, have been recommended including; the use of a transpalatal arch, palatal splint, placement of an edgewise stabilizing archwire as soon as possible postoperatively and even placing an expanded headgear inner bow into buccal tubes. Unfortunately, there have been no studies that have demonstrated an advantage to any one of these methods in minimizing relapse. As with surgically assisted rapid palatal expansion, there is also the question of how long the expanded arch needs to be retained. Simply maintaining the support for six weeks, as was recommended prior to the introduction of rigid fixation, does not appear to be sufficient. Therefore it is recommended that the expansion be held at least 10 weeks with active or passive retention appliances. This amount of time is based on the objective of holding the width until bone has healed sufficiently to withstand the soft tissue pressures causing the constriction. Orthodontists should also continue to finalize tooth position with archwires coordinated with the maxillary arch form expanded.
The amount of expansion attainable, especially in the molar region, is debatable with many surgeons believing that greater than 6.0 mm should not be attempted although up to 15 mm has been reported. The amount of expansion obtainable is dependent on the type of palatal osteotomy performed. A midline osteotomy is very limited, due to the lack of elasticity of the palatal tissue overlying the suture. For that reason, parasagittal soft tissue incisions have been recommended for those who use a midpalatal cut. In situations requiring larger than 5.0 mm of expansion, a horseshoe osteotomy should be the preferred treatment. In that osteotomy, parallel cuts are made just mesial to the medial nasal wall then they are connected across the palate behind the nasopalatine foramen. The expansion occurs with the elevation of palatal tissue from alveolus bilaterally. When the maxillary arch is expanded, the mid-portion of the palate drops down resulting in a decreased depth of the vault.
Complications are unusual with segmental maxillary osteotomies, although, if they do occur can be more significant than those associated with surgically assisted expansion. Haas, in a systematic review of the literature, noted in the nine studies that had adequate data to be included, that the most common side effect was infection. This finding is surprising, although he did note that the majority of these infections were reported in only three of the studies evaluated. Generally, infection in maxillary osteotomies has been found to be relatively rare. The next two most common complications noted were a persistent oral fistula and damage to teeth adjacent to the vertical osteotomies. These two complications are much more understandable and, fortunately, are also infrequent. Bone cuts made above the palatal tissue have to be made with care due to the inelasticity and thinness of much of the soft tissue. A fistula may occur following a small tear in this thin mucosa but they generally heal spontaneously Some may be persistent and do require a simple repair.
The vertical bone cuts necessary in segmental osteotomies carry the risk of damage to the periodontium and dental roots especially if off the midline. Orthodontists can provide assistance in preventing this type of iatrogenic tissue problem. Early planning between the surgeon and orthodontist on the location of the vertical cuts is important. It will give the orthodontist time to parallel, if not diverge, the roots in the osteotomy sites. Also, except for the midline osteotomy, having at least 1.0 mm of open contact between the adjacent teeth is desirable. In an unpublished study) of 72 patients with interdental osteotomies, it was found that closed dental contacts in the osteotomy site at the time of surgery was the most common cause of periodontal defects secondary to maxillary segmental osteotomies.
Finally, a potential complication of maxillary osteotomies that is not often discussed is the potential negative aesthetic affects in the paranasal and labial regions secondary to LeFort I osteotomy. These unfavorable soft tissue changes are also seen with segmental osteotomies and must be considered when planning which type of surgical procedure should be used in correcting a transverse discrepancy. An early study was conducted designed to look at the impact of not making a mucosal incision across the midline as is typically made with a Le Fort I osteotomy. Instead, the surgeons used small incisions and tunneling as is done with surgically assisted osteotomies. This tunneling technique resulted in minimal if any changes in the volume of the upper lip. Considering this minimal surgical exposure may be important in the surgical treatment decision for some patients with a thin upper lip ( Fig. 2 a–c).
