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Bicuspid Intrusion
Oral Maxillofacial Surg Clin N Am 19 (2007) 339–350
Correction of Skeletal Open Bite with Implant Anchored Molar/Bicuspid Intrusion Keith Sherwood, DDSa,b a
Boston University Goldman School of Dental Medicine, 100 East Newton Street, Boston, MA 02118, USA b Private Practice, Oral and Maxillofacial Surgery and Orthodontics, 80 Lindall Avenue, Hunt Medical Building, Danvers, MA 01923, USA
Skeletal open bite is one of the most challenging malocclusions for the orthodontist to accurately diagnose and predictably treat. Orthodontic correction alone, even when initiated at an early age, often leads to long-term relapse. As a result, in an effort to improve stability, combined orthodontics and orthognathic surgery are frequently seen as the treatment of choice or necessity. Recent technical advancements and clinical research in implant-assisted orthodontics has spurred interest in using miniplates and other surgical implant fixtures as anchors to allow minimally invasive correction of skeletal open bite. This article discusses the cause and diagnosis of open bite, historical perspectives on treatment, indications for surgery, use of implant anchors to facilitate correction, and surgeon–orthodontist cooperation. Literature review Etiology of open bite Open bite malocclusion is commonly seen in orthodontic practice. As a result, much of what we know about this bite abnormality comes from the orthodontic literature. It has been shown that orthodontic treatment of open bite is prone to relapse [1]. Most orthodontists consider open bite, especially in adults, to be a significant treatment challenge. In contrast, oral and maxillofacial surgeons see only a fraction of
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their orthodontic colleagues’ open bite patients, usually on referral for orthognathic surgery. The scope, risk, and cost of an osteotomy may drive some patients and orthodontists away from this option. Open bite patients are often sent for surgical correction only after orthodontic treatment has been unsuccessful. This results in a skewed perspective on the part of the surgeon regarding the incidence, etiology, and treatment of open bite and may affect postsurgical stability. For practical reasons, the orthodontist often takes the lead in the important pretreatment analysis of the origin of an open bite malocclusion. This diagnostic process is often complex, because growth and development, genetic, and habit factors must be considered. When these issues are not taken into account, unnecessary or inappropriate treatment may be instituted and the risk of orthodontic and surgical relapse increases. As with other types of dentofacial deformities, the participating oral and maxillofacial surgeon should understand the nature and etiology of open bite to communicate with the orthodontist, plan appropriate and progressive surgical treatment, and avoid complications. The nature of the open bite malocclusion can be divided into dental or skeletal, and etiology can be divided into mechanical or genetic factors. Nothing is more critical in treatment planning for the patient who has open bite than determining whether the bite deformity is of dental or skeletal origin. Dental open bite can be treated with orthodontics alone. Skeletal open bite, especially in the adult dentition, usually requires some type of surgical intervention.
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Dental open bite Mechanical factors, such as digital sucking habits, tongue thrust, and tongue posture, have been thought to contribute to dental open bite. By far the most common cause of open bite in the mixed dentition is a digital sucking habit [2]. Dental open bite usually can be managed with habit control appliances, education, and traditional orthodontic treatment. Tongue thrust long has been thought to cause dental anterior open bite because this malocclusion is often seen in patients with reverse or infantile swallowing patterns. Myofunctional therapy was considered for many years to be an integral part of open bite management. Studies have shown, however, that patients with reverse swallow pattern put less force on the anterior teeth than patients with adult swallow [3]. Swallowing is considered a physiologic process, not a learned behavior [2]. The adult swallowing pattern is not present for most children until age 6 and does not appear at all in 10% to 15% of the population [4]. In fact, tongue thrust/swallow seems to be an adaptation to open bite to create a seal between the incisors during swallowing [5]. Although tongue thrust probably does not cause open bite, tongue posturedwherein the tongue continually rests between the incisorsdseems to contribute substantially to the maintenance of dental open bite [2]. Skeletal open bite The accuracy of the diagnosis of skeletal open bite in large population studies is difficult to access. Data from the Public Health Service suggest an incidence in the adolescent US population with mature dentitions of approximately 5%, however, with a much higher proportion among blacks [6]. Current theory supports the concept that vertical jaw proportions are inherited, just like anteroposterior relationships [7]. The primary cause of skeletal open is likely genetic, which is not to suggest that mechanical factors cannot cause open bite. For example, surgical scarring after cleft surgery is thought to restrict growth and can lead to open bite. Nasal obstruction also may play a role in the development of skeletal anterior open bite. The inferior posture of the mandible and tongue seen in severe nasal obstruction probably contributes to an open bite malocclusion, maxillary constriction, and hyperdivergency. The timing and degree of obstruction needed in humans to create a change is
speculative, however, and additional factors may be necessary [8,9]. Diagnosis: skeletal versus dental Discovering the skeletal/dental nature of an open bite is critical to effective treatment. A habitderived dental open bite usually displays maxillary incisor proclination and mandibular incisor uprighting or intrusion. A skeletal open bite usually has a constellation of signs unique to the deformity. The malocclusion is characterized by normal (or even excessive) eruption of anterior teeth, downward rotation of the mandible causing hyperdivergency or long face syndrome, and excessive eruption of posterior teeth [2]. Normal or decreased ascending ramus height, a tipped palatal plane that is higher anteriorly, low position of the mental foramen, decreased posterior cranial base (S-basion), and accentuated curve of the maxillary occlusal plane and/or reverse curve of the mandibular occlusal plane also may be seen [5]. A cephalometric analysis that measures these variables is essential to diagnosis and treatment planning. The vertical dentoalveolar excess in the molar area seen with skeletal open bite is common in the maxilla, less frequently seen in the mandible, and rarely present in both jaws [5,10]. Orthodontic treatment The orthodontic literature concerning the treatment of open bite is voluminous. Because most open bite in the mixed dentition is of dental origin, habit control and standard orthodontic treatment are often effective. Few 10-year posttreatment studies involving large numbers of patients with diagnostically comparable open bites have been published [1]. Treatment of skeletal open bite is one of the most difficult malocclusions for the orthodontist to predictably treat, however, and is commonly plagued by relapse. If started early enough, growth modification treatment designed to restrict molar/bicuspid dentoalveolar vertical development may be effective. The use of high pull head gear or posterior bite blocks is extensively reported [2,11,12]. Altering the occlusal plane by uprighting teeth (multiloop edgewise archwire) also has been reported [13]. Vertical anterior elastics are often used to assist in bite closure by extruding incisors. In true skeletal open bite this orthodontic strategy frequently results in extensive relapse over time, even in younger patients, because of the recoil pull of elastic and principal fibers on incisors [14].
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Research has shown that extrusion of anterior teeth, especially on open bite patients, can lead to significant root shortening, probably because of resorption [15,16]. In older adolescents and adult patients, surgical correction of the skeletal open bite has been accepted by many as the most predictable treatment option.
long-term relapse, no orthodontic forces were placed on anterior teeth. After these articles, other studies and case reports demonstrated the safety and success of the technique [23–26].
Surgical treatment
Indications
Reports on surgical intervention to correct open bite have been recorded for more than 100 years. In 1925, Limberg provided early reports of success with vertical oblique osteotomy of the mandible; however, follow-ups on these patients indicated unsatisfactory relapse [17]. Early maxillary techniques pioneered by Conn-Stock [18], Wassmund, Wunderer, and others were limited to anterior segmental procedures. These procedures are stable but may result in excess incisal show because most open bite is caused by vertical excess in the molar area [2,10]. Later, maxillary posterior segmental intrusion procedures, reported by Schuchardt [19] and others, were stable and effective but have lost favor because of technical difficulty, risk of interruption of blood supply, and lack of flexibility. In the modern age of orthognathic surgery numerous reports and studies have demonstrated success and stability in correction of open bite with Le Fort I osteotomy [10,20].
Patient selection for the procedure begins with a determination of the dental or skeletal nature of the open bite based on the criteria discussed previously. Although usually apparent from a clinical examination, as with orthognathics, this determination should be confirmed and quantified with a cephalometric analysis. The posterior vertical excess can be determined using standards developed by Burstone, Bell, and others with linear measurements from the palatal plane or mandibular plane to the incisal edge of the buccal cusps of the first molars [5,27]. These measurements are vital in treatment planning the ideal location of the implant anchor, judging how much intrusion is needed to close an open bite, and planning the orthodontic set-up. If surgery of any kind is to be considered, the open bite should be caused primarily by posterior vertical maxillary or mandibular excess. A coexisting dental component may be present in some patients, however. In addition to a skeletal open bite, candidates for implant-anchored correction should have a permanent dentition, acceptable or orthodontically correctable incisor–lip relations, and no medical or periodontal health contraindications.
Implant-anchored orthodontic correction of open bite Recently, several case reports and limited studies described a new, less invasive approach to the treatment of skeletal open bite. Titanium miniplates normally used for internal fixation of osteotomies and fractures and other types of implants are being used as skeletal anchors to orthodontically correct open bite. Umemori and colleagues [21] first reported on the use of miniplates as orthodontic anchors in the mandible. These plates were used to orthodontically intrude lower posterior teeth, which allowed the open bite to close by mandibular autorotation. Although impressive corrections of major skeletal open bites were shown, the study was flawed by the simultaneous use of anterior vertical elastics as part of the technique. After this, Sherwood and colleagues [22] reported on the successful use of miniplates inserted on the maxilla to intrude maxillary posterior teeth, where skeletal anterior open bite often originates (Fig. 1). To clarify the actual effect of the miniplate-anchored intrusion and avoid
Materials and methods for implant-assisted open bite correction
Presurgical orthodontics and treatment planning The orthodontist must carefully prepare the patient who has open bite for treatment. Most skeletal open bite malocclusions have a two-step maxillary occlusal plane with the step in the bicuspid/canine area. Placing a continuous archwire in the brackets of a patient who has skeletal open bite leads to incisor extrusion and relapse. To avoid this problem, the orthodontist must treat the arch segmentally, which usually requires separate leveling wires being placed from canine to canine and from the bicuspids to the molars (three independent sections). The orthodontist should advance these wires until heavy rectangular sectional surgical wires are in place. The vector of elastic force from the implant anchor to the molar is buccal and vertical. It is essential that the buccal tipping forces be controlled or the open
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Fig. 1. Schematic of miniplate and screws used for orthodontic anchorage to intrude molars with elastic thread. (From Sherwood KH, Burch JG, Thompson WJ. Closing anterior open bites by intrusion of molars using titanium miniplate anchorage. Am J Orthod Dentofacial Orthop 2002;122:593–600; with permission. Copyright Ó 2002 American Association of Orthodontists.)
bite may be worsened by extrusion of the lingual cusps. This is most efficiently done with a transpalatal appliance (TPA) in the maxilla or a lingual arch in the mandible. The use of a maxillary TPA has an added benefit because tongue pressure on the appliance may contribute to molar intrusion. Placing an acrylic pad on the TPA wire is occasionally necessary for patient comfort. The TPA must be offset (relieved) from the palatal mucosa the distance that the molars are expected to be intruded (Fig. 2). The amount of intrusion necessary is determined by the degree of anterior open bite. Based on wellknown prosthodontic principles, each millimeter of molar intrusion yields a 2- to 3-mm closure of the anterior bite via mandibular autorotation. An 8-mm anterior open bite closure for example requires roughly 3 to 4 mm of intrusion at the first molar area. If the patient cannot tolerate a TPA, a maxillary lingual arch or heavy constricted buccal archwire inserted only into the headgear tubes may suffice. If a lingual arch is used, it should not be in contact with soft tissues or adjacent teeth other than the first molars to be intruded. The miniplates should be inserted after the patient is in orthodontic appliances and 2 to 10 weeks before the predicted start of intrusion mechanics. If a TPA is used, it should be inserted 1 to 2 weeks before beginning molar intrusion. If
extractions are needed to correct for crowding or sagittal discrepancies, timing of miniplate placement must be carefully considered. When bicuspids are being extracted to correct a sagittal discrepancy (ie, maxillary first bicuspids in a dental class II malocclusion), the open bite should be corrected first with sectional mechanics (sectional wires) and implant-assisted intrusion. The bicuspid space can be closed in a level occlusal plane. The implant anchors are doubly useful in this setting to assist in anchorage control for space closure.
Fig. 2. TPA to prevent buccal molar tipping. Note 5-mm offset from the palate.
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The orthodontist may determine that significant crowding requiring bicuspid extractions must be corrected before implant-anchored intrusion begins. In this circumstance the orthodontist often must use a continuous archwire. Once the space created by extraction is closed, intrusion mechanics can be instituted. To avoid inadvertent intrusion of anterior teeth during molar intrusion with a continuous wire, place the miniplate more distally, in line with the second molar. This placement directs the moment of force more posteriorly and limits potential adverse forces on the incisors. Some studies routinely use light anterior elastics during molar intrusion to counteract incisor intrusion with a continuous archwire [21]. Other clinicians have reportedly placed an orthodontic anchor screw between the central incisors for use as a brace against intrusion of the incisors [25]. To emphasize the point, if sectional archwires are used there is no risk of incisor intrusion and treatment is simplified.
Skeletal anchor surgery: surgical planning, preparation, and technique Planning fixture placement Orthodontic intrusion mechanics can be complex so that communication with the orthodontist regarding the ideal location of the implant fixture is important. Generally, a miniplate anchor should be placed adjacent to the tooth or teeth that need the most intrusiondusually the first or second molars in the anterior open bite patient. (Other implant anchors, like miniscrews or cylindrical implants, also can be used and are discussed but are more limited in the potential locations for insertion and access.) The last loop on the plate that emerges transmucosally through the buccal vestibule should be directly in line with the molar or molars that require maximum intrusion. If the first and second molars require equal intrusion, the miniplate loop should emerge between these teeth. When the orthodontist has a continuous wire in place, the miniplate loop should emerge more posteriorly and other precautions against incisor intrusion may be needed. Choosing an implant anchor The technique used to place the implant anchor is largely determined by the fixture type. Miniplates like those shown in Fig. 3A have been used extensively for open bite closure for several reasons. They are versatile fixtures because they can be
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Fig. 3. (A) Miniplates and screws used for skeletal anchorage (Leibinger/Stryker). (From Sherwood KH, Burch JG, Thompson WJ. Closing anterior open bites by intrusion of molars using titanium miniplate anchorage. Am J Orthod Dentofacial Orthop 2002;122:593– 600; with permission. Copyright Ó 2002 American Association of Orthodontists.) (B) Ortho-anchor miniscrews (Rocky Mountain Orthodontics).
placed where anchorage is needed the most. They have the virtue of three-dimensional stability because they are held in place by two or more screws. The miniplate screws are placed well away from tooth roots, avoiding the potential for root injury or interference with root movement. The exposed miniplate loop can be adjusted somewhat after surgery with bending to improve access. Although these are significant advantages, miniplates have the drawback of requiring more surgery to place and remove them than the other options. The miniplate technique is time tested and is described first. Recent case reports have demonstrated success with miniscrew (microscrew) orthodontic anchors (Fig. 3B) using a protocol similar to the miniplates [28,29]. These ‘‘ortho-anchors’’ are inserted into alveolar bone between tooth roots rather than apical to them. Concerns regarding the potential for mobility of these anchors and root injury when used in the maxilla are addressed in the discussion section. An impressive case that shows the use of miniscrew anchors to close an open bite treated and recorded by Dr. Seung Hyun Kyung is presented.
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Surgical technique For the surgeon familiar with placing implants, patient preparation is similar to that used for endosseous implant insertion. Good oral hygiene and avoiding smoking before and after surgery are highly desirable. A presurgical chlorhexidine rinse is appropriate, and most surgeons favor perioperative antibiotics. Miniplates can be placed using local anesthesia with or without intravenous or oral sedation. Local anesthesia is infiltrated into the area where the miniplate will be fixed. Surgery begins with a 1- to 2-cm vestibular incision and a full-thickness mucoperiosteal flap reflected to expose the cortical bone of the maxillary strut or lateral aspect of the mandible. An L-, Y-, or Tshaped plate is selected that affords good contact at its apical base with the best available cortical bone. This is less of an issue in the mandible than the maxilla because of the thin cortex overlying the sinus cavity. The plate should be long enoughdusually 15 mm to 20 mmdto clear the roots apically the distance that the molars will be intruded. The transoral loop must project far enough through the mucobuccal fold for orthodontic accessibility but have enough clearance from the molar band to allow for the expected intrusion. The plate must be contoured to the surface of the bone to ensure passive placement (Fig. 4). Similar to miniplate placement with osteotomy surgery, a curved hemostat snapped on the plate on the loop to be left
exposed is useful to control the plate during sizing, positioning, and fixation. Two to three miniscrews that are 3 to 5 mm in length should be used to fix the plate at its base. Once the plate is secured, one must confirm that the exposed loop is easily accessible for the orthodontist. This loop should clear the buccal gingiva by 2 mm laterally. If not, a plate bender, rongeur, or orthodontic pliar can be used to bend the loop buccally. The soft tissue is closed as would be done for orthognathics. Postoperative antibiotics, chlorhexidine rinse, and narcotic pain medication are appropriate. The patient should be checked 1 week after surgery and again before the orthodontist initiates intrusion mechanics to evaluate healing. After the first 2 weeks the chlorhexidine rinse can be discontinued and the patient is instructed to keep the exposed loop clean with a cotton swab soaked in chlorhexidine or peroxide at bedtime. Orthodontic loading of miniplate The miniplates should be allowed to heal for at least 2 weeks before initiating intrusion mechanics. In our studies at Nova Southeastern University, 8 to 10 weeks of healing was allowed before orthodontically loading the miniplates [22]. Subsequent studies have supported early loading, however [23]. Elastic thread tied firmly from the miniplate to one or both molars is commonly used to deliver the intrusion force and is generally comfortable for the patient. If desired, the orthodontist can use a dontrix gauge to measure the amount of force delivered by the elastic thread, which should be in the range of 100 g to 150 g. Alternatively, precalibrated coil springs can be used to intrude teeth to ensure that physiologic force levels are applied [23]. There may be inadequate space to place coil springs, however, especially in the mandibular buccal vestibule, and the spring may irritate the buccal mucosa or gingiva.
Case presentations Case 1 Fig. 4. Insertion of miniplate on maxillary strut in preparation for molar intrusion. Note plate contouring and three 5-mm self-tapping screws. (From Sherwood KH, Burch JG, Thompson WJ. Closing anterior open bites by intrusion of molars using titanium miniplate anchorage. Am J Orthod Dentofacial Orthop 2002;122:593– 600; with permission. Copyright Ó 2002 American Association of Orthodontists.)
Brief history A 34-year-old male patient presented for a second opinion regarding orthodontic care (Fig. 5A). He was concerned about his open bite, which made it difficult for him to eat and speak normally. Extensive orthodontic treatment in his early adolescence closed the open bite, but the malocclusion relapsed completely during
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Fig. 5. Case 1. (A) Pretreatment open bite. Note hypereruption (vertical excess) in molar area. (B) Preintrusion with segmental orthodontic leveling of open bite (lateral view). Note miniplate loop in buccal vestibule (arrow). (C) Radiograph shows miniplate placement (arrow). (D) Postintrusion of molars with closure of open bite (lateral view). (From Sherwood KH, Burch JG, Thompson WJ. Closing anterior open bites by intrusion of molars using titanium miniplate anchorage. Am J Orthod Dentofacial Orthop 2002;122:593–600; with permission. Copyright Ó 2002 American Association of Orthodontists.)
his late teens and early twenties. He was told by previous clinicians that a maxillary osteotomy would be necessary, which he was unwilling to consider. Examination There was a 9-mm anterior open bite (see Fig. 5A). The molar relationship was class I. The maxillary incisor-lip relationship was normal. A Burstone analysis showed a significant maxillary dentoalveolar vertical excess in the molar area. There was also an accentuated curve of Spee, long lower facial height, and steep mandibular plane angle.
miniscrews each (see Fig. 5B). Orthodontic leveling was performed in the upper in three independent sections, canine to canine and bicuspids to molars bilaterally (see Fig. 5C). Eight weeks after surgery, intrusion mechanics were begun. In this case, a constricted, heavy secondary archwire was used to prevent molar tipping. It was inserted only into the headgear tubes of the maxillary first molars and was lightly ligated to the anterior sectional archwire. Intrusion mechanics were continued for 5.5 months until the open bite was closed (see Fig. 5D).
Case 2 Treatment All teeth were bracketed with orthodontic appliances except for the first molars, which were banded. During orthodontic treatment, Tshaped miniplates were surgically placed on the maxillary struts, positioned between the first and second molars, and secured with two 5-mm
Brief history A 15-year-old male patient was treated unsuccessfully with orthodontics for an anterior open bite (Fig. 6A). Anterior vertical elastic use resulted in significant resorption of anterior tooth roots and, to a lesser extent, maxillary bicuspids (see Fig. 6B).
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Fig. 6. Case 2. (A) Relapsed open bite in adolescent with failed orthodontic treatment. (B) Panorex shows incisor root resorption. (C) Intrusion of first molar, bicuspid segment before extraction of lower second molars. Note step up at untreated second molar. (D) Closure of open bite after extraction of unintruded second molars. (From Sherwood KH, Burch JG. Skeletally based miniplate supported orthodontic anchorage. J Oral Maxillofac Surg 2005;63:282; with permission. Copyright Ó 2005 American Association of Oral and Maxillofacial Surgeons.)
Examination The anterior open bite was 7 mm. A Burstone analysis suggested a skeletal open bite marked by hypereruption in the maxillary and mandibular molar areas. There was significant gingivitis and poor oral hygiene. Treatment To avoid further orthodontic manipulation of the maxillary teeth, expedite treatment, and mitigate further root resorption, a slightly altered treatment plan was required. All active orthodontics would be suspended in the maxillary dentition, and intrusion mechanics would be limited to the lower posterior dentition from the first molars to the bicuspids. The unbanded lower permanent second molars would be extracted after intrusion of the first molars and bicuspids, and the third molars would be allowed to eventually erupt into the second molar space. Miniplates were placed in the mandible adjacent to the first molars. Sectional archwires were inserted into the lower arch, canine to canine and from the first molars to the bicuspids. A lingual arch attached to the first molar bands and offset from the other lower teeth was inserted into the
lower dentition. Maxillary archwires were temporarily removed. After 6 weeks of healing, intrusion mechanics were begun. After only 3 months, there was substantial intrusion of the mandibular first molar/bicuspid segments, as seen by their relation to the untreated second molars (see Fig. 6C). Extraction of the mandibular second molars allowed closure of the open bite by mandibular autorotation (see Fig. 6D).
Case 3 Brief history A 22-year-old female patient presented for treatment of a severe anterior open bite and retrognathia (Fig. 7A). The patient declined orthognathic surgery in favor of attempting correction with implant-anchored intrusion. Examination There was a substantial skeletal anterior open bite caused by vertical excess in the mandibular and maxillary molar areas, a mild class II division I malocclusion, incisor proclination and lip incompetence, a steep mandibular plane angle, and a long
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Fig. 7. Case 3. (A) Pretreatment open bite (lateral view). (B) Miniscrews in palatal midline used to intrude maxillary molars and bicuspids with elastic chain. Note offset TPA used to prevent tipping. (C) Segmental intrusion of molars and bicuspids with elastic thread off mandibular miniscrew (lateral view). (D) Postintrusion of molars and bicuspids using miniscrews shows closure of open bite (lateral view). (From Choi KJ, Choi JH, Ferguson DJ, et al. Facial improvements after molar intrusion with miniscrew anchorage. Journal of Clinical Orthodontics 2007;41(5):269–76; with permission.)
lower facial height. The upper arch was well aligned, but there was mild crowding in the lower arch. Treatment The posterior teeth in the upper and lower arches were passively splinted on the buccal tooth surfaces with FRC (composite orthodontic splint) to allow intrusion of these teeth as a unit. Two orthodontic miniscrew implants were placed in the midpalatal suture area of the maxilla in line with the first molars. These implants were splinted with self-curing resin and then an orthodontic ‘‘S-sheath’’ appliance bonded to the resin/implant complex. This sheath would accept a wire that would be used to intrude the posterior teeth with elastic chain connected to the lingual hooks on the first and second molars (see Fig. 7B). A TPA was used to control lingual tipping. Implants also were inserted into the buccal alveolus between the mandibular second premolar and first molar in the mandible. Elastic thread was connected from the implants to the molar bands to intrude the posterior segments. A lingual arch
was used to control buccal tipping (see Fig. 7C). Intrusion progressed over 4 months until the open bite was closed (see Fig. 7D). The orthodontic implants were removed for patient comfort. After extraction of the upper first bicuspids and lower second bicuspids, traditional orthodontic mechanics were used to correct the class II malocclusion, crowding, and lip incompetence. Discussion In the past, orthodontic intrusion of posterior teeth was thought to be impossible and the options for predictable treatment of skeletal open bite were limited. Implants permit a skeletally based anchorage system that enables this type of tooth movement. Although the success of treatment seems to be well established, questions about stability and safety are still being researched. Stability If implant-anchored intrusion is to be seen as an acceptable treatment alternative to major
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surgery for open bite, the issue of treatment stability must be addressed. It has been observed in orthodontic treatment that intruded teeth are more stable than extruded teeth. Reiten and Ryghs [14] have suggested that this factor may be caused by relaxation of elastic fibers around the tooth root on intrusion. Another perspective on the observed stability of intruded teeth is afforded by Proffit’s ‘‘Equilibrium Theory’’ [30], which speculates that vertical occlusal forces are responsible for maintaining the position of intruded teeth. Although there have not been adequate studies to evaluate relapse, our clinical experience thus far supports the perceived stability of intruded molars for at least 4 years after treatment. Sugawara and colleagues [31] reported some relapse of the intruded molars in radiographic studies. Similar to orthognathic surgery, however, in which a degree of skeletal relapse is often seen, the open bite correction at the dental occlusal level is maintained. The stability of the implant anchor itself also must be considered. If the anchor fails during intrusion, before the open bite is corrected and occlusal stability attained, the intruded teeth may re-erupt. No studies have compared miniplates to miniscrews as skeletal anchors; however, miniplates have been widely used in various settings with great success. Their stability is reinforced by the three-dimensional support of multiple fixation screws and the surface bone contact of the plate. In contrast, miniscrew ortho-anchors have only the threaded portion of a single screw for support. Some studies have shown that a high percentage of miniscrews, especially when placed in the maxilla, may become mobile [32,33]. The implications of this are unclear at this point. To improve stability, some clinicians place the miniscrew in the palatal midline, where bone is dense. However, this location means that intrusion elastics and mechanics are on the palate, which is uncomfortable for the patient because of tongue contact. Miniscrews placed in the dense buccal plate of the mandibular alveolus, through attached gingiva, seem to be relatively stable, although they may also move. Aside from loss of the screw during treatment, the implications of screw mobility are still being studied.
There has been no reported incidence of damage to the nerve from molar root intrusion. It is likely that the tooth root would resorb before penetrating substantially into the compact bone of the nerve canal. In contrast, molar roots may seem to penetrate into the sinus cavity radiographically, which does not seem to cause adverse sequelae for the sinus or tooth root. It is likely that the slow rate of intrusion allows the roots to remain covered by the sinus membrane, which is lifted superiorly, not unlike sinus lift surgery. The potential risk of root injury by orthoanchor miniscrews is still being analyzed. Although these devices have been shown repeatedly to be effective as orthodontic anchors for other types of orthodontic treatment, the risks of scoring cementum or interference with tooth movement by screws lodged between roots has not been evaluated adequately with long-term studies. Molar root resorption As with all orthodontic treatment, root resorption is a risk. Investigators have shown that some mild root resorption may take place with miniplate-anchored intrusion of molars [34,35]; however, it was considered clinically insignificant, did not affect dental health, and seemed to be comparable to root resorption seen with tradition orthodontic treatment. Excess orthodontic force can cause more severe root resorption and may interfere with physiologic tooth movement, however. Proffit [2] stated that 15 g to 25 g of force is needed to orthodontically intrude each tooth depending on the number of roots and tooth size. This finding means that the orthodontist needs to use roughly 100 g of force to intrude two molars and two bicuspids in each quadrant. This figure represents a substantial but not uncommon force level from an orthodontic perspective. Measuring the applied force accurately is technically difficult with elastic thread, however. Practically speaking, the orthodontist often simply ties the thread with a firm but not excessive force based on clinical experience. Alternatively, precalibrated coil springs more accurately deliver a specific force but may be impractical to use (see section on orthodontic loading of miniplate).
Damage to adjacent anatomic structures Daimaruya and colleagues [26,34] looked at the risk of orthodontically intruded posterior teeth impinging on the inferior alveolar nerve in the mandible and the sinus cavity in the maxilla.
Contraindications Although miniplate failures are rare, we have found that patients with poorly controlled periodontal disease are at greater risk for developing
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infections after orthodontic loading. Patients who have poorly controlled diabetes, are on medications that suppress the immune system, or who smoke heavily may not be good candidates for skeletal anchorage. In general, contraindications for miniplate- or miniscrew-anchored orthodontic treatment are similar to those for dental implant therapy and orthodontic treatment. Summary Miniplate- and miniscrew-anchored intrusion of posterior teeth to correct skeletal open bite seems to be a promising alternative to orthognathic surgery for many patients. Implantanchored orthodontic treatment is also an interesting option for other types of skeletal malocclusions, including certain mild class II and class III discrepancies [36,37]. It is not a substitute for osteotomies when major transverse, sagittal, or aesthetic jaw abnormalities exist, however. Skeletal anchorage represents a relatively new and exciting tool for surgeons and orthodontists who are interested in reducing major surgery exposure for some of their patients. The limits of its application require continued research and clinical experience. References [1] Lopez-Galvito G, Wallen TR, Little RM, et al. Anterior open bite malocclusion. Am J Orthod 1985; 87(3):175–85. [2] Proffit WR. Contemporary orthodontics. 2nd edition. St. Louis: Mosby Year Book; 1993. p. 127–9, 180, 236, 274. [3] Profitt WR. Lingual pressure patterns in the transition from tongue thrust to adult swallowing. Arch Oral Biol 1972;17:555–63. [4] Proffit WR, Mason RM. Myofunctional therapy for tongue thrusting. J Am Dent Assoc 1975;90: 403–11. [5] Bell WH, Proffit WR, White RP. Surgical correction of dentofacial deformities. Philadelphia: WB Saunders; 1980. p. 1061, 1070, 1071. [6] Kelley JE, Harvey CR. An assessment of the occlusion of teeth of youths 12-14 years. US Public Health Service (DHEW Pub No HRA 77-1644). Hyattsville (MD): National Center for Health Statistics; 1977. [7] Harris, Johnson MG. Heritability of craniometric and occlusal variables. Am J Orthod Dentofacial Orthop 1991;99:258–65. [8] Harvold EP, Tomer BS, Vargerik K, et al. Primate experiments on oral respiration. Am J Orthod 1981;79:359–72.
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[9] McNamara JA. Influence of respiratory pattern on craniofacial growth. Angle Orthod 1981;51: 260–300. [10] Frost Fonseca RJ, Turvey TA, Hall DJ. Cephalometric diagnosis and surgical-orthodontic correction of apertognathia. Am J Orthod 1980;78(6): 657–9. [11] Iscan HN, Sarisoy L. Comparison of the effects of passive posterior bite-blocks with different construction bites on the craniofacial and dentoalveolar structures. Am J Orthod Dentofacial Orthop 1997; 112:171–7. [12] Dellinger EL. Active vertical corrector treatment. Am J Orthod Dentofacial Orthop 1996;110(2): 145–54. [13] Kim YH. Anterior open bite and its treatment with multiloop edgewise archwire. Angle Orthod 1987; 290–321. [14] Reitan K, Ryghs P. Biomechanical principles and reactions. Orthodontics: current principles and techniques. 2nd edition. Philadelphia: Graber and Vanarsdal. p. 168–9. [15] Harris EF, Butler ML. Patterns of incisor root resorption before and after orthodontic correction in cases with anterior open bites. Am J Orthod 1992; 101(2):112–9. [16] Graber TM. Orthodontics: principles and practice. 3rd edition. Philadelphia: Saunders; 1972 p. 448– 527. [17] Limberg AA. Treatment of open bite by means of plastic osteotomy of the acending ramus of mandible. Dent Cosmos 1925;67:1191. [18] Conn-Stock G. Die chirurgische immediate gulierung der kiefer: speizule die chirurgische behandlung der prognathie. [German] Vjscher Zahnhk 1921;37:320–39. [19] Schuchardt K. Foramen des offenen bisses und ihre operativen behandlungsmo¨glichkeiten. In: Schuchardt K, editor. Fortschrift kiefer und gesichtschirurgie. Stuttgart: Thieme I; 1955. p. 1–25. [20] Bell WH, Mcbride KL. Correction of the long face syndrome by Le Fort I osteotomy. Oral Surg Oral Med Oral Pathol 1977;44:493–520. [21] Umemori M, Sugawara J, Mitani H, et al. Skeletal anchorage for open bite correction. Am J Orthod 1999;115:166–74. [22] Sherwood KH, Burch JG, Thompson WJ. Closing anterior open bites by intrusion of molars using titanium miniplate anchorage. Am J Orthod Dentofacial Orthop 2002;122:593–600. [23] Ervardi N, Keles A, Nanda R. The use of skeletal anchorage in open bite treatment: a cephalometric evaluation. Angle Orthod 2004;74(3):381–90. [24] Devincenzo JP. A new non-surgical approach for treatment of extreme dolicocephalic malocclusions. Part 1. J Clin Orthod 2006;XL(3):161–70. [25] Devincenzo JP. A new non-surgical approach for treatment of extreme dolicocephalic malocclusions. Part 2. J Clin Orthod 2006;XL(4):250–60.
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[26] Daimaruya T, Nagasaka H, Umemori M, et al. The influences of molar intrusion on the inferior alveolar neurovascular bundle and root using the skeletal anchorage system in dogs. Angle Orthod 2001;71(1): 60–70. [27] Burstone CJ, James RB, Legan H, et al. Cephalometrics for orthognathic surgery. J Oral Surg 1978; 36:269–77. [28] Park HS, Kwon TG, Kwon OW. Treatment of open bite with microscrew implant anchorage. Am J Orthod Dentofacial Orthop 2004;126(5):627–36. [29] Park HS, Kwon OW, Sung JH. Nonextraction treatment of an open bite with microscrew implant anchorage. Am J Orthod Dentofacial Orthop 2006; 130(3):391–402. [30] Profitt WR. Equilibrium theory revisited. Angle Orthod 1978;48:175–86. [31] Sugawara J, Baik UB, Umemori M, et al. Treatment and post treatment dentoalveolar changes following intrusion of mandibular molars with application of a skeletal anchorage system for open bite correction. Int J Adult Orthodon Orthognath Surg 2002;17(4): 243–53.
[32] Fritz U, Ehmer A, Diedrich P. Clinical suitability of titanium miniscrews for orthodontic anchorage: preliminary experiences. J Orofac Orthop 2004;65(5): 410–8. [33] Liou EJ, Pai BC, Lin JC. Do miniscrews remain stationary under orthodontic forces? Am J Orthod Dentofacial Orthop 2004;126(1):42–7. [34] Daimaruya T, Takahashi I, Nagasaka H, et al. Effects of maxillary molar intrusion on the nasal floor and tooth root using the skeletal anchorage system in dogs. Angle Orthod 2003;73(2): 158–66. [35] Ari-Demirkaya A, Masry MA, Erverdi N. Angle Orthod 2005;75(5):761–7. [36] Wherbein H, Feifel H, Diedrich P. Palatal implant anchorage reinforcement of posterior teeth: a prospective study. Am J Orthod Dentofacial Orthop 1999;116(6):678–86. [37] Sugawa J, Daimaruya T, Umemori M, et al. Distal movement of mandibular molars in adult patients with the skeletal anchorage system. Am J Orthod Dentofacial Orthop 2004;125(2): 130–8.
Correction of Skeletal Open Bite with Implant Anchored Molar/Bicuspid Intrusion Keith Sherwood, DDSa,b a
Boston University Goldman School of Dental Medicine, 100 East Newton Street, Boston, MA 02118, USA b Private Practice, Oral and Maxillofacial Surgery and Orthodontics, 80 Lindall Avenue, Hunt Medical Building, Danvers, MA 01923, USA
Skeletal open bite is one of the most challenging malocclusions for the orthodontist to accurately diagnose and predictably treat. Orthodontic correction alone, even when initiated at an early age, often leads to long-term relapse. As a result, in an effort to improve stability, combined orthodontics and orthognathic surgery are frequently seen as the treatment of choice or necessity. Recent technical advancements and clinical research in implant-assisted orthodontics has spurred interest in using miniplates and other surgical implant fixtures as anchors to allow minimally invasive correction of skeletal open bite. This article discusses the cause and diagnosis of open bite, historical perspectives on treatment, indications for surgery, use of implant anchors to facilitate correction, and surgeon–orthodontist cooperation. Literature review Etiology of open bite Open bite malocclusion is commonly seen in orthodontic practice. As a result, much of what we know about this bite abnormality comes from the orthodontic literature. It has been shown that orthodontic treatment of open bite is prone to relapse [1]. Most orthodontists consider open bite, especially in adults, to be a significant treatment challenge. In contrast, oral and maxillofacial surgeons see only a fraction of
E-mail address: [email protected]
their orthodontic colleagues’ open bite patients, usually on referral for orthognathic surgery. The scope, risk, and cost of an osteotomy may drive some patients and orthodontists away from this option. Open bite patients are often sent for surgical correction only after orthodontic treatment has been unsuccessful. This results in a skewed perspective on the part of the surgeon regarding the incidence, etiology, and treatment of open bite and may affect postsurgical stability. For practical reasons, the orthodontist often takes the lead in the important pretreatment analysis of the origin of an open bite malocclusion. This diagnostic process is often complex, because growth and development, genetic, and habit factors must be considered. When these issues are not taken into account, unnecessary or inappropriate treatment may be instituted and the risk of orthodontic and surgical relapse increases. As with other types of dentofacial deformities, the participating oral and maxillofacial surgeon should understand the nature and etiology of open bite to communicate with the orthodontist, plan appropriate and progressive surgical treatment, and avoid complications. The nature of the open bite malocclusion can be divided into dental or skeletal, and etiology can be divided into mechanical or genetic factors. Nothing is more critical in treatment planning for the patient who has open bite than determining whether the bite deformity is of dental or skeletal origin. Dental open bite can be treated with orthodontics alone. Skeletal open bite, especially in the adult dentition, usually requires some type of surgical intervention.
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Dental open bite Mechanical factors, such as digital sucking habits, tongue thrust, and tongue posture, have been thought to contribute to dental open bite. By far the most common cause of open bite in the mixed dentition is a digital sucking habit [2]. Dental open bite usually can be managed with habit control appliances, education, and traditional orthodontic treatment. Tongue thrust long has been thought to cause dental anterior open bite because this malocclusion is often seen in patients with reverse or infantile swallowing patterns. Myofunctional therapy was considered for many years to be an integral part of open bite management. Studies have shown, however, that patients with reverse swallow pattern put less force on the anterior teeth than patients with adult swallow [3]. Swallowing is considered a physiologic process, not a learned behavior [2]. The adult swallowing pattern is not present for most children until age 6 and does not appear at all in 10% to 15% of the population [4]. In fact, tongue thrust/swallow seems to be an adaptation to open bite to create a seal between the incisors during swallowing [5]. Although tongue thrust probably does not cause open bite, tongue posturedwherein the tongue continually rests between the incisorsdseems to contribute substantially to the maintenance of dental open bite [2]. Skeletal open bite The accuracy of the diagnosis of skeletal open bite in large population studies is difficult to access. Data from the Public Health Service suggest an incidence in the adolescent US population with mature dentitions of approximately 5%, however, with a much higher proportion among blacks [6]. Current theory supports the concept that vertical jaw proportions are inherited, just like anteroposterior relationships [7]. The primary cause of skeletal open is likely genetic, which is not to suggest that mechanical factors cannot cause open bite. For example, surgical scarring after cleft surgery is thought to restrict growth and can lead to open bite. Nasal obstruction also may play a role in the development of skeletal anterior open bite. The inferior posture of the mandible and tongue seen in severe nasal obstruction probably contributes to an open bite malocclusion, maxillary constriction, and hyperdivergency. The timing and degree of obstruction needed in humans to create a change is
speculative, however, and additional factors may be necessary [8,9]. Diagnosis: skeletal versus dental Discovering the skeletal/dental nature of an open bite is critical to effective treatment. A habitderived dental open bite usually displays maxillary incisor proclination and mandibular incisor uprighting or intrusion. A skeletal open bite usually has a constellation of signs unique to the deformity. The malocclusion is characterized by normal (or even excessive) eruption of anterior teeth, downward rotation of the mandible causing hyperdivergency or long face syndrome, and excessive eruption of posterior teeth [2]. Normal or decreased ascending ramus height, a tipped palatal plane that is higher anteriorly, low position of the mental foramen, decreased posterior cranial base (S-basion), and accentuated curve of the maxillary occlusal plane and/or reverse curve of the mandibular occlusal plane also may be seen [5]. A cephalometric analysis that measures these variables is essential to diagnosis and treatment planning. The vertical dentoalveolar excess in the molar area seen with skeletal open bite is common in the maxilla, less frequently seen in the mandible, and rarely present in both jaws [5,10]. Orthodontic treatment The orthodontic literature concerning the treatment of open bite is voluminous. Because most open bite in the mixed dentition is of dental origin, habit control and standard orthodontic treatment are often effective. Few 10-year posttreatment studies involving large numbers of patients with diagnostically comparable open bites have been published [1]. Treatment of skeletal open bite is one of the most difficult malocclusions for the orthodontist to predictably treat, however, and is commonly plagued by relapse. If started early enough, growth modification treatment designed to restrict molar/bicuspid dentoalveolar vertical development may be effective. The use of high pull head gear or posterior bite blocks is extensively reported [2,11,12]. Altering the occlusal plane by uprighting teeth (multiloop edgewise archwire) also has been reported [13]. Vertical anterior elastics are often used to assist in bite closure by extruding incisors. In true skeletal open bite this orthodontic strategy frequently results in extensive relapse over time, even in younger patients, because of the recoil pull of elastic and principal fibers on incisors [14].
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Research has shown that extrusion of anterior teeth, especially on open bite patients, can lead to significant root shortening, probably because of resorption [15,16]. In older adolescents and adult patients, surgical correction of the skeletal open bite has been accepted by many as the most predictable treatment option.
long-term relapse, no orthodontic forces were placed on anterior teeth. After these articles, other studies and case reports demonstrated the safety and success of the technique [23–26].
Surgical treatment
Indications
Reports on surgical intervention to correct open bite have been recorded for more than 100 years. In 1925, Limberg provided early reports of success with vertical oblique osteotomy of the mandible; however, follow-ups on these patients indicated unsatisfactory relapse [17]. Early maxillary techniques pioneered by Conn-Stock [18], Wassmund, Wunderer, and others were limited to anterior segmental procedures. These procedures are stable but may result in excess incisal show because most open bite is caused by vertical excess in the molar area [2,10]. Later, maxillary posterior segmental intrusion procedures, reported by Schuchardt [19] and others, were stable and effective but have lost favor because of technical difficulty, risk of interruption of blood supply, and lack of flexibility. In the modern age of orthognathic surgery numerous reports and studies have demonstrated success and stability in correction of open bite with Le Fort I osteotomy [10,20].
Patient selection for the procedure begins with a determination of the dental or skeletal nature of the open bite based on the criteria discussed previously. Although usually apparent from a clinical examination, as with orthognathics, this determination should be confirmed and quantified with a cephalometric analysis. The posterior vertical excess can be determined using standards developed by Burstone, Bell, and others with linear measurements from the palatal plane or mandibular plane to the incisal edge of the buccal cusps of the first molars [5,27]. These measurements are vital in treatment planning the ideal location of the implant anchor, judging how much intrusion is needed to close an open bite, and planning the orthodontic set-up. If surgery of any kind is to be considered, the open bite should be caused primarily by posterior vertical maxillary or mandibular excess. A coexisting dental component may be present in some patients, however. In addition to a skeletal open bite, candidates for implant-anchored correction should have a permanent dentition, acceptable or orthodontically correctable incisor–lip relations, and no medical or periodontal health contraindications.
Implant-anchored orthodontic correction of open bite Recently, several case reports and limited studies described a new, less invasive approach to the treatment of skeletal open bite. Titanium miniplates normally used for internal fixation of osteotomies and fractures and other types of implants are being used as skeletal anchors to orthodontically correct open bite. Umemori and colleagues [21] first reported on the use of miniplates as orthodontic anchors in the mandible. These plates were used to orthodontically intrude lower posterior teeth, which allowed the open bite to close by mandibular autorotation. Although impressive corrections of major skeletal open bites were shown, the study was flawed by the simultaneous use of anterior vertical elastics as part of the technique. After this, Sherwood and colleagues [22] reported on the successful use of miniplates inserted on the maxilla to intrude maxillary posterior teeth, where skeletal anterior open bite often originates (Fig. 1). To clarify the actual effect of the miniplate-anchored intrusion and avoid
Materials and methods for implant-assisted open bite correction
Presurgical orthodontics and treatment planning The orthodontist must carefully prepare the patient who has open bite for treatment. Most skeletal open bite malocclusions have a two-step maxillary occlusal plane with the step in the bicuspid/canine area. Placing a continuous archwire in the brackets of a patient who has skeletal open bite leads to incisor extrusion and relapse. To avoid this problem, the orthodontist must treat the arch segmentally, which usually requires separate leveling wires being placed from canine to canine and from the bicuspids to the molars (three independent sections). The orthodontist should advance these wires until heavy rectangular sectional surgical wires are in place. The vector of elastic force from the implant anchor to the molar is buccal and vertical. It is essential that the buccal tipping forces be controlled or the open
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Fig. 1. Schematic of miniplate and screws used for orthodontic anchorage to intrude molars with elastic thread. (From Sherwood KH, Burch JG, Thompson WJ. Closing anterior open bites by intrusion of molars using titanium miniplate anchorage. Am J Orthod Dentofacial Orthop 2002;122:593–600; with permission. Copyright Ó 2002 American Association of Orthodontists.)
bite may be worsened by extrusion of the lingual cusps. This is most efficiently done with a transpalatal appliance (TPA) in the maxilla or a lingual arch in the mandible. The use of a maxillary TPA has an added benefit because tongue pressure on the appliance may contribute to molar intrusion. Placing an acrylic pad on the TPA wire is occasionally necessary for patient comfort. The TPA must be offset (relieved) from the palatal mucosa the distance that the molars are expected to be intruded (Fig. 2). The amount of intrusion necessary is determined by the degree of anterior open bite. Based on wellknown prosthodontic principles, each millimeter of molar intrusion yields a 2- to 3-mm closure of the anterior bite via mandibular autorotation. An 8-mm anterior open bite closure for example requires roughly 3 to 4 mm of intrusion at the first molar area. If the patient cannot tolerate a TPA, a maxillary lingual arch or heavy constricted buccal archwire inserted only into the headgear tubes may suffice. If a lingual arch is used, it should not be in contact with soft tissues or adjacent teeth other than the first molars to be intruded. The miniplates should be inserted after the patient is in orthodontic appliances and 2 to 10 weeks before the predicted start of intrusion mechanics. If a TPA is used, it should be inserted 1 to 2 weeks before beginning molar intrusion. If
extractions are needed to correct for crowding or sagittal discrepancies, timing of miniplate placement must be carefully considered. When bicuspids are being extracted to correct a sagittal discrepancy (ie, maxillary first bicuspids in a dental class II malocclusion), the open bite should be corrected first with sectional mechanics (sectional wires) and implant-assisted intrusion. The bicuspid space can be closed in a level occlusal plane. The implant anchors are doubly useful in this setting to assist in anchorage control for space closure.
Fig. 2. TPA to prevent buccal molar tipping. Note 5-mm offset from the palate.
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The orthodontist may determine that significant crowding requiring bicuspid extractions must be corrected before implant-anchored intrusion begins. In this circumstance the orthodontist often must use a continuous archwire. Once the space created by extraction is closed, intrusion mechanics can be instituted. To avoid inadvertent intrusion of anterior teeth during molar intrusion with a continuous wire, place the miniplate more distally, in line with the second molar. This placement directs the moment of force more posteriorly and limits potential adverse forces on the incisors. Some studies routinely use light anterior elastics during molar intrusion to counteract incisor intrusion with a continuous archwire [21]. Other clinicians have reportedly placed an orthodontic anchor screw between the central incisors for use as a brace against intrusion of the incisors [25]. To emphasize the point, if sectional archwires are used there is no risk of incisor intrusion and treatment is simplified.
Skeletal anchor surgery: surgical planning, preparation, and technique Planning fixture placement Orthodontic intrusion mechanics can be complex so that communication with the orthodontist regarding the ideal location of the implant fixture is important. Generally, a miniplate anchor should be placed adjacent to the tooth or teeth that need the most intrusiondusually the first or second molars in the anterior open bite patient. (Other implant anchors, like miniscrews or cylindrical implants, also can be used and are discussed but are more limited in the potential locations for insertion and access.) The last loop on the plate that emerges transmucosally through the buccal vestibule should be directly in line with the molar or molars that require maximum intrusion. If the first and second molars require equal intrusion, the miniplate loop should emerge between these teeth. When the orthodontist has a continuous wire in place, the miniplate loop should emerge more posteriorly and other precautions against incisor intrusion may be needed. Choosing an implant anchor The technique used to place the implant anchor is largely determined by the fixture type. Miniplates like those shown in Fig. 3A have been used extensively for open bite closure for several reasons. They are versatile fixtures because they can be
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Fig. 3. (A) Miniplates and screws used for skeletal anchorage (Leibinger/Stryker). (From Sherwood KH, Burch JG, Thompson WJ. Closing anterior open bites by intrusion of molars using titanium miniplate anchorage. Am J Orthod Dentofacial Orthop 2002;122:593– 600; with permission. Copyright Ó 2002 American Association of Orthodontists.) (B) Ortho-anchor miniscrews (Rocky Mountain Orthodontics).
placed where anchorage is needed the most. They have the virtue of three-dimensional stability because they are held in place by two or more screws. The miniplate screws are placed well away from tooth roots, avoiding the potential for root injury or interference with root movement. The exposed miniplate loop can be adjusted somewhat after surgery with bending to improve access. Although these are significant advantages, miniplates have the drawback of requiring more surgery to place and remove them than the other options. The miniplate technique is time tested and is described first. Recent case reports have demonstrated success with miniscrew (microscrew) orthodontic anchors (Fig. 3B) using a protocol similar to the miniplates [28,29]. These ‘‘ortho-anchors’’ are inserted into alveolar bone between tooth roots rather than apical to them. Concerns regarding the potential for mobility of these anchors and root injury when used in the maxilla are addressed in the discussion section. An impressive case that shows the use of miniscrew anchors to close an open bite treated and recorded by Dr. Seung Hyun Kyung is presented.
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Surgical technique For the surgeon familiar with placing implants, patient preparation is similar to that used for endosseous implant insertion. Good oral hygiene and avoiding smoking before and after surgery are highly desirable. A presurgical chlorhexidine rinse is appropriate, and most surgeons favor perioperative antibiotics. Miniplates can be placed using local anesthesia with or without intravenous or oral sedation. Local anesthesia is infiltrated into the area where the miniplate will be fixed. Surgery begins with a 1- to 2-cm vestibular incision and a full-thickness mucoperiosteal flap reflected to expose the cortical bone of the maxillary strut or lateral aspect of the mandible. An L-, Y-, or Tshaped plate is selected that affords good contact at its apical base with the best available cortical bone. This is less of an issue in the mandible than the maxilla because of the thin cortex overlying the sinus cavity. The plate should be long enoughdusually 15 mm to 20 mmdto clear the roots apically the distance that the molars will be intruded. The transoral loop must project far enough through the mucobuccal fold for orthodontic accessibility but have enough clearance from the molar band to allow for the expected intrusion. The plate must be contoured to the surface of the bone to ensure passive placement (Fig. 4). Similar to miniplate placement with osteotomy surgery, a curved hemostat snapped on the plate on the loop to be left
exposed is useful to control the plate during sizing, positioning, and fixation. Two to three miniscrews that are 3 to 5 mm in length should be used to fix the plate at its base. Once the plate is secured, one must confirm that the exposed loop is easily accessible for the orthodontist. This loop should clear the buccal gingiva by 2 mm laterally. If not, a plate bender, rongeur, or orthodontic pliar can be used to bend the loop buccally. The soft tissue is closed as would be done for orthognathics. Postoperative antibiotics, chlorhexidine rinse, and narcotic pain medication are appropriate. The patient should be checked 1 week after surgery and again before the orthodontist initiates intrusion mechanics to evaluate healing. After the first 2 weeks the chlorhexidine rinse can be discontinued and the patient is instructed to keep the exposed loop clean with a cotton swab soaked in chlorhexidine or peroxide at bedtime. Orthodontic loading of miniplate The miniplates should be allowed to heal for at least 2 weeks before initiating intrusion mechanics. In our studies at Nova Southeastern University, 8 to 10 weeks of healing was allowed before orthodontically loading the miniplates [22]. Subsequent studies have supported early loading, however [23]. Elastic thread tied firmly from the miniplate to one or both molars is commonly used to deliver the intrusion force and is generally comfortable for the patient. If desired, the orthodontist can use a dontrix gauge to measure the amount of force delivered by the elastic thread, which should be in the range of 100 g to 150 g. Alternatively, precalibrated coil springs can be used to intrude teeth to ensure that physiologic force levels are applied [23]. There may be inadequate space to place coil springs, however, especially in the mandibular buccal vestibule, and the spring may irritate the buccal mucosa or gingiva.
Case presentations Case 1 Fig. 4. Insertion of miniplate on maxillary strut in preparation for molar intrusion. Note plate contouring and three 5-mm self-tapping screws. (From Sherwood KH, Burch JG, Thompson WJ. Closing anterior open bites by intrusion of molars using titanium miniplate anchorage. Am J Orthod Dentofacial Orthop 2002;122:593– 600; with permission. Copyright Ó 2002 American Association of Orthodontists.)
Brief history A 34-year-old male patient presented for a second opinion regarding orthodontic care (Fig. 5A). He was concerned about his open bite, which made it difficult for him to eat and speak normally. Extensive orthodontic treatment in his early adolescence closed the open bite, but the malocclusion relapsed completely during
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Fig. 5. Case 1. (A) Pretreatment open bite. Note hypereruption (vertical excess) in molar area. (B) Preintrusion with segmental orthodontic leveling of open bite (lateral view). Note miniplate loop in buccal vestibule (arrow). (C) Radiograph shows miniplate placement (arrow). (D) Postintrusion of molars with closure of open bite (lateral view). (From Sherwood KH, Burch JG, Thompson WJ. Closing anterior open bites by intrusion of molars using titanium miniplate anchorage. Am J Orthod Dentofacial Orthop 2002;122:593–600; with permission. Copyright Ó 2002 American Association of Orthodontists.)
his late teens and early twenties. He was told by previous clinicians that a maxillary osteotomy would be necessary, which he was unwilling to consider. Examination There was a 9-mm anterior open bite (see Fig. 5A). The molar relationship was class I. The maxillary incisor-lip relationship was normal. A Burstone analysis showed a significant maxillary dentoalveolar vertical excess in the molar area. There was also an accentuated curve of Spee, long lower facial height, and steep mandibular plane angle.
miniscrews each (see Fig. 5B). Orthodontic leveling was performed in the upper in three independent sections, canine to canine and bicuspids to molars bilaterally (see Fig. 5C). Eight weeks after surgery, intrusion mechanics were begun. In this case, a constricted, heavy secondary archwire was used to prevent molar tipping. It was inserted only into the headgear tubes of the maxillary first molars and was lightly ligated to the anterior sectional archwire. Intrusion mechanics were continued for 5.5 months until the open bite was closed (see Fig. 5D).
Case 2 Treatment All teeth were bracketed with orthodontic appliances except for the first molars, which were banded. During orthodontic treatment, Tshaped miniplates were surgically placed on the maxillary struts, positioned between the first and second molars, and secured with two 5-mm
Brief history A 15-year-old male patient was treated unsuccessfully with orthodontics for an anterior open bite (Fig. 6A). Anterior vertical elastic use resulted in significant resorption of anterior tooth roots and, to a lesser extent, maxillary bicuspids (see Fig. 6B).
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Fig. 6. Case 2. (A) Relapsed open bite in adolescent with failed orthodontic treatment. (B) Panorex shows incisor root resorption. (C) Intrusion of first molar, bicuspid segment before extraction of lower second molars. Note step up at untreated second molar. (D) Closure of open bite after extraction of unintruded second molars. (From Sherwood KH, Burch JG. Skeletally based miniplate supported orthodontic anchorage. J Oral Maxillofac Surg 2005;63:282; with permission. Copyright Ó 2005 American Association of Oral and Maxillofacial Surgeons.)
Examination The anterior open bite was 7 mm. A Burstone analysis suggested a skeletal open bite marked by hypereruption in the maxillary and mandibular molar areas. There was significant gingivitis and poor oral hygiene. Treatment To avoid further orthodontic manipulation of the maxillary teeth, expedite treatment, and mitigate further root resorption, a slightly altered treatment plan was required. All active orthodontics would be suspended in the maxillary dentition, and intrusion mechanics would be limited to the lower posterior dentition from the first molars to the bicuspids. The unbanded lower permanent second molars would be extracted after intrusion of the first molars and bicuspids, and the third molars would be allowed to eventually erupt into the second molar space. Miniplates were placed in the mandible adjacent to the first molars. Sectional archwires were inserted into the lower arch, canine to canine and from the first molars to the bicuspids. A lingual arch attached to the first molar bands and offset from the other lower teeth was inserted into the
lower dentition. Maxillary archwires were temporarily removed. After 6 weeks of healing, intrusion mechanics were begun. After only 3 months, there was substantial intrusion of the mandibular first molar/bicuspid segments, as seen by their relation to the untreated second molars (see Fig. 6C). Extraction of the mandibular second molars allowed closure of the open bite by mandibular autorotation (see Fig. 6D).
Case 3 Brief history A 22-year-old female patient presented for treatment of a severe anterior open bite and retrognathia (Fig. 7A). The patient declined orthognathic surgery in favor of attempting correction with implant-anchored intrusion. Examination There was a substantial skeletal anterior open bite caused by vertical excess in the mandibular and maxillary molar areas, a mild class II division I malocclusion, incisor proclination and lip incompetence, a steep mandibular plane angle, and a long
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Fig. 7. Case 3. (A) Pretreatment open bite (lateral view). (B) Miniscrews in palatal midline used to intrude maxillary molars and bicuspids with elastic chain. Note offset TPA used to prevent tipping. (C) Segmental intrusion of molars and bicuspids with elastic thread off mandibular miniscrew (lateral view). (D) Postintrusion of molars and bicuspids using miniscrews shows closure of open bite (lateral view). (From Choi KJ, Choi JH, Ferguson DJ, et al. Facial improvements after molar intrusion with miniscrew anchorage. Journal of Clinical Orthodontics 2007;41(5):269–76; with permission.)
lower facial height. The upper arch was well aligned, but there was mild crowding in the lower arch. Treatment The posterior teeth in the upper and lower arches were passively splinted on the buccal tooth surfaces with FRC (composite orthodontic splint) to allow intrusion of these teeth as a unit. Two orthodontic miniscrew implants were placed in the midpalatal suture area of the maxilla in line with the first molars. These implants were splinted with self-curing resin and then an orthodontic ‘‘S-sheath’’ appliance bonded to the resin/implant complex. This sheath would accept a wire that would be used to intrude the posterior teeth with elastic chain connected to the lingual hooks on the first and second molars (see Fig. 7B). A TPA was used to control lingual tipping. Implants also were inserted into the buccal alveolus between the mandibular second premolar and first molar in the mandible. Elastic thread was connected from the implants to the molar bands to intrude the posterior segments. A lingual arch
was used to control buccal tipping (see Fig. 7C). Intrusion progressed over 4 months until the open bite was closed (see Fig. 7D). The orthodontic implants were removed for patient comfort. After extraction of the upper first bicuspids and lower second bicuspids, traditional orthodontic mechanics were used to correct the class II malocclusion, crowding, and lip incompetence. Discussion In the past, orthodontic intrusion of posterior teeth was thought to be impossible and the options for predictable treatment of skeletal open bite were limited. Implants permit a skeletally based anchorage system that enables this type of tooth movement. Although the success of treatment seems to be well established, questions about stability and safety are still being researched. Stability If implant-anchored intrusion is to be seen as an acceptable treatment alternative to major
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surgery for open bite, the issue of treatment stability must be addressed. It has been observed in orthodontic treatment that intruded teeth are more stable than extruded teeth. Reiten and Ryghs [14] have suggested that this factor may be caused by relaxation of elastic fibers around the tooth root on intrusion. Another perspective on the observed stability of intruded teeth is afforded by Proffit’s ‘‘Equilibrium Theory’’ [30], which speculates that vertical occlusal forces are responsible for maintaining the position of intruded teeth. Although there have not been adequate studies to evaluate relapse, our clinical experience thus far supports the perceived stability of intruded molars for at least 4 years after treatment. Sugawara and colleagues [31] reported some relapse of the intruded molars in radiographic studies. Similar to orthognathic surgery, however, in which a degree of skeletal relapse is often seen, the open bite correction at the dental occlusal level is maintained. The stability of the implant anchor itself also must be considered. If the anchor fails during intrusion, before the open bite is corrected and occlusal stability attained, the intruded teeth may re-erupt. No studies have compared miniplates to miniscrews as skeletal anchors; however, miniplates have been widely used in various settings with great success. Their stability is reinforced by the three-dimensional support of multiple fixation screws and the surface bone contact of the plate. In contrast, miniscrew ortho-anchors have only the threaded portion of a single screw for support. Some studies have shown that a high percentage of miniscrews, especially when placed in the maxilla, may become mobile [32,33]. The implications of this are unclear at this point. To improve stability, some clinicians place the miniscrew in the palatal midline, where bone is dense. However, this location means that intrusion elastics and mechanics are on the palate, which is uncomfortable for the patient because of tongue contact. Miniscrews placed in the dense buccal plate of the mandibular alveolus, through attached gingiva, seem to be relatively stable, although they may also move. Aside from loss of the screw during treatment, the implications of screw mobility are still being studied.
There has been no reported incidence of damage to the nerve from molar root intrusion. It is likely that the tooth root would resorb before penetrating substantially into the compact bone of the nerve canal. In contrast, molar roots may seem to penetrate into the sinus cavity radiographically, which does not seem to cause adverse sequelae for the sinus or tooth root. It is likely that the slow rate of intrusion allows the roots to remain covered by the sinus membrane, which is lifted superiorly, not unlike sinus lift surgery. The potential risk of root injury by orthoanchor miniscrews is still being analyzed. Although these devices have been shown repeatedly to be effective as orthodontic anchors for other types of orthodontic treatment, the risks of scoring cementum or interference with tooth movement by screws lodged between roots has not been evaluated adequately with long-term studies. Molar root resorption As with all orthodontic treatment, root resorption is a risk. Investigators have shown that some mild root resorption may take place with miniplate-anchored intrusion of molars [34,35]; however, it was considered clinically insignificant, did not affect dental health, and seemed to be comparable to root resorption seen with tradition orthodontic treatment. Excess orthodontic force can cause more severe root resorption and may interfere with physiologic tooth movement, however. Proffit [2] stated that 15 g to 25 g of force is needed to orthodontically intrude each tooth depending on the number of roots and tooth size. This finding means that the orthodontist needs to use roughly 100 g of force to intrude two molars and two bicuspids in each quadrant. This figure represents a substantial but not uncommon force level from an orthodontic perspective. Measuring the applied force accurately is technically difficult with elastic thread, however. Practically speaking, the orthodontist often simply ties the thread with a firm but not excessive force based on clinical experience. Alternatively, precalibrated coil springs more accurately deliver a specific force but may be impractical to use (see section on orthodontic loading of miniplate).
Damage to adjacent anatomic structures Daimaruya and colleagues [26,34] looked at the risk of orthodontically intruded posterior teeth impinging on the inferior alveolar nerve in the mandible and the sinus cavity in the maxilla.
Contraindications Although miniplate failures are rare, we have found that patients with poorly controlled periodontal disease are at greater risk for developing
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infections after orthodontic loading. Patients who have poorly controlled diabetes, are on medications that suppress the immune system, or who smoke heavily may not be good candidates for skeletal anchorage. In general, contraindications for miniplate- or miniscrew-anchored orthodontic treatment are similar to those for dental implant therapy and orthodontic treatment. Summary Miniplate- and miniscrew-anchored intrusion of posterior teeth to correct skeletal open bite seems to be a promising alternative to orthognathic surgery for many patients. Implantanchored orthodontic treatment is also an interesting option for other types of skeletal malocclusions, including certain mild class II and class III discrepancies [36,37]. It is not a substitute for osteotomies when major transverse, sagittal, or aesthetic jaw abnormalities exist, however. Skeletal anchorage represents a relatively new and exciting tool for surgeons and orthodontists who are interested in reducing major surgery exposure for some of their patients. The limits of its application require continued research and clinical experience. References [1] Lopez-Galvito G, Wallen TR, Little RM, et al. Anterior open bite malocclusion. Am J Orthod 1985; 87(3):175–85. [2] Proffit WR. Contemporary orthodontics. 2nd edition. St. Louis: Mosby Year Book; 1993. p. 127–9, 180, 236, 274. [3] Profitt WR. Lingual pressure patterns in the transition from tongue thrust to adult swallowing. Arch Oral Biol 1972;17:555–63. [4] Proffit WR, Mason RM. Myofunctional therapy for tongue thrusting. J Am Dent Assoc 1975;90: 403–11. [5] Bell WH, Proffit WR, White RP. Surgical correction of dentofacial deformities. Philadelphia: WB Saunders; 1980. p. 1061, 1070, 1071. [6] Kelley JE, Harvey CR. An assessment of the occlusion of teeth of youths 12-14 years. US Public Health Service (DHEW Pub No HRA 77-1644). Hyattsville (MD): National Center for Health Statistics; 1977. [7] Harris, Johnson MG. Heritability of craniometric and occlusal variables. Am J Orthod Dentofacial Orthop 1991;99:258–65. [8] Harvold EP, Tomer BS, Vargerik K, et al. Primate experiments on oral respiration. Am J Orthod 1981;79:359–72.
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[9] McNamara JA. Influence of respiratory pattern on craniofacial growth. Angle Orthod 1981;51: 260–300. [10] Frost Fonseca RJ, Turvey TA, Hall DJ. Cephalometric diagnosis and surgical-orthodontic correction of apertognathia. Am J Orthod 1980;78(6): 657–9. [11] Iscan HN, Sarisoy L. Comparison of the effects of passive posterior bite-blocks with different construction bites on the craniofacial and dentoalveolar structures. Am J Orthod Dentofacial Orthop 1997; 112:171–7. [12] Dellinger EL. Active vertical corrector treatment. Am J Orthod Dentofacial Orthop 1996;110(2): 145–54. [13] Kim YH. Anterior open bite and its treatment with multiloop edgewise archwire. Angle Orthod 1987; 290–321. [14] Reitan K, Ryghs P. Biomechanical principles and reactions. Orthodontics: current principles and techniques. 2nd edition. Philadelphia: Graber and Vanarsdal. p. 168–9. [15] Harris EF, Butler ML. Patterns of incisor root resorption before and after orthodontic correction in cases with anterior open bites. Am J Orthod 1992; 101(2):112–9. [16] Graber TM. Orthodontics: principles and practice. 3rd edition. Philadelphia: Saunders; 1972 p. 448– 527. [17] Limberg AA. Treatment of open bite by means of plastic osteotomy of the acending ramus of mandible. Dent Cosmos 1925;67:1191. [18] Conn-Stock G. Die chirurgische immediate gulierung der kiefer: speizule die chirurgische behandlung der prognathie. [German] Vjscher Zahnhk 1921;37:320–39. [19] Schuchardt K. Foramen des offenen bisses und ihre operativen behandlungsmo¨glichkeiten. In: Schuchardt K, editor. Fortschrift kiefer und gesichtschirurgie. Stuttgart: Thieme I; 1955. p. 1–25. [20] Bell WH, Mcbride KL. Correction of the long face syndrome by Le Fort I osteotomy. Oral Surg Oral Med Oral Pathol 1977;44:493–520. [21] Umemori M, Sugawara J, Mitani H, et al. Skeletal anchorage for open bite correction. Am J Orthod 1999;115:166–74. [22] Sherwood KH, Burch JG, Thompson WJ. Closing anterior open bites by intrusion of molars using titanium miniplate anchorage. Am J Orthod Dentofacial Orthop 2002;122:593–600. [23] Ervardi N, Keles A, Nanda R. The use of skeletal anchorage in open bite treatment: a cephalometric evaluation. Angle Orthod 2004;74(3):381–90. [24] Devincenzo JP. A new non-surgical approach for treatment of extreme dolicocephalic malocclusions. Part 1. J Clin Orthod 2006;XL(3):161–70. [25] Devincenzo JP. A new non-surgical approach for treatment of extreme dolicocephalic malocclusions. Part 2. J Clin Orthod 2006;XL(4):250–60.
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[26] Daimaruya T, Nagasaka H, Umemori M, et al. The influences of molar intrusion on the inferior alveolar neurovascular bundle and root using the skeletal anchorage system in dogs. Angle Orthod 2001;71(1): 60–70. [27] Burstone CJ, James RB, Legan H, et al. Cephalometrics for orthognathic surgery. J Oral Surg 1978; 36:269–77. [28] Park HS, Kwon TG, Kwon OW. Treatment of open bite with microscrew implant anchorage. Am J Orthod Dentofacial Orthop 2004;126(5):627–36. [29] Park HS, Kwon OW, Sung JH. Nonextraction treatment of an open bite with microscrew implant anchorage. Am J Orthod Dentofacial Orthop 2006; 130(3):391–402. [30] Profitt WR. Equilibrium theory revisited. Angle Orthod 1978;48:175–86. [31] Sugawara J, Baik UB, Umemori M, et al. Treatment and post treatment dentoalveolar changes following intrusion of mandibular molars with application of a skeletal anchorage system for open bite correction. Int J Adult Orthodon Orthognath Surg 2002;17(4): 243–53.
[32] Fritz U, Ehmer A, Diedrich P. Clinical suitability of titanium miniscrews for orthodontic anchorage: preliminary experiences. J Orofac Orthop 2004;65(5): 410–8. [33] Liou EJ, Pai BC, Lin JC. Do miniscrews remain stationary under orthodontic forces? Am J Orthod Dentofacial Orthop 2004;126(1):42–7. [34] Daimaruya T, Takahashi I, Nagasaka H, et al. Effects of maxillary molar intrusion on the nasal floor and tooth root using the skeletal anchorage system in dogs. Angle Orthod 2003;73(2): 158–66. [35] Ari-Demirkaya A, Masry MA, Erverdi N. Angle Orthod 2005;75(5):761–7. [36] Wherbein H, Feifel H, Diedrich P. Palatal implant anchorage reinforcement of posterior teeth: a prospective study. Am J Orthod Dentofacial Orthop 1999;116(6):678–86. [37] Sugawa J, Daimaruya T, Umemori M, et al. Distal movement of mandibular molars in adult patients with the skeletal anchorage system. Am J Orthod Dentofacial Orthop 2004;125(2): 130–8.