Dr. Justin Kuriakose. Postgraduate student, Dept. of Orthodontics and Dentofacial Orthopaedics
Dr. Syamala Reddy Dental College Hospital and Research Centre,
Dr. Prasanth Kamath, MDS. Professor and Head of Department, Department of Orthodontics and Dentofacial Orthopaedics,
Dr. Syamala Reddy Dental College Hospital and Research Centre
Dr. Arun Kumar B.R, MDS. Senior Lecturer, Department of Orthodontics and Dentofacial Orthopaedics,
Dr. Syamala Reddy Dental College Hospital and Research Centre,
Dr. Rajat Scindhia D, MDS. Senior Lecturer, Department of Orthodontics and Dentofacial Orthopaedics,
Dr. Syamala Reddy Dental College Hospital and Research Centre,
Dr. Raghuraj M.B, MDS. Senior Lecturer, Department of Orthodontics and Dentofacial Orthopaedics,
Dr. Syamala Reddy Dental College Hospital and Research Centre,
In the orthodontic literature, there has been very little discussion and much less research on development or treatment of the vertical dimension. The interaction of genetic and environmental factors in the growth and development of the vertical dimension is relevant to clinical practice because it may explain why a particular treatment that alters the environment may be successful in one compliant patient but not in another. The vertical dimension problem is complex and multifactorial. The clinician must be able to recognize its numerous components and understand their interrelationships. Treatment of hyperdivergent open-bite patients must address three-dimensional dentoalveolar and skeletal problems in both jaws. When the severity of vertical deformity is so great that reasonable correction cannot be obtained by growth modification or camouflage, the combination of orthodontics and orthognathic surgery may provide the only viable treatment option.This article offers some diagnostic and treatment-planning suggestions to the orthodontist who deals with long face vertical problems.
KEY WORDS: Long face, open-bite, growth modification, orthognathic surgery.
It was not until Sassouni's description of "skeletal open bite" in the 1960's1 that excessive vertical development of the face began to receive any emphasis in cephalometric diagnosis. With the development of surgical techniques for vertical repositioning the maxilla in the 1970's the term long face syndrome was coined and delineated 2.
Before discussing the abnormal, it is prudent to understand the normal. Two of the most accepted descriptions or publications of vertical facial proportions have been published by Frakas3 and Frakas and Munro4. In these, they describe the ideal face as vertically divided into equal thirds by horizontal lines that approximate the hairline, the bridge of the nose, the ala of the nose, and menton (Fig I).5 Figure 1 also shows that in the ideal vertically proportioned face there is a further division of the lower one third of the face into an upper one third and a lower two third. These divisions of the face can be used by the clinician to help diagnose vertical dimension problems. For example, does a patient have a disproportionately long lower facial height because of vertical maxillary excess or to excessive chin height? By using these accepted proportions as a guide, the patient shown in Figure 2 has an excessive lower anterior facial height. A careful determination of the vertical proportions of the face is the first step in the diagnosis of a vertical dimension problem.
"The primary distinguishing characteristic of the long face pattern is a large total anterior facial height that manifests almost entirely in the elongation of the lower third of the face, leading to disproportions on the facial height and width indices. A major component of the problem nearly always is an inferior rotation of the posterior maxilla. As face height increases and the maxillary palatal plane and posterior teeth are more inferior, the mandible tends to rotate downward and backward. For this reason, the vertical disproportion also affects antero-posterior jaw relationships. That is, a long face patient can be described as skeletal Class I rotated to Class II, or as skeletal Class III rotated to Class I.
Another sign of long face pattern is lip incompetence (resting lip separation greater than 4 mm) .This judgement must be made with soft tissues at rest, not in a smile. Lip separation by itself can be misleading because it is strongly influenced by the length of the lips, particularly the upper lip. Lip incompetence due to excessive face height must not be confused with lip separation due to a short upper lip.
A tendency toward anterior open bite -but only two -thirds of the patients has this type of malocclusion. Deep bite may occur in the others. As the mandible rotates down and back during the development of the long face condition the incisors separates vertically, creating an open bite tendency. If the incisors erupt enough to compensate for the growth pattern, the bite can stay closed or even deep; if they do not, there will be an anterior open bite. Even in patients with open bite, excessive incisor eruption almost always occurs.
A tendency toward mandibular deficiency and Class II malocclusion- but the sagittal relationship can be anything from Class II to mild Class III. It is almost impossible for the patient to have excess face height but no problem in the antero-posterior plane of the space.
A tendency toward lower incisor crowding. As the mandible rotates down and back during the development of the long face condition, the lower incisors tend to become more upright and therefore more crowded.
A tendency toward a narrow maxilla and posterior cross bite, a finding in about half the patients.
Cephalometrically, long face patients nearly always have:
Rotation of the palatal plane down posteriorly. (i.e., the maxilla has descended posteriorly more than anteriorly ). The linear distance from the cranial base to posterior nasal spine usually is increased.
Excessive eruption of maxillary posterior teeth. (i.e., the distance from the palatal plane to the cusps of the upper teeth is increased ).
Increased mandibular plane angle. To a large extent, this is secondary to the maxillary rotation and elongation of the maxillary molars. The mandibular ramus often is short; so many patients have skeletal changes in the mandible as well as in the maxilla. The rotation usually is not related to excessive eruption of mandibular posterior teeth: linear distances from the lower border of the mandible to the cusps of the lower molars nearly always are normal.
Excessive eruption of maxillary and mandibular incisors in partial compensation for the jaw rotation. Even patients who have anterior open bite have this finding, but it is greatest in those with a deep bite.
Fields and colleagues6 have demonstrated that three cephalometric criteria in combination are necessary to quantify the long face pattern.
Increased mandibular plane angle
Increased total anterior face height
Decreased percentage of upper face height
If a patient has all three, he or she can be considered to have a long face deformity with very high confidence.
Because of the variable presence of sagittal and transverse problems in addition to the basic vertical problems and the frequent presence of more crowding in the lower than the upper arch it is particularly important for clinically assessing long face patients to use a systematic diagnostic approach to be sure that no important points have been overlooked.
Long face patients often look as if they were breathing through their mouth, but this may not be the case. Laboratory studies indicate that most children and adults with the long face condition breathe perfectly normally through the nose.7,8 On the other hand, more long face than normal children and adults have an increased oral /nasal ratio. It appears, therefore, that for some patients, mouth breathing may play a role in the long face condition, but it is difficult to indict as a frequent etiological agent.
In a number of muscle weakness syndromes, the facial appearance produces a caricature of the typical long face patient. This observation led to the idea of weak mandibular elevator muscles must cause the long face pattern. If the muscles were weak, biting force would decrease, allowing the posterior teeth to erupt too much and the mandible to rotate downward. Although adult long face patients do have below-normal occlusal forces9, pre-adolescent children who already can be recognized a long face types do not10. The long face patients appear not to gain muscle strength during adolescence, at least in the mandibular elevators, as do normal individuals.
Long face patients with an anterior open bite are very likely to be labeled as having a tongue thrust because they place the tongue tip into the opening, during swallowing and speech. The position of tongue is a necessary physiologic adaptation to the open bite, not its course. When the incisors overlap normally, the tongue can be placed behind them to create the anterior seal necessary for swallowing or articulation of consonants. With an open bite, the tongue must protrude to seal against the lips. Tongue position during swallowing and speech adapts to the position of the teeth, rather than the other way around. The best clinical demonstration is the patient's response to orthognathic surgery to correct open bite, which nearly always eliminates tongue thrust as it corrects the malocclusion. Two points are worth special emphasis with regard to long face patients: (1) Although resting tongue posture can be a significant etiological factor in dentofacial deformity, tongue position during speech and swallow is less important; and (2) The patients in whom tongue posture is most likely to be significant are not the long face types. Instead, certain class III problems are most likely to develop when tongue posture is abnormal.
Previous family studies have made it clear that vertical facial proportions have a strong inherited component. There is a racial difference-long face, open bite problems seem to be proportionately more frequent in blacks than in whites.
For any individual patient, it seems likely that both environmental influences and inherited tendencies have played a role as the long face developed. The environmental factors (largely unknown at present) probably push individuals who are susceptible because of their inherited facial proportions outside the normal range of variation.
Pre-adolescents with growth potential
Children with the long face pattern of growth generally have a maxilla that is rotated down posteriorly and/or a short mandibular ramus, which accounts for the steep mandibular plane and the large discrepancy between posterior and anterior face height. It follows logically from the description that the keys to successful growth modification would be restraining vertical development of growth of maxilla and encouraging antero-posterior mandibular growth, by controlling the eruption of teeth in both the jaws. Unfortunately, vertical facial growth is hard to modify, and it continues through adolescence and into post-adolescent years, so active retention is likely to be necessary for many years. Probably the most sensible use of any of the appliances to control vertical skeletal and dental development is to use them for the minor to moderate problems and intervene in adolescence toward the end of the growth period. That way, the problem is more manageable and treatment and retention are more circumscribed. Whatever the appliance and whenever the treatment started, retention would be critically important until growth was completed in the late teens or early 20s.
There are several possible approaches to the long face pattern of growth in preadolescent children. The two traditional methods for impeding excessive vertical growth have been (1) high-pull headgear to a maxillary fixed appliance or (2) a functional appliance that incorporates bite blocks between the teeth. The headgear applies a direct external force to oppose vertical maxillary development; the functional appliance does this indirectly, by stretching the musculature and other facial soft tissues to create a reactive force, which is then applied to the occlusal surfaces of the teeth via the bite blocks. In the order of their clinical effectiveness they are 11:
High-Pull Headgear to the Molars
High-pull headgear to the molars (figure 3) maintains the vertical position of the maxilla and inhibits eruption of the maxillary posterior teeth.
Force prescription for headgear to restrain maxillary growth:
Force of 500 to 1000gm total (half of that on each side)
Force direction slightly above the occlusal plane(through the center of resistance of the molar teeth)
Force duration at least 12 hours per day, every day, with emphasis on wearing it from early evening (right after dinner) until the next morning.
When comparisons are made using varied vertical and horizontal vectors of force, those with the greatest high-pull vector demonstrated the most vertical control of the upper molars12,13. The biggest problem with high pull headgear is that a purely vertical pull is almost impossible to achieve. Instead, the force has a significant backward component. For some patients with excessive antero-posterior growth, this is desirable. But for the majority of long face patients, the maxilla is not protrusive and only vertical force is needed. Another problem is that it does not control eruption of the lower molars, which can be a problem in some patients.
Lower molar eruption may contribute to the vertical facial changes and outstrip changes made by controlling the upper molar with the headgear.
High-Pull Headgear to a Maxillary Splint
Another headgear approach for children with excessive vertical development is the use of an acrylic occlusal splint to which the facebow is attached14. With a splint, all the teeth are controlled-not just molars. This allows vertical force to be directed against all the maxillary teeth and appears to have a substantial maxillary dental and skeletal effect with good vertical control. Perhaps more important, the head cap can be altered to bring the line of force more anteriorly, closer to the centre of resistance of the maxilla. With headgears to the first molars, if the line of force is too vertical or too far anteriorly, it will pass in front of the centre of resistance of these teeth, and the molars will tip forward. With a splint, the centre of resistance is that of the entire maxilla, and a more vertical pull is possible.
An appliance of this type would be most useful in a child with excessive vertical development of the entire maxillary arch and too much exposure of the maxillary incisors from beneath the lip (i.e., a long face child who does not have anterior open bite). To achieve both skeletal and dental correction, the patient must be compliant throughout what can be a very long treatment period. Unfortunately, the maxillary splint allows mandibular posterior teeth to erupt freely, and if this occurs, there may be neither redirection of growth nor favorable upward and forward rotation of the mandible.
Functional Appliance with Bite Blocks
A more effective alternative is the use of a functional appliance that includes posterior bite blocks. The retraction force of the headgear is replaced by the somewhat lesser "headgear effect" of the functional appliance. The primary purpose of the appliance is to inhibit eruption of posterior teeth and vertical descent of the maxilla. In a mandibular deficient patient, it would be advantageous to advance the mandible when the functional appliance impression was taken, whereas in a patient with a normal-size mandible and a largely vertical problem, the blocks would be positioned without any mandibular advancement. When the mandible is brought forward in the working bite, the stretch of the soft tissues exerts a vertical intrusive force on the posterior teeth. In children with anterior open bites, the anterior teeth are allowed to erupt which reduces the open bite, while in children without open bite, all teeth are held by the bite blocks. Because there is no compensatory posterior eruption, all mandibular growth should be directed more anteriorly.
In the short term, this type of functional appliance treatment is effective in controlling maxillary vertical skeletal and dental growth15. This tends to project mandibular growth anteriorly and helps to close anterior open bites.
High-Pull Headgear to a Functional Appliance with Bite Blocks
High-Pull headgear to a functional appliance with bite blocks, appears theoretically to be the best approach to control the long face pattern of growth16. The extraoral force increases the control of maxillary growth and allows the force to be delivered to the whole maxilla rather than to simply the permanent first molars . The high-pull headgear improves retention of the functional appliance and produces a force direction near the estimated center of resistance of the maxilla. The functional appliance provides the possibility of enhancing mandibular growth while controlling the eruption of the posterior and anterior teeth.
Adolescents with questionable growth potential
Long face patients almost always have an antero-posterior discrepancy-the majority are mandibular deficient and Class II. Often the chief complaint is that the upper incisors are too prominent. A camouflage treatment plan based on retraction of the upper incisors may be suggested if the orthodontist views the problem as Class II primarily, without recognizing the skeletal problem. This conclusion is more easily reached if no anterior open bite is present. Corecting the overjet in that way in long face adolescents is ineffective. Extraction of premolars does nothing to help correct the vertical problem. As the upper incisors are retracted, it is difficult to keep from elongating them further. The nasolabial angle will increase. If class II elastics are used, the mandible likely will rotate further down and back, making the long face worse.
The best plan for adolescents with questionable growth potential follows: attempt growth modification, using headgear to a fixed functional appliance, and counsel the patient and parents that if this conservative approach does not succeed, surgical treatment will be needed. Unlike attempts at camouflage, growth modification treatment does no harm, and it can improve the vertical and sagittal relationships.
Adults with little or no growth potential
For long face patients with no prospect for successful growth modification, there is no real alternative to surgery. A patient who has a genuine long face problem, and who refuses to consider surgical correction, is better left untreated.
Timing of Surgery
As a general rule, early jaw surgery has little inhibitory effect on further growth. For this reason, orthognathic surgery should be delayed until growth is essentially completed.
PLANNING SURGICAL-ORTHODONTIC TREATMENT
Excessive lower facial height is the primary distinguishing clinical characteristic of long face patients. It follows logically that surgery to decrease the vertical separation of the chin and nose is the key to treatment of his problem. A decrease in face height can be accomplished in three ways 17:
LeFort I ostoetomy to superiorly reposition the maxilla. When the maxilla moves up the mandible rotates around the horizontal condylar axis to move up with it, so that the chin moves upward and forward. Indirectly, the maxillary surgery repositions the mandible.
Mandibular ramus ostoetomy to bring the lower jaw forward and upward, which could be accomplished in an open-bite patient. The position of the maxilla would not be altered at all .
Mandibular inferior border ostoetomy to reposition the chin upward and forward. Rarely is this procedure adequate by itself in an adult, but it is a useful adjunct to either of the other two surgical possibilities.
In patients whose face height should be reduced, maxillary surgery is the primary procedure. Ramus osteotomy is recommended only as asecondary procedure, after the maxilla has been repositioned vertically.
The maxilla is the focus of surgical treatment in long face patients for two major reasons.
The maxilla nearly always has excessive vertical development, whereas the mandible may not be involved beyond the indirect rotation that maxillary surgery corrects. Neither normal jaw, lip function, nor good esthetics can be achieved without correcting the maxillary deformity for most patients.
Moving the maxilla up produces a stable surgical correction. Rotating the mandible at the ramus osteotomy site in a counterclockwise direction stretches soft tissues posteriorly and is notoriously unstable.
As with any surgical-orthodontic case, the orthodontic approach is oriented toward positioning the teeth pre-surgically in all three planes of space so their position will facilitate the surgical plan and the teeth will fit appropriately when the surgery is completed. To accomplish this goal, the orthodontist must know the general surgical plan and two things quite specifically:
Whether the maxilla will be kept in one piece or segmented transversely or into anterior and posterior dentoalveolar segments.
Whether the chin and inferior border of the mandible will be repositioned, or whether chin-lip balance is to be achieved by orthodontically repositioning the incisors.
Long face patients rarely have a severely exaggerated curve of Spee in the mandible, even if a deep overbite is present. As a general rule, it is preferable to level the lower arch before surgery. On the other hand, a long face patient with severe anterior open-bite often has an extreme curve of Spee in the upper arch, to the point that vertical steps exist in the arch. Usually the steps are distal to the canines. The more severe the steps, the more advantageous it is to segment the maxilla during the surgery and level the arch by repositioning the dentoalveolar segments. The orthodontist's role is to see that there is enough space between the roots of the involved teeth to allow interdental osteotomies and to level pre-surgically within the segments but not across the osteotomy sites.
The more severe the narrow maxilla and the older the patient, the better the decision to expand surgically. If the patient is young enough that it is possible to open the suture orthopaedically, pre-surgical expansion with a jack-screw appliance is acceptable. Surgically assisted palatal expansion to widen a narrow maxilla in a patient who will be scheduled for LeFort I osteotomy later is not recommended. Neither is there any reason to expand orthodontically if the dentoalveolar segments can be created with LeFort I osteotomy.
Decisions on these points must be made before the orthodontist can set the detailed plan for the pre-surgical and post-surgical orthodontics. Careful joint planning between the surgeon and orthodontist to establish the general approach to treatment and make these critical decisions is essential before any treatment begins. Informed consent requires a discussion of these issues.
Three points are of special interest for long face patients.
A LeFort I osteotomy requires a long incision in the maxillary vestibule and a mandibular inferior border osteotomy requires an incision in the mandibular anterior vestibule. Scar contraction during healing pulls the gingival attachment apically. When the attachment is questionable, the attachment should be augmented by placing gingival grafts in doubtful areas at least 2-3 months before the orgnathic surgery, preferably before the orthodontic treatment begins.
In a patient with an anterior open bite whose plan calls for a segmental maxillary osteotomy with anterior and posterior dentoalveolar segments, it is important not to level the upper arch during the pre-surgical orthodontics. Instead, the orthodontist should level within the segments. It is a mistake to level the upper arch pre-surgically because this produces a potential relapse tendency. The leveling would occur primarily by elongating the upper incisors.
If the maxillary arch will be expanded orthodontically, this should be done at the very beginning of the pre-surgical orthodontics, so the expansion can be maintained as long as possible before the expansion appliance is eventually removed. If expansion will be accomplished surgically, the orthodontist should be careful not to produce any orthodontic expansion. Indeed, in these patients any transverse tooth movement should be contraction rather than expansion of the arch. The surgical segments inevitably will relapse somewhat toward the midline, and teeth tend to move back toward the midline, after dental expansion. There is nothing to be gained but something to lose by combining the two relapse tendencies.
Orthodontic Appliance Considerations
In contemporary surgical-orthodontic treatment, a fixed orthodontic appliance serves three purposes: (1) accomplish the tooth movement needed in preparation for surgery; (2) stabilize the teeth and basal bone at the time of surgery and during healing; and (3) allow the necessary postsurgical tooth movement while retaining the surgical change. The appliance must permit the use of full dimension rectangular arch wires for strength and stability during the stabilization phase of treatment. Any of the variations of the edgewise appliance (including self-ligating brackets), in either 18- or 22-slot, are acceptable for stabilization. A modern lingual appliance can be used for presurgical orthodontics, as can clear aligners, but in both cases brackets on the facial surface of the teeth must be placed for stabilization and finishing. The standard Begg appliance does not provide the control needed for stabilization, and its Tip- Edge variant is less than optimal for stabilization. The brittleness of the ceramic brackets makes them susceptible to fracture, especially when the jaws are being tied together in the operating room so rigid fixation can be placed.
The stabilizing archwires should be placed at least 4 weeks before surgery so that they are passive when the impressions are taken for the surgical splint (usually 1 to 2 weeks before surgery). This ensures that there will be no tooth movement. The stabilizing wires are full dimension edgewise wires (i.e., 1 7 x 25 steel in the l8-slot appliance, 21 x 25TMA or steel in the 22-slot appliance). Hooks as attachments to tie the jaws together while rigid fixation is placed are needed. These can be added at the time of the splint impressions. They can be brass wires soldered to a steel stabilizing wire.
As with all orthognathic surgery patients, the orthodontist remove the splint when the patient is ready for post-surgical orthodontics. The splint should not be removed until the patient is ready to have the stabilizing archwires removed so that finishing orthodontics can be proceed. It is the surgeon's judgement as to when that step is appropriate. With maxillary surgery only, orthodontic treatment probably can resume 3-4 weeks post-surgically. With two-jaw surgery, a longer healing time seems prudent. When the stabilizing wires are removed, they should be replaced at the same appointment with working archwires and light vertical elastics. Light vertical elastics are needed to override proprioceptive impulses from the teeth that otherwise would cause the patient to seek a new position of maximum intercuspation. For long face patients, particularly those who had a maxillary anterior segment osteotomy, torque control of the upper incisors may be needed during the initial finishing. In 18-slot, 17× 25 TMA; in 22- slot, 21× 25 Niti archwire in the upper arch and 016 steel working archwire in the lower arch is recommended. With these archwires, light posterior and anterior box elastics are worn. Elastics should not be discontinued until a solid occlusion is established. Typically, patients wear the light elastics full-time including eating for the first 4 weeks, full-time except for eating for another 4 weeks, and just at night for a third 4-week period.
The trickiest part of post-surgical orthodontics for long face patients is maintaining transverse maxillary expansion, particularly surgical expansion. It takes at least 6 months following surgery for the maxillary dentoalveolar segments to stabilize transversely, so they must be held in their expanded position during the finishing orthodontics using a transpalatal arch18. The transpalatal arch should not be removed during the first postsurgical year. The patients who had transverse expansion must wear the maxillary retainer diligently- fulltime for at least six months.
The orthodontic clinician must make a careful differential diagnosis for each patient who seeks his or her care. The diagnosis must analyze all three components of a malocclusion-facial, dental, and skeletal. Each component must be carefully studied and understood so that (1) the proper questions are asked and (2) the correct diagnostic decisions are made to lead to an effective treatment plan. Growth is clearly a critical period that holds great potential for orthopedic and orthodontic corrections as well as for relapse toward the original condition. There are several possible approaches to the long face pattern of growth in preadolescent children. The orthodontist should be able to recognize the clinical situation and employ skillfully the treatment approaches for the benefit of the individual. Careful planning involving both the orthodontist and the oral maxillofacial surgeon now provides patients with an option that results in both desirable esthetics and good occlusion in adult individuals when carried out with good planning, proper execution and attention to detail.
Sassouni VA: (1969) A classification of skeletal facial types. Am J Orthod 55: 109-123.
Bell WH, Creekmore TD, Alexander RG: (1969) Surgical correction of the long face syndrome. Am J Orthod 71: 40-67.
Frakas LG: (1981) Anthropometry of the Head and Face in Medicine. New York, NY, Elsevier Science.
Frakas LG, Munro Jr: (1987) Anthropometric Facial Proportions in Medicine. Springfield, IL, Charles C. Thomas.
Proffit WR: (2000) Diagnosis and Treatment Planning in Contemporary Orthodontics. St. Louis, Mosby.
Fields HW, Proffit WR, Nixon WL: (1984) Facial pattern differences in long-faced children and adults. Am J Orthod 85: 217-223.
Warren DW, Hinton WA, Seaton D: (1988) Relationship of size of the nasal airway and nasal-oral breathing. Am J Orthod Dentofac Orthop 93: 289-293.
Fields HW, Warren DW, Black K, Phillips C: (1991) Relationships between vertical dentofacial morphology and respiration in adolescents. Am J Orthod Dentofac Orthop 99:147-I54.
Proffit WR, Fields HW, Nixon WL: (1983) Occlusal forces in normal and long face adults. J Dent Res 62: 566-570.
Proffit WR, Fields HW: (1983) Occlusal forces in normal and long face children. J Dent Res 62: 571-574.
Proffit WR, Fields HW: (2007) Contemporary Orthodontics. St. Louis, Mosby.
Ucem TT, Yuksel S: (1998) Effects of different vectors of forces applied by combined headgear. Am J Orthod Dentofac Orthop 113: 316-323.
Baumrind S, Korn EL, Isaacson Rl: (1983) Quantitative analysis of orthodontic and orthopedic effects of maxillary traction. Am J Orthod 84:384-398.
Orton HS, Slattery DA, Orton S: (1992) The treatment of severe 'gummy' Class II division 1 malocclusion using the maxillary intrusion splint. Eur J Orthod 14:216-223.
Weinbach JR, Smith RJ: (1992) Cephalometric changes during treatment with the open bite bionator. Am J Orthod Dentofac Orthop 101:367- 374.
Lagerstrom LO, Nielsen IL, Lee R, Isaacson RJ: (1990) Dental and skeletal contributions to occlusal correction in patients treated with the high-pull headgear-activator combination. Am J Orthod Dentofac Orthop 97 :495-504.
Proffit WR, White RP Jr: (1991) Surgical-Orthodontic Treatment. St. Louis, Mosby.