nonsurgical treatment of a Class II open bite - repelling magnetic posterior splints,

• The nonsurgical treatment of a Class II open bite malocclusion Michael D. Insoft, DMD," Richard A. Hocevar, DMD, b and Charles H. Gibbs, PhD c Gainesvitle, Fla. This case was treated by residents in the postgraduate orthodontic program at the University of Florida under the supervision of Dr. Hocevar. A treatment regimen that he developed to increase the strength and endurance of the masticatory muscles was used. The patient performed prescribed daily clenching and chewing exercise with resilient posterior bite-blocks and wore a hard acrylic posterior biteplane the remainder of the time. It was hoped that this approach would increase the chances of treatment success and stability. (Am J Orthod Dentofac Orthop 1996;110:598-605.) The diagnosis, treatment, and stability of treated open bite malocclusion continues to be a di- lemma, creating much controversy and debate among orthodontists. Many authors agree it is essential to distinguish between dental and skeletal open bites? '2 However, difficulty arises in the numerous inter- mediate cases where the distinction between the two is not clear. 3 Several articles have been published on characteristics associated with skeletal open bites. These include increased lower face height, 1"4-6 short posterior face height, ~'4"6-9 marked antegonial notch- ing, 1'7 increased maxillary molar dentoalveolar height, ~~ and increased gonial and mandibular plane angles.3-8"~l Several factors have been implicated in the cause of anterior open bites, including unfavorable growth patterns, ~2-15 digit sucking hab i ts , 12''4'16-2~ hered- ity, 16'17'21 an enlarged lymphatic tissue. ~8-2~ Several studies have found correlations between orofacial mus- culature and facial structure and indicated rela- tions between weak musculature and long face and anterior open bite pat terns . 23-31 Concrete establish- ments of cause-effect relations is much more elusive, however; these are classic "chicken or egg" questions. The problem in many patients may well be multifactorial, and subsequent problems that appear similar may have different causes. Perhaps because of the variety of theories on cause, a wide variety of treatment philosophies have been advocated for the correction of anterior open bites. Many orthodontists believe that without identification From the University of Florida College of Dentistry. aIn private practice, St. Petersburg, Fla. bRetired. ~Professor, Department of Oral Biology. Reprint requests to: Dr. Charles H. Gibbs, University of Florida, Department of Oral Biology, Box 100424, Gainesville, FL 32610-0424. Copyright �9 1996 by the American Association of Orthodontists. 0889-5406196/$5.00 + 0 8/1/61083 598 and elimination of the etiologic factors, treatment and stability will have a poor prognosis. 3"23"32 This in turn led to the advocation of speech therapy, tongue retraining exercises, and habit appliances as a part of the orthodontic armamentarium. 1'32'33-36 A variety of removable and fixed appliances have been developed to counter digit sucking and tongue habits, for example, obstructive cribs, various acrylic plates, and palatal spikes. 23'32'26 Some orthodontists claim success from orthodontic means alone. Cooke et al. 37 presented a case in which they extracted molars, thus moving teeth out of the "wedge" thereby causing an upward and forward autorotation of the mandible. Kim, 11 on the other hand, believes the key to success lies in the axial inclination of the posterior segments that must be upright in relation to the occlusal plane. He advocates the extraction of second or third molars and distalizing the crowns of the first molars through a technique called multiloop edgewise arch wire. In addition, while others have had little success in using the chincup and headcup, Graber 38 has found that in his practice it renders the best response. High-pull headgear to the maxillary molars is another common approach to open bite treatment. The rationale for this treatment is to intrude the maxillary molars and allow the mandible to autorotate, thereby closing the anterior open bite; some authors may dispute this. 39 Before the 1970s, treatment consisted primarily of dentoalveolar changes or modification of oral habits. While this may be adequate for some dental open bites, it is inadequate for the treatment of skeletal open bites. 37'4~ Several surgical techniques were developed to aid in the correction of anterior open bites, including three-piece sectioning of the maxilla, 42 subapical os- teotomies, 43 and corticotomies. 44 Recently, repelling magnets in posterior bite-blocks have been used to intrude the posterior segments, allow autorotation of the mandible, and thereby close the open bite. 45 Kil-
• American Journal of Orthodontics and Dentofacial Orthopedics insoft, Hocevar, and Gibbs 599 Volume 110, No. 6 Fig, 1. Pretreatment photographs. iaridis et a l . 46 conducted a study of 20 growing pa- tients, age 9 to 16 years, with skeletal anterior open bites. Half of the subjects wore removable repelling magnetic posterior splints, whereas the other half wore removable acrylic posterior bite-blocks of the same thickness. The results showed that the magnets caused a more rapid intrusion of the posterior segments. While magnets have been shown to close open bites in some cases, there may be at least some patients for whom they might not be the best treatment in the long run. Many patients with open bites seem to have hypotrophic or hypotonic masticatory musculature. Relative to average persons, their mouths seem to hang open flaccidly. As anyone who has ever tried to push
• 600 Insoft, Hocevar, and Gibbs American Journal of Orthodontics and Dentofacial Orthopedics December 1996 Table I. Muscle exercise chart Bite Strength and Endurance 2501 r cO 200] === ~'En" 150] (gJ~ =E 1ooj • Strength-lbs. B Repetitions--# E l l . V/ / V / / V / / L / / / V / / g/ / / / / . . / / / / I , " / / /1 t / / I / / / / / / 0 36 72 I 128 170 240 Days into Treatment 280 321 396 Fig, 2. Pretreatment cephalometric tracing. the opposing poles of two magnets together has noted, such magnets produce a "noxious" sort of force that might encourage some open bite patients to let their mouths hang open all the more, avoiding the magnets rather than fighting them, and discourage them from using their masticatory muscles, leading to their further weakening. Weaker muscles would not contribute to the stability of the result; stronger muscles would. Much of the publications on open bites is not supported by scientific evidence, but is instead based on unanecdotal responses. We believe that new ideas and further research into the cause, treatment, and stability of open bites need to be pursued. The treat- ment approach developed by Dr. Hocevar and illustrated in this case, endeavors to correct an anterior open bite with the use of exercises with a posterior biteplane in an attempt to intrude or at least prevent extrusion of the buccal segments during treatment. Unbeknownst to us, similar approaches with similar rationale were being tried elsewhere at about the same time, also with some success , 47-49 but exploration in this direction, including our own, is embryonic. HISTORY This 141/2-year-old postmenarchial white girl had unre- markable medical and dental histories. The patient's chief
• American Journal of Orthodontics and Dentofacial Orthopedics ]nsofl, Hocevar, and Gibbs 601 Volume 110, No. 6 Fig. 3. Posttreatment photographs. complaint was the prominence of her maxillary incisors. No oral habits were reported. Diagnosis This patient had a moderate Skeletal II pattern and a Class II, Division l dental malocclusion (ANB = 6 ~ over- jet = 12 mm). This was accompanied by an open bite pattem, which characteristically included a long lower face height, a steep mandibular plane angle (SN-MPA = 46 ~ and a 3 mm open bite. The maxillary incisor inclination was a 114 ~ to SN, and at 31~ mm to NA, and the mandibular incisor was at 82 ~ to MP, 23~ mm to NB, and 1 mm to NPg. The molars were 1/2 cusp Class II and the canines were 3/4 cusp Class II. The maxillary arch had 2 mm of spacing and the
• 602 Insoft, Hocevar, and Gibbs American Journal of Orthodontics and Dentofacial Orthopedics December 1996 J Fig. 4, Posttreatment cephalometric tracing. mandibular arch had 4 ram. The maxillary midline was correct and the mandibular midline was 2 mm to the right. She had an excessively "gummy smile," apparently because of both the vertical excess and the horizontal prominence of the maxillary incisor segment (Figs. 1 and 2). Etiologic Factor The cause appeared to be primarily genetic. The growth pattern of her facial skeleton was poor, and her orofacial musculature weak, but no specific causative factor could be identified. General Treatment Plan The treatment of choice was an orthognathic surgery option, which the mother and the patient adamantly declined. The major concern in formulating her treatment plan was that any conventional orthodontic approach for reduction of the large overjet would entail considerable risk of exacerbating some or all aspects of the vertical pattern. The patient agreed to undertake masticatory muscle exercises with posterior biteplanes, in an effort to minimize that risk. After this, maxillary first premolars were to be extracted and the overjet reduced. A muscle strengthening and endurance conditioning program was developed by Dr. Richard Hocevar in consultation with exercise physiologists at the University of Florida. To increase the strength of the major closing muscles of the mandible, a morning and evening regimen was imple- mented. The patient clenched on custom fit posterior biteplanes made of soft resilient mouthguard material, approximately 4 mm thick. A posterior biteplane of hard acrylic was wom at all times when not exercising. Every morning, one set of 12 repetitions of maximum force clenching was to be completed. Each repetition should take 10 seconds: 3 seconds smoothly increasing intensity, 4 seconds holding maximum intensity, 3 seconds smoothly decreasing intensity, for a total time of 2 minutes. Every evening, she was to clench at maximum force for as long as possible, up to 1 minute. Endurance was to be increased by chewing with her soft biteplane every evening as much as she could, up to 2 to 3 hours with medium intensity. Chewing should consist of a mixture of medium clenches, lasting from 2 to 15 seconds with rests of similar length between clenches, and simply chewing as one would chew gum. She was to begin with about 10 minutes of this exercise and work up to 2 to 3 hours as she w~s able. In theory, this type of training would strengthen the muscles of mastication and intrude the poste- rior teeth, or at least prevent their extrusion during treatment. Treatment Progress Progress was monitored by periodic testing of maximum bite force and endurance with strain gauges and transducers, incorporated in custom fit acrylic bite-blocks, linked to a computer and plotter. 5~ First, the patient would clench as hard as she could to establish her maximum biting force. Then, watching the plotter, she would clench with 80% of maxi- mum force for 2 seconds, followed by 2 seconds of relax- ation, repeated continuously for as many repetitions as she could, until she could no longer attain the 80% force level. Treatment was initiated with 13 months of posterior biteplane exercise. Maximum bite force increased from 126 to 196 pounds after 8 months of exercise and was maintained at this level through 13 months. In addition, bite endurance increased from 30 to 208 repetitions for an astounding l 1-fold increase in pound-reps. The patient accomplished remarkable development of her masticatory musculature that was impressive in appearance and to palpation. Some bite closure was noted during this period (Table I). After 13 months, upper first premolars were extracted and a 0.022-inch Beddtiot appliance (American Orthodontics Co.) s1"52 was placed with 0.014 Australian stainless steel arch wires. Two months into treatment, use of the hard acrylic posterior biteplane was reinstituted, and light Class II elastics were started. The arch wire size was increased to 0.018 by the fifth month of treatment, and a torquing auxiliary was used in the maxillary arch. Slight bit opening was placed in the upper wire 2 months later, and a J-hook anterior high-pull headgear was started. The posterior biteplane was discontin- ued after 1 year and the torquing auxiliary after 10 months. After 2 years of treatment with the Beddtiot appliance, the headgear was discontinued and 0.021 x 0.016 stainless steel ribbon arches ~3 were placed in both arches. The case was completed in the ribbon arches and the braces were removed after 26 months of Beddtiot appliance treatment and 39 months of overall treatment. RESULTS The patient was finished to a functional and esthetic Class II molar and Class I canine occlusion (Figs. 3 and 4). The ANB angle was reduced 1 ~ to 5 ~ and the mandibular plane remained at 46 ~ Overjet and overbite were ideal, and facial appearance was greatly improved. The maxil lary lip may have been retracted
• American Journal of Orthodontics and Dentofacial Orthopedics lnSOj~, Hocevar, and Gibbs Volume 110, No. 6 Fig. 5. Postretention photographs. slightly more than might have been ideal: this was necessitated by reduction of the large overjet. The maxillary incisors were retroclined and retracted 10~ mm. The mandibular incisors were tipped forward 4~ mm and there was concern about the lower incisor attached gingiva (Table II). RETENTION A maxillary wrap-around and bonded mandibular canine-to-canine retainers were delivered at the debond appointment. The maxillary retainer was worn 24 hours a day for the first year and reduced to nighttime wear in the second year (Fig. 5).
• 604 Insoft, Hocevar, and Gibbs American Journal of Orthodontics and Dentofacial Orthopedics December 1996 Fig. 6, Pretreatment to posttreatment superimpositions on cranial base. Fig. 7. Pretreatment to posttreatment superimpositions of maxilla on maxilla and mandible on mandible. Table Ih Cephalometric measurements Measurement I Norms 7-24-86 I 4-25-91 I 6-30-93 SNA 82 81 80 80 SNB 80 75 75 76 ANB 2 6 5 4 SN-MPA 36 46 46 45 IMPA 91 82 86 86 1-NPo (ram) 4 1 3 4 1-NA 22 31 21 23 1-NA (mm) 3 9 2 3 1 -NB 25 23 27 25 1-NB (nun) 4 5 7 6 1-1 angle 129 119 128 127 FINAL EVALUATION Overall, the treatment was successful. Surgery might have been a more ideal treatment plan, but the patient was not interested in this option. As of her last visit, which was 21/2 years after debond, her occlusion and gingival health were stable. She had not been wearing her maxillary retainer for the last 6 months. At this time, all cephalometric measures were well within measurement error of the posttreatment results (Figs. 6 and 7). COMMENTS We could not realistically expect to effect a significant change in the patient's growth pattern, as her growth was virtually completed by the time of the initial records. What we did hope for was a change in her orofacial structure and function of the sort that can be accomplished in other areas of the body by intensive exercise, as exemplified in the extreme by competitive body builders. We did not hope to alleviate the vertical problems significantly, but did hope to minimize the risk of worsening them. We further hoped that once the patient had developed her masticatory musculature through the formal exercise program, she would use and thus maintain her increased capacity in normal function. It may be that some patients might benefit from the use of intrusive magnets, in addition to an exercise program like that Used in this case. We wanted to test the effectiveness of exercise without confusing the question with multiple treatments at this stage. Furthermore, we thought that magnets might provoke muscle
• American Journal of Orthodontics and Oentofacial Orthopedics InsoJ~, Hocevar, and Gibbs 605 Volume l l 0 , No. 6 relaxation rather than contraction, and thus interfere with the exercise objectives in some patients. So far, our objectives seem to have been fulfilled. The treatment went as well as we had hoped, and the result has held up well for 21/2 years, 6 months after discontinuance of maxillary retention. The obvious increase in the development and tone of the masticatory musculature has remained, despite discontinuance of the formal exercise program. 
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