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Cephalometric treatment planning for superior repositioning of the maxilla and concomitant mandibular advancement
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J. max.-fac. Surg. 10 (1982)
J. max.-fac. Surg. 10 (1982) 42-49 © 1982 Georg Thierne Verlag Stuttgart • New York
Cephalometric Treatment Planning for Superior Repositioning of the Maxilla and Concomitant Mandibular Advancement William H. Bell, Douglas P. Sinn, Richard A. Finn
Summary Cephalometric prediction tracings are used in concert with biomechanical modelling to simulate jaw movements and soft tissue profile changes associated with the surgical correction of vertical maxillary excess and absolute mandibular deficiency. Cephalometric prediction studies are used to identify positional changes which have a known propensity to relapse or be stable and when used in concert with biomechanical modelling, serve as an adjunct in designing surgical procedures to achieve skeletal stability, good facial profile aesthetics, biomechanical efficiency and long-term skeletal stability.
Key-Words Dept. of Surgery, Division of Oral Surgery, Center for Correction of Dentofacial Deformities, (Director: R. V. Walker, D.D.S.) University of Texas Health Science Center, Dallas USA
Cephalometric Prediction Studies - Cephalometric Planning - Biomechanical Modelling - Vertical Maxillary Excess - Absolute Mandibular Deficiency - Le Fort I Osteotomy - Mandibular Advancement
Introduction Cephalometric prediction tracings are used in concert with biomechanical modelling to simulate jaw movements and soft tissue profile changes associated with the correction of dentofacial deformities. Biomechanical modelling is a practical method of determining whether or not the planned surgical changes are biomechanically efficient. Based upon biomechanical modelling principles, (Alexander 1968, Finn et al 1980, Throckmorton et al 1980) cephalometric prediction studies are used to identify positional changes which have a known propensity to relapse or be stable (Bell et al 1977, and Finn et al 1980). Additionally, they are used to educate the patient to the planned profile change. Finally, they serve as an adjunct in designing surgical procedures to achieve skeletal stability, good facial profile aesthetics, and biomechanical efficiency. Patients who present with vertical maxillary excess and absolute mandibular deficiency frequently require simultaneous superior repositioning of the maxilla and mandibular advancement to correct their facial aesthetic, functional and dento-skeletal problems. Planning to achieve optimal aesthetics, function and long term stability necessitates an accurate simulation of the positional changes of the maxilla and mandible to determine the amount and direction of movement required. Superior repositioning of the maxilla and simultaneous mandibular advancement is easily and predictably simulated with acetate overlay cephalometric prediction tracings. This paper will describe how cephalometric prediction studies in concert with biomechanical modelling, can be used to plan treatment for optimum aesthetics, biomechanical efficiency and long-term skeletal stability.
Method A careful and systematic clinical examination of the frontal and profile facial aesthetics is made with the patient standing, his head in adjusted natural head position and his lips in repose. The distance from the tip of the lower border of the upper lip to the incisal edge of the maxillary incisors is measured on the right and left sides.
Cephalometric Tracing A lateral head cephalogram is also made with the patient standing and his head postured in adjusted natural head position (Moorrees and Kean 1958). The radiograph, which should clearly delineate both the soft tissues and dento-skeletal structures, is exposed with the mandible in centric relation and the lip muscles relaxed. All of the maxillary and mandibular teeth, bony landmarks, and enveloping soft tissues are then traced on a sheet of acetate tracing paper (Fig. la). By using the posturally oriented lateral cephalogram, a natural horizontal reference line is drawn onto the acetate tracing paper. A vertical reference line is then drawn through subnasale, (McBride and Bell 1980, Scheideman et al 1980) perpendicular to the natural horizontal reference line (Fig. i a). A horizontal reference line is next drawn perpendicular to the natural vertical reference line at the level of the incisal edge of the maxillary central incisors (Fig. i b). Another line is drawn parallel to the first horizontal reference line. The distance between these two horizontal lines is the millimeter change calculated to correct the vertical dysplasia manifest in the anterior maxilla (Fig. lb). Based upon a correlative study of the patient and his lateral head cephalogram, the anterior maxilla is superiorly repositioned the amount necessary to expose approximately 2 mm of the maxillary incisor teeth. If and when there is a disparity between the clinical and cephalometric lip-to-tooth measurement, the clinical examination and/or cephalogram are repeated.
Construction of Templates A template of the mandible is made by tracing all the mandibular teeth, bony landmarks and enveloping soft tissues with a coloured pencil on a smaller piece of acetate tracing paper. A similar acetate overlay template of the maxilla is constructed by tracing in all the maxillary teeth and osseous landmarks. When the maxillary occlusal plane is to be levelled surgically, the planned segmentalization is simulated by cutting the maxillary acetate template in the appropriate "interdental space". A careful analysis of articulated study casts, periapical radiographs of the potential
Cephalometric Treatment Planningfor Superior Repositioning of the Maxilla
J. max.-fac. Surg. 10 (1982)
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Fig. 1 a Cephalometric tracing of all the maxillary and mandibular teeth, maxilla, mandible and enveloping soft tissues; horizontal reference line is made parallel to natural horizontal; vertical reference line, which is perpendicular to natural horizontal reference line, intersects with subnasale.
Fig. 1
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Fig. 1 b Horizontal reference line is made at the level of the incisal edge of the maxillary central incisors; the distance between this line and another superior and parallel horizontal reference line is the mm change calculated to correct the vertical dysplasia manifest in the anterior maxilla.
Fig. 1 c Maxillary and mandibular acetate overlay templates in simulated Class I canine and molar occlusion and desired overjetoverbite relationship.
Technique of Cephalometric Planning
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Fig. 1 d Mandibular portion of the maxillomandibular templates superimposed on the anatomical landmarks of the mandible of the original cephalogram.
Fig. 1 e Acetate overlay templates rotated to the planned vertical position (indicated by superior horizontal reference line); pencil point at summit of the condyles serves as the axis of rotation.
Fig. 1 f New cephalometric prediction tracing traced onto another sheet of overlayed acetate tracing paper.
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J. max.-fac. Surg. 10 (1982)
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l
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Fig, 1 g Evaluation of anterior-posterior aesthetic change with the aid of natural vertical reference line.
Fig. 1 h Maxillo-mandibulartemplates repositioned anteriorly to decrease the anterior-posterior dimension of the nose and increase the prominence of the upper lip.
interdental osteotomy sites and model surgery may all be necessary to determine the feasibility of the planned maxillary osteotomies and to finalize the details of the occlusal simulation.
Simulation of Class I Occlusion The maxillary and mandibular templates are next moved into a simulated Class I canine occlusion with the desired overjet-overbite relationship, and attached to one another with a small piece of clear tape (Fig. 1 c). This manoeuvre is completed independently of the original tracing. The mandibular portion of the attached maxillo-mandibular acetate overlay templates is then superimposed on the anatomical landmarks of the mandible of the original cephalogram (Fig. ld). With the point of a pencil positioned at the summit of the condyle to serve as the axis of rotation, the acetate overlay templates are rotated to the planned vertical position indicated by the previously drawn superior horizontal reference line (Fig. le). Based upon the anteroposterior positional change of the maxillo-mandibular relationship, a new prediction tracing is drawn onto another sheet of overlayed acetate tracing paper (Fig. lf). This is easily accomplished with the soft tissue contours except for the lower lip. The surgeon must use his artistic skills to trace in a lower lip which is based on the new anteroposterior and vertical position of the incisor teeth, attainment of lip competence and concomitant genioplasty.
Evaluation of the Aesthetic Result (Fig. I f) The natural vertical reference line is an adjunct to evaluating the new soft tissue profile. The vermillion border of the upper lip should lie approximately on the line; the chin 2±4 mm posterior to the line. These measurements which are based upon a study of normal adults (Scheideman et al, 1980) afford the clinician considerable latitude in planning treatment. Individual preferences, sex and racial considerations, are all relevant and considered before the final plan of
Fig.
1 i Final cephalometric prediction tracing based upon projected soft tissue changes; anterior maxilla raised 5 mm and advanced 8 mm; posterior maxilla raised 10 mm.
treatment is formalized. Based upon an evaluation of the results of this preliminary study of profile aesthetics by means of the cephalometric prediction study, the maxillary and mandibular templates may be adjusted to achieve a more aesthetic result - indeed the result might be considered subjectively to be aesthetic without the need for additional positional adjustment of the templates. All too frequently, however, it is not so much that absolute maxillary advancement is necessary, but instead the decision to
advance the mandible centres around the inadvisability of posterior movement of the maxilla to correct the Class II occlusal relationship. This is a central treatment planning consideration, for such movements are all too frequently calculated to produce an unaesthetic retrusive upper lip and increase the anterior-posterior prominence of the nose. These unaesthetic results must be avoided by programming total maxillary osteotomy to superiorly reposition the maxilla, with concomitant mandibular advancement surgery. Anterior-Posterior Repositioning of the Maxilla When the cephalometric prediction study, in concert with clinical analysis, indicates that the resultant maxillo-mandibular relationship will produce a facial profile with a retrusive upper lip and flattening in the paranasal and/or canine fossa areas, the maxilla is moved anteriorly to decrease the antero-posterior dimension of the nose and increase the prominence of the upper lip (Bell and Jacobs, 1980). The maxillary template is positioned superiorly, as well as anteriorly, the amount calculated to achieve aesthetic balance between the nose and upper lip and to achieve 2 mm of maxillary incisor exposure with the upper lip in repose. The surgeon's artistic sense of good facial aesthetics, rather than cephalometric norms, serves as the principle guideline to planning the amount of forward repositioning of the anterior portion of maxilla. Surgical movement of the anterior maxilla must also be planned to
Cephalometric Treatment Planning for Superior Repositioning of the Maxilla achieve a satisfactory tooth-to-bone relationship and inclination of the anterior teeth. The maxillary template is repositioned anteriorly the distance calculated to produce the desired aesthetic change in the upper lip. The knowledge that there is an approximate 0.6 to 1.0 ratio of movement of the upper lip to advancement of the underlying dento-osseous structures, serves as the basis for registering a new soft tissue profile on another piece of tracing paper (Fig. I h) (Dann et al 1976 and Freihofer 1976). If the results of the cephalometric prediction study are such that the resultant maxillo-mandibular relationship will produce a facial profile with an acute nasolabial angle and relatively prominent upper lip, the maxilla is repositioned superiorly and posteriorly to reduce the prominence of the upper lip and achieve an aesthetic lip-to-tooth relationship (2 mm of tooth exposure). Again, the knowledge that there is an approximate 0.7 to 1.0 ratio of movement of the upper lip to retraction of the underlying dento-osseous structures, serves as the basis for registering a new softtissue profile on another piece of acetate tracing paper (Bell and Dann, 1973) (Fig. 1, I). When anterior-posterior movement of the maxilla, in addition to superior repositioning is indicated, the mandibular movement necessary to achieve maxillo-mandibular harmony is simulated with an acetate overlay template of the mandible and its enveloping soft tissues. Trial repositioning of the maxillary and mandibular acetate overlay templates is made until satisfactory overjet overbite and interincisal relationships are achieved which are consistent with the planned aesthetic objectives. Based upon the projected soft tissue changes, the prediction tracing is completed by drawing a new upper and lower lip. With the "new" profile prediction completed and the maxillo-mandibular relationship established, genioplasty or rhinoplasty can be simulated on still another smaller piece of acetate tracing paper. Figure 1, I demonstrates the final cephalometric prediction tracing and the planned positional changes in the anterior and posterior maxilla. The anterior maxilla will be raised 5 mm and advanced 8 ram; the posterior maxilla will be raised 10 mm. There are important reasons for each planned movement. The positional change of the anterior maxilla is based upon the amount of tooth exposure and the retrusive appearance of the upper lip.
Repositioning the Posterior Portion of Maxilla: The positional change of the posterior maxilla is based upon the need to achieve maximal stability, level the maxillary occlusal plane (i. e. open bite) and improve the posterior smile line. The results of previous studies (Brammer et al 1980, Finn et al 1980) which have evaluated the relationship between maxillary intrusion and mandibular stability, serve as the basis for increasing stability by superior repositioning of the posterior maxilla. These investigations indicate that as the posterior maxilla is intruded, there is less posterior mandibular relapse. Based upon the results of these studies, we program treatment to intrude the posterior maxilla not only to level the maxillary occlusal plane and improve the posterior smile line, but also to increase the autorotational advancement of the mandible and biomechanical efficiency of the masticatory system. Such movements decrease the amount of absolute mandibular advancement and muscle stretching. Excessive posterior
J. max.-fac. Surg. 10 (1982)
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gingival exposure gives further support to superior repositioning of the posterior maxilla. The amount of posterior gingival exposure, however, is not the absolute determinant of the magnitude of superior movement of the posterior maxilla - it is only a relative consideration. Although suprahyoid myotomies (Steinhiiuser 1973) have not been associated with improvement of skeletal stability following mandibular advancement (Brammer et al 1980, Schendel and Epker 1980, Wessberg et al 1980) skeletal fixation devices have been proposed empirically (Poulton and Ware 1973, McNeil and Hooley 1973), and later demonstrated more conclusively (Schendel and Epker 1980, Berman and Berman 1978). Skeletal fixation is effectively accomplished by either one of two methods or a combination of both: sternomandibular brace or extra cranial suspension device. Both of these techniques have as a common denominator, maintenance of the mandible in its new position while neuromuscular alterations occur. The infra- and suprahyoid muscles are primarily affected by this means whereas the mandibular adductor muscles are more directly affected by biomechanical changes after surgery. Structural muscle adaptation to an altered environment has repeatedly been demonstrated (Goldspink et al 1974, Tabary et al 1972, Gonyea 1978, McNamara 1977). Many of these changes were accomplished in as little as 2 weeks. Thus preoperative exercising such as neck hyperextension and utilization of a cervical collar, may very well initiate these adaptive changes. Furthermore, postoperative skeletal stabilization by craniomandibular wiring techniques and/or continued use of the cervical collar, will allow for additional muscle adaptation. Decrease in passive muscle tension (Blix 1895, Bahler et al 1968, Carlson 1957), heretofore overlooked, may be favourably altered by these clinical methods of "overstretching". Biomechanical modelling has recently given us new insight into functional relationships associated with skeletal relapse following jaw surgery. The basic premise of the system favouring skeletal stability is to decrease the lever arm of the bite point and increase the adductor muscle lever arm (Throckmorton et al 1980, Finn et al, 1980, Brammer et al 1980). Observation of changes in the bite point and muscle moment arms, is easily and quickly accomplished when performing the cephalometric prediction tracings. Superior and posterior movements of the maxilla will increase mechanical efficiency by increasing the muscle moment arms after mandibular autorotation and decreasing the bite point moment arm following maxillary intrusion. Superior repositioning of the posterior maxilla consistently improves the biomechanical efficiency of the masticatory apparatus. Prudent observation of changes in bite point and muscle moment arms during cephalometric prediction studies, will provide an additional guide during treatment planning. Decreasing posterior maxillary height improves mechanical efficiency (Throckmorton et al 1980), increases autorotational advancement of the mandible, decreases absolute mandibular advancement, and increases skeletal stability (Brammer et al 1980). Although there are practical limitations to the magnitude of posterior maxillary intrusion, the complementary effect of this surgical manoeuvre on biomechanical efficiency should be appreciated and integrally incorporated into treatment planning decisions to possibly enhance long term skeletal stability and improved masticatory function.
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J. max.-fac. Surg. 10 (1982)
Case reports Case Report 1 (Fig. 2) T. W., a girl aged 17, and her parents were concerned about both her facial appearance (Fig. 2a) and poor dental occlusion (Fig. 2d). She was seen in consultation with an orthodontist for treatment of her severe anterior open bite, for which she had received orthodontic treatment beginning at age 15. A retrospective study of her preorthodontic clinical, cephalometric and occlusal records revealed a severe open bite and absolute mandibular deficiency. Maxillary and mandibular 1st molars had been extracted to facilitate partial presurgical orthodontic levelling and alignment of the maxillary and mandibular arches.
Problem List Aesthetics (Fig. 2 a): Frontal examination revealed excessive exposure of teeth and gingiva in repose (5 mm) and when smiling, lip incompetence as indicated by the 9 mm interlabial gap at rest, and flattened paranasal and canine fossa areas. Profile examination revealed an obtuse nasolabial angle, retrusive upper lip, retropositioned mandible, and long face.
Cephalometric Analysis (Fig. 2 c) The patient had a high mandibular plane angle, Sn-GoGn = 50°; excessive lower anterior facial height; anterior open bite deformity; and retropositioned mandible 24 mm posterior to natural vertical reference line.
Occtusal Analysis (Fig. 2 d) Occlusal study revealed a Class II canine and molar relationship with a 9 mm overjet, and a 6 mm open bite extending from the 1st premolar region of one side to the contralateral premolar region. There was a small reverse curve of the mandibular occlusal plane and moderate curvature of the maxillary occlusal plane. The maxillary and mandibular teeth were adequately aligned after extraction of maxillary and mandibular 1st premolars and orthodontic treatment.
Treatment Plan Plan of Surgery (Fig. 2 f) 1. Reposition the maxilla superiorly (anterior - 4 ram; posterior 10 ram) and anteriorly (8 ram) by LeFort I osteotomy to: a. correct the anteroposterior maxillary deficiency b. decrease lower anterior facial height c. partially close anterior open bite d. improve the lip-to-tooth relationship e. reduce amount of anterior and posterior gingival exposure when smiling. f. facilitate autorotational advancement of mandible g. level maxillary occlusal plane 2. Bilateral sagittal split ramus osteotomies of vertical rami to advance the mandible into Class I canine and molar relationship. 3. Cervical collar would be worn continuously two weeks before and at least 6 months after surgery to hyperextend suprahyoid muscles.
Active Treatment and Follow-up The maxillary and mandibular surgical procedures were accomplished simultaneously. (Fig. 2 f) The segmentalized maxilla was advanced 7 ram. The anterior portion of the maxilla was raised 4 mm and the posterior portion 10 ram. Intermaxillary fixation was maintained for eight weeks. Light night-time training elastics in the canine - 1st premolar area, were used for six weeks after release from intermaxillary fixation. Final levelling and interdigitation of the teeth was accomplished by four months of post-surgical orthodontic treatment.* The patient wore a cervical collar continuously day and night after surgery for 6 months to hyperextend the suprahyoid muscles and decrease relapse. To date, over a 28 month period of follow up, there has been minimal skeletal relapse. (Fig. 2 c) The use of light night-time elastics and orthodontic treatment compensated for the relatively small downward and backward movement of the mandible (2 mm), and maintained closure of the open bite and inrerdigitation of the teeth. * Orthodontic treatment by Dr. Richard Ramming, Wichita Falls, Texas.
W . H . Bell et al.
Case Report 2 Patient M. M. was a 25-year-old female with vertical maxillary excess, a relatively retrusive upper lip, retropositioned mandible, and a 55 ° mandibular plane angle (Fig. 3 a). Although her teeth were wellaligned, her Class II malocclusion remained uncorrected after three years of orthodontic treatment during adolescence.
Surgical Treatment Her maxilla was superiorly and anteriorly repositioned, by LeFort I osteotomy without bone grafting. Her mandible was concomitantly advanced to a Class I occlusion by sagittal split ramus osteotomies and her chin augmented by advancement genioplasty. Mandibular movement was primarily autorotational as a consequence of superior movement of the maxilla. The patient wore a soft cervical collar for approximately three months after surgery. During the followup period, the maxilla settled upward and forward slightly (Fig. 3 c). Mandibular stability has been excellent over a postoperative followup period of 4 years. The bite has remained closed and a Class I occlusion preserved with only minor dental adjustments.
Case R e p o r t 3 Patient E. S., a 20-year-old woman manifested an open bite deformity with a 59.1 degree mandibular plane angle (Fig. 4a, c, d). Clinical, cephalometric and radiographic studies supported the diagnosis of mandibular deficiency and vertical maxillary excess.
Surgical Treatment At surgery, her anterior maxilla was rotated upward about an axis in the area of the posterior nasal spine (Fig. 4c). The mandible was advanced with considerable counterclockwise rotation of the distal segment. Forward mandibular movement was effected at the ramus osteotomy site with little or no autorotational advancement due to minimal intrusion of the posterior maxilla. Suprahyoid myotomies were performed at the time of surgery and the patient wore a soft cervical collar for approximately three months following surgery. The mandible underwent moderate relapse after surgery (Fig. 4 c). The distal segment moved posteriorly and appeared to rotate in a clockwise manner about an axis in the molar region. The anterior maxilla apparently followed the mandible downward and backward as the length of the mandible was concomitantly decreased. The interocclusal relationship, however, was maintained by dental compensations, orthodontics and a small positional change of the maxilla. * The case illustrates the type of relapse that may occur when vertical maxillary excess and mandibular deficiency are treated without considering the posterior maxillary height. Despite the fact that the condyles remained properly positioned in the glenoid fossae after surgery, the use of suprahyoid myotomies and continual wearing of a cervical collar, there was gradual and progressive relapse after surgery. The design of the surgical plan, which was biomechanically unfavourable to the masticatory system, was implicated as a contributory cause of postoperative skeletal relapse.
Summary and Conclusions Still s t a n d i n g a n c i e n t a n d m e d i e v a l castles, c a t h e d r a l s , a q u e d u c t s a n d b r i d g e s give t e s t i m o n y to t h e success of basic b i o e n g i n e e r i n g c o n c e p t s u s e d by t h e R o m a n s a n d G r e e k s in d e s i g n i n g t h e s e s t r u c t u r e s for l o n g - t e r m stability. D e s i g n i n g a surgical p r o c e d u r e for l o n g t e r m skeletal s t a b i l i t y of t h e jaws should involve similar sound biomechanical principles. R e l a p s e f o l l o w i n g b i m a x i l l a r y s u r g e r y is i n d e e d m u l t i factorial. Stability is d e p e n d e n t o n m u s c u l o s k e l e t a l a d a p t a t i o n to surgical r e p o s i t i o n i n g of t h e jaws. T r e a t m e n t p l a n -
*Orthodontic treatment by Dr. Joseph Ainsworth, III, Dallas, Texas.
Cephalometric Treatment Planning for Superior Repositioning of the Maxilla
J. max.-fac. Surg. 10 (1982)
47
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Fig. 2 b
Fig. 2 c
Fig. 2d
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Fig. 2f Fig. 2 - Case 1: Fig. 2 a + b Facial appearance before and after (b) treatment.
Fig. 2 c Composite cephalometric tracings before and after maxillary and mandibular surgery illustrated in Fig. 2 f.
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ning should be based upon biomechanical principles designed to achieve long term skeletal stability. (Finn et al 1980) Cephalometric prediction studies used in concert with biomechanical modelling, can be used to plan surgery to reposition the maxilla superiorly and concomitantly advance the mandible to achieve long-term skeletal stability, optimal function, and improved facial profile aesthetics.
Fig, 2 d
Presurgical class II open bite malocclusion.
Fig. 2 e
Occlusion after treatment.
Fig. 2 f Plan of surgery: Le Fort I osteotomy to reposition maxilla superiorly and anteriorly; maxilla segmentalized to level maxillary occlusal plane and improve interdigitation of teeth; mandibular advancement by sagittal split ramus osteotomies; skeletal fixation accomplished by infraorbital rim and nasal buttress suspension wires and circummandibular wires.
The success and validity of the biomechanical principles described in this paper, remain to be proven with long term stability studies. Our preliminary results, however, appear to be better than those which were achieved in the past when irrelevant cephalometric norms, interdigitation of the teeth and "healing" of the osteotomized jaw bones were the sole criteria for treatment planning to achieve skeletal stability (Phillips and Bell 1978).
48
J. max.-fac. Surg. 10 (1982)
W.H. Bell et al.
M.M,
Pre
Fig. 3 a
Fig. 3 b
Fig. 3 - C a s e 2: Fig. 3 a 4- b Facial appearance before and after (b) Le Fort I osteotomy to reposition
maxilla superiorly and anteriorly repositional and mandibular advancement by sagittal split ramus osteotomies.
Fig. 3 c Composite cephalometric tracings before and after surgery.
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Fig. 4 - C a s e 3: Fig. 4 a + b Facial appearance before and (b) after Le Fort I osteotomy to reposition maxilla superiorly and anteriorly and mandibular advancement by sagittal spit ramus osteotomies. Fig. 4 c Composite cephalometrictracings before and after surgery. Fig. 4 d Pre-treatment Class II open bite malocclusion Fig. 4d
Fig. 4e
Fig. 4 e
Post-treatment occlusion.
Cephalometric Treatment Planning for Superior Repositioning of the Maxilla References Alexander, R.: Animal Mechanics. University of Washington Press, Seattle 1968, p. 13 Bahler, A. S., J. T. Fules, K. L. Zierler: The dynamic properties of mammalian skeletal muscle. J. Gen. Physiol. 51 (1968) 369 Bell, W. H., J. J. Dann, III: Correction of dentofacial deformities by surgery in the anterior part of the jaws. Amer. J. Orthod. 64 (1973) 162 Bell, W. H., T. D. Creekrnore, R. G. Alexander: Surgical Correction of the long face syndrome. Amer. J. Orthod. 71 (1977) 40 Bell, W. H., J. D. Jacobs: Combined orthodontic-surgical correction of moderate mandibular deficiency. Amer. J. Orthod. 75 (1979) 481 Behrman, T. J., S. ]. Behrman: A. A. O. M. S. Abstract. Chicago (1978) Blix, M.: Die L~inge und die Spannung des Muskels. Skand. Arch. Physiol. 5 (1895) 150 Brammer, J., R. Finn, W. H. Bell, D. Sinn, ]. Reisch, D. Dana: Stability after bimaxillary surgery to correct vertical maxillary excess and mandibular deficiency. J. Oral Surg. 38 (1980) 664 Carlson, F. D.: Kinetic studies on mechanical properties of muscle. In: Remington: Tissue Elasticity. Amer. Physiol. Soc., Washington, D. C. 1957, p. 55 Dann, J. J., III, R. J. Fonseca, W. H. Bell: Soft tissue changes associated with total maxillary advancement: a preliminary study. ]. Oral Surgery 34 (1976) 19 Finn, R. A., Throckmorton, G. S., Bell, W. H., Legan, H. L.: Biomechanical considerations in the surgical correction of mandibular deficiency. J. Oral Surg. 38 (1980) 257 Finn, R. A., G. S. Throekmorton, W. J. Gonyea, D. R. Barker, W. H. Bell: Neuromuscular characteristics of vertical maxillary dysplasias. In: Bell, Proffitt and White: Surgical correction of dentofacial anomalies. W. B. Saunders Co., Philadelphia 1980, p. 1712 Freihofer, H. P., Jr.: The lip profile after correction of retromaxillism in cleft and non-cleft patients. J. max-fac. Surg. 4 (1976) 136 Goldspink, G., C. Tabary, J. C. Tabary, C. Tardieu, G. Tardieu: Effect of denervation on the adaptation of sarcomere number and muscle extensibility to the functional length of the muscle. J. Physiol. 236 (1974) 733 Gonyea, W., G. C. Ericson, F. Bonde-Peterson: Skeletal Muscle fiber splitting induced by weight lifting exercise in cats. Act. Physiol. Scand. 99 (1977) 105
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McBride, K. L., W. H. Bell: Chin surgery. In: Bell, Proffitt and White: Surgical correction of dentofacial anomalies. W. B. Saunders Co., Philadelphia 1980, p. 1210 McNamara, J. A., D. S. Carlson, G. M. Yellich: Post-treatment adaptations to orthognathic surgery. Presented at Third International Congress for Orthodontics, Munich, Germany, November, 1977 McNeil, R. W.: Surgical-orthodontic correction of open-bite malocclusion. Amer. J. Orthod. 64 (1973) 38 McNeil, R. W., J. R. Hooley, R. J. Sundberg: Skeletal relapse during intermaxillary fixation. J. Oral Surg. 31 (1973) 212 Moorrees, C. F., M. R. Kean: Natural head position. A basic consideration of the interpretation of cephalometric radiographs. Amer. J. Phys. Anthropol. 16 (1958) 213 Poulton, D. R., W. H. Ware: Surgical-orthodontic treatment of severe mandibular retrusion (Part II). Amer. J. Orthod. 63 (1973) 327 Phillips, R. M., W, H. Bell: Atrophy of mandibular condyles after sagittal ramus split osteotomy. J. Oral Surg. 36 (1978) 45 Scheideman, G. B., W. H. Bell, H. L. Legan, R. A. Finn, J. S. Reisch: Cephalometric analysis of dentofacial normals. Amer. J. Orthod. 78 (1980) 404 Schendel, S. A., B. N. Epker: Results after mandibular advancement surgery: an analysis of 87 cases. J. Oral Surg. 38 (1980) 265 Steinha'user, E. W.: Advancement of the mandible by sagittal ramus split and suprahyoid myotomy. J. Oral Surg. 31 (1973) 516 Tabary, J. C,, C. Tabary, C. Tardieu, G. Tardieu, G. Goldspink: Physiological and structural changes in the cat's soleus muscle due to immobilization at different lengths by plaster casts. J. Physiol. 224 (1972) 231 Throckmorton, G. S., R. A. Finn, W. H. Bell: Biomechanics of differences in lower facial height. Amer. J. Orthod. 77 (1980) 410 Wessberg, G., S. Schendel, B. N. Epker: Role of suprahyoid musculature in surgical advancement of mandible. Abstract A.A.O.M.S. San Francisco, 1980
William H. Bell, D.D.S. University of Texas Health Science Center Dept. of Surgery Center for Correction of Dentofacial Deformities Dallas, Texas 75235 U.S.A.
J. max.-fac. Surg. 10 (1982)
J. max.-fac. Surg. 10 (1982) 42-49 © 1982 Georg Thierne Verlag Stuttgart • New York
Cephalometric Treatment Planning for Superior Repositioning of the Maxilla and Concomitant Mandibular Advancement William H. Bell, Douglas P. Sinn, Richard A. Finn
Summary Cephalometric prediction tracings are used in concert with biomechanical modelling to simulate jaw movements and soft tissue profile changes associated with the surgical correction of vertical maxillary excess and absolute mandibular deficiency. Cephalometric prediction studies are used to identify positional changes which have a known propensity to relapse or be stable and when used in concert with biomechanical modelling, serve as an adjunct in designing surgical procedures to achieve skeletal stability, good facial profile aesthetics, biomechanical efficiency and long-term skeletal stability.
Key-Words Dept. of Surgery, Division of Oral Surgery, Center for Correction of Dentofacial Deformities, (Director: R. V. Walker, D.D.S.) University of Texas Health Science Center, Dallas USA
Cephalometric Prediction Studies - Cephalometric Planning - Biomechanical Modelling - Vertical Maxillary Excess - Absolute Mandibular Deficiency - Le Fort I Osteotomy - Mandibular Advancement
Introduction Cephalometric prediction tracings are used in concert with biomechanical modelling to simulate jaw movements and soft tissue profile changes associated with the correction of dentofacial deformities. Biomechanical modelling is a practical method of determining whether or not the planned surgical changes are biomechanically efficient. Based upon biomechanical modelling principles, (Alexander 1968, Finn et al 1980, Throckmorton et al 1980) cephalometric prediction studies are used to identify positional changes which have a known propensity to relapse or be stable (Bell et al 1977, and Finn et al 1980). Additionally, they are used to educate the patient to the planned profile change. Finally, they serve as an adjunct in designing surgical procedures to achieve skeletal stability, good facial profile aesthetics, and biomechanical efficiency. Patients who present with vertical maxillary excess and absolute mandibular deficiency frequently require simultaneous superior repositioning of the maxilla and mandibular advancement to correct their facial aesthetic, functional and dento-skeletal problems. Planning to achieve optimal aesthetics, function and long term stability necessitates an accurate simulation of the positional changes of the maxilla and mandible to determine the amount and direction of movement required. Superior repositioning of the maxilla and simultaneous mandibular advancement is easily and predictably simulated with acetate overlay cephalometric prediction tracings. This paper will describe how cephalometric prediction studies in concert with biomechanical modelling, can be used to plan treatment for optimum aesthetics, biomechanical efficiency and long-term skeletal stability.
Method A careful and systematic clinical examination of the frontal and profile facial aesthetics is made with the patient standing, his head in adjusted natural head position and his lips in repose. The distance from the tip of the lower border of the upper lip to the incisal edge of the maxillary incisors is measured on the right and left sides.
Cephalometric Tracing A lateral head cephalogram is also made with the patient standing and his head postured in adjusted natural head position (Moorrees and Kean 1958). The radiograph, which should clearly delineate both the soft tissues and dento-skeletal structures, is exposed with the mandible in centric relation and the lip muscles relaxed. All of the maxillary and mandibular teeth, bony landmarks, and enveloping soft tissues are then traced on a sheet of acetate tracing paper (Fig. la). By using the posturally oriented lateral cephalogram, a natural horizontal reference line is drawn onto the acetate tracing paper. A vertical reference line is then drawn through subnasale, (McBride and Bell 1980, Scheideman et al 1980) perpendicular to the natural horizontal reference line (Fig. i a). A horizontal reference line is next drawn perpendicular to the natural vertical reference line at the level of the incisal edge of the maxillary central incisors (Fig. i b). Another line is drawn parallel to the first horizontal reference line. The distance between these two horizontal lines is the millimeter change calculated to correct the vertical dysplasia manifest in the anterior maxilla (Fig. lb). Based upon a correlative study of the patient and his lateral head cephalogram, the anterior maxilla is superiorly repositioned the amount necessary to expose approximately 2 mm of the maxillary incisor teeth. If and when there is a disparity between the clinical and cephalometric lip-to-tooth measurement, the clinical examination and/or cephalogram are repeated.
Construction of Templates A template of the mandible is made by tracing all the mandibular teeth, bony landmarks and enveloping soft tissues with a coloured pencil on a smaller piece of acetate tracing paper. A similar acetate overlay template of the maxilla is constructed by tracing in all the maxillary teeth and osseous landmarks. When the maxillary occlusal plane is to be levelled surgically, the planned segmentalization is simulated by cutting the maxillary acetate template in the appropriate "interdental space". A careful analysis of articulated study casts, periapical radiographs of the potential
Cephalometric Treatment Planningfor Superior Repositioning of the Maxilla
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Fig. 1 a Cephalometric tracing of all the maxillary and mandibular teeth, maxilla, mandible and enveloping soft tissues; horizontal reference line is made parallel to natural horizontal; vertical reference line, which is perpendicular to natural horizontal reference line, intersects with subnasale.
Fig. 1
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Fig. 1 b Horizontal reference line is made at the level of the incisal edge of the maxillary central incisors; the distance between this line and another superior and parallel horizontal reference line is the mm change calculated to correct the vertical dysplasia manifest in the anterior maxilla.
Fig. 1 c Maxillary and mandibular acetate overlay templates in simulated Class I canine and molar occlusion and desired overjetoverbite relationship.
Technique of Cephalometric Planning
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Fig. 1 d Mandibular portion of the maxillomandibular templates superimposed on the anatomical landmarks of the mandible of the original cephalogram.
Fig. 1 e Acetate overlay templates rotated to the planned vertical position (indicated by superior horizontal reference line); pencil point at summit of the condyles serves as the axis of rotation.
Fig. 1 f New cephalometric prediction tracing traced onto another sheet of overlayed acetate tracing paper.
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Fig, 1 g Evaluation of anterior-posterior aesthetic change with the aid of natural vertical reference line.
Fig. 1 h Maxillo-mandibulartemplates repositioned anteriorly to decrease the anterior-posterior dimension of the nose and increase the prominence of the upper lip.
interdental osteotomy sites and model surgery may all be necessary to determine the feasibility of the planned maxillary osteotomies and to finalize the details of the occlusal simulation.
Simulation of Class I Occlusion The maxillary and mandibular templates are next moved into a simulated Class I canine occlusion with the desired overjet-overbite relationship, and attached to one another with a small piece of clear tape (Fig. 1 c). This manoeuvre is completed independently of the original tracing. The mandibular portion of the attached maxillo-mandibular acetate overlay templates is then superimposed on the anatomical landmarks of the mandible of the original cephalogram (Fig. ld). With the point of a pencil positioned at the summit of the condyle to serve as the axis of rotation, the acetate overlay templates are rotated to the planned vertical position indicated by the previously drawn superior horizontal reference line (Fig. le). Based upon the anteroposterior positional change of the maxillo-mandibular relationship, a new prediction tracing is drawn onto another sheet of overlayed acetate tracing paper (Fig. lf). This is easily accomplished with the soft tissue contours except for the lower lip. The surgeon must use his artistic skills to trace in a lower lip which is based on the new anteroposterior and vertical position of the incisor teeth, attainment of lip competence and concomitant genioplasty.
Evaluation of the Aesthetic Result (Fig. I f) The natural vertical reference line is an adjunct to evaluating the new soft tissue profile. The vermillion border of the upper lip should lie approximately on the line; the chin 2±4 mm posterior to the line. These measurements which are based upon a study of normal adults (Scheideman et al, 1980) afford the clinician considerable latitude in planning treatment. Individual preferences, sex and racial considerations, are all relevant and considered before the final plan of
Fig.
1 i Final cephalometric prediction tracing based upon projected soft tissue changes; anterior maxilla raised 5 mm and advanced 8 mm; posterior maxilla raised 10 mm.
treatment is formalized. Based upon an evaluation of the results of this preliminary study of profile aesthetics by means of the cephalometric prediction study, the maxillary and mandibular templates may be adjusted to achieve a more aesthetic result - indeed the result might be considered subjectively to be aesthetic without the need for additional positional adjustment of the templates. All too frequently, however, it is not so much that absolute maxillary advancement is necessary, but instead the decision to
advance the mandible centres around the inadvisability of posterior movement of the maxilla to correct the Class II occlusal relationship. This is a central treatment planning consideration, for such movements are all too frequently calculated to produce an unaesthetic retrusive upper lip and increase the anterior-posterior prominence of the nose. These unaesthetic results must be avoided by programming total maxillary osteotomy to superiorly reposition the maxilla, with concomitant mandibular advancement surgery. Anterior-Posterior Repositioning of the Maxilla When the cephalometric prediction study, in concert with clinical analysis, indicates that the resultant maxillo-mandibular relationship will produce a facial profile with a retrusive upper lip and flattening in the paranasal and/or canine fossa areas, the maxilla is moved anteriorly to decrease the antero-posterior dimension of the nose and increase the prominence of the upper lip (Bell and Jacobs, 1980). The maxillary template is positioned superiorly, as well as anteriorly, the amount calculated to achieve aesthetic balance between the nose and upper lip and to achieve 2 mm of maxillary incisor exposure with the upper lip in repose. The surgeon's artistic sense of good facial aesthetics, rather than cephalometric norms, serves as the principle guideline to planning the amount of forward repositioning of the anterior portion of maxilla. Surgical movement of the anterior maxilla must also be planned to
Cephalometric Treatment Planning for Superior Repositioning of the Maxilla achieve a satisfactory tooth-to-bone relationship and inclination of the anterior teeth. The maxillary template is repositioned anteriorly the distance calculated to produce the desired aesthetic change in the upper lip. The knowledge that there is an approximate 0.6 to 1.0 ratio of movement of the upper lip to advancement of the underlying dento-osseous structures, serves as the basis for registering a new soft tissue profile on another piece of tracing paper (Fig. I h) (Dann et al 1976 and Freihofer 1976). If the results of the cephalometric prediction study are such that the resultant maxillo-mandibular relationship will produce a facial profile with an acute nasolabial angle and relatively prominent upper lip, the maxilla is repositioned superiorly and posteriorly to reduce the prominence of the upper lip and achieve an aesthetic lip-to-tooth relationship (2 mm of tooth exposure). Again, the knowledge that there is an approximate 0.7 to 1.0 ratio of movement of the upper lip to retraction of the underlying dento-osseous structures, serves as the basis for registering a new softtissue profile on another piece of acetate tracing paper (Bell and Dann, 1973) (Fig. 1, I). When anterior-posterior movement of the maxilla, in addition to superior repositioning is indicated, the mandibular movement necessary to achieve maxillo-mandibular harmony is simulated with an acetate overlay template of the mandible and its enveloping soft tissues. Trial repositioning of the maxillary and mandibular acetate overlay templates is made until satisfactory overjet overbite and interincisal relationships are achieved which are consistent with the planned aesthetic objectives. Based upon the projected soft tissue changes, the prediction tracing is completed by drawing a new upper and lower lip. With the "new" profile prediction completed and the maxillo-mandibular relationship established, genioplasty or rhinoplasty can be simulated on still another smaller piece of acetate tracing paper. Figure 1, I demonstrates the final cephalometric prediction tracing and the planned positional changes in the anterior and posterior maxilla. The anterior maxilla will be raised 5 mm and advanced 8 ram; the posterior maxilla will be raised 10 mm. There are important reasons for each planned movement. The positional change of the anterior maxilla is based upon the amount of tooth exposure and the retrusive appearance of the upper lip.
Repositioning the Posterior Portion of Maxilla: The positional change of the posterior maxilla is based upon the need to achieve maximal stability, level the maxillary occlusal plane (i. e. open bite) and improve the posterior smile line. The results of previous studies (Brammer et al 1980, Finn et al 1980) which have evaluated the relationship between maxillary intrusion and mandibular stability, serve as the basis for increasing stability by superior repositioning of the posterior maxilla. These investigations indicate that as the posterior maxilla is intruded, there is less posterior mandibular relapse. Based upon the results of these studies, we program treatment to intrude the posterior maxilla not only to level the maxillary occlusal plane and improve the posterior smile line, but also to increase the autorotational advancement of the mandible and biomechanical efficiency of the masticatory system. Such movements decrease the amount of absolute mandibular advancement and muscle stretching. Excessive posterior
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gingival exposure gives further support to superior repositioning of the posterior maxilla. The amount of posterior gingival exposure, however, is not the absolute determinant of the magnitude of superior movement of the posterior maxilla - it is only a relative consideration. Although suprahyoid myotomies (Steinhiiuser 1973) have not been associated with improvement of skeletal stability following mandibular advancement (Brammer et al 1980, Schendel and Epker 1980, Wessberg et al 1980) skeletal fixation devices have been proposed empirically (Poulton and Ware 1973, McNeil and Hooley 1973), and later demonstrated more conclusively (Schendel and Epker 1980, Berman and Berman 1978). Skeletal fixation is effectively accomplished by either one of two methods or a combination of both: sternomandibular brace or extra cranial suspension device. Both of these techniques have as a common denominator, maintenance of the mandible in its new position while neuromuscular alterations occur. The infra- and suprahyoid muscles are primarily affected by this means whereas the mandibular adductor muscles are more directly affected by biomechanical changes after surgery. Structural muscle adaptation to an altered environment has repeatedly been demonstrated (Goldspink et al 1974, Tabary et al 1972, Gonyea 1978, McNamara 1977). Many of these changes were accomplished in as little as 2 weeks. Thus preoperative exercising such as neck hyperextension and utilization of a cervical collar, may very well initiate these adaptive changes. Furthermore, postoperative skeletal stabilization by craniomandibular wiring techniques and/or continued use of the cervical collar, will allow for additional muscle adaptation. Decrease in passive muscle tension (Blix 1895, Bahler et al 1968, Carlson 1957), heretofore overlooked, may be favourably altered by these clinical methods of "overstretching". Biomechanical modelling has recently given us new insight into functional relationships associated with skeletal relapse following jaw surgery. The basic premise of the system favouring skeletal stability is to decrease the lever arm of the bite point and increase the adductor muscle lever arm (Throckmorton et al 1980, Finn et al, 1980, Brammer et al 1980). Observation of changes in the bite point and muscle moment arms, is easily and quickly accomplished when performing the cephalometric prediction tracings. Superior and posterior movements of the maxilla will increase mechanical efficiency by increasing the muscle moment arms after mandibular autorotation and decreasing the bite point moment arm following maxillary intrusion. Superior repositioning of the posterior maxilla consistently improves the biomechanical efficiency of the masticatory apparatus. Prudent observation of changes in bite point and muscle moment arms during cephalometric prediction studies, will provide an additional guide during treatment planning. Decreasing posterior maxillary height improves mechanical efficiency (Throckmorton et al 1980), increases autorotational advancement of the mandible, decreases absolute mandibular advancement, and increases skeletal stability (Brammer et al 1980). Although there are practical limitations to the magnitude of posterior maxillary intrusion, the complementary effect of this surgical manoeuvre on biomechanical efficiency should be appreciated and integrally incorporated into treatment planning decisions to possibly enhance long term skeletal stability and improved masticatory function.
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Case reports Case Report 1 (Fig. 2) T. W., a girl aged 17, and her parents were concerned about both her facial appearance (Fig. 2a) and poor dental occlusion (Fig. 2d). She was seen in consultation with an orthodontist for treatment of her severe anterior open bite, for which she had received orthodontic treatment beginning at age 15. A retrospective study of her preorthodontic clinical, cephalometric and occlusal records revealed a severe open bite and absolute mandibular deficiency. Maxillary and mandibular 1st molars had been extracted to facilitate partial presurgical orthodontic levelling and alignment of the maxillary and mandibular arches.
Problem List Aesthetics (Fig. 2 a): Frontal examination revealed excessive exposure of teeth and gingiva in repose (5 mm) and when smiling, lip incompetence as indicated by the 9 mm interlabial gap at rest, and flattened paranasal and canine fossa areas. Profile examination revealed an obtuse nasolabial angle, retrusive upper lip, retropositioned mandible, and long face.
Cephalometric Analysis (Fig. 2 c) The patient had a high mandibular plane angle, Sn-GoGn = 50°; excessive lower anterior facial height; anterior open bite deformity; and retropositioned mandible 24 mm posterior to natural vertical reference line.
Occtusal Analysis (Fig. 2 d) Occlusal study revealed a Class II canine and molar relationship with a 9 mm overjet, and a 6 mm open bite extending from the 1st premolar region of one side to the contralateral premolar region. There was a small reverse curve of the mandibular occlusal plane and moderate curvature of the maxillary occlusal plane. The maxillary and mandibular teeth were adequately aligned after extraction of maxillary and mandibular 1st premolars and orthodontic treatment.
Treatment Plan Plan of Surgery (Fig. 2 f) 1. Reposition the maxilla superiorly (anterior - 4 ram; posterior 10 ram) and anteriorly (8 ram) by LeFort I osteotomy to: a. correct the anteroposterior maxillary deficiency b. decrease lower anterior facial height c. partially close anterior open bite d. improve the lip-to-tooth relationship e. reduce amount of anterior and posterior gingival exposure when smiling. f. facilitate autorotational advancement of mandible g. level maxillary occlusal plane 2. Bilateral sagittal split ramus osteotomies of vertical rami to advance the mandible into Class I canine and molar relationship. 3. Cervical collar would be worn continuously two weeks before and at least 6 months after surgery to hyperextend suprahyoid muscles.
Active Treatment and Follow-up The maxillary and mandibular surgical procedures were accomplished simultaneously. (Fig. 2 f) The segmentalized maxilla was advanced 7 ram. The anterior portion of the maxilla was raised 4 mm and the posterior portion 10 ram. Intermaxillary fixation was maintained for eight weeks. Light night-time training elastics in the canine - 1st premolar area, were used for six weeks after release from intermaxillary fixation. Final levelling and interdigitation of the teeth was accomplished by four months of post-surgical orthodontic treatment.* The patient wore a cervical collar continuously day and night after surgery for 6 months to hyperextend the suprahyoid muscles and decrease relapse. To date, over a 28 month period of follow up, there has been minimal skeletal relapse. (Fig. 2 c) The use of light night-time elastics and orthodontic treatment compensated for the relatively small downward and backward movement of the mandible (2 mm), and maintained closure of the open bite and inrerdigitation of the teeth. * Orthodontic treatment by Dr. Richard Ramming, Wichita Falls, Texas.
W . H . Bell et al.
Case Report 2 Patient M. M. was a 25-year-old female with vertical maxillary excess, a relatively retrusive upper lip, retropositioned mandible, and a 55 ° mandibular plane angle (Fig. 3 a). Although her teeth were wellaligned, her Class II malocclusion remained uncorrected after three years of orthodontic treatment during adolescence.
Surgical Treatment Her maxilla was superiorly and anteriorly repositioned, by LeFort I osteotomy without bone grafting. Her mandible was concomitantly advanced to a Class I occlusion by sagittal split ramus osteotomies and her chin augmented by advancement genioplasty. Mandibular movement was primarily autorotational as a consequence of superior movement of the maxilla. The patient wore a soft cervical collar for approximately three months after surgery. During the followup period, the maxilla settled upward and forward slightly (Fig. 3 c). Mandibular stability has been excellent over a postoperative followup period of 4 years. The bite has remained closed and a Class I occlusion preserved with only minor dental adjustments.
Case R e p o r t 3 Patient E. S., a 20-year-old woman manifested an open bite deformity with a 59.1 degree mandibular plane angle (Fig. 4a, c, d). Clinical, cephalometric and radiographic studies supported the diagnosis of mandibular deficiency and vertical maxillary excess.
Surgical Treatment At surgery, her anterior maxilla was rotated upward about an axis in the area of the posterior nasal spine (Fig. 4c). The mandible was advanced with considerable counterclockwise rotation of the distal segment. Forward mandibular movement was effected at the ramus osteotomy site with little or no autorotational advancement due to minimal intrusion of the posterior maxilla. Suprahyoid myotomies were performed at the time of surgery and the patient wore a soft cervical collar for approximately three months following surgery. The mandible underwent moderate relapse after surgery (Fig. 4 c). The distal segment moved posteriorly and appeared to rotate in a clockwise manner about an axis in the molar region. The anterior maxilla apparently followed the mandible downward and backward as the length of the mandible was concomitantly decreased. The interocclusal relationship, however, was maintained by dental compensations, orthodontics and a small positional change of the maxilla. * The case illustrates the type of relapse that may occur when vertical maxillary excess and mandibular deficiency are treated without considering the posterior maxillary height. Despite the fact that the condyles remained properly positioned in the glenoid fossae after surgery, the use of suprahyoid myotomies and continual wearing of a cervical collar, there was gradual and progressive relapse after surgery. The design of the surgical plan, which was biomechanically unfavourable to the masticatory system, was implicated as a contributory cause of postoperative skeletal relapse.
Summary and Conclusions Still s t a n d i n g a n c i e n t a n d m e d i e v a l castles, c a t h e d r a l s , a q u e d u c t s a n d b r i d g e s give t e s t i m o n y to t h e success of basic b i o e n g i n e e r i n g c o n c e p t s u s e d by t h e R o m a n s a n d G r e e k s in d e s i g n i n g t h e s e s t r u c t u r e s for l o n g - t e r m stability. D e s i g n i n g a surgical p r o c e d u r e for l o n g t e r m skeletal s t a b i l i t y of t h e jaws should involve similar sound biomechanical principles. R e l a p s e f o l l o w i n g b i m a x i l l a r y s u r g e r y is i n d e e d m u l t i factorial. Stability is d e p e n d e n t o n m u s c u l o s k e l e t a l a d a p t a t i o n to surgical r e p o s i t i o n i n g of t h e jaws. T r e a t m e n t p l a n -
*Orthodontic treatment by Dr. Joseph Ainsworth, III, Dallas, Texas.
Cephalometric Treatment Planning for Superior Repositioning of the Maxilla
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Fig. 2 b
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Fig. 2f Fig. 2 - Case 1: Fig. 2 a + b Facial appearance before and after (b) treatment.
Fig. 2 c Composite cephalometric tracings before and after maxillary and mandibular surgery illustrated in Fig. 2 f.
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ning should be based upon biomechanical principles designed to achieve long term skeletal stability. (Finn et al 1980) Cephalometric prediction studies used in concert with biomechanical modelling, can be used to plan surgery to reposition the maxilla superiorly and concomitantly advance the mandible to achieve long-term skeletal stability, optimal function, and improved facial profile aesthetics.
Fig, 2 d
Presurgical class II open bite malocclusion.
Fig. 2 e
Occlusion after treatment.
Fig. 2 f Plan of surgery: Le Fort I osteotomy to reposition maxilla superiorly and anteriorly; maxilla segmentalized to level maxillary occlusal plane and improve interdigitation of teeth; mandibular advancement by sagittal split ramus osteotomies; skeletal fixation accomplished by infraorbital rim and nasal buttress suspension wires and circummandibular wires.
The success and validity of the biomechanical principles described in this paper, remain to be proven with long term stability studies. Our preliminary results, however, appear to be better than those which were achieved in the past when irrelevant cephalometric norms, interdigitation of the teeth and "healing" of the osteotomized jaw bones were the sole criteria for treatment planning to achieve skeletal stability (Phillips and Bell 1978).
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M.M,
Pre
Fig. 3 a
Fig. 3 b
Fig. 3 - C a s e 2: Fig. 3 a 4- b Facial appearance before and after (b) Le Fort I osteotomy to reposition
maxilla superiorly and anteriorly repositional and mandibular advancement by sagittal split ramus osteotomies.
Fig. 3 c Composite cephalometric tracings before and after surgery.
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Fig. 4 - C a s e 3: Fig. 4 a + b Facial appearance before and (b) after Le Fort I osteotomy to reposition maxilla superiorly and anteriorly and mandibular advancement by sagittal spit ramus osteotomies. Fig. 4 c Composite cephalometrictracings before and after surgery. Fig. 4 d Pre-treatment Class II open bite malocclusion Fig. 4d
Fig. 4e
Fig. 4 e
Post-treatment occlusion.
Cephalometric Treatment Planning for Superior Repositioning of the Maxilla References Alexander, R.: Animal Mechanics. University of Washington Press, Seattle 1968, p. 13 Bahler, A. S., J. T. Fules, K. L. Zierler: The dynamic properties of mammalian skeletal muscle. J. Gen. Physiol. 51 (1968) 369 Bell, W. H., J. J. Dann, III: Correction of dentofacial deformities by surgery in the anterior part of the jaws. Amer. J. Orthod. 64 (1973) 162 Bell, W. H., T. D. Creekrnore, R. G. Alexander: Surgical Correction of the long face syndrome. Amer. J. Orthod. 71 (1977) 40 Bell, W. H., J. D. Jacobs: Combined orthodontic-surgical correction of moderate mandibular deficiency. Amer. J. Orthod. 75 (1979) 481 Behrman, T. J., S. ]. Behrman: A. A. O. M. S. Abstract. Chicago (1978) Blix, M.: Die L~inge und die Spannung des Muskels. Skand. Arch. Physiol. 5 (1895) 150 Brammer, J., R. Finn, W. H. Bell, D. Sinn, ]. Reisch, D. Dana: Stability after bimaxillary surgery to correct vertical maxillary excess and mandibular deficiency. J. Oral Surg. 38 (1980) 664 Carlson, F. D.: Kinetic studies on mechanical properties of muscle. In: Remington: Tissue Elasticity. Amer. Physiol. Soc., Washington, D. C. 1957, p. 55 Dann, J. J., III, R. J. Fonseca, W. H. Bell: Soft tissue changes associated with total maxillary advancement: a preliminary study. ]. Oral Surgery 34 (1976) 19 Finn, R. A., Throckmorton, G. S., Bell, W. H., Legan, H. L.: Biomechanical considerations in the surgical correction of mandibular deficiency. J. Oral Surg. 38 (1980) 257 Finn, R. A., G. S. Throekmorton, W. J. Gonyea, D. R. Barker, W. H. Bell: Neuromuscular characteristics of vertical maxillary dysplasias. In: Bell, Proffitt and White: Surgical correction of dentofacial anomalies. W. B. Saunders Co., Philadelphia 1980, p. 1712 Freihofer, H. P., Jr.: The lip profile after correction of retromaxillism in cleft and non-cleft patients. J. max-fac. Surg. 4 (1976) 136 Goldspink, G., C. Tabary, J. C. Tabary, C. Tardieu, G. Tardieu: Effect of denervation on the adaptation of sarcomere number and muscle extensibility to the functional length of the muscle. J. Physiol. 236 (1974) 733 Gonyea, W., G. C. Ericson, F. Bonde-Peterson: Skeletal Muscle fiber splitting induced by weight lifting exercise in cats. Act. Physiol. Scand. 99 (1977) 105
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McBride, K. L., W. H. Bell: Chin surgery. In: Bell, Proffitt and White: Surgical correction of dentofacial anomalies. W. B. Saunders Co., Philadelphia 1980, p. 1210 McNamara, J. A., D. S. Carlson, G. M. Yellich: Post-treatment adaptations to orthognathic surgery. Presented at Third International Congress for Orthodontics, Munich, Germany, November, 1977 McNeil, R. W.: Surgical-orthodontic correction of open-bite malocclusion. Amer. J. Orthod. 64 (1973) 38 McNeil, R. W., J. R. Hooley, R. J. Sundberg: Skeletal relapse during intermaxillary fixation. J. Oral Surg. 31 (1973) 212 Moorrees, C. F., M. R. Kean: Natural head position. A basic consideration of the interpretation of cephalometric radiographs. Amer. J. Phys. Anthropol. 16 (1958) 213 Poulton, D. R., W. H. Ware: Surgical-orthodontic treatment of severe mandibular retrusion (Part II). Amer. J. Orthod. 63 (1973) 327 Phillips, R. M., W, H. Bell: Atrophy of mandibular condyles after sagittal ramus split osteotomy. J. Oral Surg. 36 (1978) 45 Scheideman, G. B., W. H. Bell, H. L. Legan, R. A. Finn, J. S. Reisch: Cephalometric analysis of dentofacial normals. Amer. J. Orthod. 78 (1980) 404 Schendel, S. A., B. N. Epker: Results after mandibular advancement surgery: an analysis of 87 cases. J. Oral Surg. 38 (1980) 265 Steinha'user, E. W.: Advancement of the mandible by sagittal ramus split and suprahyoid myotomy. J. Oral Surg. 31 (1973) 516 Tabary, J. C,, C. Tabary, C. Tardieu, G. Tardieu, G. Goldspink: Physiological and structural changes in the cat's soleus muscle due to immobilization at different lengths by plaster casts. J. Physiol. 224 (1972) 231 Throckmorton, G. S., R. A. Finn, W. H. Bell: Biomechanics of differences in lower facial height. Amer. J. Orthod. 77 (1980) 410 Wessberg, G., S. Schendel, B. N. Epker: Role of suprahyoid musculature in surgical advancement of mandible. Abstract A.A.O.M.S. San Francisco, 1980
William H. Bell, D.D.S. University of Texas Health Science Center Dept. of Surgery Center for Correction of Dentofacial Deformities Dallas, Texas 75235 U.S.A.