Dr. Ahmed M. Adawy Professor Emeritus, Dep. Oral & Maxillofacial Surg.

Former Dean, Faculty of Dental MedicineAl-Azhar University

Mandibular prognathism

Mandibular prognathismThe condition of being prognathic indicates abnormal forward projection of one or of both jaws beyond the established normal relationship with the cranial base. The word "prognathism" derives from Greek “pro”  (forward) and “gnathos” (jaw). The skeletal manifestation can be due to mandibular anterior positioning (prognathism) or growth excess (macrognathia), maxillary posterior positioning (retrognathism) or growth deficiency (micrognathia), or a combination of both. Such skeletaldisharmony between the mandible and maxilla produces a concave facial profile.  This concave profile not only seriously affects speech and masticatory function (1), but also extremely endangers psychology to patients  

Class III Malocclusion

Concave prognathic facial profile

In addition to mandibular protrusion, patients with skeletal Class III malocclusion are presented with a mesial occlusion, distinctive reverse over jet of the incisors and two-sided buccal occlusion. Mandibular prognathism is also characterized by negative ANB angle, increase in the length of the mandibular body, excessive obtuse angle of the mandible, reflected in the facial features by smoothing of the mentolabial fold and chin protrusion beyond the coronal plane, a forward position of the glenoid fossa and a short anterior cranial base (2,3)

Mandibular prognathism

Cephalometric tracing of a prognathic case

The prevalence of mandibular prognathism varies among different populations. The prevalence is highest in East Asian populations; approximately 15–23%, moderate in sub-Saharan Africans; 3–8%, and lowest in Caucasian populations; 0.48–4% (4,5). Males are affected more commonly than females

Mandibular prognathism

Several environmental and genetic components have been contributed to the development of mandibular prognathism (6). While various environmental factors have been found to contribute to the development of mandibular prognathism, heredity plays a substantial role (7). The environmental factors comprise, congenital anatomic defects (cleft lip–cleft palate), endocrine disturbance (acromegaly, gigantism, pituitary adenomas), nasal airway obstruction (enlarged tonsils), habitual posture (habit of protruding the mandible) and trauma (instrumental deliveries)

Mandibular prognathism

Mandibular prognathism in a patient with acromegaly. Macroglossia is a common finding

The treatment of mandibular prognathism is currently undertaken by a combination of orthodontic and surgical procedures. The therapeutic goals of the combined treatment are: Function; Obtain normal mastication, speech and respiratory function. Aesthetics; Establish facial harmony and balance. Stability; Avoid short- and long-term relapse. In some events, polydiastema may be present together with class III malocclusion. Polydiastema may cause various occlusal problems, which include missing teeth, dental anomalies, dental-jaw size discrepancies, and excessive overbite and overjet. Polydiastema should be treated by orthodontic means (8)

Mandibular prognathism

Further, preoperative orthodontic preparation can eliminate dentoalveolar compensations by aligning the teeth over the basal bone to allow maximal repositioning of the mandible, increase in the quantity of surgical correction, and making better functional and aesthetic results possible. Moreover, to increase the amount of surgical setback to correct mandibular prognathism, orthodontic treatment was needed to arrange the malaligned teeth in the best possible position in the individual jaws prior to surgery. Orthodontic treatment, however, can takes up to 18 months to achieve. Meanwhile, the debate between “orthodontic first”(9) and “surgery first”(10) remains unsolved

Mandibular prognathism

A thorough diagnosis and evaluation is one of the most important aspects of the overall patient management. As a result of developments in 3D imaging technology, surgeons are provided with extra information that could not be obtained from lateral cephalograms alone, thus improving the quality of preoperative planning. Multiple software programs are available for 3D planning, allowing an interaction with 3D images to simulate surgery and visualize the prediction of postoperative outcomes in soft and hard tissues. Surgical splints, manufactured using computer-aided design/computer-aided manufacturing (CAD/CAM) technology, have been developed to avoid errors in the traditional model process that can lead to suboptimal outcomes (11)

Mandibular prognathism

Two-dimensional planning; prediction of postoperative outcomes

Three-Dimensional virtual surgical planning. Maxillary advancement and mandibular setback

Surgical splints manufactured using CAD/CAM technology

In growing children, a number of treatment protocols have been used to address skeletal Class III cases, including the chincup (12), face mask (13), and maxillary protraction combined with chincup traction (14). In adults orthognathic surgery in conjunction with orthodontic treatment would be required for correction of this problem. According to the location of the sagittal jaw problem in adult skeletal Class III cases, orthognathic surgical treatment is accomplished by a mandibular setback, a maxillary advancement or a combination of the two

Mandibular prognathism

The parameters that indicate advancement of the maxilla with Le Fort I osteotomy are: Flattening of the paranasal areas, accentuated naso-genial fold, moderate flattening of the cheek-bones, obtuse nasolabial angle. In few selected cases, a true anterior position of the mandible and chin requires a mandibular set back alone. In this case, it is necessary that cheek, nose, and superior lip have a good balance. However, correction of Class III cases with mandibular osteotomy alone should be limited to clinical situations with negative over-jet not above 3-4 mm

Mandibular prognathism

Several methods have been proposed for surgical correction of mandibular prognathism. Currently, intraoral bilateral sagittal split osteotomy stands as the most popular surgical method in correction of mandibular prognathism (15,16). This intraoral approach could move the mandible in three dimensions according to a designated surgical plan, keeping the condyle in the glenoid fossa, and, most importantly, maintaining sufficient bone contact area to allow internal rigid fixation. Despite the fact that the bilateral sagittal split osteotomy is becoming increasingly popular, some centers still tend to perform intraoral vertical ramus osteotomy (17) for correction of mandibular prognathism

Mandibular prognathism

Bilateral sagittal split osteotomy

Vertical ramus osteotomy

Despite a large number of modifications of the originalbilateral sagittal splitting technique, the risk of unexpected fractures is a major disadvantage of the procedure (18). Previous reports have cited an incidence of bad splits of up to 5% despite improved preoperative diagnostics. In addition, the temporary or lasting damage of the inferior alveolar nerve remains relevant. According to the literature, postoperative damage varies from 13% to 40% (19,20). However, the introduction of ultrasonic bone-cutting surgery (piezosurgery) has changed the way of cutting the mandibular bone (21). The technique allows efficient cutting of hard tissues with minimal trauma to soft tissues. The advantages include minimal risks to the vessels and nerve in the mandibular canal

Mandibular prognathism

Relapse following mandibular setback surgery is distressing to both clinicians and patients. This has been the main reason for an unsatisfactory treatment outcome. It also has been reported that the relapse rates are among the highest for any surgical procedure (22,23). According to the author’s clinical observation, most relapse after mandibular setback surgery seems to occur during the immediate postsurgical phase within the first two months following surgery. There seems to be additional minor relapse during the period from two months to one year after surgery. Skeletal relapse ranges from 7.1% to 51.4%, with a mean value of 22.6%. Despite the long experience with this procedure, existing scientific evidence still conflicts regarding its long-term stability

Mandibular prognathism

1. Sencimen M, Gulses A, Sabuncuoglu FA, et al. Rectangular body ostectomy for the treatment of severe mandibular prognathism. J Craniofac Surg; 23: e190-e193, 2012. 2. Proffit WR, Fields HW. Contemporary orthodontics; Mosby, St. Louis, Mo, USA, 2000. 3. Chang HP, Liu PH, Yang YH, et al. Craniofacial morphometric analysis of mandibular prognathism. J Oral Rehab; 33: 183, 2006.4. Yamaguchi T, Park SB, Narita A, et al. Linkage analysis of mandibular prognathism in Korean and Japanese patients. J Dent Res; 84: 255, 2005. 5. El-Gheriani AA, Maher BS, El-Gheriani AS, et al. Segregation analysis of mandibular prognathism in Libya. J Dent Res; 82: 523, 2003. 6. Jena AK, Duggal R, Mathur VP, et al. Class - III malocclusion: Genetics or environment? A twins study. J Indian Soc Pedod Prev Dent; 23: 27, 2005.7. Tomaszewska A, Kopczynski P, Rafał Flieger R. Genetic basis of mandibular prognathism. Arch Biomed Scien; 1: 16, 2013. 8. Hwang SK, Ha JH, Jin MU, et al. Diastema closure using direct bonding restorations combined with orthodontic treatment: A case report. Rest Dent Endo; 37: 165, 2012. 9. Worms FW, Isaacson RJ, Speidel TM. Surgical orthodontic treatment planning: Profile analysis and mandibular surgery. Angle Orthod; 46: 1, 1976.

References:

10. Liou EJ, Chen PH, Wang YC, et al. Surgery‑first accelerated orthognathic surgery: Postoperative rapid orthodontic tooth movement. J Oral Maxillofac Surg; 69: 781, 2011. 11. Centenero SA, Hernández-Alfaro F. 3D planning in orthognathic surgery: CAD/ CAM surgical splints and prediction of the soft and hard tissues results – Our experience in 16 cases. J Craniomaxillofac Surg; 40: 162, 2011. 12. Graber LW. Chin cup therapy for mandibular prognathism. Am J Orthod; 72: 23, 1977. 13. McNamara JA Jr. An orthopedic approach to the treatment of Class III malocclusion in young patients. J Clin Orthod; 21: 598, 1987. 14. Chang HP, Lin HC, Liu PH, et al. Geometric morphometric assessment of treatment effects of maxillary protraction combined with chin cup appliance on the maxillofacial complex. J Oral Rehabil; 32: 720, 2005. 15. Trauner R, Obwegeser H. The surgical correction of mandibular prognathism and retrognathia and consideration of genioplasty: surgical procedures to correct mandibular prognathism and reshaping the chin. Oral Surg Oral Med Oral Pathol; 10: 677, 1957. 16. Dal Pont G. Retromolar osteotomy for the correction of prognathism. J Oral Surg Anesth Hosp Serv; 19: 42, 1961. 17. Herbert JM, Kent JN, Hinds EC. Correction of prognathism by an intraoral vertical subcondylar osteotomy. J Oral Surg; 28: 651, 1970.

References:

18. Kriwalsky MS, Maurer P, Veras RB, et al. Risk factors for a bad split during sagittal split osteotomy. Br J Oral Maxillofac Surg; 46: 177, 2008. 19. Colella G, Cannavale R, Vicidomini A, et al. Neurosensory disturbance of the inferior alveolar nerve after bilateral sagittal split osteotomy: a systematic review. J Oral Maxillofac Surg; 65: 1707, 2007. 20. Nesari S, Kahnberg KE, Rasmusson L. Neurosensory function of the inferior alveolar nerve after bilateral sagittal ramus osteotomy: a retrospective study of 68 patients. Int J Oral Maxillofac Surg; 34: 495, 2005. 21. Rana M, Gellrich NC, Rana M, et al. Evaluation of surgically assisted rapid maxillary expansion with piezosurgery versus oscillating saw and chisel osteotomy-a randomized prospective trial. Trials; 14: 49, 2013. 22 . Proffit WR, Philips C, Turvey TA. Stability after surgical orthodontic correction of skeletal Class III malocclusion. III. Combined maxillary and mandibular procedures. Int J Adult Orthodon Orthognath Surg; 4: 211, 1991. 23. Bailey LJ, Cevidanes LH, Proffit WR. Stability and predictability of orthognathic surgery. Am J Orthod Dentofacial Orthop; 26: 273, 2004.

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