Orthognathic surgery

Orthognathic surgeryDr. Ahmed M. Adawy Professor Emeritus, Dep. Oral & Maxillofacial Surg.Former Dean, Faculty of Dental MedicineAl-Azhar University

Orthognathic surgeryOrthognathic surgery is the art and science of combining orthodontics and maxillofacial surgery to correct dento-facial deformities. The word orthognathic comes from the Greek wordorqos, meaning to straighten, andgnaqos, meaning jaw. Orthognathic surgery thus, means to correct or straighten jaw deformities. Such correction may be isolated to one jaw, to that performed concurrently on both jaws. Recently, the scope of orthognathic surgery has been broaden to involves the surgical manipulation of the elements of the facial skeleton to restore the proper anatomic and functional relationship in patients with dentofacial skeletal anomalies. The treatment does not change only the bony relations of the facial structures, but soft tissues as well

Orthognathic surgery is primarily carried out in adults once growth has ceased. In childhood and adolescence, some skeletal malocclusions can be treated merely orthodontically, but once growth has ceased, this is no longer possible and additional surgery is needed. In general, orthognathic surgery to reposition the maxilla, mandible, or chin is the mainstay treatment for patients who are too old for growth modification and for dentofacial conditions that are too severe for either surgical or orthodontic camouflage. Various benefits of orthognathic surgery have been reported, including better masticatory function (1), reduced facial pain (2), more stable results in severe discrepancies (3) and improved facial esthetics (4)Orthognathic surgery

Etiology

Dentofacial skeletal anomalies generally occur as a result of growth discrepancy between the upper facial skeleton to the lower facial skeleton. Underlying genetic predisposition and acquired causes can influence the normal growth of the facial skeleton. Congenital anomalies, from syndromic conditions to facial clefts, affect normal growth and development. Traumatic events in the developing facial skeleton can disturb normal subsequent growth. Other etiologies that can result in significant dentofacial anomalies include neoplastic growth, surgical resection, and iatrogenic radiation. However, of all the etiologies, developmental anomalies represent the most common conditions requiring orthognathic surgery

Prevalence

The exact incidence of dentofacial deformities requiring orthognathic surgery is difficult to estimate because it includes a broad population of patients with deformities of congenital, developmental, and traumatic origin. Generally, however, the prevalence of dentofacial deformities has been estimated as 20% of the population world wide of which 2% warrant surgery. The number of individuals with developmental dentofacial deformities in the United States who may benefit from orthognathic surgery is estimated approximately 20% of the US population (5). In this study, the prevalence of severe Class II malocclusions (defined as > 6 mm overjet) was found to be 4.3% in the age groups of 1850 years, while that of Class III malocclusions (defined as 3 mm overjet) was 0.3%

Correction of maxillofacial deformities requires careful analysis of the soft tissue with clinical examination and supporting photographs, skeletal evaluation with standardized radiographs, dental impressions, face-bow transfers, bite registrations, and articulator-mounted models. Clinical assessment should be directed specifically at evaluating the relative position and size of each of the facial skeletal elements, the degree of zygomatic projection, and the maxillary and mandibular positions in space relative to each other and to the cranial-orbital region. The nasolabial angle, upper lip length, lip competency, labial-mental sulcus, and cervicomental angle should be documented

Diagnosis and preoperative planning

Diagnosis and preoperative planning Facial balance typically is assessed by dividing the face in thirds. The upper third is from the anterior hairline (trichion) to the glabella, the middle third from the glabella to the subnasale, and the lower third from the subnasale to the menton. When each of the thirds is equal, the face is said to be balanced and of "ideal" proportions. The lower third may be further divided into an upper third (subnasale to oral commissure) and a lower two thirds (oral commissure to menton). Additionally, in profile view the face should have a slight degree of convexity as measured from the glabella to the subnasale to the menton. Excess facial convexity, flatness, or concavity is felt to be less than ideal. However, facial proportions are only idealized concepts and have changed over time

Facial proportions

Profile analysis; angle of convexity

Any facial asymmetry should be noted along with the relationship of the maxillary dental mid line to the mandibular dental mid line and the dental mid lines to the facial mid line. The degree of dental display on repose and smile also should be recorded with the amount of gingival display. The muscles of mastication and TMJ function should be assessed. The intraoral examination should focus on the dental alignment within each arch and relationship of the dental arches to each other. The periodontal status of the teeth and the patient's hygiene should be evaluatedDiagnosis and preoperative planning

Among the steps in planning for orthognathic surgery, preoperative cephalometric tracings are noteworthy and should be performed with accuracy. Tracings are usually performed on transparent acetate paper. Tracing may aid in getting the pattern of facial profile changes. Repositioning these patterns may determine the choice of the type of osteotomy and provide an estimate of the amount of bone which must be advanced, recessed or grafted. In addition, cephalometric records are valuable in assessing the postoperative changes and accurately measure resultant relapse. Numerous cephalometric analyses have been proposed, the simplest one is that of Steiner (6,7) Diagnosis and preoperative planning

Steiner used the skull cephalometric landmarks (points) that were proposed by anthropologists and orthodontists. These points are: S = Sella turcica center N = Nasion (the fronto-nasal suture) ANS = Anterior nasal spine A = Subspinale (the most deepest point on the midline contour of the alveolar process of the maxilla) Pg = Pogonion (the most anterior point of the symphysis) B = Supramentale (the most deepest point on the midline contour of the alveolar process of the mandible) Diagnosis and preoperative planning

Anatomic landmarks

Skeletal Analysis

To initiate analytical model surgery, maxillary and mandibular impressions are taken and stone casts poured. These are subsequently mounted with a face-bow transfer onto an anatomic articulator. Landmarks, horizontal and vertical reference marks are made directly on the casts to quantify the amount, the direction and extent of jaw movement. Segmental cuts (Mock Surgery) are then performed on the casts to mimic the cuts that will be made during surgery. The casts are then remounted according to the prescribed movements determined in the treatment plan. Subsequently, surgical guide splint is fabricated, which is critical for the accurate intraoperative positioning of the maxilla and/or mandible. Splint fabrication can use self-cure or light-cure acrylicDiagnosis and preoperative planning

Dental casts mounted onto an anatomic articulator Reference lines are marked

Surgical guide splint fabrication

The final stage of the surgical planning process is transferring surgical plan to operation room. Surgical splints are used to place the osteotomized jaw bone segments into a desired position. This approach, however, has drawback for accurate simulation of real bony movement based on 2D radiographic evaluation and dental models. The limitations are directed to landmark identification and overlapping of anatomic structures, especially for patients with facial asymmetry . Further, it is impossible to simulate different surgeries with a single model. Once the model is cut, it is impossible to undo it Diagnosis and preoperative planning

The advent of virtual surgical planning has recently called into question the efficacy and accuracy of traditional analytical model surgery which is time consuming and imprecise (8). Currently three-dimensional imaging and computer simulation are used for planning office-based procedures. The system allows cephalometric analysis, can be used to perform virtual surgery and establish a definitive and objective treatment plan for correction of facial deformity,thus improving the accuracy and reliability of diagnosis and treatment.Moreover, unlike conventional model surgery on dental casts, this technology allows to virtually perform multiple simulations of different osteotomies and skeletal movements in order to evaluate multiple surgical plans (9)Diagnosis and preoperative planning

Three-dimensional imaging

3D cephalometric analysis

Computer-aided design and manufacturing (CAD/CAM) technique, Virtual surgery

Surgical splints milled onpolymethyl methacrylate

More recently, the concept of an occlusal-based orthognathic positioning system has been introduced (10). The orthognathic positioning system has the possibility to eliminate the inaccuracies commonly associated with traditional orthognathic surgery planning and to simplify the execution by eliminating surgical steps such as intraoperative measuring, determining the condylar position, the use of bulky intermediate splints, and the use of intermaxillary wire fixation. The system attempts precise translation of the virtual plan to the operating field, bridging the gap between virtual and actual surgeryDiagnosis and preoperative planning

Maxillary positioning guides firmly attached to splint with bone footplates placed over previously drilled landmarks

Mandibular positioning guide held in place by temporary screws before skeletal fixation

Genioplasty positioning guides in place after osteotomy and repositioning of skeletal segment

Indications of Orthognathic SurgeryOrthognathic surgery is performed to correct a wide range of minor and major skeletal and dental irregularities, including the misalignment of jaws and teeth. Aesthetic improvement has been cited as the main concern of patients seeking orthognathic surgery (11).Common indications for orthognathic surgery include the following: Difficulty chewing, biting, or swallowing Speech problems Breathing problems Micrognathia / Prognathia Chronic jaw pain

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Numerous risk factors may alter the treatment plan or preclude surgery, including underlying medical conditions, bleeding dyscrasias, systemic disease or local factors that may affect normal wound healing, compromised vascularity of the surgical region, a patient with unrealistic expectations, a noncompliant patient, and patients with poor oral hygiene

Contraindications ofOrthognathic Surgery

Surgical procedures Historically, the specialty of orthognathic surgery did not fully develop until Obwegeser (12,13) demonstrated the possibility of repositioning the maxilla in a stable consistent manner in 1965 and reported simultaneous repositioning of the maxilla and mandible in 1970. The most common surgical techniques currently used for the correction of dentofacial deformities, with various modifications, are the Le Fort I osteotomy of the maxilla, the bilateral sagittal split osteotomy of the mandible, the oblique ramus osteotomy of the mandible, and genioplasty

Maxillary surgical procedures

Le Fort I osteotomy is a surgical technique which is performed to correct deficiency of the midface region. Surgery for maxillary advancement is performed with an osteotomy subapical to the teeth but inferior to the infrazygomatic crest from the piriform aperture to the pterygo-maxillary junction. Osteotomy is also performed on the nasal septa and the tuberosity is separated from the pterygoid plates. Osteotomy of these strategic structures enables the displacement of the maxilla to a new desired position, where it is rigidly fixed to correct the vertical and/or sagittal discrepancies (14)

Le Fort I osteotomy

When a narrowing or widening of the dental arch is needed, or a level of the occlusal plane is desired, a segmental Le Fort I can be performed. This procedure differs from a Le Fort I mainly in the way that the maxilla is split into segments (15)Le Fort II and Le Fort III osteotomies are similar to the Le Fort I but the Le Fort II involves osteotomies to the orbital floor and the Le Fort III osteotomy involves the lateral orbital rim and zygomaMaxillary surgical procedures

Three pieces maxilla segmentationTwo pieces maxilla segmentation

Le Fort II and Le Fort III osteotomies

Surgically assisted rapid maxillary expansion is a distraction osteogenesis procedure expanding the maxilla transversally, using either a tooth-borne or a bone-borne distractor after surgery. The surgery is performed by a corticotomy from the piriform aperture to the pterygo-maxillary junction followed by a vertical osteotomy at the anterior nasal spine and the median palatal suture in order to separate the maxillary halves. The transversal widening is performed by the distractor (16)Maxillary surgical procedures

Surgically assisted rapid maxillary expansion

Mandibular surgical procedures

Bilateral sagittal split osteotomy (BSSO) has a wide range of indications and can be used in almost every possible movement, which includes the entire horizontal ramus of the mandible. The mandible can be advanced, set back, tilted or augmented with bone grafts. The surgical procedure starts with a horizontal cut through the lingual cortex of the vertical ramus above the mandibular foramen. The sagittal cut through the cortex follows the oblique line. The final osteotomy before the split is a vertical osteotomy through the buccal cortex in the mandibular body (17)

Intraoral vertical ramus osteotomy (IVRO) is a procedure mainly correcting mandibular prognathism making a vertical cut through the ramus of the mandible proximal to the mandibular foramen (17). The main advantage with IVRO compared to BSSO is a lower incidence of damage of the inferior alveolar nerve. The main disadvantage with IVRO compared to BSSO is the need of maxilla-mandibular fixation (MMF) due to the lack of possibility of rigid fixation between the segments (18)Mandibular surgical procedures

A variant of IVRO is the extraoral vertical ramus osteotomy (EVRO), making an extraoral incision, dissecting to get to the inferior border of the mandible before making the osteotomy. This has been advocated for large mandibular setbacks (> 10mm), large vertical moves and difficult facial asymmetries. Except for the risk of scarring and the risk of damaging the mandibular branch of the Facial nerve, the same risks have been reported as for IVRO (17)

Mandibular surgical procedures

Bilateral sagittal split osteotomy

Vertical ramus osteotomy

GenioplastyIn cases treating patients with micrognathia, retrognathia, prognathia, chin asymmetry or mandibular vertical height discrepancies, sliding genioplasty is a treatment option, which involves an osteotomy repositioning the chin to the desired position. This procedure is performed together with, or without orthognathic surgery to be able to achieve good aesthetic results, with fairly high predictability in soft tissue response and low complication risk (19)

Osseous genioplasty procedure

Distraction osteogenesis

Another approach to perform a movement of either the mandible or the maxilla is distraction osteogenesis, where the movement is performed gradually after surgery, using a distractor device. The main advantages of osteodistraction compared to conventional orthognathic surgery is that; it allows the soft tissue to expand simultaneously as the bone expands, it does not require bone grafts, it is possible to repeat surgery at the same site and the fact that it is a simple technique with minimal blood loss (20)

ComplicationsMost of the common complications of orthognathic surgery occur frequently enough that they must be discussed with each patient in detail. Common complications which may occur in orthognathic surgery include vascular disease, TMJ problems, nerve damage, infection, bone necrosis, vision impairment, hearing problems, and neuropsychiatric problems. Rarely complications could be fatal. Excessive bleeding has been reported as a common complication of Le Fort osteotomies. Injury to the infraorbital nerve during a Le Fort I osteotomy or the inferior alveolar nerve during a sagittal split osteotomy of the mandible typically represent a neurapraxia. TMDs may be improved somewhat by correction of a malocclusion with orthognathic surgery, however, there is a subset of patients whose symptoms worsen after surgery (21)

With any skeletal movement, the surgeon always must be aware of the potential for relapse even in the most ideal situation and with the use of rigid internal fixation. Soft-tissue forces directed against the vector of the surgical movement are significant. Generally, the most stable moves are superior and posterior maxillary impactions and mandibular setback. Advancements of the maxilla, whether vertically or sagittally, are inherently less stable, as is mandibular advancement

Complications

1. Zarrinkelk HM, Throckmorton GS, Ellis E III, et al. Functional and morphologic changes after combined maxillary intrusion and mandibular advancement surgery. J Oral Maxillofac Surg; 54: 828, 1996. 2. Rodrigues-Garcia RCM, Sakai S, Rugh JD, et al. Effects of major Class II occlusal corrections on temporomandibular signs and symptoms. J Orofac Pain; 12: 185, 1998. 3. Proffit WR, Tulloch JFC, Medland PH. Surgical versus orthodontic correction of skeletal Class II malocclusion in adolescents: Effects and indications. Int J Adult Orthod Orthognath Surg; 7: 209, 1992. 4. Tucker MR. Orthognathic surgery versus orthodontic camouflage in the treatment of mandibular deficiency. J Oral Maxillofac Surg; 53: 572, 1995. 5. Proffit WR, Fields HW Jr, Moray LJ. Prevalence of malocclusion and orthodontictreatment need in the United States: Estimates from the NHANES III survey. Int J Adult Orthod Orthognath Surg; 13: 97, 1998.6. Steiner CC. Cephalometrics in clinical practice. Angle Orthod; 29: 8, 1959. 7. Steiner CC. The use of cephalometrics as an aid to planning and assessing orthodontic treatment. Am J Orthod; 46: 721, 1960. 8.Choi JY, Song KG, Baek SH. Virtual model surgery and wafer fabrication for orthognathic surgery. Int J Oral Maxillofac Surg; 38: 1306, 2009.

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9. Hernndez-Alfaro F, Guijarro-Martnez R. New protocol for three-dimensional surgical planning and CAD/CAM splint generation in orthognathic surgery: an in vitro and in vivo study. Int J Oral Maxillofac Surg; 42: 1547, 2013.10. Polley JW, Figueroa AA. Orthognathic positioning system: intraoperative system to transfer virtual surgical plan to operating field during orthognathic surgery. J Oral Maxillofac Surg; 71: 911, 2013.11. Rivera S., Hatch J., Rugh J. Psychosocial factors associated with orthodontic and orthognathic surgical treatment. Seminars in Orthodontics; 6: 259, 2000. 12. Obwegeser HL. Surgical correction of small or retrodisplaced maxillae. The "Dish-face" Deformity. Plastic & Reconstructive Surgery; 43: 351, 1969. 13. Obwegeser HL. (1970). The one time forward movement of the maxilla and backward movement of the mandible for the correction of extreme prognathism. SSO Schweiz Monatsschr Zahnheilkd; 80: 547, 1970.14. Bell, WH. (1975). Le Fort I osteotomy for correction of maxillary deformities. J Oral Surg; 33: 412, 1975.15. Bailey, LJ. White, RP. Proffit, WR. et al. Segmental LeFort I osteotomy for management of transverse maxillary deficiency. J Oral Maxillofac Surg; 55: 728, 1997. 16. Koudstaal MJ, Poort LJ, van der Wal KGH, et al. Surgically assisted rapid maxillary expansion (SARME): a review of the literature. Int J Oral Maxillofac Surg; 34: 709, 2005.

References:

17. Bloomquist DS, Lee JJ. Mandibular orthognathic surgery. In Petersonss Principles of oral and maxillofacial surgery, 3rd Ed. Miloro M, Ghali G, Larsen P, Waite P (eds). Peoples Medical Publishing House- USA; PP 1317-64, 2012.18. Ghali GE, Sikes JW. Intraoral vertical ramus osteotomy as the preferred treatment for mandibular prognathism. J Oral Maxillofac Surg; 58: 313, 2000. 19. Chang EW, Lam SM, Karen M, et al. Sliding genioplasty for correction of chin abnormalities. Arch Facial Plast Surg; 3: 8, 2001.20. Andersson L, Kahnberg KE, Pogres MA (eds). Oral and Maxillofacial Surgery. Chichester: Wiley-Blackwell, 1149-1172, 2010. 21. Khechoyan DY. Orthognathic Surgery: General Considerations. Semin Plast Surg; 27: 133, 2013.References: