Mandibular osteotomies
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The document provides an overview of various mandibular osteotomy techniques used in orthognathic surgery. It discusses the history, indications, techniques, advantages, disadvantages, and complications of bilateral sagittal split osteotomy (BSSO), internal vertical ramus osteotomy, body osteotomies, subapical osteotomies, and genioplasty. BSSO is one of the most common techniques described, allowing advancement, setback, or rotation of the mandible with minimal soft tissue stripping, though it carries risks of nerve injury, malocclusion, and relapse. Alternative techniques such as internal vertical ramus osteotomy are discussed as being easier but providing less control over condylar positioning.
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Mandibular osteotomies
- 2. Contents • Introduction • History • Techniques • Indications • Contraindications • Advantages • Disadvantages • Procedure • Complications • Conclusion
- 3. Introduction Orthognathic surgery is a process in which dentofacial deformities and malocclusions are corrected with orthodontics and surgical operations of the facial skeleton, sometimes combined with various soft tissue procedures. The term orthognathic originates from the Greek words orthos , ‘straight’, and gnathos ‘jaw’. It is possible to correct, or “straighten”, deformities separately in either the maxilla or the mandible with many types of surgical techniques or to do procedures concurrently on both jaws.
- 4. History Extra-oral techniques • 1954 – Caldwell and Lettermen surgery in the ramus through submandibular incision • 1967 – Hinds and Girotti – skin incision parallel to post border of ramus • 1968 – Caldwell - detach coronoid process for stability
- 5. Intra-oral techniques • 1848 – Hullihen – subapical osteotomy of anterior mandible • 1957 – Obwegeser and Trauner – SSRO • Modification – Dalpont, Hunsuck, Epker and Bell • 1968 – Winstanly – IVSO • 1970 – modification by Herbert, Kent and Hinds
- 6. ANATOMICAL & PHYSIOLOGICAL CONSIDERATIONS OF MANDIBULAR OSTEOTOMIES Vascular structures NervesMuscles
- 7. Vascular supply • TMJ capsule and lateral pterygoid muscle • Pterygomassetric sling • Lingual periosteum
- 8. Nerve anatomy • Rajchel et al. (1986) - 45 Asian adults - third-molar region - 2.0 mm from the inner lingual cortex, - 1.6 to 2.0 mm from medial aspect of buccal plate, - 10 mm from the inferior border
- 9. MUSCLES Orthognathic surgery affects muscles in primarily two ways: • It changes the length of a muscle or it changes the direction of muscle function. • The muscles commonly discussed in orthognathic surgery of the mandible have been the muscles of mastication and the suprahyoid group of muscles .
- 10. Techniques Ramus procedures • Bilateral sagittal split osteotomy • Vertical ramus osteotomy • Inverted L osteotomy • C osteotomy Body procedures • Anterior • Posterior Subapical procedures • Anterior • Posterior • Total Genial procedures
- 11. Bilateral sagittal split osteotomy • Modifications
- 12. 1907 - Blair • published the horizontal flat subcondylar osteotomy of the mandible to correct class II dysgnathias by advancement of the mandibular body.
- 13. 1942 – Schuchardt • cortical osteotomy was performed in an oblique way starting from just above the lingula and reaching the buccal cortex 1 cm more caudally without touching the intra- alveolar nerve (IAN).
- 14. 1957 – Trauner and Obwegeser • increased the gap between the horizontal cuts to 25 mm, preserving IAN. (the saggital split)
- 15. 1961 – Dalpont
- 16. 1968 – Hunsuck
- 17. 1977 – Bell - Epker
- 18. 1976 – Spiessel – RIF • Introduced rigid internal fixation in the form of interfragmentary bone screws. .
- 19. Indications • Horizontal mandibular excess, deficiency, and asymmetry • Mandibular advancement • Mandibular setback of up to 7mm • Minor asymmetries
- 20. Contraindications • Severe decreased posterior mandibular body height • Extremely thin medial-lateral width of ramus • Severe ramus hypoplasia • Severe mandibular asymmetries
- 21. Step 1 • Infiltration of soft tissue with a vasoconstrictor Step 2 • Soft tissue incision Step 3 • Buccal subperiosteal dissection Step 4 • Superior subperiosteal dissection Technique
- 22. Step 5 • Medial subperiosteal dissection and exposure of the lingula Step 6 • Identification of the lingula Step 7 • Medial ramus osteotomy Step 8 • Vertical section of the osteotomy
- 24. Step 9 • Removing the notched ramus retractor and placing a channel retractor Step 10 • Buccal osteotomy of the mandibular body
- 25. Step 11 • Drilling holes for a holding wire
- 27. Step 12 • Drilling a hole for the condylar positioner Step 13 • Placing reference marks
- 28. Step 14 • Lavage Step 15 • Defining the osteotomy cut with an osteotome Step 16 • Splitting the mandible
- 29. Step 17 • Completion of the split Step 18 • Stripping the pterygomasseteric sling
- 30. Step 19 • Stripping the medial pterygoid muscle and stylomandibular ligament Step 20 • Removal of impacted third molars
- 31. Step 21 • Smoothing contact areas of bone segments Step 22 • Placement of a holding wire Step 23 • Noting the position of the inferior alveolar neurovascular bundle Step 24 • Noting the position of the third molar (or its socket)
- 32. Step 25 • Mobilization of the distal segment Step 26 • Selective odontoplasty and maxillomandibular fixation Step 27 • Removal of bone from the proximal segment
- 33. Step 29 • Tightening the holding wire Step 28 • Condylar positioning
- 34. Step 30 • Placement of the trocar Step 31 • Drilling bicortical holes and placing screws
- 35. Step 32 •Removing maxillomandibular fixation and checking the occlusion
- 36. Step 33 •Intraoperative diagnosis of a malocclusion Step 34 •Placement of intraoral and extraoral sutures Step 35 •Placement of elastics Step 36 •Placement of a pressure bandage
- 37. Advantages of BSSO • Adequate bony interface for fast healing • Advance, setback or rotate the mandible • Occlusal plane can be altered • Correct most asymmetries • No need to strip the muscles of mastication
- 38. Disadvantages of BSSO • Osteotomies on the lingual aspect - difficult • Increased incidence of nerve damage • Technically difficult • Difficult to correct large discrepancies and asymmetries
- 39. Complications • Condylar sag • Malocclusion • Unfavorable splits • Relapse • Nerve injury • TMJ dysfunction and hypomobility • Hemorrhage
- 40. Condylar sag • ‘immediate or late caudal movement of the condyle in the glenoid fossa after surgical establishment of a preplanned occlusion and rigid fixation of the bone fragments, leading to a change in the occlusion’
- 41. Types • Central
- 42. • Peripheral type I
- 43. • Peripheral type II
- 44. Malocclusion • Anterior open bite • Posterior open bite • Lateral shift • Release and reapply fixation • Post operative MMF
- 45. Unfavourable splits • Incidence – 3-20% • Proximal segment fractures • Failure to cut the inferior border before applying chiesels • Impacted third molars • Distal segment fractures • Splits short of lingula • Retromolar fracture
- 46. Relapse - Multifactorial - Expected with mandibular advancements greater than 7 mm - Relapse increases with - amount of initial advancement, - change in the mandibular plane
- 47. Nerve injury • Neuropraxia • Axonotemesis and neurotemesis of IAN • Lingual n. paraesthesia • Facial n. weakness - E/O technique
- 48. TMJ dysfunction & Hypomobility • 50% of patients – some degree of dysfunction • Causes • Prolonged immobility • Intra-articular hemorrhage • Fibrosis • Pre-existing TMJ disorders
- 49. Haemorrhage • Minor – tearing of periosteum • Major – damage to inferior alveolar, masseteric artery or retromandibular vein • Treatment • Pressure packing • Ligation • Prevention • Subperiosteal dissection • Adequate retraction of soft tissue
- 50. Internal vertical ramus osteotomy
- 51. Indications • Horizontal mandibular excess • Asymmetric set back of the mandible (on the side that moves in a posterior direction) • Minor occlusal discrepancy after Le Fort I osteotomy • Vertical correction of the mandible
- 52. Contraindications • Advancement of distal tooth bearing segments • Recent condylar fracture is a relative contraindication to IVRO • Large setbacks and lengthening the ramus (unless temporalis, medial pterygoid & masseter muscles are detached from the distal segment)
- 53. Advantages • Technically easy (faster and simpler operation) • Can correct mandibular prognathism or asymmetries • Lower incidence of permanent inferior alveolar nerve injury
- 54. Disadvantages • Difficult to control the position of the condyle • Increased healing time • Difficult to use rigid fixation intraorally • MMF for 4 to 8 weeks and long term interarch elastics to control occlusion
- 55. Step 1 • Infiltration of the soft tissue with a vasoconstrictor Step 2 • Mucosal incision- over the external oblique ridge close to the mucogingival junction Step 3 • Periosteal incision Step 4 • Subperiosteal dissection Technique
- 56. Step 5 •Placement of the retractors
- 57. Step 6 • Identificati on of landmarks
- 58. Step 7 •First vertical osteotomy Step 8 •Second vertical osteotomy
- 61. Step 9 • Subperiosteal stripping on the medial aspect of the distal segment Step 10 • Repeating the procedure on the opposite side Step 11 • Throat pack removal Step 12 • Maxillomandibular fixation
- 62. Step 13 •Checking the bone contacts Step 14 •Suturing
- 63. Complications • Bleeding • Massetric artery and vein • Reposition proximal segment, pack the osteotomy site and external pressure for 5-10min • Nerve injury • IAN: 1-8% • Nerve is loosely tethered when it enters canal • Angled shank of the saw • Rigid fixation not necessary • Unfavorable osteotomy • Abort the procedure and treat like a fracture • Continue the procedure and fix the fractured segment
- 64. • Indications • to increase both the ramus height and body length at the same time, especially when the sagittal split osteotomy is not possible (eg: congenital mandibular hypoplasia or, occasionally, acquired hypoplasia following condylar fractures or when previous surgery has disturbed the bony anatomy) Inverted L and C osteotomies
- 65. Advantages • Can correct mandibular prognathism or asymmetries • Coronoid process and temporalis muscle remain in original position • Can setback mandible greater distance • Can lengthen ramus or advance the mandible
- 66. Disadvantages • Bone grafts necessary for ramus lengthening or mandibular advancement • Healing time may be increased compared to other technique because of poor approximation of the segments when grafts are not used
- 67. Technique • Skin marking and infiltration • Incision and dissection • Exposure of ramus and identification of anti-lingular eminence
- 68. • bone cut (b/l if required) • Mobilising the mandible • Fixing into occlusion
- 69. •Confirming condylar fragment in the fossa •Measuring of the gap and making a template for graft •Interpositional bone graft
- 70. •Fixation with miniplates •Insertion of vacuum drain and closure in layers •Removal of inter-maxillary fixation and throat pack
- 71. Drawbacks • Skeletal in-stability • Farrell and Kent – reported skeletal relapse of inverted L and C osteotomies similar to that of BSSO.
- 72. Body osteotomies • History • 1907 – first described by Blair – extraoral procedure • Dingman (1944) – combination of I/O and E/O • Indications • Treatment of prognathism when there is already edentulous spaces. • Mandibular advancement • Anterior open bite closure • Progenia correction
- 73. Anatomic considerations • Distal segment is set back into a wider proximal segment - Reduction in bone contact • Torquing of proximal segment • Position of inferior alveolar nerve
- 78. Complications • Nerve damage • Damage to the roots of teeth • Periodontal defects at the osteotomy sites • Nonunion
- 79. Subapical osteotomies • Three types of mandibular Subapical osteotomies • Anterior subapical osteotomy • Posterior subapical osteotomy • Total alveolar ostetotomy
- 80. Indications of anterior subapical osteotomy • Correction of nonskeletal open bite / bimaxillary protrusion • Level the plane of occlusion • uprighting the anterior teeth to a more normal angulation
- 81. Anterior mandibular subapical osteotomy
- 82. Anterior subapical osteotomy (kole’s Procedure)
- 83. Technique Downward and posterior movements
- 84. • b/l extraction of premolars for distal movement • incision • Elevation of mucoperiosteum and revealing of mental nerve
- 85. •Making vertical cuts •Horizontal cuts well below the canine apices
- 86. • mobilization • Accurate dentolaveolar localization • Palting, closure and pressure bandage
- 87. Forward Movement • useful for correcting a Class II, division 1 deep overbite and overjet, where a sagittal split has been declined. Upward Movement
- 88. Posterior subapical osteotomy • Indications : • Correction of supraeruption of posterior mandibular teeth • Abnormal buccal or lingual positioning of teeth when orthodontics is not feasible
- 89. Total subapical osteotomy • Indications • Malocclusion due to mandibular dentoalveolar deformity • Occlusal discrepancies without associated esthetic changes • Substitute for orthodontic levelling (occasionally)
- 90. Complications • Loss of bone and / or teeth in the osteotomised segment • Loss of tooth vitality • Periodontal defects • Nonunion /malunion • Malocclusion • Neurosensory disturbances
- 91. Genioplasty • 1942 – Hofer – horizontal sliding osteotomy • 1951 – Converse – feasability of bone grafts • 1957 – Trauner and Obwegeser – horizontal osteotomy – intraoral incision • 1965 – Riechenbach – wedge ostectomy and vertical shortening of chin • Hind’s and Kent – discuss the importance of maintaining soft tissue attachment
- 92. Procedures • Horizontal osteotomy with advancement • Horizontal osteotomy with AP reduction • Double sliding horizontal osteotomy • Vertical reduction genioplasty • Vertical augmentation
- 93. Technique Step 1 • Infiltration of soft tissue with a vasoconstrictor Step 2 • Mucosal incision (distal to the canine to a similar point on the contralateral side) Step 3 • Submucosal incision
- 95. Step 5 • Establishing reference points
- 97. Step 7 • Osteotomy of the chin Step 8 • Mobilization of the chin Step 9 • Engaging the positioning wire Step 10: • Final mobilization of the chin segment
- 98. Step 11 •Refinement of the osteotomy Step 12 •Repositioning the chin
- 99. Step 13 • Countersinking holes for tricortical screw fixation
- 100. Step 14 •Placement of tricortical screws
- 101. Step 15 • Bone plate fixation as an alternative to screw fixation
- 102. Step 16 • Anteroposterior reduction of the chin
- 104. Step 18 • Vertical reduction of the chin
- 105. Step 19 • Correction of asymmetry of the chin
- 106. Step 20 • Altering the width of the chin Widening or narrowing the posterior dimension of the chin
- 107. Widening or narrowing the anterior dimension of the chin
- 108. Step 21 • Suturing the submucosal tissue Step 22 • Suturing the mucosa Step 23 • Applying a pressure dressing
- 109. Complications of genioplasty • Prolonged neurosensory disturbance • Avascular necrosis of mobilized segments • Hemorrahage causing lingual hematoma/ possible airway compromise • Unaesthetic soft tissue changes • Chin ptosis • Excessive lower tooth display • Bony resorption under alloplasts • Devitilization of teeth • Mandibular fracture • Creation of mucogingival problems • Asymmetry and unaesthetic end result
- 110. Conclusion • Increased patient awareness and our understanding of the subject is essential for better results and satisfaction. • Key – esthetics and function.
- 111. References • Oral and maxillofacial surgery Volume II Orthognathic Surgery ,Raymond J. Fonseca ,D. M. D. • Essentials of orthognathic surgey, J P Reyneke • Oral and maxillofacial surgery volume I, Peter Ward Booth. • Böckmann et al. The Modifications of the Sagittal Ramus Split Osteotomy : A Literature Review, PRS Global Open, 2014
- 113. Soft tissue changes • Movement of soft tissues of the mandible follow the hard tissue closely with exception of lower lip
- 114. Soft tissue changes - advancement • Lower lip lengthens • marked increase in facial height (high angle class II cases )
- 115. Mandibular setback • Lower lip shortens and labiomental fold deepens
- 116. Soft tissue changes • Superior mandibular repositioning • Lower lip becomes shorter • Protrusive • Smaller in area • Inferior mandibular repositioning • Lower lip becomes longer with increased area
- 118. A Retrospective Analysis of the Stability and Relapse of Soft and Hard Tissue Change After Bilateral Sagittal Split Osteotomy for Mandibular Setback of 64 Taiwanese Patients J Oral Maxillofac Surg 63:355-361, 2005 • 64 pts – average setback of 7 mm • Average setback of Pog – 5.34 mm • Soft tissue pog – 4.85 mm • Pog/ pog = 1: 0.88 at 1 yr
- 119. Skeletal Change at Surgery as a Predictor of Long-Term Soft Tissue Profile Change After Mandibular Advancement STEPHEN D. KEELING, J Oral Maxillofac Surg 54:134-144, 1996 • 20 pts – mandibular advancement • Followed for 2 yrs – cephalometics analysis • Horizontal & vertical hard tissue changes – stable for 2 yrs PO • Vertical soft tissue changes – stable for 2 yrs (p >0.08) • Horizontal soft tissue relapse by 8 wks esp lower lip & inf sulcus
- 120. Healing • Immediate post operative: • General intramedullary circulation • Osteotomy margins – avascular • Cortical ischemia in soft tissue flaps • Reduce pulpal & periodontal flow • One week of healing: • Well vascularized proximal & distal segment • No e/o soft tissue rettachment/ revascularization • Isolated areas of subperiosteal bone formation
- 121. • Two weeks post operatively: • Well perfused proximal segment, avascular zone around osteotomy & no reattachment • ed circulation at the osteotomized cortices • e/o subperiosteal bone formation • Three weeks post operatively: • Complete soft tissue reattachment • Signs of vascular anastomosis • Thickening of the reattached periosteum • Osteoids and new bone formation thru out marrow • Distinct organization of new blood vessels
- 122. • Six weeks post operatively: • Circulation reconstituted across the osteotomy site • Flaps revacularized • e/o muscle attachment • Twelve weeks post operatively: • Continuous cortex present • Bony remodelling at the site of union
Editor's Notes
- Ssro- saggital split ramus osteotomy Ivso- intraoral vertical subcondylar osteotomy (IVSO)
- Bell and Levy’s work {1970} demonstrated that blood flow through the mandibular periosteum could easily maintain a sufficient blood supply to the teeth of a mobile segment, even when the labial periosteum was degloved. subapical osteotomies need to be carefully planned to ensure as large a vascular pedicle as possible. The proximal segment of the vertical sub sigmoid osteotomy maintains its blood supply through the temporomandibular joint capsule and the attachment of the lateral pterygoid muscle. But the inferior tip of this fragment has undergone vascular necrosis in some studies. This led to the suggestion that fewer problems may occur if the cut was made above the angle of the mandible.
- digastric, stylohyoid, geniohyoid, and mylohyoid muscles.
- required prolonged intermaxillary fixation, which was already regarded as an inconvenience due to a lack of bone contact between the osteotomized segments.
- without fixation of the proximal and distal segments, this procedure only led to a minor reduction of complications.
- wider distance between the lingual and buccal cuts increased the overlapping bony amount of the segments, which rendered better stability and better results at a lower risk of pseudarthrosis
- advances and rotates the lower horizontal cut even further to the buccal cortex of the mandibular body as a vertical cut between the first and second molars. The angle created between the lingual and buccal cortical cuts was approximately 90 degrees, leading to an extension of the connecting cut along the oblique line on the lateral mandibular aspect through the mylohyoid groove on the lingual side In the same article, Dal Pont reported a less quoted alternative technique that he called the “oblique retromolar osteotomy.” The lingual horizontal corticotomy ended just behind the lingula.
- The buccal vertical cut by Hunsuck was located at the “union of the ascending ramus and the body of the mandible in the tooth bearing region.” In Hunsuck’s illustrations, this area was just distal of the second molar running down to the mandibular notch anterior of the insertion point of the masseteric muscle thought that it was not necessary to make an actual cut through the lingula as Dal Pont had done in his technique. Hunsuck was convinced that the lingual split of the Dal Pont osteotomy would occur naturally given that chisels were used to split the mandible.
- Furthermore, Epker refined the original Dal Pont technique by explaining the buccal corticotomy in detail, emphasizing the need for a complete osteotomy of the inferior mandibular cortex to avoid bad splits. Denied wide reflection of the masseteric muscle to prevent relapse. Favored 2-wire stabilization of both segments proximally low and distally high, thereby preventing the condylar sag and relapse.
- Their research showed that the screws added to the stability of the fragments and decreased healing time because of fragment compression osteosynthesis. In addition, Spiessl also favored the use of thin bone saws for precise osteotomies over thicker burrs, thereby saving as much bone as possible to reduce the gap between the split segments. Only small gaps were allowed for stable compression osteosynthesis. Spiessl also introduced a new osteotomy technique by removing the lingual aspect of the cortical bone plate covering the oblique line in the retromolar region
- Visualization of the lingula can be improved by reduction of a convex internal oblique ridge using a large trimming bur.
- d) The horizontal ramus osteotomy should be made parallel to the occlusal plane. The osteotomy should end posterior to the lingula in the fossa. (e) The distal segment will be positioned posteriorly and also tend to move superiorly in patients with mandibular setback and high occlusal plane angles. In these patients, a small segment of bone should be removed superior to the horizontal osteotomy line to prevent interference between the segments. (f) The horizontal osteotomy should be carried past the lingula; otherwise, there will be a strong tendency for the mandible to split anterior to the lingula.
- g) The buccal osteotomy is started at the lower border of the mandible and joined superiorly with the vertical ramus osteotomy. (h) The buccal osteotomy is angled slightly obliquely and posteriorly to enhance the start of the split. (i) It is mandatory to include the lingual cortex in the buccal osteotomy to ensure that it forms part of the proximal segment at the start of the split.
- Positioning of the holes for mandibular advancement. (j) For a 6-mm advancement, the holes are placed 10 mm apart (the hole in the distal segment should be posterior to that in the proximal segment). (k) After a 6-mm mandibular advancement, the holes will be 4 mm apart, ensuring a vector that will support the advancement of the tooth-bearing segment and seat the condyle.
- Positioning of holes for mandibular setback. (l) For a mandibular setback of 6 mm, the holes are placed 2 mm apart, with the hole in the proximal segment posterior to that in the distal segment. (m) After a 6-mm setback, the holes will be 4 mm apart with the vector of the holding wire supporting the tooth-bearing segment and the condyle.
- The hole for the engagement of the condylar positioner is placed in a low, anterior position on the proximal segment
- The split is started by tapping a 10-mm-wide osteotome along the vertical osteotomy, from the medial to the buccal osteotomy. A small Reyneke sagittal split separator is placed deep into the buccal osteotomy, and the lower border is engaged.
- A curved periosteal elevator is used to strip the pterygomasseteric sling from the distal bone segment and also to ensure that the split is complete at the lower and posterior borders.
- (gg) The positions of the medial pterygoid muscle (anterior and inferior) and the stylomandibular ligament (posterior and superior) on the medial aspect of the mandibular angle. (hh) The attachments of the muscle and ligament on the bone and their relation to the sagittal osteotomy are demonstrated. (ii) These attachments will interfere when the proximal segment is repositioned anteriorly or posteriorly and may lead to rotation of the proximal segment.
- (kk) The condylar positioner is placed in a hole drilled into the buccal cortex (see step 12). (ll) The condyle is carefully pushed superiorly and slightly anteriorly in the fossa by the condylar positioner and digital force on the mandibular angle. The assistant can now tighten the positioning wire.
- (a) The condyle is positioned inferiorly in the glenoid fossa with no bone contact while the teeth are in occlusion (maxillomandibular fixation) and rigid fixation is placed. (b) After removal of maxillomandibular fixation, the condyle will move superiorly, causing immediate relapse.
- In type I, the condyle is positioned inferiorly, with some fossa contact (lateral, medial, posterior, or anterior) with the maxillomandibular fixation in position (teeth in occlusion) and rigid fixation placed. This type of condylar malpositioning provides physical support to the occlusion (Fig 5-7a). Postoperative resorption or a change in condylar shape will lead to late relapse (Fig 5-7b).
- In type II, the condyle is positioned correctly in the fossa with the maxillomandibular fixation in position (teeth in occlusion); however, with the placement of rigid fixation, a torquing force is applied to the condyle and ramus of the mandible (Figs 5-8a and 5-8b). The tension on the ramus is released when the maxillomandibular fixation is removed, and the condyle will move either laterally or medially and slide inferiorly in the fossa (Fig 5-8c).
- Type I- Difficult to diagnose intraoperatively because the contact between the condyle and glenoid fossa supports the occlusion, which may lead to late relapse due to condylar resorption
- To preent Van Sickels – Skeletal fixation for 1-2 weeks Suprahyoid myotomies Orthodontic overcorrection. - Suprahyoid myotomies - large mandibular advancements accompanied by a large counterclockwise rotation
- (a) The Bauer retractors are placed to retract the soft tissue and expose the lateral surface of the ramus. One retractor is hooked into the sigmoid notch while the other is hooked around the lower border of the mandible into the antigonial notch.
- (b) The antilingular eminence corresponds to the alveolar foramen on the medial side of the ramus and gives the clinician an indication of the position of the inferior alveolar foramen. The eminence is usually situated about 10 mm above the occlusal plane, and it can be found about two-thirds posterior of the width of the mandibular ramus. A reference line (red line) is marked 2 mm posterior to the eminence from the sigmoid notch superior to the antigonial notch inferior.
- (c) A round oscillating saw is used to perform the first osteotomy 2 mm posterior to the reference line (shown at A) started superiorly, and once the surgeon feels the saw perforate the medial cortex, the blade is moved downward to the antigonial notch.. A second osteotomy Because of the increased risk of damage to the branches of the maxillary artery, which are located medially near the mandibular foramen, the oscillating saw blade should not be inserted deeply when performing this part of the procedure. It is recommended that the blade be held slightly obliquely at this stage., shown at B, is angulated slightly anteriorly and performed from the superior end of the reference line into the sigmoid notch.
- (d) The distal segment can now be easily mobilized and the osteotomized surface of the distal segment seen (arrow).
- (e) The medial pterygoid muscle and stylomandibular ligament attachments on the medial surface of the distal segment should be carefully dissected off the bone (arrow).
- The mean distance of the branching point of the maxillary artery to the tip of the condyle was 22.4 mm (range, 21.66 to 23.99 mm).
- (a 5 cm submandibular or retromandibular incision for –extra oral)
- made from the anterior border of the ascending ramus, passing distally, to behind the estimated position of the lingula then downwards to the lower border anterior to the angle, i.e. to the antegonial notch
- The ideal source is cortico-cancellous bone from the iliac crest. A solid cancellous graft can be used but the incorporation of one cortex provides reassuring stability. Some surgeons use split rib for the gap.
- To increase bone contacts
- Indications: To move the anterior mandible in every desirable direction[ant,post,sup,inf-repositioning] Incision : is started 1cm behind the planned vertical osteotomy& is carried 4-5mm below the attached gingiva & is brought to the midline & connected with the opposing incision.
- curved incision starting below the papilla distal to the site of the vertical bone cut
- by an acrylic wafer with an arch bar heavy arch wire, or an open cast silver splint, all previously prepared on the lower model after model surgery. The splint is secured with circum-mandibular wires. The osteotomy is secured with bone plates.
- Once the alveolar segment has been mobilised forwards and fixed by plates or a wafer and arch bars, the vertical gaps are packed with bone chips from the iliac crest and covered with a buccal mucosal flap rotated over the alveolar crest to be carefully sutured to the lingual mucosa with horizontal mattress sutures. Upward Movement
- The soft tissue incision is angled to maintain more submucosal tissue for later ease of suturing.
- Use a 701 bur to mark the dental midline on the bone superiorly and inferiorly to the intended osteotomy. Make small, shallow holes, keeping the roots of the incisors in mind, and score a line into the cortex to connect the holes (Fig 5-4c). Deepen the inferior hole by angling the bur superiorly and extending the hole well through the cortex. This hole is intended for the placement of a positioning wire later in the procedure. Place the hole in thick bone to ensure that the wire will not pull through (Fig 5-4d). For accurate repositioning of the chin, place reference marks approximately 15 mm lateral to the midline to assist with symmetric repositioning.
- The osteotomy should be performed at least 5 mm below the roots of the incisors and 5 mm below the mental foramen. Keep in mind that the course of the mental nerve prior to its exit through the mental foramen is approximately 5 mm inferior and anterior to the foramen.
- Perform the osteotomy with an oscillating saw by starting in the center and cutting laterally. Ensure that both cortices are osteotomized.
- Although a golden rule in orthognathic surgery is “Never change your treatment plan on the operating table,” genioplasty may be the exception. The surgeon may use clinical judgment at the time of surgery to slightly alter the repositioning of the chin for a better esthetic result.
- When tricortical bone screw fixation is contemplated, countersink two holes in the buccal cortex approximately 8 mm on either side of the marked midline of the osteotomized segment. Position the countersunk holes at least 5 mm from the superior edge of the segment to accommodate the head of the screw
- (k) A hole is drilled through all three cortices using a trocar to protect the soft tissue. (l) A trocar is used to place a tricortical screw to fixate the chin segment. At least two screws should be placed to secure the bone segment.
- Use a prefabricated chin fixation plate, an X- or H-shaped bone plate, or two straight bone plates with two screws on either side of the osteotomy. The positioning wire and digital pressure help stabilize the chin segment in its planned position
- n) For setback procedures of the chin, bone plate fixation is the method of choice. In setback procedures, the use of a positioning wire is impractical. (o) The medial aspect of the posterior area of the chin segment is removed to prevent a palpable step defect on the lower border of the mandible (arrow). (p) The labiomental fold is enhanced by contouring the anterior edge on the superior aspect of the mandible.
- Vertical increase of the chin. The chin segment is held at the planned height with a positioning wire. Two bone plates are then placed to fixate the segment. Finally, the defect is grafted.
- Vertical reduction of the chin. The lower osteotomy is performed first, and the planned amount of bone is then removed superiorly.
- (s) Lateral movement of the chin. The midline of the chin is marked below the osteotomy line and the facial midline above the osteotomy line. After mobilization of the chin, the chin segment is moved laterally until the lines coincide. (t) Propeller osteotomy. A first osteotomy (1) is performed parallel to the interpupillary line. A second osteotomy (2) is then performed parallel to the lower border of the chin. (u) The triangular segment, pedicled to the hyoid muscles, is rotated 180 degrees. (v) The two segments are secured by rigid fixation.
- (w) Widening the posterior dimension of the chin. A midline osteotomy is performed through the chin segment after placement of a bone plate on the anterior surface. The plate is now used as a hinge, widening the posterior chin, and a small bone graft is placed in the midline defect. (x) Narrowing the posterior dimension of the chin. A bone plate is placed on the anterior surface of the chin and a triangular midline ostectomy performed. The segment is now bent medially to narrow the chin.
- (y) Widening the anterior dimension of the chin. An osteotomy is performed in the center of the chin segment. (z) After increasing the anterior width of the chin, a bone graft is placed between the segments. (aa) Narrowing the anterior dimension of the chin. A midline ostectomy is performed in the center part of the chin. (bb) After removal of the ostectomized bone, the lateral segments are moved medially.
- To achieve the best esthetic results, it is mandatory that the mentalis muscles be accurately reapproximated. Mucosal suturing should follow.