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Complications of the mandibular sagittal split ramus osteotomy associated with the presence or absence of third molars
CLINICAL ARTICLES J Oral Maxillofac Surg 59:854-858, 2001
Complications of the Mandibular Sagittal Split Ramus Osteotomy Associated With the Presence or Absence of Third Molars Pushkar Mehra, BDS, DMD,* Vanessa Castro, DDS,† Rogerio Z. Freitas, DDS,‡ and Larry M. Wolford, DMD§ Purpose:
This study compared the number of unfavorable fractures after sagittal split osteotomies (SSOs) of the mandible when third molars were present or absent. Patients and Methods: The treatment records of 262 patients (500 SSOs) were retrospectively evaluated. Group 1 consisted of 250 SSOs and concomitant removal of impacted mandibular third molars and group 2 consisted of 250 SSOs with absence of third molars. A modified SSO technique with inferior border cuts was used on all patients, and the third molars, when present, were removed after separation of the proximal and distal segments. Rigid fixation was applied using bicortical bone screws. Bone plates with monocortical screws were additionally used to secure the free bony segments of the proximal segment in cases with unfavorable fracture. Results: There were 11 (2.2%) unfavorable fractures in 500 SSO procedures. The incidence of unfavorable splits was 3.2% in group 1 and 1.2 % in group 2. In group 1, all fractures occurred in teenagers, with 7 of 8 fractures extending through the extraction socket in the distal segment. Six of the 8 fractures were associated with completely impacted third molars, and 2 involved partially impacted teeth. All 3 fractures in group 2 occurred in the proximal segment. No significant difference was seen in the amount of relapse in patients with unfavorable or favorable splits. Conclusions: The occurrence of unfavorable splits is uncommon when using a modification of the SSO that includes an inferior border osteotomy. Although more unfavorable fractures occurred in teenage patients with third molars, this had no impact on the stability of the final result. © 2001 American Association of Oral and Maxillofacial Surgeons The ramus sagittal split osteotomy (SSO) is the most common osteotomy performed because of its versatility for both advancement and setback of the mandible. Introduced by Schuchart in 1942,1 the SSO was first modified and popularized by Trauner and Obwegeser in 1957.2 Early modifications of the original SSO were proposed by Dal Pont in 19613 and by Hunsuck in 1968.4 Despite its frequent use and versatility, the SSO has been described in the literature as
a technically difficult procedure, with numerous possible intraoperative complications.5,6 This has led to further modifications of the SSO technique7-17 to try to decrease the frequency of intraoperative complications and to increase the stability and predictability of the postsurgical results.5 One complication is an unfavorable fracture occurring during the SSO, which can result in infection, sequestration of the fragment, delayed union, mal-
*Formerly, Fellow in Oral and Maxillofacial Surgery, Baylor College of Dentistry, Texas A & M University System, and Baylor University Medical Center, Dallas, TX; Currently Assistant Professor, Department of Oral & Maxillofacial Surgery at Boston University School of Dental Medicine, Boston, MA. †Former Visiting Resident in Oral and Maxillofacial Surgery, Baylor College of Dentistry, Texas A & M University System, and Baylor University Medical Center, Dallas, TX; Currently in Private Practice, Brasilia, Brazil. ‡Former Fellow in Oral and Maxillofacial Surgery, Baylor College of Dentistry, Texas A&M University System, and Baylor University
Medical Center, Dallas, TX; Currently in Private Practice, Brasilia, Brazil. §Clinical Professor of Oral and Maxillofacial Surgery, Baylor College of Dentistry, Texas A & M University System, Dallas, TX; Private Practice, Baylor University Medical Center, Dallas, TX. Address correspondence and reprint requests to Dr Wolford: 3409 Worth St, Suite 400, Sammons Tower, Dallas, TX 75246; e-mail: [email protected] © 2001 American Association of Oral and Maxillofacial Surgeons
0278-2391/01/5908-0002$35.00/0 doi:10.1053/joms.2001.25013
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union, or fibrous union of the osteotomy sites.6 This can also cause postsurgical instability and mandibular dysfunction. An increased risk of unfavorable fracture has been associated with the presence of third molars at the osteotomy site.5,6,18-22 It has been postulated that this compromises the bony architecture of the mandible.18 The purpose of this retrospective study was to compare the incidence of unfavorable fractures during SSO (using a modified surgical technique) with the presence or absence of third molars and to see if there is an association between unfavorable fractures and long-term clinical outcomes and other factors specifically related to the third molars.
Patients and Methods The study included a retrospective analysis of the treatment records of 262 patients treated with SSO of the mandible in a single, solo private practice. Criteria for inclusion in the study were: 1) SSO performed for correction of dentofacial deformity and malocclusion; 2) use of rigid fixation for the SSO; and 3) a minimum of 12 months postsurgery follow-up. The patients were divided into 2 groups: group 1 included 250 SSOs of the mandible in 137 consecutive patients who underwent concomitant removal of third molars at the time of surgery and group 2 included 250 SSOs in 125 consecutive patients with either congenital absence of third molars or who had the third molars removed at least 1 year before the
FIGURE 1. Diagram of the sagittal split osteotomy. The horizontal cut is made perpendicular to the buccal cortex, extending at least 5 mm beyond the amount of mandibular advancement to control position of the proximal segment (arrows). The path of the cut in the third molar region maintains a portion of the external oblique ridge in the distal segment, thereby maintaining buccal and lingual bone in the third molar region and increasing the structural strength of the distal segment.
FIGURE 2. An inferior border osteotomy is performed using a specifically designed reciprocating saw blade. This allows for focusing of the forces required for the split to be directed at the inferior border and not superiorly at the buccal cortex.
SSO was performed. The number of unfavorable splits was determined for each group. All patients underwent SSO of the mandible by 1 surgeon using the surgical modification previously described by Wolford et al16,17 (Figs 1, 2). This modification included: 1) a horizontal cut in the buccal cortex perpendicular to the bone and extending from the distal of the second molar forward at least 5 mm farther than the amount of mandibular advancement (this controls the spatial position of the proximal segment); 2) a portion of the external oblique ridge was maintained in the posterior part of the distal segment in the third molar region (increases structural strength of this already thin area); 3) an inferior border cut with a specially designed reciprocating saw blade (Hall Surgical Division of Zimmer, Largo, FL) minimizes the splitting forces directed at the superior and buccal aspects of the proximal segment and thus reduces buccal cortex fractures; and 4) splitting by prying and spreading rather than by the use of chisels. After separating the proximal and distal segments, the third molar, when present, was sectioned with burs if necessary and was surgically removed from a buccal approach. With all favorable splits, the SSO were rigidly stabilized using two to five 2.0-mm diameter bicortical screws. All unfavorable fractures were also rigidly stabilized using three to five 2.0-mm diameter bicortical screws, with 1 screw stabilizing the posterior part of the fractured distal segment to the proximal segment. In addition, a 1.1-mm thick bone plate with 4 to 6 monocortical bone screws was used to secure the free bony proximal segment. All 262 patients had panoramic radiographs and standardized lateral cephalograms taken presurgery (T1), immediately postsurgery (T2), and at least 12 months postsurgery (T3). The T2 and T3 lateral cephalometric acetate tracings were superimposed and
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assessed by 1 examiner to calculate the long-term stability (T3-T2) of the postsurgical outcomes as measured at point B (Pt B). The unfavorable splits were then analyzed for the following factors: degree of third molar impaction; degree of third molar development; posterior mandibular height; presurgical occlusal plane angle; postsurgical alveolitis (dry socket) or infection; type of mandibular movement (advancement vs setback); long-term stability of results; and patient age at surgery. Student’s t test was used to determine the statistical significance of the data obtained, and a P value of less than .05 was considered statistically significant.
Results The average age for group 1 patients was 17.7 years (range, 13 to 44 years) and for group 2, the average age of patients was 36.6 years (range, 17 to 56 years). In the 500 SSOs performed, 489 favorable splits and 11 unfavorable fractures occurred (ie, a 2.2 % incidence of unfavorable fractures). Seven of the 11 fractures occurred in the distal segment (Fig 3A), and 4 of 11 fractures occurred in the proximal segment (Fig 3B). Group 1 (with third molars) had 5 patients with 8 unfavorable fracture in the 250 SSOs (3.2% incidence), and group 2 (without third molars) had 2 patients with 3 unfavorable fractures in the 250 SSO performed (1.2% incidence). The difference in the number of unfavorable fractures between the groups was not statistically significant (P ⬎ .05). GROUP 1 (n ⫽ 8)
The 8 fractures (3 bilateral, 1 right side, and 1 left side) occurred in 5 different patients. Five of the fractures were complete and 3 were incomplete (greenstick). Although 7 fractures occurred vertically through the third molar socket in the distal segment, 1 fracture occurred in the proximal segment. Six fractures were associated with full bony impaction of the third molar, and 2 occurred with partially impacted third molars. Comparing the 8 fractures with the degree of the third molar development showed that 1 fracture occurred with one half crown formation, 5 with two thirds crown formation, and 2 with partial root formation. All patients with unfavorable fractures were teenagers with an average age of 15.9 years (range, 15 to 16 years). GROUP 2 (n ⫽ 3)
The 3 fractures were seen in 2 patients (1 bilateral and 1 right side). All fractures were complete and occurred in the proximal segment. The 2 patients with fractures were aged 42 and 44 years, respectively.
FIGURE 3. General location of unfavorable fractures. A, Type of fracture seen in the distal segment. B, Type of fracture seen in the proximal segment.
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Average relapse at Pt B at the longest follow-up (average, 19.4 months; range, 14 to 83 months) was 0.25 mm for patients with favorable splits (n ⫽ 489) and 0.30 mm for patients with unfavorable splits (n ⫽ 11). This difference was not statistically significant (P ⬎ .05). There were no trends observed for increased risk of an unfavorable fracture relative to occlusal plane angle, type of mandibular movement (advancement or setback), and posterior mandibular height. Postsurgical infection and/or alveolitis were not encountered in any of the 500 SSOs performed.
Discussion Despite being the most common mandibular osteotomy performed today, the SSO is still considered by many to be a technically difficult procedure with several potential intraoperative complications.5,6,18,23 The occurrence of unfavorable fractures or splits in the proximal and distal segments of the mandible during SSO has been reported with an incidence ranging from 2% to 20%.6,18,23 Various modifications of the SSO have been proposed to avoid such unfavorable fractures.5,14,15,17 It has been reported that a lower incidence during SSO may be encountered with the use of a modified “spreading” SSO technique rather than with the traditional “mallet and chisel” SSO technique.18 The modification of the SSO used in this study used an inferior border osteotomy with a specially designed inferior border saw, followed by prying the segments apart with Smith spreading instruments and a 3-prong Smith spreader (W. Lorenz Surgical, Jacksonvile, FL).16,17 No chiseling or malleting was usually performed during execution of the SSO, thereby minimizing chances of unfavorable fractures or inadvertent nerve damage during instrumentation. Although the presence of third molars has been identified as a predisposing factor for unfavorable fractures during SSO,24-27 very few detailed studies are available. Guersney and DeChamplain24 presented data on 44 SSOs and found that 3 of the 5 unfavorable fractures in their study had an impacted tooth removed before surgery. Tucker23 in 1995 evaluated SSOs with and without third molars and reported the incidence of unfavorable fractures to be 4% with third molars and 3% without third molars. However, no mention was made of the location or type of fracture. Recently, Precious et al18 reported an overall incidence of 1.9% unfavorable fractures in 633 patients who underwent SSO. In that comprehensive study, the patients had third molars extracted either at the time of the SSO or at least 6 months before surgery. The authors found that unfavorable fractures were approximately 3 times less frequent when the im-
857 pacted third molars were removed at the time of the SSO (0.94 %) than when removed at least 6 months before SSO (2.62 %).18 Based on their findings, they suggested that removal of third molars at least 6 months before SSO does not reduce the incidence of unfavorable fractures and, in most cases, the third molar removal and SSO can be safely carried out in one operation.18 Epker and Fish22 recommended that third molars be removed at the time of the SSO to avoid 2 separate surgeries. El Deeb and Wolford28 also recommended that third molars be removed at the time of the SSO but, if the surgeon prefers to remove them before the SSO, it should be done at least 9 to 12 months before surgery to allow for complete socket bone fill and maturation. The buccal cortex of the mandible normally is thin posterior to the second molar, weakening this region, and this can contribute to fracture of the proximal segment.29,30 The presence of third molars can further thin and weaken this region. In the presence of third molars, the lingual cortex of the distal segment is also usually very thin, and this increases the risk of a vertical fracture through the tooth socket. When impacted third molars are removed before surgery, aggressive removal of the bone, particularly lingually, can predispose the mandible to an unfavorable fracture during surgery, especially in cases where the mandible is already thin or where anatomic irregularities exist.18,22,31,32 A vertical fracture through the third molar socket may also occur after uneventful splitting of the mandible, during removal of the impacted third molar. Surgically sectioning the impacted tooth and removing it in segments can help prevent this from occurring. The results of this study show that in the 500 SSOs performed the overall incidence of unfavorable fractures was infrequent (2.2 %), irrespective of the presence or absence of third molars. However, the degree of third molar impaction and development did affect the incidence of unfavorable splits. Complete tooth impaction was seen in 6 of the 8 fractures (75 %), and 5 of the 8 fractures (62.5%) were associated with two thirds crown formation. A relationship between the patient’s age and unfavorable splits was seen in group 1. The average age of the patients was 17.7 years (range, 13 to 44 years), which was significantly lower than for group 2 patients, where the average age was 36.6 years (range, 17 to 56 years). The average age of the patients with unfavorable fractures in group 1 was even lower at 15.9 years (range, 15 to 16 years). The age distribution for all patients in group 1 was: age 13 to 14 years, 16 patients; age 15 to 16 years, 70 patients; and age 17 years and older, 51 patients. Thus, 14% of the patients in the 15- to 16-year age group had unfavorable frac-
858 tures, whereas no patient in the other age groups had an unfavorable fracture. Young teenagers have much thinner, immature cortical bone than adults and, with additional thinning caused by development of the coronal portion of the third molar, this patient population may have a greater predisposition to unfavorable fractures. However, younger patients have greater bone elasticity and, during the splitting, incomplete microfractures can occur, accounting for the greater incidence of greenstick fractures in group 1 (37.5%) than in group 2 (0 %). Thus, greater care must be taken during surgery in the young teenage patient with third molars to avoid unfavorable splits.
Conclusions The results of this study show that when using a modification of the SSO that includes an inferior border cut, the occurrence of unfavorable splits is infrequent, irrespective of the presence or absence of third molars. When third molars are present during the SSO, unfavorable fractures usually occur in young, teenage patients. Although more unfavorable splits may occur in the presence of third molars, this has no adverse influence on the success or stability of the SSO surgery provided that the surgeon is able to complete the split and rigidly stabilize the bony segments.
References 1. Schuchart K: Ein Beitrag zur chirurischen Kieferorthopadie unter Berucksichtigung ihrer Bedeutung fur die Behandlung angeborener under worbener Kieferdeformitaten bie Soldaten. Dtsch Zahn- Mund-Kieferhk 9:73, 1942 2. Trauner R, Obwegeser H: The surgical correction of mandibular prognathism and retrognathia with consideration of genioplasty. Oral Surg Oral Med Oral Pathol 10:677, 1957 3. Dal Pont G: Retromolar osteotomy for the correction of prognathism. J Oral Surg 19:42, 1961 4. Hunsuck EE: A modified intraoral sagittal splitting technique for correction of prognathism. J Oral Surg 26:250, 1968 5. Marquez IM, Stella JP: Modification of sagittal split ramus osteotomy to avoid unfavorable fracture around impacted third molars. Int J Adult Orthod Orthognath Surg 13:183, 1998 6. O’Ryan FS: Complications of orthognathic surgery. Oral Maxillofac Surg Clin North Am 2:593, 1990 7. Epker BN: Modifications in sagittal osteotomy of the mandible. J Oral Surg 35:157, 1977 8. Brusati R, Fiamminghi L, Sesenna E, et al: Functional disturbances of the inferior alveolar nerve after sagittal osteotomy of the mandibular ramus: Operating technique for prevention. J Maxillofac Surg 9:123, 1981
COMPLICATIONS OF MANDIBULAR SSO 9. MacIntosh RB: Experience with the sagittal split osteotomy of the mandibular ramus: A 13-year review. J Maxillofac Surg 9:151, 1981 10. Lines P: Modification of the sagittal split ramus technique. J Oral Maxillofac Surg 40:245, 1982 11. Leonard MS, Ziman P, Bevis R, et al: The sagittal split osteotomy of the mandible. Oral Surg Oral Med Oral Pathol 60:459, 1985 12. Kitajima T, Handa Y, Naitoh K: A modification of the sagittal splitting technique. J Craniomaxillofac Surg 17:53, 1989 13. Niederdellmann H, Shetty V: Technical improvement in the sagittal split ramus osteotomy. Oral Surg Oral Med Oral Pathol 67:25, 1989 14. Loh FC: Technical modification the sagittal split mandibular ramus osteotomy. Oral Surg Oral Med Oral Pathol 74:723, 1992 15. Max D, Rotskoff K: A modified technique for the sagittal split osteotomy. J Oral Maxillofac Surg 51:1050, 1993 16. Wolford LM, Davis WM: The mandibular inferior border split: A modification in the sagittal split osteotomy. J Oral Maxillofac Surg 48:92, 1990 17. Wolford LM, Bennett MA, Rafferty CG: Modification of the mandibular ramus sagittal split osteotomy. Oral Surg Oral Med Oral Pathol 64:146, 1987 18. Precious DS, Lung KE, Pynn BR, et al: Prence of impacted teeth as a determining factor of unfavorable splits in 1256 sagittalsplit osteotomies. Oral Surg Oral Med Oral Pathol 85:362, 1998 19. Van Sickels JE, Jeter TS, Theriot BA: Management of an unfavorable lingual fracture during a sagittal split osteotomy. J Oral Maxillofac Surg 43:808, 1985 20. Bell W: Surgical Correction of Dentofacial Deformities: New concepts, vol III. Philadelphia, PA, Saunders, 1985, p 738 21. Epker BN, Wolford LM: Dentofacial Deformities (ed 1). St Louis, MO, Mosby, 1986, p 232 22. Epker BN, Fish LC: Dentofacial Deformities. Integrated Orthodontic and Surgical Correction, vol 1 (ed 1). St Louis, MO, Mosby, 1986, p 232 23. Tucker MR: Sagittal ramus osteotomy with and without third molars. J Oral Maxillofac Surg 53:80, 1995 24. Guersney LH, DeChamplain: Sequelae and complications of the intraoral sagittal osteotomy of the mandibular rami. Oral Surg Oral Med Oral Pathol 32:176, 1971 25. Turvey TA: Intraoperative complications of sagittal osteotomy of the mandibular ramus: Incidence and management. J Oral Maxillofac Surg 43:504, 1985 26. Epker BN, Stella JP, Fish LC: Dentofacial Deformities. Integrated Orthodontic and Surgical Correction, vol 1 (ed 2). St Louis, MO Mosby, 1995, pp 193-367 27. Terry BC, White RR Jr: Mandibular ramus surgery, in Proffit WR, White RP Jr (eds): Surgical-Orthodontic Treatment. St Louis, MO, Mosby, 1991, pp 264-274 28. El Deeb M, Wolford LM: Complications of orthognathic surgery. Clin Plast Surg 16:825, 1989 29. Smith BR, Rajchel JL, Waite DE, et al: Mandibular ramus anatomy as it relates to the medial osteotomy of the sagittal split ramus osteotomy. J Oral Maxillofac Surg 49:12, 1991 30. Schubert W, Kobienia BJ, Pollock RA: Cross-sectional area of the mandible. J Oral Maxillofac Surg 55:689, 1997 31. Kaplan PA, Tu HK, Koment MA, et al: Radiography after orthognathic surgery, II. Surgical complications. Radiography 166:199, 1988 32. Jonsson E, Svatrz K, Welander V: Sagittal split technique. Part I. Immediate postoperative conditions: A radiographic follow-up study. Int J Oral Surg 8:75, 1979
Complications of the Mandibular Sagittal Split Ramus Osteotomy Associated With the Presence or Absence of Third Molars Pushkar Mehra, BDS, DMD,* Vanessa Castro, DDS,† Rogerio Z. Freitas, DDS,‡ and Larry M. Wolford, DMD§ Purpose:
This study compared the number of unfavorable fractures after sagittal split osteotomies (SSOs) of the mandible when third molars were present or absent. Patients and Methods: The treatment records of 262 patients (500 SSOs) were retrospectively evaluated. Group 1 consisted of 250 SSOs and concomitant removal of impacted mandibular third molars and group 2 consisted of 250 SSOs with absence of third molars. A modified SSO technique with inferior border cuts was used on all patients, and the third molars, when present, were removed after separation of the proximal and distal segments. Rigid fixation was applied using bicortical bone screws. Bone plates with monocortical screws were additionally used to secure the free bony segments of the proximal segment in cases with unfavorable fracture. Results: There were 11 (2.2%) unfavorable fractures in 500 SSO procedures. The incidence of unfavorable splits was 3.2% in group 1 and 1.2 % in group 2. In group 1, all fractures occurred in teenagers, with 7 of 8 fractures extending through the extraction socket in the distal segment. Six of the 8 fractures were associated with completely impacted third molars, and 2 involved partially impacted teeth. All 3 fractures in group 2 occurred in the proximal segment. No significant difference was seen in the amount of relapse in patients with unfavorable or favorable splits. Conclusions: The occurrence of unfavorable splits is uncommon when using a modification of the SSO that includes an inferior border osteotomy. Although more unfavorable fractures occurred in teenage patients with third molars, this had no impact on the stability of the final result. © 2001 American Association of Oral and Maxillofacial Surgeons The ramus sagittal split osteotomy (SSO) is the most common osteotomy performed because of its versatility for both advancement and setback of the mandible. Introduced by Schuchart in 1942,1 the SSO was first modified and popularized by Trauner and Obwegeser in 1957.2 Early modifications of the original SSO were proposed by Dal Pont in 19613 and by Hunsuck in 1968.4 Despite its frequent use and versatility, the SSO has been described in the literature as
a technically difficult procedure, with numerous possible intraoperative complications.5,6 This has led to further modifications of the SSO technique7-17 to try to decrease the frequency of intraoperative complications and to increase the stability and predictability of the postsurgical results.5 One complication is an unfavorable fracture occurring during the SSO, which can result in infection, sequestration of the fragment, delayed union, mal-
*Formerly, Fellow in Oral and Maxillofacial Surgery, Baylor College of Dentistry, Texas A & M University System, and Baylor University Medical Center, Dallas, TX; Currently Assistant Professor, Department of Oral & Maxillofacial Surgery at Boston University School of Dental Medicine, Boston, MA. †Former Visiting Resident in Oral and Maxillofacial Surgery, Baylor College of Dentistry, Texas A & M University System, and Baylor University Medical Center, Dallas, TX; Currently in Private Practice, Brasilia, Brazil. ‡Former Fellow in Oral and Maxillofacial Surgery, Baylor College of Dentistry, Texas A&M University System, and Baylor University
Medical Center, Dallas, TX; Currently in Private Practice, Brasilia, Brazil. §Clinical Professor of Oral and Maxillofacial Surgery, Baylor College of Dentistry, Texas A & M University System, Dallas, TX; Private Practice, Baylor University Medical Center, Dallas, TX. Address correspondence and reprint requests to Dr Wolford: 3409 Worth St, Suite 400, Sammons Tower, Dallas, TX 75246; e-mail: [email protected] © 2001 American Association of Oral and Maxillofacial Surgeons
0278-2391/01/5908-0002$35.00/0 doi:10.1053/joms.2001.25013
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union, or fibrous union of the osteotomy sites.6 This can also cause postsurgical instability and mandibular dysfunction. An increased risk of unfavorable fracture has been associated with the presence of third molars at the osteotomy site.5,6,18-22 It has been postulated that this compromises the bony architecture of the mandible.18 The purpose of this retrospective study was to compare the incidence of unfavorable fractures during SSO (using a modified surgical technique) with the presence or absence of third molars and to see if there is an association between unfavorable fractures and long-term clinical outcomes and other factors specifically related to the third molars.
Patients and Methods The study included a retrospective analysis of the treatment records of 262 patients treated with SSO of the mandible in a single, solo private practice. Criteria for inclusion in the study were: 1) SSO performed for correction of dentofacial deformity and malocclusion; 2) use of rigid fixation for the SSO; and 3) a minimum of 12 months postsurgery follow-up. The patients were divided into 2 groups: group 1 included 250 SSOs of the mandible in 137 consecutive patients who underwent concomitant removal of third molars at the time of surgery and group 2 included 250 SSOs in 125 consecutive patients with either congenital absence of third molars or who had the third molars removed at least 1 year before the
FIGURE 1. Diagram of the sagittal split osteotomy. The horizontal cut is made perpendicular to the buccal cortex, extending at least 5 mm beyond the amount of mandibular advancement to control position of the proximal segment (arrows). The path of the cut in the third molar region maintains a portion of the external oblique ridge in the distal segment, thereby maintaining buccal and lingual bone in the third molar region and increasing the structural strength of the distal segment.
FIGURE 2. An inferior border osteotomy is performed using a specifically designed reciprocating saw blade. This allows for focusing of the forces required for the split to be directed at the inferior border and not superiorly at the buccal cortex.
SSO was performed. The number of unfavorable splits was determined for each group. All patients underwent SSO of the mandible by 1 surgeon using the surgical modification previously described by Wolford et al16,17 (Figs 1, 2). This modification included: 1) a horizontal cut in the buccal cortex perpendicular to the bone and extending from the distal of the second molar forward at least 5 mm farther than the amount of mandibular advancement (this controls the spatial position of the proximal segment); 2) a portion of the external oblique ridge was maintained in the posterior part of the distal segment in the third molar region (increases structural strength of this already thin area); 3) an inferior border cut with a specially designed reciprocating saw blade (Hall Surgical Division of Zimmer, Largo, FL) minimizes the splitting forces directed at the superior and buccal aspects of the proximal segment and thus reduces buccal cortex fractures; and 4) splitting by prying and spreading rather than by the use of chisels. After separating the proximal and distal segments, the third molar, when present, was sectioned with burs if necessary and was surgically removed from a buccal approach. With all favorable splits, the SSO were rigidly stabilized using two to five 2.0-mm diameter bicortical screws. All unfavorable fractures were also rigidly stabilized using three to five 2.0-mm diameter bicortical screws, with 1 screw stabilizing the posterior part of the fractured distal segment to the proximal segment. In addition, a 1.1-mm thick bone plate with 4 to 6 monocortical bone screws was used to secure the free bony proximal segment. All 262 patients had panoramic radiographs and standardized lateral cephalograms taken presurgery (T1), immediately postsurgery (T2), and at least 12 months postsurgery (T3). The T2 and T3 lateral cephalometric acetate tracings were superimposed and
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assessed by 1 examiner to calculate the long-term stability (T3-T2) of the postsurgical outcomes as measured at point B (Pt B). The unfavorable splits were then analyzed for the following factors: degree of third molar impaction; degree of third molar development; posterior mandibular height; presurgical occlusal plane angle; postsurgical alveolitis (dry socket) or infection; type of mandibular movement (advancement vs setback); long-term stability of results; and patient age at surgery. Student’s t test was used to determine the statistical significance of the data obtained, and a P value of less than .05 was considered statistically significant.
Results The average age for group 1 patients was 17.7 years (range, 13 to 44 years) and for group 2, the average age of patients was 36.6 years (range, 17 to 56 years). In the 500 SSOs performed, 489 favorable splits and 11 unfavorable fractures occurred (ie, a 2.2 % incidence of unfavorable fractures). Seven of the 11 fractures occurred in the distal segment (Fig 3A), and 4 of 11 fractures occurred in the proximal segment (Fig 3B). Group 1 (with third molars) had 5 patients with 8 unfavorable fracture in the 250 SSOs (3.2% incidence), and group 2 (without third molars) had 2 patients with 3 unfavorable fractures in the 250 SSO performed (1.2% incidence). The difference in the number of unfavorable fractures between the groups was not statistically significant (P ⬎ .05). GROUP 1 (n ⫽ 8)
The 8 fractures (3 bilateral, 1 right side, and 1 left side) occurred in 5 different patients. Five of the fractures were complete and 3 were incomplete (greenstick). Although 7 fractures occurred vertically through the third molar socket in the distal segment, 1 fracture occurred in the proximal segment. Six fractures were associated with full bony impaction of the third molar, and 2 occurred with partially impacted third molars. Comparing the 8 fractures with the degree of the third molar development showed that 1 fracture occurred with one half crown formation, 5 with two thirds crown formation, and 2 with partial root formation. All patients with unfavorable fractures were teenagers with an average age of 15.9 years (range, 15 to 16 years). GROUP 2 (n ⫽ 3)
The 3 fractures were seen in 2 patients (1 bilateral and 1 right side). All fractures were complete and occurred in the proximal segment. The 2 patients with fractures were aged 42 and 44 years, respectively.
FIGURE 3. General location of unfavorable fractures. A, Type of fracture seen in the distal segment. B, Type of fracture seen in the proximal segment.
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Average relapse at Pt B at the longest follow-up (average, 19.4 months; range, 14 to 83 months) was 0.25 mm for patients with favorable splits (n ⫽ 489) and 0.30 mm for patients with unfavorable splits (n ⫽ 11). This difference was not statistically significant (P ⬎ .05). There were no trends observed for increased risk of an unfavorable fracture relative to occlusal plane angle, type of mandibular movement (advancement or setback), and posterior mandibular height. Postsurgical infection and/or alveolitis were not encountered in any of the 500 SSOs performed.
Discussion Despite being the most common mandibular osteotomy performed today, the SSO is still considered by many to be a technically difficult procedure with several potential intraoperative complications.5,6,18,23 The occurrence of unfavorable fractures or splits in the proximal and distal segments of the mandible during SSO has been reported with an incidence ranging from 2% to 20%.6,18,23 Various modifications of the SSO have been proposed to avoid such unfavorable fractures.5,14,15,17 It has been reported that a lower incidence during SSO may be encountered with the use of a modified “spreading” SSO technique rather than with the traditional “mallet and chisel” SSO technique.18 The modification of the SSO used in this study used an inferior border osteotomy with a specially designed inferior border saw, followed by prying the segments apart with Smith spreading instruments and a 3-prong Smith spreader (W. Lorenz Surgical, Jacksonvile, FL).16,17 No chiseling or malleting was usually performed during execution of the SSO, thereby minimizing chances of unfavorable fractures or inadvertent nerve damage during instrumentation. Although the presence of third molars has been identified as a predisposing factor for unfavorable fractures during SSO,24-27 very few detailed studies are available. Guersney and DeChamplain24 presented data on 44 SSOs and found that 3 of the 5 unfavorable fractures in their study had an impacted tooth removed before surgery. Tucker23 in 1995 evaluated SSOs with and without third molars and reported the incidence of unfavorable fractures to be 4% with third molars and 3% without third molars. However, no mention was made of the location or type of fracture. Recently, Precious et al18 reported an overall incidence of 1.9% unfavorable fractures in 633 patients who underwent SSO. In that comprehensive study, the patients had third molars extracted either at the time of the SSO or at least 6 months before surgery. The authors found that unfavorable fractures were approximately 3 times less frequent when the im-
857 pacted third molars were removed at the time of the SSO (0.94 %) than when removed at least 6 months before SSO (2.62 %).18 Based on their findings, they suggested that removal of third molars at least 6 months before SSO does not reduce the incidence of unfavorable fractures and, in most cases, the third molar removal and SSO can be safely carried out in one operation.18 Epker and Fish22 recommended that third molars be removed at the time of the SSO to avoid 2 separate surgeries. El Deeb and Wolford28 also recommended that third molars be removed at the time of the SSO but, if the surgeon prefers to remove them before the SSO, it should be done at least 9 to 12 months before surgery to allow for complete socket bone fill and maturation. The buccal cortex of the mandible normally is thin posterior to the second molar, weakening this region, and this can contribute to fracture of the proximal segment.29,30 The presence of third molars can further thin and weaken this region. In the presence of third molars, the lingual cortex of the distal segment is also usually very thin, and this increases the risk of a vertical fracture through the tooth socket. When impacted third molars are removed before surgery, aggressive removal of the bone, particularly lingually, can predispose the mandible to an unfavorable fracture during surgery, especially in cases where the mandible is already thin or where anatomic irregularities exist.18,22,31,32 A vertical fracture through the third molar socket may also occur after uneventful splitting of the mandible, during removal of the impacted third molar. Surgically sectioning the impacted tooth and removing it in segments can help prevent this from occurring. The results of this study show that in the 500 SSOs performed the overall incidence of unfavorable fractures was infrequent (2.2 %), irrespective of the presence or absence of third molars. However, the degree of third molar impaction and development did affect the incidence of unfavorable splits. Complete tooth impaction was seen in 6 of the 8 fractures (75 %), and 5 of the 8 fractures (62.5%) were associated with two thirds crown formation. A relationship between the patient’s age and unfavorable splits was seen in group 1. The average age of the patients was 17.7 years (range, 13 to 44 years), which was significantly lower than for group 2 patients, where the average age was 36.6 years (range, 17 to 56 years). The average age of the patients with unfavorable fractures in group 1 was even lower at 15.9 years (range, 15 to 16 years). The age distribution for all patients in group 1 was: age 13 to 14 years, 16 patients; age 15 to 16 years, 70 patients; and age 17 years and older, 51 patients. Thus, 14% of the patients in the 15- to 16-year age group had unfavorable frac-
858 tures, whereas no patient in the other age groups had an unfavorable fracture. Young teenagers have much thinner, immature cortical bone than adults and, with additional thinning caused by development of the coronal portion of the third molar, this patient population may have a greater predisposition to unfavorable fractures. However, younger patients have greater bone elasticity and, during the splitting, incomplete microfractures can occur, accounting for the greater incidence of greenstick fractures in group 1 (37.5%) than in group 2 (0 %). Thus, greater care must be taken during surgery in the young teenage patient with third molars to avoid unfavorable splits.
Conclusions The results of this study show that when using a modification of the SSO that includes an inferior border cut, the occurrence of unfavorable splits is infrequent, irrespective of the presence or absence of third molars. When third molars are present during the SSO, unfavorable fractures usually occur in young, teenage patients. Although more unfavorable splits may occur in the presence of third molars, this has no adverse influence on the success or stability of the SSO surgery provided that the surgeon is able to complete the split and rigidly stabilize the bony segments.
References 1. Schuchart K: Ein Beitrag zur chirurischen Kieferorthopadie unter Berucksichtigung ihrer Bedeutung fur die Behandlung angeborener under worbener Kieferdeformitaten bie Soldaten. Dtsch Zahn- Mund-Kieferhk 9:73, 1942 2. Trauner R, Obwegeser H: The surgical correction of mandibular prognathism and retrognathia with consideration of genioplasty. Oral Surg Oral Med Oral Pathol 10:677, 1957 3. Dal Pont G: Retromolar osteotomy for the correction of prognathism. J Oral Surg 19:42, 1961 4. Hunsuck EE: A modified intraoral sagittal splitting technique for correction of prognathism. J Oral Surg 26:250, 1968 5. Marquez IM, Stella JP: Modification of sagittal split ramus osteotomy to avoid unfavorable fracture around impacted third molars. Int J Adult Orthod Orthognath Surg 13:183, 1998 6. O’Ryan FS: Complications of orthognathic surgery. Oral Maxillofac Surg Clin North Am 2:593, 1990 7. Epker BN: Modifications in sagittal osteotomy of the mandible. J Oral Surg 35:157, 1977 8. Brusati R, Fiamminghi L, Sesenna E, et al: Functional disturbances of the inferior alveolar nerve after sagittal osteotomy of the mandibular ramus: Operating technique for prevention. J Maxillofac Surg 9:123, 1981
COMPLICATIONS OF MANDIBULAR SSO 9. MacIntosh RB: Experience with the sagittal split osteotomy of the mandibular ramus: A 13-year review. J Maxillofac Surg 9:151, 1981 10. Lines P: Modification of the sagittal split ramus technique. J Oral Maxillofac Surg 40:245, 1982 11. Leonard MS, Ziman P, Bevis R, et al: The sagittal split osteotomy of the mandible. Oral Surg Oral Med Oral Pathol 60:459, 1985 12. Kitajima T, Handa Y, Naitoh K: A modification of the sagittal splitting technique. J Craniomaxillofac Surg 17:53, 1989 13. Niederdellmann H, Shetty V: Technical improvement in the sagittal split ramus osteotomy. Oral Surg Oral Med Oral Pathol 67:25, 1989 14. Loh FC: Technical modification the sagittal split mandibular ramus osteotomy. Oral Surg Oral Med Oral Pathol 74:723, 1992 15. Max D, Rotskoff K: A modified technique for the sagittal split osteotomy. J Oral Maxillofac Surg 51:1050, 1993 16. Wolford LM, Davis WM: The mandibular inferior border split: A modification in the sagittal split osteotomy. J Oral Maxillofac Surg 48:92, 1990 17. Wolford LM, Bennett MA, Rafferty CG: Modification of the mandibular ramus sagittal split osteotomy. Oral Surg Oral Med Oral Pathol 64:146, 1987 18. Precious DS, Lung KE, Pynn BR, et al: Prence of impacted teeth as a determining factor of unfavorable splits in 1256 sagittalsplit osteotomies. Oral Surg Oral Med Oral Pathol 85:362, 1998 19. Van Sickels JE, Jeter TS, Theriot BA: Management of an unfavorable lingual fracture during a sagittal split osteotomy. J Oral Maxillofac Surg 43:808, 1985 20. Bell W: Surgical Correction of Dentofacial Deformities: New concepts, vol III. Philadelphia, PA, Saunders, 1985, p 738 21. Epker BN, Wolford LM: Dentofacial Deformities (ed 1). St Louis, MO, Mosby, 1986, p 232 22. Epker BN, Fish LC: Dentofacial Deformities. Integrated Orthodontic and Surgical Correction, vol 1 (ed 1). St Louis, MO, Mosby, 1986, p 232 23. Tucker MR: Sagittal ramus osteotomy with and without third molars. J Oral Maxillofac Surg 53:80, 1995 24. Guersney LH, DeChamplain: Sequelae and complications of the intraoral sagittal osteotomy of the mandibular rami. Oral Surg Oral Med Oral Pathol 32:176, 1971 25. Turvey TA: Intraoperative complications of sagittal osteotomy of the mandibular ramus: Incidence and management. J Oral Maxillofac Surg 43:504, 1985 26. Epker BN, Stella JP, Fish LC: Dentofacial Deformities. Integrated Orthodontic and Surgical Correction, vol 1 (ed 2). St Louis, MO Mosby, 1995, pp 193-367 27. Terry BC, White RR Jr: Mandibular ramus surgery, in Proffit WR, White RP Jr (eds): Surgical-Orthodontic Treatment. St Louis, MO, Mosby, 1991, pp 264-274 28. El Deeb M, Wolford LM: Complications of orthognathic surgery. Clin Plast Surg 16:825, 1989 29. Smith BR, Rajchel JL, Waite DE, et al: Mandibular ramus anatomy as it relates to the medial osteotomy of the sagittal split ramus osteotomy. J Oral Maxillofac Surg 49:12, 1991 30. Schubert W, Kobienia BJ, Pollock RA: Cross-sectional area of the mandible. J Oral Maxillofac Surg 55:689, 1997 31. Kaplan PA, Tu HK, Koment MA, et al: Radiography after orthognathic surgery, II. Surgical complications. Radiography 166:199, 1988 32. Jonsson E, Svatrz K, Welander V: Sagittal split technique. Part I. Immediate postoperative conditions: A radiographic follow-up study. Int J Oral Surg 8:75, 1979