Introduction and review of literature
Mandibular retrognathia is the underdeveloped retruded position of the mandible to the maxilla. The retrognathic face has a characteristic convex-appearing profile with or without class II malocclusion 1.
Many etiological factors have been claimed as predisposing causes for mandibular retrognathia. Condylar trauma at early age is one of the most reported causes. Pierr Robin and Treacher-Collins syndromes are congenital conditions associated with retrognathia 2.
Facial deformity and functional disabilities including malocclusion, temporomandibular joint (TMJ) dysfunction and upper airway obstruction are commonly reported complications of mandibular retrognathia 3.
Many treatment modalities have been advocated to treat mandibular retrognathia. Various mandibular osteotomies including bilateral body osteotomies, inverted L-shaped, vertical ramus and bilateral sagittal split osteotomies (BSSOs) were reported as different treatment options. Also, distraction osteogenesis (DO) is a surgical modality claimed to have the advantage of bigger mandibular advancement and the creation of new bone with limited surgical complications 4.
There is good evidence that BSSO and DO are appropriate techniques for the treatment of mandibular retrognathia in nonsyndromic cases with nearly comparable levels of patient distress. However, the scientific evidence predicting the potentially better results of these modalities is still insufficient. The current study was conducted to compare the two techniques in treating mandibular retrognathia.
Aim of the study
The present study aimed to compare clinically and radiographically BSSO and DO in treating and correcting mandibular retrognathia.
Patients and methods
This study was carried out on 12 patients (eight female and four male) with ages ranging from 18 to 35 years (mean 23 years). The retrognathia was bilateral, congenital in five patients and consequent complication to TMJ ankylosis occurred in seven patients (Table 1). All cases were suffering from upper airway problems ranging from night snoring to obstructive sleep apnea (OSA). The 12 patients were divided equally into two groups. In group I, mandibular retrognathia was treated by BSSO, whereas DO was the treatment of choice in group II. Every patient in both groups was subjected to physical and clinical examinations. Preoperative clinical photographs and study models were obtained. Radiological examination including orthopantogram, lateral cephalometric radiographs, and three-dimensional computed tomography (3D-CT) imaging were performed for all cases. Linear and angular cephalometric measurements were taken to determine the amount of mandibular lengthening needed to correct the retrognathic mandible and to determine the vector of distractor. Preoperative and postoperative cephalographs for every patient were digitized and traced using a computer software (DBS Win, v.4.5; Frankfurt, Durr Dental, Germany). For every patient in the BSSO group, presurgical orthodontic preparation was performed including the treatment of any crowding or irregularities and leveling and alignment of dentition. Model surgery was performed using a semi-adjustable articulator with the face bow (DBS Win, v.4.5; Durr Dental) for transferring jaw relationship and construction of the final surgical splint. Consent for the operation was taken from every patient. Preoperative surgical investigations for every patient in both groups were carried out. All patients started a steroid regimen the night before operation by taking intravenous dexamethasone 4 mg ampule to decrease postoperative edema. General anesthesia was used for all patients in both groups.
Surgical procedures for group I (bilateral sagittal split osteotomy)
The incision was started on the anterior border of the vertical ramus midway between the occlusal planes, carried downward through the middle of the retromolar fossa to a point 5 mm behind the second molar and then laterally and forward distal to the first molar. The periosteum was reflected to expose the lateral cortex of the mandible down to the inferior border and antegonial notch. Using a periosteal stripper, the attachment of temporalis was removed to the level of the sigmoid notch; the periosteum was then elevated from the medial surface of the vertical ramus to gain access for the medial cut. Paramount care was given to avoid injury to the inferior alveolar nerve (IAN). The osteotomy was started by making a horizontal bone cut through the medial cortex of the vertical ramus from a point posterior to and above the lingula to the anterior border. Using Landman Bur and Micromotor (New Jersey, USA), the horizontal cut was carried out to a half thickness of the ramus. The vertical cut through the buccal cortex was made just distal to the second molar, extending from the inferior border to the external oblique ridge extending just into the cancellous bone (Fig. 1). The vertical and horizontal cortical cuts were then connected and the split was accomplished using narrow bone osteotoms. The same procedures were repeated on the other side. The mandible was moved in its new position and stabilized by maxillomandibular fixation using occlusal acrylic splint based on the presurgical model. For semirigid internal fixation of the sagittal osteotomy, three 2.3-mm Titanium lag screws, with 11 mm length on each side, were inserted. The maxillomandibular fixation was released to check the occlusion and the proper condylar seat. The mucosal wounds were repaired using 3–0 black silk suture material. The patients were put under heavy elastics, intermaxillary fixation during the first postsurgical 15 days. Light class I elastics for a third week was used for muscle rehabilitation and occlusion orientation.
Surgical steps for distraction osteogenesis
In group II, mandibular lengthening was carried out using a bilateral extraoral distraction device (Molina unidirectional distractor for adults; New Jersey, USA) with four pins in four cases, whereas in the other two cases, lengthening was performed with a bilateral intraoral distraction device with a six-microscrew (15×7 mm) horizontal distractor (KLS Martin Group; Frankfurt, Germany). The mandibular border was outlined on the skin surface with a surgical marker as a point of reference for the osteotomy line and sites of placement of extraoral pins. An intraoral mucosal incision along the oblique line of the ramus was performed. Subperiosteal dissection was performed to elevate the entire lateral periosteal surface, and then lateral corticotomy using Landman Bur and Micromotor was performed just distal to the lower third molar. The distractor devices used were with horizontal vector to lengthen the mandible in a purely horizontal plane. The self-drilling pins of the extraoral device were inserted percutanously through a trocar with preservation of the parallelism of the four pins in each side, and then the extraoral device was fixed. For fixation of the intraoral device, a single percutaneous stab incision was made for the placement of a transbuccal retractor and a screw driver. A suitable bone osteotome was used to complete the medial wall osteotomy, liberating the mandibular segments for distraction. The distraction device was checked using the device activator. The mucosal wound was closed with a 3–0 black silk suture material. Elastic bandage on both sides to minimize edema was used. Patients were instructed for the postoperative follow-up regimen. For group II, activation of the distractors was started after a latent period of 7 days at 1 mm rate once per day. The elongation was continued till achievement of class III occlusion to compensate for the expected postsurgical relapse. The consolidation period extended for 120 days. The device was removed when radiographic evidence of new cortical bone formation was established on orthopantomogram (OPG) radiograph. At that time, the distractors were removed under general anesthesia for intraoral devices and sedation for extraoral devices. After surgical intervention, optimal interdigitation of the teeth was tried through the final orthodontic treatment.
Postoperative radiographic follow-up
For group I (BSSO) cases, immediate postsurgical and 3-, 6-, and 12-month postsurgical lateral cephalometric and OPG radiographs were performed. For group II cases, immediate postoperative, postactivation, and 3-, 6-, and 12-month postsurgical lateral cephalometric and OPG radiographs were taken. Both angular and linear measurements were recorded and compared. For both groups, 3D-CT imaging was performed 1 year after surgery.
All figures are approved by ethical committee.
The current study included 12 adult patients with mandibular retrognathia and class II malocclusion. The patients had a preoperative high mandibular plane angle. OSA was recorded in seven patient, whereas night snoring was found in five patients.
In group I cases, mandibular advancement was between 6 and 7 mm. In one case, fracture of the proximal segment occurred during separation; it was managed by additional lag screw fixation. In another case, the proximal segment was too small due to a short ramus that led to difficulty during fixation with a lag screw. It was managed by miniplate and monocortical screw osteosynthesis.
Postsurgical edema of oral and paraoral tissues was more severe in BSSO cases. Through the use of perioperative steroids, all cases showed improvement at the end of the second postsurgical day leading to improvement in swallowing and breathing.
In group II patients, mandibular lengthening ranged between 10 and 16 mm. In one case, left impacted lower third molar was an obstacle and was extracted to facilitate device fixation. Also, during removal of the intraoral device in another two cases, exposure of the devices was not easy. Bimanual examination revealed the osteotomized segments, and the regenerated, clinically stable, new bone was seen gapping the previous distraction regenerate. The same clinical stability was observed after removal of the extraoral device in the other cases.
In the DO group, patients did not complain of any pain at the beginning of activation. Towards the end of the activation phase, the resistance to mandibular lengthening increased and was felt as heaviness and tolerable pain in the submental region. A decreased range of jaw movement was seen clinically in all cases in the DO group during both activation and consolidation phases. The range of motion returned to the normal preoperative range in all patients after 1–2 weeks.
One case in DO showed bilateral looseness in the extraoral device leading to delayed clinical stability of the osteotomized segments after the consolidation phase. This was managed by device removal and application of intermaxillary fixation (IMF) for 3 weeks. After removal of IMF, the osteotomized segments together with the distraction regenerate became clinically stable. Also, the inflamed skin scar around the pins of the extraoral device was observed in another case and was treated by local care.
No vascular necrosis was seen in any case in both groups. Two cases, one in each group, developed occlusal disharmony, and were managed by orthodontic treatment after the end of the follow-up period.
Regarding the improvements of the upper airway obstruction, in the BSSO group, night snoring disappeared 3 months after surgery in five cases, whereas in one case, some improvement with less attacks of OSA was recorded. In contrast, in the DO group, obvious improvement of OSA was reported in all cases with the begging of activation phase. More improvement was observed toward the end of consolidation phases. One year after surgery, the clinical findings documented complete cure of OSA with patent airway, normal breathing, and normal sleep in all cases. (An article discussing the upper respiratory changes in this study will be published soon).
Almost all the patients in both groups experienced esthetic improvement with correction of the convex retrognathic face and sella - nasion - B point (SNB) and A point - nasion - B point (ANB) values (Figs 2 and 3). Also, significant improvement of upper airway obstruction was reported. These improvements had a definite positive psychological impact on the patients, which was reflected as increased social communication and interaction with others.
In the current study, an orthopantogram revealed bone healing of the osteotomized segments 1 year postoperatively in all cases in the BSSO group. Also, evidence of new bone formation was found 1 year after surgery in the distraction regenerate in all patients in the DO group, including the patient who had clinical instability of the osteotomized segments. 3D-CT images were used to qualitatively view the overall effects of both techniques of mandibular advancement on the lower facial third. The images revealed a change in severe class II skeletal and dental relationship to an edge-to-edge relationship in DO cases, whereas in the BSSO group, the severe class II was changed into class I skeletal and dental relationship.
In the BSSO group, the mean advancement of the mandible was 6.7 mm. Relapse at point B (decrease in SNB) was first recorded 3 months after surgery and reached 19.5% as a mean percentage of relapse of the original advancement 1 year after surgery. In the DO group, the mean lengthening of the mandible was 12 mm. Relapse at point B was first reported 6 months after surgery, and a mean percentage of relapse of 10.8% was recorded 1 year after surgery. In both groups, changes of SNB, ANB, and the posterior movement at point B were statistically significant 1 year after surgery (P<0.05).
Mandibular retrognathia is a common problem in maxillofacial surgery. Facial deformity, malocclusion, and upper airway obstruction are the main reported complications of mandibular retrognathia 1,2. Several treatment techniques for retrognathia have been described. Flexibility in repositioning the distal fragments and broad bony overlap of osteotomized segments are the main advantages of BSSO 1. Neurosensory impairment of the IAN was reported as the major disadvantage 5. DO is a surgical technique that appears to have some advantages for large lengthening, creation of new bone and limited surgical complications. It enables bone lengthening at early childhood, teenage, and adulthood 6,7.
In the current study, mandibular retrognathia was treated at adulthood. Sadakah et al. 6 reported correction of retrognathia in early childhood in cases with severe congenital mandibular hypoplasia. Another study 7 reported treatment of mandibular retrognathia in actively growing children to overcome problems related to airway, occlusion, and mastication function. Proffit and Turvey 8 recommended delaying surgical correction of mandibular retrognathia until adulthood unless there is upper airway problem to avoid growth changes of the facial skeleton at a young age.
In the BSSO group, one case (number 5) was excluded from the statistical analysis due to its extremely variable postoperative data. The radiological findings for that case recorded 38% relapse 3 months after surgery, 44.6% relapse after 6 months, and 60% relapse after 1 year after surgery. That case had postankylotic retrognathia, no evidence of mandibular condyles, very small proximal segments with short rami and a high preoperative mandibular angle (53°).
In the current study, condylar trauma at an early age had the highest incidence (58%) in the etiologic factors of mandibular retrognathia, which agreed with El-Gazzar et al. 9. This is predominantly because TMJ condylar fracture might not be recognized and the problems are the result of delay and/or inadequate treatment and follow-up. In the mean time, all cases with postankylotic retrognathia were suffering from OSA, which was in accordance with findings from Sadakah et al. 10.
In the present work, postoperative edema was more obvious in BSSO cases than in mandibular distraction osteogenesis (MDO) cases, which was in accordance with the findings of Schreude et al. 11. This might be attributed to the more surgical maneuvering in sagittal split cases. Our postoperative clinical findings proved that the use of steroids minimized postoperative edema, which prevented postoperative upper airway obstruction in many cases. This agreed with Dan et al. 12 who reported that the use of preoperative steroids in maxillofacial surgery minimizes postoperative edema in oral and paraoral tissues.
Stability of the osteotomized or the distracted segment is of paramount importance during the healing phase. Radiological findings of the current study reported bone healing in all BSSO cases 6 months after surgery. This might be due to good fixation of the osteotomized segments. This coincided with the results of Ow et al. 13, who reported that semirigid fixation in BSSO promotes bone healing and skeletal stability. Evidence of new bone formation in the MDO group was reported at the end of the consolidation period. One year after surgery, the radiological results documented new bone formation in the distraction regenerate. This might be attributed to the stability of the distraction device during both the latent and the consolidation periods and sufficient consolidation time. This was in accordance with Crago and Proffit 14, who recommended extending the period of consolidation up to 120 days in large lengthening cases. Moreover, McCarthy et al. 15 reported that stable fixation of the osteotomized bone segments is a critical factor in successful distraction.
Relapse is a multifactorial phenomenon. A high preoperative mandibular angle, big advancement, inadequate fixation, and consolidation periods are the main factors for relapse in BSSO 11,16. In the present study, the mean percentage of relapse was 10.8% one year postoperatively in the MDO group. This might be due to the stability of the device during the operative period. Ow and Cheung 16 reported a mean percentage of relapse of 5.36% in their study. The authors reported mandibular lengthening between 6.5 and 8 mm and a mean preoperative mandibular angle of 40° in congenital mandibular retrognathic cases compared with 10–16 mm mandibular advancement and 49.16° mandibular angle in our cases of postankylotic mandibular retrognathia.
Ow and Cheung 13 reported a high mean of relapse (29.6%) in cases of high mandibular plane angle in BSSO patients for advancement between 6 and 10 mm within the first year. In the current study, despite the high mandibular plane angle (44–52°), the mean percentage of relapse was 19.5%. This may be attributed to the absence of postoperative condylar sage or delayed condylar resorption proved in the postoperative radiographic follow-up, the limited mandibular advancement (7 mm) and the preoperative and postoperative orthodontic treatment performed in our cases.
The present study revealed a higher mean of relapse of 19.5% in BSSO cases compared with 10.8% as the mean in group II (MDO). In BSSO, stretching of the soft tissue was acute compared with the gradual rate in MDO cases. Simultaneous soft tissue adaptations together with new bone formation are of paramount importance for minimizing postoperative relapse in the distraction group. In the mean time, the over-lengthening performed in MDO cases compensated for the postoperative relapse, and the mandible formed an accepted skeletal relationship with the maxilla in most of the cases.
In the current study, looseness of the extraoral device and delayed union were recorded in one case that was managed by removal of device and IMF for 3 weeks. This may be due to the instability of the osteotomized segments together with large mandibular lengthening (16 mm) in that case. One year after surgery, new bone formation in the distraction regenerate was observed. Intermaxillary fixation provided more stability in this case.
IAN deficit was reported in one case in the BSSO group. This might be attributed to the fracture of the proximal segment that occurred in this case. This complication was managed by neurotonics, and the follow-up showed improvement 6 months after surgery. In the MDO group, no IAN deficit was observed; this may be due to the gradual traction that proved to preserve the IAN without injury. This agreed with the results of Schreude et al. 11, who reported less IAN deficit with MDO than BSSO in treating mandibular retrognathia.
The postoperative clinical follow-up revealed the cure of OSA in all MDO cases with patent airway, normal breathing and normal sleep. In the BSSO group, night snoring disappeared in five cases, whereas mild improvement of OSA was observed in one case. The results also reported obvious improvements in the facial appearance and correction of the convexity of the retrognathic profile in almost all cases in both groups. Mandibular DO verified the goals in cases with postankylotic retrognathia and OSA, whereas BSSO verified the goals in cases with congenital mandibular retrognathia and night snoring.
Conflicts of interest
There are no conflicts of interest.
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