Short-term stability and muscle adaptation after mandibular advancement surgery with and without suprahyoid myotomy in juvenile Macaca mulatta

The purpose of this study was to examine the short-term adaptations that occur within the mandible and anterior digastric muscle complex after mandibular advancement with and without suprahyoid myotomy in 20 juvenile rhesus monkeys. The results showed that the animals that did not undergo myotomy experienced relapse equivalent to 13% of the surgical advancement. Those animals that underwent a myotomy of the digastric muscle complex showed complete stability of the surgical lengthening of the mandible. Both groups of animals grew normally after the fixation period when compared to age-matched control animals. Analysis of adaptations within the digastric muscle complex was performed with the use of radiopaque muscle and tendon markers. The results showed an immediate lengthening of the entire digastric muscle complex with mandibular advancement surgery in the group that underwent advancement without myotomy. Further analysis showed that most lengthening in these animals occurred at the connective tissue interfaces of the complex--at the muscle-bone and muscle-tendon interfaces. No significant changes in sarcomere or fiber length were found in the group that did not undergo myotomy, although there was a significant shortening of muscle fibres resulting from loss of serial sarcomeres in the myotomy group. Comparison of histochemical characteristics of the anterior digastric muscle before and after surgery revealed the following findings: (1) there were no significant differences in percentage of composition between control and experimental muscles; (2) despite fixation of the jaws and myotomy, there was no evidence of atrophy of the anterior digastric muscle at any experimental interval; and (3) the type I fibers of the anterior digastric muscle underwent significant stretch-induced hypertrophy after lengthening. The results of this study support the hypothesis that tension produced by stretching of the connective tissues associated with the digastric muscle complex can contribute to postsurgical relapse of the surgically advanced mandible. However, no adverse effect on future growth of the mandible was observed from stretching the digastric muscle complex by mandibular advancement surgery in juvenile subjects.     

Adaptation of the suprahyoid muscle complex to mandibular advancement surgery

The suprahyoid musculature has been implicated as one of the major factors responsible for relapse after mandibular advancement surgery. Previous studies have also indicated that the muscle and connective tissues comprising the suprahyoid complex must adapt to increased length brought about by mandibular advancement for skeletal stability to be achieved. The purpose of this study was to provide quantitative data concerning the immediate changes and long-term adaptations that take place within the suprahyoid complex over a 2-year period after mandibular advancement. Mandibular advancement was performed on ten adult Macaca mulatta monkeys with and without suprahyoid myotomy (n = 5/group). Six animals were used as controls. Mandibular length and changes in the length of the various anatomic regions of the suprahyoid complex were evaluated radiographically with the aid of radiopaque bone, muscle, and tendon markers implanted preoperatively. The results for the nonmyotomy group showed that the suprahyoid complex was elongated approximately two thirds the amount of mandibular lengthening, the major immediate adaptations within the suprahyoid complex after the surgical procedure occurred at the muscle-bone interface and the muscle-tendon interface, the change in length at the muscle-tendon junction was maintained throughout the 2-year follow-up period, indicating that significant long-term adaptations took place primarily at that location, and no significant short-term changes or long-term adaptations were seen within the anterior digastric muscle or the intermediate digastric tendon. Within the myotomy group, it was found that the suprahyoid complex recoiled immediately after myotomy such that the anterior belly of the digastric muscle became separated from the advanced distal mandibular segment by more than twice the amount of mandibular lengthening, the anterior digastric muscle remained essentially at this posterior position throughout the 2-year follow-up period, and though not significant, there was a trend for a decrease in the length of the anterior digastric muscle belly. On the basis of these results, it was concluded that both short-term changes and long-term adaptations to lengthening of the suprahyoid complex as a result of mandibular lengthening occur primarily within the connective tissues comprising the muscle-tendon and muscle-bone interfaces, not within the muscle fibers themselves.     

The role of suprahyoid myotomy in surgical advancement of the mandible via sagittal split ramus osteotomies

The suprahyoid muscles have been implicated as primary effectors of relapse following surgical advancement of the deficient mandible. Accordingly, suprahyoid myotomy and/or the use of cervical collars have been recommended as adjunctive procedures to minimize postoperative relapse. This computerized morphometric evaluation of 16 patients revealed that suprahyoid myotomy is not essential to skeletal stability following surgical advancement of the mandible.     

Maxillomandibular growth 2 years after mandibular advancement surgery with and without suprahyoid myotomy in juvenile Macaca mulatta

There is conflict in the literature on whether continued and harmonious growth occurs after mandibular advancement in growing persons. The studies available are difficult to interpret because of the differing age ranges and the questionable growth potential inherent within the mandibular deficient patient. This study was performed to isolate the major question of interest to clinicians: Does the mandibular advancement surgical procedure inhibit future growth in a normally growing person? Six juvenile male Macaca mulatta monkeys were divided equally into two experimental groups. Group MAA had mandibular advancement surgery of approximately 4 mm. Group MAD had a similar surgical procedure with detachment of the suprahyoid musculature. All underwent 4 to 5 weeks of maxillomandibular fixation. Serial computerized cephalograms with the aid of bone markers were used to analyze the changes during a 2-year follow-up period. The postsurgical changes of the two experimental groups were compared statistically with control growth data on a large sample of normal Macaca mulatta animals available in our laboratory. The results showed the following. (1) There were significant short-term differences in the stability of the mandibular advancement between experimental groups. Group MAA (suprahyoid musculature attached) experienced significant relapse during the period of maxillomandibular fixation. Group MAD (suprahyoid musculature detached) experienced no relapse. (2) During the 2-year follow-up period after fixation, the rate and amount of mandibular growth in both experimental groups were not significantly different from age-matched controls or from each other. (3) At the end of the 2-year experimental period, the advanced mandibles were longer than the mandibles in age-matched controls.(ABSTRACT TRUNCATED AT 250 WORDS)     

Condylar position following mandibular advancement: Its relationship to relapse

Forty-one patients who elected to receive a bilateral sagittal osteotomy to advance the mandible were examined clinically and radiographically to assess condylar position preoperatively and at three specific times post-operatively. Parameters designed to measure changes in condylar and distal fragment position were located on tracings and digitized for statistical analysis. Changes in distal fragment position included advancement and clockwise rotation during the surgical interval and significant posterior relapse with continued clockwide rotation during the period of maxillomandibular fixation. A small amount of counterclockwise rotation associated with interocclusal splint removal was seen following fixation release. No significant condylar movement was seen during the surgical interval. During the period of maxillomandibular fixation, both condyles exhibited a significant superior movement, and the left condyle also moved posteriorly. No changes in condylar position were noted following release of fixation. The clinical significance of these condylar movements is not clear. Despite minimal changes, 18 patients, six of whom had had no preoperative symptoms and one of whom had exhibited reciprocal clicking, complained of temporomandibular joint pain or noise postoperatively. This suggests that maintenance of condylar position during surgery may not prevent temporomandibular joint dysfunction. In addition, the observed 37% relapse in surgical advancement in the absence of significant condylar distraction implies the interaction of other factors in the relapse process.     

Stability of skeletal class III malocclusion after combined maxillary and mandibular procedures: rigid internal fixation versus wire osteosynthesis of the mandible.

PURPOSE: The aim of this study was to evaluate skeletal stability after double-jaw surgery for correction of skeletal Class III malocclusion to assess whether there were any differences between wire and rigid fixation of the mandible. PATIENTS AND METHODS: Thirty-seven Class III patients had Le Fort I osteotomy stabilized with plate and screws for maxillary advancement. Bilateral sagittal split osteotomy for mandibular setback was stabilized with wire osteosynthesis and maxillomandibular fixation for 6 weeks in 20 patients (group 1) and with rigid internal fixation in 17 patients (group 2). Lateral cephalograms were taken before surgery, immediately after surgery, 8 weeks after surgery, and 1 year after surgery. RESULTS: Before surgery, both groups were balanced with respect to linear and angular measurements of craniofacial morphology. One year after surgery, maxillary sagittal stability was excellent in both groups, and bilateral sagittal split osteotomy accounted for most of the total horizontal relapse observed. In group 1, significant correlations were found between maxillary advancement and relapse at the posterior maxilla and between mandibular setback and postoperative counterclockwise rotation of the ramus and mandibular relapse. In group 2, significant correlations were found between mandibular setback and intraoperative clockwise rotation of the ramus and between mandibular setback and postoperative counterclockwise rotation of the ramus and mandibular relapse. No significant differences in postoperative skeletal and dental stability between groups were observed except for maxillary posterior vertical position. CONCLUSIONS: Surgical correction of Class III malocclusion after combined maxillary and mandibular procedures appears to be a fairly stable procedure independent of the type of fixation used to stabilize the mandible.     

Short- and long-term skeletal relapse after mandibular advancement surgery

This study analyzes short- and long-term skeletal relapse after mandibular advancement surgery and determines its contributing factors. Thirty-two consecutive patients were treated for skeletal Class II malocclusion during the period between 1986 and 1989. They all had combined orthodontic and surgical treatment with BSSO and rigid fixation excluding other surgery. Of these, 15 patients (47%) were available for a long-term cephalography in 2000. The measurement was performed based on the serial cephalograms taken preoperatively; 1 week, 6 months and 14 months postoperatively; and at the final evaluation after an average of 12 years. Mean mandibular advancement was 4.1 mm at B-point and 4.9 mm at pogonion. Representing surgical mandibular ramus displacement, gonion moved downwards 2 mm immediately after surgery. During the short-term postoperative period, mandibular corpus length decreased only 0.5 mm, indicating that there was no osteotomy slippage. After the first year of observation, skeletal relapse was 1.3 mm at B-point and pogonion. The relapse continued, reaching a total of 2.3 mm after 12 years, corresponding to 50% of the mandibular advancement. Mandibular ramus length continuously decreased 1 mm during the same observation period, indicating progressive condylar resorption. No significant relationship between the amount of initial surgical advancement and skeletal relapse was found. Preoperative high mandibulo-nasal plane (ML-NL) angle appears to be associated with long-term skeletal relapse.     

Causes, location, and timing of relapse following rigid fixation after mandibular advancement

The purpose of this study was to evaluate two different groups of patients who underwent bilateral sagittal split osteotomy for mandibular advancement. One group demonstrated no relapse, whereas a second group had documented relapse. The following questions were asked: 1) What factors contribute to relapse? 2) At what site in the mandible is movement seen? and 3) During what period does movement occur? A retrospective lateral cephalometric serial analysis was performed on 50 patients at multiple time intervals. Criteria for a candidate include 1) mandibular advancement surgery with rigid fixation, with or without genioplasty, 2) no maxillary surgery, and 3) relapse of 25% or more of the advancement. Of the 50 patients analyzed, 13 (26%) showed relapse of 25% or more and served as the relapse group. Twelve patients showed no relapse and served as the comparison group. Multiple-regression analysis for the relapse group showed that magnitude of advancement, increasing gonial arc and changing mandibular plane significantly accounted for 84.9% of the variance observed in relapse (P less than .001). Repeated-measures ANOVA showed that the majority of relapse occurred in the first 6 weeks after surgery (68%, P less than .05). Results of a paired t test showed that a significant change occurred in all the linear and angular measures except SN-AR-GO (P less than .05).     

Electromyography of the suprahyoid musculature following mandibular advancement with and without rigid fixation

The purpose of this investigation was to determine if the activity of the suprahyoid musculature changes following advancement of the mandible and the use of rigid or nonrigid fixation. Ten monkeys underwent mandibular advancement; six underwent 6 weeks of maxillomandibular fixation (MMF), and four had rigid fixation without MMF. Electromyography (EMG) of the suprahyoid musculature was performed preoperatively, and at 3, 7, and 10 weeks postoperatively. The results of this study fail to demonstrate an increase in suprahyoid EMG activity following mandibular advancement. Furthermore, there were no differences between the groups with different types of fixation.     

Positional change of the hyoid bone after bilateral sagittal split osteotomy with rigid and wire fixation.

The purpose of this study was to compare positional changes of the hyoid bone and the amount of postsurgical compensation in mandibular position in patients who received either wire or rigid fixation after surgery. Data were analyzed from 97 patients (25 males and 72 females) who were randomized to receive wire (43) or rigid (54) fixation after mandibular advancement surgery as part of a multicenter clinical trial. Radiographs were digitized before surgery (T2), immediately after surgery (T3), and 8 weeks (T4), 6 months (T5), 1 year (T6), and 2 years (T7) after surgery. The wire group had greater sagittal relapse of the hyoid bone at T6 (P =.007), which persisted at T7 (P =.02). Both groups showed upward movement of the hyoid bone after surgery. There was no relationship between the vertical change in the the hyoid bone position and the vertical position of mandible (B point y coordinate, mandibular plane). However, there was a relationship between the horizontal hyoid bone position and B point during the postsurgical period (rigid, r = 0.450; wire, r = 0.517). The direct distance from the hyoid bone to basion increased (P <.001) in both groups at T3 and then recovered its original length after 8 weeks (P <.001). The rigid group showed no significant change in distance from the hyoid to the genial tubercles, but the wire group showed recovery of the muscle length at T6 (P <.05) and T7 (P <.05).     

A comparison of synovial fluid pressure after immediate versus gradual mandibular advancement in the miniature pig.

PURPOSE: Mandibular advancement is a commonly performed surgical procedure for the treatment of mandibular hypoplasia. With the increased use of rigid fixation, there has been a decrease in the amount of relapse but an increase in the amount of force transmitted to the condyles. Gradual advancement of the mandible by distraction osteogenesis slowly overcomes the soft-tissue envelope and may decrease the amount of force exerted on the condyles. The purpose of this study was to develop an animal model to measure the magnitude of pressure associated with immediate versus gradual mandibular advancement. MATERIALS AND METHODS: A 2.0-mm pressure transducer was placed in the superior joint space in 2 miniature pigs. In the first animal, immediate advancement of the mandible with rigid fixation was performed. The synovial fluid hydrostatic pressures were measured prior to surgery and postoperatively. A second animal underwent gradual advancement with distraction osteogenesis. The synovial fluid hydrostatic pressures were measured prior to and after each activation of the distraction device. The condyles were examined radiographically and microscopically. RESULTS: The superior joint space fluid pressures increased and remained elevated over a 5-week period after immediate advancement. In the gradually advanced mandible, the pressures were elevated but returned to near baseline prior to the activation the following day. CONCLUSION: This animal model is useful to directly measure the pressure that is exerted on the condyle. This will allow further studies to compare methods for mandibular advancement. It is likely that gradual advancement of the mandible by distraction osteogenesis produces less force and causes less condylar resorption than large mandibular advancement stabilized with rigid fixation.     

Stability of mandibular advancement procedures: bilateral sagittal split osteotomy versus distraction osteogenesis

The aim of this study was to compare the postoperative stability of the mandible after a bilateral lengthening procedure, either by bilateral sagittal split osteotomy (BSSO) or distraction osteogenesis (DOG). All patients who underwent mandibular advancement surgery between March 2001 and June 2004 were evaluated; 26 patients in the BSSO group and 27 patients in the DOG group were included. The decision to use the intraoral distraction or BSSO for mandibular advancement primarily depended on the patient's choice. In both groups, standardized cephalometric radiographs were taken preoperatively, postoperatively (BSSO group) or directly post-distraction (DOG group) and during the last study measurement in May 2005. The cephalometric analysis was performed using the following measurements: Sella/Nasion-Mandibular point B and Sella/Nasion-Mandibular Plane. Point B was used to estimate relapse. This study showed no significant difference in relapse between the BSSO and the DOG group measured 10-49 months after advancement of the mandible (p>0.05). There is no postoperative difference in the stability between BSSO and DOG after mandibular advancement after 1 year.     

Stability of the mandible after advancement and use of dental plus skeletal maxillomandibular fixation: an experimental investigation in Macaca mulatta

This study examined short-term stability of the mandible following advancement surgery and the use of skeletal suspension wires plus dental maxillomandibular fixation. Twenty-four adult female Macaca mulatta underwent bilateral sagittal ramus osteotomy and advancement of approximately 6 mm. All animals had dental maxillomandibular fixation secured by bonding the upper and lower teeth together with an orthodontic composite resin. In half of the animals, the use of circummandibular wires connected to pyriform aperture wires were additionally applied. Tantalum bone markers were placed and cephalograms analyzed during the first six postoperative weeks to evaluate skeletal stability. A statistically significant mean horizontal relapse at the mandibular symphysis occurred in the group without the skeletal wires, whereas no relapse occurred in the group with the skeletal wires. A significant difference in the vertical displacement of the anterior mandible occurred, with an inferior movement of the symphysis in the group without skeletal wires, and a superior movement of the symphysis in the group with skeletal wires. The results of this study indicate that the use of skeletal suspension wires is advantageous in the prevention of horizontal and vertical skeletal relapse.     

Superior repositioning of the maxilla combined with mandibular advancement: mandibular RIF improves stability.

Postsurgical changes in 24 patients who had rigid internal fixation (RIF) of the mandible with screws after combined superior repositioning of the maxilla and mandibular advancement were compared with 53 patients who underwent the same surgery but who had intraosseous wire fixation, skeletal suspension wires, and 8 weeks of maxillomandibular fixation (MMF). During the first 8 weeks after surgery, the mean posterior relapse of the mandible was greater in the MMF group than in the RIF group (for example, -1.1 mm versus 0.15 mm at B point), and the percentage of patients with clinically significant vertical and horizontal changes was greater in the MMF group. By 1 year, there had been slight additional mean relapse in the MMF group (-1.5 mm net relapse at B point, with 42% of the patients showing 2 mm or more relapse). In the RIF group, the mandible was more likely to be repositioned forward than posteriorly (net mean change at B point, 0.7 mm forward; 33% had 2 mm or more forward movement). In the RIF group, all but one of the patients (96%) were judged to have an excellent clinical result; in the MMF group, the corresponding figure was 60%.     

Long term stability of mandibular advancement procedures: bilateral sagittal split osteotomy versus distraction osteogenesis

The aim of this study was to compare the postoperative stability of the mandible after a bilateral lengthening procedure, either by bilateral sagittal split osteotomy (BSSO) or distraction osteogenesis (DO). All patients who underwent mandibular advancement surgery between March 2001 and June 2004 were evaluated. There were 17 patients in the BSSO group and 18 patients in the DO group. The decision to use intra-oral distraction or BSSO for mandibular advancement primarily depended on the choice of the patient and their parents. In both groups, standardized cephalometric radiographs were taken preoperatively, postoperatively (BSSO group) or directly post-distraction (DO group) and during the last study measurement in May 2008. Cephalometric analysis was performed using the following measurements: sella/nasion-mandibular point B and sella/nasion-mandibular plane. Point B was used to estimate relapse. This study showed no significant difference in relapse between the BSSO and the DO groups measured 46-95 months after advancement of the mandible (P>.05). It can be concluded from this study that there is no postoperative difference in the stability between BSSO and DO after mandibular advancement after 4 years.     

Longitudinal study of combined orthodontic and surgical treatment of Class II malocclusion with deep overbite

Twenty-one patients who had undergone orthodontic treatment in combination with mandibular advancement surgery to treat Class II malocclusion and deep overbite were followed up. Median vertical relapse at the bony chin (after a mean followup of 16 months) was found to be 2.9 mm (44%). Sagittal advancement was found to have good stability; most of the patients exhibited some additional anterior movement of the chin during the follow-up period. At the same time, the entire mandible rotated counterclockwise and the gonial angle increased. Individual response to treatment varied greatly; two patients exhibited major horizontal relapse. Controlling the position of the mandibular proximal segment seemed to be the most important factor in posttreatment stability of this sample.     

Adaptation of the suprahyoid muscle complex to large mandibular advancements

The purpose of this study was to provide quantitative data concerning the changes and adaptations that take place within the suprahyoid complex to larger mandibular advancements. Mandibular advancement of 6.5 mm was performed on 12 adult rhesus monkeys. Six underwent maxillomandibular fixation (MMF) using the dentition, six underwent MMF using the dentition plus skeletal suspension wires. Mandibular position and changes in the length of the various anatomic regions of the suprahyoid complex were evaluated cephalometrically with the aid of radiopaque bone, muscle, and tendon markers implanted preoperatively. Relapse of the mandible in the dental MMF animals was 27% of the advancement, whereas there was none in the dental plus skeletal MMF group. Results of adaptations within the suprahyoid complex showed that 1) the suprahyoid complex was elongated slightly less than the mandible, and 2) the major adaptations (lengthening) occurred at the muscle-bone interface, the muscle-tendon interface, and within the belly of the anterior digastric muscle. On the basis of these results, it was concluded that adaptations within the suprahyoid complex to mandibular lengthening occur first at the connective tissue attachments of the muscle, and then within the muscle belly itself. The methods of dealing with the potentially distracting forces from the stretch within the suprahyoid complex are discussed.     

Skeletal stability after mandibular advancement with rigid versus wire fixation.

PURPOSE: This study examined the stability of skeletal changes after mandibular advancement surgery with rigid or wire fixation up to 2 years postoperatively. PATIENTS AND METHODS: Subjects for this multisite, prospective, clinical trial received rigid (n = 78) or wire (n = 49) fixation. The rigid cases were fixed with three 2-mm bicortical position screws and 1 to 2 weeks of skeletal maxillomandibular fixation with elastics, and the wire fixation subjects were fixed with inferior border wires and had 6 weeks of skeletal maxillomandibular fixation with 24-gauge wires. Cephalometric radiographs were obtained before orthodontics, immediately before surgery, and at 1 week, 8 weeks, 6 months, 1 year, and 2 years after surgery. Linear cephalometric changes were referenced to a cranial base coordinate system. RESULTS: Before surgery, both groups were balanced with respect to linear and angular measurements of craniofacial morphology. Mean anterior sagittal advancement of the mandibular symphysis was 4.92 +/3.01 mm in the rigid group and 5.11 +/- 3.09 mm in the wire group, and the inferior vertical displacement was 3.37 +/- 2.44 in the rigid group and 2.85 +/- 1.78 in the wire group. The vertical changes were similar in both groups. Two years postsurgery, the wire group had 30% sagittal relapse of the mandibular symphysis, whereas there was no change in the rigid group (P < .001). Both groups experienced changes in the orientation and configuration of the mandible. CONCLUSIONS: Rigid fixation is a more stable method than wire fixation for maintaining mandibular advancement after sagittal split ramus osteotomy.     

The stability of double jaw surgery: A comparison of rigid versus wire fixation

The subjects of this study were 35 patients who underwent simultaneous surgery for superior repositioning of the maxilla and advancement of the mandible. They were studied cephalometrically for a comparison of the postsurgical stability of two commonly used fixation techniques: (1) rigid fixation with bone plates and (2) skeletal-wire fixation. One surgeon performed the operations on all 35 patients, and both groups were studied for an average of 15 months after surgery. Results showed that, although the maxilla remained relatively stable after surgery with both fixation techniques, rigid fixation tended to improve stability, primarily by eliminating relapse in excess of 2 mm. Mandibular stability was much greater with rigid fixation: the amount of relapse of the horizontal projection of B point with this method was 6%, while in the skeletal-wire sample it was 26%. Increased rotational stability between the proximal and distal segments of the mandible appeared to be a major factor in the improved overall stability of the rigid-fixation sample. The amount of mandibular relapse was found to be correlated to the amount of advancement in the wire-fixation sample, but not in the rigid-fixation sample.     

Relapse following mandibular advancement with dental plus skeletal maxillomandibular fixation

This study examines the short-term stability of the mandible following mandibular advancement surgery in which skeletal suspension wires were used in addition to dental maxillomandibular fixation. Twenty adults underwent sagittal ramus osteotomies. No concomitant surgical procedures were performed. Maxillomandibular fixation consisted of wiring between the upper and lower orthodontic brackets and circummandibular wires connected to the piriform aperture or anterior nasal spine wires for eight weeks. Cephalograms were analyzed during this period to evaluate skeletal stability. A statistically insignificant mean horizontal relapse of 8.9% was found at pogonion during the period of fixation. Significant vertical intrusion of the anterior mandible occurred, however, with a mean superior movement of pogonion of 0.83 mm (P less than or equal to 0.05). Dental changes noted were uprighting of the maxillary incisors and flaring of the mandibular incisors. In comparison with the results of other studies in which dental maxillomandibular fixation was used alone, the results of this study indicate that the use of skeletal suspension wires is advantageous in the prevention of horizontal skeletal relapse.