Mobility of the mandible following advancement and maxillomandibular or rigid internal fixation: an experimental investigation in Macaca mulatta

This study examined the postsurgical range of mandibular motion following sagittal advancement osteotomy in Macaca mulatta when either maxillomandibular or rigid osseous fixation were used. Seventeen adult female Macaca mulatta underwent sagittal advancement osteotomy of approximately 4 to 6 mm. Six had 6 weeks of maxillomandibular fixation and eleven had rigid osseous fixation with no maxillomandibular fixation. Mandibular range of motion was measured by the change in the angle of the posterior aspect of the mandibular ramus from a closed-mouth and an open-mouth cephalogram. Parametric tests were used to statistically analyze the results. The results of this investigation showed that the animals who did not undergo maxillomandibular fixation maintained a greater range of motion in the early postsurgical period and obtained preoperative mobility by 12 weeks postsurgery. The animals who underwent six weeks of maxillomandibular fixation showed statistically significant decreases in range of motion when compared to the rigid fixation group at each period of time postsurgery, with significant reductions from preoperative values at 12 weeks postsurgery.     

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.     

Histologic examination of the temporomandibular joint after mandibular advancement with and without rigid fixation: an experimental investigation in adult Macaca mulatta

This study evaluated the histologic response of the temporomandibular joint (TMJ) following mandibular advancement using rigid and nonrigid fixation in monkeys. Twelve adult female rhesus monkeys underwent sagittal ramus osteotomies with advancement. Six of them were placed into maxillomandibular fixation (MMF); six underwent bicortical bone-screw fixation without MMF. Changes in condylar position were quantified using lateral cephalograms with the aid of bone markers. The animals were killed at 6 weeks and the TMJs were prepared for histologic analysis. Three measures of condylar cartilage thickness were obtained for each animal and were correlated to changes in position of the condyle. Animals who underwent MMF showed a tendency for anterior movement of the condyles; animals who underwent rigid fixation showed a tendency for posterior condylar position. Thicker cartilage layers were found in the MMF animals. Animals who had posterior displacement of the condyles showed evidence of resorption of the posterior surface of the condyle and anterior surface of the postglenoid spine. There was a significant correlation between a change in the horizontal position of the condyle and the thickness of the posterior aspect of the condylar cartilage. The results of this study indicate that alterations in condylar position may induce remodeling changes within the TMJ.     

Growth of the mandible after replacement of the mandibular condyle: an experimental investigation in Macaca mulatta.

PURPOSE: The study goal was to investigate growth of the mandible after temporomandibular joint reconstruction in juvenile monkeys. MATERIALS AND METHODS: Sixteen juvenile monkeys (Macaca mulatta) were used as experiment subjects. Animals were equally divided into 4 experimental groups based on the method of temporomandibular joint reconstruction after bilateral condylar excision via extraoral vertical ramus osteotomies. Group Condyle animals had their condylar segments immediately replaced to serve as surgical controls. Group Bone animals were reconstructed with a bony strut. Group sternoclavicular joint (SCJ) animals were reconstructed with the sternal end of their clavicles. Group costochondral junction (CCJ) animals were reconstructed with costochondral junction of ribs. Standardized lateral cephalometric radiographs with the aid of tantalum bone markers were used to evaluate mandibular growth. Twenty animals were used as controls and were allowed to grow undisturbed for an 18-month period (Group Control). RESULTS: All animals showed good mandibular function and a Class I molar relationship after an 18-month follow-up period. Statistical and graphic comparisons showed no significant difference in mandibular growth among any of the groups. CONCLUSIONS: The results of this investigation suggest that, within the limits of this model, the choice of autograft for condyle replacement may be irrelevant.     

Effect of maxillomandibular fixation on condylar growth in juvenile Macaca mulatta: a cephalometric and histologic study

The effect of maxillomandibular fixation on the growth of the mandibular condyle was studied in eight control and eight experimental male juvenile monkeys. All animals had metallic implants placed throughout the craniofacial complex in order to facilitate cephalometric analysis of growth-related changes in the maxillomandibular complex during jaw immobilization. Every 3, 6, 12, and 24 wk after insertion of the appliance two experimental animals were killed for histologic analysis. Cephalometric analysis indicated no major deviation from normal maxillary or mandibular growth in the experimental animals. The condylar growth in the experimental animals was comparable with that of the controls. Histologic analysis indicated that the articular connective tissue in experimental joints remained the same thickness as in the controls. On the postero-superior aspect of the condyle, the thickness of the prechondroblastic-chondroblastic cell layer was reduced by 70–80% in the experimental animals. On the posterior aspect this cell layer was not visible after 12 wk of fixation, but was replaced by a periosteum-like, cell-rich tissue which appeared to be active in appositional formation of cancellous bone. These results indicate that long-term maxillomandibular fixation does not cause major alterations in the growth of condyle or the entire mandible despite a profound decrease of the prechondroblastic-chondroblastic cell layer in the postero-superior and posterior regions of the condyle. The growth is probably due to a compensatory appositional bone formation along the surface of the condyle. It is also concluded that jaw mobility is not a prerequisite for normal maxillary or mandibular growth.     

Mandibular advancement: skeletal and dental changes during fixation.

Skeletal and dental changes that occurred during maxillomandibular fixation after surgical advancement of the mandible were examined in 21 patients. Serial cephalometric monitoring showed skeletal relapse with compensatory dental changes in every case; the pattern of relapse varied. Common hypotheses currently expressed and applied by clinicians for presurgical prediction of such treatment results were objectively assessed for validity on the basis of the patient sample studied. The findings indicate that single variables cannot be isolated as being solely responsible for specific postsurgical changes.     

Growth of the mandible following replacement of the mandibular condyle with the sternal end of the clavicle: an experimental investigation in Macaca mulatta.

This study was designed to investigate the long-term effects of transplanted clavicles to the temporomandibular joint (TMJ) in juvenile monkeys. Sixteen juvenile female monkeys (Macaca mulatta) were used in this experiment. Eight animals were used as controls and were allowed to grow undisturbed for an 18-month period (group control). Eight animals were divided into two groups and underwent bilateral condylar excision via extraoral vertical ramus osteotomies. Four of these animals had their condylar segments removed and immediately replaced to serve as surgical controls (group condyle). The other four underwent condylar replacement with the sternal end of their clavicles (group SCJ). Standardized lateral cephalometric radiographs with the aid of tantalum bone markers were used to evaluate maxillary and mandibular growth. One-way analysis of variance (ANOVA) was used to determine the significance of differences between groups. All animals showed good mandibular function and a class I molar relationship following an 18-month evaluation period. Statistical analysis showed there was no significant difference in maxillary or mandibular growth between any of the three groups. The results of this investigation show that the sternal end of the clavicle may be a viable option in mandibular condylar transplant surgery.     

Stability of extraoral vertical ramus osteotomy: plate fixation versus maxillomandibular/skeletal suspension wire fixation

The objective of this cephalometric study was to evaluate skeletal stability and time course of postoperative changes in 2 groups of mandibular prognathism patients following extraoral oblique vertical ramus osteotomy (VRO). One group (n = 22) received maxillomandibular fixation and skeletal suspension wires (MMF group) for a period of 8 weeks. In the other group (n = 22), the segments were rigidly fixed with plates and the patients were allowed to function immediately after surgery. Lateral cephalograms were taken on 5 occasions: immediately presurgical, immediately postsurgical, 8 weeks postsurgical, 6 months postsurgical, and 1 year postsurgical. During the first 8 weeks after surgery, the MMF group demonstrated posterior movement of the mandible, with an increase in mandibular plane angle, shortening of the rami, and dental compensations. Upon release of MMF and skeletal suspension wiring, a small anterior relapse tendency was observed, but the net setback 1 year after surgery was still greater than the actual surgical setback. In the plate fixation group, postoperative changes were mainly in the form of a small anterior relapse tendency in the range of 10% of the surgical setback. The results indicate that the use of plate fixation with VRO, while eliminating the inconvenience for the patient of several weeks of MMF and preventing the early side effects observed in the MMF group, also resulted in a more predictable surgical procedure, with excellent stability 1 year after surgery.     

Stability of the mandible following advancement: a comparison of three postsurgical fixation techniques

This study examines short-term stability of the mandible following mandibular advancement surgery by means of three standard techniques of postsurgical fixation. Twenty-two adult female rhesus monkeys (Macaca mulatta) underwent sagittal ramus advancement osteotomy of approximately 4 to 6 mm. Six animals had dental maxillomandibular fixation alone. Six animals had dental plus skeletal maxillomandibular fixation with circummandibular wires connected to pyriform aperture wires. Ten animals had rigid internal fixation with bicortical bone screws between the proximal and distal segments without maxillomandibular fixation. Radiographic cephalograms with the aid of tantalum bone markers and dental amalgams were analyzed during the first 6 postoperative weeks to evaluate skeletal and dental stability. Rigid internal fixation and the use of dental plus skeletal maxillomandibular fixation were both equally effective in the prevention of postsurgical relapse. However, in the animals in which only dental maxillomandibular fixation was used, statistically significant changes (relapse) occurred when compared with either of the other groups.     

Long-term mandibular adaptations to protrusive function: an experimental study in Macaca mulatta

Twenty-three male juvenile rhesus monkeys (Macaca mulatta) were used in an experimental study of long-term mandibular adaptations to induced protrusive function. Serial protrusive appliances were placed in 11 experimental animals and mandibular adaptations were monitored cephalometrically. Twelve animals were used as controls. After 48 weeks significant increases in increments of condylar growth and in overall mandibular length were noted in the treated animals. At the end of the 144-week experimental period, the mandibles of the treated animals were 5 to 6 mm longer than those of the control animals. The results of this study do not support the hypothesis that the mandible has a genetically predetermined length.     

Stability two years after mandibular advancement with and without suprahyoid myotomy: an experimental study

Ten adult rhesus monkeys underwent mandibular advancement surgery of 4-6 mm with and without suprahyoid myotomy. Serial lateral cephalograms using radiopaque bone markers were obtained during maxillomandibular fixation and for 96 weeks after release of fixation to determine the effects of suprahyoid myotomy on short-term and long-term adaptations in the advanced mandible. The non-myotomy group exhibited a significant reduction in the length of the advanced mandible (relapse) during the fixation period but showed no significant change in mandibular length after release of fixation. The myotomy group exhibited no relapse during the fixation period and after release of fixation displayed a slight but statistically significant increase in mandibular length. This supports the hypothesis that stretching of the suprahyoid musculature as a result of mandibular advancement surgery is a major factor leading to skeletal relapse.     

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)     

Long-term maxillomandibular skeletal and dental changes in children with cleft lip and palate after maxillary distraction

Long-term skeletal and dental changes were examined in 8 children with cleft lip and palate who underwent maxillary distraction to allow the maxilla to catch up to their mandibular growth at the treatment point. Changes in the overjet (OJ), overbite (OB), and positions of the anterior nasal spine (ANS), upper incisors (U1), pogonion (Pog), and lower incisors (L1) were measured on preoperative to 36 months postoperative lateral-cephalograms. In most of the children, the long-term changes after the maxillary distraction resulted in an inferior growth of the maxilla and anteroinferior growth of the mandible. This seems to suggest that maxillary distraction performed during childhood needs considerable overcorrection. However, if the maxilla is distracted to an adult position during childhood, the masticatory functions of the children will markedly deteriorate until their jaws grow. Therefore, we believe that one goal of maxillary distraction during childhood can be to allow the maxilla to catch up to the mandibular growth of the children at the treatment point.     

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.     

Comparison of different distraction rates in the mandible: an experimental investigation.

This study evaluated bone distracted in rabbit mandibles at different intervals and with different daily rates of distraction histologically with the goal of attaining a universally accepted distraction protocol. Osteogenesis was investigated in mandibles distracted at different rates in 24 New Zealand rabbits using a custom-made submerged distractor. Distraction was started on the third postoperative day for a total of 10 mm. The animals were divided into four groups each containing six rabbits. Group 1 was distracted 0.5 mm twice a day; Group 2 was distracted 1.0 mm once a day; Group 3 was distracted 1.0 mm twice a day and Group 4 was distracted 2.0 mm once a day. All the animals were sacrificed 6 weeks after completion of distraction. Half of the distracted mandibles were decalcified for H&E staining and polarized light microscopy studies. Sections of the undecalcified half of the samples were stained with Goldner's stain. The results indicate that a distraction rate of 1.0 mm per day produced the best osteogenesis among the tested rates. There was no great difference in osteogenesis between 1.0 mm once a day and 0.5 mm twice a day. However, 0.5-mm distraction may result in immature bone healing. Distraction of 1.0 mm twice a day resulted in incomplete osteogenesis, while distraction of 2.0 mm once a day resulted in fibrous union. It is clear from these results that a shorter period of device fixation should be achieved by methods other than rapid distraction.     

Stability after rigid fixation of simultaneous maxillary impaction and mandibular advancement osteotomies

The purpose of this study was to investigate the short- and long-term stability of bimaxillary surgery following LeFort I (LF-1) impaction with simultaneous bilateral sagittal split ramus osteotomy (BSSO) and mandibular advancement using the technique of rigid internal fixation (RIF). In order to assess the postoperative maxillary and mandibular movement pattern in 26 patients with vertical maxillary excess and mandibular deficiency, cephalograms were taken immediately preoperatively, and 1 week, 2 months, and 1 year after surgery. With paired t-test showing no statistically significant postoperative change for the point A of the maxilla from immediate postsurgery to longest follow-up (P> 0.05), the used technique of "RIF LF-I impaction and RIF BSSO advancement" tended to render excellent postsurgical stability in the horizontal (0.1+/-0.8mm mean posterior movement) and vertical (0.1+/-0.5mm mean inferior movement) direction. There was no instance of maxillary relapse of >2mm. Regarding mandibular BSSO advancement, the point B showed a significant vertical upward movement (1.6+/-1.2mm) (P< 0.001) and a slight horizontal forward movement (0.3+/-2.0mm) (P> 0.05) at 1-year follow-up. The incidence of posterior relapse of >2mm accounted for 11.5%. The data confirm the concept that the bimaxillary approach of "LF-I impaction and BSSO advancement" using the described technique of RIF is a stable procedure in the treatment of open bite patients classified as vertical maxillary excess in combination with mandibular deficiency.     

A comparative study of skeletal and dental stability between rigid and wire fixation for mandibular advancement

This study examined the skeletal and dental stability after mandibular advancement surgery with rigid or wire fixation for up to 2 years after the surgery. Subjects for this multisite, prospective, randomized, clinical trial were assigned to receive rigid (n = 64) or wire (n = 63) fixation. The rigid cases received three 2-mm bicortical position screws bilaterally and elastics; the wire fixation subjects received inferior border wires and 6 weeks of skeletal maxillomandibular fixation with 24-gauge wires. Cephalometric films were obtained before surgery, and at 1 week, 8 weeks, 6 months, 1 year, and 2 years after surgery. Skeletal and dental changes were analyzed using the Johnston's analysis. Before surgery both groups were balanced with respect to linear and angular measurements of craniofacial morphology. Mean anterior advancement of the mandibular symphasis was 5.5 mm (SD, 3.2) in the rigid group and 5.6 mm (SD, 3.0) in the wire group. Two years after surgery, mandibular symphasis was unchanged in the rigid group, whereas the wire group had 26% of sagittal relapse. Dental compensation occurred to maintain the corrected occlusion, with the mandibular incisor moving forward in the wire group and posteriorly in the rigid group. However, at 2 years after surgery, when most subjects were without braces, the overjet and molar discrepancy had relapsed similarly in both groups.     

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.     

Rigid versus wire fixation for mandibular advancement: Skeletal and dental changes after 5 years

The bilateral sagittal split osteotomy (BSSO) is the most common surgical procedure for the correction of mandibular retrognathism. Commonly, the proximal and distal segments are fixated together with either wire or rigid screws or plates. The purpose of this study was to compare long-term (5 years) skeletal and dental changes between wire and rigid fixation after BSSO. In this multisite, prospective, randomized clinical trial, the rigid fixation group received three 2-mm bicortical position screws, and the wire fixation group received inferior border wires and 6 weeks of skeletal maxillomandibular fixation with 24-gauge wires. Cephalometric films were obtained 2 weeks before surgery and at 1 week, 8 weeks, 6 months, 1 year, 2 years, and 5 years after surgery. Linear cephalometric changes were referenced to a cranial base coordinate system. Before surgery, both groups were comparable with respect to linear and angular measurements of craniofacial morphology. Both groups underwent similar surgical changes. Skeletal and dental movements occurred in both groups throughout the study period. Five years after surgery, the wire group had 2.2 mm (42%) of sagittal skeletal relapse, while the rigid group remained unchanged from immediately postsurgery. Surprisingly, at 5 years, both groups had similar changes in overbite and overjet. This was attributed to dental changes in the maxillary and mandibular incisors. Although rigid fixation is more stable than wire fixation for maintaining the skeletal advancement after a BSSO, the incisor changes made the resultant occlusions of the 2 groups indistinguishable.