Osseointegrated titanium implants for maxillofacial protraction in monkeys.

Titanium implants were placed surgically into the maxillary, zygomatic, frontal, and occipital bones of four pigtail monkeys. After a 4-month healing period, the implants were exposed and abutments were placed. Extraoral traction appliances were then attached to the abutments. The cranial implants were used to support the framework of the traction appliance; those in the facial bones were used to attach springs that delivered a protraction force. The application of force varied among animals. In animal A, the force was applied to the maxilla. In animal B, the force was applied to the zygomatic bones. Animals C and D had force applied to both the maxillary and zygomatic bones. A tensile force of 600 gm per side was maintained until approximately 8 mm of maxillary anterior displacement had occurred. This amount of movement required 12 weeks of force application in animals A and B, and 18 weeks in animals C and D. Cephalometric and dry skull analyses showed that the amount of skeletal protraction was significant. The findings also demonstrated that it was possible to control the direction of maxillary protraction. The facial implants remained immobile throughout the experiment.

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 postoperatively. 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 clockwise 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.

Masticatory muscle transposition in primates: effects on craniofacial growth.

The effects of early transposition of the masticatory muscles on the craniofacial growth and development of infant primates are documented with the aid of serial cephalometry, EMG's, and dry-skull preparations. The bilateral posterior transposition of the insertion of the masseter and temporalis muscles was followed by a significant superior and anterior rotation of the midfacial growth pattern as well as by marked skeletal morphological changes. The study documents the ability to change skeletal craniofacial growth patterns by altering muscle attachments.

Measurement of condylar loading forces by instrumented prosthesis in the baboon.

Mathematical models have been developed to predict hypothetical forces acting on the mandibular condyles during mastication, but no direct measurements of condylar forces in vivo have been reported. This preliminary study presents the technical development of an instrumented prosthesis which was implanted in the mandibular ramus of a baboon, and some preliminary data collected while measuring with this prosthesis the condylar forces exerted during simulated mastication under general anaesthesia. Simulated mastication was induced by stimulating the motor tracts of the trigeminal nerve bilaterally, and the forces in response to increasing amperage were recorded. The pathogenesis of TMJ degeneration may be more fully understood by directly measuring the direction and magnitude of forces acting on the condyles during function. In addition, the future development of a total TMJ replacement for traumatized, deranged, or degeneratively impaired joints, must be accomplished with reliably engineered prostheses based upon direct force measurements.

Experimentally induced ankylosis and facial asymmetry in the macaque monkey.

Six Macaca nemestrina were used for induction of ankylosis by different methods. One TMJ capsule was either (a) mechanically damaged, (b) injected with sodium morrhuate, or (c) injected with a strain of Staphylococcus aureus. The other capsule served as a control. Facial asymmetry of varying degrees was evident from dry-skull preparations and histologically. Sodium morrhuate caused the least degree of alteration; mechanical damage, the most. The effects of Staph. aureus injection into the TMJ seemed to depend upon the length of time elapsed since injection. In one animal there was no change at autopsy after two injections several weeks apart, once on each side; in the other, the capsule injected initially showed no change at autopsy, whereas that injected several weeks prior to autopsy was considerably altered. Induction of ankylosis was achieved with varying degrees of success, causing differing degrees of facial asymmetry.

The effects of early Le Fort I osteotomies on craniofacial growth of juvenile Macaca nemestrina monkeys.

Le Fort I osteotomies were performed on three juvenile Macaca nemestrina monkeys with midface deficiencies from prior extraoral traction. The maxillas of these monkeys were moved anteriorly an amount necessary to achieve about 8 mm. of horizontal overjet. Interosseous wires were used to stabilize the segments; the animals were not placed in intermaxillary fixation. Craniofacial growth in the three experimental monkeys and in three control monkeys was monitored for 2 years with serial cephalometric radiographs. Compared to the controls, the maxillas of the experimental animals demonstrated less anterior growth, and this was manifested clinically in anterior dental cross-bite relationships. Histologic examination of the circummaxillary sutural complex revealed normal morphology. It is concluded, therefore, that early Le Fort I osteotomies significantly affect subsequent maxillary growth in monkeys and that this effect probably is due to formation of scar tissue.

Occlusal concepts for the orthognathic surgeon.

A review of modern occlusal concepts is of great value to the orthognathic surgeon in treating dentofacial deformities. A thorough knowledge of occlusion is essential in the correct diagnosis and treatment of patients requiring surgical alterations in their occlusal relationships. Following these surgical alterations, a critical postoperative evaluation is important in determining the timing and need for occlusal equilibration and/or restorative measures.

The use of an anatomic articulator in segmental orthognathic surgery.

We have tried to discuss briefly the pertinent theory, mechanics, and clinical use of an anatomic articulator in segmental orthognathic surgery. Many of the concepts and clinical uses of the articulator may be applicable to the full range of orthognathic surgical procedures. Many of the ideas presented here may seem needlessly detailed or irrelevant to the uninitiated. It is this attention to details and thoroughness that ultimately determine how closely our treatment will achieve the "ideal" functional and esthetic goals. We must measure the effectiveness of an anatomic articulator by the three original goals of maxillary segmental surgery: 1. Improvement of the patient's esthetic and facial harmony. 2. Improvement of the centric and functional occlusal relationships. 3. Maintenance of the long-term health and function of the teeth, periodontium, temporomandibular joints, and associated structures. I believe that these three criteria will be more closely achieved by the use of an anatomic articulator in segmental maxillary surgery. If the orthognathic surgeon is to be more than a technician performing prescription surgery, a thorough knowledge of the functional stomatognathic system is essential.

Macrogenia: a study of treatment results, with surgical recommendations.

1. A retrospective cephalometric study of patients who underwent reduction genioplasties showed large variations in soft-tissue response to osseous reduction. 2. The vertical and horizontal soft-tissue changes coincident to osseous reduction were less than expected. The maximum soft-tissue change observed was approximately 50 per cent that of the hard tissue removed. On the average, the vertical soft-tissue change was about 30 per cent and the horizontal was 25 per cent, when degloving procedures were combined with some form of ostectomy. 3. A considerable length of time is necessary before the soft-tissue changes are stable after reduction genioplasty. In some cases, significant changes occurred up to 8 to 10 months postoperatively. 4. A classification of macrogenia is proposed, based upon a more exact anatomic description of the deformity. 5. On the basis of this classification, the results of the present study, and more recent clinical results, recommendations for the surgical treatment of macrogenia are made.