Scientific Poster Session

canted occl& planes, laterognathia and/or bypass bites. A three-dimensional understanding of the skeletal and dental deformity is mandatory in the presurgical evaluation of such patients. Conventional dental articu- lators are limited in th& true representation of the individual craniofacial skeleton in that the intercondylar distance and the correction for earpost to condylar axis is set only to approximate that found in the average adult. Conventional articulators do not accurately repre- sent true autorotation of the mandible. Conventional model surgery on such articulators does not allow presurgical visualization of the mandibular ramus or address proximal and distal fragment relationship follow- ing ramus surgery. The choice of ramus procedure, the necessity for bone grafting and fragment contouring, and the feasibility of rigid flxation therefore tend to be arbitrarily determined. The Orthognathic Surgery Simu- lating Instrument (O.S.S.I.), designed by Dr. Joe Hall Morris, allows the surgeon to more easily plan surgical corrections in the laboratory with a greater degree of accuracy and ultimate clinical simulation.

Since its development sixteen years ago, the O.S.S.I. has been used at our institution to plan surgical correc- tion for patients with facial asymmetries. The initial patient evaluation includes clinical and radiographic studies comprised of submentovertex, lateral cephalomet- ric and panorex radiographs. The intercondylar distance and condylar axis from the earpost offset is measured from these radiographs with correction for magnifica- tion and is then transferred to the instrument. The casts are mounted on the O.S.S.I., and the customized facsim- ile rami are secured to the mandibular cast. Following maxillary repositioning, surgical cuts are made on the facsimile rami and the mandible is then repositioned. Characteristics of the occlusion, ramus fragment relation- ships, amount of bone grafting needed, necessity for fragment contouring, and feasibility of rigid fixation can then be assessed.

An accurate three-dimensional representation of the rami, condyles, intercondylar distance and true rotation of the mandible on the condylar axis allowed for more accurate and reliable treatment planning. Some of the advantages found using the O.S.S.I. in treatment plan- ning for these patients with facial asymmetries included a more appropriate selection of ramus procedure based on overall ramus fragment apposition. Clinically insignif- icant changes in the final occlusion could be adjusted to allow for a better ramus fragment relationship. Case planning for the correction of asymmetries of the poste- rior maxilla in the horizontal plane revealed that often poor fragment relationship was translated to the mandi- ble. This may have led to compromised facial esthetics, delayed healing, and difficulty in application of rigid fixation. Visualizing such outcomes pre-operatively al- lows for appropriate adjustments in the position of the

maxilla or mandible. Decreased surgical time due to pre-operative knowhxlge of the necessity for and amount of bony contouring and bone gmfting is also an advan- tage. In our patient population, close correlation was consistently evident in the comparison of facsimile ramus to intraoperative ramus fragment positions.

References

Hill, S.C.: Cepbalometric planning and model surgery, in Bell W.H. (ed): Surgical Correction of Dentofacial DefomdtiekNew Concepts. Phiidalphia, PA, Saunders, 1985, pp 217-226

Ellis, E.: Use of the orthoguathic surgery simulating inatrument in the presurgical evaluation of facial asymmetry. J Oral Maxillofac Surg 42:805,1984

Departmental funding

POSTER 5 Getmmid Gnas- of D&c Re~idoning Pmcedms Leslie B. Heffez, DDS, MS, Univ. of Illinois, Dept. of OMS, 801 S. Paulina St., Chicago, IL 60680 (Crawford, G.L., Jordan, S.)

Disc repositioning procedures have been advocated for the treatment of internal derangements of the temporomandibular joint. Arthroscopy has again brought into question the feasibility and efficacy of repositioning displaced discs. In this study we critically evaluate the geometry of repositioning discs using cadaver and mag- netic resonance (MR) image models.

Lateral, central, and medial sag&al planes of four histologic specimens and five MR images were utilized yielding 27 sections/images. These specimens/images were projected at a standard magnification of 7.3. The posterior attachment-disc-condyle-glenoid fossa relation- ships were then traced onto acetate paper. Mock disc repositioning surgery was performed for each serial histological section and image. The disc was reposi- tioned to a standard location as determined by a previously designed model. The following measure- ments were then obtained: anterior capsule to most anterior aspect of repositioned disc and length of poste- rior attachment resected. Additional observations were made including the necessity of discoplasty or deforma- tion (bending) at the thin zone to permit the disc to geometrically fit into the available joint space. The data from the lateral, central, and medial sections was cor- rected to represent actual measurements and analyzed.

In accomplishing mock surgery and analyzing the data, only geometrical aspects of the procedure were considered. Viscoelastic molding of the disc to existing joint space was not considered. Results from the study

MOMS . 1991 115

Scientific Poster Session

show that there was deformation of the disc in all sagittal planes. 55% of repositioned discs required deformation (bending) at the thin zone. All joints needed discoplasty in at least one section to reposition the disc in available joint space. All specimens/images required repositioning posteriorly to place the disc in standard position with the mean distance moved ranging from 2.9 mm to 11.8 mm. All specimens required resection of the posterior attach- ment with the mean lateral distance 5.6 mm and the mean medial distance 4.1 mm. In all cases there was an increasing amount of tissue needed to be resected in each joint as the sections/images moved from medial to lateral. The morphology of only two joints were consis- tent from lateral to medial.

On the basis of the material studied, the following observations may be made: gross disc deformation occurs in all planes concomitant with disc displacement; deformation of the disc is not uniform; repositioning of the displaced disc requires a posterolateral rotation, necessitating release of anteromedial tissues; disco- plasty is necessary in the absence of molding/remodeling of the tissue; the disc histologically is not precisely demarcated from the posterior attachment.

We conclude that from a geometrical aspect the feasibility of disc repositioning procedures must be evaluated on a case by case basis. This approach has promise for developing geometrical criteria for disc repositioning surgery and an intra-articular three dimen- sional model.

References

Dolwick, M.F., Sanders, B.: TMJ Internal Derangement and Arthro- sis. St Louis, MO, Mosby, 1985

Heffez, L., Jordan, S., Going, R.: Determination of the radiographic position of the temporomandibular joint disk. Oral Surg Oral Med Oral Path01 65:272-280,1988

and mechanical stretching devices. Many varieties of mechanical devices have been fabricated over the years. We chose to use the Therabyte Jaw Exerciser for our study. Along with these intermittant-use devices, “con- tinuous passive motion devices” have recently become available. However, despite the many different modali- ties available, insufficient experimental data exists for the guidance of exercise therapy for the population of patients with decreased range of motion of the mandible secondary to radiation therapy.

Subjects were chosen from patients referred to the OMS Service for treatment of decreased mouth opening secondary to radiation therapy. To be included, subjects had a maximum interincisal opening of 20 mm. For each category of patients, groups of six to nine patients were pseudorandomly assigned as follows: Group 1; unas- sisted manual exercise. Group 2; tongue depressor therapy combined with the group one regimen. Group 3; the group 1 regimen combined with the use of the Therabite Jaw Exerciser.

Each patient returned to the clinic at weekly intervals for evaluation and objective measurement was made of maximal incisal opening, lateral and protrusive jaw movement. Patients were also asked to make subjective judgement of pain, range of motion, and well-being.

Objective measurements were statistically analyzed and comparisons were made of actual measurement, change in measurement, and ratio to initial measure- ment. Subjective evaluations were also evaluated.

Group 3 patients consistently outperformed the other two groups by both objective and subjective standards. One possible reason for this finding (that was not measured) was discovered on interviewing patients. That is, that Group 3 patients felt more in control of their treatment and thus exhibited greater compliance.

References

POSTER 6 Evaluation of Oral Exercise Regimens for Jaw Hypomobility

Lubit, C.E.: An appliance for jaw dilation in prolonged posttrau- matic and postsurgical trismus and fibrosis. J Oral Maxillofac Surg 38:541-542,198O

Bell, W.H., et al: Muscular rehabilitation after orthognathic surgery. OS 56:226-235,1983

Robert B. Currivan, DMD, 1411 Madison Ave. #lE, NY, NY 10029 (Buchbinder, D.) Departmental funding

This study assessed the efficacy of different oral exercise regimens and tested the hypothesis that mechan- ically assisted exercise is more efficacious then the prescription of manual exercise alone or in combination with tongue depressor stretching.

The literature shows that even if exercise is almost universally accepted as therapeutic, it is not clear which exercises are most likely to be beneficial. Many manual, mechanical and electrical approaches have been de- scribed the most popular of which include isometric and range of motion exercises, tongue depressor therapy,

POSTER 7 Aggressive Fibromatosis of the Jaws: Combined Surgical-Chemotherapeutic Approach Lloyd A. Darlow, DMD, MD, Division of Oral & Maxillofacial Surgery, Hospital of the University of Pennsylvania, Philadelphia, PA 19104 (Quinn, P.D.)

The fibromatoses comprise a group of tumors with both benign and malignant characteristics. Aggresive fibroma-

116 AAOMS . 1991