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Benson, B.J. and Keith, D.A.: Patient response to surgical and nonsurgical treatment for internal derangement of the temporomandibulsr joint. J Oral Maxillofac Surg 43:770, 1985.

Diagnostic MR Imaging of the TMJ: Sensitivity and Spec- ificity. Randall M. Wilk, DDS (Harms, S.E., Wolford, L.M.) Dept. of OMS, Louisiana State University School of Dentistry, 1100 Florida Ave., New Orleans, LA 70119

Magnetic resonance imaging is frequently used in the evaluation of TMJ disorders. Information on many changes in the joint are appreciated. Previous reports’** have not evaluated the sensitivity or specificity of the images for specific findings with the exception of frac- tured prostheses.

87 joints were examined prospectively with MRI that subsequently underwent an open surgical procedure over a 2Yz year period. MRI’s were evaluated by radiologists unaware of clinical findings. Surgical results were re- ported by a surgical observer other than surgeon, who was unaware of the MRI findings of the study. Disc po- sition, disc shape, perforations, bony changes and adhe- sions were evaluated.

Results were analyzed in a matrix relating MRI- observed results and surgery-observed results yielding true and false positives, and true and false negatives for the MRI exam. Sensitivity and specificity were calculated using standard formulae.

Disc position Disc shape Perforations Bony changes Adhesions

Sensitivity (%) Specificity (%)

98.8 100 96.2 97.1 34.6 100 98.1 83.3 27.3 98.1

MRI exams are highly sensitive for disc position, shape and bony changes but insensitive for perforations or adhesions.

The exam is more sensitive than specific generally and may be of considerable usefulness with proper interpre- tation with cognizance of its advantages and limitations.

References:

1. Harms, S.E., Wilk, R.M., Wolford, L.M. et al: “The tem- poromandibular joint: Magnetic resonance imaging using surface coils.” Radiology 157:1:133-136, October, 1985.

2. Kneeland, J.B., Ryan, D.E., Carrera, G.F. et ah “Failed temporomandibular joint prostheses: MR imaging.” Ra- diology 165: 1: 179, October, 1987.

ABSTRACT SESSION V ON ORTHOGNATHIC SURQERY

SATURDAY, OCTOBER 1,4:00-6:00 PM MODERATOR: ROGER H. KALLAL, DDS,

Olympia Fields, IL REACTOR PANEL:

FELICE S. O’RYAN, DDS, OAKLAND, CA JOHN P.W. KELLY, DMD, MD, BOSTON, MA

The Effect of LeFort III Osteotomy on Mandibular Growth in Patients With Crouton and Apert Syndromes. Bing

Hong Bu, DDS (Kaban, L.B., Vargervik, K.) Dept. of OMS, University of California, San Francisco, CA 94143- 0440

Midface advancement by LeFort III osteotomy is a common procedure in craniofacial surgery. There are however, no data on the effect of midface advancement on mandibular growth. This is a retrospective study of 38 patients (from 2 craniofacial centers) who had LeFort III osteotomy. The aims of this investigation were to docu- ment the size and shape of the mandible in Crouzon and Apert syndromes, to compare these parameters to normal standards and to determine the effect of downward and forward movement of the midface (resulting in clockwise rotation of the mandible) on mandibular growth patterns.

There were 22 patients with Crouzon and 16 patients with Apert syndrome who were classified as either grow- ing (n = 15) or non-growing (n = 23) at the time of op- eration. The growing patients were operated upon at a mean age of 9 years 9 months (mean follow-up 6 years 6 months), and the non-growing at a mean age of 17 years 11 months (mean follow-up 4 years 2 months). All pa- tients had completed growth at the time of inclusion in this study.

Lateral cephalograms were traced using sella, nasion (when possible) and the vascular markings of the anterior cranial base for superimposition. Pogonion, condyle, go- nion and mandibular plane were also traced. From these landmarks 2 angular and 3 linear measurements were made and 1 ratio was calculated: gonial angle, inclination of mandibular plane to anterior cranial base (MP-SN), mandibular body length, effective mandibular body length, ratio of mandibular ramus to body length. All re- sults were analyzed by the student t-test.

The syndrome patients had: 1) increased gonial angle, 2) increased MP-SN, 3) increased ramus height and 4) increased ratio of ramus height to body length when com- pared to normal standards. When comparing patients op- erated upon during growth with those operated upon when growth was completed, mandibular size and shape were the same in both groups. LF III osteotomy had no effect on growth of the mandible. Inclination of the man- dible to the anterior cranial base was increased by the operation but remained unchanged during the follow-up period.

The results of this study indicate that the mandible in Crouzon and Apert syndromes has a vertical growth pat- tern with a large gonial angle and that LeFort III osteot- omy with downward and forward movement, performed during growth, has no effect on the ultimate size and shape of the mandible.

References:

Kaban, L.B., et al: Midface position after LeFort III advance- ment. Plast & Reconstr Surg. 73:758-767, 1984.

Kreborg, S., Aduss, H.: Pre- and post- surgical facial growth in patient’s with Crouzon’s and Apert’s syndromes. Cleft Palate J 23: Supplement No. 1, 78-90, 1986.

Internal Screw Fixation: Retentive Strength and Placement Pattern Comparison. William L. Foley, DMD (Frost, D.E., Paulin, W.B., Tucker, MR.) University of North Carolina School of Dentistry, CB#7450, Chapel Hill, NC 27599-7450. Merck Sharp & Dohme Resident Award Win- ner

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Internal screw fixation (ISF) of the sag&al split ramus osteotomy (SSRO) has become increasingly popular in recent years. To date there is no published data compar- ing the retentive strength of various screws employed in fixation systems or the transverse strength of various fix- ation techniques. This study compares the retentive (uniaxial pull-out) strength of five commonly used fixa- tion systems and the transverse strength (ridigity) of six commonly used fixation techniques in sagittal osteoto- mies.

Bone from a freshly killed adult mongrel canine was used to evaluate the uniaxial pull-out strength of four groups of bone screws and one group of Kirschner pins. Thirty screws or pins from each group were tested. An Instron machine was used to subject the screws to uniax- ial tension loading to the point of failure. Failure point was recorded in kg of tension applied. Rib bone from a freshly killed pig was utilized as a model for sag&al os- teotomies. These osteotomies were lixed with six differ- ent ISF techniques. A total of 30 specimens (five for each fixation technique) were tested. One end of each speci- men was embedded in acrylic resin and an Instron ma- chine was used to introduce a compressive load 2.8 cm distal to where the specimen was embedded in acrylic resin. The load required to deflect the specimen 3 mm at the point of compression was recorded in kg and consid- ered to be failure of stabilization.

Results of uniaxial pull-out tests revealed that in all cases failure occurred at the metal-bone interface. Nested analysis of variance and Tukey pairwise comparisons re- vealed a significant difference (p > 0.0001) in uniaxial pull-out strength between the Kirschner pin group and the four screw groups tested. No significant difference was noted between the four screw groups tested. Results of compressive loading on sagittal osteotomies revealed that in all cases failure occurred in the fixation allowing the distal segment to rotate at the osteotomy site. The Stu- dent-Neuman-Keuls test was used to perform pairwise comparisons among the groups and revealed a significant difference (p > .05) in transverse strength between screw placement patterns. Kirschner pins were shown to have significantly less (p > .05) transverse strength than screws placed in a similar pattern. No significant differ- ence in transverse strength was demonstrated between compression (lag) and bicortical (position) screws placed in the same patterns. No significant difference in trans- verse strength was demonstrated between bicortical (po- sition) screws placed at 60” to the bone surface and those placed at 90” to the bone surface in the same pattern.

References:

Spiessl, B.: Rigid internal fixation after sagittal split osteotomy of ascending ramus. Concepts in Maxillofacial Bone Sur- gery. NY: Springer-Verlag, 1976.

Jeter, T.S., et al: Modified techniques for internal fuation of sag&al ramus osteotomies. J Oral Maxillofac Surg 42:270- 272, 1984.

NIDR Grant DE 05215

Intraoperative Monitoring of Trigeminal Evoked Potentials During Sagittai Split Osteotomies. Daniel L. Jones, (Wol- ford, L.M.) 10315 White Elm, Dallas, TX 75243

The inferior alveolar branch of the trigeminal nerve (IAN) is subject to damage during bilaterial sag&al split osteotomy (BSSO), a common maxillofacial surgical pro-

cedure. The purpose of this pilot study was to evaluate the use of somatosensory evoked potentials (SEP) to as- sess the functional state of the IAN during surgery. SEPs have been reliably recorded from the trigeminal distribu- tion, and used intraoperatively to monitor neural function during spinal surgery.

SEPs were recorded bilaterally from ten patients (3 male, 7 female) undergoing BSSO. Recording electrodes were secured with surgical staples on the scalp overlying vertex and inion, and subcutaneous stimulating elec- trodes inserted one centimeter apart over the mental fo- ramina. SEPs were recorded during four events occurring in surgery; 1) baseline recordings after anesthestic induc- tion, but prior to the initial incision, 2) during the man- dibular bone cuts, 3) during splitting of the mandible, and 4) following rigid fixation of the mandible with bone screws. Analysis of the latencies and amplitudes of the SEP waveforms revealed a triphasic response occurring approximately 15-30 milliseconds following stimulation. When the IAN was retracted medially during the bone cuts, the mean amplitudes of these peaks were signifi- cantly decreased, while the mean latencies were signili- cantly increased. However, in all cases the SEP wave- form returned to baseline values within a period of 5-10 minutes following retraction being released. No consis- tent changes were seen in the SEPs recorded at other times during the surgical procedure. Thus, intraoperative SEPs were shown to be a sensitive index of nerve func- tion, but no long lasting neural deficits were observed to occur during the four periods examined in this patient sample.

References

Barker, G.R., Bennett, A.J., and WastelI, D.G.: Applications of trigeminal somatosensory evoked potentials (TSEPs) in oral and maxillofacial surgery. British J. Oral Maxillofac Sur. 25:308-313, 1987.

Grndy. B.L.: Intraoperative monitoring of sensory evoked po- tentials. Anesthesiology. 58:72-87, 1983.

Histochemical Analysis of the Masseter and Temporalis Muscle 12 Weeks After Mandibular Advancement Using Rigid and Non-Rigid Fixation Kathleen H. Mayo, DDS, (Ellis, E., Carlson, D.S.) University of Michigan School of Dentistry, 1011 N. University, Dept. of OMFS, Ann Arbor, MI 48109-1078

In a previous study of occlusal bite force following mandibular advancement using rigid and non-rigid fixa- tion, it was found that significant reductions in bite force occur in both groups at 12 weeks following surgery, al- though the rigidly fixed monkeys had greater bite force than those which underwent maxillomandibular futation (MMF). The purpose of this investigation was to describe the histochemical characteristics and cross-sectional ar- eas of the superficial masseter and temporalis muscles in aault rhesus monkeys following mandibular advancement using rigid and non-rigid fixation.

Eleven adult female rhesus monkeys underwent man- dibular advancement via the sag&al ramus osteotomy and were randomly divided into two experimental groups based upon the method of postsurgical fixation used. Group MMF (n = 6) underwent 6 weeks of MMF. Group RF (n = 5) had bicortical screws placed without MMF. Immediately prior to sacrifice at 12 weeks postsurgery, biopsies of the anterior masseter and temporalis muscles