Development of anterior disk displacement in the temporomandibular joint: An autopsy study

INTERNAL

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Ireland, V. E.: The problem of the clicking jaw. Ann Dent 11:3, 1952. Rickettes, R. M.: Laminagraphy in the diagnosis of TMJ disorders. J Am Dent Assoc 46:620, 1952. Thompson, J. R.: Concepts regarding function of the stomatognathir system. J Am Dent Assoc 48~626, 1954. Norgaard, F.: Arthrography of the mandibular joint. Acta Radio1 25~679, 1944. Wilkes, C. H.: Arthrography of the temporomandibular joint in patients with the TMJ pain-dysfunction syndrome. Minn Med 61:645, 1978. Katzberg, R. W., Anderson, Q. N., and Helms, C. A.: Arthrography. In Helms, C. A., Katzberg, R. W., and Dolwick, M. F., editors: Internal Derangements of the Temporomandibular Joint. San Francisco, 1983, Radiology Research and Educational Foundation. Ramfjord, S. P., and Ash, M. M.: Occlusion, ed 2. Philadelphia, 1971, W. B. Saunders Co., pp 248250. Farrar, W. B.: Diagnosis and treatment of anterior dislocation of the articular disc. NY J Dent 40~348, 1971. Dawson, P. E.: Evaluation, Diagnosis, and Treatment of Occlusal Problems. St. Louis, 1974, The C. V. Mosby Co., pp 54-60. Helkimo, M.: Studies on function and dysfunction of the masticatory system. II: Index for anamnestic and clinical dysfunction and occlusal state. Swed Dent J 67:101, 1974. Steele, R. G. D., and Torrie, G. H.: Principles and Procedures of Statistics with Special Reference to the Biological Sciences. New York, 1960, McGraw-Hill Book Co., Inc., pp 379-381. Jarabek, J. R.: An electromyographic analysis of muscular and temporomandibular joint disturbances due to imbalances in occlusion. Angle Orthod 26:170, 1956.

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Farrar, W. B.: Treatments. In Farrar, W. B., and McCarty, W. L.: A Clinical Outline of Temporomandibular Joint Diagnosis and Treatment, ed 7. Montgomery, Ala., 1982, Normandie Publications. Dolwick, M. F., and Riggs, R. R.: Diagnosis and treatment of internal derangements of the temporomandibular joint. Dent Clin North Am 27:561, 1983. McNeil, C.: Nonsurgical management. In Helms, C. A.: Katzberg, R. W., and Dolwick, M. F.: Internal Derangements of the Temporomandibular Joint. San Francisco, 1983, Radiology Research and Education Foundation. Isberg-Hold, A.: Temporomandibular Joint Clicking. Stockholm, 1980, Department of Oral Radiology, Karolinska Institute, School of Dentistry. Carraro, J. J., and Caffesse, R. G.: ElTect of occlusal splints on TMJ symptomatology. J PR~STHET DENT 40:563, 1978. Bell, W. E.: Clinical Management of Temporomandibular Disorders, ed 1. Chicago, 1982, Yearbook Medical Publishers, Inc., p 91. Okeson, J., Moody, P. M., Kemper, J. T., and Calhoun, T. C.: Evaluation of occlusal splint therapy. J Craniomandib Pratt 1:48, 1983. Ramfjord, S. P., and Ash, M. M.: Occlusion, ed 2. Philadelphia, 1971, W.B. Saunders Co., p 62.

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Development of anterior disk displacement in the temporomandibular joint: An autopsy study Gustaf Hellsing, Karolinska

L.D.S., Odont.Dr.,*

Institutet, School of Dentistry,

and Anders Holmlund, Huddinge,

T

emporomandibular joint (TM J) disk derangement has been extensively documented.‘-5 Anterior disk displacement (ADD) is thought to be either permanent (without reduction), that is, the whole disk stays in front of the condyle during all types of movement, or reversible (with reduction), that is, the disk is repositioned during condylar translation. Permanent ADD is reported to cause severe derangement of disk shape: from a healthy biconcave appearance to a biconvex lump of tissue. Frequent perforation of the posterior disk attachment is also reported to occur.6 FarraS found ADD in 25% of the entire population. Westesson’ broadened the concept of ADD to include oblique

*Associate **Assistant THE

Professor, Professor,

JOURNAL

Department Department

OF PROSTHETIC

of Stomatognathic of Oral Surgery. DENTISTRY

L.D.S.**

Sweden

Physiology.

or partial ADD (only the lateral part of the disk is anteriorly displaced). Reciprocal clicking is said to be a significant clinical sign of an ADD with reduction5 An important implication of this observation is that occlusal rehabilitation to the returned mandibular position would involve increased risk for development of disk displacement. Conventional clinical wisdom has identified centric relation (CR) as a reliable reference point for prosthodontic treatment; therefore, some degree of confusion has arisen. Furthermore, the proponents of the ADD philosophy suggest that retrodiskal tissue will become more and more stretched, to the point that repositioning of the disk at the end of translation will cease to occur and a “closed-lock” situation or permanent ADD develops. Clicking no longer occurs and mouth opening 397

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is severely limited (<20 to 30 mm). Advanced disk derangement can occur. The aim of the present study was to test the probability of the described hypothesis using TMJ cadaver specimens.

MATERIAL

AND METHODS

Fifty complete cadaver TMJs with intact capsules were prepared.6 The fresh specimens were immediately mounted with stable support for the temporal bone; and the soft tissue lateral to the joint, including the lateral capsular wall, was removed. The lateral parts of condyle, disk, and temporal fossa were easily examined (Fig. 1). The condyle was manipulated as far backward and upward as possible into a position that will be referred to as CR. Positional relationships among the joint components were carefully observed. Condylar translatory movements were carried out manually with strong upward pressure and different degrees of simultaneous condylar rotation with determined attempts to push the disk forward. Careful auscultation was performed during these manipulations to determine if clicking sounds could be heard. Color photographs were taken of fossa, disk, and condyle for documentation purposes. The condyle-disk assembly was cut out, and attempts were made to reposition the disk according to the predissection CR position. The posterior disk attachment was inspected for possible perforation. In routine postmortem examination, the cranium is opened and its contents removed. We took advantage of this procedure and excised the roofs of the glenoid fossae in 15 cadavers. The superior disk surface and the posterior disk ligament were inspected in CR and during manually performed condylar movements. In a parallel study, 50 cadaver TMJs were arthroscoped to observe disk position and joint clicks. Overall we studied 115 TM Js for disk position and clicking sounds.

Fig. 2. A, Temporal joint component. B, Superior surface of condyle-disk assembly. Note accurate fit between two joint surfaces: positive/negative relationship.

RESULTS The posterior edge of the disk was situated anterior to the top of the condyle in 14 of the 50 dissected joints. In 30 specimens a superior position was noted, and in one casethe position was judged as oblique. Two joints were excluded because the position was difficult to define. Three specimens with severe arthrotic damage

Fig. 1. Typical TMJ specimen with anterior disk position from cadaver of 72-year-old woman. Note healthy appearance of all three joint components: temporal fossa, disk, and condyle. A, Centric relation (CR). Condyle-disk assembly fits well in temporal fossa, which provides a definite stop for upwardly and/or backwardly directed condylar force. Even distribution of these forces over large area may be expected; also explanatory illustration of good CR recording repeatability. B, 1 = Temporal bone; 2 = condyle (black dot at arrow indicates lateral pole); 3 = posterior edge of disk; 4 = eustachian tube; and 5 = space between lower part of condylar head and temporal bone. C, When condyle is moved forward it is unavoidably guided downward by convexity of eminence. Simultaneously all condylar load is transferred to location of convexity. Thickest cartilage layers of temporal bone and eminence take over load with central thin part of disk in between. D, Condyle smoothly glides forward, clearly beyond reach of posterior disk edge despite attempts to push disk forward. E, Intermediate phase of forward condylar and disk movement. F, Thin central part of disk is load bearing. Convexity of eminence is visible. G, Condyle is moved maximally downward and three joint components, temporal fossa with eminence, disk, and condyle, are visible. H, Condyledisk assembly after removal from temporal bone. Disk position in front of slightly irregular vertex of condyle is approximately same as in CR before removal. THE

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were also excluded. No specimen with disk derangement was observed except specimens with advanced arthrosis deformans and disk perforations. No ADD without reduction was observed. Fig. 1, A, shows a typical sagittal TM J view in CR. The posterior edge of the disk is clearly anterior to the top of the condyle. This is more evident in Fig. 1, G, where the disk was reorientated to the best of our ability after removal of the condyle-disk assembly. The convexity of the eminence forced the condyle immediately downward in artempts to move it forward. This led unavoidably to immediate transfer of the load to the area of the lower part of the eminence where this convexity is located. In all cases of anterior disk position in CR, the condyle easily slipped under the posterior band of the disk during translation, usually with a space between as seen in Fig. 1, B and C. We did not observe any specimen in which it was possible to push the disk ahead of the condyle while the movement was carried out; nor did we observe any tendency for the posterior disk band to impede condylar translation from CR. No perforation of the posterior disk attachment was seen, and no clicking sound was heard from any of the 115 joints. In the 50 dissectedjoints, the disk was perforated in nine specimens as a consequence of arthrosis deformans, and apparent arthrotic lesions were seen in 11 joints. DISCUSSION It must be emphasized that an exact determination of disk position during dissection of TMJ specimens is uncertain. The condyle-disk assembly can be removed for inspection only after circular excision of the disk. Clearly, a risk of change in disk position is evident. The reported high frequencies of ADD,’ ’ and of anterior disk position in the present study, may therefore be exaggerated to some degree. Observational certainty regarding disk position in 50 arthroscoped TM Js was also iimited. We failed to identify a single specimen with disk derangement other than arthrotic lesions in 115 cadavers. Fourteen of the 50 dissected specimens showed a disk position anterior to the superior surface of the condyle. All looked healthy with or without minor remodelings of fossa and/or condyle. An anterior disk position may therefore be considered within normal range of anatomic variability and not necessarily a displacement. Our observations do not exclude the possibility that ADD exists. It does, however, appear to be far less frequent than has been proposed by some authorsi.’ and the etiology assessed in the present study seems unlikely. Bell” proposed a more probable explanation for development of ADD. During power strokes and maximum intercuspation, the superior lateral pterygoid muscle contracts strongly and may dislocate the disk anteriorly. Reduction is then accom400

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plished by posterior traction of the superior retrodiskal tissues during forward condylar translation. Other speculations include the possibility that the lateral ligament, which is tightly inserted at the lateral condylar pole, may be detached as a result of traumatic injury. Disk movements lateromedially would then be possible, and anterior displacement may result. It is certainly questionable, however, whether the disk can actually be pushed forward. The present study does not lend support to the assumptions that an anterior disk orientation in itself would cause disk derangement or that perforations of the posterior disk attachment are frequent. From a teleological standpoint, it would be expected that areas of the eminence and condyle that contain the thickest cartilage layer” are load-bearing during function, with the thin occlusal central area of the disk between. Fig. 1, B to E, show that during TM J translation the latter assumption is valid. During most movement until the condyle has passed the eminence, the load will be confined to the aforementioned areas. This seems to be an inevitable consequence of the convexity of the eminence, which forces the condyle-disk assembly downward in any forward movement. Unfortunately, many illustrations of the mandibular joint anatomy in the recent dental literature are erroneous or misleading. The disk is often reproduced as a cushion on top of the condyle. Conclusions regarding condylar function and dysfunction seem to have been drawn from such drawings. In contrast, dissectional studies such as the present one fail to confirm the possibility of condylar slippage behind the disk. The condyle-disk assembly conforms precisely to the temporal fossa (Fig. 2). Retrusion of the mandible into CR therefore means that the joint load will be distributed over large areas of all three joint components. This accurate fit seems to explain why such good repeatability is achieved clinically when CR is recorded.‘!.” The widely accepted supposition that CR is a “ligamentous” position regulated by the temporomandibular ligament seems less likely.14 This ligament looked fairly weak in many of the dissected specimens. In any case, it seems improbable that it would provide the long-standing accurate stability that must be a condition for accurate, repeatable CR recording. If occlusal disturbances exist, they may guide the mandible into an intercuspal position (IP) different from CR, and the accurate fit among the joint components will be lost. Occlusal equilibration can therefore be viewed as a procedure that allows the condyle-disk assembly to be seated in its most stable position. The IP may then coincide with the so-called muscle position, that is, the position in which closure occurs without tooth form interferences. This should induce relaxation MARCH

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of the jaw muscles (the superior lateral pterygoid included) with a fair probability for restitution of an ADD. In a clinical follow up study,15 146 patients treated for mandibular pain-dysfunction symptoms were reinvestigated 7 years after treatment. Initially, 12% of the patients had a maximal opening of less than 30 mm. Conservative treatment, in most cases occlusal stabilization by means of an acrylic resin bite splint and/or equilibration, led to increased opening ability without recurrence of reduced opening in any patient during the following 7 years. It is not clear whether permanent ADD had caused the limitation in these patients, but it may be concluded that orthodox treatment cured most of these patients. Mandibular retrusion into CR, the single reliable reference position that exists”-” during equilibration of a splint or natural dentition, may still be considered therapeutically meaningful, and it does not seem to involve increased probability for development of ADD.

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CONCLUSIONS Within the limits of a cadaver study, we suggest the following conclusions. 1. ADD is a rare phenomenon. Anterior disk position may be a normal variant. 2. The hypothesis that ADD occurs when the condyle slips behind the disk and then is more or less inevitably aggravated because the condyle pushes the disk forward during translation is not very probable. 3. Perforations of the posterior disk attachment appear to be rare. 4. The retruded condylar position is still a clinically important reference position, and its use involves low probability for development of ADD. 5. TMJ clicking is difficult to induce in autopsy specimens.

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Pringle, J.: Displacement of the mandibular meniscus and its treatment. Br J Surg 6~385, 1918. Wakeley, C.: The causation and treatment of displaced mandibular cartilage. Lancet 2:543, 1929. Ireland, V. E.: The problem of “the clicking jaw”. Proc R Sot Med 44~363, 1951. Farrar, W.: Characteristics of the condylar path in internal derangements of the TM J, J PROSTHET DENT 39:3 19, 1978. Eckerdahl, 0.: Tomography of the temporomandibular joint. Acta Radio1 [Diag] [Suppl] (Stockh) 329:1, 1973. Dolwick, M. F., Katzberg, R. W., and Helms, C. A.: Internal derangements of the temporomandibular joint: Fact or fiction? J PROSTHET DENT 49~415, 1983. Westesson, P-L.: Double-contrast arthrography and internal derangement of the temporomandibular joint. Swed Dent J (Suppl 13) 1982. Bell, W. E.: Clinical Management of Temporomandibular Disorders. Chicago, London, 1982, Year Book Medical Publishers. Hansson, T., oberg, T., Carlsson, G. E., and Kopp, S.: Thickness of soft tissue layers and the articular disk in the temporomandibular joint. Acta Odontol Stand 35:77, 1977. Helkimo, M., Ingervall, B., and Carlsson, G. E.: Comparison of different methods in active and passive recording of the retruded position of the mandible. Acta Odontol Stand 29:423, 1971. Hellsing, G., Isberg-Helm, A., and McWilliam, J.: A comparative study of two techniques for recording centric relation. Dentomaxillofac Radio1 125, 1983. Hellsing, G., and McWilliam, J,: Repeatability of the mandibular retruded position. J Oral Rehabil (in press). Posselt, U.: Physiology of Occlusion and Rehabilitation. Oxford, 1969. Mejersjo, C., and Carlsson, G. E.: Long-term results of treatment for temporomandibular joint pain-dysfunction. J PROSTHET

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REFERENCES 1.

THE

Annandale, T.: Displacement of the inter-articular the lower jaw and its treatment by operation. 1887.

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cartilage of Lancet 1:411,

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