Section 05 Eccentric Movements



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Section 05 - Eccentric Movements
Handout

Abstracts

001. Posselt, U. Movement areas of the mandible. J Prosthet Dent 7:375-385, 1957.

002. Aull, A. E. Condylar determinants of occlusal patterns. J Prosthet Dent 15:826-846, 1965.
        Kurth, L. E. Discussion. J Prosthet Dent 15:847-849, 1965.

003. Stuart, C. E. Accuracy in measuring functional dimensions and relations in oral prosthesis. J Prosthet Dent 9:220-236, 1959.


        Boucher, C. O. Discussion. J Prosthet Dent 9:237-239, 1959.

004. Clayton, J. A., Kotowicz, W. E. and Zahler, J. M. Pantographic tracings of mandibular movements and occlusion. J Prosthet Dent 25:389-396, 1971.

005. Lundeen, H. C. and Wirth, C. G. Condylar movement patterns engraved in plastic blocks. J Prosthet Dent 30:866-875, 1973.

006. Gibbs, C. H., et al. Chewing movements in relation to border movements at the first molar. J Prosthet Dent 46:308-322, 1981.

007. Mongini, F. and Capurso, U. Factors influencing pantographic tracings of mandibular border movements. J Prosthet Dent 48:585-598, 1982.

008. Gibbs, C. H., Mahan, P., Wilkinson, T. M. and Mauderli, A. EMG activity of the superior belly of the lateral pterygoid muscle in relation to other jaw muscles. J Prosthet Dent 51:691-702, 1984.

009. Levinson, E. Nature of the side shift in lateral mandibular movements and its implications in clinical practice. J Prosthet Dent 52:91-98, 1984.

010. Simonet, P. Influence of TMJ dysfunction on Bennett movement as recorded by a modified pantograph. Part I: Literature review. J Prosthet Dent 46:437-442, 1981.

011. Hobo, S. A kinematic investigation of mandibular border movement by means of an electronic measuring system. a. Part II: A study of the Bennett movement. J Prosthet Dent 52:642, 1984. b. Part III: Rotational centers of lateral movement. J Prosthet Dent 52:66-72, 1984.

012. Preiskel, H.W. Lateral translatory movements of the mandible: Critical review of investigations. J Prosthet Dent 28:46-57, 1972.

013. McCollum, B. B. and Stuart, C. E. A Research Report. Scientific Press, South Pasadena, CA.

014. Santos, J., et al. Vectorial analysis of the static equilibrium of forces generated in the mandible in centric occlusion, group function and balanced occlusion relationships. J Prosthet Dent 65:557-567, 1991.

015. Theusner, J., et al. Axiographic tracings of temporomandibular joint movements. J Prosthet Dent 69:209-215, 1993. 

016. Clayton, J. A., Kotowicz, W. E. and Meyers, G. A. Graphic recordings of mandibular movements: Research criteria. J Prosthet Dent 25:287-298, 1971. 

Section 05: Eccentric Movements
(Handout)

 Definitions:



     1. eccentric: adj. 1. not having the same center 2. deviating from a circular path 3, located elsewhere
than at the geometric center 4. any position of the mandible other than that which is normal position.
     2. border movement: mandibular movement at the limits dictated by anatomic structures, as viewed
in a given plane
     3. laterotrusion: n. condylar movement on the working side in the horizontal plane. This term may be
used in combination with terms describing condylar movement in other planes, for example laterodetrusion, lateroprotrusion, lateroretrusion, and laterosurtrusion. (also called Bennett's movement).
     4. laterodetrusion n. lateral and downward movement of the condyle on the working side.
     5. laterosurtrusion n. lateral and upward movement of the condyle on the working side.
     6. lateroretrusion n. a lateral and backward movement of the condyle on the working side.
     7. lateroprotrusion n. a protrusive movement of the mandibular condyle in which there is a lateral component.
     8. mandibular translation the translatory (medio-lateral) movement of the mandible when viewed in the frontal plane. While this has not been demonstrated to occur as an immediate horizontal movement when viewed in the frontal plane, it could theoretically occur in an essentially pure translatory form in the early
part of the motion or in combination with rotation in the latter part of the motion or both. (mandibular lateral translation also called Bennett's side shift).
     a. immediate mandibular lateral translation the translatory portion of lateral movement in which the nonworking side condyle moves essentially straight and medially as it leaves the centric relation position.
     b. early mandibular lateral translation the translatory portion of lateral movement in which the greatest portion occurs early in the forward movement of the nonworking side condyle as it leaves centric relation.
     c. progressive mandibular lateral translation 1. the translatory portion of mandibular movement when
viewed in a specified body plane 2. the translatory portion of mandibular movement as viewed in a specific body plane that occurs at a rate or amount that is directly proportional to the forward movement of the nonworking condyle.
     9. Bennett angle obs. the angle formed between the sagittal plane and the average path of the advancing condyle as viewed in the horizontal plane during lateral mandibular movements (GPT-4).
    10. Fischer angle eponym for the angle formed by the intersection of the protrusive and nonworking condylar paths as viewed in the sagittal plane.
    11. pantograph n. 1. an instrument used for copying a planar figure to any desired scale in dentistry, an instrument used to graphically record in one or more planes paths of mandibular movement and to provide information for the programming of an articulator.
    12. pantographic tracing a graphic record of mandibular movement in three planes as registered by the styli on the recording tables of a pantograph; tracings of mandibular movement recorded on plates in the horizontal and sagittal planes.

History:

     Bonwill- described a 4 inch triangle between mandibular incisors and each condyle. Also proposed


         a concept of bilateral balanced occlusion.
     Balkwill – discovered that during lateral jaw movement, the translating condyle moved medially.
     VonSpee- observed that the occlusal plane of the teeth followed a curve in the sagittal plane.
         (curve of Spee).
     Christensen (1901)  – observed the opening of posterior teeth in mandibular protrusion.
     Bennett (1908) – described immediate side shift (Bennett movement).
     Gysi (1910)  – develops one of first articulators to allow for Balkwill-Bennett movements.
     Monson (1916) – develops spherical theory, one of first three dimensional occlusal concepts.
     Hanau (1921) – advocated bilateral balanced occlusion with eccentric mandibular movements.
     Pankey-Mann (1920’s) – amalgamation of Monson theory and Meyer functionally generated
         path to obtain bilateral balance. Pankey-Mann-Schuyler eliminated balancing side contacts,
         emphasized incisal guidance, and proposed long centric.

     McCollum (1920’s) – Gnathology – study mandibular movement:


        1. Propose colinear hinge axis,
        2. Develop pantographic recording of three dimensional envelope of motion
        3. Maximum intercuspation of teeth when condyles are in hinge position
        4. Bilateral balance with eccentric jaw movement.

Movement of the Mandible:

     1. Posselt examined mandibular movement using a Gnatho-Thesiometer to measure the mandibular position of natural teeth. Recordings were made of both habitual and extreme positions with opposing teeth in occlusion.        How were his measurements made?


     What were his observations and conclusions?

     2. Mandibular movement during chewing can vary greatly within the prescribed envelope. Gibbs, et.al. , performed a study of chewing and border movements of five subjects with good occlusion and two subjects with malocclusions. What did they observe about opening and closing strokes? Closing and opening strokes differed markedly. Opening strokes were typically anterior and medial to closing strokes.


     Chewing movements were found to differ greatly until final closure, where a similarity was noted. Most chewing paths nearing final closure coincided or nearly coincided with the working-side lateral border path in both frontal and sagittal views.
     The movement of the first molar on the working side had a small anterior component during closure. What does this indicate? Chewing function occurred in the lateral retrusive range until gliding tooth contact occurred. (Retrusive slides are seldom seen on the working side during chewing)
     How did the working side movement compare to the non-working side? The non-working first molar
closed from an anterior medial aspect and had a posterior component of movement.
     What did they conclude regarding neuromuscular control and occlusal interferences?
     How did this compare to what Clayton, et.al., found in their study of pantographic tracings of
mandibular movements?

     3. Condylar movement determines tooth occlusal patterns. Or do tooth occlusal patterns determine condylar movement? Aull described nine possible variations in the direction of the condylar path of the working (rotating) condyle. Describe these nine variations:


     Which one did he fail to observe in his study of 50 patients(100 condyles)?
     Did he find a symmetry in condylar inclinations? No, only one pair of 50 was symmetrical.
     Side shift is the only condylar determinant that affects both the vertical and horizontal components of the posterior teeth. What general effect will an increase in laterotrusion have on occlusal morphology? shorter cusps, gentler cusp slopes, shallower, broader fossae. 
     Laterotrusion accompanied by an upward movement of the same condyle has what effect on the
cusp length?
     Laterotrusion accompanied by downward movement has what effect on cusp length?
     As intercondylar distance is increased, what happens to the angle formed by the transverse and oblique
path of the cusp in its movements?
     As laterotrusion increases, what happens to this angle?
     Did Kurth agree with Aull's conclusions?
     What did Levinson report regarding the nature of side shift in mandibular movement?
     What impact would the presence of (or lack of) an immediate side shift have on articulator selection?

     4. The clinical significance of lateral mandibular movements is controversial. What did Preiskel conclude?


     What are some of the difficulties encountered in studying the lateral side shift of the mandible (as discussed by Simonet)
     What were Hobo's conclusions regarding lateral side shift from the use of an electronic measuring system?

     5. Mandibular motion is produced by muscle activity. According to McCollum, is the path of mandibular movement determined primarily by the anatomy of the joint or the activity of the  musculature?


     Would Gysi concur?
     The masseter and temporalis muscles function to close and retrude the mandible. Do they contribute
to lateral movements?
     Which muscles are the most active participants in lateral movements?
     What happens to the activity of the masseter and medial pterygoids in retruded contact position?
     What did Santos, et.al. determine regarding the relationship between cusp steepness and forces generated?

Recording mandibular movement:  

     1. Fabrication of an esthetic and functional restoration for the patient routinely requires the effective use of an appropriate articulator. One of the roles of the prosthodontist is to transfer information from the patient to the articulator in such a manner so that the articulator closely simulates mandibular movement to the degree required by the restoration. Attempts to record mandibular movement are as historical as the study of mandibular movement itself, and include a variety of intraoral and extraoral tracing mechanisms, as well as photographic, radiographic, electronic, and electromyographic studies.


     Stuart describes the recording of mandibular movement. Which movements does he record, and how are they registered?
     What is the significance of recording border movements? Border movements are constant enough in position, direction, and path as to be dependable and repeatable. When the true boundary movements are recorded and transferred, all other movements are automatically included in the circumscribed areas of movement.
     Upon which issues do Boucher and Stuart agree?
disagree?

     2. According to Mongini and Capurso, what factors influence the tracing patterns of mandibular border movements?


     What effect does an internal derangement have on tracings?
     What effect does severe muscle tension have on tracings?
     What can be done to help address the effect of severe muscle tension?
     What effect did Theusner, et.al., observe regarding the tracings obtained from symptomatic patients?
     Were these considered to be adaptive or pathologic changes?

     3. Lundeen and Wirth recorded mandibular movement by engraving plastic blocks and photographing the engravings. Did they observe immediate side shift?


     Was a greater side shift observed with firm lateral guidance of the body of the mandible by the dentist, or with passive guidance at the chin point?
     Did the length of the central bearing screw affect the engravings?

     4. Clayton, et.al. examined the effect of various factors on graphic tracings. What did they determine regarding the effect of changes in the occlusal vertical dimension?


     Regarding changes in the central bearing guiding surface?
     Regarding tooth guidance?

Summary:  The intricacies of mandibular movement, while intensely studied, discussed, and debated, are still fraught with uncertainties. Nevertheless, these questions should not deter the diligent practitioner from the pursuit of additional understanding and the effective restoration of his patients based upon the prevailing standard of care and evidence based decision making.

- Abstracts -

05-001. Posselt, U. Movement areas of the mandible. J Prosthet Dent 7:375-385, 1957.

Purpose: To elucidate the shape and dimension of the contact area of movement of the anterior measuring point, and of the points on the condyles. Individual variations were also studied.
Literature Review: Hanau and Fischer described the shape of this contact movement area. Fischer described this contact movement area in dentulous subjects as " broken and more or less uneven". Fehr writes that the condyle movement area is larger for the left side than the right. Gysi and Fischer illustrate the areas of movement a rhomboid. Gysi carried out his investigations on edentulous persons. No investigations were on record at that tie concerning the contact area of movement of a point in the anterior part of the mandible or for the condyles.
Materials & Methods: 5 people with almost complete dentitions were measured with a Gnatho-thesiometer. The positions of the measuring points (1 close to the infradentale and 2 in the middle of each condyle) were enlarged and traced on paper in the 3 planes at right angles. Stone models were made with the help of the drawings.
Results/Discussion: The area of movement of a point on the anterior part of the mandible can be projected on a plane surface by graphic registration in both dentulous and edentulous subjects provided that any vertical cusp guidance has been eliminated. The triangle, which connects the three measuring points, corresponds to BONWILL’s Triangle.
     Contact area of movement of the anterior measuring point: rhomboid shape but markedly asymmetric. In the vertical plane, different levels were noted and individual variations evident.
     Areas of movement of the condylar points: the shapes in all 3 planes differed widely along with the extreme and in extreme positions.
Summary/Conclusion: The areas of movement for three points on the mandible were recorded in the 3 planes with the aid of a Gnatho-thesiometer. The paths of movement cannot be measured with a Thesiometer. Lines can be drawn from one point to another and an approximation secured. The results of this investigation support observations from previous studies that differences exist between habitual and extreme positions.

05-002. Aull, AE. Condylar determinants of occlusal patterns. J Prosthet Dent15:826-846,1965.

     Condylar tracings from 50 patients were analyzed. A Stuart facebow, axis-orbital plane indicator, pantographic tracing device, and articulator were used. The following findings were obtained.
     Condylar variation: Only one of the fifty pairs of condyles had bilateral symmetry. The average steepness for the right and left sides were 36.6O and 37.7O Intercondylar distance: The average distance is 55.5 mm. Range was 45 -70 mm Bennett movement: All had mandibular movement with a side shift.

Summary of condylar determinants on occlusion by Aull:

1. Increasing the steepness of the eminencies increases the requirements for steeper sloping cusp on the balancing side.
2. Increasing the curvature of the eminencies has the same effect on the tracings as if the eminencies is increased.
3. As laterotrusion (side shift) is increased shorter cusp are required (mainly the balancing side is effected). If the rotating condyle also moves upward the working side cusps are more effected.
4. Laterotrusion accompanied by downward movement requires longer cusps on both sides (mostly on working).
5. As intercondylar distance is increased, the more acute the angle becomes between the transverse and oblique paths of the cusps points.
6. Increase intercondylar distance, increase eminence slant, increase laterotrusion, the more obtuse the angle between the transverse and oblique paths of the cusps points.
7. An immediate laterotrusion which equals a distributed laterotrusion will have a more blunt angle, and the balancing lines will diverge more in the central fossa.
8. When the laterotrusive rotating condyle retrudes, the angle made between the working and balancing tracing is more obtuse than that made between the same type of tracings made with a protruding laterotrusive rotating condyle.
9. As the slant or curvature of the eminencies is increased, the slant of the pure protrusive tracing is also increased.

Kurth, LE. Discussion. J Pros Dent 15:847-849, 1965.

Kurth said if you are not trying to achieve bilateral balanced occlusion there is no need for all the diagnostic tracings.

05-003. Stuart, C. E. Accuracy in measuring functional dimensions and relations in oral prosthesis. J PROSTHET DENT 9: 220-236, 1959.



Purpose: Discuss the use of the articulator as a diagnostic tool.
Discussion:

A. Purpose of the articulator


     1. Record
         a. Receive and register craniodental and maxillo-mandibular relations.
         b. Receive and register the three dimensions of the oral organ.
         c. Receive and register the axes of mandibular rotations.
         d. Guide the dentist to incorporate all these factors into the prosthesis.
         e. Store all the dimensional information .

B. Anatomy and physiology of the articulator


    1. It should be put together in such a way that it can be reproducible, without compromise. It should fit the   anatomy and physiology of the oral organ.

C. Hinge axis


     1. To provide a point in the third dimension, a line is extended from the hinge axis to the lower border of the orbit , to the right side of the nose and marked.

D. Mandibular movement recorder


     1. Two parts
        a. Upper bow- holds vertical and horizontal recording plates in the condylar areas and carries writing styluses in the anterior crossbar.
        b. Mandibular bow- carry vertical and horizontal styluses in the condylar areas and horizontal recording plates on the front bar.

     2. The recorder has two styluses to write the Gothic arch tracing, two to write the effect of the anterior condylar glidings, and two to write the effects of the lateral condylar glidings.

     3. Border movements are used because in such a simple movement as straight protrusion the patient seldom can make the same movement twice. The habitual positions vary according to postures, health, muscular and nervous states. When they are transferred to the articulator they become boundary positions, and automatically all other movements are included in the circumscribed areas of movements.

E. Condylar path tracings: The tracing is composed of two parts: a forwardly drawn tracing and a backward tracing. Each tracing in itself is made up of two parts joined at the point of centric relation as indicated by the stylus.


     1. The two Gothic arch tracings show the effects of the lateral and anterior movements of the condyle, and they are influenced by any opening and closing.
     2. The reverse tracing of each anterior condyle serves as an index of the upward or downward path direction of the outward rotating condyle. The reverse tracing of the Bennett line is an index of the backward or forward path direction of the outward moving rotating condyle.

F. Magnetic styluses: Tracings are written by a frictionless ball-point stylus magnetically controlled, and preserved with adhesive cellophane. After the record lines are made and covered, the upper and lower face-bows are cemented together in centric relation with stone.

G. Transfer of jaw relations: The recorded lines are used to set the articulator. The articulator consists of two main frames, and upper and a lower.
     1. Upper frame- centered on the lower and maintained in centric relation by a spring-loaded arm. Carries all the cams that direct the gliding of the condyle mechanisms, the right and left glides for the sideshifts (the Bennett movements), and the right and left fossa cusps carry the eminentias under which the condyles glide.
     2. Lower frame- carries the mechanical condyles and simulates the mandible. The cams, or guide controls of the mechanical condyles, when set, remain fixed in relation to the upper teeth and dental arch. The mechanical condyles and their axes remain fixed in relation to the lower teeth.

Boucher, C.O. Discussion. J Prosthet Dent 9: 237-239, 1959.



Purpose: Discussion by Dr. Charles E. Stuart.
Discussion: Dr. Boucher states that any instrument that is adjusted solely by a series of these records can be absolutely correct only in the exact positions at which the records were made. He says that any movements made by the patient when the teeth are out of contact are of no importance to the arrangement of teeth. It is desirable to have any movements that may be made while the teeth are in contact reproduced on the articulator. This is necessary so the occluding surfaces of the teeth can be shaped in harmony with each other, in any position in which they came in contact. The articulator should approximate these movements of the mandible that may occur when teeth are in contact, this involves: (1) the correct relation of the two casts to the opening axis of the instrument, (2) the establishment of the correct centric relation, (3) the development of guiding surfaces in the mechanical counterparts of the TMJ so the casts may assume the same relations to each other that the denture foundations have to each other in the mouth while the teeth are in contact.
     Dr. Boucher states that orientation of the face-bow and the cast to the arbitrary facial and cranial landmarks seems unnecessary, except for the convenience of observing the anterior teeth and the occlusal curvature on the articulator. The directions of the styluses should not be mistaken with the directions of the actual movements of the mandible. A posterior movement by the working side condyle is likely to be developed by the fact that the tracing is made as an extension of the horizontal axis of the mandible.
    The use of magnetic styluses appears to be a problem, since there is a possibility of the weight of the recording device altering the normal position and movements of the mandible. This would be difficult to demonstrate or prove.
     The clutches must be cemented to the teeth during registrations, making it impossible for denture construction. This is important since the resiliency of the supporting tissues would likely produce errors in the registrations.

Dr. Boucher emphasizes Dr. Stuarts suggestion of using an interocclusal record to mount the casts in centric relation, otherwise all other articulator adjustment would be incorrect

05-004. Clayton, J. A., Kotowicz, W. E. and Zahler, J. M. Pantographic tracings of mandibular movements and occlusion. J Prosthet Dent 25:389-396, 1971.

Purpose: To determine the relationship of functional movements (chewing) to the border tracings recorded by a pantograph.
Methods & Materials: Clutches were fastened to the maxillary and mandibular teeth of four subjects so as not to interfere with tooth contacts during function. Border tracings were made from centric relation guided by the author and unguided tracings from centric occlusion. The subjects were then instructed to chew test foods: gum, uncooked carrots, and peanuts. These movements were recorded and compared to the initial sets of tracings. After the recordings were completed one patient had occlusal interferences removed and a second set of tracings made.
Results: The functional movements contacted the border tracings frequently. The movements did not go beyond the border tracings. The chewing pattern was heaviest on the patients favored side. The tougher the consistency of the food the more the patient favored one side versus the other. The two subjects who had no occlusal interferences had a larger area of coverage than the two patients who had interferences. After removal of the interferences one of the subjects produced recordings that were closer to the border tracings.
Conclusions: the authors conclude that subjects can function to the border tracings provided that no interferences are present which may deflect the functional movements away from the border tracings. They also conclude that occlusion in harmony with border tracings may be the most physiologic. These conclusions are pretty amazing considering the fact that there were only four subjects.

05-005. Lundeen, H.C., Wirth, C.G. Condylar movement patterns engraved in plastic blocks. J Prosthet Dent 30:866-875, 1973.



Purpose: To report findings of an investigation designed to test the reliability and reproducibility of a method of three-dimensional tracing of mandibular movements in plastic blocks.
Methods & Materials: 50 patients without pain or limited mandibular movement utilized. All patients were premedicated with 0.4mg of atropine sulfate, 150mg sodium pentobarbital, and 50 mg meperidine as intravenous medication prior to recording session. Condylar movement patterns were recorded as three-dimensional engravings in clear plastic blocks using turbine air drills. The drills cut a pathway in the plastic block that corresponds to movements of the mandible. The blocks are attached to the upper bow of the recorder assembled on the patient’s transverse hinge axis and secured by locking the bows to the clutches with attachment tubes filled with plaster. The engravings of the condylar movement patterns made by the turbine air drills in the plastic blocks were photographically enlarged to permit comparisons between patients.
Results: The protrusive pathways of 50 superimposed tracings of the recordings showed similarity of the right and left sides. At a point corresponding to 5mm of protrusive movement, the angle formed with the axis-orbital plane was a minimum of 25 degrees, a maximum of 65 to 75 degrees, with a median of approximately 40 degrees. The tracings of the lateral pathways were also similar on the right and left sides. At a point corresponding to 5mm of lateral movement of the balancing condyle, the angle formed with the axis-orbital plane was a minimum of 25 degrees, a maximum of 75 degrees, with a median of 45 to 50 degrees. A superior view of the recordings showed the immediate side shift (Bennett movement) and the Bennett angle as two identifiable portions of the lateral movement. Once the immediate side shift had occurred, very little variation was seen in the rest of the movements for the different subjects.
Conclusion: The results of the recordings of condylar movements of the 50 subjects were superimposed and compared in three views showing the protrusive and lateral pathways as well as the superior view of the immediate side shift. Similarities in the tracings were noted in all three views for the 50 subjects tested. The study was designed to compare the shapes of the lateral boundaries of condylar movement. No attempt was made to relate these characteristics to the occlusal relations of the teeth.

05-006. Gibbs, C.H. et al. Chewing movements in relation to border movements at the first molar. J Prosthet Dent 46:308-322, 1981.



Purpose: To identify movements during chewing which are characteristic of subjects with malocclusion.
Materials & Methods: There were seven adults in this study, five with good occlusion and two with malocclusion. Data was collected with unilateral chewing of cheese, raisins, gum, carrots and peanuts. He jaw movements were measured with photo-optical transducers mounted between maxillary and mandibular facebows. Clutches were well designed and cemented to the facial surfaces of teeth (well below the chewing surfaces.)
     The patient sat upright, with head unrestrained during the chewing recording. The data was processed by computer, and the overall accuracy was 0.125 mm.
Results: In the first malocclusion, a 28 year old woman with minor posterior interferences, dysfunction symptoms (pain on palpation of lateral pterygoid muscle).
     The first molar movement on the working side had a small anterior component during closure, indicating that chewing function occurred on the lateral retrusive range for chewing soft as well as hard food. Chewing closure movements occurred posterior to the lateral borders until tooth gliding occurred. Retrusive slides are seldom seen on the working side during chewing.
In the second malocclusion, there was a 67 year old man with severe wear. His jaw motion was continuous as teeth slid over one another from working to non working side.
Conclusions: In certain malocclusions, the neuromuscular system exerts fine control during chewing to avoid particular occlusal interferences. Present restorative procedures based on lateral border registration are applicable to functional chewing movements.
     The region between the terminal hinge axis and the working-side lateral border path is seldom used and does not involve tooth contact. The harder the food , the more lateral and rearward the closing movement. In adults, opening is usually medial to the closing movement when viewed in the frontal plane.  

05-007. Mongini, F. and Capurso, U. Factors influencing pantographic tracings of mandibular border movements. J Prosthet Dent 48:585-598, 1982.



Purpose: To study how the characteristics of the pantographic tracings can be utilized as a diagnostic aid and to evaluate the influence of anatomic and neuromuscular factors on the tracing pattern.
Methods and Materials: Three different studies were performed. The first study consisted of 50 patients all with the signs of dysfunction of the somatognathic system; the second study, 20 patients from the first group, underwent occlusal rehabilitation. The third study of 20 patients utilized 10 patients from the second study and underwent biofeedback induced muscle relaxation. Temporomandibular joint radiographs, noises, condylar location and shape, patient tenderness and spasms, and mandibular movements were parameters considered. Two pantographs were made and evaluated for immediate side shift, sagittal displacement, deviation, restrictions and other abnormalities.
Results: See article for pantographic tracings and correlation.
Conclusion:

  1. Articular and neuromuscular factors influence the tracing patterns of the mandibular border movements.

  2. Internal derangement of the TMJ with the condylar disk incoordination leads to typical pantographic tracings. The shape of the condyle also affects the type of tracing.

  3. Severe muscle tension leads to very irregular tracings and are dramatically improved after relaxation. An initial protrusion of the movement of the orbiting condyle probably accounts for the incoordination of the lateral pterygoid muscles.

  4. Biofeedback therapy is a valuable therapeutic tool in dysfunctional patients. This confirms their value as a therapeutic tool in dysfunctional patients.

  5. Improvements in the tracings after therapy may be equally due to the improvement of the articular situation or increased muscle relaxation and coordination.

05-008. Gibbs, C. H., Mahan, P. , Wilkinson, T.M. and Mauderli, A. EMG activity of the superior belly of the lateral pterygoid muscle in relation to other jaw muscles. J Prosthet Dent 51: 691-702, 1984.

Purpose: The paper describes the activities of the superior lateral pterygoid (SLP) and the inferior lateral pterygoid (ILP) in relation to the masseter, temporal, anterior belly of the digastric and medial pterygoid muscles during some basic jaw positions and movements.
Methods and Materials: Eleven subjects were monitored in individual sessions of about 3 hours duration.
     The EMG activities of the SLP, ILP and medial pterygoid muscles were monitored using fine insulated wire electrodes inserted directly into the muscles. The masseter, temporal and digastric muscles were monitored by means of electrodes placed on the skin over the muscles.
Results/Conclusions:
     1. The EMG activity of the SLP was similar but not identical to the EMG activity of the anterior fibers of the temporal muscle. The SLP muscle was active in clenching, especially clenching in retruded contact. It was moderately active in ipsilateral movement and showed little activity in other basic jaw positions.
     2. In contrast to the SLP muscle, ILP muscle was active in protrusive, opening and contralateral positions. It was minimally active during clenching in retruded contact, while the SLP muscle achieved its greatest EMG activity at this position.
     3. The anterior fibers of the temporal muscle are active in elevating the mandibular condyles and mandible during clenching. They also assist the digastric muscles in retruding and posturing the mandible ipsilaterally.
     4. The anterior belly of the digastric muscle depresses and retrudes the mandible. In protrusion it opposes the masseter and medial pterygoid muscles to keep the teeth separated while the ILP protrudes the mandible. It is active in isometric clenching, which stiffens it to protect the teeth in the event of an unexpected rapid closing movement such as fracture of brittle food.
     5. The medial pterygoid and superficial masseter are strong elevators during clenching in the intercuspal position and assist in the protrusion of the mandible by the prevention of wide opening. The medial pterygoid muscle is active during lateral movements as an agonist and antagonist, but its activity diminishes to a low level at the extreme ipsilateral position.
     6. Activity of the elevating superficial fibers of the masseter and medial pterygoid muscles is greatly reduced in the retruded contact position. Perhaps this is a mechanism that protects the posterior band of the disc from injury by the condyle during bruxing and chewing.
     7. Simultaneous EMG activity (cocontraction) of shortening and lengthening muscles is commonly involved in basic jaw movements and appears to be important for fine control, mandibular stability and stiffening of antagonistic muscles to provide protection in the event of unexpected rapid mandibular movement.

 

5-009.  Levinson, E. The nature of side shift in lateral mandibular movement and its implications in clinical practice. J Prosthet Dent 52:91-98, 1984.



Purpose: To investigate mandibular side shift.
Materials and Methods: Skulls were examined, tracings from patients and a fully adjustable articulator were examined.
Results: ISS would not occur if the condyles were fully seated.
Conclusion: When using a one handed push back technique the centric relation position can be improperly recorded and an ISS can be evident. However this article supports Dawson that the immediate side shift does not occur when the condyle are fully seated. Therefore, a semiadjustable articulator is adequate for the laboratory phase of occlusal reconstruction.

010. Simonet, P. Influence of TMJ dysfunction on Bennett movement as recorded by a modified pantograph. Part I: Literature review. J Prosthet Dent 46:437-442, 1981.



Purpose: To review the literature regarding Bennett movement.
Subject: Examining the importance of and difficulties encountered in studying Bennett movement (lateral side shift of the mandible), based on reviewing existing literature.
Discussion: While Bennett is generally given credit for his description of lateral shift, credit should be shared with Ferrein (1748) , Bell (1831), and Ulrich (1896). Bennett used two incandescent light bulbs attached to the mandible, and using lenses, focused the images on the wall, where they were traced during mandibular motion.
     In 1926, Gysi repeated Bennett's study, developed an articulator allowing some lateral component. He believed that incisal guidance was more important than condylar guidance in determining cusp inclination. Landa proposed no movement in the working condyle, but disregarded the role of the lateral pterygoids, which was studied by Sicher.
     The important role of neuromusculature was presented by Boucher, Jacoby, and McMillan. The influence of TMJ dysfunction on neuromuscular activity and Bennett movement has been speculated in different studies. DePietro applied the concept of instantaneous centers of rotation to the movement. Mongini, comparing lateral polytomographics of the TMJ with pantographic tracings performed on subjects with TMJ dysfunction, found a significant relationship between condylar shapes and tracing patterns.
     Credit for the development of the pantograph is given to the Gnathological Society. Cotte, in 1969 found that, although lateral movements could be registered, side shift of the mandible was minimal or absent. In 1978, Lundeen, using the same instrumentation, found an average shift of 0.75mm, with 80% shifting 1.5mm or less. Gibbs found average lateral movement was around 0.4mm. In 1979, Bellanti and Martin found only 13% demonstrated Bennett movement of more than 0.2mm.
     Conclusion: This review points out the difficulties in studying lateral side shift, as well as contradictory results from various investigations. It seems reasonable to conclude that 1) Bennett movement accompanies most lateral jaw movements, but the amount and timing varies between individuals, and may be influenced by muscle incoordination and TMJ dysfunction. 2) the axis around which all lateral movements occur may be oblique rather than vertical and perpendicular to the subject's hinge axis. Disagreement still exists regarding: 1) the immutability of its magnitude throughout occlusal therapy and 2) the possible relationship between TMJ dysfunction and Bennett movement

05-011. Hobo, S. A kinematic investigation of mandibular border movement by means of an electronic measuring system. a. Part II: A study of the Bennett movement. J Prosthet Dent 52:642, 1984.



Purpose: To analyze the motion of the working condyle during lateral movement of the mandible.
Methods and Materials: Fifty adults from 20 to 50 years of age with an orthognathic maxillomandibular relationship and no apparent TMJ disorders were selected for evaluation of Bennett movement (lateral shift of the working condyle) kinematically via an electronic measuring device with an accuracy of + 0.06mm. Intraoral custom made clutches containing sensors recorded right and left border movements. Calculations made external to the TMJ at intervals of 52-58 mm from the mid-sagittal plane were compared to the computer-assisted electronic recordings made at the condylar axis.
Results: Bennett movement is the lateral shift of the working condyle along the terminal hinge axis (transverse horizontal axis). The orbits of the working side on the horizontal and frontal planes were more effected as the distance from the mid-sagittal changed as compared to the orbits in the sagittal plane. When the distance was small, the working condyle moved forward and downward. When the distance was large, the working condyle moved backward and upward. When the distance from the mid-sagittal plane was an average of about 55mm, the condyle moved in a straight lateral direction.
Conclusions: It was found that at orbits 55mm from the midpoint of the terminal hinge axis the orbits shift straight laterally on the terminal hinge axis and do not show any deviation in the sagittal plane. Based on these findings, it was believed that the Bennett movement was a straight lateral shift of the working condyle along the terminal hinge axis. It was stated that the previous reports that the working condyle rotates and translates in various directions, which created the impression that Bennett movement is complex, might have been caused by mislocation of the targets for measurement.

05-011b. Hobo, S. A kinematic investigation of mandibular border movement by means of an electronic measuring system. Part III: Rotational center of lateral movement. J Prosthet Dent 52: 66-72, 1984.



Purpose: To explain and illustrate the rotational center of the mandible.
Methods and Materials: Fifty adults from 20 to 50 years of age with an orthognathic maxillomandibular relationship and no apparent TMJ disorders were studied. Terminal hinge reference points 12mm anterior to the external auditory meatus formed the posterior points of a plane whose anterior reference point was 43mm above the incisal edge of tooth #8. Maxillary and mandibular reference points were secured in acrylic resin Stuart clutches. Right- and left-lateral border movements of the 50 subjects were recorded and the average movement of the field of the intercondylar axis and the targets on the intercondylar axis 65mm from the midpoint was computed.
Results: A converging point was identified on the working side where the field of motion became a minute region approximately 0.3mm long in a vertical direction and 0.1mm wide in an anteroposterior direction in the sagittal plane. The converging point existed approximately 55mm from the midpoint of the terminal hinge axis.
Conclusions: This converging point was at the point of intersection between the terminal hinge axis and the intercondylar axis, which appeared at the conclusion of the lateral movement. The net side-shift caused by translation of the mandible along the terminal hinge axis is equal in the nonworking and the working sides. A point approximately 55mm from the midpoint on the intercondylar axis is the kinematic rotational center of the mandible during lateral movement.

05-012. Preiskel, H.W. Lateral translatory movements of the mandible: Critical review of investigations. J Prosthet Dent 28: 46-57, 1972.



Purpose: Discuss the movements executed by the condyle on the working side.
Discussion: With wide opening and the jaw moving to the right, the working condyle moved in an almost direct lateral line. This has been termed the " Bennett movement". He only investigated his own jaw movement, his right side was larger than his left side, and he was missing the mandibular posteriors. Bennett was aware of the risks of drawing general conclusions from this.
     The condyle is pear shaped when viewed from above, and the glenoid fossa is wedge shape with the lateral section opening out sharply. The medial section of the condyle was rigidly contained within bone, but the lateral aspect has freedom of movement. Fischer, a Swiss dentist, suggested that lateral mandibular movements occur about an axis inclined forward, inward, and medially, involving the working-side condyle in rotation in the frontal plane.
     Sicher, points out that mandibular movements are described by muscle activity rather than by bone contacts or ligaments. He feels that the temporomandibular ligament limits mandibular displacement so that the condyles cannot brace themselves against the fossa.
     The neurophysiology of this area is unclear, since the ligament contains nerve endings susceptible to stretching, but there may be an absence of muscle spindles in the external pterygoid muscle.
     Photographic methods have found: (1) the pathway of the working side condyle on voluntary lateral sliding movements was different from that of lateral movements made with the teeth out of contact, (2) a direct lateral movement of the condyle was present in voluntary lateral movements of the mandible. This is one of the best designed experiments, however only two subjects were discussed.
     Cinefluorographic studies show the absence of lateral translation. Electromyographic studies cannot differentiate between isotonic and isometric contractions, and no direct conclusions can be drawn by the action of individual muscles.
     Tracing devises usually have a clutch, that may alter the centric occlusion and alter jaw movements. Lateral movements are assessed at an increased vertical dimension of occlusion. Some pantographs were unable to reproduce consistent results from one patient. Another pantograph was joined to an articulator and eccentric records were made. The line records were reproduced, but the differences in articulator settings were considerable. Isaacson modified McCollums recording device and found the Bennett movement near the vertical dimension of occlusion in all 26 patients examined.

Conclusion: Lateral translatory movements of the human mandible have yet to be completely evaluated.

05-013. McCollum, B. B. and Stuart, C. E. A Research Report. Scientific Press, South Pasadena, CA.

      See reference:

05-014. Santos, J., et al. Vectorial analysis of the static equilibrium of forces generated in the mandible in centric occlusion, group function and balanced occlusion relationships. J Prosthet Dent 65:557-567, 1991.



Purpose: Mechanical analysis based on a static equilibrium of forces in an effort to support various and prevailing stomatognathic concepts of occlusal function.
Materials & Methods: Two-dimensional mechanical models were designed to represent frontal projections of maxillomandibular relations focusing on only the coronal aspect of molars and both condyles. The objective was to ascertain the instantaneous static equilibrium of forces when different interocclusal eccentric relationships were imposed on these models. Templates representing a functional projection of the maxilla and the mandible were fabricated. The buccal and lingual occlusal inclines were assigned steeper angles on the right side than the left. The relationships were imposed on a centric occlusion position, a group function and a cross arch balanced occlusion relationship.
Results & Discussion: All of the studies in this area have values and limitations influenced by the complexity of the biomechanical elements added to the artificially created models. Biologic systems demonstrate ranges of variability. Neuromuscular control may contribute to or override a condition of static equilibrium. For any load applied to a given body, there will be a reaction of equal intensity and direction, provided the force is exerted on a flat surface. When forces are applied against inclined surfaces they will be decomposed into vectors with different directions and magnitudes.
     1. The concentration of forces generated in a stable centric occlusion produces less loading response in the joints.
     2. The working side of the dentition accepts increased load and increased reaction in the contralateral balancing condyle in an observation of balanced occlusion.
     3. The best approach for a uniform distribution of forces acting upon the masticatory position is erect cusps with similar angulations for both sides of the dental arches. When cusps are less steep, resultant forces in the dentition increase.
Summary & Conclusions: This study, using a mechanical model, simulates a system in function and provides a vectorial analysis based on static equilibrium of forces generated in a mandible at 10 different positions(1 in centric and 9 in eccentric positions). Positions were in a balanced occlusion and in group function. The most revelant conclusion seems to be the findings that cusp inclines and condylar path inclination have a profound influence on the forces acting within the joints and dentition.

05-015. Theusner, J., et al. Axiographic tracings of temporomandibular joint movements. J Prosthet Dent 69:209-215, 1993. 



Purpose: To investigate the spatial patterns of condylar movements and to determine if they differ between individuals who are symptom-free and those who have subclinical symptoms. Also the biomechanics of the TMJ were documented by studying the range of condylar movements during maximum jaw movements.
Materials & Methods: Forty-nine volunteers (24 men and 25 women) between 22 and 56 years were selected. The only criteria for their selection was that they were not in or seeking TMD therapy. On all 49 volunteers (symptomatic and asymptomatic), three dimensional condylar movements were recorded with a hinge axis tracing system axiograph during maximum opening , protrusion, and mediotrusion. Tracings that were displayed in sagittal and frontal planes were measured to evaluate the biomechanics of the TMJ.
Results & Conclusions: The only differences between the groups (symptomatic and asymptomatic) were in the right joint, recorded in the sagittal plane during maximal opening an the Bennett angle. The symptomatic group had a much longer condylar path. and a smaller Bennett angle compared with the asymptomatic group.

These results were interpreted to be indication of adaptive morphologic instead of pathologic changes. The authors concluded that alterations in condylar tracings should be cautiously considered as an indicator of joint pathology.



05-016. Clayton, J. A., Kotowicz, W. E. and Meyers, G. A. Graphic recordings of mandibular movements: Research criteria. J Prosthet Dent 25:287-298, 1971. 

Purpose:  To determine whether or not graphic tracings of mandibular movements could be affected by:
     1. Changes in the VDO
     2. Changes in the central bearing guidance surface
     3. Tooth guidance
Vertical Dimension Changes:  The orientation of the styli and recording table affected graphic tracings of mandibular movement when the VDO was changed. Cusps gliding on inclines involved changes in vertical dimension. Studies of mandibular movements should have the recording device oriented to the terminal hinge axis so that changes in vertical dimension do not cause different tracings. Inconsistencies previously recorded by other studies, could be due to mechanical errors in the positioning of the recording device.
Central Bearing Surfaces, Shapes and Graphic Tracings:  The shape of the central bearing surface can affect graphic tracings depending on the angulation of the styli recording movement. Graphic tracings of mandibular movements recorded against different bearing surfaces will coincide if the styli is "zeroed." Graphic tracings will be different for each surface if the styli are angled backward or forward from the "zeroed" position.
Tooth Guidance, Chewing and Graphic Tracings:  Unguided tracings made by the patient with the teeth in contact may not be true border tracings. Tooth interferences and muscles may deflect movement away from the border position. Border tracings should be guided when teeth are in contact, or a central bearing surface should be used to eliminate the influence of tooth interfernces and muscle conditioning on theses interferences. The position of the styli can affect the graphic recording of functional movements. the angle of the styli and the positions of the styli in relationship to the terminal hinge axis should be reported.
Graphic Tracings v.s. Pantographic Tracings: Graphic tracings are recordings made on the patient from which conclusions are drawn about mandibular movements directly from the tracings. Pantographic tracings are recordings of mandibular movements from a patient that are transferred to an articulator and then conclusions are drawn after the movement of the casts on the instrument. 


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