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Functional movements of the mandible
Functional
movements
of the mandible
Charles H. Gibbs, Ph.D.,* Theodore Messerman, D.D.S.,** James B. Reswick, D.Sc.,*** and Harry J. Derda**** Case Western Reserve University, Cleveland, Ohio
M
ore than 60 years ago Norman BennetP noted in his paper “A Contribution to the Study of the Movements of the Mandible” that “. . . I cannot help thinking that more frequent collaboration between workers in different fields, meeting on borderline subjects, would result in the elucidation of questions which present much difficulty to the specialist.” This study and report is based on findings of just such a collaborative effort among medical engineers, a clinician, and computer scientists at Case Western Reserve University. This report focuses on the results of our jaw motion studies in relation to two primary objectives. The first objective was to provide an accurate and extensive study of jaw motion and maxillamandibular relationship during chewing. This would enable articulator specifications to be made, which would enable the dentist to build and test prosthetic appliances in an actual functional relationship as it occurs in the mouth. These articulator specifications would be based on the common recognizable elements of jaw movements involved in chewing, regardless of the effect of various occlusal schemes. The second basic objective was to determine the manner and degree that differing states of occlusion affect jaw motion during chewing. Data providing extensive statistics comparing subjects with “normal” occlusions and with malocclusions, may enable dentists to prevent periodontal and temporomandibular disease and consequent tooth loss. Research DE 03500. *Research
project
under
Associate,
sponsorship
Engineering
of United
States Public
Health
Service
Grant
No.
Design Center.
““Senior Research Associate, Engineering Design Center, and Research Associate, School of Dentistry, Deceased. ***Director of Engineering and Director, Ranch0 Los Amigos Hospital, Downey, Calif. ****Instrument Maker and Head, Precision Machine Shop, Engineering Design Center.
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SUBJECTS Jaw motion data were obtained from 12 subjects: four with “normal” OCC~Usions, four with rehabilitated occlusions that clinically fulfilled the authors’ criteria for ideal occlusion, and four with obvious malocclusions. Our criteria for ideal occlusion are ( 1) all the teeth are present with perhaps the exception of the third molars; (2) the teeth are in good arch alignment; (3) there is no abnormal wear on the occlusal surfaces and the teeth are free of any restorative dentistry except perhaps small occlusal amalgams; (4) the teeth intercuspate with their respective antagonists in normal order according to Angle’s First Classification, and (5) the gingival tissues are normal in all areas, having sulci around all the teeth of normal depth. The four subjects in this study with “normal” occlusion essentially fulfilled these criteria of ideal occlusion. This report describes the motions at the central incisor and at the right and left condyles. Observations for the chewing of soft and hard foods and gum, as well as for the physiologic rest position, are included. The food was prepared in morsel sizes, consequently, incisive movements are not included in these data. APPARATUS A complete system for the study of human jaw motion has been developed at Case Western Reserve University. 1-s The instruments of this system were specially designed to be noninterfering in function, and to permit preconscious chewing according to the tenets of reflex action. This system measures all six degrees of motion of the jaw with respect to the unconstrained head position. It records this information for playback to a jaw motion reproducer mechanism which is also used for computer analysis (Fig. 1). The motion of all jaw points (i.e., condyles, coronoid processes, teeth, etc.) are known, and a wide variety of parameters of jaw motion including screw axes of rotation can be calculated by the computer. This system is termed the Case Gnathic Replicator and it records jaw motion with six incremental transducers mounted between an upper maxillary reference bow and a lower-jaw-mounted face-bow. The moving parts of the system weigh 60 Gm. (Fig. 2). The maximum measuring error is 0.005 inch (0.13 mm.). High precision is needed in the all-important intercuspal range where pathologic forces of tooth-to-tooth contact can occur. Pulse signals from the six transducers are recorded on multichannel tape at normal chewing speed. The reproducer mechanism duplicates jaw motion by mechanically moving a cast replica of the subject’s jaw. This mechanism is controlled by the subject’s tape recorded jaw motions so that the cast replica moves in precisely the same manner as the original movements of the subject’s jaw, but at one tenth the speed. The maximum error for reproducing jaw motion is 0.010 inch (0.25 mm.) in the range of intercuspation. The cast replicas are visible from nearly all angles, and information of intercuspation and contact can be gained by direct observation of their motion (Fig. 3). The clutches, which attach the measuring instrumentation to the teeth, are cemented to the labial surfaces of the anterior teeth well below the chewing surfaces. The clutches do not interfere with lip sealing at closure (Fig. 4) .
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and Derda
.I. I’rosthei. Decrmhrr-.
Dcnr. 197 I
Fig. 1. The Case Gnathic Replicator system measures all six degrees of mc>tion of the jaw with respect to the unconstrained head position. It records this informatiorl for playback to L jaw motion reproducer mechanism and for computer analysis.
RESULTS The working side and definition of the working functional nzouenzent. ‘I’hc subjects were asked to chew first on one side and then on the other side. Two sides.* indicators were found useful in differentiating the “food” and %onfood” First, the direction of lateral movement of the central incisor near closure occurt~ed away from the chewing side. That is, with the food on the left side, the central incisor moved from left to right during the TFM,? and with the food on the right *The “food” side is the one on which the food was replaced originally. Some food undoubtedly moved to the other side during the chewing sequence. Our definition of working and nonworking sides depends on directions of jaw movement during closure and not on food position. TThe TFM (Terminal Functional Movement j : “It is the terminal portion of the path of mandibular movement operating in the range of intercuspation in power closure. It operate: in a range of about 5 mm.“6
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Fig. 2. A recording session with a subject, the measuring instrument, the Replica ttor, an da tape ret :o*.der. The moving parts of the measuring instrument weigh 60 Gm.
Fig. 3. After a period of jaw motion Replicator and inspected for contacting
duplication, points.
the stone casts can be removed
from
the
60%
Gibbs, Messerman,
Fig. 4. The The clutches
Reswick,
I. I’rosthet. Urnt.
and Derda
clutches are cemented to the anterior teeth do not interfere with lip sealing at closure.
Ilecembrr
well
below
the chewin
18:: 1
suri~~.~-
side, the central incisor moved from right to left during the TFM. Xinctv-sr>.er! per cent of the chews closed in a lateral direction opposite to the “food“ sick>. The second indicator to differentiate the “food” and “nonfood” sides was the motion at the condyles. The condylc on the “food” side reached a maximum vr~ti.. cal position during closure before the condyle on the “nonfood” side. The condylr~ on the “food” side then maintained its maximum vertical position during the remaining portion of the closing stroke. The condyle on the “nonfood“ side us~ral t!, reached its maximum vertical position as the central incisor reached clos~ue. Vim+.one per cent of the chews showed the condyle on the “food” side to rcac.h ;I nrasimum vertical height before the condyle on the “nonfood” side. The measurements vvere carried out on four srrbjects with Cinornial” occlusions w hilt chc\virr,g hard and soft. foods and gu~n. and four subjects with malocclusions, ‘Therefore, these two measurements provided a means for defining a “working” side is the side on which an d “nonworking” side. For this report. the working upward and rearward position first. X one of the condylrs reachrs a maximurrr lateral movement of the central inc,isor (actually the entire mantliblc ! ust1.111:~ occurs medially away from the side of thr working condyle. Fig. 5 is a plot printed by the computer of the vertical position versus rime of the central incisor and condyles for a typical subject with a %ormal” occlusion. During the closing stroke the left condyle reached its maximum height first, :dtw which both the right condyle and the central incisor reached their maximum height at approximately the same time. Since thr left condyle reached its maximum height first, it is the working side condyle and the same (left) side is c‘onsidered to be the “food” (working) side. Eighty-six per cent of the chews of subjects with a “normal” occlusion eating soft and hard foods showed a definite working side condyle. Since the presence of a working side condyle is an important constraint in controlling jaw closure, jaw movement during the part of the closing stroke when one condyle is at its maximum vertical height is termed the \Yorking Functional Movement (WFM) . AS later plots will show, the vvorking side condyle ib nearly stationary only in a sagittal view since it moves medially (Bennett movement ) an average of 0.01’ inch during the WFM.
Functional
Volume 26 Number G
Left
movements
of the mandible
Side WorkinS
Subject
609
BLT5S3
Vertical notion of the Central Incisor in the UFM
7
-
-Tim
in the WFM
TIE3 .IN SECONDS
Fig. 5. Vertical
motion of the central incisor and condyles versus time for a subject with “normal” occlusion while eating soft food. During the closing stroke, the left condyle reached its maximum height first; therefore, the left side is termed the working side, and it is most likely that the food is on the left side. The right condyle and central incisor reached maximum height at about the same time. The central incisor curve shows a series of flat tops, indicating that this jaw point stopped about 0.2 second at closure.
The average amount of vertical movement of the central incisor for subjects occlusion during the WFM was 0.24 inch. Therefore it appears with “normal” that the working side condyle is an important control of jaw closure throughout the intercuspal range. The remaining 14 per cent of the chews did not show a definite working side condyle and exhibited nearly symmetrical closure of the jaw with little lateral movement. These symmetrical closures showed the condyles and central incisor to reach their terminal vertical positions simultaneously. The “normal” occlusion (Fig. 5) exhibits good closure repeatability, i.e., the central incisor returns to the same terminal position at closure. The central incisor vertical position vs. time curve shows a series of flat tops, These Aat sections indicate that this point on the jaw stopped for a period of time at closure. This stoppage time is about 0.2 second or 15 per cent of the chew cycle. Jaw pressure may have been high during these long periods of jaw closure since the working condyle (left) varied about 0.01 inch (0.25 mm.) while the central incisor remained stationary. Figure 5 also indicates that it is typical for both condyles to begin moving immediately downward and forward upon opening. Therefore, during chewing, the jaw did not hinge about two working condyles at any time for this group of patients.
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and Derda
Time
in
Seconds
Fig. 6. Vertical motion of the central incisor and condyles versus time for a subject with malocclusion eating soft food. These curves show a series of round tops, indicating that the jaw movement did not stop at closure. Similar plots for subjects with “normal” occlusion show stoppage of the jaw movement at closure. Viewing extended position vs. time plots similar to that in Fig. 5 for subjects with “normal” occlusion chewing soft or hard food demonstrated that: 1. The first few chews did not attain full closure at the central incisor (the and when full closure was not atfood bolus was large and anteriorly placed), tained, there was no stoppage of the jaw movement. 2. After the first few chews, full closure was reached by the central incisor at a very repeatable position (within a few thousandths of an inch:1 ; then the jaws remained closed for a period of time. 3. The terminal position at the condyles varied about 0.02 inch (0.5 mm) or about 10 per cent of their total movement. 4. In the first chews of a series, the working side condyle reached its terminal position first. This pattern changed toward the end of the chewing series where the condyles moved more symmetrically. We believe that this change on condylar action is primarily due to anteroposterior movement and softening of the food. Subjects with malocclusion produced vertical position vs. time plots quite different from corresponding plots from subjects with “normal” occlusion (Fig. 6). Repeatability at closure of the central incisor for the subject in Fig. 6 is poor. shows The central incisor position vs. time plot of this subject with malocclusion no stoppage of jaw movement at closure. (The position vs. time plots appear round topped instead of flat topped.) Occlusions grouped for chewing of soft foods showed that a greater percentage of chews with stoppage at closure occurs for occlusion than for subjects with malocclusion. This was subjects with “normal” significant to the five per cent level.
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Fig. 7. Paths of motion of the central incisor in the frontal plane while chewing soft food.
The arrow heads were drawn by the computer 0.1 second after the beginning of the closing movements. Many of the closing paths are lateral to the medial opening paths. These paths are smooth and uniform with good terminal position repeatability. Most subjects exhibited a reduction in the amount of jaw opening as the chewing neared the swallowing action. Paths of motion at the central incisor. Paths of motion of the central incisor in the frontal plane for three subjects with “normal” occlusion and one subject with repaired occlusion are shown in Fig. 7. Smooth uncrossed motions that return very nearly to the same closed position are typical for subjects with “normal” occlusion. These central incisor paths appear to be quite uniformly distributed within the functional borders of the plots. However, arrow heads drawn by computer for each path (0.1 second after the beginning of closure) indicate that many of the closing paths are lateral to the medial opening paths. This is a reflection of the working side condyle guiding the jaw through its lateral excusion during the working functional movements. Fig. 7 illustrates how these plotted paths of motion can show the presence of a gliding contact between teeth during chewing. A sharp break in angle is evident in the closing portion of the incisor path of subject C. G. The dense line shows a region where many paths coincide, indicating a physical constraint which occurred most surely from tooth contact. Subject C. G. had an anterior fixed partial denture and his occlusion may not have been normal. For comparison, corresponding plots for central incisor motion during chewing of chewing soft food are shown for four subjects with malocclusion (Fig. 8). Irregular, self-crossing motions are typical for subjects with malocclusion. The “closed” positions of these paths are not as repeatable as are closed positions for subjects with “normal” occlusion. Paths of motion of the central incisor during the chewing of gum, soft food,
612
Gibbs, Messerman,
miT2SL ?z3locclusior.
Resmick,
and Derda
GvrlSL M?locclusion
KJTIAI fhlocclusion
MSTlSL
Malocclusion
Fig. 8. Paths of motion of the central incisor in the frontal plane of four subjects with malocclusion chewing soft food. The arrow heads were drawn by the computer 0.1 second after the beginning of the closure. Irregular self-crossing motions are typical for subjects with malocclusion.
BL "N~rrnal'~ Occlusion Gum
AL ?~ormal" Occlusiorl Soft Food
P:: Mllocclusior .?oft Food
BL "Normal" Occlusion Hard Food
IF:: Malocclusion Hard Food
/ ;,~ ,
i.
,
Scale
,
k I
c
r;l:;,,
-4
Fig. 9. Paths of motion in the frontal plane of the central incisor during chewing of gum, soft food, and hard food for two subjects. The paths of motion appear to be more dependent upon the individual than upon the type of food being chewed.
Volume 26 Number 6 PLT3Sl "Normal" Occlusion
Functional BLT%3 "N0lYW.1" Occlusion
movements
of
the mandible
613
CGTlS2 Repaired Occlusion
Fig. 10. Paths of motion of the central incisor in the sagittal plane for chewing soft food. The arrow heads drawn by the computer 0.1 second after the beginning of the closure indicate many closing paths are rearward of the opening path.
and hard food for two subjects are shown in Fig. 9. These chewing plots for the same subject eating different foods appear to be quite similar. The border outlines in the TFM are similar for all three plots of subject B. L. with “normal” occlusion. The three plots of motion for subject B. W. with malocclusion are more irregular and self-crossing. Therefore, paths of motion of the central incisor appear to be more dependent on the individual subject than on the type of food being chewed. Paths of motion in the sagittal plane are shown in Fig. 10. Arrowheads drawn for each orbit 0.1 second after the beginning of closure indicate that many closing paths are rearward of the opening paths. The interocclusal distance at the central incisor during rest was measured for occlusion. The rest position was made in relation four subjects with “normal” to the most closed (intercuspal) position. These measurements were made after the removal of the reference fork which is a period of rest before the entry of food. The subjects were not aware that any rest position measurements were being recorded. The vertical opening in relation to the intercuspal position at this rest position ranged from 0.086 to 0.234 inch with an average of 0.155 inch (4.0 mm.). The distance rearward ranged from 0.005 to 0.059 inch with an average of 0.035 inch (0.9 mm.) . The interocclusal distance at the central incisor, measured during the pronunciation of the letter “M,” was on the average 0.040 inch less open than after the “bite” fork removal and 0.090 inch anterior to the “bite” fork removal position.
614
Gibbs, Messerman,
Reswick,
and Derda
SAGITTAL VIEW
,
I23 Fig. 11. Paths of motion in the sagittal plane of the central incisor and right condyle during chewing show the condyle motion to be about 40 per cent of the amount of motion at thr central incisor. Therefore, the use of the letter “M” for establishing the interocclusal distance may be useful in reference to the vertical relation, but is too far forward to establish the anteroposterior relation. Paths of motion at the condyles. As shown in Fig. 11 (the directional arrows drawn by the computer tend to obscure motion paths in reproduction), there is considerable motion at the condyle during chewing. This motion amounts to about 40 per cent of the motion at the central incisor. As the jaw opens, the condyles move downward and forward. As the jaw closes, the condyles move upward and rearward. Typical condyle motion is further described in Fig. 12 which shows sagittal, frontal, and horizontal views in orthographic projection. These plots show about 0.060 inch (1.5 mm.) of total lateral motion (Bennett movement) present at thr: condyle. Since numerous chews were plotted, each individual path is not distinguishable. The closed position was quite repeatable and is labeled in this figure. The sagittal view in Fig. 12 is of particular interest since it shows about 0.070 inch ( 1.8 mm.) variation perpendicular to its path. The variation in the condylar orbits is investigated further in Fig. 13, which shows sagittal views of right and left condyle motion for four subjects. Arrow heads drawn 0.1 second after the beginning of closure show the closing paths to be posterior and inferior to the opening paths. projections To further investigate the motions at the condyles, orthographic into sagittal, frontal, and horizontal planes of one chew were plotted (Fig. 14) . The working condyle moved medially 0.025 inch (0.6 mm.) during the WFM. This medial movement during the WFM ranged from 0 to 0.042 inch with an occlusion. average of 0.017 inch (0.4 mm.) for the four subjects with a “normal” Closed position repeatability at the condyles was studied by recording the radius of a sphere to include 70 per cent of the closure positions for each condyle. By eliminating 30 per cent of the closures, those positions in which the jaw did not attain full closure at the central incisor are automatically discarded. These radii ranged from 0.01 to 0.06 inch. This small range is significant since it means the
Volume 26 Number 6
Functional
I
.5 Inch
movements
of the mandible
615
J
Scale
deft condyle Subject PL "Normal" Occlusion Chewing Soft Food
L
Fig. 12. Sagittal, chewing.
Closed Position
frontal,
and horizontal
condyle is not positioned at greatly jects with an obvious malocclusion.
views in orthographic
different
points
projection
of a condyle
during
along the fossae, even for sub-
DISCUSSION Jaw motion exhibited a working side condyle for most chews during the final part of the closing stroke. This working began with the central incisor 0.24 inch from closure on the average for subjects with a “normal” occlusion, indicating that this constraint aids in the control of closure in the intercuspal range (TFM) where tooth contact and pathologic forces can occur. This part of the final closing stroke is the WFM. The medial movement during closure is greatest at the central incisor. The medial movement at the working condyle during the WFM of four of the subjects with “normal” occlusion ranged from 0 to 0.042 inch. The average was 0.017 inch (0.4 mm.) . Therefore, during the WFM, the working condyle appears to be stationary in the sagittal view only. In 1908 Bennett’* reported that the condyle for one subject moved laterally about 0.12 inch for lateral protrusive gliding of the teeth. The actual presence of a Bennett type of movement during chewing has been controversial for many years. In a cinefluorographic study of one subject, Landall found no lateral movement
616
Gibbs,
Messernlan,
Reswick,
and Derda
Y!?? ’ I--
.I. I’rosthet. Drrrmhrr.
Lkut. 19il
SC8.k
1~~
-2 ’
b
BLTSS3(1,21!7'0,750) "Normal" Occlusion Scft Food
CWTm (l,h700,700) Malocclusion Soft Food
I'BTlSh (1,9~,1160) Malocclusion Soft Food
wTlS5 (1,2120,380)
RIGHTCONDOLE (Non-Working) Fig. 13. Sagittal views of right and left condyles second after the beginning the opening paths.
of closure
during show the closing
LEFT CONDYLE (Working) chewing. The arrow heads drawn paths to be posterior and inferior
0.1 to
at the condyles during closure. Landa’s study, however, may have been limited to chews of symmetrical condyle movement before swallowing instead of the usual closing pattern of a working and nonworking condyle. However, the presence of a medial movement during closure while chewing has been convincingly shown by this report and by others.lO, *z-14 Hildebrandl” reported a medial movement of the working side condyle of 0.040 to 0.080 inch. This is greater than the 0 to 0.040 inch movement reported here, since he included the total medial movement and did not limit it to the WFM. Hickey and associateP reported a 0.012 inch medial movement “during maintained contact in chewing” which corresponds to values reported here, and 0.029 to 0.062 inch total medial movement for one subject. They measured this movement by photographing a pin inserted into the condyle. In the sagittal view, their condyle pin moved downward and forward as the teeth came into closure, appearing to be contradictory to our findings of a
Volume 26 Number 6
Functional
L
.s Inch Scale
movements
of the mandible
617
1
Braced (Working) Condyle Subject HFTlS5 (1,3232,100) ~U0rnra1~~ Occlusion Chewing Soft Food
Fig. 14. Sagittal, frontal, and horizontal views in orthographic projection of a working side condyle during chewing. A 0.025 inch medial movement occurred during the working functional movement. The arrow heads were drawn by the computer 0.1 second after the beginning of closure. closure position at the most upward and rearward position on the condyle path. These seemingly different findings are not contradictory however; the difference occurred because our paths were measured for a point at the approximate center of the condyle (calculated by computer from motion of three other jaw points), while their pin movement measurements were made lateral to the condyle. When the nonworking condyle moved upward and rearward about a “center of rotation” within the working side condyle, lateral points, such as a pin in the condyle, would move downward and forward. The sagittal view of the condyle paths is of particular interest, since it usually shows the closing orbits inferior and rearward to the opening orbits. Similar findings can be seen in paths of motion described by Koivumaa.s This may occur because of the difference in the medial-lateral position of the condyles during opening and closing movements. Another possibility is that these paths are indications of forces applied at the condyles. If this is true, the closing path lying inferior and rearward to the opening path, as reported here, would indicate an upward
618
Gibbs, Messerman,
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and Derda
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Prosthet. December.
Dent. 1971
force on the condyle rather than a downward force as is usually supposed. Sitrcr: there is no anterior movement of the condylcs about the teeth at final closure for most subjects (the important exception \vas C, G., with heavy contact on ~3 fixed partial denture), the force at final closure at the condyles appears to brs small, if any. Perhaps the posterior teeth protect the temporomandibular joint fror~~ strong forces. If the vertical dimension of the posterior teeth becomes too short in relation to the vertical dimension of the anterior teeth: the temporomandibulat joint pain syndrome sometimes results. An equilibrium analysis of the; ,;a\\ 11) Frankel and Burstein’” shobvs that force need not be transmitted at th
Volume 26 Number 6
that jaw motion occlusal health.
Functional is affected
by the occlusion
movements and may
of the mandible
be useful
619
in diagnosing
SUMMARY Starting from the closed position, a typical motion of the mandible can be summarized as follows: Both condyles begin the opening immediately downward and forward. Early in the closing stroke, the entire mandible moves laterally. The working side (lateral) condyle moves upward and rearward and reaches its terminal position at the most vertical rearward position of its path before the teeth approach each other far enough to intercuspate. This working side condyle appears to be nearly stationary in the sagittal view for the remaining part of the closing stroke, which is termed the Working Functional Movement (WFM) . During the WFM, the working side condyle moves medially to its closed position, while the nonworking side condyle goes upward and laterally to its closed position. The food is usually on the same side as the working side condyle. The paths of motion of the condyles are quite similar for subjects with “normal” occlusions and malocclusions. The closed position repeatability is similar, ranging from 0.01 to 0.06 inch. This is in contrast to the paths of motion of the central incisor where differences among subjects with “normal” and malocclusion are easily detected. Of particular interest is the fact that for a higher percentage of chews, the central incisor remains motionless at closure for more subjects with “normal” occlusion than for subjects with malocclusions. CONCLUSIONS The presence of a working side condyle during typical chewing, as described in this report, is an important constraint which aids in the control of closure in the intercuspal range where tooth contacts and resulting forces can occur. This constraint is significant for functional articulator design since it specifies two of the six degrees of freedom. A mechanism which coordinates the medial movement of the working condyle, with the upward, rearward lateral path of the nonworking condyle and with the medial, upward path of the central incisor, could complete the functional articulator. Finally, the measuring instrumentation used in this study apparently did not significantly affect the chewing motions, since the basic motion was typical regardless of large influences such as various test foods and different types of occlusion. David C. Cannon, MS., designed and constructed the measuring instrumentation. Computer programming of the jaw motion data was performed by Thomas G. Szymanski, Edward Janecek, Bob Lattie, and Neal Nomiyama. Mouth appliances were constructed by Paul J. Yungmann.
References 1. Cannon, D. C., Reswick, J. B., and Messerman, T.: Instrumentation for the Investigation of Mandibular Movements, Case Institute of Technology, E. D. C. Report No. EDC 4-64-8. 2. Gibbs, C. H., Reswick, J. B., and Messerman, T.: The Case Gnathic Replicator for the Investigation of Mandibular Movements, Case Institute of Technology, E. D. C. Report No. EDC 4-66-14.
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3. Gibbs, C. H., Reswick, J. B., and Messerman, T.: Functional Movements of the Mandible, Case Western Reserve University, E. D. C. Report No. EDC 4-69-24. 4. Messerman, T.: A Means for Studying Mandibular Movements, J, PROSTHI:T. DENT, 17: 36-43, 1967. 5. Messerman, T., Reswick, J. B., and Gibbs, C. Ii.: Investigation of Functional Mandibular Movement, Dent. Clin. North Am. 13: 629-642, 1969. 6. Messerman, T.: A Concept of Jaw Function with Related Clinical Application, .j PROSTHET. DENT. 13: 135, 1963. Glossary of Prostho7. The Nomenclature Committee, Academy of Denture Prosthetics: dontic Terms, ed. 3, J. PROSTHET. DENT. 20: 443-480: 1968. 8. Koivumaa, K.: Cinefluorographic Analysis of the Masticatory Movements of the Mandible, Suom. Hammaslaak. Toim. 57: 306-368, 1961. 9. Schweitzer, J. M.: Masticatory Functions in Man, J. PROSTHET. DENT. 12: 262-291, 1962. 10. Ulrich, J.: The Human Temporomandibular Joint: Kinematics and Actions of the Masticatory Muscles, J. PROSTHET. DENT. 9: 399-406, 1959 (reprinted from his original publication of 1896). 11. Landa, J. S.: A Critical Analysis of the Bennett Movement, Part I, J. PROSTHET. DEXI 8: 709-726, 1958. 12. Bennett, N. G.: A Contribution to the Study of the Movements of the Mandible, Pro<:. Roy. Sot. Med. (odont sect.) I (3): 79-98. 1908. 13. Hildebrand, G. Y.: Studies in the Masticatory Movements of the Human Lower jaw, Skand. Arch. Physiol. Suppl. 61, 1931. 14. Hickey, J. C., Allison, M. L., Woelfel, J. B., Boucher, C. O., and Stacy. R. W.: Man dibular Movements in Three Dimensions, J. PROSTHET. DENT. 13: 72-92, 1963. 15. Frankel, V. H., and Burstein, A. H.: Orthopaedic Biomechanics, Philadelphia, 1969, Lea & Febiger, Publishers, pp. 19-22. 16. Page, H. L.: Temporomandibular Joint Physiology and Jaw Synergy, Dent. Dig. 60: 54-59, 1954. 17. Schweitzer, J. M.: Masticatory Function in Man, J. PROSTHET. DENT. 11: 625-647, 1961. 18. Graf, H., and Zander, H. A.: Tooth Contact Pattern in Mastication, J. PROSTHET. DEN.I’. 13: 1055-1066, 1963. 19. Pameijer, N. H., Glickman, I., and Roeber. F. W.: Intra-occlusal Telemetry. Part II. Registration of Tooth Contacts in Chewing and Swallowing, J. PROSTHET-. DENT. 19: 151-159, 1968. Acta. Odont. Stand. 24: Suppl. 44: 1966. 20. Ahlgren, J.: Mechanism of Mastication, 21. Ahlgren, J.: Pattern of Chewing and Malocclusion of Teeth, Acta. Odont. Stand, 25: 3-14, 1967. 22. Bewersdorff, H. J,: Electrognahographie Elektronische dreidimensionale Messung und Registrierung von Kieferbewegungen, Odontol. Tidskr. 77, 1969. 23. Yamashita, A.: Electrophysiological Studies on the Masticatory System, a paper presented to the American Equilibration Society, Feb. 1, 1968. DRS. GIBBS AND DERD~: ENGINEERING DESIGN CENTER CASE WESTERN RESERVE T.JNI~ERSITY CLEVELAND, OHIO 44106 DR. RESWICK : RANCHO Los AMIGOS DOWNYSY, CALIF.
HOSPITAL
movements
of the mandible
Charles H. Gibbs, Ph.D.,* Theodore Messerman, D.D.S.,** James B. Reswick, D.Sc.,*** and Harry J. Derda**** Case Western Reserve University, Cleveland, Ohio
M
ore than 60 years ago Norman BennetP noted in his paper “A Contribution to the Study of the Movements of the Mandible” that “. . . I cannot help thinking that more frequent collaboration between workers in different fields, meeting on borderline subjects, would result in the elucidation of questions which present much difficulty to the specialist.” This study and report is based on findings of just such a collaborative effort among medical engineers, a clinician, and computer scientists at Case Western Reserve University. This report focuses on the results of our jaw motion studies in relation to two primary objectives. The first objective was to provide an accurate and extensive study of jaw motion and maxillamandibular relationship during chewing. This would enable articulator specifications to be made, which would enable the dentist to build and test prosthetic appliances in an actual functional relationship as it occurs in the mouth. These articulator specifications would be based on the common recognizable elements of jaw movements involved in chewing, regardless of the effect of various occlusal schemes. The second basic objective was to determine the manner and degree that differing states of occlusion affect jaw motion during chewing. Data providing extensive statistics comparing subjects with “normal” occlusions and with malocclusions, may enable dentists to prevent periodontal and temporomandibular disease and consequent tooth loss. Research DE 03500. *Research
project
under
Associate,
sponsorship
Engineering
of United
States Public
Health
Service
Grant
No.
Design Center.
““Senior Research Associate, Engineering Design Center, and Research Associate, School of Dentistry, Deceased. ***Director of Engineering and Director, Ranch0 Los Amigos Hospital, Downey, Calif. ****Instrument Maker and Head, Precision Machine Shop, Engineering Design Center.
604
Volume 26 Number 6
Functional
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SUBJECTS Jaw motion data were obtained from 12 subjects: four with “normal” OCC~Usions, four with rehabilitated occlusions that clinically fulfilled the authors’ criteria for ideal occlusion, and four with obvious malocclusions. Our criteria for ideal occlusion are ( 1) all the teeth are present with perhaps the exception of the third molars; (2) the teeth are in good arch alignment; (3) there is no abnormal wear on the occlusal surfaces and the teeth are free of any restorative dentistry except perhaps small occlusal amalgams; (4) the teeth intercuspate with their respective antagonists in normal order according to Angle’s First Classification, and (5) the gingival tissues are normal in all areas, having sulci around all the teeth of normal depth. The four subjects in this study with “normal” occlusion essentially fulfilled these criteria of ideal occlusion. This report describes the motions at the central incisor and at the right and left condyles. Observations for the chewing of soft and hard foods and gum, as well as for the physiologic rest position, are included. The food was prepared in morsel sizes, consequently, incisive movements are not included in these data. APPARATUS A complete system for the study of human jaw motion has been developed at Case Western Reserve University. 1-s The instruments of this system were specially designed to be noninterfering in function, and to permit preconscious chewing according to the tenets of reflex action. This system measures all six degrees of motion of the jaw with respect to the unconstrained head position. It records this information for playback to a jaw motion reproducer mechanism which is also used for computer analysis (Fig. 1). The motion of all jaw points (i.e., condyles, coronoid processes, teeth, etc.) are known, and a wide variety of parameters of jaw motion including screw axes of rotation can be calculated by the computer. This system is termed the Case Gnathic Replicator and it records jaw motion with six incremental transducers mounted between an upper maxillary reference bow and a lower-jaw-mounted face-bow. The moving parts of the system weigh 60 Gm. (Fig. 2). The maximum measuring error is 0.005 inch (0.13 mm.). High precision is needed in the all-important intercuspal range where pathologic forces of tooth-to-tooth contact can occur. Pulse signals from the six transducers are recorded on multichannel tape at normal chewing speed. The reproducer mechanism duplicates jaw motion by mechanically moving a cast replica of the subject’s jaw. This mechanism is controlled by the subject’s tape recorded jaw motions so that the cast replica moves in precisely the same manner as the original movements of the subject’s jaw, but at one tenth the speed. The maximum error for reproducing jaw motion is 0.010 inch (0.25 mm.) in the range of intercuspation. The cast replicas are visible from nearly all angles, and information of intercuspation and contact can be gained by direct observation of their motion (Fig. 3). The clutches, which attach the measuring instrumentation to the teeth, are cemented to the labial surfaces of the anterior teeth well below the chewing surfaces. The clutches do not interfere with lip sealing at closure (Fig. 4) .
606
Gibbs, Messerman,
Reswick,
and Derda
.I. I’rosthei. Decrmhrr-.
Dcnr. 197 I
Fig. 1. The Case Gnathic Replicator system measures all six degrees of mc>tion of the jaw with respect to the unconstrained head position. It records this informatiorl for playback to L jaw motion reproducer mechanism and for computer analysis.
RESULTS The working side and definition of the working functional nzouenzent. ‘I’hc subjects were asked to chew first on one side and then on the other side. Two sides.* indicators were found useful in differentiating the “food” and %onfood” First, the direction of lateral movement of the central incisor near closure occurt~ed away from the chewing side. That is, with the food on the left side, the central incisor moved from left to right during the TFM,? and with the food on the right *The “food” side is the one on which the food was replaced originally. Some food undoubtedly moved to the other side during the chewing sequence. Our definition of working and nonworking sides depends on directions of jaw movement during closure and not on food position. TThe TFM (Terminal Functional Movement j : “It is the terminal portion of the path of mandibular movement operating in the range of intercuspation in power closure. It operate: in a range of about 5 mm.“6
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Fig. 2. A recording session with a subject, the measuring instrument, the Replica ttor, an da tape ret :o*.der. The moving parts of the measuring instrument weigh 60 Gm.
Fig. 3. After a period of jaw motion Replicator and inspected for contacting
duplication, points.
the stone casts can be removed
from
the
60%
Gibbs, Messerman,
Fig. 4. The The clutches
Reswick,
I. I’rosthet. Urnt.
and Derda
clutches are cemented to the anterior teeth do not interfere with lip sealing at closure.
Ilecembrr
well
below
the chewin
18:: 1
suri~~.~-
side, the central incisor moved from right to left during the TFM. Xinctv-sr>.er! per cent of the chews closed in a lateral direction opposite to the “food“ sick>. The second indicator to differentiate the “food” and “nonfood” sides was the motion at the condyles. The condylc on the “food” side reached a maximum vr~ti.. cal position during closure before the condyle on the “nonfood” side. The condylr~ on the “food” side then maintained its maximum vertical position during the remaining portion of the closing stroke. The condyle on the “nonfood“ side us~ral t!, reached its maximum vertical position as the central incisor reached clos~ue. Vim+.one per cent of the chews showed the condyle on the “food” side to rcac.h ;I nrasimum vertical height before the condyle on the “nonfood” side. The measurements vvere carried out on four srrbjects with Cinornial” occlusions w hilt chc\virr,g hard and soft. foods and gu~n. and four subjects with malocclusions, ‘Therefore, these two measurements provided a means for defining a “working” side is the side on which an d “nonworking” side. For this report. the working upward and rearward position first. X one of the condylrs reachrs a maximurrr lateral movement of the central inc,isor (actually the entire mantliblc ! ust1.111:~ occurs medially away from the side of thr working condyle. Fig. 5 is a plot printed by the computer of the vertical position versus rime of the central incisor and condyles for a typical subject with a %ormal” occlusion. During the closing stroke the left condyle reached its maximum height first, :dtw which both the right condyle and the central incisor reached their maximum height at approximately the same time. Since thr left condyle reached its maximum height first, it is the working side condyle and the same (left) side is c‘onsidered to be the “food” (working) side. Eighty-six per cent of the chews of subjects with a “normal” occlusion eating soft and hard foods showed a definite working side condyle. Since the presence of a working side condyle is an important constraint in controlling jaw closure, jaw movement during the part of the closing stroke when one condyle is at its maximum vertical height is termed the \Yorking Functional Movement (WFM) . AS later plots will show, the vvorking side condyle ib nearly stationary only in a sagittal view since it moves medially (Bennett movement ) an average of 0.01’ inch during the WFM.
Functional
Volume 26 Number G
Left
movements
of the mandible
Side WorkinS
Subject
609
BLT5S3
Vertical notion of the Central Incisor in the UFM
7
-
-Tim
in the WFM
TIE3 .IN SECONDS
Fig. 5. Vertical
motion of the central incisor and condyles versus time for a subject with “normal” occlusion while eating soft food. During the closing stroke, the left condyle reached its maximum height first; therefore, the left side is termed the working side, and it is most likely that the food is on the left side. The right condyle and central incisor reached maximum height at about the same time. The central incisor curve shows a series of flat tops, indicating that this jaw point stopped about 0.2 second at closure.
The average amount of vertical movement of the central incisor for subjects occlusion during the WFM was 0.24 inch. Therefore it appears with “normal” that the working side condyle is an important control of jaw closure throughout the intercuspal range. The remaining 14 per cent of the chews did not show a definite working side condyle and exhibited nearly symmetrical closure of the jaw with little lateral movement. These symmetrical closures showed the condyles and central incisor to reach their terminal vertical positions simultaneously. The “normal” occlusion (Fig. 5) exhibits good closure repeatability, i.e., the central incisor returns to the same terminal position at closure. The central incisor vertical position vs. time curve shows a series of flat tops, These Aat sections indicate that this point on the jaw stopped for a period of time at closure. This stoppage time is about 0.2 second or 15 per cent of the chew cycle. Jaw pressure may have been high during these long periods of jaw closure since the working condyle (left) varied about 0.01 inch (0.25 mm.) while the central incisor remained stationary. Figure 5 also indicates that it is typical for both condyles to begin moving immediately downward and forward upon opening. Therefore, during chewing, the jaw did not hinge about two working condyles at any time for this group of patients.
610
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and Derda
Time
in
Seconds
Fig. 6. Vertical motion of the central incisor and condyles versus time for a subject with malocclusion eating soft food. These curves show a series of round tops, indicating that the jaw movement did not stop at closure. Similar plots for subjects with “normal” occlusion show stoppage of the jaw movement at closure. Viewing extended position vs. time plots similar to that in Fig. 5 for subjects with “normal” occlusion chewing soft or hard food demonstrated that: 1. The first few chews did not attain full closure at the central incisor (the and when full closure was not atfood bolus was large and anteriorly placed), tained, there was no stoppage of the jaw movement. 2. After the first few chews, full closure was reached by the central incisor at a very repeatable position (within a few thousandths of an inch:1 ; then the jaws remained closed for a period of time. 3. The terminal position at the condyles varied about 0.02 inch (0.5 mm) or about 10 per cent of their total movement. 4. In the first chews of a series, the working side condyle reached its terminal position first. This pattern changed toward the end of the chewing series where the condyles moved more symmetrically. We believe that this change on condylar action is primarily due to anteroposterior movement and softening of the food. Subjects with malocclusion produced vertical position vs. time plots quite different from corresponding plots from subjects with “normal” occlusion (Fig. 6). Repeatability at closure of the central incisor for the subject in Fig. 6 is poor. shows The central incisor position vs. time plot of this subject with malocclusion no stoppage of jaw movement at closure. (The position vs. time plots appear round topped instead of flat topped.) Occlusions grouped for chewing of soft foods showed that a greater percentage of chews with stoppage at closure occurs for occlusion than for subjects with malocclusion. This was subjects with “normal” significant to the five per cent level.
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Fig. 7. Paths of motion of the central incisor in the frontal plane while chewing soft food.
The arrow heads were drawn by the computer 0.1 second after the beginning of the closing movements. Many of the closing paths are lateral to the medial opening paths. These paths are smooth and uniform with good terminal position repeatability. Most subjects exhibited a reduction in the amount of jaw opening as the chewing neared the swallowing action. Paths of motion at the central incisor. Paths of motion of the central incisor in the frontal plane for three subjects with “normal” occlusion and one subject with repaired occlusion are shown in Fig. 7. Smooth uncrossed motions that return very nearly to the same closed position are typical for subjects with “normal” occlusion. These central incisor paths appear to be quite uniformly distributed within the functional borders of the plots. However, arrow heads drawn by computer for each path (0.1 second after the beginning of closure) indicate that many of the closing paths are lateral to the medial opening paths. This is a reflection of the working side condyle guiding the jaw through its lateral excusion during the working functional movements. Fig. 7 illustrates how these plotted paths of motion can show the presence of a gliding contact between teeth during chewing. A sharp break in angle is evident in the closing portion of the incisor path of subject C. G. The dense line shows a region where many paths coincide, indicating a physical constraint which occurred most surely from tooth contact. Subject C. G. had an anterior fixed partial denture and his occlusion may not have been normal. For comparison, corresponding plots for central incisor motion during chewing of chewing soft food are shown for four subjects with malocclusion (Fig. 8). Irregular, self-crossing motions are typical for subjects with malocclusion. The “closed” positions of these paths are not as repeatable as are closed positions for subjects with “normal” occlusion. Paths of motion of the central incisor during the chewing of gum, soft food,
612
Gibbs, Messerman,
miT2SL ?z3locclusior.
Resmick,
and Derda
GvrlSL M?locclusion
KJTIAI fhlocclusion
MSTlSL
Malocclusion
Fig. 8. Paths of motion of the central incisor in the frontal plane of four subjects with malocclusion chewing soft food. The arrow heads were drawn by the computer 0.1 second after the beginning of the closure. Irregular self-crossing motions are typical for subjects with malocclusion.
BL "N~rrnal'~ Occlusion Gum
AL ?~ormal" Occlusiorl Soft Food
P:: Mllocclusior .?oft Food
BL "Normal" Occlusion Hard Food
IF:: Malocclusion Hard Food
/ ;,~ ,
i.
,
Scale
,
k I
c
r;l:;,,
-4
Fig. 9. Paths of motion in the frontal plane of the central incisor during chewing of gum, soft food, and hard food for two subjects. The paths of motion appear to be more dependent upon the individual than upon the type of food being chewed.
Volume 26 Number 6 PLT3Sl "Normal" Occlusion
Functional BLT%3 "N0lYW.1" Occlusion
movements
of
the mandible
613
CGTlS2 Repaired Occlusion
Fig. 10. Paths of motion of the central incisor in the sagittal plane for chewing soft food. The arrow heads drawn by the computer 0.1 second after the beginning of the closure indicate many closing paths are rearward of the opening path.
and hard food for two subjects are shown in Fig. 9. These chewing plots for the same subject eating different foods appear to be quite similar. The border outlines in the TFM are similar for all three plots of subject B. L. with “normal” occlusion. The three plots of motion for subject B. W. with malocclusion are more irregular and self-crossing. Therefore, paths of motion of the central incisor appear to be more dependent on the individual subject than on the type of food being chewed. Paths of motion in the sagittal plane are shown in Fig. 10. Arrowheads drawn for each orbit 0.1 second after the beginning of closure indicate that many closing paths are rearward of the opening paths. The interocclusal distance at the central incisor during rest was measured for occlusion. The rest position was made in relation four subjects with “normal” to the most closed (intercuspal) position. These measurements were made after the removal of the reference fork which is a period of rest before the entry of food. The subjects were not aware that any rest position measurements were being recorded. The vertical opening in relation to the intercuspal position at this rest position ranged from 0.086 to 0.234 inch with an average of 0.155 inch (4.0 mm.). The distance rearward ranged from 0.005 to 0.059 inch with an average of 0.035 inch (0.9 mm.) . The interocclusal distance at the central incisor, measured during the pronunciation of the letter “M,” was on the average 0.040 inch less open than after the “bite” fork removal and 0.090 inch anterior to the “bite” fork removal position.
614
Gibbs, Messerman,
Reswick,
and Derda
SAGITTAL VIEW
,
I23 Fig. 11. Paths of motion in the sagittal plane of the central incisor and right condyle during chewing show the condyle motion to be about 40 per cent of the amount of motion at thr central incisor. Therefore, the use of the letter “M” for establishing the interocclusal distance may be useful in reference to the vertical relation, but is too far forward to establish the anteroposterior relation. Paths of motion at the condyles. As shown in Fig. 11 (the directional arrows drawn by the computer tend to obscure motion paths in reproduction), there is considerable motion at the condyle during chewing. This motion amounts to about 40 per cent of the motion at the central incisor. As the jaw opens, the condyles move downward and forward. As the jaw closes, the condyles move upward and rearward. Typical condyle motion is further described in Fig. 12 which shows sagittal, frontal, and horizontal views in orthographic projection. These plots show about 0.060 inch (1.5 mm.) of total lateral motion (Bennett movement) present at thr: condyle. Since numerous chews were plotted, each individual path is not distinguishable. The closed position was quite repeatable and is labeled in this figure. The sagittal view in Fig. 12 is of particular interest since it shows about 0.070 inch ( 1.8 mm.) variation perpendicular to its path. The variation in the condylar orbits is investigated further in Fig. 13, which shows sagittal views of right and left condyle motion for four subjects. Arrow heads drawn 0.1 second after the beginning of closure show the closing paths to be posterior and inferior to the opening paths. projections To further investigate the motions at the condyles, orthographic into sagittal, frontal, and horizontal planes of one chew were plotted (Fig. 14) . The working condyle moved medially 0.025 inch (0.6 mm.) during the WFM. This medial movement during the WFM ranged from 0 to 0.042 inch with an occlusion. average of 0.017 inch (0.4 mm.) for the four subjects with a “normal” Closed position repeatability at the condyles was studied by recording the radius of a sphere to include 70 per cent of the closure positions for each condyle. By eliminating 30 per cent of the closures, those positions in which the jaw did not attain full closure at the central incisor are automatically discarded. These radii ranged from 0.01 to 0.06 inch. This small range is significant since it means the
Volume 26 Number 6
Functional
I
.5 Inch
movements
of the mandible
615
J
Scale
deft condyle Subject PL "Normal" Occlusion Chewing Soft Food
L
Fig. 12. Sagittal, chewing.
Closed Position
frontal,
and horizontal
condyle is not positioned at greatly jects with an obvious malocclusion.
views in orthographic
different
points
projection
of a condyle
during
along the fossae, even for sub-
DISCUSSION Jaw motion exhibited a working side condyle for most chews during the final part of the closing stroke. This working began with the central incisor 0.24 inch from closure on the average for subjects with a “normal” occlusion, indicating that this constraint aids in the control of closure in the intercuspal range (TFM) where tooth contact and pathologic forces can occur. This part of the final closing stroke is the WFM. The medial movement during closure is greatest at the central incisor. The medial movement at the working condyle during the WFM of four of the subjects with “normal” occlusion ranged from 0 to 0.042 inch. The average was 0.017 inch (0.4 mm.) . Therefore, during the WFM, the working condyle appears to be stationary in the sagittal view only. In 1908 Bennett’* reported that the condyle for one subject moved laterally about 0.12 inch for lateral protrusive gliding of the teeth. The actual presence of a Bennett type of movement during chewing has been controversial for many years. In a cinefluorographic study of one subject, Landall found no lateral movement
616
Gibbs,
Messernlan,
Reswick,
and Derda
Y!?? ’ I--
.I. I’rosthet. Drrrmhrr.
Lkut. 19il
SC8.k
1~~
-2 ’
b
BLTSS3(1,21!7'0,750) "Normal" Occlusion Scft Food
CWTm (l,h700,700) Malocclusion Soft Food
I'BTlSh (1,9~,1160) Malocclusion Soft Food
wTlS5 (1,2120,380)
RIGHTCONDOLE (Non-Working) Fig. 13. Sagittal views of right and left condyles second after the beginning the opening paths.
of closure
during show the closing
LEFT CONDYLE (Working) chewing. The arrow heads drawn paths to be posterior and inferior
0.1 to
at the condyles during closure. Landa’s study, however, may have been limited to chews of symmetrical condyle movement before swallowing instead of the usual closing pattern of a working and nonworking condyle. However, the presence of a medial movement during closure while chewing has been convincingly shown by this report and by others.lO, *z-14 Hildebrandl” reported a medial movement of the working side condyle of 0.040 to 0.080 inch. This is greater than the 0 to 0.040 inch movement reported here, since he included the total medial movement and did not limit it to the WFM. Hickey and associateP reported a 0.012 inch medial movement “during maintained contact in chewing” which corresponds to values reported here, and 0.029 to 0.062 inch total medial movement for one subject. They measured this movement by photographing a pin inserted into the condyle. In the sagittal view, their condyle pin moved downward and forward as the teeth came into closure, appearing to be contradictory to our findings of a
Volume 26 Number 6
Functional
L
.s Inch Scale
movements
of the mandible
617
1
Braced (Working) Condyle Subject HFTlS5 (1,3232,100) ~U0rnra1~~ Occlusion Chewing Soft Food
Fig. 14. Sagittal, frontal, and horizontal views in orthographic projection of a working side condyle during chewing. A 0.025 inch medial movement occurred during the working functional movement. The arrow heads were drawn by the computer 0.1 second after the beginning of closure. closure position at the most upward and rearward position on the condyle path. These seemingly different findings are not contradictory however; the difference occurred because our paths were measured for a point at the approximate center of the condyle (calculated by computer from motion of three other jaw points), while their pin movement measurements were made lateral to the condyle. When the nonworking condyle moved upward and rearward about a “center of rotation” within the working side condyle, lateral points, such as a pin in the condyle, would move downward and forward. The sagittal view of the condyle paths is of particular interest, since it usually shows the closing orbits inferior and rearward to the opening orbits. Similar findings can be seen in paths of motion described by Koivumaa.s This may occur because of the difference in the medial-lateral position of the condyles during opening and closing movements. Another possibility is that these paths are indications of forces applied at the condyles. If this is true, the closing path lying inferior and rearward to the opening path, as reported here, would indicate an upward
618
Gibbs, Messerman,
Reswick,
and Derda
j.
Prosthet. December.
Dent. 1971
force on the condyle rather than a downward force as is usually supposed. Sitrcr: there is no anterior movement of the condylcs about the teeth at final closure for most subjects (the important exception \vas C, G., with heavy contact on ~3 fixed partial denture), the force at final closure at the condyles appears to brs small, if any. Perhaps the posterior teeth protect the temporomandibular joint fror~~ strong forces. If the vertical dimension of the posterior teeth becomes too short in relation to the vertical dimension of the anterior teeth: the temporomandibulat joint pain syndrome sometimes results. An equilibrium analysis of the; ,;a\\ 11) Frankel and Burstein’” shobvs that force need not be transmitted at th
Volume 26 Number 6
that jaw motion occlusal health.
Functional is affected
by the occlusion
movements and may
of the mandible
be useful
619
in diagnosing
SUMMARY Starting from the closed position, a typical motion of the mandible can be summarized as follows: Both condyles begin the opening immediately downward and forward. Early in the closing stroke, the entire mandible moves laterally. The working side (lateral) condyle moves upward and rearward and reaches its terminal position at the most vertical rearward position of its path before the teeth approach each other far enough to intercuspate. This working side condyle appears to be nearly stationary in the sagittal view for the remaining part of the closing stroke, which is termed the Working Functional Movement (WFM) . During the WFM, the working side condyle moves medially to its closed position, while the nonworking side condyle goes upward and laterally to its closed position. The food is usually on the same side as the working side condyle. The paths of motion of the condyles are quite similar for subjects with “normal” occlusions and malocclusions. The closed position repeatability is similar, ranging from 0.01 to 0.06 inch. This is in contrast to the paths of motion of the central incisor where differences among subjects with “normal” and malocclusion are easily detected. Of particular interest is the fact that for a higher percentage of chews, the central incisor remains motionless at closure for more subjects with “normal” occlusion than for subjects with malocclusions. CONCLUSIONS The presence of a working side condyle during typical chewing, as described in this report, is an important constraint which aids in the control of closure in the intercuspal range where tooth contacts and resulting forces can occur. This constraint is significant for functional articulator design since it specifies two of the six degrees of freedom. A mechanism which coordinates the medial movement of the working condyle, with the upward, rearward lateral path of the nonworking condyle and with the medial, upward path of the central incisor, could complete the functional articulator. Finally, the measuring instrumentation used in this study apparently did not significantly affect the chewing motions, since the basic motion was typical regardless of large influences such as various test foods and different types of occlusion. David C. Cannon, MS., designed and constructed the measuring instrumentation. Computer programming of the jaw motion data was performed by Thomas G. Szymanski, Edward Janecek, Bob Lattie, and Neal Nomiyama. Mouth appliances were constructed by Paul J. Yungmann.
References 1. Cannon, D. C., Reswick, J. B., and Messerman, T.: Instrumentation for the Investigation of Mandibular Movements, Case Institute of Technology, E. D. C. Report No. EDC 4-64-8. 2. Gibbs, C. H., Reswick, J. B., and Messerman, T.: The Case Gnathic Replicator for the Investigation of Mandibular Movements, Case Institute of Technology, E. D. C. Report No. EDC 4-66-14.
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Gibbs, Messerman, Reswick, ancl I&r&
3. Gibbs, C. H., Reswick, J. B., and Messerman, T.: Functional Movements of the Mandible, Case Western Reserve University, E. D. C. Report No. EDC 4-69-24. 4. Messerman, T.: A Means for Studying Mandibular Movements, J, PROSTHI:T. DENT, 17: 36-43, 1967. 5. Messerman, T., Reswick, J. B., and Gibbs, C. Ii.: Investigation of Functional Mandibular Movement, Dent. Clin. North Am. 13: 629-642, 1969. 6. Messerman, T.: A Concept of Jaw Function with Related Clinical Application, .j PROSTHET. DENT. 13: 135, 1963. Glossary of Prostho7. The Nomenclature Committee, Academy of Denture Prosthetics: dontic Terms, ed. 3, J. PROSTHET. DENT. 20: 443-480: 1968. 8. Koivumaa, K.: Cinefluorographic Analysis of the Masticatory Movements of the Mandible, Suom. Hammaslaak. Toim. 57: 306-368, 1961. 9. Schweitzer, J. M.: Masticatory Functions in Man, J. PROSTHET. DENT. 12: 262-291, 1962. 10. Ulrich, J.: The Human Temporomandibular Joint: Kinematics and Actions of the Masticatory Muscles, J. PROSTHET. DENT. 9: 399-406, 1959 (reprinted from his original publication of 1896). 11. Landa, J. S.: A Critical Analysis of the Bennett Movement, Part I, J. PROSTHET. DEXI 8: 709-726, 1958. 12. Bennett, N. G.: A Contribution to the Study of the Movements of the Mandible, Pro<:. Roy. Sot. Med. (odont sect.) I (3): 79-98. 1908. 13. Hildebrand, G. Y.: Studies in the Masticatory Movements of the Human Lower jaw, Skand. Arch. Physiol. Suppl. 61, 1931. 14. Hickey, J. C., Allison, M. L., Woelfel, J. B., Boucher, C. O., and Stacy. R. W.: Man dibular Movements in Three Dimensions, J. PROSTHET. DENT. 13: 72-92, 1963. 15. Frankel, V. H., and Burstein, A. H.: Orthopaedic Biomechanics, Philadelphia, 1969, Lea & Febiger, Publishers, pp. 19-22. 16. Page, H. L.: Temporomandibular Joint Physiology and Jaw Synergy, Dent. Dig. 60: 54-59, 1954. 17. Schweitzer, J. M.: Masticatory Function in Man, J. PROSTHET. DENT. 11: 625-647, 1961. 18. Graf, H., and Zander, H. A.: Tooth Contact Pattern in Mastication, J. PROSTHET. DEN.I’. 13: 1055-1066, 1963. 19. Pameijer, N. H., Glickman, I., and Roeber. F. W.: Intra-occlusal Telemetry. Part II. Registration of Tooth Contacts in Chewing and Swallowing, J. PROSTHET-. DENT. 19: 151-159, 1968. Acta. Odont. Stand. 24: Suppl. 44: 1966. 20. Ahlgren, J.: Mechanism of Mastication, 21. Ahlgren, J.: Pattern of Chewing and Malocclusion of Teeth, Acta. Odont. Stand, 25: 3-14, 1967. 22. Bewersdorff, H. J,: Electrognahographie Elektronische dreidimensionale Messung und Registrierung von Kieferbewegungen, Odontol. Tidskr. 77, 1969. 23. Yamashita, A.: Electrophysiological Studies on the Masticatory System, a paper presented to the American Equilibration Society, Feb. 1, 1968. DRS. GIBBS AND DERD~: ENGINEERING DESIGN CENTER CASE WESTERN RESERVE T.JNI~ERSITY CLEVELAND, OHIO 44106 DR. RESWICK : RANCHO Los AMIGOS DOWNYSY, CALIF.
HOSPITAL