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Comparison of two methods for measurement of immediate Bennett shift
TEMPOROMANDIBULAR
JOINT
l
OCCLUSION
SECTION EDITOR GEORGE A. ZARB
ComParison of two methods immidiate Bennett shift T. F. Lundeen,
M.S., D.M.D.,*
University of North Carolina,
and F. Mendoza,
School of Dentistry,
for measurement
of
M.A.**
Chapel Hill, N.C.
I
n 1908 a British dental researcherobservedthat the mandibular condylestranslate toward the working side during jaw movements,a movement now referred to as the Bennett shift.’ The most popular semiadjustable articulators in use today (Hanau, Teledyne Hanau, Buffalo, N.Y.; Dentatus, Almore International Inc., Portland, Ore.; and Whip Mix, Whip-Mix Corp., Louisville, Ky.) are capableof producing a lateral shift of the condyle on the working side with an effect that can be illustrated graphically. Fig. 1 illustrates pure rotational movement to the right condyle. As a result the right condyle translatesanteriorly by following the arc of a circle with a diameter equal to the intercondylar width. The angle (sometimescalled the Bennett angle) ABC is approximately 7.5 degreesfor a 110 mm diameter and 25 mm maximum anterior translation. Fig. 2 showsthe result of a lateral shift. The working condyle has shifted away from the midline and produced a correspondingshift in the final position of the translating condyle. Note the new position of point c in Fig. 2. It is a commonassumptionthat the actual path followed by the translating condyle is a straight line as traced by the dashedline bc in Fig. 2. Note how the Bennett angle abc is increased; this is often called a progressiveBennett shift (PBS).’ It has been demonstrated that this straight-line movement rarely occurs.3-5 Measuring the Bennett angle at maximum lateral movementdoesaccount for a shift but provides no information on when and how it occurs.6 There are available at least two semiadjustable articulators that can approximate actual Bennett shift (Denar, Denar Corp., Anaheim, Calif., and Whip Mix). Both articulators are basedmechanically on the assumptionthat all the lateral shift occursimmediately (immediate Bennett shift [IBSJ) and the remaining movement is essentially an arc of a circle. The differencesamong PBS, IBS, and actual jaw movementsare
*Assistant Professor, Operative Dentistry. **Dental student.
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
center
of rotetion i
Right
110 m m radius
LOfl
Fig. 1. Geometric construction of pure rotational lateral jaw movement showing arc of nonworking condyle.
e
: bi Right
shifted 110 m m mdius
position .
\ .
Left
Fig. 2. Geometric construction of a combined shift of center of rotation and rotation during lateral jaw movement. This results in a new final position (c) of working condyle. illustrated in Fig. 3. Note that the approximated IBS exceedsthe experimentally observedshift near centric occlusion. The differencesbetweenPBS and IBS are important in the nonworking movementson the molar teeth.’ The
243
LUNDEEN
Bennett
[//jP
obsened
Bennett
approximated
shift
immediate
Bennett
shift
pathway of the distofacial cusp tip of the mandibular first molar is drawn over the surface of the maxillary first molar antagonist (Fig. 4). For the same amount of total shift, the IBS pathway is more medial than the PBS pathway. The cross-hatched area betweenthe two pathways is an area of potential nonworking (balancing) contact. It is believed that this contact is undesirable.RIn addition, it is noted that castings made on articulators with PBS capability frequently demonstrate nonworking contactsintraorally that could not be made on the articulator. Therefore, it seemsthat IBS capability could be useful in the elimination of nonworking contacts prior to intraoral adjustment of the casting. This article addressesthe question of how IBScapable articulators can be best adjusted for this function. The simplest and most familiar method is to make interocclusal records in extreme lateral jaw movementpositions.The recordsare then put between the mounted casts,and the walls of the condylar boxes are adjusted appropriately. An alternative method is to measurethe jaw movement on the hinge axis over the surface of the skin in front of the ear.
AND
METHODS
Nine asymptomatic patients with good occlusions were selected. At the first appointment irreversible hydrocolloid (Jeltrate, L. D. Caulk Co., Milford, Del.) impressionsof both dental arches were made, rinsed, and poured immediately in die stone (Glastone, Ranson and Randolph Co., Toledo, Ohio). Earpiece facebow (Whip-Mix Corp.) and wax centric relation records (Articulating Wax, Mizzy Inc., Clifton Forge, Va.) were made and used to mount the casts on an articulator (Whip Mix 8300, Whip-Mix Corp.) according to the manufacturer’s directions. At a second appointment IBS was measuredextraorally by use of the Flag System (Almore International Inc.) and 244
MENDOZA
shift
Fig. 3. Possible alternative pathways of movement of nonworking condyle from intercuspal position to final shifted position.
MATERIAL
AND
Fig. 4. Effect of Bennett shift on surface of maxillary right first molar. Immediate Bennett shiBt (IBS) pathway lies medial to progressive .Bennett shift (PBS) pathway. Cross-hatched area between two pathways is area of potential nonworking interferences.
Hinge Axis Recorder System (Almore International Inc.) (Fig. 5). The flags and hinge axis recorder were attached to the teeth by clutches with a heavy silicone impression putty, Citricon (Sybron/Kerr, Romulus, Mich.). .The hinge axis wis located and used as a starting reference for all measurements. Eccentric movement was guided with firm pressure directed medially at the angle of the mandible. This movement was repeated several times until a consistentrecording could be made. The recordings were made on the surface of the flag covering the translating condyle. A loose-fitting pin was placed in the hinge axis locator, and a rubber stopper was zeroed over the hinge axis position. A limited protrusive movement of the translating condyle was made with firm, medially directed pressureover the angleof the mandible. The movement of the pin was measuredto the nearest 0.1 mm with a Boley gauge. After the extraoral measurements,interocclusalrecords were made by the sametechnique but at the extreme limits of lateral movement. These were recorded in a polyether impressionmaterial (Ramitec, Premier Dental Products Co., Norristvwn, Pa.) and plastic record trays (Superbite, Harry J. Bosworth Co., Chicago, Ill.). The patient applied heavy medial pressure at the angle of the mandible for the duration of the set. The recording of the IBS from the interoeclusal records was obtained from the articulator after it was adjusted.These were recorded to the nearest0.25 mm,
RESULTS
AND
DISCUSSION
The results are summarized in Table I. The extraoral measurementswere consistently larger by approximately 0.5 mm. These results were significant at p = .05 by paired t-tests. FEBRUARY
1984
VOLUME
51
NUMBER
2
IMMEDIATE
BENNETT
SHIFT
MEASUREMENT
Fig. 5. Experimental apparatus for measurement of Bennett shift over nonworking condyle. Hinge axis was located prior to all measurements.
In all patients the interocclusal records involved tooth contact. As the teeth came into progressively greater contact, the condyles were progressively centered in the fossa with respect to the medial-lateral axis. Therefore, the degreeand especially the position of tooth contact decreasedthe amount of Bennett shift recorded in an interocclusal record. The material used was soft and offered no resistanceto closure during the setting process.We believe that patients tend to close the jaws progressively during the time required for the material to set; this reducesthe total IBS measurement. It has been noted that extreme lateral jaw shifts are recorded when patients bite very hard food.6 Perhaps very hard but indentable occlusal recording materials might more effectively measureIBS. The clutches were attached to the teeth by a silicone impression putty. This was a reasonably stable arrangement, but it did cause some problems. Any movement during setting causedthe clutch to be loose and required replacement. Disposable clutches and quick-set plaster are recommendedas better alternatives. All clutches increasethe vertical dimensionsand prevent tooth contact. The extraoral measurement had one clear advantage. The movements were visible and repeatable. Often the patients required some training to obtain adequate lateral jaw movement. Visibility and repeatability proved to be essential to obtain a consistent measurement.Interocclusal records do not allow any verification that what they measure has in fact been recorded. All the interocclusal records in the present study were made after “training” with extraoral measurement apparatus. This was necessarybecausevolTHE
JOURNAL
OF PROSTHETIC
DENTISTRY
Table I. Immediate Bennett shift
Right Right Left Left
extraoral intraoral extraoral intraoral
Average men.
N
I
Sx
9 9
1.66 1.04
1.29 0.63
9 1.50 9 0.96
1.16 0.74
age 24.7 years.
Results
1 1
Sex of patients;
7
df; t = 3.2;
7 df; t = 2.7;~
three
women
p = .05
= .05
and six
untary lateral movementstend to be lessthan guided lateral ones.9 The manufacturer recommendsallowing only 3 mm of anterior translation, but we allowed more in the present study. This may have led to inflated measurements.
SUMMARY IBS was measured by an intraoral interocclusal record and an extraoral method. The extraoral method gave significantly greater values statistically. Although more time consuming,the extraoral method provided a means of verification that is not obtainable by interocclusal records. REFERENCES 1. 2. 3.
Bennett, N. G.: A contribution to the study of the movement of the mandible. J PROSTHET DENT 8~41, 1958. Guichet, N. F.: Procedures of Occlusal Treatment. A Teaching Atlas. Anaheim, Calif., 1969, Denar Corp. Aull, A. E.: Condylar determinants of occlusal patterns. J PROSTHET
DENT
15:826,
1965.
245
LUNDEEN
4.
5.
6.
Lundeen, H. C., and Wirth, C. G.: Condylar movement patterns engraved in plastic blocks. J PROSTHET DENT 30~866, 1973. Lundeen, H., C., Shyrock, E. F., and Gibbs, C. H.: An evaluation of mandibular border movements: Their character and significance. J PROSTHET DENT 40~442, 1978. Hickey, J. C., Lundeen, H. C., and Bohannan, H. M.: A new articulator for use in teaching and general dentistry. J PROSTHET
7.
8.
DENT
l&425,
9.
AND
MENDOZA
tals of Fixed Prosthodontics. Chicago. 1% it Quintessence Publishing Co.. Inc. Simonet, P. F., and Clayton, J. A.: Inffuence of TMJ dysfunction on Bennett movement as recorded by a modified pantograph. Part III: Progress report on c-lrnical study. J PROSTHET
DENT
46~652.
1981.
Refmnt requests to:
1967.
Gibbs, C. H., Lundeen, H. C., Mahan, P. E., and Fujimoto, S.: Chewing movements in relation to border movements at the first molar. J PROSTHET DENT 45~308, 1981. Shillingburg, H. T., Hobo, S., and Whitsett, L. D.: Fundamen-
ARTICLES
DR.
THOMAS
F. LWDEEN
UNIVERSITY OF NORTH CAROLINA SCHOOL OF DENTISTRY 209 H CHAPEL HILL 1 NC 27514
TO APPEAR IN FUTURE ISSUES
Sterilization
of complete dentures with sodium hypochlorite
Robert W. Rudd, D.D.S., M.S., E. Steve Senia, D.D.S., M.S., Ferne K. McCleskey, Ernest D. Adams, Jr., M.S.
Experimental
occlusal discrepancies and nocturnal
B.S., and
bruxism
J. D. Rugh, Ph.D., N. Barghi, D.D.S., and C. J. Drago, D.D.S., M.S.
Comparative teeth
observations
of the use of cusp and zero-degree posterior
N. Sridhar Shetty, D.D.S.
Dycak Physical properties Vered Shorer, D.M.D.,
and resistance to amalgam condensation
Zvia Hirschfeld,
Errors of oblique cephalometric edentulous mandible
D.M.D.,
and Rafael Grajower,
radiographic
Ph.D.
projections of the
W. H. A. Steen, Drs.
Repairing
a crown-sleeve
Noah Stern, D.M.D.,
coping prosthesis. Part III
M.S.D., and Maya Zalkind,
D.M.D.
The effect of a corrugated channel on the retentive properties of an obturator-reinforced composite resin dowel-core system Anthony H. L. Tjan, Dr.Dent.,
D.D.S., Sung B. Whang, D.D.S., and Gary D. Miller,
Physical properties of a polycarboxylate tan&&Wride preparation Mitsuhiro
246
Tsukiboshi,
D.D.S., D.Med.Sc.,
cement containing
D.D.S.
a
and Yoshiaki Tani, D.D.S., D.Med.Sc.
FEBRUARY
1984
VOLlJlWE
51
NUMBER
2
JOINT
l
OCCLUSION
SECTION EDITOR GEORGE A. ZARB
ComParison of two methods immidiate Bennett shift T. F. Lundeen,
M.S., D.M.D.,*
University of North Carolina,
and F. Mendoza,
School of Dentistry,
for measurement
of
M.A.**
Chapel Hill, N.C.
I
n 1908 a British dental researcherobservedthat the mandibular condylestranslate toward the working side during jaw movements,a movement now referred to as the Bennett shift.’ The most popular semiadjustable articulators in use today (Hanau, Teledyne Hanau, Buffalo, N.Y.; Dentatus, Almore International Inc., Portland, Ore.; and Whip Mix, Whip-Mix Corp., Louisville, Ky.) are capableof producing a lateral shift of the condyle on the working side with an effect that can be illustrated graphically. Fig. 1 illustrates pure rotational movement to the right condyle. As a result the right condyle translatesanteriorly by following the arc of a circle with a diameter equal to the intercondylar width. The angle (sometimescalled the Bennett angle) ABC is approximately 7.5 degreesfor a 110 mm diameter and 25 mm maximum anterior translation. Fig. 2 showsthe result of a lateral shift. The working condyle has shifted away from the midline and produced a correspondingshift in the final position of the translating condyle. Note the new position of point c in Fig. 2. It is a commonassumptionthat the actual path followed by the translating condyle is a straight line as traced by the dashedline bc in Fig. 2. Note how the Bennett angle abc is increased; this is often called a progressiveBennett shift (PBS).’ It has been demonstrated that this straight-line movement rarely occurs.3-5 Measuring the Bennett angle at maximum lateral movementdoesaccount for a shift but provides no information on when and how it occurs.6 There are available at least two semiadjustable articulators that can approximate actual Bennett shift (Denar, Denar Corp., Anaheim, Calif., and Whip Mix). Both articulators are basedmechanically on the assumptionthat all the lateral shift occursimmediately (immediate Bennett shift [IBSJ) and the remaining movement is essentially an arc of a circle. The differencesamong PBS, IBS, and actual jaw movementsare
*Assistant Professor, Operative Dentistry. **Dental student.
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
center
of rotetion i
Right
110 m m radius
LOfl
Fig. 1. Geometric construction of pure rotational lateral jaw movement showing arc of nonworking condyle.
e
: bi Right
shifted 110 m m mdius
position .
\ .
Left
Fig. 2. Geometric construction of a combined shift of center of rotation and rotation during lateral jaw movement. This results in a new final position (c) of working condyle. illustrated in Fig. 3. Note that the approximated IBS exceedsthe experimentally observedshift near centric occlusion. The differencesbetweenPBS and IBS are important in the nonworking movementson the molar teeth.’ The
243
LUNDEEN
Bennett
[//jP
obsened
Bennett
approximated
shift
immediate
Bennett
shift
pathway of the distofacial cusp tip of the mandibular first molar is drawn over the surface of the maxillary first molar antagonist (Fig. 4). For the same amount of total shift, the IBS pathway is more medial than the PBS pathway. The cross-hatched area betweenthe two pathways is an area of potential nonworking (balancing) contact. It is believed that this contact is undesirable.RIn addition, it is noted that castings made on articulators with PBS capability frequently demonstrate nonworking contactsintraorally that could not be made on the articulator. Therefore, it seemsthat IBS capability could be useful in the elimination of nonworking contacts prior to intraoral adjustment of the casting. This article addressesthe question of how IBScapable articulators can be best adjusted for this function. The simplest and most familiar method is to make interocclusal records in extreme lateral jaw movementpositions.The recordsare then put between the mounted casts,and the walls of the condylar boxes are adjusted appropriately. An alternative method is to measurethe jaw movement on the hinge axis over the surface of the skin in front of the ear.
AND
METHODS
Nine asymptomatic patients with good occlusions were selected. At the first appointment irreversible hydrocolloid (Jeltrate, L. D. Caulk Co., Milford, Del.) impressionsof both dental arches were made, rinsed, and poured immediately in die stone (Glastone, Ranson and Randolph Co., Toledo, Ohio). Earpiece facebow (Whip-Mix Corp.) and wax centric relation records (Articulating Wax, Mizzy Inc., Clifton Forge, Va.) were made and used to mount the casts on an articulator (Whip Mix 8300, Whip-Mix Corp.) according to the manufacturer’s directions. At a second appointment IBS was measuredextraorally by use of the Flag System (Almore International Inc.) and 244
MENDOZA
shift
Fig. 3. Possible alternative pathways of movement of nonworking condyle from intercuspal position to final shifted position.
MATERIAL
AND
Fig. 4. Effect of Bennett shift on surface of maxillary right first molar. Immediate Bennett shiBt (IBS) pathway lies medial to progressive .Bennett shift (PBS) pathway. Cross-hatched area between two pathways is area of potential nonworking interferences.
Hinge Axis Recorder System (Almore International Inc.) (Fig. 5). The flags and hinge axis recorder were attached to the teeth by clutches with a heavy silicone impression putty, Citricon (Sybron/Kerr, Romulus, Mich.). .The hinge axis wis located and used as a starting reference for all measurements. Eccentric movement was guided with firm pressure directed medially at the angle of the mandible. This movement was repeated several times until a consistentrecording could be made. The recordings were made on the surface of the flag covering the translating condyle. A loose-fitting pin was placed in the hinge axis locator, and a rubber stopper was zeroed over the hinge axis position. A limited protrusive movement of the translating condyle was made with firm, medially directed pressureover the angleof the mandible. The movement of the pin was measuredto the nearest 0.1 mm with a Boley gauge. After the extraoral measurements,interocclusalrecords were made by the sametechnique but at the extreme limits of lateral movement. These were recorded in a polyether impressionmaterial (Ramitec, Premier Dental Products Co., Norristvwn, Pa.) and plastic record trays (Superbite, Harry J. Bosworth Co., Chicago, Ill.). The patient applied heavy medial pressure at the angle of the mandible for the duration of the set. The recording of the IBS from the interoeclusal records was obtained from the articulator after it was adjusted.These were recorded to the nearest0.25 mm,
RESULTS
AND
DISCUSSION
The results are summarized in Table I. The extraoral measurementswere consistently larger by approximately 0.5 mm. These results were significant at p = .05 by paired t-tests. FEBRUARY
1984
VOLUME
51
NUMBER
2
IMMEDIATE
BENNETT
SHIFT
MEASUREMENT
Fig. 5. Experimental apparatus for measurement of Bennett shift over nonworking condyle. Hinge axis was located prior to all measurements.
In all patients the interocclusal records involved tooth contact. As the teeth came into progressively greater contact, the condyles were progressively centered in the fossa with respect to the medial-lateral axis. Therefore, the degreeand especially the position of tooth contact decreasedthe amount of Bennett shift recorded in an interocclusal record. The material used was soft and offered no resistanceto closure during the setting process.We believe that patients tend to close the jaws progressively during the time required for the material to set; this reducesthe total IBS measurement. It has been noted that extreme lateral jaw shifts are recorded when patients bite very hard food.6 Perhaps very hard but indentable occlusal recording materials might more effectively measureIBS. The clutches were attached to the teeth by a silicone impression putty. This was a reasonably stable arrangement, but it did cause some problems. Any movement during setting causedthe clutch to be loose and required replacement. Disposable clutches and quick-set plaster are recommendedas better alternatives. All clutches increasethe vertical dimensionsand prevent tooth contact. The extraoral measurement had one clear advantage. The movements were visible and repeatable. Often the patients required some training to obtain adequate lateral jaw movement. Visibility and repeatability proved to be essential to obtain a consistent measurement.Interocclusal records do not allow any verification that what they measure has in fact been recorded. All the interocclusal records in the present study were made after “training” with extraoral measurement apparatus. This was necessarybecausevolTHE
JOURNAL
OF PROSTHETIC
DENTISTRY
Table I. Immediate Bennett shift
Right Right Left Left
extraoral intraoral extraoral intraoral
Average men.
N
I
Sx
9 9
1.66 1.04
1.29 0.63
9 1.50 9 0.96
1.16 0.74
age 24.7 years.
Results
1 1
Sex of patients;
7
df; t = 3.2;
7 df; t = 2.7;~
three
women
p = .05
= .05
and six
untary lateral movementstend to be lessthan guided lateral ones.9 The manufacturer recommendsallowing only 3 mm of anterior translation, but we allowed more in the present study. This may have led to inflated measurements.
SUMMARY IBS was measured by an intraoral interocclusal record and an extraoral method. The extraoral method gave significantly greater values statistically. Although more time consuming,the extraoral method provided a means of verification that is not obtainable by interocclusal records. REFERENCES 1. 2. 3.
Bennett, N. G.: A contribution to the study of the movement of the mandible. J PROSTHET DENT 8~41, 1958. Guichet, N. F.: Procedures of Occlusal Treatment. A Teaching Atlas. Anaheim, Calif., 1969, Denar Corp. Aull, A. E.: Condylar determinants of occlusal patterns. J PROSTHET
DENT
15:826,
1965.
245
LUNDEEN
4.
5.
6.
Lundeen, H. C., and Wirth, C. G.: Condylar movement patterns engraved in plastic blocks. J PROSTHET DENT 30~866, 1973. Lundeen, H., C., Shyrock, E. F., and Gibbs, C. H.: An evaluation of mandibular border movements: Their character and significance. J PROSTHET DENT 40~442, 1978. Hickey, J. C., Lundeen, H. C., and Bohannan, H. M.: A new articulator for use in teaching and general dentistry. J PROSTHET
7.
8.
DENT
l&425,
9.
AND
MENDOZA
tals of Fixed Prosthodontics. Chicago. 1% it Quintessence Publishing Co.. Inc. Simonet, P. F., and Clayton, J. A.: Inffuence of TMJ dysfunction on Bennett movement as recorded by a modified pantograph. Part III: Progress report on c-lrnical study. J PROSTHET
DENT
46~652.
1981.
Refmnt requests to:
1967.
Gibbs, C. H., Lundeen, H. C., Mahan, P. E., and Fujimoto, S.: Chewing movements in relation to border movements at the first molar. J PROSTHET DENT 45~308, 1981. Shillingburg, H. T., Hobo, S., and Whitsett, L. D.: Fundamen-
ARTICLES
DR.
THOMAS
F. LWDEEN
UNIVERSITY OF NORTH CAROLINA SCHOOL OF DENTISTRY 209 H CHAPEL HILL 1 NC 27514
TO APPEAR IN FUTURE ISSUES
Sterilization
of complete dentures with sodium hypochlorite
Robert W. Rudd, D.D.S., M.S., E. Steve Senia, D.D.S., M.S., Ferne K. McCleskey, Ernest D. Adams, Jr., M.S.
Experimental
occlusal discrepancies and nocturnal
B.S., and
bruxism
J. D. Rugh, Ph.D., N. Barghi, D.D.S., and C. J. Drago, D.D.S., M.S.
Comparative teeth
observations
of the use of cusp and zero-degree posterior
N. Sridhar Shetty, D.D.S.
Dycak Physical properties Vered Shorer, D.M.D.,
and resistance to amalgam condensation
Zvia Hirschfeld,
Errors of oblique cephalometric edentulous mandible
D.M.D.,
and Rafael Grajower,
radiographic
Ph.D.
projections of the
W. H. A. Steen, Drs.
Repairing
a crown-sleeve
Noah Stern, D.M.D.,
coping prosthesis. Part III
M.S.D., and Maya Zalkind,
D.M.D.
The effect of a corrugated channel on the retentive properties of an obturator-reinforced composite resin dowel-core system Anthony H. L. Tjan, Dr.Dent.,
D.D.S., Sung B. Whang, D.D.S., and Gary D. Miller,
Physical properties of a polycarboxylate tan&&Wride preparation Mitsuhiro
246
Tsukiboshi,
D.D.S., D.Med.Sc.,
cement containing
D.D.S.
a
and Yoshiaki Tani, D.D.S., D.Med.Sc.
FEBRUARY
1984
VOLlJlWE
51
NUMBER
2