- Email: [email protected]
More on the Bennett movement
MORE ON THE BENNETTMOVEMENT RAYMOND COHEN,
D.D.S.
New York? N. Y.
I
1908, BENNETT~ reported the results of an experiment he performed in order to study and evaluate the movements of the mandible. Of his entire experiment, the part the dental profession remembers is that portion where Bennett describes a lateral shift of the condyle in any lateral excursion of the mandible. This is known today as the Bennett movement. N
Landas has spent much time and effort in trying to disprove this contention of Bennett’s. The movement that Bennett describes is merely a statement of a fact. It is not possible for the mandible to move laterally without either one or both condyles to move with a lateral component of motion. The entire mandible is a solid body from condyle to condyle. It is inconceivable that the mandible can move laterally without some lateral movement of either one or both condyles. The fact that Landa has not been able to see this indicates either that his experiments were inadequate or that his observations were incorrect. Landa interpreted only half of what Bennett said about the movement of the condyle. Bennett showed that it was not only the condyle on the working side that moved laterally during lateral excursion of the mandible but that there is a lateral movement of the condyle on the balancing side. This latter point was completely ignored in Landa’s study. Landa, in his conclusions, takes issue with the use of the word “considerable” by Bennett. In his article Bennett mentions the fact that in extreme lateral movement of the condyle it (the condyle) moved 3 mm. This is “considerable” to Bennett. To others, 3 mm. may not be “considerable.” Draw a triangle with two equal sides and one shorter side to represent the mandible (Fig. 1) . Let the terminals of the shorter side represent the centers of rotation of each of the condyles A and B. Let the other point of the triangle represent a point in the mandible in, the incisor area, C. XY is a straight line passing through C which is perpendicular to the hinge axis AB. The point C if moved to X would represent a straight protrusive movement of the mandible. AE and BF are straight lines drawn parallel to XY and pass through points A and B, respectively. These lines, AE and BF, represent a straight protrusive movement of condyles A and B. Move incisor point C in any direction laterally away from the line XY; for example, to point D. (Point C on the mandible, in lateral movement, always moves more or less forward.) In order for the incisor point. C to move to D, one of several things occurs at points A and B: Received
for
publication
Oct.
24,
1958. 788
Volume 9 Number 5
BENNETT
7s9
MOVEMENT
1. If there is pure rotation at B, A will move forward and to the right ; thus, condyle B will exhibit no Bennett movement but condyle A will. 2. If condyle B moves directly to the right, condyle A will move forward and to the right. Thus, both condyles will execute the Bennett movement. 3. If condyle B moves directly forward, condyle A will move forward and to the right. Condyle B does not have a Bennett movement but A does. While this type of movement is a possibility, it is not very likely to occur. In the many condylar registrations I have recorded I have seen this type of movement very seldom. 4. If B moves backward and to the right, A will move forward and to the right. Thus, both condyles execute a Bennett movement.
x
Fig. I.-A
diagrammatic
representation
of man&bular
motion in a horizontal
plane.
Using the diagram (Fig. 1)) it is not possible to move the triangle ABC by moving point C to point D without either or both points A and B leaving lines AE and BF. Therefore, there must be a lateral movement of one or both condyles in any lateral movement of the mandible. Since the mandible is a solid body of bone from condyle to condyle, it is physically impossible for the mandible to move laterally without causing one or both condyles to move with a lateral component of motion (Bennett movement). The significance of the Bennett movement to dentistry and to humanity lies in the fact that it is the movement of the mandible occurring during mastication. It is a factor that influences the relationship of the mandible to the maxillae at the time when the greatest amount of muscular force is applied to the teeth.* It is *Granger,
E. R.: Personal communication.
790
COHEN
J. Pros. Den. Sept..Oct., 1959
for this reason that it is so very important to reproduce the Bennett movement. It has been shown that.the path of movement of the condyle is immutable,3 and thanks to McCollum4 and the Gnathological Society it is possible to record and reproduce exactly the various paths of movement of the condyle-including the Bennett movement REFERENCES
1. Bennett, N. G.: A Contribution to the Study of the Movements of the Mandible, J. PROS. DEN. 8:41-54, 1958. 2. Landa, J. S.: A Critical Analysis of the Bennett Movement, J. PROS. DEN. 8:709-726, 865-879, 1958. 3. Cohen, R.: The Relationship of Anterior Guidance to Condylar Guidance in Mandibular Movement, J. PROS. DEN. 6:758-767, 1956. 4. McCollum, B. B.: A Research Report. Fundamentals Involved in Prescribing Restorative Dental Remedies, D. Items Interest 61:522-530, 641-648, 724-736, 852-863, 942-950, 1939. 1350 BROADWAY NEW YORK 18, N. Y.
D.D.S.
New York? N. Y.
I
1908, BENNETT~ reported the results of an experiment he performed in order to study and evaluate the movements of the mandible. Of his entire experiment, the part the dental profession remembers is that portion where Bennett describes a lateral shift of the condyle in any lateral excursion of the mandible. This is known today as the Bennett movement. N
Landas has spent much time and effort in trying to disprove this contention of Bennett’s. The movement that Bennett describes is merely a statement of a fact. It is not possible for the mandible to move laterally without either one or both condyles to move with a lateral component of motion. The entire mandible is a solid body from condyle to condyle. It is inconceivable that the mandible can move laterally without some lateral movement of either one or both condyles. The fact that Landa has not been able to see this indicates either that his experiments were inadequate or that his observations were incorrect. Landa interpreted only half of what Bennett said about the movement of the condyle. Bennett showed that it was not only the condyle on the working side that moved laterally during lateral excursion of the mandible but that there is a lateral movement of the condyle on the balancing side. This latter point was completely ignored in Landa’s study. Landa, in his conclusions, takes issue with the use of the word “considerable” by Bennett. In his article Bennett mentions the fact that in extreme lateral movement of the condyle it (the condyle) moved 3 mm. This is “considerable” to Bennett. To others, 3 mm. may not be “considerable.” Draw a triangle with two equal sides and one shorter side to represent the mandible (Fig. 1) . Let the terminals of the shorter side represent the centers of rotation of each of the condyles A and B. Let the other point of the triangle represent a point in the mandible in, the incisor area, C. XY is a straight line passing through C which is perpendicular to the hinge axis AB. The point C if moved to X would represent a straight protrusive movement of the mandible. AE and BF are straight lines drawn parallel to XY and pass through points A and B, respectively. These lines, AE and BF, represent a straight protrusive movement of condyles A and B. Move incisor point C in any direction laterally away from the line XY; for example, to point D. (Point C on the mandible, in lateral movement, always moves more or less forward.) In order for the incisor point. C to move to D, one of several things occurs at points A and B: Received
for
publication
Oct.
24,
1958. 788
Volume 9 Number 5
BENNETT
7s9
MOVEMENT
1. If there is pure rotation at B, A will move forward and to the right ; thus, condyle B will exhibit no Bennett movement but condyle A will. 2. If condyle B moves directly to the right, condyle A will move forward and to the right. Thus, both condyles will execute the Bennett movement. 3. If condyle B moves directly forward, condyle A will move forward and to the right. Condyle B does not have a Bennett movement but A does. While this type of movement is a possibility, it is not very likely to occur. In the many condylar registrations I have recorded I have seen this type of movement very seldom. 4. If B moves backward and to the right, A will move forward and to the right. Thus, both condyles execute a Bennett movement.
x
Fig. I.-A
diagrammatic
representation
of man&bular
motion in a horizontal
plane.
Using the diagram (Fig. 1)) it is not possible to move the triangle ABC by moving point C to point D without either or both points A and B leaving lines AE and BF. Therefore, there must be a lateral movement of one or both condyles in any lateral movement of the mandible. Since the mandible is a solid body of bone from condyle to condyle, it is physically impossible for the mandible to move laterally without causing one or both condyles to move with a lateral component of motion (Bennett movement). The significance of the Bennett movement to dentistry and to humanity lies in the fact that it is the movement of the mandible occurring during mastication. It is a factor that influences the relationship of the mandible to the maxillae at the time when the greatest amount of muscular force is applied to the teeth.* It is *Granger,
E. R.: Personal communication.
790
COHEN
J. Pros. Den. Sept..Oct., 1959
for this reason that it is so very important to reproduce the Bennett movement. It has been shown that.the path of movement of the condyle is immutable,3 and thanks to McCollum4 and the Gnathological Society it is possible to record and reproduce exactly the various paths of movement of the condyle-including the Bennett movement REFERENCES
1. Bennett, N. G.: A Contribution to the Study of the Movements of the Mandible, J. PROS. DEN. 8:41-54, 1958. 2. Landa, J. S.: A Critical Analysis of the Bennett Movement, J. PROS. DEN. 8:709-726, 865-879, 1958. 3. Cohen, R.: The Relationship of Anterior Guidance to Condylar Guidance in Mandibular Movement, J. PROS. DEN. 6:758-767, 1956. 4. McCollum, B. B.: A Research Report. Fundamentals Involved in Prescribing Restorative Dental Remedies, D. Items Interest 61:522-530, 641-648, 724-736, 852-863, 942-950, 1939. 1350 BROADWAY NEW YORK 18, N. Y.