Dentistry – Apparatus – Work support
Reexamination Certificate
2000-01-10
2001-09-11
Lucchesi, Nicholas D. (Department: 3732)
Dentistry
Apparatus
Work support
Reexamination Certificate
active
06287113
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an articulator that is used to reproduce human jaw movement, in particular articulation, when dental prostheses (for example, dentures etc. to replace lost teeth) are constructed.
2. Description of the Related Art
Previously known articulators will be described below, together with their limitations.
(1) What an Articulator is
The jaw performs the functions of eating and speaking etc. and, in order to achieve these functions, performs truly many different types of movement. Construction of dental prostheses is an important technique in dental treatment in order to recover lost function, and in this connection, it is important to have a good understanding and grasp of jaw movement. Thus, reproduction of jaw movement is indispensable in order to achieve good insertion of the dentures, good articulation of the upper and lower rows of dentures, and good chewing movement.
There is a considerable degree of individuality as regards the chewing movement of individuals. In order to construct good dentures, a device for reproducing jaw movement, in particular articulation, i.e. an articulator is indispensable, and a great amount of efforts is being made to develop these devices. However, an accurate full reproduction articulator corresponding faithfully to the jaw movement of individual persons has not yet appeared.
(2) Conditions for Articulation Reproduction
In reproducing (characterizing) the movement of any object, not only the jaw, the start and end positions of movement of the object should be characterized. Specifically, if the position prior to movement of an object K is K
0
and its position after the movement is K
1
, the change of position K
0
→K
1
constitutes the movement of the object K. If the jaw is thought of as a rigid body, the position of the rigid body as a whole i.e. the jaw is characterized by characterizing the positions of three points of the rigid body. Clinically, the three points A, B, C shown in
FIG. 26
of the accompanying drawings are employed for these three points, but this is for the sake of convenience, and any points on the rigid body including the jaw could be used. Referring to
FIG. 27
, if the positions prior to and after the movement are respectively indicated as A
0
, B
0
, C
0
and A
1
, B
1
, C
1
, the jaw movement can be reproduced by characterizing A
0
, A
1
, B
0
, B
1
and C
0
, C
1
(see the arrows in FIG.
27
).
(3) Terms Used to Describe Occlusion
Referring to
FIG. 28
, in dentistry, general terms such as front plane, side plane and horizontal plane are replaced by frontal plane, sagittal plane and occlusal plane, respectively. Also, the area where movement of the jaw occurs is termed the working side, and the opposite area is termed the non-working side (or balancing side). Although in recent years the term “balancing side” has tended to become obsolete, in this characterization, this side will be referred to as the “balancing side”.
The jaw consists of the maxilla and mandible and chewing is performed by articulation of the respective teeth. The maxilla is included in the skull, while the mandible is suspended by muscles and tendons from the cranium, so that only the mandible is moved. The mandible consists of the row of teeth, the body of mandible, and the condyles. In
FIG. 28
, the condyle at point A is the condyle on the movement side, and so is called the working side condyle, while the condyle at point B is called the balancing side condyle. In the middle of the mandible, i.e., the incisal region, the mesial point of central incisors on the left and right is called the incisal point, and the center point of the condyle is called the condylar point. Reproduction of chewing movement is characterized by the three points: left and right condylar points and the incisal point.
(4) Mandibular Movement
a) Incisal Path and Condylar Path
Mandibular movement is performed in five directions, namely, protrusively, laterally to left and right, opening and posteriorly. In this process, as shown in
FIG. 29
, movement of the condyle is regulated by the form of the associated joint cavity in which the condyle is accommodated. The line joining the left and right condylar points is called the “intercondylar axis”. When the two condyles perform sliding movement over the surfaces of the joint cavities, the incisal points can perform rotary movement about the occasional intercondylar axis. The loci of the movement of the condylar points and the incisal point are respectively called the condylar path and incisal path.
b) Protrusive Movement
When protrusive movement is performed, as shown in
FIGS. 29 and 30
, the condyles move anteriorly and downwards along the shape of the joint cavities. This is on average about 30 degrees (30°) with reference to the occlusal plane, and is called the inclination of sagittal condylar path during protrusive movement, abbreviated to the inclination of protrusive sagittal condylar path. The protrusive sagittal condylar path inclinations are often different between the left and right condyles. The incisal point likewise moves anteriorly and downwards, constrained by the shape of the incisors of the maxilla. The clinical reference value with respect to the occlusal plane is 10°.
c) Lateral Movement
As shown in
FIG. 31
, in the case of lateral movement (where the jaw moves to left or right), the balancing side condyle executes a large movement for what is only a slight movement of the working side condyle. Like the protrusive movement, the balancing side condyle executes anterior and downwards movement along the shape of the joint cavity; the inclination of sagittal condylar path when this movement happens is called the lateral sagittal condylar path inclination and is generally larger than the protrusive condylar path inclination, the difference of these angles being termed the Fischer angle (considered to be about 15° on average).
Also, during lateral movement, the working side condyle is known to move outwards in the working direction. This outward movement is called “Bennett movement” after the name of its discoverer. Since the mandible is unitary, if the working side condyle moves outwards, the balancing side condyle is pulled inwards. As a result, the balancing side condyle moves forward, downwards and inwards. The inwards angle with respect to the sagittal direction i.e. the angle of lateral condylar path is called the “Bennett angle”.
(5) Characterization of Mandibular Movement
If it can be characterized to what extent the three points (left and right condyles and incisor) move vertically, left/right and anteriorly/posteriorly, the entire mandibular movement can be characterized. Also, the direction of movement of a given point is the direction of the line of intersection of the two planes that characterize the direction of movement of that point. That is, two planes are necessary and sufficient in order to characterize the direction of movement of a given point.
Hereinbelow, the planes that characterize the three points (left and right condyles and incisor) will be described.
As already stated, the mandibular movement is effected in opening, protrusively, posteriorly, and laterally (working side and balancing side). Of these, mouth-opening movement is a movement to release occlusion, so this may be excluded from the requirements for the articulator. Also, if the characterizing plane for protrusive movement is used for posterior movement, it would be sufficient to obtain planes characterizing the three movements: protrusively, working side and balancing side. Since two planes are required for a single movement in respect of each point, reproduction of the three types of movement by each point requires six planes. Also, if the positions of the two condylar points are characterized, the left and right and anterior/posterior positions of the incisal points are relatively characterized from the two condylar points and the amount of vertical opening thereof is characterized by arbitrary choice of the technician/doctor or cont
Lucchesi Nicholas D.
McCormick Paulding & Huber LLP
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