Curve Spee - what is this?
What is the Spee curve. In order to answer this question, it is necessary to find out everything about occlusion.
What is occlusion?
Occlusion refers to any contacts of the lower and upper jaws. The modern concept of this term includes the interactions of chewing musculature, teeth, temporomandibular joints in dysfunction and function. The occlusal surface of natural teeth is considered to be part of the tooth surface from the top of the tubercle to the deepest point of the central fissure. It is characterized by anatomical features that are genetically adapted to the function of chewing food.
Elements of the occlusal surface
The following elements are present on the occlusal surface: the bases of the tubercles, their apices, additional and central fissures, rays, marginal fossae limiting the occlusal table, triangular racemes of the rays of the tubercles, crests. The inner slopes of the dental hillocks face the central fissure.
The concept of group contacts of the rows of teeth provides for the presence on the working side of the buccal premolar tubercles, canines, including molars of the lower and upper jaws. The balancing side excludes occlusal contacts, and at the same time the maxillary palatal tubercles stand against the mandibular buccal. When the lower jaw moves forward, the mesial rami of the lower cheek tubercles slide along the upper teeth of the distal rays, and the slopes of the lingual tubercles distal of the lateral upper teeth slide along the slopes of the mesial lateral lower teeth.
When performing excessive protrusive mandibular movements, characteristic erosion areas are formed on the upper teeth of the distal rays and the inferior tubercular mesial slopes of hard tissues on the surface of the lower vestibular and upper incisors of the palatine surface.
What is the Spee and Wilson curve? About this further.
How is chewing food?
In the case of lateral movements of the lower jaw, the rays of the outer lateral buccal tubercles of the lower teeth slip on the working side along the slopes of the inner upper buccal teeth, and the internal slopes of the inferior labial tubercles slide along the slopes of the outer palatine upper tubercles. There is an establishment of the same contact between the buccal tubercles of premolars and molars.
Fangs protect the hard tissues and periodontal teeth of the lateral teeth from excessive loads during chewing, and therefore, when manufacturing bridges, special attention is paid to stabilizing the prosthesis to avoid periodontal injury.
With symmetrical contact of canines in the lateral occlusions, a uniform load on the TMJ, teeth, chewing muscles and periodontium upon chewing is ensured. All this is provided by the Spee curve.
In the palatal( occlusal) surface of the upper canines and incisors from the distal and mesial sides, there are 2 marginal ridges connected by a dentate tubercle in the lower third of the tooth.
Between this tubercle and the middle of the edge of the incisor is a palatal median shaft, having grooves on both sides. The dental cusp is the most protruding part of the tooth, the place where occlusal contacts occur. This is the great curvature of the compensating curve of Heine.
Palatine tubercles of the upper and buccal lower chewing teeth are called basic, as they produce crushing food and determine the nature of movements within the occlusal mandible field, including the redistribution of the masticatory forces so that the main chewing load is received by the dental axle.
Why are occlusal curves needed?
Genital bumps of upper and lingual lower chewing teeth are called protective, not supporting. They are slightly in contact with antagonists in the central occlusion or, as some authors believe, they have no such contact. These knobs carry out the function of dividing food and creating on its slopes a sliding surface of antagonists, protecting the cheeks and tongue during chewing from getting them between the teeth. Deepening the Heine curve is necessary for a normal mastication of food.
Non-planar( spot) uniform, multiple contacts of antagonist teeth are the most favorable form of occlusion for the masticatory function that is created when modeling the occlusal surface. In this case, it is possible to carry out food processing of any consistency. The distribution of the masticatory pressure occurs throughout the tooth axis, with a minimal load on the periodontium, and with small point contacts, there is a decrease in the erasure of the masticatory planes. By contact of fissures and tubercles, the stability of the lower jaw is created with central occlusion according to the pestle principle in the mortar, including no obstacles for moving the lower jaw along the occlusal field. This is provided by the Spee curve( in the photo below you can see its schematic image).
If there are no teeth?
In the absence of teeth, that is, the loss of the occlusal surface, an occlusal plane is used to restore it, passing through three points: the vertices of the second lower molars( their distal-buccal tubercles) and the incisal point. This plane is used to establish the model of the lower jaw in the articulator, for example, using a balancer.
The occlusal surface of a row of teeth in the horizontal plane does not lie, it forms a sagittally directed curve: concave for the lower and convex for the upper jaw. Such a curve is called the Rhine curve or the occlusal sagittal curve. It is part of a circle whose center is approximately in the center of the orbit.
What else is remarkable about the Spee curve?
Also, in the opinion of Spee, the researcher and practitioner, the occlusal curve is completely connected with the articular path, since it together with the curve of a row of teeth is formed by one radius, and accordingly, the teeth and the joint head slide one circle forward and the steeper the slope of the articular path, theThe occlusal curve is more uniformly concave. Such assumptions, made by the scientist, met many objections. Other scientists argue that the occlusal curve can not be called a segment of a circle. In its continuation, the sagittal curve of Spee often passes below or above the articular path, and its center is not in the orbit. What is the need for a sagittal curve of occlusion?
With mandibular forward movement of the spine and downward, the joint head slides along the slope of the articular tubercle. Accordingly, the lower jaw( the posterior part of it) drops downwards and forms a gap in the region of the lateral teeth between the rows of teeth. The contact of the bumps of the lateral teeth is possible only if the masticatory surfaces of the teeth are located along the sagittal line. Following this teaching, the occlusal straight line is called of the compensation curve .
The radius is determined in 5.8-21.2 centimeters, the average value is 6.5-8.5 cm. The deepest point of the occlusal curve is the mesial tubercle of the lower first molar.
The article describes in detail the Spee curve.