What is the Spee curve. In order to answer this question, you need to find out everything about occlusion.
What is occlusion?
Occlusion is any contact between the lower and upper jaws. The modern concept of this term includes the interaction of chewing muscles, teeth, temporomandibular joints with dysfunction and function. The occlusal surface of natural teeth is the part of the tooth surface from the top of the tubercle to the deepest place of the central fissure. It is characterized by anatomical features that are genetically adapted for the function of chewing food.
Occlusal surface elements
The following elements are present on the occlusal surface: the bases of the tubercles, their vertices, additional and central fissures, slopes, marginal fossae, limiting the occlusal table, the ridges of the hillocks of the tubercles are triangular, ridges. The central fissure faces the inner slopes of the dental tubercles.
The concept of group contacts of the rows of teeth provides for the presence on the working side of the buccal premolar tubercles, fangs, including molars of the lower and upper jaws. The balancing side excludes occlusal contacts, and the maxillary palatine tubercles stand against the mandibular buccal. When the lower jaw moves forward, the mesial slopes of the lower buccal tubercles glide along the upper tooth distal slopes, and the slopes of the lingual tubercles distal lateral upper teeth glide along the slopes of the mesial lateral teeth.
When excessive protrusive mandibular movements are performed, characteristic areas of abrasion are formed on the upper teeth of the distal slopes and lower teeth of the 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 it further.
How is chewing food?
When making lateral movements with the lower jaw, the slopes of the outer lateral buccal tubercles of the lower teeth glide on the working side along the slopes of the upper upper cheek teeth, and the inner slopes of the lower tooth lingual tubercles glide along the slopes of the external palatine upper tubercles. The establishment of the eponymous contact of the buccal tubercles of premolars and molars occurs.
Fangs protect hard tissues and periodontal teeth from too large loads during chewing, and therefore, when making bridges, special attention is paid to stabilizing prostheses to avoid periodontal injury.
With symmetrical fang contacts in the lateral occlusions, a uniform load on the TMJ, teeth, masticatory muscles and periodontal during chewing is ensured. All this is provided by the Spee curve.
The palatine (occlusal) surface of the upper canines and incisors from the distal and mesial sides has 2 marginal ridges connected by a dental tubercle in the lower third of the tooth.
Between this tubercle and the middle of the incisal edge there is a palatine median roller having grooves on both sides. The protruding part of the tooth, the place where the occlusal contacts occur, is called the dental protuberance. This is the large curvature of the Spee compensation curve.
The palatine tubercles of the upper and buccal lower chewing teeth are called abutments, since they produce crushing of food and determine the nature of movements within the field of the occlusal lower jaw, including the redistribution of masticatory forces so that the main axis of chewing takes the dental axis.
Why are occlusal curves needed?
The buccal tubercles of the upper and lingual lower chewing teeth are called protective, not supporting. They slightly contact with antagonists in central occlusion or, as some authors believe, do not have such contact. These tubercles carry out the function of separating food and creating on their slopes a sliding surface for antagonists that protect the cheeks and tongue during chewing from getting them between the teeth. Deepening the Spee curve is necessary for normal chewing of food.
Non-planar (point) uniform, multiple contacts of antagonist teeth are the most favorable form of occlusion for chewing function, which is created when modeling the surface of occlusion. In this case, it is possible to conduct food processing of any consistency. The distribution of masticatory pressure occurs along the entire dental axis, with a minimal load on the periodontium, and with small point contacts, the erasure of the masticatory planes decreases. The contact of the fissures and tubercles creates stability of the lower jaw with central occlusion according to the principle of the pestle in the mortar, including no obstacles for moving the lower jaw along the occlusal field. This is ensured by the Spee curve (in the photo below you can see its schematic image).
If teeth are missing?
In the absence of teeth, that is, loss of the occlusal surface, an occlusal plane passing through three points is used to restore it: the tops of the second lower molars (their distal-buccal tubercles) and the incisor point. This plane is used to install the model of the lower jaw in the articulator, for example, using a balancer.
The occlusal surface of a number 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 a Spee curve or an occlusal sagittal curve. It is part of a circle whose center is approximately located in the center of the orbit.
What else is remarkable for the Spee curve?
Also, according to Spee, a researcher and practitioner, the occlusal curve is completely connected with the articular path, since it along with the curve of a number of teeth is formed by one radius, and accordingly, the teeth and articular head glide along the same circle forward and the steeper the slope of the joint path, the more uniform the occlusal curve is concave. Such assumptions made by the scientist met with many objections. Other scientists argue that the occlusal curve cannot 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.
Why is there a need for a sagittal occlusion curve?
With the mandibular movement forward and downward, the articular head glides along the slope of the articular tubercle. Accordingly, the lower jaw (its posterior part) goes down and forms a gaping in the region of the posterior teeth between the rows of teeth. Contact of the tubercles of the posterior teeth is possible only if the chewing surfaces of the teeth are located along the sagittal line. Following this teaching, the occlusal line is called the compensation curve .
The radius value is determined in 5.8-21.2 centimeters, the average value is 6.5-8.5 cm. The deepest point of the occlusion curve is the mesial tubercle of the lower first molar.
The article describes the Spee curve in detail.