Dentistry – Prosthodontics – Cutting edge shape or arrangement
Reexamination Certificate
1999-05-07
2001-08-14
Lewis, Ralph A. (Department: 3732)
Dentistry
Prosthodontics
Cutting edge shape or arrangement
Reexamination Certificate
active
06273723
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a set of prefabricated molars for a set of removable full dentures.
In the dental field, i.e. the technical dental field, prefabricated produced molars are being used with complete full dentures, hybrid dentures and partial dentures and are applied by persons, who are missing some, or all of their teeth. These prefabricated produced molars are being secured and become part of the denture, and together with its synthetic material, forms a solid unit. Such dentures are quite different from crowns and bridges, where the individual molars will be reconstructed completely, meaning they are being constructed in a dental laboratory and will be cemented directly to the previously prepared stump of a tooth.
Hybrid dentures completely cover structures that are located underneath, making securing the dentures to the stumps of the teeth, and through recently invented prefabricated implanted roots (implants) possible, by implementing a push-button-like system. They are, however, with possible exceptions, basically constructed like a normal removable denture, which has prefabricated molars attached to its base.
2. Description of the Prior Art
In the past century, prefabricated molars were made of porcelain and placed in dentures, which had no consequent and specified form relating to their function. Beginning in 1908, A. Gysi developed prefabricated molars, which were strictly constructed according to functional principles. The result of the development currently consists of three different construction types of prefabricated molars, with each clearly defining its functionality, which was actually produced and is still being utilized in the dental field i.e. technical dental field to date. The individual molars are securely anchored in the framework of the denture and have functional contact with the opposing teeth. Each tooth influences the stability of the entire denture and the other teeth of the same denture, since all teeth are securely connected to the framework of the denture. It is therefore important to pay attention to the impact of each individual molar when under the pressure of chewing, as well as the functional impact of all molars together, when constructing the denture. If a denture is to be made at the same time for both, the maxilla and for the mandible, the impact of the reciprocal functionality of the individual molar pairs, as well as all molars together, must be observed.
With “classical” defined type 1 construction (according to A. Gysi; for example compare patents CH-109795, CH-199038 and CH-88645), the molars are equivalent to the shape of the human molars, with perhaps some deviations. They however have no roots but only show the crown of the tooth, which is the part that protrudes from the gum and is visible with natural teeth. In the following description, the term “cusp” or “dental cusp” refers to the conical shaped pointed or rounded eminence on or near the masticating surface of the tooth which occludes with the antagonizing tooth of the opposite dental arch, and the term “fossa” refers to a shallow depression concavity or a hollow depressed area. The oral/palatal cusps of the upper molars which face the tongue, bite in the direction of a central fossa of the lower molars and/or a dental cusp in contact with two opposing teeth, which form central fossa when put together. The buccal cusp of the lower molars, which point toward the cheeks, fit into the central fossa of an upper molar or in the central fossa which was formed by two upper molars and make contact with the outer buccal cusp of the upper molars. The fitting into each central fossa of all cusps is called “classical occlusion”.
When moving the mandible, in relation to the maxilla, which is attached to the scull, the cusp of the upper molar forms, stabilized contacts in the shape of gliding surfaces and is therefore essential. According to A. Gysi, all molars of the upper denture shall remain in contact with the lower denture, in order to prevent tipping when the patient moves the mandible. This way the denture will always be supported by a large surface area on both sides (bilateral balancing).
The disadvantage of this type 1 construction is that the functional contact between the outer buccal cusp of the upper and the lower molars very often causes a tipping of the upper and/or the lower denture, when rough and hardly processed bolus is still present. In order to prevent this situation, the molars must be placed in the tongue area, in order for the outer pressure-bearing cusp to be positioned at least in the center of the carrying alveoli ridge, which will however restrict the tongue area considerably. The contact of the outer buccal cusp however may be eliminated, in order to shift the chewing forces inward lingual. The shape and the position of the premolars without bolus being present, makes it impossible or at least very difficult, to stabilize the gliding contact through movements to the side and partially by displacement movements of the mandible, as it is required for the bilateral balancing. Since the molars will be under functional pressure when chewing bolus, the stability of one-sided use is essential. Also between meals and while sleeping, intensive functional contact of the teeth without bolus, will occur.
Resolving the aforementioned disadvantages, molars have been developed according to a construction of type 2 (according to A. Gerber; for example compare patents CH-405601, U.S. Pat. No. 3,305,926 and CH-607686), where the bilateral balancing remains secured and the dentures remain stable and even on the base. That means that they are resting on the appropriate jawbone of the alveoli ridge. For stability reasons the palatal/oral inner upper cusp of the upper molars, which are pointed toward the tongue, are dominantly being used for chewing, in conjunction with the lower central fossa of a molar, or with a central fossa created by two molars. The cusp in this instance, is in general convex-shaped and the appropriate central fossa is in general concave-shaped, so that the molars (in perspective to the upright-positioned denture carrier) create a vertical line of force at a random slant. The outer buccal cusp of the upper molars however do not show any or only show a clearly reduced contact, which is very small and which is located closely near the upper central fossa. The center for chewing and the chewing force are clearly being shifted to the inside (oral), toward the center of the mouth and not to the outside of the upper and lower alveoli ridges, which means not outside the bone structure which carries the masticatory force; since the masticatory forces, which take place outside of the center of the upper and lower alveoli ridges, may cause the denture to tip. The upward outward pressure against the upper and slightly outward-tipped buccal cusp, of the upper molars will completely be deleted or will at least be drastically reduced. This way there is plenty of room for the tongue, without loss of stability by the masticatory force, compared to the construction of type 1. The molar-relief essentially complies with the natural model, however with partially clear deviations.
During a normal and one-sided chewing process, with the bolus being large and hard in the beginning, making the contact of the molars impossible, the outer buccal cusp are not being used. This is called “lingualized occlusion”.
During sideways motions of the maxilla, without bolus being present, all molars remain in constant contact with one another (bilateral equilibration balancing), where only the inner palatal molars have contact with the opposing tooth. The upper outer cusp overlap the lower outer cusp, clearly without any contact, since they could make the denture tip when bolus is present.
These molars have the disadvantage, when type 2 construction has been applied that their chewing efficiency is smaller then the chewing efficiency of the molars of the construction type 1. The functionality of the convex-shaped cusp with the conca
Brown Martin Haller & McClain LLP
Lewis Ralph A.
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