WO2000003658A1

WO2000003658A1 - Exchangeable retainer hook and matrix hook for removable partial dentures

Info

Publication number: WO2000003658A1
Application number: PCT/ES1999/000229
Authority: WO
Inventors: Urbano Antonio SANTANA PENÍN; María Jesús José MORA BERMÚDEZ
Original assignee: Universidade De Santiago De Compostela
Priority date: 1998-07-17
Filing date: 1999-07-17
Publication date: 2000-01-27
Also published as: ES2150371A1; ES2150371B1

Abstract

Exchangeable retainer hook and matrix hook for removable partial dentures, consisting of flexible U-shaped wires of stainless steel having non parallel branches, a circular elliptic cross-section, etc. The cross-section of the matrix hook is 1/10 mm larger than the cross-section of the retainer hook. They can be made by using pliers specifically designed for this process or industrially. They can substitute positively hooks which are currently used owing to their characteristics: they are exchangeable, actuatable, aesthetic and inexpensive.

Description

TITLE

Replaceable retaining hook and matrix hook for removable partial dentures.

DESCRIPTION

Replaceable retaining hook and matrix hook for removable partial dentures.

Generally, removable partial dentures (PPR) are used to rehabilitate the extensive partial toothless patient. Bone-implanted dental implants are also used, but they require special conditions (especially a quantity and quality of bone that only half of the patients possess, and of these, for psychological / social / economic reasons another considerable percentage is also limited to receive them ). Therefore, the majority of partial toothless patients are carriers of removable partial dentures (PPR). PPR can be placed in the upper jaw or in the jaw, or both.

They usually have a metal part in the form of a palatal plate in the upper jaw and a lingual bar in the case of the mandibular to join the areas with artificial prosthetic teeth that are generally on both sides of the same arch. The most frequent situation is the absence of premolars and molars after the canine in the jaw. In order for these PPRs to remain in place, in a stable manner, "retaining" hooks are commonly used (they are called by their function) that embrace nearby natural teeth (or lined with prosthetic crowns) or "pillars" of the prosthesis .

In order for the retainers to function properly (and not be harmful to the abutment teeth) they need to be combined with other elements, typical of the PPR: the reciprocal hook, the guide plane (which prevent the tooth from being displaced by the presence of the retainer), and occlusal stops (so that the prosthesis does not sink excessively into the gum or mucosa) with its connector (which connects them to the lingual bar or the palatal plate). This complex of elements embrace the abutment tooth, keeping it stabilized in all directions, which is what is called tripodization. In order for the tripodization to be correct, it is necessary that the complex formed by the retaining hook, the occlusal stop and the guide plane embrace the abutment tooth by more than 180 °; without this tripodization, the abutment tooth could be pushed out of its original position, or the prosthesis could result separated from the abutment tooth towards the toothless spaces, especially when there are no teeth limiting behind the toothless gap, which is the most common partial toothlessness.

The retainers currently used are usually metallic and generally form part of the PPR's own metal structure or skeleton, being made in one piece by the casting method. These retainers have some limitations: a) The most frequent problem is due to the fact that the metals used are not flexible and can eventually break down due to physical fatigue, accident, or when the wearer (or his dentist) intends to activate them (pressing them to gird them better on the pillar). It usually occurs because the retainers become unadjusted after a variable period of use. b) Forged steel retaining hooks are also used by placing them in the resin of the removable chairs (Rudd KD, Morrow RM, Rhoads JE. Dental Laboratory Procedures. Vol III: Removable partial dentures. 2nd ed. St. Louis: CV Mosby , 1986; 273-98). They are difficult to adapt and accidentally deform easily. c) The rejection in the majority of patients since the hooks are visible when the abutments are located in anterior areas of the mouth, not presenting the appearance of natural teeth, and causing discomfort to the patient who is not resigned to place these prostheses (complex to teach metal, avoid smiling, put your hand in front of your mouth, etc.).

To try to solve these problems, other types of retainers that are currently used on occasion have been designed, although they also have limitations:

1) Place a retainer through the lingual area. In fact, it is not visible, but it requires prosthetic crowns as pillars (Pardo-Mindan S, Ruiz-Villandiego JC. A flexible lingual clasp as an esthetic alternative: A clinical report. J Prosthet Dent 1993; 69: 245-6), can be difficult to obtain a correct tripodization and affect the position of the abutment or prosthesis.

2) The so-called "precision attacks" or joining means, devices with different shapes, for example hinges, have also been designed. But they are expensive, difficult to adjust, usually overload the pillars, difficult to keep clean, etc.

3) The steel hooks proposed by Belles (Belles DM. The twin-flex clasp: an esthetic alternative. J Prosthet Dent 1997; 77: 450-2) are aesthetic, but are limited to anterior teeth of the upper jaw, require a thickening of the plaque (with increased discomfort for the patient), allergic problems may occur

(due to the metal components of the weld), and it is expensive to replace (since to weld it may be necessary to remove the teeth because they can burn with the weld). We describe an invention consisting of two hooks: matrix hook and retaining hook. The retaining hook is virtually invisible, re-adjustable for an unlimited number of times (flexible steel wire), easily replaceable if it breaks (without the need for any modification of the prosthesis), easy to perform, it can be used in any location of the mouth and In any type of partial dentures (either only resin or with metal skeleton), it is not expensive and is virtually invisible, that is, it can present excellent esthetics.

Both hooks, matrix and retainer, can be manufactured industrially, made manually, or a combination of both by making specific pliers.

RETAINER HOOK AND MATRIX HOOK

Figure 1 represents the retaining hook: the hook branches, mesial branch (Fig. 1, ma) will be close to the abutment tooth and will be the one that configures the retention of the hook; the distal branch (Fig. 1, da) will be inserted into the base of the prosthesis, usually made of resin; and the central part of the U (Fig. 1, cp).

The retaining hook consists of a U-shaped wire, stainless steel (or materials used in dentures) and flexible. The branches of the U (Figure 1) must be disparate (convergent or divergent), generally divergent approximately 15 °, being in turn asymmetric, that is, that the angulation of the mesial branch (ma) will be approximately 90 °, in so much so that the distal branch (da) will form an approximate angle of 105 ° with the central part (cp) of the U; 4 cm long approximately each branch (although they can be made in several sizes from 3 to 10 cm); 4 to 10 mm long approximately in the central part of the U; and approximately 0.8 mm of circular section (elliptical, semicircular, etc.). The matrix hook, of similar technical characteristics to the retaining hook described above, with the only difference that the section of the wire is one tenth of a mm thicker. First, the prosthesis is made with the bed by including the matrix hook in the correct way (which will be the one that subsequently adopts the retaining hook), that is, the mesial branch in contact with the abutment tooth close to the toothless space, the part central at the level of the lingual surface (although hidden in it), and the distal branch under artificial teeth or, preferably, between them, in the interdental space. Depending on the size of the teeth, this should be the length of the central part of the hook. This procedure is performed on the prosthesis pattern, which is usually wax. The matrix hook is included and positioned in the formwork plaster when this prosthesis pattern is molded. When heating the wax and volatilizing it, this matrix remains so that the resin that is placed in place of the wax takes its form. By hardening the resin from the base of the prosthesis the matrix can be removed; in this way there is a configured bed that can receive the replaceable retaining hook, which will enter effortlessly, and that will be retained in that position thanks to its shape.

The retaining hook is included in the base of the prosthesis, hidden under artificial teeth, that is, in the denture resin. It can be extracted, so that it cannot be chemically bonded or welded to the resin. It must have a tenth of a mm less than the orifice of the resin into which it is introduced, it is retained in it in a stable manner thanks to the retentive form in dovetail. The disparallel branches allow it to be held in the physically or mechanically retained position once it was introduced into the corresponding bed thanks to this retention form. To configure the bed in which the retaining hook is housed, a 1/10 mm thick matrix hook must be used, placing it in the wax pattern from which the prosthesis is obtained.

Although not essential, the matrix hook can also be constructed with an extension towards the area of the central part, following the horizontal branches. This extension can simply be a continuation of the straight branches of the U, the matrix hook then becoming an H-shaped structure. In this case, the shape of the U-part must retain the same characteristics mentioned above; the extension can also be such that you configure a handle, that is, it could be similar to an A. This extension / s allow you to better take the matrix, making it easier to remove from the base of the PPR, such as We will describe later in the procedure.

The branches (of the matrix hook and retaining hook) will be linearly straight, to allow removal of the matrix and subsequently the entry of the retaining hook without mechanical impediments. To adapt the replaceable hook to the abutment tooth only It requires making a small bend, at the exit of the prosthesis through the external area, twisting it towards the abutment tooth. You can make a gentle, gentle curve with your hand, and finish adapting it with the help of suitable pliers, and refine your fit in the mouth, once the remaining ends are trimmed. The position of the hook in the prosthesis is easily done.

It can be used in both maxillary and mandibular prostheses, or simultaneously in both using different hooks appropriate to each case.

Also in the same prosthesis a hook of the type we describe can be used and in other parts of the prosthesis another type of conventional hook. As an example we describe the procedure in the jaw with distal extension:

1) A diagnostic model and design of the metal structure is carried out with the help of the parallelizer.

2) The usual dental preparations (beds for occlusal stops and guide planes) are made on the abutment teeth and polished.

3) The metal structure is made. A groove is made therein at the angle between the retentive grid and the guide plane so that it can accommodate a 0.9 mm diameter tube. The metal structure is tested in the mouth, corrected impression of the bases is made and a corrected model is obtained (Stewart KL, Rudd KD, Knebker WA. Clinical removable partial dentures, altered cast procedure. St. Louis: CV Mosby, 1983; 398 -400), intermaxillary relationships are obtained and mounted on articulator

4) The matrix hook is placed in such a way that the mesial branch is located on the previously prepared groove, attached to the abutment tooth and protruding from the vestibular. The central part of the hook (cp) will be positioned such that it coincides approximately with the lingual surface of the prosthesis. To achieve this, it may be necessary to slightly modify the angles that make up the branches with the central part of the matrix hook; The important thing is not to modify the length of the central part. Naturally, if this is done in this way, when installing the retaining hook it should be modified in the same way approximately. 5) Artificial teeth are placed. It may be necessary, subsequently, to remove the tooth that remains on the hook to correctly reposition it, or correct the angulation of the retainer branches and adapt them better to the specific case. They come back to put the tooth (s). It waxes conventionally. Thus the central part of the

U is flush to the internal or lingual surface of the PPR pattern, as described in section 4 above. If the matrix hook had extensions, they would be protruding by lingual, being free, not including in the wax. For vestibular, the ends of the hook branches (about 3 cm) will remain exposed.

6) This pattern is placed with the corrected model in the muffle; both vestibular extensions of the matrix hook will be covered and fixed to the plaster of the base of the muffle (the lingual extensions would also be covered, if the matrix hook had them). Thus, when the lid is lifted after the removal of the wax, the hook / s are firmly attached to the plaster of the base of the muffle.

7) The pattern is processed by resin. The set of the muted prosthesis with its model in the articulator can be traced to adjust the occlusion. This is possible since a split model must be used, which allows a position identical to that previously used to place the teeth. 8) The prosthesis is removed, and it is finished. The matrix hook is removed, extracting it by lingual. To do this, in the first place any excess resin is eliminated in this area that prevents the extraction of the matrix hook. Subsequently it can be pushed from the outside area using a pliers or an instrument such as a mosquito clamp. Then, once the matrix hook is removed, the vestibular or external end of the duct is extended slightly, close to the abutment tooth, configuring as a infundibulum, to allow a small movement of the wire, so that it can be folded without excessive tension, avoiding having to set an acute angle, but curved and gentle.

9) The retaining hook is now placed (Fig. 1) that will fit perfectly, because it is one tenth of a mm thinner than its matrix. The mesial area is slightly twisted by hand to bring it closer to the abutment tooth. It is cut leaving only about 4-5 mm. Subsequent modifications to correctly adjust the tooth will be carried out after the test in the mouth by means of an appropriate curvature pliers. The length can be reduced after adjustment, so that it is sufficiently retentive but not visible. The distal branch is cut by a disc, at the level of the outer surface. 10) It is tested and just adjusted in the mouth. It is essential that the occlusal rest and its connector are correctly designed to obtain a correct hug, of more than 180 'as in any removable partial prosthesis.

The use of these hooks offers advantages over other options: Cheap, due to the low cost of the material and the short time required for its realization; simple to perform (does not require any specific type of equipment); can be activated in case of loss of tension; if it breaks, it can be replaced without requiring any modification of the prosthesis (simply making a new "U" wire and inserting it into its housing); very aesthetic; if the butt-reciprocal-plane guide-hook complex tripodizes the assembly correctly with respect to the pillar; it is flexible (it does not traumatize the abutment during the insertion of PPR in the mouth); does not require welding; You do not need to increase the thickness of the PPR anywhere; and can be used in any location and on natural pillars or restored using fixed prostheses. The drawback that it presents is that the individual adaptation curve to each pillar must be done manually and cannot be done in a prefabricated way, due to the conception, the way of use and action.

Claims

1.- Replaceable retaining hook and matrix hook for removable partial dentures, consisting of flexible stainless steel wires (and / or prosthetic materials) in the form of U. The branches of the U are disparate approximately 15 ° (divergent or convergent). ; one of them forms approximately an angle of 90 ° with the central part of it, while the other forms an angle of 105 ° and both branches are approximately 4 cm long each (although they can be made in several sizes from 3 to 10 cm); 4 to 10 mm long approximately in the central part of the U; and about 0.9-0.8 mm of circular section (elliptical, semicircular, etc.); for application in dentures.

2. Matrix hook, according to claim 1, characterized in that the section of the wire will be 1/10 mm larger than the section of the retaining hook.