Dentistry – Apparatus – Having gauge or guide
Reexamination Certificate
2000-03-06
2001-04-17
Lewis, Ralph A. (Department: 3732)
Dentistry
Apparatus
Having gauge or guide
C433S036000
Reexamination Certificate
active
06217326
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a mould for producing a tooth model from a dental impression.
2. Background Art
Such moulds are known in the form of cup-shaped formed bodies.
To produce a tooth model from a dental impression, the dental impression is filled with a plastic modelling material which hardens. Immediately after filling the dental impression with the modelling material in rare cases, while the modelling material is still soft, a mostly rubber-like mould is applied to the peripheral wall of the dental impression in order, by filling the mould up to a predetermined height, to obtain a base on the tooth model.
To produce artificial teeth, said base is trimmed parallel to the occlusal plane mechanically by grinding; the result is a so-called toothed rim made of modelling material.
Then a drill and a twist drill are used to drill blind holes in the base of the toothed rim, in each case under the teeth to be restored, adjacent teeth or antagonists, and metal pins are introduced and preferably glued into the blind holes.
After subsequent isolation of the base mostly using an alginate-based isolating material, the toothed rim with the glued-in pins is basally aligned and introduced into a mould, which is filled to a height of around two centimeters with preferably the same plastic modelling compound, until the base of the toothed rim is just completely wetted by the plastic modelling compound. Said compound after it has hardened forms the base for the toothed rim; toothed rim and base together form the finished tooth model.
After hardening and mechanical trimming of the base, the toothed rim is sawn in each case at right angles to the tangent predefined by the individual tooth groups right down to the base such that the model teeth to be restored, neighbouring teeth, maxillomandibular segments or any other model teeth or model tooth groups may be individually removed from the base and precisely repositioned by means of the pins.
Such a saw-cut model is a prerequisite for producing any type of artificial tooth from dental impressions.
Another way of producing model bases is such that the parallel-trimmed, conventionally produced toothed rims are provided in a special drilling apparatus with the blind holes for the pins and at the same time mirror-image holes are drilled into a prefabricated base plate made of plastic material for receiving the pins, which are to be glued into the toothed rim, together with the toothed rim. Removal of the prepared teeth is effected by the conventional saw-cut technique. Although this dispenses with the outlay for processing a second plastic modelling compound for producing the base, expensive equipment is necessary.
A particular problem associated with producing tooth models, in particular toothed rims, is the filling of the mostly hydrophobic dental impression with the hydrophilic modelling material, usually dental plaster. The narrow indentations of the individually moulded teeth, undercuts occasioned by the tooth shape and fine delineation of the textured surface of the teeth in most cases promote bubble formation in the tooth model which often makes it necessary to produce a second tooth model. Such a second tooth model however is mostly of an inferior quality to the first tooth model because the removal of the latter from the dental impression simultaneously leads to the breaking-off of fine edges and surface structures as well as fine interdental lamellae or lamellae in the sulcus region.
In addition, defects attributable to the shaping by the dentist to obtain the dental impression are frequently only detectable on the tooth model. Because of the elaborate process of producing the latter, however, defects are mostly not spotted until several days after taking the impression from the patient. In many cases the patient has to be brought back for a new impression to be taken, which entails a high outlay and often leads to poorer impression results because a common consequence of the initial treatment is a tendency to bleed during the follow-up treatment.
SUMMARY OF THE INVENTION
The object of the invention is to provide a mould for producing a tooth model from a dental impression, which enables a simpler processing technique involving only a lower number of working steps and by means of which the number of error sources is reduced and tooth models of greater precision are obtained.
In the mould according to the invention, the bottom wall of the mould is formed by the impression tray used to produce the dental impression, wherein the dental impression for producing the tooth model remains on the impression tray.
The impression tray at least in portions of its outer surface has a precisely predetermined geometry and may without reworking be connected precisely and tightly to the peripheral wall of the mould.
As will become even clearer from the detailed description below, production of a tooth model using the mould according to the invention saves time and costs. In particular, compared to conventional production of the toothed rim, there is no need for mechanical trimming, drilling of the blind holes for the pins or manufacture of the base plate involving repeat processing of modelling material, nor is there any need for expensive equipment for producing the toothed rim.
The use of the mould according to the invention is to a large extent error-tolerant and may be extensively automated.
The invention also makes it possible for the tooth model to be produced directly at the dental surgery. All the dentist need do, after production of the dental impression, is clamp the used impression tray together with the impression itself into the peripheral wall and introduce into the mould thus obtained an adequate amount of modelling material over the dental impression. Only the tooth model thus obtained is then passed on to the dental technician.
Producing the tooth model at the dental surgery also has the advantage that minor defects of the dental impression are easier to spot on the tooth model and the dentist in said case may immediately take another impression from the patient before the latter leaves the premises.
A mould is tightly closed on all sides.
The mould during filling may therefore be acted upon by a pressure below or above atmospheric. The former has the advantage of keeping bubble formation very low. In both cases, the modelling material flows well even into small interstices.
It is moreover possible for a mould prior to introduction of the modelling material, to be thoroughly rinsed with a wetting agent or another treatment medium so that the surface of the impression is optimally prepared for subsequent contact with modelling material.
A mould also easily allows the production of a tooth model which, at its base side, is already flat without machining of the modelling material.
In said case, the development of the invention is advantageous in view of a bubble-free quality of the—during casting—top end face of the tooth model.
The development of the invention also serves to achieve bubble-free, complete filling of the mould with modelling material.
The effect achieved by the development of the invention is that the feeding of modelling material is automatically terminated when the mould is completely full of modelling material.
Sealing connections may be realized in a simple and reliable manner between the peripheral wall and the impression tray and/or the peripheral wall and the model plate.
The development of the invention is advantageous in view of precise, reproducible positioning of a model plate on the peripheral wall.
The development of the invention allows the realization of a tooth model which may then, by means of saw cuts effected transversally relative to the mandibular arch, be made into a saw-cut model in which individual teeth or tooth groups are removable and precisely repositionable.
For said purpose positioning pins may be used, which are embedded in the tooth model and in each case have a positioning portion projecting above the tooth model.
The blind recesses in the
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