Dental prosthesis fabrication

Abstract

A method is disclosed for forming an accurate stone cast from a dental hydrocolloid impression, used for the purpose of prosthetic fabrication, such as dental prostheses. The dental stone catalyst, calcium sulfate dihydrate, is engaged onto the internal surface of set hydrocolloid impression. This catalyst, placed in the area between impression material and wet, mixed stone, will act to hasten the initial setting of dental stone that is in closest proximity to the impression. The result is a stratified set of the stone. Setting of the wet, mixed dental stone occurs first at the impression / stone interface. The setting radiates outwardly, away from the impression / stone interface. The mixed stone better resists distortion upon setting and the resultant set stone cast is more accurate.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]This application is a continuation of U.S. patent application Ser. No. 11 / 878,337 filed Jul. 23, 2007.FIELD OF INVENTION[0002]This invention relates generally to making better fitting removable dental appliances and indirect dental restorations, and, more specifically, this invention relates to making accurate stone dental casts and models.DESCRIPTION OF PRIOR ART[0003]Stone dental casts need be very accurate replicas of the dentition. The cast, along with other exact measurements and guidelines supplied by the dentist, enables the laboratory to make crowns, dentures, partial dentures, and obturators. These items are referred collectively as dental prostheses.[0004]Other special applications, such as oral snoring devices, orthodontic appliances, bleaching trays, and nightguards, and surgical stents, may also be prescribed by the dentist and are also made from dental impressions.[0005]Once a cast is made, it can be sectioned so that segmen...

AI Technical Summary

Benefits of technology

[0025]Some inventors attribute a smooth stone cast and easy separation of the set cast from the impression as indications of accuracy. This is the case in two U.S. Pat. Nos. 5,907,002 and 3,620,778. Present day dental casts are distorted due primarily to shrinkage. Any reference to easy separation of dental cast would have this inventor immediately equate to dental cast shrinkage. Most casts today exhibit distortion due to shrinkage.

Problems solved by technology

However, many practitioners will still use the term “cast” and “model” interchangeably and do not distinguish between the two terms.

A tremendous problem exists with indirect dentistry.

Dental appliances and indirect restorations seldom have a perfect fit.

Indeed, dentures do require multiple appointments to finalize.

And usually, the final outcome is a slight disappointment.

There are so many steps in the dentist office, along with an equally complex arrangement in the laboratory, that dentists believe the solution for ill-fitting prosthetics, can never be achieved.

Similar to the irregularities associated with dentures, acrylic nightguards also usually end up with a compromised outcome.

It is very time consuming to troubleshoot an ill-fitting nightguard, in fact, many dentists have resorted to a soft inside liner attached to the hard outside acrylic shell.

However, the soft liner is not as durable and long lasting as all hard acrylic.

It is difficult to locate areas of distortions and most dentists allow up to an hour of office time to adjust and cement a crown.

They write of the possibility that the final outcome may be that the appliance cannot be adjusted adequately.

Although it is true, that a bond is needed to the tray, any severe defect such as tray separation would create a gross discrepancy in fit of final appliance.

Impression tray design alone has never made a further refinement in the fit of our dental castings.

He feels that recovery from deformation applied during time to remove the impression causes dimensional instability.

With all of the impression materials on the market today, including the new ones introduced by Kamohara, there is very little improvement in the reliability of indirect dentistry.

They feel distortion occurs in the modeling process.

He states that inaccuracies occur with the master cast.

He further feels that the problem, however, exists in the plastic trays used in the profession as well as subsequent modeling of the impression.

His invention does not yield a better fitting crown.

Present day dental casts are distorted due primarily to shrinkage.

Most casts today exhibit distortion due to shrinkage.

These alginate formulas are all good performers as impression materials, however the ingredients of alginate have never acted to cause any type of catalyst effect on the wet, mixed stone poured into and against it.

Stone dental casts made from alginate exhibit just as great a distortion as with other dental impression materials.

It may help to provide a smoother cast surface, but does not provide a more accurate cast.

However, the potency of potassium sulfate as a dental stone catalyst is unclear to the profession.

Many impression materials have incorporated potassium sulfate, but none have produced accurate casts.

Because the correlation between a stratified stone set and cast accuracy is unknown, the effective amount and combination of stone setting catalyst ingredients remains undiscovered.

Also, even adding the potassium sulfate solution directly to wet mixed gypsum, this inventor could still not verify any difference in setting time as compared to a control mix.

Although, it has never been proven how the accuracy of the final prosthesis is affected, specifically from the setting stone distortion.

This uncontrolled distortion causes inaccuracies in the dental cast and, ultimately, in the final dental prosthesis.

This distortion would ultimately lead to inaccurate restorations.

The crown will not fit.

Although digital images are an improvement in efficiency, cost is certainly a factor.