The making of dental impressions is a precise art because of the necessity of forming a mold in which an accurate model of dental anatomy may be made. Heretofore, it has been customary for many years to mix the material in which the impression is to be made from certain ingredients and then disposing the same in a conventional impression tray of various types. It is obvious that if the material in which the impression is to be made is relatively readily flowable, it is capable of entering fissures and interstices, whereby, when the mold material is introduced into the molded cavity of the impression, it will be capable of reproducing the minute as well as the major features of the dental anatomy. Obviously; however, the more viscous the impression material, the less likelihood there is of small details of the anatomy being reproduced in the mold of which the pattern is to be made.
Examples of previous techniques in the use of dental impression material in an impression tray or otherwise, heretofore, are found in the prior art U.S. Pat. No. 3,390,458 to Lytton dated July 2, 1968, represents a special type of device for making dental impressions particularly capable of pressing the surrounding gum away from a tooth around the gingival, whereby the pattern molded from the impression will extend below the gum line.
Another example of the use of a conventional tray is the subject matter of U.S. Pat. No. 3,552,601 to Jahn dated May 13, 1975. In this patent, there is provided a spacer hood which is stretched over the impression material and the impression tray is inserted into the mouth of a patient and the patient is asked to close his mouth in biting on the impression material. To form a more precise impression, the spacer hood then is removed, a secondary impression material is applied and the impression tray again is introduced into the mouth of the patient so that a second impression may be taken.
A more recent development in the production of loaded dental impression trays which are pre-filled with impression material comprises the subject matter of U.S. Pat. No. 4,553,936 to Wang dated Nov. 19, 1985, and assigned to the assignee of the present invention. In this disclosure a transparent impression tray is provided which is filled with a light-curable impression material. When thus filled, the impression material is covered with a light-opaque covering which extends across the top and ends of the tray and the exterior surfaces of the tray are covered with light-opaque material such as metal foil; the foil serving an additional advantage of reflecting actinic light which is applied to the transparent tray and thus causes the light to permeate the entire mass of the impression material when such artificial light is applied thereto.
The prior art methods of using dental impression materials are cumbersome to use in the dental operatory or laboratory because many of the prior art materials are cured using two-component self-cured systems, and must therefore be prepared in the operatory or laboratory immediately prior to use. It is difficult for the practitioner to keep air voids out of the material when it is mixed; and after the preparation has begun, he has a limited time, usually about 5 minutes, in which to use the material before it self cures or begins to cure. Consequently, batches of dental impression materials made in the operatory and laboratory sometimes have to be discarded and the procedures repeated
Also, it is sometimes difficult for the practitioner to judge the correct amount of material to be used to obtain an impression, and excess material has a tendency to escape from the tray and become loose in the mouth, and said loose material may cause the patient discomfort and trigger the gagging reflex. When flowable impression materials are used, the tendency of the material to flow out of a dental tray may cause similar problems.
Accordingly, there is a need in the art for means and a method for obtaining dental impressions whereby the practitioners time in the operatory is reduced, there is less mess involved, the amounts of impression material to be used are premeasured, the dental impression material to be used is free of air voids, where means are provided to prevent dental impression material from flowing out of a tray, and provides for increased patient comfort
It has been found that the above objectives can be obtained by using a light activated, prepackaged, premeasured impression material