Preform for molding custom dental impression trays

A preform consisting of a planar section of a thermoplastic having a glass transition temperature a few degrees above body temperature and a softening point below about 160.degree. F. is used to form custom, quadrant, dental impression trays. The preform is of uniform thickness except for a raised ridge, extending across both sides of the sheet, terminating in an elongated handle at one end, and dividing the preform into a pair of asymmetrical sections shaped to fit the buccal and the lingual musculature along a dental arch. The tray may be heated above its softening point and the side sections bent in a common direction about the central ridge so that their ends extend substantially parallel with one another to form a trough having a U-shaped cross-section. If the sections are bent in a first direction about the ridge a tray useful for the maxillary left or the mandibular right quadrants results; if the sections are bent in the opposite direction a tray useful for the maxillary right or the mandibular left is formed. The heat-softened preform may be placed in the patient's mouth, over a quadrant of the dental arch, and allowed to harden in the mouth to provide a custom impression tray.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a thermally moldable preform useful for creating 
custom, quadrant, dental impression trays and to a method of forming trays 
using the preform. 
2. Prior Art 
As is a preliminary step to the formation of a denture, a trough-shaped 
impression tray is filled with a casting material and brought into contact 
with the section of the dental arch of which the impression is to be made. 
In the process of forming a sectional impression a quadrant impression 
tray is employed that fits over half the dental arch and has a projecting 
handle at its forward end. These quadrant trays are available in either a 
first form that may be used with either the maxillary left quadrant or the 
mandibular right quadrant, or a second form that may be used with either 
the maxillary right quadrant or the mandibular left quadrant. The 
appropriate tray is filled with impression material and brought into 
contact with a section of the dental arch to form an impression. The 
resultant casting is used to form a custom impression tray which closely 
follows the contours of the dental arch and teeth so that when it is 
filled with impression material a final impression may be taken having 
relatively constant wall thickness to equalize the pressure on all points. 
Typically, the time and expertise required to form a final impression tray 
from the initial impression necessitates two vists or considerable waiting 
from the patient to the dentist; one to form the initial impression and a 
second to form the final impression using the final tray. 
Copending patent application Ser. No. 843,433 entitled "Anatomical 
Intra-Orally Moldable Dental Impression Tray and Method of Using the Same" 
discloses a thermally moldable impression tray that may be used by a 
dentist to form a final impression in a single session, eliminating the 
delay and cost of the two-step process. The impression tray of that 
application is formed of a thermo-plastic having a glass transition 
temperature slightly above body temperature and below a temperature that 
would cause discomfort to the patient's mouth. The impression tray is 
heated above its softening temperature externally of the mouth and is then 
placed within the mouth and shaped to conform to the patient's oral 
tissue. The tray is then allowed to cool below its glass transition 
temperature while in the mouth. When removed and chilled to room 
temperature, the resultant tray has all the attributes of a custom 
impression tray and may be immediately used to form a final impression. 
The previous application discloses full impression trays of a first type 
for use within the mandibular section and of a second type for use with a 
maxillary section. 
The present invention constitutes an application of the principles of that 
previous invention to quadrant impression trays in a novel manner that 
eliminates the need for provision of different forms of quadrant trays for 
use with different dental sections. 
SUMMARY OF THE INVENTION 
The present invention provides a preform of a material having the same 
physical properties as the materials used with the thermally moldable 
denture of patent application Ser. No. 843,443. The preform is a sheet of 
a uniform thickness with the exception of a raised ridge that extends 
along both surfaces to divide the preform into a pair of asymmetrical 
sections. The central ridge projects beyond the side sections at one end 
to form an elongated handle. One of the side sections has an edge contour 
adapted to fit the lingual musculature of the mouth while the other 
section has an edge contour shaped to fit the buccal tissue. 
When the preform is heated above the softening temperature of the plastic, 
as by immersing it in heated water, the side sections may be bent in a 
common direction about the central ridge to create an impression tray 
having an approximately U-shaped cross-section. If the sections are bent 
in a first direction, so that their sides forming a first surface of the 
preform oppose one another, the resulting tray will fit two diagonally 
opposed dental quadrants, for example, the mandibular right and the 
maxillary left. If the bend is formed in the opposite direction, so that 
the surfaces of the sections forming the second side of the preform oppose 
one another, then the preform will serve for use with the opposite two 
quadrants, i.e., the maxillary right and the mandibular left. 
The final shaping of the tray is preferably performed in the patient's 
mouth with the concave side of the ridge in position over the teeth of the 
appropriate quadrant. In this manner the side sections may be shaped into 
close fit with other contacting tissues. 
If necessary to achieve a better fit, the preform may be trimmed while in 
its softened state. The preform is preferably allowed to cool below its 
glass transition temperature while in position in the patient's mouth so 
as to retain the exact desired form. Once cooled to approximately mouth 
temperature, the preform may be removed and used in exactly the same 
manner as any other custom impression tray. 
The preform and the method of the present invention thus achieves the dual 
advantages of allowing the formation of a custom impression tray quickly, 
simply, and in a single sitting, and additionally allows an impression 
tray for any of the mouth quadrants to be formed with a single preform. 
The preforms of the present invention may be made available in more than 
one size so that the selected preform will make a good approximate fit 
with the mouth of the patient.

A preform made in accordance with the present invention, as illustrated in 
FIGS. 1-3, constitutes a planar section, generally indicated at 10, of a 
thermoplastic having a glass transition temperature above human body 
temperature and below a temperature at which the plastic may be inserted 
in a patient's mouth without substantial discomfort to the patient or 
burning of the patient's mouth tissue. The softening temperature of the 
thermoplastic, i.e., the temperature at which the material may be readily 
manually molded, will typically be somewhat higher than the glass 
transition temperature and this softening temperature should also be below 
the temperature at which discomfort or burning may occur if the plastic is 
inserted into the patient's mouth. The upper limit of the glass transition 
temperature will typically be about 135.degree. F. while the upper limit 
of the softening temperature may be slightly higher. 
Thermoplastics having these physical characteristics and additionally 
having the proper chemical characteristics for dental use are well known 
and readily available. 
The preform 10 is created by molding appropriate plastic components under 
appropriate conditions of temperature and pressure in matched molds. 
The preform 10 consists of a sheet having raised ridges 12 and 14 formed on 
opposed sides of the sheet, directly opposite to one another, to divide 
the sheet into a pair of sections or flanges 16 and 18. The sections 16 
and 18 are asymmetrical with respect to one another and the ridge section 
12-14 extends beyond the flanges 16 and 18 at one end to form an elongated 
handle 20. 
Grooves 22 are formed into the thickness of the sections 16 and 18 on both 
sides of the sheet, along opposed sides of the ridges 12 and 14. In a 
preferred embodiment of the invention the sections 16 and 18 may have a 
thickness of approximately 0.050 inches and the thickness of the preform 
at ridges 12 and 14 may be approximately 0.090 inches. Thus the ridges are 
each raised approximately 0.020 inches above the side sections. The 
grooves 22 may be 0.010 inches in depth. 
The edge contours of the side sections 16 and 18 are such as to generally 
conform to the typical oral tissue on the lingual and buccal sides 
respectively when the preform is shaped into a completed tray as shown in 
FIG. 4 or 5. Accordingly, the lingual section 16 will have a contour more 
normal to the handle 20 than the buccal section 18. 
In use, the preform 10 is heated above the softening temperature of the 
thermoplastic by immersion in heated water or by use of an infrared lamp 
or a heat blower or the like. The dentist may then bend the two side 
sections 16 and 18 about the central ridge section 12-14 in either of two 
directions, depending upon the quadrant of the patient's mouth with which 
the tray is to be used. The grooves 22 act as bending lines to facilitate 
proper shaping of the tray. The side sections may be bent in a first 
direction, shown in FIG. 4, so that the ridge 12 is on the concave side of 
the resulting U-shaped trough. This tray is useful with the maxillary left 
or mandibular right quadrants. Alternatively, the side sections may be 
bent in the opposite direction so that the ridge section 14 is on the 
concave side of the trough resulting in the tray of FIG. 5, useful for the 
maxillary right and mandibular left quadrants. 
While still in its softened state the partially formed tray may be inserted 
in the patient's mouth in the manner illustrated in FIG. 5 so that the 
ridge section is in contact with the top of the teeth on the desired 
quadrant. The tray may then be bent into the desired final, custom shape. 
If trimming the tray is necessary the tray may be removed from the mouth 
before it is softened or it may be removed from the mouth and reheated 
above its glass transition temperature and trimmed with scissors or the 
like. The tray is then reinserted in the mouth, properly positioned and 
formed, and allowed to cool below its glass transition temperature while 
in the mouth so as to insure achievement of the desired shape. 
The resulting tray is then ready for immediate use in the manner of any 
custom final impression tray.