Method for forming a coronal replacement for a tooth and product for casting the crown

The invention provides a tubular dental mold form with at least one scalloped end and a method, utilizing the form, for forming a universal crown in situ on a tooth stump. In a preferred form, scalloped edges, of different depths, are formed at both ends and are circumferentially offset on one end with respect to the other end.

This application is directed to a method for forming a universal crown and 
a universal mold form for casting such a crown in situ on a tooth stump. 
It is not an uncommon problem met with by dental practitioners where the 
crown of a tooth has been broken in whole or in part, and a replacement 
must be quickly provided to prevent further damage to the tooth. Such 
situations may also involve the need to remove the nerve, and fully bore 
out the nerve canal. 
Temporary crowns have generally been formed by applying various materials, 
e.g., curable composites, in small portions, to gradually build up the 
crown surface above the cleaned tooth stub, e.g., after a root canal 
operation. This has taken a great deal of time and can only be 
accomplished with great difficulty, even when a dental post was present to 
support the temporary crown, as shown, for example in the copending 
applications. In the past it has also been attempted to apply a tube, 
having one closed end and filled with composite, over the end of a tooth 
stub. When an upper tooth was being worked on, the closed tube was 
inverted; this also was not found to be wholly satisfactory because of the 
need to invert the tube, and further because such tubes did not fit 
closely around the base of the tooth, adjacent the gum, without causing 
damage to or tearing of the gingiva attachment. 
It is an object of the present invention to provide a simple and efficient 
means of forming a temporary crown on a tooth stub, especially after the 
stub has been treated to remove the nerve from the canal, to quickly and 
straightforwardly obtain a compressed and condensed temporary crown 
pending completion of the permanent crown composite. 
In accordance with the present invention, there is provided a dental mold 
form of a generally tubular shape, wherein at least one end of the form 
has a double scallop shape, wherein one scallop is more deeply indented 
than the opposing scallop. Preferably, the tube is formed of a material 
which will maintain its shape and most preferably is formed with an oval 
cross section. 
The scalloped end has a generally sinusoidal form, having two convex curved 
portions and two concave curved portions. One of the concave portions is 
indented at least about 0.015 inches, and most preferably at least about 
0.02 inches greater in depth. Most preferably the second end of the hollow 
tube is also scalloped, with the concave portions and convex portions 
being 90 degrees out of phase with the scallops on the opposite end of the 
tube. The scalloped tube is approximately at least about 9 millimeters in 
length and preferably not more than about 15 millimeters in length. 
In accordance with the method of this invention, the tube is placed around 
a prepared tooth stub. In the case of a fully broken off tooth stub, where 
the coronal part has been fully removed, the nerve canal is cleared of any 
remaining nerve tissue. The tubular mold form is then placed around the 
tooth, so as to fit tightly around the tooth at least at the base of the 
tooth stub, i.e., at the portion immediately adjacent the gum line or 
gingiva. The scalloped end is so placed that the concave portions extend 
along the thickness of the tooth, and form an arc around the gum line. 
Curable composite material is packed into the tube, above and around the 
tooth, so as to be pressed tightly against, and in intimate contact with 
the remaining tooth substructure. After the composite has cured, the form 
is removed and the cured remaining crown material can then be formed by 
grinding with commonly available dental tools to the desired size and 
shape for a temporary condensed crown. 
This method and the use of the special tube form in accordance with this 
invention permits the relatively fast and easy formation of a crown formed 
of condensed material, such as dental composite, free of voids or 
porosities, where food particles, discolorants and bacteria could 
accumulate. Such a crown will provide an intimate and tight fit with the 
tooth stub and the adjacent teeth so as to form a highly efficient and 
inexpensively prepared temporary, or even a permanent, crown. 
This invention provides an additional benefit when multiple adjacent teeth 
are being treated. In a further preferred embodiment of this invention, a 
slit can be formed on opposing sides of the tube form, in the portions 
located in the interdental area. When this is done, the material packed 
into the tube form can extrude through the wall of the tube, forming a 
contact with the adjacent teeth to prevent floating, and to maintain the 
position of the teeth. When several adjacent teeth are being treated to 
form crowns, the series of contact elements formed by the side extrusions 
through the tube wall slits, can be used to form a connecting, splinted 
structure for the multiple coronal restoration.

Referring to the drawings, the preferred tube form of the present 
invention, generally indicated by the numeral 10, has an oval 
cross-section as shown in FIGS. 2 through 5. The size of each of the major 
and minor axes of the tube is determined by the width and thickness of the 
particular teeth for which the tube is to be used. For example, a tube 
having a major axis of 0.32 inches and a minor axis of 0.18 inches can be 
used for a stub of an upper anterior tooth, as is shown in FIG. 1. 
Generally, upper anterior teeth are less than 11 mm. in width; lower 
anterior teeth have a width of about 5 mm.; bicuspids have a width of from 
6 to about 8 mm.; and molars have a width in the range of about 12 to 
about 16 mm. 
The scalloped end portions 8,9, are shown as being 90 degrees out of phase, 
respectively; on each end are two unequal concave portions 12,13, one of 
which is at least of approximately 0.015 inches greater depth, and 
preferably not more than about 0.030 in, greater depth. In one most 
preferred embodiment, the offset between the two concave indents 12,13 are 
about 0.025 in. The convex portions 14,15 also vary by the same amounts, 
especially when the tube forms 10 are made by the preferred method. The 
scalloped ends permit tightly fitting the form tubes 10 over a tooth stub, 
when the orientation of the tube form relative to the tooth is such that 
the deeper concavity 13, is fitted over the higher portion of the gum, as 
shown in FIG. 1. 
The tube form 10 of the present invention is preferably constructed of an 
intra-orally safe, light transmitting material, transparent or 
translucent, most preferably between 3 and 8 thousandths of an inch in 
thickness. Such materials are well known. In addition, these materials 
should also have a sufficiently high elasticity modulus such that at the 
desired wall thickness the tube form will hold its shape, but can be 
elastically deformed by finger pressure to accommodate the slightly 
different sizes and shapes of teeth. The wall thickness of the tube form 
is limited by the spacing between teeth such that a form can be placed 
over a tooth stub, and fit in the gap between the stub being crowned and 
the adjacent tooth. 
In the tube form shown by FIGS. 6 through 9, the tube wall 20 is 
manufactured in corrugated form, so as to permit expansion to accommodate 
different size teeth, without actual stretching of the material. Such a 
corrugated tube form is otherwise formed of the same size and shape as the 
tube form disclosed by FIGS. 2-5. 
The light transmitting wall material for the tube form permits the use of 
light curable composite for forming the crown. Alternatively, it is also 
included within the scope of this invention to utilize autopolymerizing 
resin, or other material which is cured by means other than the 
application of light, such as by the application of heat or water. In such 
cases, the tube form wall material need not be light transmissive. 
Although the tube forms of the present invention can be formed having a 
circular cross-section, the oval tube cross-section shown in the drawings 
is preferred because it more closely matches the shape of teeth; in 
addition, the tube form can be placed on either the wider but less thick 
anterior teeth, or on the thicker, but less wide, bicuspids. The tube 
forms which have a scalloped edge at both ends, permit the placement of 
the proper concave indent at the interdental gum line, by turning the tube 
upside down, i.e., turning it 180 degrees about an axis perpendicular to 
the longitudinal axis of the tube, and rotating it 90 degrees about its 
longitudinal axis, so that the highest portion of the gum line engages the 
most deeply cut indent, or scallop 13. Thus, the alternate shallower and 
deeper scalloping of the tube ends, accommodate the range of differing 
natural gum curvatures and slopes found in the normal population. 
The tube form 10 is placed around the tooth stub as shown in FIG. 1, and 
pushed tightly against the lower portion of the tooth stub to form a tight 
contact at the gum line. At the same time, the scalloped bottom ends 
prevent damage to the tooth gingiva attachments during the casting 
procedure. The dentist can then form, as with a scalpel, small openings 
31,32 through the portion of the tube wall touching or opposite the 
adjacent teeth, to permit extrusion of a small amount of, e.g., the 
curable composite material 31',32' therethrough; when hardened, this 
extruded material provides a contact with the adjacent teeth to prevent 
floating, or movement, of the teeth. 
The end of the tube form extending beyond the tooth line can be trimmed, or 
shortened, and pressed together, before placing the crown material into 
the tube, to provide for the formation of a cast form more closely 
conforming to the intended final appearance or shape of the crown. After 
the crown material, or composite, has hardened or cured, the tube wall 
material can be removed by cutting and tearing away from the crown, thus 
leaving the extruded contact material 31', 32' in place. After the tube is 
removed, the cast shape can then be further formed by cutting away excess 
material, leaving a proper size temporary crown and one having the 
desirable intimate and tight contacts both with the stump being covered 
and with respect to adjacent teeth. 
This form can also be used for forming the necessary mold when casting 
crowns, inlays or posts and cores by the direct technique, when 
accomplished in situ. The cured material can then be shaped to the desired 
form and sent to a laboratory for casting into the final metal material 
through, for example, the lost wax process. By so doing, the dentist 
avoids the need for taking costly impressions, making casts and having 
most of the process done by a dental laboratory. When the tubular forms 
are formed of material having a somewhat greater rigidity, they can be 
formed in several different sizes, to for example accommodate the upper 
anterior teeth, the lower anterior teeth, both upper and lower bicuspids 
and upper and lower molars. Alternatively, a single basic form size can be 
used for more than one of these teeth depending on the individual. 
The material for forming the tube form preferably can be formed of the 
following orally safe materials: polypropylene, Teflon, and other safe 
polyolefins. 
The tube forms of this invention can be manufactured by extruding a long 
tube of material having the desired cross-sectional size, as shown in FIG. 
10, and cutting the tube to the desired length, and with the desired 
scalloped end edges.