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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a prefabricated dental pontic, a connector
for a pontic, and an assembly for forming a dental bridge.
2. Description of the Prior Art
Crown and bridge prosthodontics is the science and art of the complete
restoration of one or more teeth and the replacement of one or more
natural teeth with an artificial device. A bridge is used to replace at
least one missing tooth and is supported by natural teeth. A bridge which
is not cast in one piece includes a pontic which fills the edentulous
space and a connector which connects the pontic to a retaining member such
as a crown formed on an abutment tooth adjacent the pontic. In the
conventional bridge, the pontic is joined to the retainer by means of a
solder joint which forms the connector.
The primary purpose of the dental bridge is to receive the forces of
occlusion and to transmit them through the abutments so that occlusion is
restored to the patient, thereby contribution to mastication. The bridge
should also augment the ability of the patient to enunciate and maintain
the positions of the opposing teeth. The present day construction of a
dental bridge is a time consuming, involved and complex process which
requires the application of many independent procedures including the
following: waxing, spruing, investing, casting, cleaning, trimming,
cutting and stoning. The process, as conventionally practiced, is referred
to colloquially as the "lost wax casting method" and, at present, is the
universally accepted procedure for making a bridge. In following this
procedure, not only is it time consuming, but each step must be
meticulously followed with the dental technician paying strict attention
to detail to assure accuracy of the cast product and proper fit. It is
also difficult to make any adjustments to a cast bridge to compensate for
errors.
Construction a bridge from a prefabricated pontic offers the advantage of
speed, simplicity, and substantial cost savings over the cast bridge.
Although many previous attempts have been made to construct prefabricated
pontic assemblies for fabricating a non-preparatory bridge to metal
retainers, such prior art constructions have either been too unwieldly for
practical use or were unable to provide a proximal joint of sufficient
strength to permit the bridge to meet acceptable clinical standards. The
proximal joint formed heretofore between a metal retainer and a pontic
using solder was known to be weak.
SUMMARY OF THE INVENTION
The prefabricated pontic of the present invention eliminates waxing,
spruing, investing and casting. The pontic is joined to abutment teeth
preferably using the pontic connector of the present invention to form a
proximal joint which is comparable in strength to the joint of a cast
bridge. Moreover, the pontic of the present invention is easily fitted and
adjusted into proper alignment between the abutment teeth.
The prefabricated pontic of the present invention is adapted to join metal
retaining member(s) mounted upon abutment teeth separating an edentulous
space in the fabrication of a bridge, and comprises a metal body having a
mesiodistal dimension shorter than the span between the abutment teeth and
an arm extending from each opposite end of the metal body, having a
trough-like channel for placement between the metal body and the retaining
members.
The pontic connector of the present invention connects a prefabricated
pontic having an arm extending from each opposite end thereof to a
retaining member on an abutment tooth or teeth for forming a solder joint
therebetween in the fabrication of a bridge, and comprises means for
mounting the connector to the arm of the pontic at a location adjacent the
abutment tooth, and a thin metal member projecting from said mounting
means with said metal member being pliable and adjustable for adaptation
to a surface of the retaining member so as to hold the pontic in an
aligned position relative to the retaining member in preparation for
soldering and for reinforcing the solder joint formed at the attachment of
the arm to the retaining member.
The present invention is also directed to an assembly for fabricating a
dental bridge between metal retainers mounted on abutment teeth separating
an edentulous space comprising; a prefabricated pontic having a metal body
with a mesiodistal dimension shorter than the span between the abutment
teeth, and an arm having a trough-like channel extending from each
opposite end adjacent the abutment teeth, and means for connecting each
arm to a metal retainer at the interproximal in preparation for soldering.
BRIEF DESCRIPTION OF THE DRAWINGS
Other advantages of the present invention will become apparent from the
following detailed description of the invention when read in conjunction
with the following drawings of which:
FIG. 1A is a side elevation of a prefabricated pontic in accordance with
the present invention in preparation for placement between metal retainers
in a working model of two abutment teeth representative of a canine and
premolar;
FIG. 1B is an end view in cross-section of the prefabricated pontic of FIG.
1A taken along the lines 1B--1B thereof;
FIG. 2 is a view in perspective of the pontic connector of the present
invention;
FIG. 3 is a side elevation of the prefabricated pontic of FIG. 1A shown
fitted in position abutting the adjacent retaining members with the pontic
connector of FIG. 2 mounted on each of the arm of the pontic;
FIG. 4 shows the arrangement of FIG. 3 in side elevation with each of the
pontic connectors adapted to the retaining members on a working model for
fabricating a three-unit bridge;
FIG. 5 is a view in perspective of a preferred anterior prefabricated
pontic in accordance with the present invention;
FIG. 6 is an end perspective view of the pontic of FIG. 5; and
FIG. 7 is a side elevation of an alternate embodiment of a prefabricated
pontic of the present invention shown in position between two retaining
members in a working model for a three-unit bridge.
DETAILED DESCRIPTION OF THE INVENTION
The prefabricated pontic of the present invention is identified in the
drawings of FIG. 1A, 3, 4, 5 and 7, respectively, with the reference
numeral 10 and may be used in the preparation of either a molar or
anterior restoration. In each case, the pontic (10) comprises a metal body
(12) and an arm (14) extending from each opposite end of the metal body
(12). The pontic (10) may be fabricated from any desired metal or from a
metal alloy composition, although the selection of the metal or metal
alloy should meet the standards of compatibility for use in the oral
cavity. Accordingly, the pontic should preferably include gold as at least
one of its constituent elements. In addition, any conventional
manufacturing method may be used to prefabricate the pontic (10),
including conventional die casting and metal stamping.
The metal body (12) may be shaped into any design or configuration and may
be a solid mass of metal or have open spaces. Moreover, the geometrical
shape of the metal body (12) may vary considerably, based upon whether a
molar or anterior restoration is involved. Although the geometry of the
pontic metal body (12) is not critical to the present invention, it is
preferred that the configuration of the metal body for a posterior
restoration form a cradle-like geometry as shown in FIGS. 1, 3 and 4 in
accordance with the principles of construction taught and described in
U.S. Pat. No. 4,231,740, the disclosure of which is herein incorporated by
reference. The cradle-like geometrical structure should have a large,
occlusal concavity (16). The metal body (12) should also have relatively
large, open spaces (17) and (18) in the wing-like arms (19) and (20),
which extend outwardly toward the buccal and lingual surfaces of the
restoration. The open spaces provide an open metal framework. The
underside (21) of the body (12) may loop occluso-gingivally to form an
arch. The length ("L") of the metal body (12) must be shorter
mesiodistally than the span ("S") between the abutment teeth.
The preferred metal body design for an anterior restoration, as shown in
FIGS. 5 and 6, may follow the general teachings of U.S. Pat. No.
4,318,697, the disclosure of which is herein incorporated by reference.
The primary difference in design between the posterior and anterior design
is the addition of an occlusal brace (22) which extends substantially
upright directed to the occlusal, and a depending blade-like extension
(23) which is directed gingivally. A pair of wing-like arms (24) and (25)
extend outwardly toward the buccal and lingual surfaces of the restoration
with open spaces (26) to form an open metal framework having a concave
geometry. Although the anterior tooth is smaller in dimension than a
posterior tooth, it is essential to the present invention that the length
of the metal body (12) for both the anterior and posterior pontic be
shorter mesiodistally than the span ("S") between the abutment teeth, so
as to provide space for the arms (14) of the pontic (10) in the
fabrication of a bridge, as will be explained in greater detail hereafter.
The arms (14) of the pontic (10) are preferably symmetrical and of the same
uniform dimension in thickness, although such symmetry and equivalent
dimensional thickness is not necessary. It is, however, an essential
element of the present invention that the arms (14) form a trough-like
channel (30). The trough-like channel (30) should preferably be
"U-shaped," although a "V-shape" or box-shape with an open top would
functionally serve the same purpose. In this regard, any geometry which
would provide a reasonably deep depression (30) occluso-gingivally would
be acceptable. The depth ("D") of the trough-like channel (30) depends on
the restoration, but should in general have a depth greater than 0.5 mm,
and generally between 0.5 mm to 2 mm deep, and with 1 mm to 1.5 mm being
optimum.
The pontic (10) should be prefabricated with an arm length (X) which is
intentionally longer than is required to fit the pontic between the
abutment teeth so that the pontic arms may be shortened to accommodate for
differences in spacing ("S") between any two abutment teeth. Accordingly,
the length of each arm (14) on each side of the metal body (12) may be
shortened to accurately fit the pontic into relatively tight engagement
between the abutment teeth. Each arm (14) may be of any length, with the
only requirement that it be long enough to form the trough-like channel
(30).
Each arm (14) of the pontic (10) should be relatively rigid to provide a
strong attachment to the adjacent metal retaining members (35). Each
retaining member (35) may represent any type metal retainer, either full
or partial, that is cemented to an abutment tooth for retaining a bridge.
The metal retaining members (35) are shown in the figures for purposes of
illustration representing metal copings for constructing full crowns. The
preferred metal-retaining member (35) is a prefabricated metal coping as
described in U.S. Pat. Nos. 4,459,112 and 4,492,579. The coping, as
described in the aforementioned patents, is formed from a thin metal foil
of two or more layers of metal arranged in a prefolded configuration with
a plurality of foldable sections, which are folded over in preparation for
adapting the coping to a die of the preferred tooth to be restored. The
coping is then adapted to the die and heat treated.
Once the pontic (10) is fitted into a secure position abutting the metal
retainers (35), the arms (14) may be soldered to the metal retainers (35)
to form a solder joint at the interpromixal. This will usually require a
highly skilled technician to form a sufficiently strong solder joint.
A prefabricated metal connector (40), as shown in FIGS. 2, 3 and 4, is
preferably used to hold the parts together and in alignment for conducting
a soldering operation. The metal connector (40) also reinforces the solder
joint formed at the point of attachment with the retaining members (35).
The prefabricated metal connector (40) consists of a thin member (41) in
the form of band having a hole (42) and a thin metal extension or rim (43)
projecting from the band (41). The arm (14) is fitted through the hole
(42). The rim (43) should be very pliable so that it is readily bent over
and adapted to one or more surfaces of the adjacent metal retainer (35).
Although an annular band (41) is preferable, the band need not cover a
full 360 degrees. Alternatively, the band member (41) may represent any
clip-on means for providing attachment to the arm (14). In like manner,
the rim (43) may be of any geometrical shape. In fact, the rim (43) need
only extend in one direction from the band (41). Moreover, the rim (43)
may be irregular in shape so that it covers a greater occlusal surface
area, particularly for a molar restoration. The hole (42) should
accommodate the arm (14) and as such may be rounded or "U-shaped", to
match the shape of the arm (14).
The connector (40), and more particularly the rim (43), should be composed
of a soft metal material which makes the rim easily adaptable to the
retainer. The composition of the material should also be compatible with
its use in the oral cavity and as such should be of a nonoxidizing metal
or metal alloy. Moreover, the connector (40) or only its rim (43) can be
formed from a multilayer construction with one layer having a melting
temperature higher than the melting temperature of the solder so that such
layer will retain its integrity after soldering. As such, one layer of the
connector (40) can be used as the solder material which upon application
of a flame from a Bunsen burner or in a furnace will melt to form the
solder joint.
FIG. 3 shows the pontic (10) of FIG. 1 with its arms (14) sized and fitted
into position abutting the adjacent retainers (35) in the working model of
the abutment teeth for fabricating a dental bridge. The connectors (40)
are mounted about the arm (14) before the pontic (10) is fitted in place.
The rim (43) of the connector (40) is then bent over using appropriate
dental tools to adapt the connector (40) to one or more surfaces of the
retaining member (35) as shown in FIG. 4. The prefabricated assembly is
now ready to be soldered. A conventional soldering operation is performed
using any dental solder at a soldering temperature of 1050.degree. C. or
higher. The connector (40) ca have one layer composed of a soldering
composition as earlier explained. Additional solder may be added using a
solder material of any desired shape, such as a strip or a "U-shaped"
member to match the shape of the arm (14). The trough-like channel formed
by the arm (14) permits the solder to collect, flow and fill into the
depression, thereby forming a strong solder joint around the area where
the arm (14) joins the retainer (35). The arm (14) is thus able to
transfer the load to the retainer (35). The reinforced solder joint has
been shown to be stronger than the retaining member (35).
An alternate embodiment in which a prefabricated connector is not used is
shown in FIG. 7. The arms (14) are cut open at their ends to form a
bifurcated pair of arm connectors (47) and (48), which are adapted to the
buccal and lingual surfaces of the retainer (35). The trough-like channel
in the arm (14) is still essential to form a bed for the solder.
Although the invention has been described in connection with the
fabrication of three-unit bridge, it should be apparent that the invention
is equally applicable to the fabrication of a two-unit cantilever bridge
or a multiple-unit bridge using two or more pontics. For the cantilever
bridge, one arm of the pontic may be removed. For a multiple-unit bridge,
two pontics may be joined by connecting the arms to one another. The arms
may be united by welding and/or soldering and may be dimensioned to permit
one arm to nest into another.
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