Flexible post in a dental post and core system

A dental post and core system having an inelastic flexible post. The post, which may be radiopaque and tooth colored, conforms to the natural curved contours of a root canal to reduce machining of the tooth and mechanical weakening of the tooth structure. The post is made of a material having a plurality of fibers, wherein at least one or more of the fibers is non-axially aligned with respect to a straight axis extending from a coronal end to an apical end of a root of the tooth, such as non-axially aligned fibers twisted together, or such as randomly dispersed fibers in a plastic composite. Since not all the fibers are axially aligned, increased strength is achieved by reduction of the possibility of an axially extending fault crack in the resin of the post.

BACKGROUND OF THE INVENTION 
The present invention generally relates to a dental post and core system 
for endodontically-treated teeth. More specifically, this invention 
relates to a passive dental post and core system having a flexible 
inelastic post, wherein the post is made from a material having a 
plurality of distributed fibers, wherein at least one of the fibers 
extends non-axially aligned with respect to a straight axis extending from 
the apical end to the opposite coronal end of a root of a tooth. For 
example, the fibers may be a bundle of fibers, a longitudinally twisted 
bundle, a twisted braid, a woven lattice, a helically wrapped bundle of 
fibers, or a composite of randomly dispersed fibers in a binder. 
In each case, at least one of the fibers extends non-axially aligned with 
respect to the straight axis of a root of a tooth. 
For example, in a bundle of fibers, while some of the fibers may extend 
parallel to the straight axis of the root, at least one or more of the 
fibers extend in an axial direction which is not parallel to straight axis 
of a root of a tooth. That is, at least one or more of the fibers extends 
in a transverse or angled direction away from the straight axis of the 
root of a tooth. 
With respect to a longitudinally twisted bundle, a twisted braid, a 
helically wrapped bundle of fibers, the twisting or helical wrap of the 
fibers causes many, but not necessarily all, of the fibers to extend 
non-axially. Concerning a woven lattice of fibers, while one set of fibers 
could extend axially parallel to the straight axis of the root, the other 
intersecting set of fibers extends in a direction which is non-axially 
aligned with respect to the straight axis of the root. Even if most of the 
weft of a weave of a plurality of fibers extends parallel to the straight 
axis of the root, at least one or more fibers constituting the warp of the 
weave of fibers extends non-axially with respect to the straight axis of 
the root of the tooth. 
Moreover, concerning a composite of randomly dispersed fibers, there is 
always the possibility of one or more of the fibers being axially aligned 
to the straight axis of the root of a tooth. However, in order to be 
randomly dispersed, at least one or more of the fibers extends non-axially 
with respect to the straight axis of the root of a tooth. 
Preferably, the post is radiopaque and bears a color simulating that of a 
natural tooth. 
Rigid dental post and core systems are widely utilized to restore 
endodontically-treated teeth. Post and core restorations are routinely 
used to create an adequate foundation for the final restorative step, 
which may be a crown, onlay, or a fixed partial denture abutment. 
Generally, a post is provided for retention and lateral stability of the 
restoration. The core provides support for the crown. Two general types of 
post and core systems are known in the art: "active" or screw-in type 
systems and "passive" type systems. Active post and core systems 
mechanically engage the walls of the root canal and tooth dentin. Passive 
post and core systems are bonded in a reformed root canal utilizing 
cements and the like. 
Two major problems are encountered when restoring an endodontically-treated 
tooth. Firstly, the tooth is more susceptible to fracture, and secondly, 
there is generally less coronal structure with which to work. The greater 
susceptibility of a tooth to fracture after endodontia may result from the 
tooth being more brittle. However, studies of the changing mechanical 
properties of pulpless teeth do not generally support this theory equating 
dryness with reduced mechanical strength. It appears that the greater 
susceptibility for fracture in an endodontically treated tooth results 
from mechanical weakening of the tooth during root canal therapy and 
refinement of the root canal. Improvements in restoration techniques that 
reduce mechanical weakening are therefore desirous. 
An endodontically-treated tooth is generally severely compromised either 
due to trauma or neglect. Thus, traumatic fractures, removal of old 
restorations and carious tissue, and preparation of root canal access may 
not leave enough tooth to maintain the "dome effect" of the tooth or to 
retain a crown. 
The stress concentrations in a tooth resulting from the rigid post and core 
systems of the prior art also play a vital role in tooth fracture. Stress 
concentrations can be impacted through system design and/or restoration 
techniques. Various studies and investigations into the susceptibility of 
endodontically-treated teeth to fracture and the contribution of rigid 
dental post and core systems to such fracture have been conducted. A 
Comparison of Intracanal Stresses in a Post Restored Tooth Utilizing the 
Finite Element Method, Cailleteau, Johnny G., Rieger, Monty R. and Akin, 
J. Ed, Journal of Endodontics, Vol. 18, No. 11, November 1992, pp. 
540-544, reports that placement of a rigid post within a tooth alters the 
pattern of stress along the root canal as compared with an intact tooth. 
Instead of strengthening the tooth the post stiffens the coronal posted 
section and shifts the flexure point apically. The effect of this 
stiffening causes the nonposted apical portion of the tooth to deform at 
the lost apex, resulting in a stress increase in that portion of the canal 
wall. Also, the cyclic loading and unloading of an incisor during 
mastication requires consideration of fatigue failure. Since the maximum 
bending stresses occur in connection with the apex of the post, any 
inclusions or defects within the wall of the dentin near the apical end of 
the post would create stress concentrations that increase the risk of a 
fatigue crack formation. Defects and microfractures introduced during 
endodontic treatment and post access preparation could become areas 
contributing to stress concentrations. Studies have also shown that more 
intact tooth structure provides better resistance to fracture than a 
metallic post. There is also evidence that stresses in the tooth tend to 
increase as the post diameter increases. 
A flexible post eliminates these problems. A post and core system utilizing 
a flexible post shifts the stress concentrations coronally, eliminates the 
introduction of defects during post access preparation and lost placement, 
and leaves more of the tooth intact. 
The main function of a post is to provide retention to the core. Relieved 
of its expectation to facilitate resistance to tooth fracture, the post 
can be designed to optimize its retentive properties. Several factors 
govern the retentiveness of endodontic posts. The shape of the post and 
its length are among the essential factors. Tapered dowels have been found 
to be significantly less retentive than parallel-sided posts. A serrated 
5.5-mm parallel-sided dowel was found more retentive than an 8-mm tapered 
post. Tapered posts provide high shoulder stresses but have an undesirable 
wedging effect. The wedging effect results in part from the prior art 
placement of a straight rigid post in a naturally curved and varying 
diameter root canal. Active posts are very retentive, but may impose too 
much stress on the tooth, especially compromised teeth. Thus it appears 
that a passive, serrated, parallel-sided post is a preferred structure for 
dental post and core systems. A flexible, passive, serrated parallel-side 
post provides the previously-mentioned advantages in preventing tooth 
fracture and additionally permits the post to extend for a greater length 
into the root canal for improved retention. 
In addition to post shape and length, adequate retention is a function of 
cementing mechanisms. Various cementing medium have been studied. 
Utilization of low viscosity resin cement in combination with smear layer 
removal can be considered a universal post cementation technique. In 
addition to good retention, this cementing technique offers the benefits 
of a cement with very little resistance to post insertion, thereby 
minimizing stresses applied to tooth structure during cementation. 
HoWever, the invention of the present disclosure is not limited by the 
cementing process used. 
An elastic, wire pin having a plurality of flexible, radially extending 
fins along its length is disclosed in German Patent No. DE 3643-219 to 
Weisskircher. While providing some advantages over the prior art rigid 
post, the "high degree of elasticity" of the Weisskircher pin will cause 
it to try and retain its initial shape in the root canal. During and after 
placement, flexing of the pin will cause the apical end of the pin to lay 
against the wall of the root canal. Stress concentrations in the tooth as 
known for rigid posts will thereby be induced. A pin formed from wire also 
has low retention characteristics and tends to rotate within the root 
canal. Radial fins are utilized in the Weisskircher disclosure to resist 
rotation of the wire pin. However, these radial fins may become further 
sources of stress concentrations and fatigue failure as the wire pin 
rotates. No prior art known to the present Applicants discloses or 
suggests a flexible post in a dental post and core system that is flexible 
and inelastic, that conforms to the shape of the root canal to eliminate 
the stress concentrations that facilitate tooth fracture. 
U.S. Pat. No. 4,778,389 to Salvo discloses a dental post construction to 
eliminate lateral stress in a tooth wherein a rigid, split post is formed 
by parallel sections joined at a marginal top portion of the post head. 
U.S. Pat. No. 5,073,112 to Weil discloses a dental post having an active 
portion and a passive portion. 
U.S. Pat. No. 5,074,792 to Bernadat discloses a passive post and core 
system comprising a rigid peg disposed in a porous sheath formed of 
high-strength filaments, wherein the peg has a set of parallel radially 
extending fins extending from the peg. The filaments in Bernadat are found 
in the sheath surrounding the peg, not in the peg itself. 
U.S. Pat. No. 732,922 of Clark describes a pin for teeth which is flexible, 
but only by virtue of the fact that the pin includes a base and two 
tapered pins extending from the base, with a space therebetween, so that 
the tapered pins can close toward each other within the space. 
U.S. Pat. No. 4,952,150 of Schiwiora discloses a tooth root post which 
includes a tip of solid flexible metal or metal alloys. In contrast, in 
the present invention, the root post is made of a plurality of metallic or 
non-metallic fibers, as opposed to a solid piece of metal. 
U.S. Pat. No. 4,934,936 of Miller describes a serrated dental post. U.S. 
Pat. Nos. 622,670 of Dwight and 1,218,289 of Maker both disclose solid 
threaded posts with a core spacer neck extending therearound. 
International Search Publication No. WO 91/07142 (PCT/FR90/00831) to 
Reynaud et al. discloses a dental post and core system having a post 
formed from equally-tensioned fibers of composite material. In Reynaud, 
the fibers of the composite material are all laid axially within the post 
and embedded within a resin. Because the fibers are equally tensioned and 
extend only axially aligned and continuous, any modification of the post 
in Reynaud may cause a major spreading, continuous, fault line crack in 
the resin of the post, thus losing integrity of the Reynaud post. 
In contrast, in the present invention at least one or more of the fibers 
extends in a direction which is non-axially aligned with respect to the 
straight axis extending from the apical end to the opposite coronal end of 
a root of a tooth. Because there is a plurality of directions with respect 
to the fibers, such as at least one fiber running non-axially, the 
possibility of a spreading, continuous fault line crack is significantly 
reduced, thereby achieving unexpected beneficial results not suggested in 
Reynaud. 
U.S. Pat. No. 4,936,776 to Kwiatkowski discloses a translucent post and 
core structure to minimize gingival discoloration adjacent a dental 
restoration. 
U.S. Pat. No. 3,949,476 to Kahn discloses a "direct" method of restoring an 
abraded or broken tooth. 
Swiss Patent No. 1,457,914 to Stomatology Research Institute discloses a 
method of making a pin stump insert. 
West German Patent No. 1,541,209 to Kurer discloses the now conventional 
threaded, screw-in type active post. 
Currently-marketed dental post and core systems such as the FLEXI-POST; the 
DENTATUS POST, the RADIX POST and the BRASSELEAR screw posts all advocate 
screwing threaded rigid posts into straight paths machined into the tooth 
dentin. The present day posts are also generally formed from rigid metals 
such as steel, titanium and other alloys which do not flex in the same 
manner as a natural tooth. This differential in flexibility between the 
natural tooth and the post may cause tooth fracture when the restored 
tooth is stressed during mastication or from trauma. Cast posts are 
subject to these same limitations and require an additional laboratory fee 
and an additional visit to the dentist to complete the procedure. 
A means to quickly and easily identify the components of a post and core 
system is also needed in the prior art. Presently, there is either no 
color-coding of post and core systems or the color identification consists 
of an inconspicuous dot of color. Brightly-colored means of identifying 
post and core systems would significantly advance the art. The lack of a 
color protocol in the prior art creates confusion, eye strain and a sloppy 
work environment. The inability to readily identify each post and core by 
sight creates problems before, during and after the procedure is 
completed. Firstly, before the procedure is initiated the dentist and 
staff must select the post and core and isolate it from others that may be 
very close in size. During the procedure the dentist must carefully avoid 
confusing the selected post and core. After the procedure the used and 
unused devices must be readily identified for contamination control. 
Further, a post and core system installed by one dentist may later require 
an emergency or other procedure by a different dentist in a completely 
different part of the world. Color-coded identification would eliminate 
uncertainty and guesswork. 
The post and core system of the present invention overcomes all of these 
limitations of the prior art. 
SUMMARY OF THE INVENTION 
The present invention is a dental post and core system that includes a 
flexible post. The flexible post conforms to the curvature of the root 
canal during placement and reduces mechanical weakening of an 
endodontically-treated tooth by eliminating stress concentrations at the 
apical end of the post, by reducing the size of canal access preparations 
and by allowing more intact tooth to be retained. 
The present invention also provides a method of restoring an 
endodontically-treated tooth that reduces the time and equipment needed 
during a procedure and lessens the chance that a dentist will perforate or 
fracture the canal wall during placement of a post. 
In a preferred embodiment of the dental post and core system of the present 
invention the post includes a core spacer and a flexible, post reinforcing 
rod extending apically from the core spacer. The core spacer may be 
flexible, resilient or otherwise deformable and may be selectively 
attachable or integrally formed with a post reinforcing rod. A core may be 
selectively attached to the upper portion of the core spacer, integrally 
formed with the core spacer or built-up to custom specifications. 
A further embodiment of the present invention is a mutable flexible post. 
The mutable post of the present invention comprises a bundle of reinforced 
plastic or metal fibers that have at least one or more fibers which 
extends non-axially aligned with respect to the straight axis extending 
from the coronal end to the apical end of a tooth. The post may also be 
selectively flared at the coronal aspect to provide a core seat or to 
provide extra surface area to scaffold a core. 
OBJECTS OF THE INVENTION 
An object of this invention is to provide a passive and bondable dental 
post and core system for endodontically-treated teeth. 
Another object of this invention is to provide a dental post and core 
system that reduces the susceptibility for tooth fracture in 
endontically-treated teeth. 
A further object of this invention is to provide a method for restoring 
endodontically-treated teeth that reduces the susceptibility for tooth 
fracture. 
Another object of the present invention is to provide a dental post and 
core system that reduces the mechanical weakening of tooth structure by 
relieving stress concentrations. 
Another object of the present invention is to provide a dental post and 
core system that reduces the risk of a dentist creating perforations and 
microfractures during post placement. 
It is also an object of the present invention to provide a flexible post in 
a dental post and core system that automatically adjusts to the contours 
of a root canal during placement. 
Another object of this invention is to provide a post and core system 
having a flexibility that closely mimics the flexibility of the pulp and 
dentin tissue of a natural tooth. 
Another object of the present invention is to provide a dental post and 
core system that reduces the amount of time required to restore an 
endodontically-treated tooth. 
It is also an object of this invention to provide a dental post and core 
system that can be safely and quickly installed by any dentist in a single 
visit. 
Another object of this invention is to provide a dental post and core 
system formed from material that can be readily shaven to accommodate 
canal irregularities and in-between root canal sizes without loosing its 
physical properties. 
Another object of this invention is to provide a dental post and core 
system that is radiopaque. 
Another object of this invention is to provide a method of restoring 
endodontically-treated teeth that eliminates drilling for post placement 
and that can be installed using inexpensive, readily available endodontic 
drills. 
Another object of this invention is to provide a post in a dental post and 
core system that fits intimately within a root canal and that accepts 
standard dental cements. 
Another object is to provide a color-coded dental post and core system for 
identification purposes. 
A further object of the present invention is to provide dental post and 
core system that substantially fits all teeth. 
It is another object of the present invention to provide a dental post and 
core system that can be provided in standardized sizes for mass production 
efficiencies. 
A still further object of this invention is to provide a restoration system 
for teeth previously classified as hopeless and difficult, such as 
hemisected and dilacereted teeth and other conditions of extreme loss of 
tooth structure. 
These and other objects and advantageous of the improved dental post and 
core system of the present invention will be apparent to those skilled in 
the art from the following description of preferred embodiments, claims 
and appended drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 illustrates in a lateral cross-sectional view a first preferred 
embodiment of the dental post and core system 1 of the present invention. 
First system 1 generally comprises a core 10 and flexible post 11. Post 11 
includes a core spacer 20 and a flexible inelastic post reinforcing rod 30 
extending apically from the core spacer 20. The post reinforcing rod 30 
may be cylindrical or tapered. Further, core spacer 20 may be flexible 
and/or resilient. In the first dental post and core system 1, core spacer 
20 and reinforcing rod 30 are shown to be separately constructed. A bore 
21 in core spacer 20 selectively engages an upper portion 31 of post 
reinforcing rod 30. 
However, core spacer 20 and reinforcing rod 30 may be integrally formed 
without departing from the spirit and scope of the present invention. The 
separable construction of core spacer 20 and the reinforcing rod 30 
permits fabrication of built-up post and core systems 1 in a variety of 
configurations from readily identifiable components. Core 10 is seated on 
the core spacer 20 and a crown 2, for example, is placed over the core 10, 
as known in the art. 
The teachings of the present invention may be utilized for restoration of 
multi-rooted teeth having two, three or four diverging canals. In the 
second dental post and core system 1 for a double-rooted tooth illustrated 
in FIG. 2 it can be seen that second system 1 includes a second core 
spacer 20 having two bores 21a, 2lb, which engage respective flexible post 
reinforcing rods 30. 
The advantages of a flexible post 11 in a dental post and core system are 
numerous. Firstly, a flexible post 11 can follow the contours of the root 
canal 3. This method of placement eliminates or reduces the amount of 
drilling required for root canal therapy and for preparation of the canal 
access. The reinforcing rods 30 can be appropriately sized to permit use 
of commonly-used dental drills. More intact tooth is left in place which 
has been shown to provide the best resistance to a tooth fracture. 
The flexible inelastic post reinforcing rod 30 of the present invention 
also eliminates stress concentrations in a canal wall and dentin due to 
the apical lateral movement of rigid and elastic posts. Utilizing a 
flexible post 11, the intracanal stress at the apical level is shifted 
coronally to the area of maximum stress. The core spacer 20 absorbs the 
intracanal stresses by deformation of the body of the core spacer 20. Core 
spacer 20 therefore can be seen to serve as both a seat for the core 10 
and as a stress absorber. 
A flexible post 11 also reaches further apically which provides greater 
retention. This is specifically applicable to the restoration of teeth 
that have suffered extreme loss of tooth structure where to gain adequate 
retention the length of the post must enter the curved portion of the root 
canal 3. 
In the first preferred embodiment of the flexible post 11 in the first 
dental post and core system 1 of the present invention, illustrated in an 
exploded, perspective view in FIG. 3, the core spacer 20 and the flexible 
post reinforcing rod 30 are formed from identical material. This, however, 
should not be understood to be a limitation of the present invention. 
The core spacer 20 may be formed of a first material to optimize its stress 
resistance characteristics; reinforcing rod 30 may be formed of a second 
material to optimize its retention characteristics. 
Core spacer 20 and post reinforcing rod 30 are preferably formed from 
reinforced plastics, such as fiberglass polyester composites similar to 
those used win the construction of fishing poles, flexible ceramic resin 
composites, graphites, teflons, polycarbonates and the like. Metals, such 
as metal oxides, metal salts or pure or alloyed metals like gold, silver 
titanium, steel, platinum, palladium and the like, can be processed into 
fibers and bound in a matrix of resin or other binders for fabrication of 
the core spacer 20 and post reinforcing rod 30. The flexibility of these 
materials is close to the flexibility of the natural tooth and therefore 
will reduce the flexibility differential of the intact tooth and the 
inserted post 11. 
Fiberglass polyester composites and the like, such as ceramic resins, 
graphite, graphite composites, teflons, polycarbonates, silicon carbide, 
polyamide, zirconium and aluminum silicate are also well suited for 
in-office etching of the surfaces of the core spacer 20 and reinforcing 
rod 30 for better and stronger cementation. Reinforcing rod 30 may also be 
treated with dental adhesives and bonding agents such as silane urethane, 
bisgma and acrylic resins to increase retention. Core spacer 20 and post 
reinforcing rod 30 also preferably include an appropriate amount of 
radiopaque material such as titanium oxide, barium sulfate and other 
materials known in the dental industry to insure X-ray documentation and 
render the object opaque to radiographic imaging. 
The first preferred embodiment of the flexible post 11 is preferably color 
coded for identification purposes. In the first preferred flexible post 
11, the core spacer 20 and reinforcing rod 30 are color identified 
according to the inside diameter of the bore 21 in core spacer 20, 
identified in FIG. 3 by the letter "B", and the outside diameter of the 
reinforcing rod 30, identified in FIG. 3 by the letter "D". In the 
preferred embodiment the reinforcing rods 30 are formed having the 
following diameters "D": 0.036 inch, 0.040 inch, 0.050 inch, 0.060 inch, 
and 0.070 inch. The bores 21 of the respective core spacers 20 have a 
corresponding bore diameter "B" (marginally larger than rod diameter "D") 
for snug engagement of the spacer 20 to an upper portion 31 of the post 
reinforcing rod 30. Bright colors are preferably used. 
The following color protocol is preferred: 
______________________________________ 
"D" Color 
______________________________________ 
inch White 
inch Yellow 
inch Red 
inch Blue 
inch Green 
______________________________________ 
A second dental post and core system 2 for multi-rooted teeth, as 
illustrated in FIG. 2, may have a second core spacer 20' wherein the 
respective first and second bores 21a, 2lb are sized differently for 
placement of reinforcing rods 30 of a different size. Prefabricated 
multiple root dental post and core systems 2 having differently sized 
reinforcing rods 30 will be multicolored in accordance with the above 
protocol. For example, a second core spacer 20' may have a yellow ring 
around first bore 21a and a white ring around second bore 2lb to indicate 
that this core spacer 20' is to be utilized with a 0.040 inch reinforcing 
rod 30 in first bore 21a and a 0.036 inch reinforcing rod 30 in second 
bore 2lb. 
FIG. 4 illustrates in a front plan view of a second preferred embodiment of 
a reinforcing rod 40 constructed in accordance with the teachings of the 
present invention. Second reinforcing rod 40 is a tapered, flexible 
elongated member 41. The outer wall of the elongated member 41 includes a 
plurality of displaced circumferential serrations 42 and a channel 43 
extending longitudinally between the respective serrations 42. The 
combination of flexibility in the second reinforcing rod 40 and the 
displacement of the respective serrations 42 is believed to reduce the 
wedging effect of rigid posts as known in the art. It is also known that 
alternatively serrations which are not circumferential may also be 
employed, such as arcuate segments or threaded indentations. 
A third preferred embodiment of a reinforcing rod 50 is illustrated in FIG. 
5. Third reinforcing rod 50 comprises a closed flexible sheath 51 having a 
compressible gel 52 disposed within the interior of the sheath 51. During 
placement of the third reinforcing rod 50, the wall 51a of the sheath 51 
deforms to the varying diameter and curvature of the root canal. 
From the foregoing, it should be readily understood that the respective 
first, second and third reinforcing rods 30, 40 and 50 may be utilized in 
conjunction with a core spacer 20 or a prefabricated or built-up core 10 
may be attached directly to the coronal end of the reinforcing rod 30, 40, 
50. 
A prefabricated core 10 for attachment directly to a reinforcing rod 20, 
40, 50 may include a bore 21 extending therethrough, as illustrated for 
the core spacer 20 of the present invention. Reinforcing rods 30, 40 find 
50 may be pre-cut or formed in an extended length to provide a margin of 
safety for mistakes in measuring. 
The core spacer 20 of the present invention may be prefabricated in 
standard sizes or built-up in the dentist's office. The external shape of 
core spacer 20 generally corresponds to the concavity of the chamber 
termed in root canal therapy. In teeth with a shallow concavity, standard 
dental drills may be used to machine a countersunk region 5 in the tooth 
(FIG. 7) for receipt of core spacer 20 or a built-up core spacer 20'. 
FIGS. 6 and 7 illustrate a preferred embodiment of a built-up core spacer 
20' constructed in accordance with the teachings of the present invention. 
The flexible reinforcing rod 30 is placed into the root canal 3 (FIG. 7). 
Built-up core spacer 20' is then formed about the coronal end of first 
reinforcing rod 30 by injection of any of the suitable fast-setting 
liquids or pastes known in the art. Built-up core spacer 20' initially 
extends to the top of the tooth dentin 4 and into any fractures 4a or the 
like in the tooth. A recessed ring 25 is then countersunk into the top of 
the built-up core spacer 20' along the inside edge of the tooth to form a 
central, raised portion 26 of the built-up core spacer 20'. It is 
preferred that the floor 25a of the recessed ring 25 is approximately 1.5 
mm below the top of the tooth dentin 4. As can be seen in the 
cross-sectional view of the built-up core spacer 20' illustrated in FIG. 
8, a core 10 is seated onto the top of the central, raised portion 26 and 
the floor 25a of the recessed ring 25. Preferably, sufficient lateral 
space is left so that the crown 2 may be fitted over the core 10 to 
likewise rest on the floor 25a of the recessed ring 25, approximately 1.5 
mm below the top of the tooth. 
A mutable flexible post 100 is illustrated in FIG. 8 and a mutable post 
reinforcing rod 130 is illustrated in FIG. 9. Mutable post 100 and mutable 
post reinforcing rod 130 are preferably formed from a bundle of reinforced 
plastic or other fibers 101 cemented together at the central portion 101b 
and the lower portion 101c of tile fibers 101. The upper portion 101a of 
the fibers 101 is loosely compacted so that the upper portion 101a may be 
selectively flared to provide additional surface area to scaffold a 
built-up core. Flaring of the upper portion 101a of the fibers 101 may be 
performed at the factory or in the dentist's office using standard 
crimping pliers. A prefabricated core (not shown) may be attached to the 
coronal aspect of the mutable post 100 when it is disposed in its unflared 
position. 
As shown in FIG. 9 the mutable reinforcing rod 130 constructed in 
accordance with the teachings of the present invention may likewise be 
utilized in a flared or unflared position. A first core spacer 20 is 
attached to the coronal end of the mutable reinforcing rod 130. The 
mutable post 11' comprising a first core spacer 20 and a mutable 
reinforcing rod 130, may be used to support a prefabricated core, or the 
coronal end of the mutable post 11' may be flared to form a scaffold for a 
built-up core. An advantage of this preferred embodiment of the present 
invention is that a single construction can be used for either a 
prefabricated dental post and core system or a mutable post reinforcing 
rod 130 to support a built-up core. 
Post 11 may be made without core spacer 20. Moreover, post 11 may be made 
from a material having a plurality of distributed fibers, wherein at least 
one of the fibers extends non-axially aligned with respect to a straight 
axis extending from the apical end to the opposite coronal end of a root 
of a tooth. For example, the fibers of post 11 may be a bundle of fibers, 
a longitudinally twisted bundle, a twisted braid, a woven lattice, a 
helically wrapped bundle of fibers, or a composite of randomly dispersed 
fibers in a binder. 
In each case, at least one of the fibers of post 11 extends non-axially 
aligned with respect to the straight axis of a root of a tooth. 
For example, in a bundle of fibers, such as the conical bundle of fibers 
shown in FIG. 10A, while some of the fibers may extend parallel to the 
straight axis A--A of the root, at least one or more of the fibers extend 
in a non-axial direction which is not parallel to straight axis A--A of a 
root of a tooth. That is, at least one or more of the fibers extends in a 
transverse or angled direction away from the straight axis A--A of the 
root of a tooth. 
With respect to a longitudinally twisted bundle, such as shown in FIG. 10H, 
a twisted braid, such as shown in FIG. 10C, a helically wrapped bundle of 
fibers, such as shown in FIG. 10B, the twisting or helical wrap of the 
fibers causes many, but not necessarily all, of the fibers to extend 
non-axially. 
Concerning a woven lattice of fibers, such as shown in FIGS. 10D or 10E, 
while one set of fibers could extend axially parallel to the straight axis 
A--A of the root, the other intersecting set of fibers extends in a 
direction which is non-axially aligned with respect to the straight axis 
A--A of the root. Moreover, as shown in FIG. 10G, even if most of the weft 
of a weave of a plurality of fibers extends parallel to the straight axis 
A--A of the root, at least one or more fibers constituting the warp of the 
weave of fibers extends non-axially with respect to the straight axis of 
the root of the tooth. Furthermore, as shown in FIG. 10F, instead of a 
true weave, a bundle of axially aligned fibers may have at least one or 
more non-axially aligned fibers constituting a strap collar containing the 
remaining fibers (whether axially aligned or not) therein. 
While the bundles of fibers shown in FIGS. 10A-10I are shown without core 
spacers, such as core spacer 20 in FIG. 1, similar core spacers may 
alternately be provided, or the ends of the bundles of fibers may be 
flared, such as shown in the conical bundle in FIG. 10A or the twisted 
bundle shown in FIG. 10H. 
As shown in FIG. 10I, concerning a composite of randomly dispersed fibers, 
there is always the possibility of one or more of the fibers being axially 
aligned to the straight axis A--A of the root of a tooth. However, in 
order to be randomly dispersed, at least one or more of the fibers extends 
non-axially with respect to the straight axis A--A of the root of a tooth. 
The fibers in FIGS. 10A-10I may be formed from metal or non-metallic fibers 
in a composite, such as within a plastic material. Alternately, the 
coronal end may be flared by loose compacting of the coronal end, or by 
mechanical undercutting of the coronal end. 
In addition, the post is both flexible and inelastic, so that the post can 
bend but generally maintain its original length. For example, in flexing, 
one side is extended, and the other side is compressing about an axis. 
FIG. 11 is a perspective view in partial section of a further alternate 
embodiment for a flexible inelastic post 220 with a plurality of randomly 
dispersed particles 221, such as beads or other shaped particles, within a 
binder 222. 
The flexible post of the present invention also leads to improved methods 
of endodontia that eliminate drilling for post placement. 
Various changes, additions and modifications of the present invention may 
be made to the preferred embodiments without departing from the spirit and 
scope of the present disclosure. Such changes, additions find 
modifications within a fair reading of the following claims are intended 
to be part of the present invention.